TREATMENT TECHNOLOGY BACKGROUND DOCUMENT 

?f3 1/- I~ o S"S~ 

Larry Rosengrant Section Chief 

Laura Lopez Project Officer 

U.S. Environmental Protection Agency Office of Solid Waste 

401 M Street, SW 

Washington, DC 20460 

January 1991 
TABLE OF CONTENTS 

Section 

EXECUTIVE SUMMARY 

Applicability ......... . Underlying Principles of Operation . Description of the Treatment Process ...... . Waste Characteristics Affecting Performance (WCAPs) Design and Operating Parameters ...... . 

I. TREATMENT TECHNOLOGIES 

A. DESTRUCTION TECHNOLOGIES 

1. 

1.1 

1.2 

1.3 

1.4 

1.5 

1.6 

2. 

2.1 

2.2 

2.3 

2.4 

'2.5 

2.6 

3. 

3.1 

3.2 

3.3 

3.4 

3.5 

3.6 

BIOLOGICAL TREATMENT 

Applicability .•........ 

Underlying Principles of Operation ..... Description of Biological Treatment Processes ... Waste Characteristics Affecting Performance (WCAPs). Design and Operating Parameters .... Refsrences . . . • . 

CHEMICAL OXIDATION . . . . . . . 

Applicability . • . . . . . . . . . Underlying Principles of Operation ..... Description of Chemical Oxidation Processes .... Waste Characteristics Affecting Performance (WCAPs). Design and Operating Parameters 

References . . . . . 

CHEMICAL REDUCTIOK . . . . . . . . 

Applicability ......... . Underlying Principles of Operation ... Description of Chemical Reduction Process ..... Waste Characteristics Affecting Performance (WCAPs). 

Design and Operating Parameters •........ 

References . . . . . . . . . . . . . . . . . . . . . 

f\docunent\15254031.01.001 

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, 
Section 

4. 

4.1 

4.2 

4.3 

4.4 

4.5 

4.6 

5. 

5.1 

5.2 

5.3 

5.4 

5.5 

5.6 

6. 

6.1 

6.2 

6.3 

6.4 

6.5 

6.6 

TABLE OF CONTENTS (CONTINUED) 

ELECTROLYTIC OXIDATION OF CYANIDE 

Applicability ..........• 

Underlying Principles of Operation • . . . . . . Description of Electrolytic Oxidation of Cyanide Process . . . . . . . . . . . . . . . . . . . .. Waste Characteristics Affecting Performance (WCAPs). Design and Operating Parameters 

References . . 

INCINERATION . . . . . . . . . . 

App 1 i cabil i ty . . . . . . . . . . . Underlying Principles of Operation . Description of Incineration Process . . . . . . . . Waste Characteristics Affecting Performance {WCAPs). _Design and Operating Parameters 

References . . . . 

WET AIR OXIDATION 

Applicability .••........... 

Underlying Principles of Operation ... Description of Wet Air Oxidation Process ••.... 

Waste Characteristics Affecting Performance {WCAPs). Design and Operating Parameters • . . . . . ... References . . . . . . . . . . . . . . . . . . . . . 

B. TECHNOLOGIES THAT REDUCE THE SOLUBILITY OR LEACHABILITY 

OF METALS 

Page No. 

38 

38 

38 

39 

39 

40 

43 

44 

44 

45 

46 

54 

57 

63 

64 

64 

66 

66 

67 

70 

73 

1. AMALGAMATION . . . . . . . . . . . 74 

1.1 Applicability •....• o . • . 74 

1.2 Underlying Principles of Operation •.. o . . . 74 

1.3 Description of Amalgamation Treatment Processes o . 75 

1.4 Waste Characteristics Affecting Performance (WCAPs)o 75 

1.5 Design and Operating Parameters o o . o . 77 

1. 6 References • o o o o o • 0 • o o o o . o • o • o o • 80 

f\dacument\15Z54031.01.001 i i 
TABLE OF CONTENTS (CONTINUED) 

Section ( 

2. CHEMICAL PRECIPITATION . 

2.1 Applicability .......... . 2.2 Underlying Principles of Operation .... . 2.3 Description of Chemical Precipitation Process ... 2.4 Waste Characteristics Affecting Performance (WCAPs). 

2.5 Design and Operating Parameters 

2.6 References . 

3. ENCAPSULATION ......•.. 

3.1 

3.2 

3.3 

3.4 

3.5 

3.6 

Applicability .......... . Underlying Principles of Operation . Description of Encapsulation Processes .. Waste Characteristics Affecting Performance 

Design and Operating Parameters 

References • . . • • . . . . • • • . 

4. STABILIZATION OF METALS . . . . 

4.1 Applicability .......... . 4.2 Underlying Principles of Operation . 

. . . . (WCAPs). 

4.3 Description of Stabilization Process •....... 

4.4 Waste Characteristics Affecting Performance (WCAPs). 

4.5 Design and Operating Parameters 

4.6 References • . . ... 

5. VITRIFICATION • . • . . . ..• 

5.1 Applicability ......•.• 

5.2 Underlying Principles of Operation . • 

5.3 Description of Vitrification Processes ••..... 

5.4 Waste Charatteristics Affecting Performance (WCAPs). 

5.5 Design and Operating Parameters ..•....... 

5. 6 References . . . . . . . . . . . . . . . . . . . . . 

f\document\15254031.01.001 iii 

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101 .. 

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115 

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124 
TABLE OF CONTENTS (CONTINUED) 

Section • 

t. 

II. REMOVAL TECHNOLOGIES 

A. RECOVERY, REUSE, AND/OR SEPARATION TECHNOLOGIES FOR 

ORGANICS 

1. CARBON ADSORPTION . . . . . . . . 

Page No. 

125 

1.1 Applicability . . . . . . . . . . 125 

1.2 Underlying Principles of Operation . . . 125 

1.3 Description of Carbon Adsorption Process . . . . . . 125 

1.4 Waste Characteristics Affecting Performance (WCAPs). 129 

1.5 Design and Operating Parameters . . . . 130 

1.6 References . . . . . . . . • 133 

2. 

2.1 

2.2 

2.3 

2.4 

2.5 

2.6 

3. 

3.1 

3.2 

3.3 

3.4 

3.5 

3.6 

4. 

4.1 

4.2 

4.3 

4.4 

4.5 

4.6 

DISTILLATION TECHNOLOGIES . . .. 

Applicability . . • . . • . . . . . .•. 

Underlying Principles of Operation . . ... Description of Distillation Processes .....•. 

Waste Characteristics Affecting Performance (WCAPs). Design and Operating Parameters . • . • . References • . • . • . • 

EXTRACTION TECHNOLOGIES . . . . . 

Applicability ..•.......• 

Underlying Principles of Operation • 

Description of Extraction Processes • . . . •••. 

Waste Characteristics Affecting Performance (WCAPs). Design and Operating Parameters ..•.. 

References • • • . • . • • . . 

FUEL SUBSTITUTION . . . . . . . . . 

Applicability • . . . . . . ... . Underlying Principles of Operation .. . Description of Fuel Substitution Process .•.... 

Waste Characteristics Affecting Performance (WCAPs). Design and Operating Parameters .....•.... 

References • • • . • . . . . . . . . . . . • . . . 

f\documant\15Z5~031.01.001 iv 

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137 

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150 

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157 

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158 

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170 

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174 

174 

177 

179 

183 

, 
TABLE OF CONTENTS (CONTINUED) 

Section ( Page No. 

B. RECOVERY AND/OR SEPARATION TECHNOLOGIES FOR METALS 

1. ACID LEACHING o o o o o o o o o o 184 

1.1 Applicability o 0 o 0 0 0 o o 0 o 184 

102 Underlying .Principles of Operation o o 184 

1o3 Description of Acid Leaching Process o o .. 0 0 0 185 

1o4 Waste Characteristics Affecting Performance (WCAPs)o 186 

1o5 Design and Operating Parameters 188 

1o6 References o o o 0 o o o o 190 

2. FILTRATION TECHNOLOGIES o o o o 191 

2 o1 App 1 i cab i1 i ty 0 0 o o o 0 o o 0 o 

202 Underlying Principles of Operation 2o3 Description of Filtration Processes o 0 .. 0 0 0 0 

2.4 -waste Characteristics Affecting Performance (WCAPs)o 2o5 Design and Operating Parameters 

2o6 References 0 o . 0 o • o o . o o 

3. 

3 o1 

3o2 

3o3 

3.4 

3.5 

.3 .6 

4. 

4.1 

4.2 

4.3 

4.4 

4.5 

4.6 

HIGH TEMPERATURE METALS RECOVERY o 

Applicability • o o • 0 • o o 0 o 

Underlying Principles of Operation 0 0 0 0 0 0 

Description of High Temperature Metals Recovery 

Process . . . . . . . . . . . . . . . . . . . . . Waste Characteristics Affecting Performance (WCAPs). Design and Operating Par~ters 

References 0 o . o • o 

ION EXCHANGE . . . o • o o o o o o 

Applicability • o o •. o o o 0 o 

Underlying Principles of Operation o 

Description of Ion Exchange Process o o o o o o . o 

Waste Characteristics Affecting Performance (WCAPs). 

Design and Operating Parameters o o o o o o o o o • 

References 0 o • 0 o • 0 0 0 0 o 0 . 0 0 0 o o o 0 . 

f\docunent\15254031.01.001 v 

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191 

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220 

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TABLE OF CONTENTS (CONTINUED) 

Section • Page No. 

(_ 

5. RETORTING . . . . . . . . . . . . . 221 

5.1 Applicability . . . . . . . . . . . 221 

5.Z Underlying Principles of Operation . 221 

5.3 Description of Retorting Process . . . . . . . . . . 222 

5.4 Waste Characteristics Affecting Performance (WCAPs}. 225 

5.5 Design and Operating Parameters . . . . . . . . . . 227 

5.6 References • . . . . . . . . . . • . . . . . . . . 228 

III. TECHNOLOGIES APPLICABLE TO MIXED WASTE 

(RADIOACTIVE/HAZARDOUS) 

INTRODUCTION . . . . . . . 229 

A. TECHNOLOGIES FOR WASTES CONTAINING ORGANICS AND 

IHOR6AHICS OTHER THAN METALS . . . . . 

1. 

2. 

3. 

Carbon Adsorption .... Distillation Technologies Extraction Technologies .. 

B. TECHNOLOGIES FOR MIXED WASTES CONTAINING METALS 

1. 

2. 

3. 

4. 

5·. 

6. 

Acid Leaching . . . . . . .. . Chemical Precipitation . . .. . Filtration ••.•....... 

High Temperature Metals Recovery . Ion Exchange • • . • . . . . . . . Stabilization of Metals ....• 

C. TECHNOLOGIES FOR MJXED WASTES IN SPECIAL TREATABILITY 

231 

231 

231 

232 

233 

233 

233 

233 

233 

234 

234 

GROUPS . . . . • . • . • . . • 235 

1. 

2. 

3. 

4. 

Amalgamation • 

Encapsulation 

Vitrification 

Incineration • 

REFER!NCES . . • . . • . . . 

f\document\15254031.01.001 vi 

235 

235 

236 

237 

238 
TABLE OF CONTENTS {CONTINUED} 

Section ( Page No. 

APPENDIX A List of Best Demonstrated Available Technology (BOAT) Background Documents and Associated BDAT(s) A-1 

LIST OF FIGURES 

Figure 

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Activated Sludge System .... . Trickling Filter System ..... . Anaerobic Digestion ....... . Continuous Chemical Reduction System Liquid Injection Incineration System Rotary Kiln Incineration System .. Fluidized Bed Incineration System . Fixed Hearth Incineration System .. Continuous Wet Air Oxidation System ... Continuous Chemical Precipitation System •. 

Circular Clarifier Systems Inclined Plate Settler System Carbon Adsorption Systems Plot of Breakthrough Curve . Batch Distillation System . Fractionation System •... 

Steam Stripping System ... Thin Film Evaporation System Screw Flight Dryer •............. 

Two-Stage Mixer-Settler Solvent Extraction System Packed and Sieve Tray Solvent Extraction Columns . High Temperature Metals Recovery System ... . Two-Step Cation/Anion Ion Exchange System ..... . Retorting Process (Without a Scrubber and Subsequent Wastewater Discharge) .•........... 

Retorting Process (With a Scrubber and Subsequent Wastewater Discharge) .............. . 

f\document\15254031.01.001 vii 

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# ' 
EXECUTIVE SUMMARY 

-

This doc~ent provides a discussion of the treatment technologies 

applicable to wastes that are subject to the Land Disposal Restrictions (LOR), 

which were mandated by Congress as part of the 1984 Hazardous and Solid Waste 

Amendments (HSWA) to the Resource Conservation and Recovery Act (RCRA). This 

document does not include every possible technology that may be used to treat 

wastes subject to the LOR, but discusses those most corrvnonly used. The 

technologies discussed include those that are demonstrated (commercially 

available) and have been proven to substantially diminish the toxicity of 

hazardous constituents and/or to reduce the likelihood of migration of such 

constituents from the waste of concern. These technologies include those that 

treat wastewaters* and those that treat nonwastewaters. 

Treatment performance data from technologies discussed in this docume~t 

were the basis for the detennination of the Best Demonstrated Avail abl'e 

Technology (BOAT), from which the Land Disposal Restrictions treatment standarcfs 

were promulgated (as numerical standards or methods of treatment). Information 

supporting the development of these treatment standards may be found in the 

applicable background documents prepared for EPA's Office of Solid Waste, Waste 

Treatment Branch. These BOAT background documents contain information on the 

following: industries affected and t"ii~tc: characterization, applicable and 

demonstrated treatment technologies for the wastes of concern, determination of 

BOAT, and treatment performance data with design and operating conditions. 

*For the purpose of the Land Disposal Restrictions rule, wastewaters are 

defined as wastes containing less than or equal to 1 percent (weight basis) filterable solids and less than or equal to 1 percent (weight basis) total organic carbon (TOC). Wastes not meeting this definition 

are classified as nonwastewaters. 

f:\document\15Z5403l.Ol.OOZ viii 
The methodology EPA used to develop the BOAT treatment standards is 

described in twa separate documents: Generic Quality Assurance Project Plan for 

Land Disposal Re-strictions Program ("BOAT") (USEPA 1990) and Methodology for 

Developing BDA~- Treatment Standards (USEPA 1990). The second document also 

discusses the petition process to be followed in requesting a variance from the 

BOAT treatment standards. 

Appendix A lists the background documents developed for the BOAT program, 

identifying the technologies and the types of constituents treated (e.g., 

organics, inorganics, metals, etc.) when present in actual treatment performance 

data. 

The treatment performance data and the design and operating data (see 

Section 5 of this executive sumary for a discussion of design and operating 

data} contained in these documents may be used to help determine whether a 

treatment system has been designed and operated properly. The treatment 

' performance data from these background documents may be used to compare th'e 

performance of a treatment system of concern treating the same or similar 

constituents (provided the waste matrices are not significantly dissimilar). 

Comparisons can be made of the destruction or removal efficiencies, the level of 

treatment achieved, and the design and operating parameters of a system (for 

example, feed rate, temperature, and oxygen concentration for incineration 

systems or concentration of nutrients, dissolved oxygen, residence time, etc. for 

biologi~al treatment systems). 

One document that may be particularly helpful is the F039 (Multisource 

Leachate) background document, Volumes A through E (USEPA 1990). This document 

contains comprehensive treatment performance data covering the complete list of 

P and U waste code constituents. The nonwastewater data, for the most part, were 

derived from 11 incineration test burns for the organics and from stabilization 

treatment for the metals. The wastewater data were derived from various sources 

such as EPA's Office of Water's Industrial Technology Division (lTD), the 

f:\document\15254031.01.002 ix 

, 
National Pollutant Discharge Elimination System (NPDES), Water Engineering 

Research. Laborat~ry (WERL), and other data sources avail able to the Agency. 

These above-me~t i oned data were generally considered to represent 1 eng-term 

samp 1 i ng, with many data sets meeting EPA's criteria for qua 1 ity assurance/ 

qua 1 ity contra 1. Hence, treatment performance data from the F039 background 

document and other BOAT documents may be used as a basis for comparison when 

evaluating the performance of other treatment systems. 

The Agency wishes to point out that additional information on treatment 

technologies may be obtained through EPA's Alternative Treatment Technology 

Information Center (ATTIC), operated by the Office of Environmental Engineering 

and Technology Demonstration. The ATTIC is an information retrieval network that 

provides up-to-date technical information on innovative treatment methods for 

hazardous wastes. The ATTIC provides information on innovative treatment 

technologies, cost analysis, and migration and s~pling data bases; provides 

information on experts who can be contacted for assistance; and is a source for 

locating and ordering documents. 

Also, the EPA Office of Waste Programs Enforcement has tapes and manuals 

for Inspectors of Incinerators (only available to EPA personnel). Information 

include an introduction to incinerator design, air pollution control, and 

regulatory guidance. Further information may be obtained by contacting the 

Regio~al RCRA training coordinator. 

The treatment technologies presented in this document have been organized 

into three separate groups according to how they treat waste and to what types 

of waste they are applicable: (1) treatment technologies that destroy or reduce 

the migration of wastes; (2) removal technologies that separate or recover 

constituents for recycle/reuse or treatment; and (3) technologies that treat 

mixed waste, i.e., hazardous/radioactive waste. Although some of the 

technologies can belong to more than one group, each technology has been placed 

in the group where it is most commonly used. 

f:\document\15254031.01.002 X 

1 
The remainder of this introduction describes the purpose and contents of 

each o( the various e 1 ements presented in each technology section: 

app 1 i cabil ity, ~nderl yi ng principles of ope rat ion, description of the techno 1 ogy, 

waste characteristics affecting performance, and design and operating parameters. 

Specifically explained are what information is provided in each technology 

subsection, how the Agency uses this information as part of its BOAT program, 

and, when applicable, haw the Agency intends to modify the treatment technology 

discussions as more treatment data and information become available. 

1. Applicability 

{a) Information Provided. The applicability section contains information 

on the general a~plication of the treatment technology to various wastes. EPA's 

analysis of applicability is performed in consideration of the parameters and 

constituents known to affect treatment selection. That is, in order to ident1_f:Y 

whether a treatment technology was applicable to any particular waste stream, the 

Agency considered all parameters and characteristics associated with a hazardous 

waste that could affect the selection of a treatment technology. EPA uses the 

acronym PATS (i.e., parameters affecting treatment selection) for these 

parameters. 

EPA's list of PATS, shown in Table 1, identifies all known constituents and 

parameters that are needed to select a technology or technology train for a given 

waste.· 

It is important to point out that in developing this ltst, EPA's goal was 

to determine the demonstrated technology or treatment technology train that would 

best treat all of the constituents in the waste (i.e., achieve the lowest 

concentration in the residual). Accordingly, EPA will add components to the 

treatment train as long as they are demonstrated and will achieve statistically 

significant reduction in the concentrations of the constituents. (Note: the 

statistical analysis that the Agency uses to determine whether a significant 

f:\document\1525~031.01.002 xi 
Table 1 List of Parameters Affecting Treatment Selection 

l 

BOAT list metals content 

BOAT list organics content 

Content of other BOAT constituents (sulfides and fluorides) 

Biological oxygen demand (BOD) 

Btu content 

Presence of complexed metals 

Cyanide content 

Filterable solids content 

Oil and grease content 

Oxidation state 

pH 

Total organic carbon (TOC) content 

Total organic halides (TOX) content 

Viscosity 

Water content 

Selectivity value 

Sublimation temperature 

Ash fusion temperature 

f:\document\15254031.01.002 xH 
reduction in constituents has occurred is referred to as Analysis of Variance 

(ANOVA). Refer to the Methode 1 ogy for De vel oping BOAT Treatment Standards 

document~for further information.) 

t 

{b) EPA's Use of This Information. EPA uses the PATS as the basis for 

making decisions regarding whether a particular technology is "demonstrated" for 

a particular waste. The Agency is performing treatment tests on specific wastes 

to NdemonstrateN the treatment of the waste using the technology, to develop 

treatment standards, and to set the criteria by which other wastes can be 

regulated using the demonstrated technology. 

The PATS analysis will sometimes show that several technologies are 

applicable for treating the waste. EPA will prioritize these technologies based 

on its analysis of available data and information regarding the effectiveness of 

the various technologies. For organics, EPA's preference will be technologies 

that recover or destroy the compounds; for metals, the Agency's preference wi11 

be technologies that result in recovery of the metals. ; 

In some instances, analysis of a particular par~eter affecting treatment 

selection will not be possible or would be meaningless with regard to selecting 

a treatment system. For example, the BOO of a contaminated soil is essentially 

meaningless since the soil is not likely to be treated in a biological wastewater 

treatment system. 

(c) Use of New Data and Information. As data become available either 

from industry or through EPA's BOAT data collection program, EPA will modify the 

PATS analysis to further refine specific concentration ranges for which various 

technologies can handle various parameters. 

f:\document\15254031.01.002 xiii 

' 
2. Underlying Principles of Operation 

(a) InfDrmation Provided. For each treatment technology EPA provides the 

fundamental theory of operation of the technology. This section is not meant to 

provide a detailed discussion on the specific complex physical, chemical, or 

biological mechanisms by which treatment occurs. Instead, the discussion 

describes the mechanisms involved so that one can understand what characteristics 

can affect the performance of the technology. For example, the underlying 

principle of chemical precipitation is that metals in wastewater are removed by 

adding a treatment chemical to form a metal precipitate that is generally 

insoluble and therefore settles out of solution. Formation of the precipitate 

and the settling mechanism are the principles controlling technology performance. 

(b) Use of Information Provided. The theory of operation is necessary 

as the precursor to analyzing which waste characteristics can affect the . . .. 

performance of a gtven treatment technology. That is, the pri nci pl es cif 

treatment operation are used as the rationale and basis on which nn: Agendy 

determines what waste characteristics can affect performance. Accordingly, waste 

characteristics affecting performance (WCAPs), which are discussed below, must 

be understood from the standpoint of how each waste characteristic inhibits or 

interferes with the fundamental operation of the treatment technology. 

3. Description of the Treatment Process 

This section provides a brief description of the principal components of 

a treatment technology .. It is intended to provide a basic understanding of the 

equipment used and the treatment sequence. This presentation relates the 

discussion on underlying principles of operation with the later discussion of the 

design and operating parameters important to effective wast2 treatment. 

Simplified block diagrams are provided in this section. The information 

presented is general in nature to avoid attempting to show all combinations and 

permutations that are possible in describing a particular technology. 

f:\document\15254031.01.002 xiv 
4. Waste Characteristics Affecting Performance (WCAPs) 

. 

(a) Information Provided. The WCAPs are based on the underlying 

principles of the treatment technology. For example, the underlying principle 

of chemical precipitation is formation of the insoluble metal precipitate and the 

settling of the precipitate out of solution. WCAPs for this technology are those 

parameters that affect the chemical reaction of the metal compound or the 

solubility of the metal precipitate (i.e., formation) and/or affect the ability 

of the precipitated compound to settle. The WCAPs include (a) the concentration 

and type of metals, (b) the concentration of total dissolved sol ids, (c) the 

concentration of complexing agents, and {d) the concentrations of ail and grease. 

The first three parameters can affect precipitate formation, and the last 

parameter can affect settling rate. 

EPA's selection of WCAPs for the various treatment systems is based on.a 

literature review, as well as information obtained during plant sampling visi~s 

that test the treatment technology. EPA is aware that in same cases analytical 

methods are not available to measure the specific waste characteristics that 

affect treatment. In such instances, EPA measures the parameter that most 

closely approximates the actual parameter of concern. For example, a WCAP for 

steam stripping is the relative volatility of a component. Because relative 

volatility cannot be measured, EPA uses boiling point as the best measure of 

assessing the WCAP of relative volatility. 

The analysis of waste characteristics affecting performance is conducted 

where EPA already has determined from a PATS analysis that an untested waste 

could be treated effectively by the same BOAT technology as another waste for 

which treatment performance data are available. The WCAP analysis is then used 

to determine whether the treatment standards from the tested waste can be 

transferred to the untested waste. Simply stated, this analysis compares, for 

two separate wastes, the characteristics that affect the level of treatment that 

can be achieved. Where this comparison shows that the untested waste can be 

f: \doclll•nt\15ZS.C03l.CLCC2 XV 
treated as well or better, the Agency will transfer the treatment standards to 

the untested waste. 

~ 

For example, for wastes that can be treated using chemical precipitation, 

if the Agency tests a waste containing lead at a given level, it will transfer 

the treatment standards developed from the test to a second lead-containing waste 

if the second waste meets the following WCAP-based conditions: 

• The lead concentration is similar to that of the tested waste; 

• The second waste has a lower total dissolved solids level; 

• The concentration and type of other metals are similar to those of the 

tested waste; and 

• The untested waste has a concentration of oil and grease similar to or 

less than that of the tested waste. 

(b) Use of Information Provided. In applying the WCAP analyses, it ~s 

important to remember that the technology itself and the associated design and 

operating conditions are fixed (i.e., they are fixed at the values that existed 

for the already tested waste). EPA does not assume that, where WCAPs for the 

untested waste show that it would be significantly harder to treat, the addition 

of another treatment component or a change in design and operating conditions 

will result fn the untested waste achieving the same performance as that of the 

previously tested waste. EPA is aware that modifying the treatment system or 

operating conditions could result in similar treatment. However, the Agency is 

not certain, without demonstrating through testing, that treatment levels 

associated with BOAT standards (normally in the low (<10) part per million or 

part per billion range) can be achieved by simply changing treatment conditions. 

Accordingly, EPA is very cautious in its decisions to transfer treatment 

standards where the WCAP analysis shows that treatment modifications are needed 

from the previously tested waste. 

f:\document\15254031.01.002 xvi 
(c) Use of New Data and Information. In developing the WCAPs for the 

various treatment technologies, EPA found little and, in some cases, no 

information ont.-the relative importance of the various WCAPs for a given 

technology (i.e., which waste characteristics have the most significant impact 

on treatment performance). Where information was available with regard to the 

specific WCAPs that are important when assessing the performance of a particular 

technology, EPA was unable to find any supporting data that would quantify the 

relative impact of each of the WCAPs on treatment performance. 

As data become available either from industry or through EPA's BOAT data 

collection program, EPA may modify the WCAP analysis to further refine the 

parameters identified as affecting treatment technology performance. As 

previously noted, before it adopts a new WCAP, the Agency must understand how the 

parameters affect treatment relative to the underlying principles of operation. 

5. Design and Operating Parameters . ' 

EPA uses design and oparating information in several ways. First, this 

information is used, in conjunction with the Agency's BOAT data collection 

program, in determining whether a particular treatment system is well designed. 

That is, the Agency assesses design data prior to determining whether to test a 

particular piece of equipment or treatment train for potential use in the 

develQprnent of BOAT treatment standards. EPA obtains operating data during the 

course of an Agency-~ponsored treatment test to ensure that the treatment system 

is well operated. Secondly, EPA expects facilities to provide the appropriate 

design and operating data when submitting treatment data to be considered in the 

development of the BOAT treatment standards. Again, the Agency assesses these 

data to · determine whether the treatment system ~as we 11 designed and we 11 

operated. 

For example, some of the critical design and operating parameters for steam 

stripping include the number of equilibrium stages in the column, the temperature 

f:\docum.nt\15Z5403l.Ol.OOZ xvii 

I 
at which the unit is designed to operate, and how well the design temperature is 

controlled. In evaluating performance data from a steam stripping operation, the 

Agency would ex~ine the design specifications (e.g., the basis for selecting the 

number of stages and design temperature) for the treatment unit in order to 

determine the extent to which the hazardous constituents could be expected to 

volatilize. After the design specifications are established, the Agency would 

collect data (e.g., hourly readings of the column temperature) throughout the 

operation of the treatment process demonstrating that the unit was operating 

according to design specifications. If the data collected vary considerably from 

the design requirements, that variation could form the basis for determination 

that the treatment unit was improperly operated. If the temperature data show, 

for example, that for significant periods of time the temperature varied 

considerably from the design requirements, the Agency would not usa these data 

to determine the levels of performance achievable by BOAT. 

. . Finally, EPA requires facilities petitioning for a treatment variance to 

submit the plant's design values and the operating data during the time of tbe 

treatment period to ensure that the treatment system was well designed and well 

operated. 

f:\document\15254031.01.002 
l 

I. TREATMENT TECHHOLOIH ES 

A. DESTRUCTION TECHNOLOGIES 
1. BIOLOGICAL TREATMENT 

1.1 ApPi i cabil i ty 

Biological treatment can typically be divided into two ciassifications: 

aerobic biological treatment and anaerobic biological treatment. Aerobic 

biological treatment takes place in the presence of oxygen, while anaerobic 

biological treatment is an oxygen-devoid process. 

Aerobic biological treatment is a treatment technology applicable to 

wastewaters containing biodegradable organic constituents ~nd :ome nonmetallic 

inorganic constituents including sulfides and cyanides. Four of the most common 

aerobic biological treatment processes are (a) activated sludge, (b) aerated 

lagoon, (c) trickling filter, and (d) rotating biological contactor (RBC). The 

activated sludge and aerated lagoon processes are suspended-growth processes ~n 

which microorganisms are maintained in suspension with the liquid. The trickling 

filter and the RBC are attached-growth processes in which microorganisms grow on 

any inert medium such as rocks, slag, or specifically designed ceramic or plastic 

materials. This section discusses these four processes as well as the powdered 

activated carbon (PAC) adsorption process, which is a variation of the activated 

sludge treat~ent. 

_Anaerobic digestion is best suited to wastes with a moderate to high pH, 

honhalogenated hydrocarbons, moderate to low organic loadings, and low to zero 

biological oxygen demand. The waste should also be in a semisolid or sludge 

form. Anaerobic biological treatment typically takes place in an anaerobic 

digester. 

1.2 UnderlYing Principles of Operation 

The basic principle of operation for aerobic biological treatment processes 

is that living, oxygen-requiring microorganisms decompose organic and nonmetallic 

inorganics constituents into carbon dioxide, water, nitrates, sulfates, simpler 

f:\~cument\15254031.01.003 1 
low-molecular-weight organic byproducts, and cellular biomass. Wastes that can 

be degradad by a_given species or genus of organisms may be very limited. A 

mixture of orga~sms may be required to achieve effective treatment, especially 

for wastes containing mixtures of organic compounds. Nutrients such as nitrogen 

and phosphorus are also required to aid in the biodegradation process. 

The aerobic biodegradation process can be represented by the following 

generic equation: 

microorganisms > H 0 + COz + biomass nutrients 2 

Microorganisms produce enzymes that catalyze the biodegradation reactions, 

degrading the organic waste to obtain energy for cell metabolism and cell growth. 

Aerobic biological treatment of wastewaters containing organic constituents 

results in the net accumulation of a biomass of expired microorganisms consist~~g 

mainly of cell protein. However, the cellular biomass or sludges may al~o 

contain entrained constituents from the wastewater or partially degraded 

constituents. These sludges must be periodically removed (•wasted•) to maintain 

proper operation of the aerobic biological treatment system. 

The basic principle of operation of anaerobic biological treatment is that 

microorganisms in the absence of oxygen transform organic constituents and 

nitrogen-containing compounds into carbon dioxide and methane gas. Often other 

nutrients such as nitrogen and phosphorus are necessary to aid digestion. The 

anaerobic biological treatment process can be described by the fall owing 

equation: 

ex Hy + microorganisms > CO + CH4 + biomass nutrients 2 

f: \docunent\152~031.01. 003 2 

1 
1.3 Description of Biological Treatment Processes 

- 1.3 .1 Ac~ vated Sludge 

The activated sludge process is currently the most widely used biological 

treatment process. This is partly the result of the fact that recirculation of 

the biomass, which is an integral part of the process, allows microorganisms to 

adapt to changes in wastewater composition with a relatively short acclimation 

time and also allows a·greater degree of control over the acclimated bacterial 

pop~:lation. 

An activated sludge system consists of an equalization basin, a settling 

tank, an aeration basin, a clarifier, and a sludge recycle line. Wastewater is 

homogenized in an equalization basin to reduce variations in the feed, which may 

cause process upsets of the microorganisms and diminish treatment efficiency. . . 

Settleable solids are then removed in a settling tank. 

Next, wastewater enters an aeration basin, where an aerobic bacterial 

population is maintained in suspension and oxygen, as well as nutrients, is 

provided. The contents of the basin are referred to as the mixed 1 i quor. Oxygen 

is supplied to the aeration basin by mechanical or diffused aeration, which also 

aids in keeping the microbial population in suspension. The mixed liquor is 

continuously discharged from the aeration basin into a clarifier, where the 

biomass is separated from the treated wastewater. A portion of the biomass is 

recycled to the aeration basin to maintain an optimum concentration of acclimated 

microorganisms in the a~ration basin. The remainder of the separated biomass is 

discharged or Nwasted.• The biomass may be further dewatered on sludge drying 

beds or by sludge filtration (which is further discussed in Section 11.8.2} prior 

to disposal. The clarified effluent is discharged. A schematic diagram of an 

activated sludge treatment system is shown in Figure 1. 

f: \docllll!nt\15254031. 01.003 3 
. 

WASTEWATER EQUALIIA TIOH 

IHfLUEHT .. TANK ~ 

8ETTLINO 

TANK f-+ 

OXYGEN 

AND 

NUTRIENTS 

• 

AERATION 

BASIN 

~ 

BASIN 

EFFLUENT CLARIFIER 

-

SLUDGE RECYCLE t 

\ .. ... . ' . 

Figure 1 Activated Sludge System 

1-+-

... 

•' "" 

TREATED 

EFFLUENT 

TO DISPOSAL 

WASTE SLUDGE 

TO SLUDGE 

fiLTRATION 

AND DISPOSAL 

. ....-... 
The recycled biomass is referred to as activated siudge. The term 

nactivateG" is u_sed because the biomass contains living and acclimated 

mict·oorganisms ~at metabolize and assimilate organic material at a higher rate 

when returned to the aeration basin. This occurs because of the low 

food-to-microorganism ratio in the sludge from the clarifier. 

An important variation on the activated sludge process is the Powdered 

Activated Carbon Treatment (PACT) process. This process offers a combined 

treatment and pretreatment system in which noncompatible and toxic constituents 

are adsorbed onto activated carbon, while microorganism-compatible waste remains 

in solution. Powdered activated carbon is added directly to the aeration basin 

of the activated sludge treatment system. Overall removal efficiency is improved 

because compounds that are not readily biodegradable or that are toxic to the 

microorganisms are aasorbed onto the surface of the powdered activated carbon. 

The carbon is removed from the wastewater in the c lari fi er a 1 ong with the 

biological sludge. Usually, the activated carbon is recovered, regenerated, and 

recycled. 

1.3.2 Aerated Lagoon 

, ' 

Like an activated sludge system, an aerated lagoon is a suspended-growth 

process. The aerated lagoon system consists of a large pond or tank that is 

equipp~d with mechanical aerators to maintain an aerobic environment and to 

prevent settling of the suspended biomass. Initially, the population of 

microorganisms in an aerated lagoon is much lower than that in an activated 

sludge system because there is no sludge recycle. Therefore, a significantly 

longer residence time is required to achieve the same effluent quality. However, 

this longer residence time may be an advantage when complex organic chemicals are 

to be degraded. Also, the microorganisms in aerated lagoons are more resistant 

to process upsets caused by feed variations than those in activated sludge 

systems because of the larger tank volumes and longer residence times used. The 

effluent from the aerated lagoon may flow to a settling tank for removal of 

suspended solids. Alternatively, the mechanical aerators in the system may be 

f:\document\15254031.01.003 5 
shut off for a period of time to facilitate settling prior to discharge of the 

effluent.· The se!_tled sol;ds are generally dewatered prior to disposal. 

l. 

1.3.3 Trickling Filters 

A trick.l ing filter is an attached-growth biological treatment process. The 

system consists of an equalization basin, a settling tank, a filter medium, an 

influent wastewater distribution system, an under drain system, a clarifier, and 

a recirculation line. The filter medium consists of a bed of ~n inert material 

to which the microorganisms attach themselves and through which the wastewater 

is percolated. Rocks or synthetic material such as plastic rings and saddles are 

typically used as filter media. Fall owing equa 1 izati on and settling of 

settleable solids in the wastewater, it is distributed over the top of the filter 

medium by a rotating distribution ann or a fixed distributor system. The 

wastewater forms a thin layer as it flows downward through the filter and over .. 

the microorganism layer on the surface of the medium. As the distribution ~ 

rotates, the microorganism layer is alternately exposed to a flow of wastewater 

and a flow of air. In the fixed distributor system, the wastewater flow is 

cycled on and off at a specified dosing rate to ensure that an adequate supply 

of oxygen is available to the microorganisms. Oxygen from air reaches the 

microorganisms through the void spaces in the medium. Figure 2 is a diagram of 

a trickling filter system. 

A trickling filter system is typically used as a roughing filter to reduce 

the organic loading on a downstream activated sludge process. Trickling filters 

can be used for the tr~atment of wastewaters that could potentially produce 

~bulkingN sludge (i.e., a sludge with poor settling characteristics and poor 

compactability in an activated sludge process) because the microbial solids that 

slough off the trickling filter medium are relatively dense and can be readily 

removed in a clarifier. 

f:\dor.ument\15254031.01.003 6 
- --~·---------------- --- ··--~·--·-

WASTEWATER WASTE DISTRIBUTOR INFLUENT--~~-,------~------r------r------,-----~ 

Figure 2 Trickling Filter System 

TREATED ."'A--~ EFFLUENT 

TO CLARIFIER 

,r" 
1.3.4 Rotating Biological Contactor 

A rotatirg- biological contactor (RBC) consists of a series of closely 

spaced, parallel disks that are rotated at an average rate of 2 to 5 revolutions 

per minute while submerged to 40 percent of their diameters in a contact tank 

containing wastewater. The disks are constructed of polystyrene, polyvinyl 

chloride, or similar materials. Each disk is covered with a biological s1ime 

that degrades dissolved organic constituents present in the wastewater. As the 

disk is rotated out of the tank, it carries a film of the wastewater into the 

air, where oxygen is available for aerobic biological decomposition. As excess 

biomass is produced, it sloughs off the disk and is separated from the treated 

effluent in a clarifier. The sloughing off process is similar to that which 

occurs in a trickling filter. There is no recycle of sludges or recirculation 

of treated effluent in an RBC process. Several RBCs are often operated in 

series, with the effluent from the last RBC being discharged. Biological solids 

are usually dewatered prior to disposal. 

1.3.5 Anaerobic Biological Treatment 

In anaerobic biological treatment, the influent sludge is settled and 

equalized, then pumped to the anaerobic digester (Figure 3) along with an 

alkaline adjustment additive. There may or may not be mechanical agitation of 

the digester. After an adequate residence time to allow for proper digestion, 

~he dtgester contents are allowed to settle. .The supernatant is pumped to an 

aerobic treatment area (typically to an activated sludge unit), while the sludge 

is taken to disposal areas or subjected to additional treatment, such as drying 

or incineration. 

1.4 Waste Characteristics Affecting Performance (WCAPsl 

In determining whether biological treatment will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste 

and whether performance levels can be transferred, EPA examines the following 

f:\document\15254031.01.003 8 
SLUDGE INFlUENT ~ EQUALIZAT10N .,_....,....., SLUOOE TANK 

ALKALINITY .... ADJUSTMENT 'Q- I ~~ 

ADDITIVE 

PUMP 

d$fl~E 

t GAS COMPRESSION 

~~~-, I FlOATING I I COVER 

I 

I 

MIXERS 

DIGESTER (CONCRETE) 

RECYCLE SLUDGE 

Figure 3 Anaerobic Digestion 

SUPERNAl ANT TO 

ACTIVATED SLUDGE 

SLUDGE SLUDGE 

EFFLUENT HOLDING 

BASIN 

PUMP 
waste characteristics: (a) the r<ltio of the biological oxygen demand to the 

total organic carbon content, (b) the concentration of surfactants, and (c) the 

concentration or-toxic constituents and waste characteristics. 

l. 

1.4.1 Ratio of Biological Oxygen Demand to Total Organic Carbon Content 

Because organic constituents in the waste effectively serve as a food 

supply for the microorganisms, it is necessary that a significant percentage be 

biodegradable. If they. are not, it will be difficult for the microorganisms to 

successfully acclimate to the waste and achieve effective treatment. The 

percentage of biodegradable organics can be estimated by the ratio of the 

biological oxygen demand (BOD) to the total organic carbon (TOC) content. Since 

the biological oxygen demand is a measure of the amount of oxygen required for 

complete microbial oxidation of biodegradable organics, the BOD analysis is 

mostly relevant to aerobic biological treatment. (In anaerobic biological 

treatment, BOO is one of the main restrictive characteristics in that BOD must 

be relatively low or zero.) If the ratio of BOO to TOC in an untested waste 1~ 

significantly lower than that in the tested waste, the system may not achieve the 

same performance and other, more applicable technologies may need to be 

considered for treatment of the untested waste. 

1.4.2 Concentration of Surfactants 

Surfactants can affect biological treatment performance by forming a film , 

on organic constituents, thereby establishing a barrier to effective 

biodegradation. If the concentration of surfactants in an untested waste is 

significantly higher than that in the tested waste, the system may not achieve 

the same performance and other, more applicable technologies may need to be 

considered for treatment of the untested waste. 

f:\document\15254031.01.003 10 
1.4.3 Concentration of Toxic Constituents and Waste Characteristics 

A number at constituents and waste characteristics have been identified as 

potentially toxic to microorganisms. Specific toxic concentrations have not been 

determined for most of these canst i tuents and waste characteristics. The 

constituents and waste characteristics found to be potentially toxic to 

microorganisms include metals and oil and grease, ammonia, and phenols. High 

concentrations of dissolved solids are treated more effectively by anaerobic 

treatment than by aerobic treatment. If the concentration of toxic constituents 

and waste characteristics in an untested waste is significantly higher than that 

in the tested waste, the system may not achieve the same performance and other, 

more applicable technologies may need to be considered for treatment of the 

untested waste. 

1.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a biologica-l 

treatment system, EPA examines the following parameters: (a) the amount of 

nutrients, (b) the concentration of dissolved oxygen, (c) the food-tomicroorganism ratio, (d) the pH, (e) the biological treatment temperature, 

{f) the mean cell residence time, (g) the hydraulic loading rate, (h) the 

settling time, and {i) the degree of mixing. 

For many hazardous organic constituents, analytical methods are not 

available or the constituent cannot be analyzed in the waste matrix. Therefore, 

it would normally be impossible to measure the effectiveness of the biological 

treatment system. In these cases EPA tries to identify measurable parameters or 

constituents that would act as surrogates in order to verify treatment. 

For organic constituents, each compound contains a measurable amount of 

total organic carbon (TOC). Removal of TOC in the biological treatment system 

indicates removal of organic constituents. Hence, TOC analysis is likely to be 

f:\dccument\15254031.01.003 11 
an adequate surrogate analysis where the specific organic constituent cannot be 

measured. 

{_ 

However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden (i.e., the TOC 

analysis may not be sensitive enough to detect changes at the milligrams per 

liter (mg/1) level in matrices where total organic concentrations are hundreds 

or thousands of mg/1). In these cases other surrogate parameters should be 

sought. For example, if a specific analyzable constituent is expected to be 

treated as well as the unanalyzable constituent, the analyzable constituent 

concentration should be monitored as a surrogate. 

1.5.1 Amount of Nutrients 

Nutrient addition is important in controlling the growth of microorganisms 

because an insufficient amount of nutrients results in poor microbial growth wi~h 

poor biodegradation of organic constituents. The principal inorganic nutrien~s 

used are nitrogen and phosphorus. In addition, trace amounts of potassium, 

calcium, sulfur, magnesium, iron, and manganese are also used for optimum 

microbial growth. The percent distribution of nitrogen and phosphorus added to 

microorganisms varies with the age of the organism and the particular 

environmental conditions. The total amount of nutrients required depends on the 

net mass of organisms produced. 

EPA monitors the amount of nutrients added and their method of addition to 

the wastewater to ensure that a sufficient supply is provided to achieve an 

effective growth of microorganisms. 

1.5.2 Concentration of Dissolved Oxygen 

A sufficient concentration of dissolved oxygen (DO) 1s necessary to 

metabolize and degrade dissolved organic constituents in aerobic treatment. The 

DO concentration is controlled by adjusting the aeration rate. The aeration rate 

f:\document\1SZS4031.01.003 12 
must be adequate to provide a sufficient DO concentration to satisfy the BOD 

requiremeAts of t~e waste, as well as to provide adequate mixing to keep the 

microbial popu1t_tion in suspension (for activated sludge and aerated lagoon 

processes). The reverse is true for anaerobic treatment, in that DO must be 

absent for anaerobic treatment to occur. EPA monitors the DO concentrations 

continuously, if possible, to ensure that the system is operating at the 

appropriate design condition and to diagnose operational problems. 

1.5.3 Food-to-Microorganism Ratio 

The food-to-microorganism (F/M) ratio, which applies only to activated 

sludge systems, is a measure of the amount of biomass available to metabolize the 

influent organic loading to the aeration unit. This ratio can be determined by 

dividing the influent BOD concentration by the concentration of active biomass, 

also referred to as the mixed liquor volatile suspended solids (HLVSS). The F/H . . ... 

ratio is controlled by adjusting the wastewater feed rate or the sludge recycfe 

rate. If the F/M ratio is too high, too few·microorganisms will be available to 

degrade the organics. EPA periodically analyzes the influent BOD and the 

aeration unit's MLVSS concentrations to ensure that the system is operating at 

the appropriate design condition. 

1.5.4 pH 

Generally, neutral or slightly alkaline pH favors microorganism growth. 

The optimum range for most microorganisms used in biological treatment systems 

is between 6 and 8. Treatment effectiveness is generally insensitive to changes 

within this range. However, pH values outside the range can lower treatment 

performance. EPA monitors the pH continuously, if possible, to ensure that the 

system is operating at the appropriate design condition and to diagnose 

operational problems. 

f:\doc~nt\15254031.01.003 13 
1.5.5 Biological Treatment Temperature 

Microbial 'growth can occur under a wide range of temperatures, although the 

majority of the microbial species used in aerobic biological treatment processes 

are active between 20 and 3S"C (68 to 95"F}. For anaerobic systems, the 

temperature is typically between 30 and 70"C (86 to ISS"F}. The rate of 

biochemical reactions in cells increases with temperature up to a maximum above 

which the rate of activity declines and microorganisms either die off or become 

less active. EPA monitors the biological treatment temperature continuously, if 

possible, to ensure that the system is operating at the appropriate design 

condition and to diagnose operational problems. 

1.5.6 Mean Cell Residence Time 

In activated sludge, aerated lagoon, and anaerobic digestion systems, t~e 

mean cell residence time (HCRT) or sludge age is the length of time organisms ar.e 

retained in the unit before being drawn off as waste sludge. By controlling t~e 

MCRT, the growth phase of the microbial population can be controlled. The MCRT 

must be long enough to allow the organisms in the unit to reproduce. The MCRT 

is determined by dividing the total active microbial mass in the unit (HLVSS) by 

the total quantity of microbial mass withdrawn daily (wasted). EPA monitors the 

MCRT to ensure that a sufficient number of microorganisms are present in the 

unit. 

1.5.7 Hydraulic Loading Rata 

The hydraulic loading rate determines the length of time the organic 

constituents are in contact with the microorganisms and, hence, the extent of 

biodegradation that occurs. In trickling filters, the hydraulic loading rate 

also determines the shear velocities on the microbial layer. Excessively high 

hydraulic loading rates may wash away the microbial layer faster than it can grow 

back. However, the hydraulic loading rate must be high enough to keep the 

microbes moist and to remove dead or dying microbes that have lost their ability 

f:\document\15254031.01.003 14 

1 

f 
to cling to the filter media. For all aerobic biological treatment processes, 

the hydrayl ic loading rate is controlled by adjusting the wastewater feed rate. 

In addition, fo~RBCs, the hydraulic loading rate can be controlled by changing 

the disk speed or adjusting the submersion depth. EPA monitors the wastewater 

feed rates to ensure that the hydraulic loading provides sufficient time to 

achieve an effective biodegradation of organic constituents in the wastewater. 

1.5.8 Settling Time 

Adequate settling time must be provided to separate the biological solids 

from the mixed liquor. Activated sludge systems cannot function properly if the 

solids cannot be effectively separated and a portion returned to the aeration 

basin. EPA monitors the settling time to ensure effective solids removal. 

1.5.9 Degree of Mixing 

Mixing provides greater uniformity of the wastewater feed in the 

equalizatior. basin to reduce variations that may cause process upsets of the 

microorganisms and diminish treatment efficiency. For activated sludge and 

aerated lagoon systems, sufficient aeration in the aeration unit provides mixing 

to ensure adequate contact between the microorganisms and the organic 

constituents in the wastewater. The quantifiable degree of mixing is a complex 

assess~ent that include~, among other factors, the amount of energy supplied, the 

length of time the material is mixed, and the related turbulence effects of the 

specific size and shape of the mixing unit. The degree of mixing is beyond the 

scope of simple measur.ement. EPA, however, evaluates the degree of mixing 

qualitatively by considering whether mixing is provided ~nd whether the type of 

mixing device is one that could be expected to achieve uniform mixing of the 

wastewater. 

f:\document\152S403l.Ol.OOJ 15 
1.6 References 

. Barley, J., and Ollis, D. 1977. Biochemical engineering fundamentals. New 

York: Hctraw-Hill Book Co. 

Burchett, H., and Tshobanoglous, G. 1974. Facilities for controlling the 

activated sludge process by mean cell residence time. Journal Water 

Pollution Control Federation. Vol. 46, no. 5 (May 1974), p. 973. 

Clark, J.W., Viessman, W., and Ha1t111er, H. 1977. Water supply and pollution control. New York: Harper & Row, P~blishers. 

Eckenfelder Jr., W.W., Patoczka, J., and Watkins, A. 1985. Wastewater 

treatment. Chemical engineering. September 2, 1985. 

Johnson, S.J. 1978. Biological treatment. Unit operation for treatment of 

hazardous industrial wastes. Park Ridge, N.J.: Noyes Data Corporation. 

Kobaya5hi, H., and Rittmann, B. 1982. Microbial removal of hazardous organic compounds. Environmental Science and Technology. Vol. 16, no. 3, 

pp. 170-183. . . 

Metcalf & Eddy, Inc. 1979. Wastewater engineering: treatment, disposal, reuse. 

New York: McGraw-Hill Book Co. : 

Nemerow, N.L. 1978. Industrial water pollution origins, characteristics. and 

treatment. Reading, Mass.: Addison-Wesley Publishing Company. 

Perry, R., and Green, 0. 1984. Ch~mical engineers' handbook. 6th ed. New York: 

McGraw-Hill Book Co. 

Rittmann, 8. 1987. Aerobic biological treatment. Environmental Science and 

Technology. February 1987. p. 128. 

USEPA. · 1985. U.S. Environmental Protection Agency. Final report. Assessment 

of treatment technologies for hazardous waste and their restrictive waste 

characteristics. Vol 1. Washington, D.C.: U.S. Environmental Protection 

Agency. 

USEPA. 1986. U.S. Environmental Protection Agency. Best demonstrated available 

technology background document for FOOl-FOOS spent solvents. Vol. 1, 

EPA/530-SW-86-056. pp. 4-43. Washington, D.C.: U.S. Environmental 

Protection Agency. 

f:\document\1525403l.Ol.003 16 

' I 
2. CHEMICAL OXIDATION 

2.1 Appi~cability 

Chemical oxidation is a treatment technology used to treat wastes 

containing organics. It is also used to treat sulfide wastes by converting the 

sulfide to sulfate. The destruction of cyanides in wastes is usually 

accomplished by chemical oxidation. Chemical oxidation can also be used to 

change the oxidation state of metallic compounds to valences that are less 

soluble, such as converting arsenic in wastes to the relatively insoluble 

pentavalent state. 

Chemical oxidation is applicable to dissolved cyanides in aqueous 

solutions, such as wastewaters from metal plating and finishing operations, or 

to inorganic sludges from these operations that contain cyanide-compounds. For 

cyanides, chemical oxidation is most applicable to solutions containing less than 

500 mg/1 of cyanides when the cyanides are in a form that can be easily 

disassociated in water to yield free cyanide ions. If cyanides are present in 

water as a tightly bound complex ion (e.g., ferrocyanide), only limited treatment 

may occur. If the waste contains greater than 500 mg/1 of cyanide, but no more 

than about 100,000 mg/1, electrolytic oxidation may be more appropriate. See 

Section I.A.4. 

Chemical oxidation may also be used for destruction of the organic 

component of organometallic compounds in wastes, thus freeing the metal component 

for treatment by chemical precipitation or stabilization. Organic compounds such 

as EDTA, NTA, citric acid, glutaric acid, lactic acid, and tartrates are often 

used as chelating agents to prevent metal ions from precipitating out in 

electroless plating solutions. When these spent plating solutions require 

treatment for metals removal by chemical precipitation, the organic chelating 

agents must first be destroyed. Chemical oxidants, potassium permanganate in 

particular, are effective in releasing metals from complexes with these organic 

compounds. 

f:\document\15254031.01.004 17 
2.2 Underlying Principles of Operation 

- The basil principle of operation for chemical oxidation is that inorganic 

cyanides, some -dissolved organic compounds, and sulfides can be chemically 

oxidized to yield carbon dioxide, water, salts, simple organic acids. and, in the 

case of sulfides, sulfates. Metallic ions such as arsenites can be oxidized to 

higher, less soluble valences such as arsenates. The principal chemical oxidants 

used are hypochlorite, chlorine gas, chlorine dioxide, hydrogen peroxide, ozone, 

and potassium permanganate. The reaction chemistry for each is discussed below. 

2.2.1 Oxidation with Hypochlorite or Chlorine (Alkaline Chlorination) 

This type of oxidation is carried out using sodium hypochlorite (NaOC1}, 

calcium hypochlorite (Ca(OC1) 2), chlorine gas (Cl 2}, or sometimes chlorine 

dioxide gas (Cl02). The reactions are normally conducted under slightly ~r 

moderately alkaline conditions. Alkaline chlorination of cyanide is a two-step 

process usually operated at a pH of 10 to 11.5 for the first step and 8.5 for tfie 

second step. The toxic gas cyanogen chloride (CNCl) is formed as a reaction 

intermediate in the first step of this process and may be liberated if the pH is 

less than 10 and incomplete reaction occurs. Example reactions for the oxidation 

of cyanide, phenol, and sulfide using sodium hypochlorite are shown below: 

Cyanide: CN- + NaOCl .. OCN- + NaCl {Step 1) 

20CN- + 3Na0Cl .. C03 z- + C02 + N2 + 3NaCl {Step 2) 

Phenol: 0H + 14Na0Cl • 6C02 + 3H20 + 14NaCl 

Sulfide: s· + 4NaOC1 ~ so,· + 4NaC1 

Chlorine dioxide also oxidizes the same pollutants under identical 

conditions. Chlorine dioxide first hydrolyzes to form a mixture of chlorous 

f:\document\15254031.01.004 18 
(HC102

) and chloric (HC103) acids. These acids act as the oxidants, as shown in 

the equattons belQw, for phenol: 

2Cl02 + H20 ~ HC102 + HC103 

C6H50H + 7HC102 • 6C02 + 3H20 + 7HC1 

3C6H50H + 14HC103 .. 8C02 + 9H20 + 14HC1 

2.2.2 Peroxide Oxidation 

Peroxide oxidizes the same constituents that alkaline chlorination 

oxidizes under similar ~onditions. The relevant reactions are the following: 

2.2.3 Oxidation with Ozone (Ozonation) 

' ' 

Ozone is an effective oxidizing agent for the treatment of organic 

compou~ds and for the oxidation of cyanide to cyanate. Cyanogen gas (C2N2

) is 

a reaction intermediate in this reaction. Further oxidation of cyanate to carbon 

dioxide and nitrogen compounds (N2 or NH3) occurs slowly with ozone. The 

oxidation of cyanide to-cyanate proceeds by the following reaction: 

The rates of ozonation reactions can be accelerated by supplying 

ultraviolet (UV) radiation during treatment. Some literature sources indicate 

that even the cyanide complexes most difficult to treat, the iron-cyanide 

complexes, can be oxidized completely. 

f:\document\1525403l.Ol.JO• 19 
2.2.4 Oxidation with Potassium Permanganate 

Potassium<P.ermanganate can also be used to oxidize the same constituents 

as the other chemical oxidants. The reactions of potassium permanganate with 

phenol and sulfide at acidic pHs and with cyanide at pH 12 to 14 are as follows: 

In cyanide oxidation using potassium permanganate, cyanide is oxidized only to 

cyanate. Further oxidation of cyanate can be accomplished by acid hydrolysis or 

by the use of another oxidizing agent. 

2.2.5 S02/A1r Oxidation . . 

Cyanide can be oxidized to cyanate in an aqueous solution by bubbling air 

containing from 1 to 10 percent 502 through the waste. The 502 is also oxidized 

to sulfate in this reaction. This treatment process occurs by the following 

reaction: 

This oxidation reaction requires the use of a soluble copper salt catalyst. 

Copper sulfate {CuS04) is most often used. 502/air oxidation is used frequently 

in the treatment of wastewaters from gold production, which contain both cyanide 

and thiocyanate, because 502/air oxidizes cyanide more strongly than thiocyanate 

while alkaline chlorination and other co11111on oxidizing agents oxidize thiocyanate 

more strongly than cyanide. As with potassium permanganate, further oxidation 

of cyanate can be accomplished by acid hydrolysis or by the use of another 

oxidizing agent. 

f:\docum!nt\15254031.01.004 20 
2.3 Description of Chemical Oxidation Processes 

2.3.1 Al~line Chlorination 

Alkaline chlorination can be accomplished by either batch or continuous 

processes. For batch treatment, the wastewater is transferred to a reaction 

tank, where the pH is adjusted and the oxidizing agent is added. In some cases, 

the tank may be heated to increase the reaction rate. For oxidation of most 

compounds, a slightly to moderately alkaline pH is used. It is important that 

the tank be well mixed for effective treatment to occur. After treatment, the 

wastewater is either directly discharged or transferred to another process for 

further treatment. 

In the continuous process, automatic instrumentation is used to control pH, 

reagent addition, and temp.erature. An oxidation-reduction potential (ORP) sensar 

is usually used to measure the extent of reaction. 

In both types of processes, agitation is typically provided to maintain 

thorough mixing. Typical residence times for these and other oxidation processes 

range from 1 to 2 hours. 

2.3.2 Peroxide Oxidation· 

The peroxide ox1dat1on process is run under similar conditions, and with 

similar equipment, to those used in the alkaline chlorination process. Hydrogen 

peroxide is added as a ]iquid solution. 

2.3.3 Ozonatton 

Ozonation can be conducted in a batch or continuous process. The ozone for 

treatment is produced onsite because of the hazards of transporting and storing 

ozone as we 11 as its short she 1 f 1 i fe. The ozone gas is supplied to the react I on 

vessels by injection into the wastewater. The batch process uses a single 

f:\dbcument\15254031.01.004 21 
reaction tank. As with alkaline chlorination, the amount of ozone added and the 

reaction ~ime usee!_ are determined by the type and concentration of the oxidizable 

contaminants, a~~ vigorous mixing should be provided for complete oxidation. 

In continuous operation, two separate tanks may be used for reaction. The 

first tank receives an excess dosage of ozone. Any excess ozone remaining at the 

outlet of the second tank is recycled to the first tank, thus ensuring that an 

excess of ozone is maintained and also that no ozone is released to the 

atmosphere. As with alkaline chlorination, an ORP control system is usually 

necessary to ensure that sufficient ozone is being added. 

2.3.4 Permanganate Oxidation 

Pennanganate oxidation is conducted in tanks in a manner similar to that 

used for alkaline chlorination, as discussed previously. Potassium permanganate 

is normally dissolved in an auxiliary tank and added as a solution. As with t~e 

other oxidizing agents, ORP (for continuous processes) and excess oxidizing ageat 

(for batch processes) are monitored to measure the extent of reaction. 

2.3. 5 S02

/A1 r Oxidation 

S02/air oxidation of cyanide depends on efficient mixing of air with the 

waste to ensure an adequate supply of oxygen. Because of this factor, the 

equipment requirements for this process are si~ilar to those for ozonation. 502 

is sometimes supplied with the air by using flue gas containing 502 as the air 

source. Otherwise, sulfur fn the +4 oxidation state can be fed as gaseous 

sulfur dioxide (502), liquid sulfurous acid (H2S03), sodium sulfite (Na2S03) 

solution, or sodium bisulfite {NaHS03) solution. Sodium bisulfite solution, made 

by dissolving sodium 10etabisulfite (Na2S205) in water, is the most frequently 

used source of 502 • This process is usually run continously, with the addition 

of oxidizing agent and acid/alkali being controlled through continuous monitoring 

of ORP and pH, respectively. 

f: \docunent\15254031. 01.0~ 22 

1 

-

J 
2.4 Waste Characteristics Affecting Performance (WCAPs) 

In determt~ing whether chemical oxidation will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste 

a~d whether performance levels can be transferred, EPA examines the following 

waste characteristics: (a} the concentration of other oxidizable contaminants 

and (b) the concentration of metal salts. 

2.4.1 Concentration of Other Oxidizable Compounds 

The presence of other oxidizable compounds in addition to the constituents 

of concern will increase the demand for oxidizing agents and, hence, potentially 

reduce the effectiveness of the treatment process. As a surrogate for the amount 

of oxidizable organics present, EPA analyzes for total organic carbon (TOC) in 

the waste .. Inorganic requcing compounds such as sulfide may also create a dema~d 

for additional oxidizing agent; EPA also attempts to identify and analyze far 

these canst i tuents. If TOC and/or inorganic reducing compound concentrat i ens t'n 

the untested waste are significantly higher than those in the tested waste, the 

system may not achieve the same performance. Additional oxidizing agent may be 

required to effectively oxidize the waste and achieve the same treatment 

performance, or other, more applicable treatment technologies may need to be 

considered for treatment of the untested waste. 

2.4.2 Concentration of Metal Salts 

Metal salts, especially lead and silver salts, will react with the 

oxidizing agent(s) to fona metal peroxides, chlorides, hypochlorites, and/or 

chlorates. These reactions can cause an excessive consumption of oxidizing 

agents and potentially interfere with the effectiveness of treatment. 

An additional problem with metals in cyanide solutions is that 

metal-cyanide complexes are sometimes formed. These complexes are negatively 

charged metal-cyanide ions that are extremely soluble. Cyanide in the complexed 

f:\document\1SZ5403l.Ol.OC4 23 
form may not be oxidizable, depending on the strength of the metal-cyanide bond 

in the complex and the type of oxidizing agent used. Iron complexes (for 

example, the fe~ocyanide ion, Fe(CN) 6-

4

) are the most stable of the complexed 

cyanides. 

If the concentrations of metal salts and/or metal-cyanide complexes in the 

untested waste are significantly higher than those in the tested waste, the 

system may not achieve the same performance. Additional oxidizing agent and/or 

a different oxidizing agent may be required to effectively oxidize the waste and 

achieve the same treatment performance, or other, more applicable treatment 

technologies may need to be considered for treatment of the untested waste. 

2.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a chemical 

oxidation system, EPA examines the following parameters: {a) the residence ti~, 

(b) the amount and type of oxidizing agent, (c) the degree of mixing, (d) the pff, 

(e) the oxidation temperature, and (f) the amount and type of catalyst. 

For many hazardous organic constituents, analytical methods are not 

available or the constituent cannot be analyzed in the waste matrix. Therefore, 

it would normally be impossible to measure the effectiveness of the chemical 

oxidation treatment system. In these cases EPA tries to identify measurable 

parameters or constituents that would act as surrogates to verify treatment. 

For organic cons~1tuents, each compound contains a measurable amount of 

total organic carbon {TOC). Removal of TOC fn the chemical oxidation treatment 

system will indicate removal of organic constituents. Hence, TOC analysis fs 

likely to be an adequate surrogate analysis where the specific organic 

constituent cannot be measured. 

However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden (i.e., the TOC 

f: \doc~~~~ent\15254031.01. 004 24 
analysis may not be sensitive eno~gh to detect changes at the milligrams/liter 

(mg/1) 181/el in matrices where total organic concentrations are hundreds or 

thousands of mg/~). In these cases other surrogate parameters should be sought. 

For example, if a specific analyzable constituent is expected to be treated as 

well as the unanalyzable constituent, the analyzable constituent concentration 

should be monitored as a surrogate. 

2.5.1 Residence Time 

The residence time impacts the extent of volatilization of waste 

contaminants. For a batch system, the residence time is controlled by adjusting 

the treatment time in the reaction tank. for a continuous system, the waste feed 

iate is controlled to make sure that the system is operated at the appropriate 

design residence time. EPA monitors the residence time to ensure that sufficient 

time is provided to effectively oxidize the waste. 

2.5.2 Amount and Type of Oxidizing Agent 

Several factors influence the choice of oxidizing agents and the amount to 

be added. The amount of oxidizing agent required to treat a given amount of 

oxidizable cunstituent(s) will vary with the agent chosen. Enough oxidant must 

be added to ensure complete oxidation; the specific amount depends on the type 

of ox.idizable compounds in the waste and the chemistry of the oxidation 

reactions. Theoretically, the amount of oxidizing agent to be added can be 

computed from oxidation reaction stoichiometry; in practice, an excess of oxidant 

should be used. Testing for excess oxidizing agent will determine whether the 

reaction has reached completion. In continuous processes, oxidizing agent is 

added by automated feed methods. The amount of oxidizing agent needed is usually 

measured and controlled automatically by an oxidation-reduction potential (ORP) 

sensor. EPA examines the amount of oxidant added to the chemical oxidation 

system to ensure that it is sufficient to effectively oxidize the waste and, for 

continuous processes, examines how the facility ensures that the particular 

addition rate is maintained. EPA also tests for excess oxidizing agent for batch 

f:\document\1525~031.01.004 25 
processes and continuously monitors the ORP for continuous processes to ensure 

that excess oxidLzing agent, if possible, is supplied. 

t 

2.5.3 Degree of Mixing 

Process tanks must be equipped with mixers to ensure maximum contact 

between the oxidizing agent and the waste solution. Proper mixing also limits 

the production of any solid precipitates from side reactions that may resist 

oxidation. Mixing also provides an even distribution of tank contents and a 

homogeneous pH throughout the waste, improving oxidation of wastewater 

constituents. The quantifiable degree of mixing is i complex assessment that 

inC"ludes, among other factors, the amount of energy supplied, the length of time 

the material is mixed, and the related turbulence effects of tt.c specific size 

and shape of the tank. This is beyond the scope of simple measurement. EPA, 

however, evaluates the degree of mixing qualitatively by considering whether 

mixing is provided and whether the typ~ of mixing device is one that could be 

expected to achieve uniform mixing of the waste solution. 

2.5.4 pH 

, ' 

Operation at the optimal pH maximizes the chemical oxidation reactions and 

may, depending on the oxidizing agent being used, limit the formation of 

undesirable reaction byproducts or the escape of cyanide from solution as HCN, 

CNCl, or C2N2 gas. The pH is controlled by the addition of caustic, lime, or 

acid to the solution. In most cases, a slightly or moderately alkaline pH is 

used, depending on the tJpe of oxidizing agent being used and the compound being 

treated (see Section 2.2, Underlying Principles of Operation). In alkaline 

chlorination treatment of organics, a slightly acidic pH may be selected as an 

optimum. In permanganate oxidation, a pH of 2 to 4 is often selected. EPA 

man itors the pH cant 1 nuousl y, if pass i b 1 e, to ensure that the system 1 s operating 

at the appropriate design condition and to diagnose operational problems. 

f:\document\1525~031.01.00~ 26 

, 

' 
2.5.5 Oxidation Temperature 

Temperature affects the rate of reaction and the solubility of the 

oxidizing agent in the waste. As the temperature is increased, the solubility 

of the oxidizing agent, in most instances, is increased and the required 

residence time, in most cases, is reduced. EPA monitors the oxidation 

temperature continuously, if possible, to ensure that the system is operating at 

the appropriate design condition and to diagnose operational problems. 

2.5.6 Amount and Type of Catalyst 

Adding a catalyst that promotes oxygen transfer and thus enhances oxidation 

has the effect of lowering the necessary reactor temperature and/or improving the 

level of destruction of oxidizable compounds. For waste constituents that are 

more difficult to oxidize, catalyst addition may be necessary to effectively 

destroy the constituent(s) of concern. Catalysts typically used for this purpose 

include copper bromide and copper nitrate.. If a catalyst is required, EPA 

examines the amount and type added, as we 11 as the method of addition of the 

catalyst to the waste, to ensure that effective oxidation is achieved. 

f: \docU!IInt\15254031. 01.004 27 
2.5 References 

- Gurnham, C.F. 1985. Principles of industrial waste treatment. New York: John 

Wi 1 ey ana·Sons. 

Gural, M.D., and Holden, T.E. 1988. The effect of copper and iron complexation 

on removal of cyanide by ozone. Ind. Eng. Chem. Res. 27(7}:1157-1162. 

McGraw-Hill. 1982. Encyclopedia of science and technology. Vol. 3, p. 825. 

New York: McGraw-Hill Book Co. 

Metcalf & Eddy, Inc. 1986. Briefing: Technologies applicable to hazardous 

waste. Prepared for U.S. Environmental Protection Agency, Hazardous Waste 

Engineering Research Laboratory. Cincinnati, Ohio: U.S. Environmental 

Protection Agency. 

Nutt, S.G., and Zaidi, S.A. 1983. Treatment of cyanide-containing wastewaters 

by the copper-catalyzed 502/air oxidation process. In Proceedings of the 

38th Industrial Waste Conference, Purdue University, West lafayette, Indiana, Hay 10-12, 1983. Stoneham, Mass.: Butterworth Publishers. 

Patterson, J.W. 1985. Industrial wastewater treatment technology. 2nd e<t. 

Stoneh~1, Mass.: Butterworth Publishers. 

Schroeter, J., and Painter, C. 1987. Potassium permanganate oxidation of 

electroless olating wastewater. Carus Chemical Company, 1001 Boyce Memorial Drive, P.O. Box 1500, Ottawa, Illinois 61350. 

Weast, R.C., ed. 1978. Handbook of chemistry and phvsics. 58th ed. Cleveland, 

Ohio: CRC Press. 

f:\docunent\15254031.01.004 28 
3. CHEMICAL REDUCTION 

3.1 App~cability 

Chemical reduction is a treatment technology used to reduce hexavalent 

chromium and selenate ions to the less soluble trivalent chromium ion and 

elemental selenium, respectively. It is also used to treat oxidizing wastes 

containing reducible organics and inorganic oxidizers such as calcium 

hypochlorite, hydrogen peroxide (and other peroxides), and nitric acid. Because 

this technology frequently requires that the pH be in the acidic range, it would 

not normally be applicable to wastes that contain significant amounts of cyanide 

or sulfide. In such wastes, lowering of the pH can result in the release of 

toxic gases such as hydrogen cyanide or hydrogen sulfide. 

Hexavalent chromium is usually present in wastes from the plating industry, 

metal surface preparation processes, the chromium pigments industry, and leather 

tanning processes. Selenates are frequently found in some mining and or-e 

processing wastes. Organic and inorganic oxidizers are found in propellant 

explosives and in the chemical manufacturing industries. 

3.2 UnderlYing Principles of Operation 

!he basic principle of chemical reduction is to reduce the valence of the 

oxidizer in solution. •Reducing agents• used to effect the reduction include the 

sulfur compounds sodium sulfite (Na2S03), sodium bisulfite (NaHS03), sodium 

metabisulfite (Na2S205

) ,_sulfur dioxide (502

), and sodium hydrosul fide (NaHS). 

The ferrous form of iron (Fe.2) is a popular reducing agent in many cases. 

Elemental magnesium (Hg), zinc (Zn), and copper (Cu) are also effective reducing 

agents. Frequently, hydrazine (N2H2) is used as a reducing agent also. Typical 

reduction reactions are as follows: 

f:\document\15254031.01.005 
H2

02 + 2H+ + 

Hydrogen Peroxide 

t. 

4Zn + 

Metallic Zinc Nitrate Ion 

Ferrous iron 

+ 

Zinc Ion 

2Fe·3 

Ferric Iron 

NH/ + 3H20 

Anlnonium Ion 

H2{Cr.6

) 2

07 + 3Na2S03 + 3H2S04 + {Cr.3)

2(S04)

3 + 3Na SO~ + 4H2

0 

Chromic Acid Sodium Sulfuric Chromium Sodium ~ulfite Acid Sulfate Sulfate 

H2Se03 + 2503 250~ + Se 

Selenic Acid Sulfite Ion Sulfate Ion Elemental Selenium 

These reactions are usually accomplished at pH values from 2 to 3. 

3.3 ·Description of Chemical Reduction Process r 

. The chemical reduction treatment process can be operated in a batch or 

continuous mode. A batch system consists of a reaction tank, a mixer to 

homogenize the contents of the tank, a supply of reducing agent, and a source of 

acid and base for pH control. A co~tinuous chemical reduction treatment system, 

as shown in Figure 4, usually includes a holding tank upstream of the reaction 

tank for flow and concentration equal izat1on. It also typically includes 

i~strumentation to automatically control the amount of reducing agent added and 

the pH of the reaction tank. The amount of reducing agent is controlled by the 

use of a sensor called an oxidation-reduction potential (ORP) cell. The ORP 

sensor electronically measures, in millivolts, the level to which the 

oxidation/reduction (redox) reaction has proceeded at Figure 4 any given time. 

It must be noted, however, that the ORP reading is very pH dependent. 

Consequently, if the pH is not maintained at a steady value, the ORP will vary 

somewhat, regardless of the level of chemical reduction. 

f:\document\15254031.01.005 30 
REDUCING 

AGENT 

FEED 

8Y8TEII 

WASTEWATER ---- INFLUENT 

I 

I 

I 

I 

I I 

DO 

CRt ....A pH 

IIHQD 

REDUCTION 

REACTION TANK 

r-------------------------1 

: ELECTRICAL CONTROLS : 

! 'i) IIIXER ! 

• .1. • ~-------------------------· 

ACID • 

FEED 

SYSTEM 

ALKALI 

FEED 

8Y8TEII 

I 

I 

I 

0 

... ..... 

PRECIPITATION 

TANK 

Ftgure 4 Continuous Chemtcal Reduction System 
When chemical reduction is used for treating hexavalent chromium, the 

trivalent chromium that is formed is either reused or further treated by 

stabilization and land disposed. likewise, far selenium reduction, the 

precipitated efemental selenium may be recovered or stabilized and disposed of. 

3.4 Waste Characteristics Affecting Performance (WCAPs) 

In determining whether chemical reduction will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste, 

and whether performance levels can be transferred, EPA examines the following 

waste characteristics: {a) the concentration of other reducible compounds and 

(b) the concentration of oil and grease. 

3.4.1 Concentration of Other Reducible Compounds 

The presence of other reducible compounds {also called oxidizers) fn 

addition to the BOAT list constituents of concern will increase the demand of 

reducing agents, thereby potentially reducing the effectiveness of the treatment 

process. As a surrogate for the amount of organic oxidizers present in the 

waste, EPA might analyze for total organic carbon (TOC) in the waste. Inorganic 

oxidizing compounds such as ionized metals (e.g., silver, selenium, copper, 

mercury) may also create a demand for additional reducing agent. EPA might 

attempt to identify and analyze for these metal constituents. If TOC or 

~norganic oxidizer concentration in the untested waste is significantly higher 

than that in previously tested wastes, the system may not achieve the same 

performance as that achieved previously. Additional reducing agent may be 

required to effectively reduce the untested waste and achieve the same treatment 

performance, or other, more applicable treatment technologies may need to be 

considered for treatment of the untested waste. 

f:\document\15Z54031.01.005 32 
3.4.2 Concentration of Oil and Grease 

EPA belie(es that oil and grease compounds could cause monitoring problems 

because of fouling of instrumentation {e.g., electrodes for pH and ORP sensors}. 

If the concentration of oil and grease in an untested waste is significantly 

higher than that in a tested waste, the untested system may not achieve the )arne 

performance. Therefore, other, more applicable treatment or pretreatment 

technologies may need to be considered for treatment of the untcstea waste. 

3.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a chemical 

reduct ion system, EPA examines the fall owing parameters: {a} the residence time, 

{b) the amount and type of reducing agent, {c) the degree of mixing, {d) the pH, 

and (e) th~ reduction temperature. 

For many hazardous organic constituents, analytical methods are no't 

available or the constituent cannot be analyzed in the waste matrix. Therefore, 

it would normally be impossible to measure the effectiveness of the chemical 

reduction treatment system. In these cases EPA tries to identify measurable 

parameters or constituents that would act as surrogates to verify treatment. 

for organic constituents, each compound contains a measurable amount of 

total organic carbon {TOC). Removal of TOC in the chemical reduction treatment 

system indicates removal of organic constituents. Hence, TOC analysis is likely 

to be an adequate surr.ogate analysis where the specific organic constituent 

cannot be measured. 

However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden {i.e., the TOC 

analysis may not be sensitive enough to detect changes at the milligrams per 

liter (mg/1) level in matrices where totai organic concentrations are hundreds 

or thousands of mg/1 )". In these cases other surrogate para.11eters should be 

f: \d~t.ment\1525•031.01.005 33 
sought. For example, if a specific analyzable constituent is expected to be 

treated a~ well !S the unanalyzable constituent, the analyzable constituent 

concentration skould be monitored as a surrogate. 

3.5.1 Residence Time 

The residence time affects the extent of reaction of waste contaminants 

with reducing agents. For a batch system, the residence time is controlled by 

adjustment of the treatment time in the reaction tank. For a continuous system, 

the waste feed rate is controlled to make sure that the system is operated at the 

appr?priate design residence time. EPA monitors the residence time to ensure 

that sufficient time is provided to effectively reduce the waste. 

3.5.2 Amount and Type of Reducing Agent 

Several factors influence the choice of reducing agents and the amount to 

be added. The amount of reducing agent required to treat a given amount rif 

reducible constituent will vary with the agent chosen. Enough reducing agent 

must be added to ensure complete reduction; the specific amount will depend on 

the type of reducible compounds in the waste and the chemistry of the reduction 

reactions. Theoretically, the amount of reducing agent to be added can be 

computed from reduction reaction stoichiometry. In practice, however, an excess 

of red.ucing agent should be used. Testing for excess reducing agent, if 

possible, will determine whether the reaction has reached completion. 

In continuous processes, the addition of reducing agent fs usually 

accomplished by automated feed methods. The amount of reducing agent needed fs 

usually metered and controlled automatically by an oxidation-reduction potential 

(ORP) sensor. EPA ex~ines the amount of reduction agent added to the chemical 

reduction system to ensure that ft is sufficient to effectively reduce the waste 

and, for continuous processes, examines how the facility ensures that theparticular addition rate is maintained. EPA may also test for excess reducing 

agent in the system effluent. For continuous processes, EPA monitors the ORP to 

f:\docum.nt\15254031.01.005 34 
ensure that enough reducing agent is supplied. EPA may also monitor pH to 

determine· whether_ it is controlled to the appropriate optimum range. For 

continuous syst~s, pH is monitored to ensure that it is kept steady to avoid 

changes in ORP caused by pH variations. 

3.5.3 Degree of Mixing 

Process tanks must be equipped with mixers to ensure maximum contact 

between the reducing agent and the waste oxidizing solution. Proper mixing also 

homogenizes any solid precipitates that may be present, or that may form from 

side reactions, so that they can also be reduced if necessary. Mixing provides 

an even di stri but ion of tank contents and a homogeneous pH throughout the waste, 

improving reduction of wastewater constituents. The quantifiable degree of 

mixing is a complex assessment that includes, among other factors, the amount of 

energy supplied, the length of time the material is mixed, and the related 

turbulence effects of the specific size and shape of the tank. This is beyond 

the scope of simple measurement. EPA, however, evaluates the degree of mixing 

qualitatively, using engineering judgment, by considering ··hether mixing is 

provided and whether the type of mixing device is one that could be expected to 

achieve uniform mixing of the waste solution. 

3 .5.4 pH 

For batch and continuous systems, the pH affects the reduction reaction. 

The reaction speed is usually significantly reduced at higher pH values 

(typically above 4.0) .. It is worth noting that some reduction reactions may 

proceed better under alkaline conditions, in which case pH must be properly 

controlled to the appropriate alkaline range. For a batch system, the pH can be 

monitored intermittently during treatment. For a continuous system, the pH must 

be continuously monitored because it affects the ORP reading. EPA monitors the 

pH to ensure that the system i~ op~rating at the appropriate design condition and 

to diagnose operational problems. 

f:\document\15254031.01.005 35 
3.5.5 Reduction Temperature 

Temperature- affects the rate of reaction and the solubility of the 

t. 

reactants in the waste. As the temperature is increased, the solubility of the 

reactants, in most instances, is increased and the required residence time, in 

most cases, is reduced. EPA may monitor the reduction temperature to ensure that 

the system is operating at the appropriate design condition and to diagnose 

operational problems. 

f:\document\15ZS4031.01.005 36 

' 
3.6 References 

McGraw-Hill. :t982. Encyclopedia of science and technology. Vol. 9, pp. 714-718. New York: McGraw-Hill Book Co. 

Nebergall et al. General chemistry. 5th ed. Lexington, Mass.: O.C. Heath and 

Company. 

Patterson, J.W. 1985. Industrial wastewater treatment technology. 2nd ed. 

Stoneham, Mass.: Butterworth Publishers. 

f:\dccument\15254031.01.005 37 
4. ELECTROLYTIC OXIDATION OF CYANIDE 

- 4.1 Appticability 

Electrolytic oxidation is a treatment technology with demonstrated 

applicability to the treatment of wastes containing high concentrations of 

cyanide in solution. Because of excessive retention time requirements, the 

process is often applied as preliminary treatment for highly concentrated cyanide 

wastes, prior to more conventional chemical cyanide oxidation. 

This treatment technology is used in industry for the destruction of 

cyanide in (a) concentrated spent plating solutions and stripping solutions, 

(b) spent heat treating baths, (c) alkaline descalers, and (d) metal passivating 

(rust-inhibiting) solutions. Electrolytic oxidation has been demonstrated 

successfully for treatment of wastes containing concentrations of cyanide up to 

100,000 mg/1. However, for concentrations of cyanide 1 ower than 500 mg/1, 

chemical oxidation treatment may be more efficient (see Section I.A.2}. , 

4.2 Underlying Principles of Operation 

The basic principle of operation for electrolytic oxidation of cyanide is 

that concentrated cyanide waste subject to an electrolytic reaction with 

dissolved oxygen in an aqueous solution is broken down to the gaseous products 

~arbon dioxide (C02}, nitrogen (N2), and ammonia (NH ~. The process is conducted 

at elevated temperatures for periods ra~~ing from several hours to over a week, 

depending on the initi.al cyanide concentration and the desired final cyanide 

concentration. The theoretical destruction process that takes place at the 

anodes is described by the following reaction: 

cyanide 

ion 

oxygen 

f:\document\15254031.01.006 

Electricity 

----:1> 

38 

2C02 

carbon 

dioxide 

+ 

nitrogen electrons 
The effectiveness of electrolytic oxidation is dependent on the 

conductiyity of the waste, which is a function of several waste characteristics 

including the Concentration of cyanide and other ions in solution. As the 

process continues, the waste becomes less capable of conducting electricity as 

the cyanide concentration is reduced, causing the electrolytic reaction to be 

much less efficient at longer retention times. 

4.3 Description of Electrolytic Oxidation Process 

Typically, electrolytic destruction of cyanide takes place in a closed 

cell. This cell consists of two electrodes suspended in an aqueous solution, 

with direct current (DC) electricity supplied to drive the reaction to 

completion. The temperature of the bath containing the cyanide waste is 

maintained at or above s2•c (125.F). Sodium chloride may be added to the 

solution as an electrolyte (conductor) to increase the conductivity of the waste 

being treated. Since the reaction may take days or weeks, water is usually add~d 

to the tank periodically to make up for losses due to evaporation from the heated 

tank. This is necessary to ensure that the electrodes remain fully submerged so 

that a full flow of current is maintained in the solution during treatment. 

Following treatment, the treated waste is usually further treated' in a 

conventional chemical oxidation system to destroy residual cyanides. 

4.4 Waste Characteristics Affecting Performance (WCAPsl 

In determining whether electrolytic oxidation will achieve the same level 

of performance on an u~tested waste that it achieved a previously tested waste 

and whether performance levels can be transferred, EPA examines the following 

waste characteristics: (a) the concentration of other oxidizable materials and 

(b) the concentration of reducible metals. 

f:\document\1SZS403l.Ol.006 39 
f 

4.4.1 Concentration of Other Oxidizable Materials 

The pre~nce of oxidizable organics (such as oil and grease and 

surfactants) and the presence of inorganic ionic species in a reduced state (such 

as trivalent chromium or sulfide) may increase the treatment time required to 

achieve destruction of cyanide because these materials may be oxidized 

preferentially to the cyanide in solution. If concentrations of other oxidizable 

materials are significantly higher in the untested waste than in the tested 

waste, the system may not achieve the same performance. Longer reaction time may 

be required to oxidize cyanide and achieve the same treatment performance, or 

other, more applicable treatment technologies may need to be considered for 

treatment of the untested waste. 

4.4.2 Concentration of Reducible Metals 

The electrolytic process may cause some of the more easily reduced metals 

in the waste, such as copper, to plate out onto the cathode as the pure met~l. 

ThP. plating of metals onto the cathode may result in changes 1n current density 

and, hence, may change the rate of cyanide oxidation. If the concentration of 

reducible metals in the untested waste is significantly higher than that in the 

tested waste, the system may not achieve the same performance and other, more 

applicable treatment technologies may need to be considered for treatment of the 

untested waste. 

4.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of an 

electrolytic oxidation system, EPA examines the following parameters: (a) the 

oxidation temperature, (b) the residence time, (c) the pH, (d) the electrical 

conductivity, (e) the electrode spacing and surface area, and (f) the degree of 

mixing. 

f:\document\15254031.01.006 40 
4.5.1 Oxidation Temperature 

For the ~Jectrolytic process, elevated temperatures are used. Normal 

temperatures range from 52 to 93'C (125 to 200'F). The temperature can be raised 

by increasing the flow of steam to the coils or jacket supplying heat to the 

reactor contents. EPA monitors the oxidation temperature to ensure that the 

system is operating at the appropriate design condition and to diagnos~ 

operational- problems. 

4.5.2 Residence Time 

Electrolytic oxidation is usually a batch process. The time allowed to 

complete the reaction is an important factor in electrolysis and is dependent on 

the initial concentration of the waste and the desired final cyanide 

concentration. The rate of cyanide destruction decreases as the cyani:de 

concentration decreases {i.e., the rate of cyanide destruction asymptotica1ly 

approaches zero). Typical residence times range from periods of several ho~rs 

to more than a week. EPA observes the residence time to ensure that sufficient 

time is provided to effectively destroy the cyanides in the wastes. 

4.5.3 pH 

. Typical solutions for electrolytic oxidation have a pH ranging from 11.5 

#to 12.0. The pH must be maintained in the alkaline range to prevent liberation 

of toxic hydrogen cyan;de. Typically, pH is controlled by the addition of 

caustic or lime. EPA-monitors the pH to ensure that the treatment system is 

operating at the appropriate design condition and to diagnose operational 

problems. 

4.5.4 Electrical Conductivity 

The so1ution must have an electrical conductivity high enough to allow the 

reaction to proceed at an acceptable rate. If the conductivity is not high 

f:\document\15254031.01.006 41 

' 
enough, it can be improved by adding an electrolyte such as sodium chloride. The 

conductivity of-the waste during the reaction is normally determined by 

monitoring botit-.the current and voltage of the cell. EPA monitors the electrical 

conductivity to ensure that the treatment system is operating at the appropriate 

design condition. 

4.5.5 Electrode Spacing and Surface Area 

The spacing and surface area of the electrodes directly impact the current 

flowing through the waste. The reaction rate is increased by both closer 

electrode spacing and more electrode surface area because each increases the 

current density in the cell. EPA observes the electrode spacing and surface area 

to ensure that sufficient current density is provided to effectively destroy the 

cyanides in the waste. 

4.5.6 Degree of Mixing 

Electrolytic destruction of cyanides requires good mixing in the reaction 

vessel. Mixing helps ensure an adequate supply of oxygen (from the air} for the 

electrochemical reaction (see Section 4.2, Underlying Principles of Operation}, 

enhances mass transfer to promote the oxidation reaction, and keeps suspended 

solids in suspension. Mixing may be provided by the bubbling of air from the 

bottom of the reactor, or an external source of mixing may be provided. The 

'quantifiable degree of mixing is a complex assessment that includes, among other 

factors, the amount of energy supplied, the length of time the material is mixed, 

and the related turbulence effects of the size and shape of the reaction vessel 

used. The degree of mixing is beyond the scope of simple measurement. EPA, 

however, evilluates the degree of mixing qualitatively by considering whether 

mixing is provided and whether the type of mixing device is one that could be 

expected to achieve uniform mixing of the waste. 

f:\document\15254031.01.006 42 
4.6 References 

Cushni e, G.C., t..Jr. 1985. Electroplating wastewater pollution control technology. p. 205. Park Ridge, N.J.: Noyes Publications. 

Easton, J.K. 1967. Electrolytic decomposition of concentrated cyanide plating 

wastes. Journal Water Pollution Control Federation 39(10):1621-1626. 

Patterson, J.W. 1985. Industrial wastewater treatment technology. 2nd ed., pp. 123-125. Stoneham, Mass. Butterworth Publishers. 

Pearson, G.J., and Karrs, S.R. 1984. Electrolytic cyanide destruction. In 

Proceedings for plating and surface finishing, pp. 2 and 3. 

Roy, C.H. 1981. Electrolytic wastewater treatment. In a series of American 

Electroplaters Society, Inc., illustrated lectures, pp. 8-10. 

f:\document\15254031.01.006 43 

: 

. 

1 
5. INCINERATION 

5.1 Appj~cability 

Incineration is a treatment technology applicable to the treatment of 

wastes containing a wide range of organic concentrations and low concentrations 

of water, metals, and other inorganics. The four most common incineration. 

systems are liquid injection, rotary kiln, fluidized bed, and fixed hearth. 

Liquid injection incineration is applicable to wastes having sufficiently 

low viscosity values (less than 750 saybolt universal seconds (Sus) such that the 

waste can be atomized in the combustion chamber. However, viscosity is 

temperature dependent so that while liquid injection may not be applicable to a 

waste at ambient conditions, it may become applicable when the waste is heated. 

In addition, the number of waste particles and the concentration of suspended 

solids need to be sufficiently low to avoid clogging of the burner nozzle (or 

atomizer openings). 

Rotary kiln, fluidized bed, and fixed hearth incineration are applicable 

to wastes having a wide range of viscosity, particle size, and suspended solids 

concentration. 

Incineration of highly explosive constituents may require treatment in 

units that are specially designed and fitted with certain explosion-proof 

equipment. Incinerators for corrosive waste should be equipped, if necessary, 

with pollution control ~evices to remove corrosive gases that may be generated 

from the burning of corrosive waste. The incineration of hazardous waste must 

be performed in accordance with the incinerator design and emissions regulations 

in 40 CFR 264, Subpart 0. 

f:\document\15254031.01.007 44 
-,-- ~-

5.2 Underlying Principles of Operation 

The basic- principle of operation for incineration is the thermal 

decomposition hf organic constituents via cracking and oxidation reactions at 

high temperatures (usually between 760 and ISSO"C (1400 and 3000"F) to convert 

them into carbon dioxide and water vapor along with nitrite oxides, nitrates, and 

arrmonia (for nitrogen-containing wastes); sulfur oxides and sulfate {for sulfurcontaining wastes); or halogen acids (for halogenated wastes). 

In liquid injection incineration the organic constituents in the waste are 

volatilized and the chemical bonds are destabilized. Once the chemical bonds are 

brqken, these canst ituen ts react with oxygen to form carbon dioxide, water vapor, 

and other aforementioned compounds. 

In rotary kiln and fixed hearth incineration, two chambers are involved in 

the incineration process. In the primary chamber, the organic constituents-in 

the waste are volatilized. During this volatilization process, some of the 

organic constituents oxidize to form carbon dioxide and water vapor. In the 

secondary chamber, the chemical bonds are destabilized, resulting in the organic 

constituents reacting with oxygen to form carbon dioxide, water vapor, and other 

aforementioned compounds. 

In fluidized bed incineration, a single chamber contains the fluidizing 

sand and a freeboard section above the sand. The fluidized bed aids in the 

volatilization and combustion of the organic waste constituents. The sand in the 

bed provides a sufficient heat capacity to volatilize organic constituents. The 

forced air used to fluid.ize the bed provides sufficient oxygen and turbulence to 

enhance the reactions of organics with oxygen to form carbon dioxide, water 

vapor, and other aforementioned compounds. Additional time for conversion of the 

organic constituents is provided by the freeboard above the fluidized bed. 

f:\document\152SC031.Dl.DD7 45 

' 
5.3 Description of Incineration Processes 

The physi ~1 form of the waste determines the appropriate feed method into 

the incinerati~~ system. Liquids are pumped into the combustion chamber through 

nozzles or via specially designed atomizing burners. Wastes containing suspended 

particles may need to be screened to avoid clogging of small nozzle or atomizer 

openings. Sludges and slurries are fed using positive displacement pumps and 

water-cooled injection ports. Bulk solid wastes may require shredding for 

control of particle size. Wastes may be fed to the combustion chamber via rams, 

gravity feed, air lock feeders, vibratory or screw feeders, or belt feeders. 

Containerized waste is gravity-fed or ram-fed. 

Although sustained combustion is possible with waste heat content as low 

as 2230 kcal/kg (4010 Btu/lb), wastes are typically blended to a net heat content 

of 4450 kcal/kg (8000 Btu/lb) or higher or auxiliary fuel is used in the 

combustion chambers to raise the heat content to a level sufficient to sustain 

the combustion process. 

Following incineration of wastes, fly ash particulates, acid gases (halogen 

acids), and other gaseous pollutants (nitric oxides (NOx) and sulfur oxides 

(SOx)) are further treated in an air pollution control system. Particulate 

emissions from most waste combustion systems generally have particle diameters 

less t~an 1 micron and require high-efficiency collection systems to minimize air 

emissions. The most common air pollution control system used includes a quench 

(for gas cooling and conditioning), followed by a high-energy venturi scrubber* 

(for particulate and acid gas removal), a packed bed or plate tower absorber (for 

acid gas removal), and a demister (for vapor mist plume elimination). 

Packed bed or plate tower scrubbers are commonly used without venturi 

scrubbers in the air pollution control systems at liquid injection incinerator 

*A venturi is a short tube or duct with a tapering constriction that causes an 

increase in the velocity of fluid flow and a corresponding decrease in pressure. 

f:\document\15254031.01.007 46 
facilities, where absorption of gasscus ii~llutants is more important than 

particul,ate control. (Wastes burned in liquid injection incinerators typically 

have a low ashcontent and, hence, generate a low level of fly ash particulates.) 

Some liquid injection incinerator facilities do not employ any air 

pollution control system because the wastes burned contain low levels of both ash 

and halogen content, thereby generating low {i.e., untreatable) levels of fly ash 

particulates and acid gases. 

Many air pollution control system designs in recent years have begun to 

incorporate waste heat boilers as a substitute for gas quenching as a means of 

energy recovery. Wet electrostatic precipitators (ESP), ionizing wet scrubbers 

(IWS), and fabric filters are also being incorporated into newer systems because 

these devices have high removal efficiencies for small particles and a lower 

pressure drop than that of venturi scrubbers. 

The inorganic constituents of wastes (noncombustible ash) are not destroyed 

by incineration. These materials, depending on their composition, exit the 

incinerator as either bottom ash from the combustion chamber or fly ash 

particulates suspended in the combustion gas stream. Bottom ash is typically 

either air-cooled or quenched with water following discharqe from the combustion 

chamber. This waste is then stabilized (if levels of leachable metal 

constituents of concern are found) and/or land disposed. 

Fly ash particulates, as well as acid gases and other gaseous pollutants, 

are entrained 1n the s~rubber waters of the air pollution control system and 

collected in the sumps of recirculation tanks. Here the acids are neutralized 

with caustic and much of the water is returned to the air pollution control 

system. Eventually, a portion or all of these scrubber waters are discharged for 

treatment and disposal when the total dissolved solids level becomes excessively 

high. Scrubber waters are discharged either to a settling tank or lagoon or to 

a chemical precipitation system (if treatable levels of soluble metal constituents of concern are found) to remove these solids prior to their land 

f:\document\15254031.01.007 47 

i 

' 
disposal. Depending on the nature of the remaining dissolved constituents and 

their concentrations, treated scrubber waters may be returned to the air 

pollution contrlll_ system, further treated in filtration processes, or discharged. 

Bel ow are descriptions of the incineration processes for the four most 

common incine~ator systems. 

5.3.1 Liquid Injection 

In a liquid injection incineration system, a burner or nozzle atomizes the 

waste and injects it into the combustion chamber, where it is incinerated in the 

presence of air or oxygen. A forced-draft system supplies the combustion chamber 

with air to provide oxygen for combustion and turbulence for mixing. The 

combustion chamber is usually a cylinder lined with refractory (i.e., heatresistant) brick and can be fired horizontally, vertically upward, or vertically 

downward. Figure 5 illustrates a liquid injection incineration system. 

5.3.2 Rotary Kiln 

A rotary kiln is a slowly rotating, refractory-lined cylinder that is 

mounted at a slight incline from the horizontal. Solid wastes enter at the high 

end of the kiln, and liquid or gaseous wastes generally enter through atomizing 

nozzl~s in the afterburner section of the kiln. A forced-draft system supplies 

the kiln with air to provide oxygen for combustion and turbulence for mixing. 

Rotation of the kiln enhances the exposure of the solids to the heat, thereby 

aiding their volatilization as well as providing additional mixing of the solids 

with air combustion. In addition, the rotation causes the ash to move to the 

lower end of the kiln, from which it is removed. Rotary kiln systems usually 

have a secondary combustion chamber or afterburner following the kiln for further 

combustion of the volatilized waste constituents. Figure 6 is a diagram of a 

rotary kiln incineration system. 

f:\document\15254031.01.007 48 
AUXILIARY fUEL 

LIQUID OR GASEOUS 

WASTE INJECTION 

:--:aunNER 

AIR . 

-

:::BURNER 

flY ASH PARTICULATF. 9 

AND COMBUSTION GASES 

TO AIR POLLUTION CONTROl. SYSTEM 

AND/OR THE ATMOSPHERE 

t 

I 

PRIMARY AFTERBURNER 

COMBUSTION (SECONDARY 

COMBUSTION CHAMBER CHAMBEHt 

~ 

BOTTOM ASH TO 8lABIUZATION 

AND/OR LAND DISPOSAL 

Figure 5 L1qu1d Injection lnctneratton System 

·--
SOL.ID 

t. 

Fl.. Y ASH PART1Ctii..A -rES 

AND COMBUsnON GASES TO 

AJR POLLUTION CONTROL 

i 

UQUID OA GASEOUS 

WASTE IN..IECTlON -------...,...1 

AFTERBURNER 

AUXIUARY FUE~----------..1 BURNER ._.-~--...J 

WASTE 

INFL.UENT~ 

BO'TTOM ASH TO 

STAIIUZATION 

AND/OR LAND DISPOSAL 

Figure 6 Rotary Kiln Incineration System 

50 
5.3.3 Fluidized Bed 

A fluidiz~ bed incinerator consists of a column containing inert particles 

such as sand, which is referred to as the bed. Air, driven by a blower, enters 

the bottom of the bed to fluidize the sand. Air passage through the bed provides 

oxygen for combustion and promotes rapid and uniform mixing of the injected waste 

material within the fluidized bed. The fluidized bed has an extremely high heat 

capacity (approximately three times that of flue (combustion) gases at the same 

temperature), thereby providing a large heat reservoir. The injected waste 

reaches incineration temperature quickly and transfers the heat of combustion 

back to the bed. The freeboard above the fluidized bed provides additional time 

for combustion of organic constituents. Because of the excellent mixing 

properties associated with fluidized bed incinerators, they can operate at lower. 

temperatures more effectively than other incinerators. Figure 7 is a diagram of 

a fluidized bed incineration system. .. 

5.3.4 Fixed Hearth Incineration 

Fixed hearth (also called controlled air or starved air} inciner3tion is 

a two-stage combustion process. Wa~te is ram-fed into the first stage, or 

primary chamber, and burned at less than stoichiometric conditions (not enough 

oxygen for complete combustion). The resultant smoke and pyrolysis products, 

consi s.ti ng primarily of volatile hydrocarbons and carbon monoxide, a 1 ong with the 

typical products of combustion, pass to the secondary chamber. Here additional 

air is injected to complete the combustion process. This two-stage process 

generally yields low fly ash particulate and carbon monoxide (CO} emissions. The 

primary chamber combustion reactions and resultant combustion gas velocities are 

maintained at low levels by the starved air conditions so that particulate 

entrainment and carryover in the combustion gases are minimized. Figure 8 is a 

diagram of a fixed hearth incineration system. 

f:\document\15254031.01.007 51 

, 
BURNER 

FREEBOARD 

BOTTCU ASH TO STABIUZATION 

4HD/OA LAND DISPOSAL 

Ft.Y ASH 

PARTICULATES 

t-----1• ANC COMBUSTION 

GASES TO AIR 

POLLUTION 

CONTROL SYSTEM 

... --MAKE·UP 

SANC 

Figure 7 Fluidized Bad Incineration System 

52 
U1 

w WASTE 

IN.JECTION 

. 

AIR -

.. 

COMBUSTION 

PRIMARY 

~ 

CHAMBER 

~BURNER 

BOTTOM AStt TO STABILIZATION 

AND/OR LAND DISPOSAL 

AIR 

• 

SECONDARY 

COMBUSTION 

CHAMBER 

Figure 8 Ftxed Hearth Jnc1neratton System 

FLY ASH PARTICULATES 

AND COMBUSTION GASES 

TO AIR POLLUTION 

CONTROL SYSTEM 

~~ 

DURNER1~ AUXILIARY 

FUEL 

·--
5.4 Waste Characteristics Affecting Performance (WCAPs} 

In deternti_ning whether incineration will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste 

and whether performance levels can be transferred, EPA examines the following 

waste characteristics: (a) the thermal conductivity of the waste, (b) the 

component boiling points, (c) the component bond dissociation energies, (d) the 

heating value of the waste, (e) the concentration of explosive constituents, and 

{f) the concentration of noncombustible constituents. 

5.4.1 Thermal Conductivity of the Waste 

A major factor determining whether a particular constituent will volatilize 

is the transfer of heat through the waste. For rotary kiln, fluidized bed, and 

fixed hearth incineration, heat is transferred through the waste by radiation, 

convection, and conduction. 

EPA examined all three methods of heat transfer. For a given incinerator, 

heat transferred through various wastes by radiation and convection is more a 

function of the design and type of incinerator than of the waste being treated; 

therefore, EPA believes that conduction would be the primary cause of heat 

transfer differences between wastes. Heat flow by conduction is proportional to 

the temperature gradient across the material. The proportionality constant, 

referred to as the thermal conductivity, is a property of the material to be 

incinerated. 

Thermal conductivity measurements, as part of a treatability comparison for 

two different wastes to be treated by a single incinerator, are most meaningful 

when applied to wastes that are homogeneous (i.e., uniform throughout). As 

wastes exhibit greater degrees of nonhomogenaity, thermal conductivity becomes 

less accurate in predicting treatability because the measurement essentially 

reflects heat flow through regions having the greatest conductivity (i.e., the 

path of least resistance) and not heat flow through all parts of the waste. 

f:\dacument\15254031.01.007 54 
Nevertheless, EPA believes that thermal conductivity may provide the best measure 

of performance tr.ansfer. If the thermal conductivity of an untested waste is 

significantly l~er than that of the tested waste, the system may not achieve the 

same performance. Higher temperatures may be required to improve heat transfer 

through the waste and achieve the same treatment performance, or other, more 

applicable treatment technologies may need to be considered for treatment of the 

untested wastes. 

5.4.2 Component Boiling Points 

Foll~wing transfer of heat to a constituent within a waste, the 

constituent's removal depends on its volatility. EPA recognizes, however, that 

volatilities are difficult to measure or calculate directly for the types of 

wastes generally treated by incineration because the wastes usually consist of 

a mixture of components. However, because the volatilities of components are 

usually inversely proportional to their boiling points (i.e., the higher the 

boiling point, the lower the volatility), EPA uses the boiling points of waste 

components as a surrogate waste characteristic for volatility. If the boiling 

points of waste components in the untested waste are significantly higher than 

those in the tested waste, the system may not achieve the same performance. 

Higher temperatures may be required to volatilize less volatile components and 

achieve the same treatment performance or other, more applicable treatment 

technqlogies may need to be considered for treatment of the untested wastes. 

5.4.3 Component Bond Dissociation Energies 

The activation energy is the amount of heat energy needed to destabilize 

molecular bonds so that the exothermic combustion reactions can proceed. 

Typically, the activation energy required for incineration of solids is greater 

than that required for liquids, and the activation energy required for liquids 

is higher than that required for gases. However, the activation energies for 

components are difficult to measure or calculate directly and usually must be 

determined empirically. The bond dissociation energy is the amount of energy 

f:\~ument\15254031.01.007 55 
needed to break each of the individual bonds in a molecule. Theoretically, the 

bond disS"Ociation_energy and the activation energy are equivalent. However, 

other energy eff1!_cts including interactions between different molecular bonds may 

have a significant influence on the activation energy. Nevertheless, EPA 

believes that bond dissociation energy is the best indicator for activation 

energy and therefore uses it as a surrogate waste characteristic. If the bond 

dissociation energies of waste components in an untested waste are significantly 

higher than those in the tested waste, the system may not achieve the same 

performance. Higher temperatures may be required to destabilize molecular bonds 

for waste components with high bond dissociation energies and achieve the same 

treatment performance, or other, more applicable treatment technologies may need 

to be considered for treatment of the untested waste. 

5.4.4 Heating Value of the Waste 

.. 

The amount of heat released from the exothermic combustion reactions of'a 

waste is referred to as its heating value. To maintain combustion, the heatidg 

value of a waste must be sufficient to heat incoming waste up to the appropriate 

design incineration temperature and provide the necessary activation energy for 

additional combustion reactions to occur. Higher waste heating values are 

required for higher incineration temperatures and higher amounts of excess oxygen 

to sustain combustion without auxiliary fuel consumption. Low heating values for 

an organic waste are usually caused by high concentrations of water or 

halogenated compounds. If the heating value of an untested waste is 

significant 1 y 1 ower than that of the tested waste, the system may not achieve the 

same performance. Auxiliary fuel may be required to provide the necessary heat 

to maintain combustion and achieve the same treatment performance, or other, more 

applicable treatment technologies may need to be considered for treatment of the 

untested waste. 

f:\document\15Z54031.01.007 56 
5.4.5 Concentration of Explosive Constituents 

Explosive -constituents may interfere with the smooth operation of an 

incinerator, clusing process upsets resulting in ineffective treatment of the 

waste. If the concentration of explosive constituents in an untested waste is 

significantly higher than that in the tested waste, the system may not achieve 

the same performance and other, more applicable treatment technologies may need 

to be considered for treatment of the untested waste. 

5.4.6 Concentration of Noncombustible Constituents 

Noncombustible constituents include water, metals, and other inorganics. 

High concentrations of noncombustible constituents result in low waste heating 

values, requiring auxiliary fuel; large quantities of bottom ash, requiring 

stabilization treatment (if treatable levels of leachable metal constituents of 

concern are present) and/or disposal; and large quantities of fly ash 

particulates and volatile metals in the combustion gases, requiring removal tn 

an air pollution control system and treatment in a settling tank or lagoon or by 

means of a chemical precipitation system (if treatable levels of soluble metal 

constituents of concern are present) followed by disposal. Volatile metals such 

as arsenic may also fuse to the refractory walls in the combustion chamber, 

inhibiting effective operation of the incinerator. If the concentration of 

noncombustible constituents in an untested waste is significantly higher than 

that iA the tested waste, the system mJy not achieve the same performance and -

other, more applicable treatment technologies may need to be considered for 

treatment of the ur.tested waste. 

5.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of an 

incineration system, EPA examines the following parameters: (a) the incineration 

temperature, (b) the concentration of excess oxygen in the combustion gas, 

(c) the concentration of carbon monoxide in the combustion gas, (d) the waste 

f:\dOcument\15254031.01.007 57 
feed rate, and (e) the degree of waste/air mixing. In addition, incineration of 

hazardou~waste myst be performed in accordance with the incineration design and 

emissions regulra:tions in 40 CFR 264, Subpart 0. For many hazardous organic 

constituents, analytical methods are not available or the constituent cannot be 

analyzed in the waste matrix. Therefore, it would normally be impossible to 

measure the effectiveness of the incineration treatment system. In these cases 

EPA tries to identify measurable parameters or constituents that would act as 

surrogates to verify treatment. 

For organic constituents, each constituent contains a measurable amount of 

total organic carbon (TOC). Removal of TOC in the incineration treatment system 

indicates removal of organic constituents. Hence, TOC analysis is likely to be 

an adequate surrogate analysis where the specific organic constituent cannot be 

measured. 

However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden (i.e., the TOC 

analysis may not be sensitive enough to detect changes at the milligrams per 

liter (mg/1) level in matrices where total organic concentrations are hundreds 

or thousands of mg/1). In these cases other surrogate parameters should be 

sought. For example, if a specific analyzable constituent is expected tc be 

treated as well as the unanalyzable constituent, the analyzable constituent 

concentration should be monitored as a surrogate. 

5.5.1 Incineration Temperature 

Temperature provides an indirect measure of the energy available (i.e., 

Btu/hr) to both volatilize organic waste constituents and overcome their 

activation energy. As the design temperature in the combustion chamber 

increases, more constituents with lower volatilities and higher activation 

energies ~ill be destroyed. EPA monitors the incineration temperature 

continuously to ensure that the system is operating at the appropriate design 

condition and to diagnose operational problems. 

f:\document\15254031.01.007 58 
5.5.2 Concentration of Excess OxYgen in the Combustion Gas 

A sufficient supply of oxygen must be supplied to the combustion chamber 

t 

to effectively incinerate the organic waste constituents. The stoichiometric or 

minimum theoretical oxygen requirement to completely combust the waste is based 

on the amounts of combustible constituents in the waste. If perfect mixing could 

be achieved and the waste burned instantaneously, only the stoichiometric amount 

of oxygen would be needed for complete combustion. However, neither of these 

phenomena occur in commercial incinerators. The amount of excess oxygen in a 

given incinerator depends on the degree of waste/air mixing achieved in the 

combustion chamber and the desired degree of combustion gas cooling. Because 

excess air (oxygen) supplied to the combustion chamber acts as a diluent in the 

combustion process, it reduces the overall temperature in the incinerator {i.e., 

maximum theoretical incineration temperatures are achieved at zero percent excess 

air). This temperature reduction might be desirable to limit refractory 

degradation·when high-heating value wastes are being burned. However, when low-, 

heating-value wastes are being burned, exces.s air should be minimized to keep tfie 

system temperature as high as possible. Even with high-heating-value waste, it 

is desirable for equipment design considerations to limit the amount of excess 

air to some extent so that combustion chamber volume and downstream air pollution 

control system sizes can be limited. 

An inadequate supply of oxygen, on the other hand, will lead to ineffective 

i_ncinerat ion with higher concentrations of carbon monoxide (CO) and organic 

products of incomplete combustion (PICs), resulting in a heavier load on the air 

pollution control system. Typically, 20 to 60 percent excess oxygen is required 

to provide adequate waste/oxygen contact and, subsequently, effective 

incineration of the waste. EPA monitors the concentration of excess oxygen in 

the combustion gas continuously to ensure that the system is operating at the 

appropriate design condition and to diagnose operational problems. 

f: \doclftllnt\15254031. 01.007 59 
5.5.3 Concentration of Carbon Monoxide in the Combustion Gas 

The concan~ration of carbon monoxide in the combustion gas provides an 

indication of the extent to which organic waste constituents are converted to 

carbon dioxide and water vapor. Higher carbon monoxide levels are an indication 

of ineffective incineration with the presence of greater amounts of unreacted or 

partially reacted organic waste constituents in the combustion gas, resulting in 

a heavier load on the air pollution control system. Higher carbon monoxide 

levels can result from an ir.sufficient incineration temperature; an inadequate 

supply of excess oxygen; a waste feed rate that is too high, resulting in an 

insufficient residence time for the waste; and improper mixing in the combustion 

chamber. EPA monitors the concentration of carbon monoxide in the combustion gas 

continuously to ensure that the system is operating at the appropriate design 

conditions and to diagnose operational problems. 

5.5.4 Waste Feed Rate 

The waste feed rate determines the residence time of the waste in the 

combustion chamber. Sufficient residence time must be provided to allow for 

volatilization of the organic waste constituents, mixing with oxygP.n in the 

combustion chamber, and completion of the combust ion reactions. The total 

residence time required for these processes to occur depends on the incineration 

temperature, the amount of excess oxygen provided in the combustion chamber, the 

degree of waste/air mixing in the combustion chamber, the size and type of 

incinerator used, the physical form of the waste, and the waste particle size 

(which determines the amount of waste surface area available for heat transfer). 

Typical incinerator residence times range from approximately 2 seconds for liquid 

and gaseous wastes in liquid injection incinerators and the afterburner, 

freeboard, and secondary cc~bustion chamters of rotary kiln, fluidized bed, and 

fixed hearth incinerators to 30 minutes to 1 hour for solid wastes in a rotary 

kiln incinerator. EPA monitors the waste feed rate continuously to ensure that 

sufficient residence time is provided to effectively incinerate organic waste 

constituents. 

f:\document\15254031.01.007 60 
5.5.5 Degree of Waste/Air Mixing 

The incin\ration temperature, the amount of excess oxygen, and the 

residence time required to achieve effective incineration of a waste all depend 

to some extent on the degree of waste/air mixing in the combustion chamber. For 

liquid injection incinerators, the degree of waste/air mixing is primarily 

detennined by the specific burner design and the degree of atomization of the 

waste/air mixture achieved. The degree of atomization is dependent on the 

viscosity of the liquid waste and the amount of solid impurities present. If the 

waste viscosity exceeds 750 Sus or the amount of solid impurities is too high, 

the degree of atomization may not be fine enough, resulting in ineffect·ive 

incineration. 

For rotary kiln incineration, the degree of waste/air mixing is detennined 

by the airflow rate into the kiln as well as the rate of rotation (revolutions 

per minute (RPM)) of the kiln. As the airflow rate is increased, the degree of 

waste/air mixing is improved although this also reduces the incinerati~n 

temperature and residence time of the combustion gases. Increasing the rate of 

rotation of the kiln also improves waste/air mixing; however, the residence time 

of the waste solids is also reduced. Typical rotation rates for rotary kilns 

range from 0.3 to 1.5 meters per minute (1 to 5 feet per minute) • 

.For fluidized bed incineration, the degree of waste/air mixing is indicated 

by the pressure drop through the bed caused by the airflow rate used to fluidize 

the bed. The higher the pressure drop, the greater the degree of mixing in the 

fluidized bed. However, this also reduces the incineration temperature and the 

residence time of the waste solids and combustion gases. 

For fixed hearth incineration, the degree of waste/air mixing is determined 

by the airflow rate into the combustion chamber. As the airflow rate is 

increased, the degree of waste/air mixing is improved. However, this also 

reduces the incineration temperature and the residence time of the combustion 

gases. 

f:\document\15254031.01.007 61 
The quantifiable degree of waste/air mixing is a complex assessment that 

is difficult to express in absolute terms. However, for liquid injection 

incineration, E~ evaluates the degree of mixing qualitatively by examining the 

burner design and detennining whether it could be expected to achieve effective 

atomization of the waste/air mixture. For rotary kiln incineration, EPA 

estimates the degree of mixing by monitoring the airflow rate into the kiln as 

well as the kiln's rate of rotation to ensure that effective mixing of the waste 

and air is achieved. For fluidized bed incin~ration, EPA estimates the degree 

of mixing by man i torfng the pressure drop through the bed to ensure that 

effective mixing of waste and air is achieved. For fixed hearth incineration, 

EPA estimates the degree of mixing by monitoring the airflow rate into the 

combustion chamber to ensure that effective mixing of the waste and air is 

achieved. 

f:\doc~t\15254031.01.007 62 
5.6 References 

Ackerman, O.G., ~cGaughey, J.F., and Wagoner, D. E. 1983. At sea incineration 

of PCB-containing wastes on board the H/T vulcanus. 600/7-83-024. U.S. 

Environmental Protection Agency, Washington, D.C. 

Bonner, T.A., et al. 1981. Engineering handbook for hazardous waste 

incineration. Prepared by Monsanto Research Corporation for U.S. 

Environmental Protection Agency. PB 81-248166. 

Holler, J.J., and Christiansen, 0.8. 1984. Dry scrubbing of hazardous waste 

incinerator flue gas by spray dryer absorption. In Proceedings of the 

77th annual APCA meeting. 

Novak, R.G., Troxler, W.L., and Dehnke, T.H. 1984. Recovering energy from 

hazardous waste incineration, Chemical engineering progress 91:146. 

Oppelt, E.T. 1987. Incineration of hazardous waste, JAPCA val. 37, no. 5, May 

1987. 

Santoleri, J.J. 1983. Energy recovery--a by product of hazardous waste 

incineration systems. In Proceedings of the 15th Hid-Atlantic Industriar 

Waste Conference on Toxic and Hazardous Waste. 

Vogel, G., et al. 

incinerated. 

Agency. 

, 

' 

1983. Compos it ion of hazardous waste streams current 1 y 

Prepared by Mitre Corp. for U.S. Environmental Protection 

Vogel, G., et al. 1986. Incin~ration and cement kiln capacity for hazardous 

waste treatment. In Proceedings of the 12th Annual Research Symposium on 

Incineration and Treatment of Hazardous Wastes, Cincinnati, Ohio. 

f:\document\15254031.01.007 63 

l 

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' ' 

6. WET AIR OXIDATION 

- 6.1 Apilicability 

Wet air oxidation is a treatment technology applicable to wastewaters 

containing organics and oxidizable inorganics such as cyanide. The process is 

typically used to oxidize sewage sludge, regenerate spent activated carbon, and 

treat process wastewaters. Wastewaters treated using this technology include 

pesticide wastes, petrochemical process wastes, cyanide-containing metal 

finishing wastes, spent caustic wastewaters containing phenolic compounds, and 

some organic chemical production wastewaters. 

This technology differs from other treatment technologies generally used 

to tre~t wastewaters containing organics in the following ways. First, wet afr 

oxidation can be used to treat wastewaters that ~ave higher organic 

concentrations than are normally handled by biological treatment, caroon 

adsorption, and chemical oxidation but may be too dilute to be effectively 

treated by thermal processes such as incineration. Wet air oxidation is most 

applicable for waste streams containing dissolved or suspended organics in the 

500 to 50,000 mg/1 range. Below 500 mg/1, the rates of wet air oxidation of most 

organic constituents are too slow for efficient application of this technology. 

For these more dilute waste streams, biological treatment, carbon adsorption, or 

chemical oxidation may be more applicable. For more concentrated waste streams 

_(above 50,000 mg/1), thermal processes such as incineration may be more 

applicable. Second, wet air oxidation can be applied to wastes that have 

significant concentrations of metals (roughly 2 percent), whereas biological 

treatment, carbon adsorption, and chemical oxidation may have difficulty in 

treating such wastes. 

It is important to point out that wet air oxidation proceeds by a series 

of reaction steps and the intermediate products formed are not always as readily 

oxidized as are the original constituents. Therefore, the process does not 

always achieve complete oxidation of the organic constituents. Accordingly, in 

f:\document\15254031.01.008 64 
applying this technology it is important to assess potential products of 

incomplete oxida.tion to determine whether further treatment is necessary or 

whether this tt~hnology is appropriate at all. 

Studies of the wet air oxidation of different compounds have led to the 

following empirical observations concerning a compound's susceptibility to wet 

air oxidation based on its chemical structure: 

1. Aliphatic compounds, even with multiple halogen atoms, can be 

destroyed within conventional wet air oxidation conditions. 

Oxygenated compounds (such as low-molecular-weight alcohols, 

aldehydes, ketones, and carboxylic acids) are formed, but these 

compounds are readily biotreatable. 

2. Aromatic hydrocarbons, such as toluene, acenaphthene, or pyrene, are 

easily oxidized. r 

. 3. Halogenated aromatic compounds can be oxidized provided there is at 

least one nonhalogen functional group present on the ring (e.g., 

pentachlorophenol (-OH) or 2,4,6-trichloroaniline (-NHz)). 

4. Halogenated aromatic compounds, such as 1,2-dichlorobenzene, and PCBs, 

such as Aroclor 1254, are resistant to wet air oxidation under 

conventional conditions. 

5. Halogenated.ring compounds, such as the pesticides aldrin, dieldrin, 

and endrin, are expected to be resistant to conventional wet air 

oxidation. 

6. DDT can be oxidized, but results in the formation of intractable oils 

in conventional wet air oxidation. 

f: \doc~~nent\152~031. 01.008 65 

1 
) 

7. Heterocyclic compounds containing oxygen, nitrogen, or sulfur are 

· expect~d to be destroyed by wet air oxidation because the 0, N, or s 

atom~_provide a point of attack for oxidation reactions to occur. 

6.2 Underlying Principles of Operation 

The basic principle of operation for wet air oxidation is that the enhanced 

solubility of oxygen in water at high temperatures and pressures aids in the 

oxidation of organics. The typical operating temperature for the wet air 

oxidation treatment process ranges from 175 to 325"C (347 to 617'F). The 

pressure is maintained at a level high enough to prevent excessive evaporation 

of the liquid phase at the operating temperature, generally between 300 and 

3000 psi. At these eleva ted temperatures and pressures, the so 1 ubi 1 i ty of oxygen 

in water is dramatically increased, thus providing a strong driving force for the 

oxidation. The reaction must take place in the aqueous phase because the 

chemical reactions involve both oxygen (oxidation) and water (hydrolysis). The 

wet air oxidation process for a specific organic compound generally involve~ a 

number of oxidation and hydrolysis reactions in series, which degrade the initial 

compound by steps into a series of compounds of simpler structure. Complete wet 

air oxidation results in the conversion of organic compounds into carbon dioxide, 

water vapor, arrmonia (for nitrogen-containing wastes), sulfate (for 

sulfur-containing wastes), and halogen acids (for halogenated wastes). 

However, treatable quantities of partial degradation products may remain 

in the treated wastewaters from wet air oxidation. Therefore, effluents from wet 

air oxidation processe~ may be given subsequent treatment including biological 

treatment, carbon adsorption, or chemical oxidation before being discharged. 

6.3 Description of Wet Air Oxidation Process 

A conventional wet air oxidation system consists of a high-pressure liquid 

feed pump, an oxygen source (air compressor or liquid oxygen vaporizer), a 

f:\document\1525~031.01.008 66 
reactor, heat exchangers, a vapor-liquid separator, and process regulators. A 

basic flow diagr~m is shown in Figure 9. 

(_ 

A typical batch wet air oxidation process proceeds as follows. First, a 

copper catalyst solution may be mixed with the aqueous waste stream if 

preliminary testing indicates that a catalyst is necessary. The waste is then 

pumped into the reaction chamber. The aqueous waste is pressurized and heated 

to the design pressure and temperature. After reaction conditions have been 

established, air is fed to the reactor for the duration of the design reaction 

time. At the completion of the wet air oxidation process, suspended solids or 

gases are removed and the remaining treated aqueous waste is either discharged 

directly to disposal or fed to a biological treatment, carbon adsorption, or 

chemical oxidation treatment system if further treatment is necessary prior to 

discharge ta disposal. 

Wet air oxidation can also be operated in a continuous process. In 

' continuous operation, the waste is pressurized, mixed with pressurized air or 

oxygen, preheated in a series of heat exchangers by the hot reactor effluent and 

steam, and fed to the reactor. The waste feed f1 ow rate centro 1 s the reactor 

residence time. Steam is fed into the reactor column to adjust the column 

temperature. The treated waste is separated in a gas-1 i quid separator, with the 

gases treated in an air pollution control system and/or discharged to the 

atmos~here, and the liquids either further treated, as mentioned above, and/or 

·discharged to disposal. 

6.4 Waste Characteristics Affecting Performance CWCAPsl 

In determining whether wet air oxidation will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste 

and whether performance levels can be transferred, EPA examines the following 

waste characteristics: {a) the chemical oxygen demand and (b) the concentration 

of interfering substances. 

f:\document\15254031.01.008 67 

1 
0\ 

Ol 

PRESSURIZED 

WASTEWATI:R 

IHflUEHT 

PRESSURIZED 

AIR OR 

OXYOEH 

BE ACTOR 

STEAM 

STEAM 

Figure 9 Continuous Wet A1r Ox1dat1on System 

,r" 

VENT OASES TO 

AIR POLLUTION 

----41• CONTROL SYSTEM 

ANDIOR THE 

ATMOSPHERE 

GAS-LIQUID 

SEPARATOR 

TREATED 

EFFLUENT 

'----__. TO FUR'JttER 

TREATMENT 

AND/OR 

DISPOSAL 
6.4.1 Chemical Oxygen Demand 

The chem~al oxygen demand (COD) of the waste is a measure of the oxygen 

required for complete oxidation of the oxidizable waste constituents. The limit 

to the amount of oxygen that can be supplied to the waste is dependent on the 

solubility of oxygen in the aqueous waste and the rate of dissolution of oxygen 

from the gas phase to the liquid phase. This sets an upper limit on the amount 

of oxidizable compounds that can be treated by wet air oxidation. Thus, high-COD 

wastes may require dilution for effective treatment to occur. If the COD of the 

untested waste is significantly higher than that of the tested waste, the system 

may not achieve the same performance. Pretreatment of the waste or dilution as 

part of treatment may be needed to reduce the COD to within levels treatable by 

the dissolved oxygen concentration and to achieve the same treatment performance, 

or other, more applicable treatment technologies may need to be considered for 

treatment gf the untested waste. 

6.4.2 Concentration of Interfering Substances 

In some cases, addition of a water-soluble copper salt catalyst to the 

waste before processing is necessary for efficient oxidation treatment (for 

example, for oxidation of some halogenated organics). Other metals have been 

tested and have been found to be less effective. Interfering substances for the 

wet air oxidation process are essentially those that cause the formation of 

·insoluble copper salts when copper catalysts are used. To be effective in 

catalyzing the oxidation reaction, the copper ions must be dissolved in solution. 

Sulfide, carbonate, and other negative ions that form insoluble copper salts may 

interfere with treatment effectiveness if they are present in significant 

concentrations in wastes for which copper catalysts are necessary for effective 

treatment. If an untested waste for which a copper catalyst is necessary for 

effective treatment has a concentration of interfering substances (including 

sulfide, carbonate, or other anions that form insoluble copper salts) 

significantly higher than that in a tested waste, the system may not achieve the 

f:\document\1525~031.01.008 69 

1 
same performance and other, more applicable treatment technologies may need to 

be consid~red for treatment of the untested waste. 

t. 

6.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a wet air 

oxidation system, EPA examines the following parameters: (a) the oxidation 

temperature, (b) the residence time, (c) the excess oxygen concentration, (d) the 

oxidation pressure, and (e) the amount and type of catalyst. For many hazardous 

organic constituents, analytical methods are not available or the constituent 

cannot be analyzed in the waste matrix. Therefore, it would normally be 

impossible to measure the effectiveness of the wet air oxidation treatment 

system. In these cases EPA tries to identify measurable parameters or 

constituents that would act as surrogates to verify treatment. 

For organic constituents, each compound contains a measurable amount of 

total organic carbon (rOC). Removal of roc in the wet air oxidation treatment 

system indicates removal of organic constituents. Hence, TOC analysis is likely 

to be an adequate surrogate analysis where the specific organic constituent 

cannot be measured. 

However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden (i.e. 1 the roc 

analysis may not be sensitive enough to dete.ct changes at the milligrams per 

liter (mg/1) level in matrices where total organic concentrations are hundreds 

or thousands of mg/1). In these cases other surrogate parameters should be 

sought. For example, if a specific analyzable constituent is expected to be 

treated as well as the unanalyzable constituent, the analyzable constituent 

concentration should be monitored as a surrogate. 

f:\document\1SZS4031.01.008 70 
6.5.1 Oxidation Temperature 

Temperatu_re is the most important parameter affecting the system. The 

design temperature must be high enough to allow the oxidation reactions to 

proceed at acceptable rates. Raising the temperature increases the wet air 

oxidation rate by enhancing oxygen solubility and oxygen diffusivity. The 

process is normally operated in the temperature range of 175 to 32S"C (347 to 

617.F), depending on the hazardous constituent(s) to be treated. EPA monitors 

the oxidation temperature continuously, if possible, to ensure that the system 

is operating at the appropriate design condition and to diagnose operational 

problems. 

6.5.2 Residence Time 

The residence time impacts the extent of oxidation of waste contaminants. 

For a batch system, the residence time is controlled directly by adjusting the 

r 

treatment time in the reaction tank. For a continuous system, the waste feed 

rate is controlled to make sure that the system is operated at the appropriate 

design residence time. Generally, the reaction rates are relatively fast for the 

first 30 minutes and become slow after 60 minutes. Typical residence times, 

therefore, are approximately 1 hour. EPA monitors the residence time to ensure 

that sufficient time is provided to effectively oxidize the waste. 

~.5.3 Excess OxYg~n Concgntration 

The system must ~e designed to supply adequate amounts of oxygen for the 

compounds to be oxidized. An estimate of the amount of oxygen needed can be made 

based on the COO content of the untreated waste; excess oxygen shou 1 d be supp 1i ed 

to ensure complete oxidation. The source of oxygen is compressed air or a 

high-pressure pure oxygen stream. EPA monitors the excess oxygen concentration 

(the concentration of oxygen in the gas leaving the reactor) continuously, if 

possible, by sampling the vent gas from the gas-liquid separator to ensure that 

an effective amount of oxygen or air is being supplied to the waste. 

f:\document\15254031.01.008 71 
6.5.4 Oxidation Pressure 

The desi~ pressure must be high enough to prevent excessive evaporation 

of water and volatile organics at the design temperature. This allows the 

oxidation reaction to occur in the aqueous phase, thereby improving treatment 

effectiveness. Typical oxidation pressures range from 900 to 3000 psig. EPA 

monitors the oxidation pressure continuously, if possible, to ensure that the 

system is operating at the appropriate design condition and to diagnose 

operational problems. 

6.5.5 Amount and Type of Catalyst 

Adding a catalyst that promotes oxygen transfer and thus enhances oxidation 

has the effect of 1 owering the necessary reactor temperature and/or improving the 

level of destruction of oxidizable compounds. For waste constituents that are 

more difficult to oxidize, the addition of a catalyst may be necessary to 

effectively destroy the constituent(s) of concern. Catalysts typically used for 

this purpose include copper bromide and copper nitrate. If a catalyst is 

required, EPA examines the amount and type added, as we 11 as the method of 

addition of the catalyst to the waste, to ensure that effective oxidation is 

achieved. 

f: \doclllll!nt\15254031.01. 008 72 

, 

. 
6.6 References 

Detrich, H.J., landall, T.L., and Canney, P.J. 1985. Wet air oxidation of 

hazardous organics in wastewater. Environmental Progress 4:171-197. 

Randa 11, T. L. 1981. Wet oxidation of toxic and hazardous compounds, Zimpro technical bulletin I-610. Presented at the 13th Hid-Atlantic Industrial 

Waste Conf~rence, June 29-30, 1981, University of Delaware, Newark, Del. 

USEPA. 1990. U.S. Environmental Protection Agency, Office of Solid Waste. Best 

demonstrated available technology {BOAT} background document addendum for 

acrylonitrile wastes. Washington, D.C.: U.S. Environmental Protection 

Agency. 

f:\dacument\15254031.01.008 73 

, 
L 

I. TREATMENT TECHNOLOGIES (CONTINUED) 

B. TECHNOLOGIES THAT REDUCE THE SOLUBILITY OR 

LEACHABILITY OF METALS 

t 

I 
1. AMALGAMATION 

1.1 ApPlicability 

The term amalgamation refer.s to two types of processes that can be used as 

treatment for mercury wastes. Neither amalgamation process significantly reduces 

the leachability of mercury; both processes only. convert it into a more easily 

processed fcrm. In both processes, a solid alloy of mercury and a base metal, 

such as zinc, is formed. This alloy can be subsequently processed by retorting 

to recover mercury. 

The two processes differ from each other in the types of wastes managed. 

The first process is applicable only to solutions containing dissolved mercury 

salts. The principal current use for the process is in treatment of wastewaters 

containing organomercury salts. The second process is usable only for wastes 

rich in elemental mercury. Since the use of this second process is merely a 

convenience to avoid handling mercury in liquid fonn, its use is negligible. 

Both processes are applicable only to wastes containing mercury where selective 

recovery of the mercury is deemed viable. 

1.2 Underlying Principles of Operation 

Jhe amalgamation processes depend on the ability of mercury to form low-

~elting-point solid alloys with metals such ar copper and zinc, which have the 

thermodynamic capability of simultaneously reducing mercuric and mercurous salts 

to elemental mercury •. Basically, an excess of the less noble metal (zinc or 

copper) is contacted with a waste containing mercury or mercury salts. The 

chemical react ton reducing the mercury in the mercury salts occurs and the 

elemental mercury liberated forms an alloy with the excess matal added. For zinc 

and mercuric nitrate, the reaction may be written: 

f:\docunent\1SZS4031.01.009 74 

, 
Hg t Zn • mercury zinc amalgam 

1.3 Description of Amalgamation Treatment Processes 

The two types of amalgamation processes are operated as follows: 

1. The aqueous replacement process {solution process) involves addition 

of excess base metal, such as zinc, to a wastewater solution 

containing dissolved mercury salts. The elemental zinc, or other base 

metal, reacts with the mercuric or mercurous salts to fonn elemental 

mercury, which subsequently alloys with the excess base metal to form 

a solid amalgam (or alloy) that can be recovered by filtration and 

then sent for mercury recovery if applicable. Generally, finely 

divided zinc {zinc dust) is used. The high surface area of this 

material allows for rapid reaction and alloy formation. 

2. The nonaqueous process, which is seldom used, involves contacting 

waste 1 iquid mercury with finely divided zinc powders. The mass 

rapidly solidifies into a solid amalgam, which may be more easily 

managed than 1 i quid mercury. This type of process i s typ i ca 11 y 

limited in utility only to waste scrap elemental mercury. 

1.4 Waste Characterization Affecting-Performance CVCAPs) I 

In determininq whether amalgamation will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste 

and whether performance levels can be transferred, EPA examines the following 

waste characteristics: (a) the chemical form of the mercury, (b) the solution 

pH, (c) the presence of sol ids, and (d) the presence of other interfering 

materials. 

f:\docum~nt\1525~031.01.009 75 

, 

I 

I 
1.4.1 Chemical Form of the Mercury 

The soluttQn process requires that the mercury be present in the form of 

a dissolved mercury salt. As a result, the process is not applicable to wastes 

containing insoluble mercury compounds. The nonaqueous process is applicable 

only to waste scrap mercury in elemental form. 

1. 4. 2 So 1 uti on PH. 

The solution process involves reactions of finely divided zinc with mercury 

salts in solution. Reactions such as those consuming zinc by reaction with the 

acidic content of wastewaters are undesirable. Therefore, the pH of the 

wastewater solution should be adjusted to near neutral value before the process 

is used. This characteristic does not apply to the second process, where scrap 

liquid mercury is a required feedstock. 

1.4.3 Presence of Solids 

The solution process is aimed at recovery of a solid amalgam that can be 

shipped to mercury reprocessors. The presence of other sol ids in the amalgam may 

be undesirable. Therefore, if mercury is to be recovered, wastewater solutions 

should be filtered to remove extraneous solids before the process is used. This 

characteristic does not apply to the second process. 

1.4.4 Presence of Interfering Matari'als · 

The solution process requires a clear solution as a feedstock. Solutions 

containing oils, greases, and emulsified or suspended materials need to be 

pretreated before use of the process. The presence of many other dissolved 

salts, such as those of copper, which can react with zinc, is also undesirable, 

but does not exclude use of the process. The presence of such salts will 

increase the amounts of zinc required for process operation. 

f:\document\15254031.01.009 76 
The nonaqueous process requires elemental mercury as a feedstock. Scrap 

mercury contamina_ted with oils, greases, and emulsion is better managed by 

retorting dire~ly since these interfering substances may inhibit amalgam 

formation. 

1.5 Design and Operating Parameters 

1.5.1 Solution Process Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a solution 

process, EPA examines the following parameters: (a) temperature, (b) degree of 

mixing, (c) zinc usage, (d) solution pretreatment, and (e) residual mercury in 

the treated wastewater. 

1.5.1.1 Temperature 

The solution process is normally operated at ~tent. temperature but can 

be run at temperatures up to about so•c to enhance the reaction rate between zinc 

and dissolved mercury salts. EPA will examine the basis for the choice of 

operating temperature and temperatura monitoring equipment to ensure proper 

process operation. 

1.5.1.2 Degree of Mixing 

Finely divided zinc powder ts normally added to the solution containing the 

mercury compound. To e.nsure adequate contact between the zinc par:ticles and 

mercury ions present in solution, good agitation is needed. EPA will examine the 

equipment used to determine that the treatment vessel contains the proper 

stirring equipment. 

f:\document\15254031.01.009 77 
1.5.1.3 Zinc Usage 

Sufficien~zinc must be added to the solutions to ensure that all of the 

mercury present is converted to an amalgam. To achieve this end, the 

concentration of mercury in the sol uti on to be processed must be known to 

estimate the minimum amount of zinc to be added. EPA will examine a facility's 

calculations for zinc addition for individual batches to ensure proper operation. 

1.5.1.4 Solution Pretreatment 

In a properly operated unit, the mercury-containing solutions processed 

should be clear and free of oil, grease, and suspended solids when introduced to 

the processing equipment. EPA will inspect the solutions entering the process 

to ensure that proper pretreatment is being used. 

1.5.1.5 Residual Mercury Levels in Treated Liquid Phase 

One tinal design and operating parameter of importance is the concentration 

of mercury in the treated water after amalgam removal. For a properly designed 

and operated unit, both the entering and final mercury concent~ations should be 

determined on a batch-by-batch basis. EPA will examine these records to ensure 

proper operation. EPA will a 1 so determi n_e_ proper operatJon- by_ exa~~~i nation of 

capabi.l ities for posttreatment to precipitate any residual mercury from the 

treated wastewaters prior to their discharge. Amalgamation processes are 

normally used as part of treatment trains devoted to recovering elemental 

mercury. The reaction of zinc with mercury salts in solution occurs rapidly at 

higher mercury salt concentrations but may become very slow as the concentration 

falls to low levels. As a result, treated solutions are likely to contain some 

residual mercury salts requiring separate treatment. 

f:\document\1SZS4031.01.009 78 

, 

! 
1.5.2 Nonaqueous Precess Design and Operating Par~ters 

The nonaqu~~us (solid) process is very rarely used on a significant scale. 

Generally, waste mercury is either retorted or redistilled as such without 

formation of amalgams. There are, however, a few instances in which it might be 

desirable to amalgamate elemental mercur~, the most important ·of which is when 

the mercury is contaminated by radioisotopes. The solid process invohing 

amalgamation with zinc is basically simple, and there are two design and 

operating parameters of concern: (a) the amount of zinc used and (b) the adequacy 

of the mixing. 

1.5.2.1 Amount of Zinc Used 

The properties of the final amalgam prepared will depend on the ratio of 

zinc powder to mercury used. Mercury and zinc form amalgams over a very wide 

composition range. However, it is necessary to add sufficient zinc so that an 

alloy that is solid at room temperature is obtained. This entails using 

sufficient zinc to ensure that an amalgam with at least 25 percent zinc content 

is obtained. 

1.5.2.2 Adequacy of Mixing 

To fonn uniform zinc-mercury amalgams, the constituents need to be 

unifonnly mixed. Historically, such amalgams have been prepared in small 

quantities. If a facility desires to process mercury by this route in higher 

volumes, a specially designed mixing system may be needed. EPA will examine the 

design and operation of the mixing system to determine whether adequate mixing 

is likely to be achieved. 

f: \doc~nnt\15ZS<C031.01.009 79 

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' 
1.6 References 

Mellor, J.W., f9.48. Comprehensive treatise on theoretical and inorganic 

chemistry. Vol. 4, pp. 1022-1049. London, U.K.: Longmans Green. 

Signer, W., andNowakfot., 1978. Mercury compounds. In Kirk-Othmerencvclopedia 

of chemical technology. Vol. 15, pp. 157-171. New York: John Wiley 

Interscience. 

Rissmann, E.F., and Schwartz, S., 1989. Treatment of wastes containing arsenic, 

selenium, thallium, and mercury compounds. In Proceedings of the 44th 

Industrial Waste Conference, Purdue University. pp. 643-648. Ann Arbor, 

Mich.: Lewis Publishers. 

f:\ja:ument\15254031.01.009 80 

l 
2. CHEMICAL PRECIPITATION 

2.1 App!.icability 

Chemical precipitation is a treatment technology applicable to wastewaters 

containing a wide range of dissolved and other metals, as well as other inorganic 

substances such as fluorides. This technology removes these metals and 

inorganics from solution in the form of insoluble solid precipitates. The solids 

formed are then separated from the wastewater by settling, clarification, and/or 

polishing filtration. 

For some wastewaters, such as chromium plating baths or plating baths 

containing cyanides, the metals exist in solution in a very soluble form. This 

solubility can be caused by the metal's oxidation state (for example, hexavalent 

chromium wastewaters) or by complexing of the metals (for example, high 

cyanide-containing wastewaters). In both cases, pretreatment, such as hexavalent 

chromium reduction or oxidation of the metal-cyanide complexes, may be required 

before the chemical precipitation process can be applied effectively. In the 

case of arsenic, the arsenic-containing solution is normally treated first with 

oxidizing agents such as alkali hypochlorite solution to convert the lowervalence arsenic compound to arsenate. The arsenic ion is then typically 

precipitated out as ferric arsenate. Some compounds must be reduced prior to 

precipitation. For instance~ sel inites and selenates are oxidants and are 

readily reduced to elemental selenium, which is insoluble in aqueous solutions. 

Sulfur dioxide, sulfides, sulfites, and ferrous ion are all effective for this 

reduction reaction. 

Chemical precipitation may also be applicable to mixed waste for separating 

radionucl ides from other hazardous canst ituents in wastewaters. Speci fie 

conditions of pH, temperature, and precipitating reagent addition are required 

to selectively remove part or all of the radioactive component as a precipitate. 

f:\document\1SZ5403l.Ol.Ol0 81 
2.2 UnderlYing Principles of Operation 

The basic~rinciple of operation of chemical precipitation is that metals 

and inorganics in wastewater are removed by the addition of a precipitating agent 

that converts the soluble metals and inorganics to insoluble precipitates. These 

precipitates are settled, clarified, and/or filtered out of solution, leaving a 

lower concentration of metals and inorganics in the wastewater. The principal 

precipitation agents used to convert soluble metal and inorganic compounds to 

less soluble forms include lime (Ca(OH) 2), caustic (NaOH), sodium sulfide (Na2S), 

and, to a lesser extent, soda ash (Na2C03), phosphate (P04·), and ferrous sulfide 

(FeS). 

The solubility of a particular compound depends on the extent to which the 

electrostatic forces holding the ions of the compound together can be overcome. 

The solubility changes significantly with temperature, with most metal compounds 

becoming more soluble as the temperature increases. Additionally, the solubility 

is affected by other constituents present in the wastewater, including other ions 

and complexing agents. Regarding specific ionic forms, nitrates, chlorides, and 

sulfates are, in general, more soluble than hydroxides, sulfides, carbonates, and 

phosphates. 

Once the so 1 ub 1 e meta 1 and inorganic compounds have been converted to 

precipitates, the effectiveness of chemical precipitation is determined by how 

successfully the precipitates are physically removed. Removal usually relies on 

a settling process; that is,. a particle of a specific size, shape, and 

composition will settle.at a specific velocity, as described by Stokes' Law. For 

a batch system, Stokes' Law is a good predictor of settling time because the 

pertinent particle parameters essentially remain constant. In practice, however, 

settling time for a batch system is normally determined by empirical testing. 

For a continuous system, the theory of settling is complicated by such factors 

as turbulence, short-circuiting of the wastewater, and velocity gradients, thus 

increasing the importance of empirical tests to accurately determine appropriate 

settling times. 

f:\document\15254031.01.010 82 
2.3 Description of Chemical Precipitation Process 

The equi~ent and instrumentation required for chemical precipitation vary 

depending on whether the system is batch or continuous. Both systems are 

discussed below. 

For a batch system, chemical precipitation requires a feed system for the 

treatment chemicals and a react ion tank where the waste can be treated and 

allowed to settle. When lime is used, it is usually added to the reaction tank 

in a slurry form. The supernatant liquid is generally analyzed before discharge 

to ensure that settling of precipitates is adequate. 

For a continuous system, additional tanks are necessary, as well as the 

instrumentation to ensure that the system is operating properly. A schematic of 

a continuous chemical precipitation system is shown in Figure 10. In this 

system, wastewater is fed into an equalization tank, where it is mixed to provide 

more uniformity, thus minimizing the variability in the typP. and concentration 

of constituents sent to the reaction tank. 

Following equalization, the wastewater is pumped to a reaction tank where 

precipitating agents are added. This is done automatically by using 

instrumentation that senses the pH of the system for hydroxide precipitating 

agen~s, or the oxidation-reduction potential (ORP) for nonhydroxide precipitating 

-agents, and then pneumatically adjusts the position of the treatment chemical 

feed valve until the design pH or ORP value is achieved. (The pH and ORP values 

are affected by the concentration of hydroxide and nonhydroxide precipitating 

agents, respectively, and are thus used as indicators of their concentrations in 

the reaction tank.) 

In the reaction tank, the wastewater and precipitating agents are mixed to 

ensure commingling of the metal and inorganic constituents to be removed and the 

precipitating agents. In addition, effective dispersion of the precipitating 

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Following reaction of the wastewater with the stabilizing agents, 

coagulating or flocculating compounds are added to chemically assist the settling 

process. Coagulants and flocculants increase the particle siie and density of 

the precipitated solids, both of which increase the rate of settling. The 

coagulant or flocculating agent that best improves settling characteristics 

varies depending on the particular precipitates to be settled. 

Settling can be conducted in a large tank by relying solely on gravity or 

can be mechanically assisted through the use of a circular clarifier or an 

inclined plate settler. Schematics of the two settling systems are shown in 

Figures 11 and 12. Following the addition of coagulating or flocculating agents, 

the wastewater is fed to a large settling tank, circular clarifier, or inclined 

plate settler, where the precipHated sol ids are removed. These solids are 

generally further treated in a sludge filtration system to dewater them prior to 

disposal. Sludge filteration is discussed in Section 11.8.2 of this document. 

The supernatant liquid effluent can be further treated in a polishing 

filtration system to remove precipitated residuals both in cases where the 

settling system is underdesigned and in cases where the particles are difficult 

to settle. Polishing filtration is discussed in Section II.B.2 of this document. 

2.4 Waste Characteristics Affecting Performance (WCAPsl 

In determining whether chemical precipitation will achieve the same level 

of perfonnance on an untested waste that it achieved on a previous 1 y tested waste 

and whether performance levels can be transferred, EPA examines the following 

waste characteristics: (a) the concentration and type of metals, {b) the 

concentration of total dissolved solids {TOS), {c) the concentration of 

complexing agents, and (d) the concentration of oil and grease. 

f:\document\15254031.01.010 85 
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2.4.1 Concentration and Type of Metals 

For most ~etals, there is a specific pH at which the metal precipitate is 

least soluble. As a result, when a waste contains a mixture of many metals, it 

is not possible to operate a treatment system at a single pH or ORP vaiue that 

is optimal for the removal of all metals. The extent to which this affects 

treatment depends on the particular metals to be removed and their respective 

concentrations. One alternative is to operate multiple precipitations, with 

intermediate settling, when the optimum pH occurs at markedly different levels 

for the metals present. If the concentration and type of metals in an untested 

waste differ from and ar.e significantly higher than those in the tested waste, 

the system may not achieve the same performance. Additional precipitating 

agents, alternate pH/ORP values, and/or multiple precipitations may be required 

to achieve the same treatment performance, or other, more applicable treatment 

technologies may need to be considered for treatment of the untested waste. 

2.4.2 Concentration of Total Dissolved Solids 

High concentrations of total dissolved solids (TDS) can interfere with 

precipitation reactions, as well as inhibit settling. Poor precipitate formation 

and flocculation are results of high TDS concentrations, and higher 

concentrations of solids are found in the treated wastewater residuals. If the 

TDS concentration in an untested waste is significantly higher than that in the 

-tested waste, the system may not achieve the same performance. Higher 

concentrations of precipitating agents may be required to achieve the same 

treatment performance, .or'other, more applicable treatment technologies may need 

to be considered for treatment of the untested ~aste. 

2.4.3 Concentration of Complex1ng Agents 

A metal complex consists of a metal ion surrounded by a group of other 

inorganic or organic ions or molecules (often called ligands). In the complexed 

form, metals have a greater solubility. Also, complexed metals inhibit the 

f:\document\152S4031.01.010 as 

, 
reaction of the metal with the precipitating agents and therefore may not be 

removed as effectively from solution by chemical precipitation. However, EPA 

does not have '~alytical methods to determine the concentration of complexed 

metals in wastewaters. The Agency believes that the best indicator for complexed 

metals is to analyze for compl~xing agents, such as cyanide, chlorides, EDTA, 

anunonia, amines, and methanol, for which analytical methods are available. 

Therefore, EPA uses the concentration of complexing agents as a surrogate waste 

characteristic for the concentration of metal complexes. If the concentration 

of complexing agents in an untested waste is significantly higher than that in 

the tested waste, the system may not achieve the same performance. Higher 

concentrations of precipitating agents may be required to achieve the same 

treatment performance, or other, more applicable treatment technologies may need 

to be considered for treatment of the untested waste. 

2.4.4 Concentration of Oil and Grease 

The concentration of oil and grease in a waste inhibits the settling of the 

precipitate by creating emulsions that require a long settling time. Suspended 

oil droplets in water tend to suspend particles such as chemical precipitates 

that would otherwise settle out of solution. Even with the use of coagulants or 

flocculants, the settling of the precipitate is less effective. If the 

concentration of oil and grease in an untested waste h significantly higher than 

that .in the tested waste, the system may not achieve the same performance. 

·Pretreatment of the waste may be required· to -reduce the oil and grease 

concentration and achieve the same treatment performance, or other, more 

applicable treatment technologies may need to be considered for treatment of the 

untested waste. 

2.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a chemical 

precipitation system, EPA examines the following parameters: (a) the pH/ORP 

value; (b) the precipitation temperature; (c) the residence time; (d) the amount 

f:\document\1SZS4031.01.010 89 
and type of precipitating agents, coagulants, and flocculants; (e) the degree of 

mixing; ind {f) t~e settling time. 

t_ 

2.5.1 pH/ORP Value 

The pH/ORP value in continuous chemical precipitation systems is used as 

an indicator of the concentration of precipitating agents in the reaction tank 

and thus is used to regulate their addition to the tank. The pH/ORP value also 

affects the solubility of metal pr·ecipitates formed and therefore directly 

impacts the effectiveness of their removal. EPA monitors the pH/ORP value 

continuously, if possible, to ensure that the system is operating at the 

appropriate design condition and to diagnose operational problems. 

2.5.2 Precipitation T~perature 

The precipitation temperature affects the solubility of the metal 

precipitates. Generally, the lower the temperature, the lower the solubility of 

the metal precipitates and vice versa. EPA monitors the precipitation 

temperature continuously, if possible, to ensure that the system is operating at 

the appropriate design condition and to diagnose operational problems. 

2.5.3 Residence Time 

the residence time impacts the extent of the chemical reactions to form 

metal precipitates and, as a result, the amount of precipitates that can be 

settled out of solution~ For batch systems, the residence· time is controlled 

directly by adjusting the treatment time in the reaction tank. For continuous 

systems, the wastewater feed rate is controlled to make sure that the system is 

operating at the appropriate design residence time. EPA monitors the residence 

time to ensure that sufficient tfme is provided to effectively precipitate 

metals and inorganics from the wastewater. 

f:\document\15254031.01.010 90 
2.5.4 Amount and Type of Precipitating Agents, Coagulants, and Flocculants 

The amountand type of precipitating agent used to effectively treat the 

wastewater depends on the amount and type of metal and inorganic constituents in 

the wastewater to be treated. Other design and operating parameters, such as the 

pH/ORP value, the precipitation temperature, the residence time, the amount and 

type of coagulants and flocculants, and the settling time, are determined by the 

selection of precipitating agents. The addition of coagulants and flocculants 

improves the settling rate of the precipitated metals and inorganics and allows 

for smaller settling systems (i.e., lower settling time) to achieve the same 

degree of settling as a much larger system. Typically, anionic polyelectrolyte 

flocculating agents are most effective with metal precipitates, although cationic 

or nonionic polyelectrolytes also are effective. Typical doses range from 0.1 

to 10 mg/1 of the total influent wastewater stream. Conventional coagulants, 

such as alum (aluminum sulfate), are also effective, but must be dosed at much 

higher concentrations to achieve the same result. Therefore, these coagulants 

add more to the settled sludge volume requiring disposal than do the 

polyelectrolyte flocculants. EPA examines the amount and type of precipitating 

agents, coagulants, and flocculants added, and their method of addition to the 

wastewater, to ensure effective precipitation. 

2.5.5 Degree of Mixing 

Mixing provides greater uniformity of the wastewater feed and disperses 

precipitating agents, coagulants, and flocculants throughout the wastewater to 

ensure the most rapid precipitation reactions and settling of precipitate solids 

possible. The. quantifiable degree of mixing is a complex assessment that 

includes, among other things, the amount of energy supplied, the length of time 

the material is mixed, and the related turbulence effects of the specific size 

and shape of the tank. This is beyond the scope of simple measurement. EPA, 

however, evaluates the degree of mixing qualitatively by considering whether 

mixing is provided and whether the type of mixing device is one that could be 

expected to achieve uniform mixing of the wastewater. 

f:\document\15254031.01.010 91 
2.5.6 Settling Time 

Adequate ~ttling time must be provided to make sure that removal of the 

precipitated solids from the wastewater has been completed. EPA monitors the 

settling time to ensure effective solids removal. 

f:\document\15254031.01.010 92 
2.6 References 

Cherry, K.F. 19~?- Plating waste treatment. pp. 45-62. Ann Arbor, Mich.: Ann 

Arbor Sci en·ce Pub 1 i shers, Inc. 

Cushnie, G.C., Jr. 1985. Electroplating wastewater pollution control technology. pp. 48-62, 84-90. Park Ridge, N.J.: Noyes Publications. 

Cushnie, G.C., Jr. 1984. Removal of metals from wastewater: neutralization and 

precipitation. pp. 55-92. Park Ridge, N.J.: Noyes Publications. 

Gurnham, C.F. 1955. Principles of industrial waste treatment. pp. 224-234. New 

York: John Wiley and Sons. 

Kirk-Othmer. 1980. Flocculation. In Encyclopedia of chemical technology, 3rd 

ed., vol. 10, pp. 489-516. New York: John Wiley and Sons. 

USEPA. 1983. U.S. Environmental Protection Agency. Treatability manual: Vol. 

III, Technology for control/removal of pollutants, p. 111.3.1.3.2. 

EPA-600/2-82-00lC. Washington, D.C.: U.S. Environmeotal Protection 

Agency. 

f:\document\15254031.01.010 93 

~ I 

l 
3. ENCAPSULATION 

3.1 Appti cabi 1 ity 

Encapsulation processes refer to a family of processes wherein high-solids 

nonwastewaters are mixed with an organic polymeric substance-or with asphalt. 

The mixture is then allowed to cure into a solid mass pr1or to disposal. These 

processes are applicable to a wide variety of wastes. They are not applicable 

to wastes containing materials that decompose at high temperatures or to wastes 

containing oxiders that can react with the binder materials. Also, some aromatic 

solvents such as xylene and to~uene can diffuse through the encapsulating agent. 

Oils, greases, and some chelating agents may interfere with the hardening and 

solidification of the encapsulating material. EPA believes that encapsulation 

technologies are applicable primarily to wastes containing hazardous metal 

constituents. Encapsulation may i11111obilize hazardous organics as well as metals; 

however, incineration is more applicable to organics since incineration destroys 

organics completely, whereas encapsulation can only i11111obilize them. 

3.2 UnderlYing Principles of Operation:· - - :: 

There are a numb~r of very sf mil ar encapsulation processes that differ from 

each other only in the encapsulating agent used. In all of the processes, the 

waste.is first dried to remove moisture. The waste is then usua}ly reheated and 

1nixed with hot asphalt or thermoplastic material such as polyethylene. The 

mixture is then cooled to solidify the mass.. The ratio of matrix {fixative or 

encapsulating agent) to waste is generally high {i.e., 1:1 or 1:2 fixative to 

waste on a dry basis). The matrix, once solidified, coats the waste to minimize 

leaching. 

3.3 Description of Encapsulation Processes 

Encapsulation processes can take the form of macroencapsulation, 

microencapsulation, or both. Microencapsulation is the containment of individual 

f:\document\15Z54031.01.011 94 

1 

• 
waste particles in the polymer or asphalt matrix. Macroencapsulation is the 

encasement of a mass of waste in a thick polymer coating. The waste mass may 

have been micro~capsulated prior to macroencapsulation. 

3.3.1 Microencapsulation 

Microencapsulation processes typically involve the following unit 

operations in series: 

• Predrying of the waste to remove entrained moisture. 

• Mixing of the heated waste with molten encapsulating agent (asphalt, 

polyethylene, thermosetting resins). 

• Cooling of the hot mixture to allow the mixed mass to harden into a 

solid mass. 

Generally, ratios of matrix to waste used are high compared to those of 

pozzolanic stabilization processes (i.e., for encapsulation the ratio ts in the 

1:1 to 1:2 range). Mixing is generally done at 120 to 130°C depending on the 

melting characteristics of the matrix and the type of equipment used for mixing. 

A few processes differ from the above description in that polymerization of 

monomers mixed with waste is conducted at ambient or near ambient temperatures 

i-n the presence of catalysts. The monomer (or monomeric mixture) then 

polymerizes at room temperature, coating the individual waste particles. 

3.3.2 Macroent4psulat1on 

The macroencapsulation process of hazardous waste solids usually involves 

two steps. In the first step, the hazardous wastes may be chemically treated by 

using low-cost dehydrating agents such as lime, kiln dust, or Portland cement. 

This operation does not increase the volume of the solids significantly because 

f:\document\15254031.01.011 95 

, 
only a small amount of dehydrating agent is needed to dewater the solids. The 

resulting·mixtures are friable, and they can easily be ground. 

( 

In the second step, the dehydrated sludges are ground and the particles may 

be microencapsulated, typically by a polybutadiene binder. Then the mass is 

macroencapsulated, or coated, typically by high-density polyethylene. 

The typical apparatus for macroencapsulation processes features heated or 

cooled molds, a method of waste and hardened product manipulation, and hydraulics 

for mold actuation. The molds typically contain electrical band heaters and 

water cooling channels. After the polymer coating hardens, the mold is split to 

facilitate product demolding. 

3.4 Waste Characteristics Affecting Performance (WCAPsl 

In determining whether encapsulation will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste 

and whether performance levels can be transferred, EPA examines the following 

waste characteristics: {a) the water content of the waste; {b) the presence of 

oxiding agents in the waste; (c) the presence of certain organic solvents; 

(d) the presence of oils, greases, and chelating agents; and {e) the presence of 

thermally unstable materials in the waste::·These characteristics are described 

below .. 

3.4.1 Water Content 

The processes normally require a dry solid waste. Wet solids need to be 

dried at elevated temperature, or chemically treated, to remove entrained 

moisture before they can be mixed with molten polymers, asphalt, or monomeric 

mixtures. The presence of free water interferes with the elevated temperature 

encapsulation processes by forming steam during the mixing and preventing a 

smooth coating of the particles. In ambient temperature processes, water may 

f:\document\15Z54031.01.011 96 
react with the polymerization catalyst, preventing it from initiating the 

polymerization reactions. 

3.4~2 Presence of Oxidizing Agents 

Strong oxidization salts such as nitrites, chlorates, or perchlorates will 

react with the organic matrix materials and slowly deteriorate the matrix. These 

oxidants may also react spontaneously with the heated matrix material to cause 

a fire or explosion. Wastes containing such strong oxidants should not be 

managed by polymer encapsulation processes. 

3.4~3 Presence of Organic Solvents 

Organic solvents, particularly aromatic solvents, may be capable of 

dissolving the polymer matrix material. They will also cause significant air 

emissions due to volatilization during the mixing of the heated waste and matrix 

materials. The process should not be used. on wastes containing such solvents 

unless the wastes have been pretreated to remove such materials. 

3.4.4 Presence of Oils, Greases, and Chelat1ng Agents 

Oils, greases, and organic chelating agents are likely to dissolve in and 

migrate through the polymeric matrices used for encapsulation. They may also, 

to some extent, coat individual waste particles and prevent firm 

microencapsulation binding between waste particles and the polymer matrix 

surrounding them. Beca~se of the ability of these organics to diffuse through 

polymeric matrices, wastes containing oils, greases, and organic chelating agents 

should not be managed by polymer encapsulation. 

3.4.5 Presence of Ther.ally Unstable Materials 

Hydrated salts are likely to decompose during the initial hot mixing of 

matrix and waste materials, liberating water vapor. These salts will also 

f:\docum.nt\15254031.01.011 97 

, 
rehydrate during cooling and thus interfere with the uniform coating of waste 

particles·by the matrix polymer. Wastes containing hydrated salts should not be 

managed by thislprocess. Salts that are known to cause such problems include 

hydrated sodium sulfate, magnesium sulfate, and hydrated metal chlorides. The 

soluble hydrates need to be removed from the waste by chemical or physical means 

before the wastes are managed by polymer microencapsulation. 

3.5 Design and Operating Parameters 

There are five design and operating parameters for this set of processes: 

(a) the choice of the polymeric matrix material, (b) the mixing equipment used, 

(c) the ratio of polymer to waste used, (d) process temperature control, and (e) 

air emissions control. These are described in the following paragraphs. 

3.5.1 Choice of Polymeric Matrix 

Several polymeric matrices are available for use in these encapsulation 

processes. These include asphalt, polyethylene, thenmosetting plastics (such as 

urea formaldehyde type resins), and resins that can be polymerized under ambient 

temperature in the presence of a catalyst. The choice of the polymeric matrix 

detenmines the temperature and equipment to be used and strongly influences the 

needed cure time. It also determines to some degree the choice of ~~stes that 

can be accepted because of differences in the properties of the polymers. EPA 

will examine the basis for the choice of polymer matrix, available test data, and 

the wastes being accepted for processing. 

3.5.2 Mixing Equ1pient Used 

For microencapsulation, polymers or monomers and catalysts must be well 

mixed with wastes to ensure that uniformly coated waste particles are produced. 

EPA will examine the design and operating characteristics of the mixing system 

to ensure that it is capable of generating uniform mixes. 

f:\document\15Z5403l.Ol.Oll 98 
3.5.3 Ratio of Polymer to Waste Used 

-

Sufficien\ polymer must be used to ensure that the waste is uniformly 

coated. Generally, a 1:1 or 1:2 polymer-to-waste ratio on a weight basis is 

used. EPA will examine the basis for the choice of polymer-to-waste ratio used 

to ensure that sufficient polymer is being added. 

3.5.4 Process Temperature Control 

To achieve uniform mixing, the encapsulation matrix must be in a 1 iquid 

state. The melting points of the different thermoplastic polymers will differ 

from each other. During mixing of the molten polymer and waste, the temperature 

needs to be maintained above the thermoplastic polymer melting point and below 

the point at which polymer vaporization or thermal decomposition begins. Thus, 

for a given thermoplastic polymer, there is only a certain temperature range in 

which the process can be satisfactorily operated. For thermosetting resins the 

temperature selected must be appropriate to cause polymerization (hardening) 

after thorough mixing. EPA will examine data on the properties of the polymers, 

including decomposition, to ensure that a proper operating temperature was 

selected. EPA will also ex~ine the temperature control instrumentation in use 

to ensure that it is operating properly. 

3.5.5 Air Emissions Control 

Heating of mixtures of waste with polymers or asphalt can cause the release 

of hydrocarbon air emis~ions that may include volatile components of the waste, 

plasticizers present in the polymers, polymer decomposition products, and lowmolecular-weight ingredients of the asphalt. In a properly operating system, air 

emissions testing may be needed during at least initial operation to determine 

levels of emissions and to assess the need for air emissions control. EPA will 

ex~ine such air monitoring data to determine whether air emissions control 

systems are appropriate. The Agency will also examine the iir emissions control 

f:\document\15254031.01.011 99 
systems in use to ensure that they are operating and in proper operating 

condition: 

f:\documant\15254031.01.011 100 

1 . 
3.6 References 

Pierce, J., and Wesilind, P.A. 1981. Hazardous waste management. pp. 82-4. Ann 

Arbor, Mich.: Ann Arbor Science Publishers. 

Rich, G., and Cherry, K. 1987. Hazardous waste treatment technologies. Chapter 6, pp. 9-3. Northbrook, Ill.: Purdue Publishing Company. 

f:\docunent\15254031.01.011 101 
4. STABILIZATION OF METALS 

Stabilization is a treatment technology applicable to wastes containing 

leachable metals and having a high filterable solids content, low total organic 

carbon (TOC) content, and 1 ow oi 1 and grease content. This technology is 

commonly !!~~d to treat residuals generated from treatment of wastes such as 

electroplating wastewaters, incineration ash residues, and characteristic 0-metal 

wastes such as cadmium (0006), chromium (0007), lead (0008), and mercury (0009). 

For wastes with recoverable levels of metals, high temperature metals recovery 

and retorting technologies may be applicable. 

Stabilization refers to a broad class of treatment processes that 

inunobilize hazardous constituents in a waste. Related technologies are 

encapsulation and thermoplastic binding. However, EPA considers stabilization 

technologies to be distinct from the other technologies in that their operational 

principles are significantly different. Stabilization typically requires a 

chemica 1 reaction between the waste and the stabilizing agent for- effective 

treatment, while thermoplastic binding and encapsulation usually e~ploy physical 

containment of hazardous particulates by the encapsulating agent. 

4.2 Underlying Principles of Operation 

The basic principle of operation for stabilization is that leachable metals 

in a waste are i11111obilized following the addition of stabilizing agents and other 

chemicals. The leachability is reduced by the formation of a lattice structure 

and/or chemical bonds that chemically bind the metals to the solid matrix and 

thereby limit the amount of metal constituents that can be leached when water or 

a mild acid solution comes into contact with the waste material. Stabilization 

is most effective when the waste metal is in its least soluble state, thereby 

decreasing the potential for leaching. For example, hexavalent chromium is much 

more soluble and more difficult to stabilize than trivalent chromium. 

f:\document\1SZS4031.01.012 102 
The two principal stabilization processes used are cement-based and 

lime/pozzolan-based processes. A brief discussion of each is provided below. 

In both cement-~ased and lime/pozzolan-based techniques, the stabilizing process 

can be modified through the use of additives, such as silicates, that control 

curing :-ates, reduce permeability, and enhance the properties of the solid 

materia 1. 

4.2.1 Portland Cement-Based Process 

Portland cement is a mixture of powdered oxides of calcium, silica, 

aluminum, and iron, produced by kiln burning of materials rich in calcium and 

silica at high temperatures (i.e., 1,400 to 1,5oo·c (2,552 to 2,732.F}). When 

the anhydrous cement powder is mixed with water, hydration occurs and the cement 

begins to set. The chemistry involved is complex because many different 

reactions occur depending on the composition of the cement mixture. 

As the cement begins to set, a colloidal gel of indefinite composition and 

structure is formed. Over time, the gel swells and forms a matrix composed of 

interlacing, thin, densely packed silicate fibrils. Constituents present in the 

waste slurry (e.g., hydroxides and carbonates of various metals} are incorporated 

into the interstices of the cement matrix. The high pH of the cement mixture 

tends to keep metals in the form of insoluble hydroxide and carbonate salts. It 

has been hypothesized that metal ions may also be incorporated into the crystal 

-structure of the cement matrix, but this hypothesis has not been verified. 

4.2.2 L1me/Pozzo1an-lased Process _,. 

Pozzolan, which contains finely divided, noncrystalline silica (e.g., fly 

ash or components of cement kiln dust), is a material that is not cementitious 

in itself, but becomes so upon the addition of lime. Metals fn the waste are 

converted to insoluble silicates or hydroxides and are incorporated into the 

interstices of the binder matrix, thereby inhibiting leaching. 

f:\document\152>4031.01.012 103 
4.3 Description of Stabilization Process 

The stabilization process consists of a weighi~g device, a mixing unit, and 

a curing vessel or pad. Commercial concrete mixing and handling equipment is 

typically used in stabilization processes. Weighing conveyors, metering cement 

hoppers, and mixers similar to concrete batching pl~n~s have been adapted in some 

operations. When extremely dangerous materials are treated, remote-control and 

in-drum mixing equipment, such as that used with nuclear waste, is employed. 

In most stabilization processes, the waste, stabilizing agent, and other 

additives, if used, are mixed in a mixing vessel and then transferred to a curing 

vessel or pad and allowed to cure. The actual operation (equipment requirements 

and process sequencing) depends on several factors including the nature of the 

waste, the quantity of the waste, the location of the waste in relation to the 

disposal sjte, the particular stabilization formulation used, and the curing 

rate. Following curing, the stabilized solid formed ts recovered from the 

processing equipment and disposed of. 

4.4 Waste Characteristics Affecting Performance CWCAPsl 

In determining whether stabilization will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste 

and w~ether performance levels can be transferred, EPA examines the following 

-waste characteristics: (a) the concentration of fine particulates, (b) the 

concentration of oil and grease, (c) the concentration of organic compounds, 

(d) the concentration of sulfate and chloride~nds, and (e) the solubility 

of the metal c~mpound. 

4.4.1 Concentration of Fine Particulates 

For both cement-based and lime/pozzolan-based processes, very fine solid 

materials (1.e., those that pass through a Ko. 200 mesh sieve (less than 74 ~m 

particle size)) weaken the bonding between waste particles and the cement or 

f:\document\15Z540Jl.Ol.Ol2 104 
lime/pozzolan binder by coating the particles. This coating inhibits chemical 

bond formation, t~ereby decreasing the resistance of the material to leaching. 

If the concentration of fine particulates in an untested waste is significantly 

higher than that in the tested waste, the system may not a chi eve the same 

performance. Pretreatment of the waste may be required to reduce the fine 

particulate concentration and achieve the same treatment performance, or other, 

more applicable treatment technologies may need to be considered for treatment 

of the untested waste. 

4.4.2 Concentration of Oil and Grease 

Oil and grease in both cement-based and 1 i me/pozzol an-based systems result 

in the coating of waste particles and the weakening of the bond between the 

particle and the stabilizing agent, thereby decreasing the resistance of the 

material to leaching. If the concentration of oil and grease in the untested 

waste is significantly higher than that in the tested waste, the system may not 

achieve the same performance. Pretreatment may be required to reduce the oil and 

grease concentration and achieve the same treatment performance, or other, more 

applicable treatment technologies may need to be considered for treatment of the 

untested waste. 

4.4.3 Concentration of Organic Compounds 

Organic compounds in the waste interfere with the stabilization chemical 

reactions and bond formation, thus inhibiting curing of the stabi1ized material. 

This interference results in a stabilized waste having decreased resistance to 

leaching. -If the total organic carbon {TOC} content of the untested waste is 

significantly higher than that of the tested waste, the system may not achieve 

the same performance. Pretreatment may be required to reduce the TOC and achieve 

the same treatment performance, or other, more applicable treatment technologies 

may need to be considered for treatment of the untested waste. 

f:\documant\15254031.01.012 105 
4.4.4 Concentration of Sulfate and Chloride Compounds 

Sulfate ~d chloride compounds interfere with the stabilization chemical 

reactions, weakening bond strength and prolonging setting and curing time. 

Sulfate and chloride compounds may reduce the dimensional stability of the cured 

matrix, thereby increasing leachability potential. If the concentration of 

sulfate and chloride compounds in the untested waste is significantly higher than 

that in the tested waste, the system may not achieve the same performance. 

Pretreatment may be required to reduce the sulfate and chloride concentrations 

and achieve the same treatment performance, or other, more applicable treatment 

technologies may need to be considered for treatment of the untested waste. 

4.4.5 Solubility of the Metal Compound 

The metal to be stabilized should be in its least soluble state, or the 

stabilized waste may exhibit a potential for increased leachability. 

Pretreatment may be required to chemically reduce or oxidize the metal to a lower 

solubility state and achieve maximum stabilization performance. For example, 

hexavalent chromium is much more soluble and more difficult to stabilize than 

trivalent chromium. 

4.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a 

stabilization system, EPA examines the following par~ters: (a} the amount and 

type of stabilizing ageo.t,...and additives~. (.b.),.;tl\er.~ee. .. of mixing, (c} the 

residence time, (d} the stabilization temperature and humidity, and (e} the form 

of the metal compound. 

4.5.1 Amount and Type of Stabilizing Agent and Additives 

The stabilizing agent and additives used will determine the chemistry and 

structure of the stabilized material and therefore its leachability. Stabilizing 

f:\doc~t\15254031.01.012 106 

1 
agents and additives must be carefully selected based on the chemical and 

physical characteristics of the waste to be stabilized. To select the most 

effective type tf stabilizing agent and additives, the waste should be tested in 

the laboratory with a variety of these materials to determine the best 

combination. 

The amount of stabilizing agent and additives is a critical parameter in 

that sufficient stabilizing materials are necessary to properly bind the waste 

constituents of concern, making them less susceptible to leaching. The 

appropriate weight ratios of stabiHzing agent and additives to waste are 

established empirically by setting up a series of laboratory tests that allow 

separate leachate testing of different mix ratios. The ratio of water to 

stabilizing agent (including water in waste) will also impact the strength and 

leaching characteristics of the stabilized material. Too much water will cause 

low strength; too little will make mixing difficult and, more important, may not 

allow the chemical reactions that bind the hazardous constituents to be fully 

completed. EPA evaluates the amount of stabilizing agent, water, and other 

additives used in the stabilization process to ensure that sufficient stabilizing 

materials are added to the waste to effectively i11111obilize the ~aste constituents 

of concern. 

4.5.2 Degree of Mixing 

Hhfng is necessary to ensure homogeneous distribution of the waste, 

stabilizing agent, and additives. Both undermixing and overmixing are 

undesirable. The fi,rst· condition results in a nonhomogeneous mixture; 

consequently, areas will exist within the waste where waste particles are neither 

chemically bonded to the stabilizing agent nor physically held within the lattice 

structure. Overmix1ng, on the other hand, may inhibit gel formation and ion 

adsorption in some stabilization systems. Optimal mixing conditions are usually 

determined through laboratory tests. The quantifiable degree of mixing is a 

camp 1 ex assessment that inc 1 udes, among other factors, the amount of energy 

supplied, the length of time the material is mixed, and the related turbulence 

f:\document\15254031.01.012 107 
effects of the specific size and shape of the mix tank or vessel. The degree of 

mixing i~ ~eyond_the scope of simple measurement. EPA, however, evaluates the 

degree of mix~iig ~ual itatively by considering whether mixing is provided and 

whether the type of mixing device is one that could be expected to achieve 

homogeneous distribution of the waste, stabilizing agent, and additives. 

4.5.3 Residence Time 

The residence time or duration of curing ensures that the waste particles 

have had sufficient time in which to incorporate into lattice structures and/or 

form stable chemical bonds. The time necessary for complete stabnization 

depends on the waste and the stabilization process used. The performance of the 

stabilized waste (i.e., the levels of waste constituents in the leachate) will 

be highly dependent on whether complete stabilization has occurred. Typical 

residence times range from 7 to 28 days. EPA monitors the residence time to 

ensure that sufficient time is provided to effectively stabilize the waste. 

4.5.4 Stabilization Temperature and Humidity 

Higher temperatures and lower humidity increase the rate of curing by 

increasing the rate of evaporation of water from the stabilization mixtures. If 

temperatures are too high, however, the evaporation rate can be excessive, 

resul.ting in too little water being available for completion of the stabilization 

·reaction. EPA monitors the stabilization temperature and humidity continuously, 

if possible, to ensure that the system is operating at the appropriate design 

conditions and to diagnose operational problems. 

4.5.5 For. of the Metal Compound 

Ideally, the waste metal to be stabilized should be in its least soluble 

state to reduce leaching of the stabilized waste. Pretreatment such as chemical 

oxidation or chemical reduction may be required to oxidize or reduce the metal 

to a state of lower solubility. Additionally, the solubility of the metal can 

f:\docuaent\152S4031.01.012 108 
be decreased by precipitating it with an appropriate compound. For example, 

ferric arsenate js less soluble and less leachable than calcium arsenate. EPA 

can monitor sctJubility of the metal by performing a standard leaching test 

(Extraction Procedure (EP) or Toxicity Characteristic Leaching Procedure (TCLP)) . 

. ~ -.. 

f:\document\15254031.01.012 109 
4.6 References 

Ajax Floor Prod&cts Corp. n.d. Product literature: technical data sheets, 

Hazardous Waste Disposal System. P.O. Box 161, Great Meadows, N.J. 07838. 

Austin, G.T. 1984. Shreve,s chemical process industries. 5th ed. New York: 

McGraw-Hill Book Co. 

Bishop, P.L., Ransom, S.B., and Grass, D.L. 1983. Fixation mechanisms in 

solidification/stabilization of inorganic hazardous wastes. In .;,.:Pr:..::o::..:::c~e::.:ed~i~n~g s=--=o:.:..f~t:.:.h:..:e~3~8;.;::t~h~l:.:.n~d=u =s t:::.:-r~i .-a 1"---'=W=a s::;-:t;.::e~Co~n:.:..;f e:.:.r..::.e.:.:.;n c=e , May 10 -12 , 1983 , at 

Purdue University, West Lafayette, Indiana. 

Conner, J.R. 1986. Fixation and solidification of wastes. Chemical 

Engineering. Nov. 10, 1986. 

Cullinane, M.J., Jr., Jones, L.W., and Malone, P.G. 1986. Handbook for 

stabilization/solidification of hazardous waste. U.S. Army Engineer 

Waterways Experiment Station. EPA report no. 540/2-86/001. Cincinnati, 

Ohio: U.S. Environmental Protection Agency. 

Electric Power Research Institute. 1980. FGO sludge disposal. annual. 2nd ed. 

Prepared by Michael Baker Jr., Inc. EPRI CS-1515 Project 1685-1. Palo 

Alto, Calif.: Electric Power Research Institute. 

Malone, P.G., Jones, L.W., and Burles, J.P. Application of solidification/ 

stabilization technology to electroplating wastes. Office of Water and 

Waste Management. SW-873. Washington, D.C.: U.S. Environmental Protection Agency. 

Mishuck, E., Taylor, D.R., Telles, R., and Lubowitz, H. 1984. Encapsulation/ 

fixation CE/Fl mechanisms. Report no. DRXTH-TE-CR-84298. Prepared by 

S-Cubed under Contract no. DAAK11-81-C-0164. 

Pojaselt RB. 1979. Solid-waste disposal: solidification. Chemical Engineering 

86(17): 141-145. 

USEPA. 1980. U.S. Environmental Protection Agency. U.S. Army Engineer 

Waterways· Experiment Station. Guide to the disposal of chemically 

stabilized and solidified waste. Pre~ared forMERL/0~ under Interagency 

Agreement No. EPA-IAG-04-0569. PB 81 181 505. Cincinnati, Ohio: U.S. 

Environmental Protection Agency. 

f:\document\15254031.01.012 110 
5. VITRIFICATION 

5.1 App'kicabil ity 

Vitrifkation technologies include glass and shg vitrification and 

elevated-temperature calcination processes. Vitrification processes involve 

dissolving the waste at high temperatures into glass or a glasslike matrix. 

Calcination involves merely heating the material at high temperatures. 

High-temperature vitrification is applicable to nonwastewaters containing 

arsenic* or other characteristic toxic metal constituents that are relatively 

~onvolatile at the temperature: at which the process is operated. This 

technology is a 1 so applicable to many wastes containing organometa 11 i c compounds, 

where the organic portion of the compound can be completely oxidized at 

process-operating conditions. Afterburners may be required to convert unburned 

organics to carbon dioxide. 

The process is not generally applicable to volatile metallic compounds or 

to wastes containing high levels of constituents that will interfere with the 

vitrification process. High levels of chlorides and other halogen salts should 

be avoided in the ~~stes being processed because they interfere with glassmaking 

processes and cause corrosion problems. 

Calcination processes are applicable to inorganic wastes that do not 

contain volatile constituents. 

*Volatile arsenic compounds are usually converted to nonvolatile arsenate salts 

such as calcium arsenate prior to use of this process. In ordinary glass- making, arsenic volatilization problems are minimized by adding arsenic 

as arsenate salts. 

f:\dccument\15254031.01.013 111 

, 
5.2 Underlying Principles of Operation 

The basic\>rinciples of operation for vitrification technologies depend on 

the technology used. In glass and slag vitrification processes, the waste constituents become chemically bonded inside a glasslike matrix in many cases. In 

all instances, the waste becomes surrounded by a glass matrix that immobilizes 

the waste constituents and retards or prevents their reintroduction into the 

environment. Arsenates are converted to silicoarsenates, and other metals are 

converted to silicates. 

High-temperature calcination processes remove water of hydration from the 

toxic metal-bearing sol ids, convert hydroxides present to oxides, and sinter the 

material, reducing its surface area to a minimum. Conversion of hydroxides to 

oxides and minimization of available surface area retard surface reactions that 

would reintroduce the material into the environment. Calcination may also be 

accompanied by chemical reaction if a material such as lime is blended with the 

waste before it is heated. For example, lime will react with arsenic oxides at 

higher temperatures to form calcium arsenate, and this material will then be 

sintered at elevated temperatures. Brief descriptions of each of the 

high-temperature processes are given in the following subsections. 

5.2.1 Glass Vitr1f1cat1on 

In the glass vitrification process, the waste and normal glassmaking 

constituents are first blended together and then fed to a glassmaking furnace, 

where the mixed feed materials are introduced into a pool of molten glass. The 

feed materials then react with each other to form additional molten glass, in 

which particles of the waste material become dissolved or suspended. The molten 

glass is subsequently cooled. As it cools, it solidifies into a solid mass that 

contains the dissolved and/or suspended waste constituents. Entrapment and 

chemical bor.ding within the glass matrix render the waste constituents 

unavailable for reaction. 

f:\document\152540~1.01.013 112 

, 

I 

c 
5.2.2 Slag Vitrification 

Slag vit~ification differs from glass vitrificatior. in that finely ground 

slag from metal-refining processe~ and waste are premixed and fed to the same 

type of furnace as that used for glassmaking. The slag liquifies at the process 

temperature {1100 to 1200"C), and the waste constituents either dissol'le or 

become suspended ir. the molten slag. Subsequent cooling of the slag causes it 

to solidify, trapping the waste inside a glassl ike matrix and rendering it 

unavailable for chemical reaction or migration into the environment. 

5.2.3 High-Temperature Calcination 

In the high-tr:mperature calcination process, the waste is heated in a 

furnace or kiln to between 400 and aoo·c. In some instances, the waste may be 

blended wi~h lime prior. to heating. In those cases, chemical reaction may occur 

during the calcining process. Water present as either free water or water of 

hydration is evaporated, and hydroxides present are thermally decomposed to the 

corresponding oxides and water vapor. At the higher temperatures, the surface 

area of the dehydrated material is decreased by thermal sintering. Conversion 

of hydroxides to oxides and substant 1a 1 1 asses of surface area render the 

material less reactive in the environment and lower the leachability of 

characteristic toxic metals present. In general, the higher the calcination 

temp~ratures used, the- more camp 1 ete the 1 os~ of water and the greater the 

-accompanying loss of surface area, resulting in lower leachability potential. 

5.3 Description of Vitrification Processes 

This chapter discusses three types of high-temperature stabilization 

processes, which differ considerably from each other. Individual process 

descriptions are given in the following subsections. 

f:\aocument\15ZS4031.01.013 113 
5.3.1 Glass Vitrification 

Soda ash,t lime, silica, boron oxide, and other glassmaking constituents are 

first blended with the waste to be treated. The amount of waste added to the 

blend is dependent on the waste composition. Different metal oxides have 

differing solubility limits in glass matrices. The blended waste and glass raw 

material mixture is then fed to a conventional, heated glass electric furnace. 

The introduced material typically is added through a port at the top of the 

furnace and falls into a pool of molten glass. The glass constituents dissolve 

in the molten glass and form additional glass. Molten glass is periodically 

withdrawn from the bottom of the furnace and cooled. This material then 

solidifies on cooling into solid blocks of glasslike material. Organics present 

in the feed mixture undergo combustion at the normal operating temperatures of 

1100 to 140o•c and are fully oxidized to carbon dioxide and water vapor. 

The top of the furnace is normally cooled so that volatile materials, such I 

as arsenic oxides, that are present in the feed mixtures can condense on the 

cooled surface and fall back into the melt, where they can undergo chemical 

reaction to form silicoarsenates involved in the glassmaking process. Host of 

the arsenic used in making glass by this method is present as salts such as 

calcium arsenate. This approach was introduced into the glass industry to 

minimize fugitive arsenic losses. 

Gases, such as carbon dioxide, that are liberated during the glassmaking 

process exit the furna~e through the top and are generally wet-scrubbed prior to 

reentering the atmosphere. 

5.3.2 Slag Y1tr1f1cat1on 

The slag vitrification process is basically similar to glass vitrification 

except that granulated slag, instead of the normal glassmaking constituents, is 

blended with the waste for feed to the system. A pool of liquid slag is present 

f:\dacument\15254031.01.013 114 

1 
in the furnace, and the blended raw material mix typically is introduced at the 

top of tne furna~e and falls into this molten slag. The granulated slag-waste 

mixture liquiftes to form additional slag. Slag is periodically withdrawn from 

the slag pool and cooled into blocks. 

The type of furnace used for glass vitrification can also be used for slag 

vitrification. The operating parameters are similar. 

5.3.3 High-Temperature Calcination 

In the high-temperature calcination process, wastes containing inorganic 

compounds are fed to ovens or kilns, where they are heated to high temperatures 

(i.e., 500 to 9oo·c) to drive off water of hydration and to convert hydroxides 

present to the corresponding oxides. This process is primarily applicable to 

inorganic wastes that contain nonvolatile constituents. 

The waste is heated in the oven or kiln to the desired temperature, 

moisture and water of hydration are driven off; and, at the 500 to goo·c 

temperature range, hydroxides decompose to the corresponding oxides and water 

vapor. The high-temperature treatment also significantly reduces the surface 

areas of the oxides formed by sintering, thereby reducing the reactivity of the 

material. After the waste material has been calcined at an elevated temperature, 

it is. withdrawn from the oven or kiln, cooled, and either land disposed or 

*forwarded to another process, such as stabilization, for further treatment. 

5.4 Waste Characteristics Affecting Performance (WCAPsl 

The waste characteristics affecting perfonnance are different for the two 

vitrification processes and the calcination process. Accordingly, they are 

discussed separately in the following subsections. 

f:\document\l52540Jl.Ol.OlJ 115 

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5.4.1 Waste Characteristics Affecting Performance (WCAPs} 

In determning whether vitrification will achieve the same level of 

performance on an untested waste as on a previously tested waste, and whether 

performance levels can be transferred, EPA examines the following waste 

characteristics that affect performance of the vitrification processes: 

(a) organic content of the waste, (b) concentrations of specific metal ions in 

the waste, (c) concentrations of compounds in the waste that interfere with the 

glassmaking process, and (d) moisture content of the waste. 

5.4.1.1 Organic Content 

At process operating temperatures ( 1100 tv l~ijO'C), organics are combusted 

to carbon dioxide, water, and other gaseous products. The combustion process 

liberates heat, reducing the external energy requirements for the process. 

The amount of heat liberated by combustion is a function of the Btu value 

of the waste. The Btu content merely changes the energy input needs for the 

process and does not affect waste treatment performance. The amount of material 

that may not oxidize completely is a function of the organic halogen content of 

the waste. The presence of these halogenated organics does impact process 

performance because sodium chloride has a low solubility in glass. The presence 

of high chlorides results in a porous glass that 1s undesirable. If the 

balogenated organic content of an untested waste is the same as or less than that 

present in an already tested waste, the system should achieve the same 

performance for organic.destruction. 

5.4.1.2 Concentrations of Specific Metal Ions 

Most metal oxides have solubility limits in glass matrices. Hence, their 

concentration determines the amount of glass-forming materials or slag with which 

they must be reacted in this process to generate a nonleaching slag or glass. 

The solubility limits of most common metal oxides and salts in glass are found 

f:\document\15254031.01.013 116 

, 
in the Handbook of Glass Manufacture and other treatises on glass production. 

Oxides far which_ extensive solubility information is available are alumina, 

antimony oxide,_arsenic oxides, barium oxide, cadmium oxide, chromium oxides, 

copper oxides, cobalt oxides, iron oxides, lead oxides, manganese oxides, nickel 

oxides, selenium oxides, tin oxides, and zinc oxides. Analysis for individual 

metal concentrations in the waste can be performed according to EPA-approved 

methods. If the concentrations of specific metals in an untested waste are less 

than those in a tested waste, then the same ratio of slag or glass raw materials 

to waste may be used for vitrification purposes. If, however, the concentration 

of metal is greater than that in the tested waste, a different formulation must 

be used. 

5.4.1.3 Concentrations of Deleterious Materials 

Some waste constituents, such as chlorides, fluorides, and sulfates, 

interfere with the vitrification process if they are present at high levels. 

These salts have 1 imited solubilities in glass; therefore, when they are present, 

additional glass-fanning raw materials must be added to compensate for their 

presence. The solubility limits of various salts in glasses are discussed in 

references on glass production such as the Handbook of Glass Manufacture. 

Generally, if the concentrations of such materials in an untested waste are lower 

than those in a tested waste, then the same ratio of glass-forming constituents 

to wa~te may be used. Reducing agents such as carbon or ferrous salts reduce 

arsenates and selenates to lower valence compounds that are more volatile. These 

compounds should not be present in significant quantities in arsenic- or 

selenium-containing wa$tes to be vitrified. 

5.4.1.4 Moisture Content 

Materials fed to the vitrification process should be reasonably dry (i.e., 

contain less than 5 percent free moisture). If a waste has excess moisture above 

this level, it should be thermally dried before it is blended with glass-forming 

f:\document\15254031.01.013 117 

1 

. 
materials; otherwise, it may react violently when introduced to the molten glass 

or slag pool. 

t. 

5.4.2 Waste Characteristics Affecting Performance of High-Temperature Calcination 

In determining whether high-temperature calcination will achieve the same 

level of performance on an untested waste as on a previously tested waste and 

whether performance levels can be transferred, EPA examines the following waste 

characteristics that impact the performance of the high-temperature calcination 

process: (a) the organic content of the waste, (b) the moisture content of the 

waste, and (c) the inorganic composition of the waste. These characteri sties are 

discussed below. 

5.4.2.1 Organic Content 

Calcination temperatures normally used are too low to initiate combustion 

of some types of organic compounds. However, they are high enough to cause 

volatilization of organics, which have to be removed from process off-gases. For 

these reasons, the presence of significant levels of organi~s is undesirable but 

can be handled with appropriate air pollution controls. Organics, per se, do not 

interfere with the conversion of oxides to hydroxides or with sintering 

processes. Afterburners may be required on vitrification units managing high9rgantc-content wastes to ensure complete combustion of the organics present. 

5.4.2.2 Moisture Content 

Excess water that has to be removed from the waste by heating increases the 

amount of time needed to bring the waste to the calcination temperature. For 

this reason, wastes with high moisture content should be dewatered prior to the 

use of this process. 

f:\doc~t\l5ZS403l.Ol.OlJ 118 
5.4.2.3 Inorg~nic Composition 

Cal cinatid'n temperatures are normally selected based on the temperatures 

at which hydroxides are thermally decomposed-to the corresponding oxides and 

water vapor. To select an optimum operating temperature, one should know the 

approximate composition of the waste. A few toxic metal oxides have fairly low 

volatilization temperatures. Arsenic oxide,_-selenium dioxide, and mercuric oxide 

all volatilize below soo·c. High-temperature calcination should not be used for 

wastes that contain these volatile constituents unless the wastes are blended 

with materials such as lime, which will react with the constituents before they 

can_ vaporize. Nonvolatile arsenic compounds such as ferric and calcium arsenates 

can be calcined without concern for vaporization of material. 

-~ 

5.5 Design and Operating Parametarj 

·' 

The design and operating parameters for the vitrification processes are 

similar t: each other, but differ considerably from those for high-temperature 

calcination. The foilo~ing subsections discuss these two technologies 

separately. 

5.5.1 Design and Operating Par~ters for Vitrification Processes 

.In assessing th~- effectivenuo-~e design and operation of a 

vitrification system, EPA examines t~~·ingparameters: (a) the composition ~ of the vitrifying agent, (b) the oper&l-fosli&emperature, (c) the residence time, 

and (d) the vitrificat}on.furnace design. ---

5.5.1.1 Composition of the VitrifYing Agent 

Slag and various glassmaking for"'IIIUlaiions are used as vitrifying agents. 

The choice of the vitrifying agent is detarmined by the solubility of the waste 

constituents to be vitrified. Different inorganic oxides have differing 

solubilities in various glass matrices. 

f:\document\15254031.01.013 119 

1 ; 
For slags, the presence of carbon or other reducing agents is undesirable 

when arsenic-bearing or selenium-bearing wastes are vitrified. Carbon or ferrous 

salts in the sl•g reduce arsenates in the waste to arsenic trioxide, which has 

a low volatilization temperature. In a similar manner, these same reducing 

agents reduce selenates to elemental selenium, which also has a low 

volatilization temperature. When slags are used for vitrifying arsenic-bearing 

and selenium-bearing wastes, EPA monitors the composition of the granulated slags 

to ensure that they do not contain significant concentrations of carbon or 

ferrous salts. 

In glass vitrification, various glassmaking formulations can be used. EPA 

examines the proposed formulations to ensure that the toxic metal ion 

concentrations of the final product do not exceed solubility limits. Hence, EPA 

examines the material balances based on waste composition and glassmaking 

additives a~d the published solubility limits for metal oxides in variQUS glasses 

to ensure that the vitrified product is indeed a glass containing the solubinzed 

toxic waste constituents. 

5.5.1.2 Operating Temperatura 

Vitrification furnaces are normally operated in the 1100 to 1400'C range. 

The exact operating temperature is usually selected based on the desired 

composition of the final product. Furnaces are normally equipped with automatic 

temperature control systems._EEA examines the basis of choice for operating 

temperatures and the nature and physical condition of the tenperaturemonitoring 

and control equipment to ensure that the system is being properly operated. 

5.5.1.3 Residence Till8 

Sufficient time must be allowed for the materials added to glass furnaces 

to reach operating temperatures and then undergo the chemical reactions needed 

to produce glasses. Residence times are normally on the order of 1 to 2 hours 

for processes operated at 1100 to 1200'C. For glasses or slags requiring 

f: \docur.ent \15254031.01.013 120 

, 
slightly higher temperatures, slightly longer residence times are usually 

selected.· EPA examines the basis for the facility's choice of residence times 

to ensure that the system is well operated. 

5.5.1.4 Vitrification Furnace Design 

Vitrification furnaces normally incorporate the following design features: 

• Withdrawal of the product in liquid form from the base of the furnace. 

• Maintenance of a liquid pool of product in the furnace. 

• Addition of product constituent mix at the top of the furnace. 

• Design of the top area of the furnace in a manner that allows for 

cooling of this area. (This is important because volatile constituents 

of the input feed may vaporize from the melt. The cool top area allows 

these constituents to condense and fall back into the melt.) 

• Presence and proper operation of an a1r emissions control afterburner 

and scrubbing system to manage vent gas emissions from the system such 

as volatilized noncombusted organics and hydrogen chloride vapors from 

combustion of any chlorinated organics present. 

EPA examines the furnace~ t~ b~ 11sed for waste· vi tri ffcat"ian·ta ensure that 

the design features mentioned above are present since they are important for 

proper operation of the systems. 

f: \doc~~~~e~~t\15254031.01. 013 121 
5.5.2 Design and Operating Parameters for High-Temperature Calcination 

Systems 

t 

In assessing the effectiveness of the design and operation of a 

high-temperature calcination process, EPA examines the following parameters: 

(a) the operating temperature, (b) the residence time, and (c} the air emission 

control units in place on the ovens or kilns used. 

5.5.2.1 Operating Temperature 

Calcination temperatures of from 500 to 900"C have been used in industry. 

The calcination temperature selected is generally a temperature above which metal 

hydroxides present will decompose to the corresponding oxides. Data on 

decomposition temperatures of some metal hydroxides are given in Table 2. The 

temperature chosen is normally high enough to cause extensive sintering (surface 

area loss) of the oxides formed, while at the same time not volatilizing these 

materials. EPA examines the technical basis for selection of the calcining 

temperature to determine whether the system is properly operated. EPA also 

examines the temperature monitoring and control systems in place to determine 

whether they are properly operated and reliable. 

Table 2 Metal Hydroxide Decomposition Temperatures 

Metal hydroxide 

Cadmium hydroxide Chromic acid 

Lead hydroxide Nickel hydroxide Zinc hydroxide 

Source: Weast 1977. 

f:\document\15ZS4031.01.013 

Decomposition temperature ("C) 

122 

300 

400 

145 

230 

125 

1 I 

1 

l 
5.5.2.2 Residence Time 

Calcinatie~ is generally a batch process, and sufficient time must be 

allowed far samples to be brought to the operating temperature. Residence times 

of several hours are normally used to minimize the effects of heat-up time. EPA 

examines the technical basis for the choice of residence time to ensure that 

sufficient heating at the required temperature is allowed to complete the 

dehydration and sintering processes. Residence time is a function of the time 

needed to bring the calcination furnace or kiln to the desired temperature and 

the time needed to campl ete the dehydration and si ntering processes at tt:e 

selected temperature. 

5.5.2.3 Air Emission Control Systems 

During the calcination process, water vapor is driven off as it is formed 

by the decomposition of hydroxides present in the waste. These hot gases exit 

the calcination furnace or kiln as they are·formed. Some particulates from the 

waste material, as well as organics present in the waste, may become entrained 

in these vent gases. Therefore, for air poll uti on control purposes, the 

calcination units must be equipped with wet or dry particulate coliection systems 

that are properly designed and operated. If wastes containing organics are 

processed by high-temperature calcination, the calcination furnaces need to be 

equipP.ed with afterburners to combust organic vapors emitted. EPA examines the 

aesign basis, physical condition, and maintenance of these air emission control 

units to determine whether they are properly designed, maintained, and operated. 

EPA also examines the system of management in use for· bandling and subsequent 

treatment of the collected particulates to ensure that these finely divided waste 

particles are properly managed. 

f:\document\15254031.01.013 123 

1 
5.6 References 

Penberthy, L. t 1984. Electric melting of glass. In Handbook of glass manufacture. Vol. I, pp. 387-399. New York: Ashlee Publishing Co. 

Penberthy, L. 1981. Method and apparatus for converting hazardous material to 

a relatively harmless condition. U.S. Patent 4299.611. November 10, 

1981. 

Steitz, W.R., Hibscher, C.W., and Mattocks, G.R. 1984. Electric melting of 

glass. In Handbook of glass manufacture. Vol. I, pp. 400-428. New York: 

Ashlee Publishing Co. 

Tooley, F.V. 1984. Raw materials. In Handbook of glass manufacture. Vol. I, 

pp. 19-56. New York: Ashlee Publishing Co. 

Twidwell, L.G., and Mehta, A.K. 1985. Disposal of arsenic bearing copper smelter flue dust. In Nuclear and chemical waste management. Vol. 5, pp. 297-303. Butte, Mont.: Montana College of Mineral Science and 

Technology. 

Weast, R.C., ed. 1978. Handbook of chemistry and ohys1cs. 58th ed. Cleveland, 

Ohio: CRC Press. 

f:\document\15Z54031.01.013 124 

1 
( 

II. REMOVAL TECHNOLOGIES 

A. RECOVERY, REUSE*, AND/OR SEPARATION TECHNOLOGIES 

FOR ORGANICS 

*The Agency encourages pollution prevention efforts such as those In recovery and reuse practices (see 40 CFR 

Part 261.1 for the definition of reus•. reclal1111tlon, and recycltng). He-ever, the Agency recognizes that 

currently there Is some confusion over the definition of what constitutes 1 solid waste that has led to the 

proltferatlon of so-called "shul recycltng~ by sane facilities. 5114111 recycltng are tllegitiiMte waste 

1111nagement practices wharelly hazardous wast• 1111terlah having no saleabl• value (no 1114rket for reuse) are 

claimed to be recycled/reused tn order to escape the stringent RCR.A hazardous waste definitions. 
1. CARBON ADSORPTION 

1.1 AppMcability 

Carbon adsorption is a treatment technology used to treat wastewaters 

containing dissolved organics at concentrations less than about 5 percent and, 

to a lesser extent, dissolved metal and other inorganic contaminants. The most 

effective metals removal is achieved with metal complexes. 

The two most colll!lon carbon adsorption processes are the granular activated 

carbon (GAC), which is used in packed beds, and the powdered activated carbon 

(PAC), which is added loosely to wastewater. This section discusses the GAC 

process; the PAC process is discussed in Section I.A.1 of this document, i.e., 

Biological Treatment. 

1.2 Underlying Principles of Operation 

The basic principle of operation for carbon adsorption is the mass transfer 

and adsorption of a molecule from a liquid or gas onto a solid surface. 

Activated carbon is manufactured in such a way as to produce extremely porous 

carbon particles whose internal surface area is very large (500 to 1,400 square 

meters per gram of carbon). This porous structure attracts and holds (adsorbs) 

organi~ molecules as well as certain metal and inorganic molecules. 

Adsorption occurs because (a) the contaminant has a low solubility in the 

waste, (b) the contaminant has a greater affin1 tr ror the carbon than for the 

waste, or (c) a combination of the two. The amount of contaminants that can be 

adsorbed by activated carbon ranges from 0.10 to 0.15 gram per gram of carbon. 

1.3 Description of Carbon Adsorption Process 

In GAC systems, the carbon is packed 1 n a co 1 umn and the wastewater f s 

passed through the carbon bed(s). The flow can be either down or up through the 

f:\document\15ZS4031.01.014 125 

1 
vertical column(s). Figure 13 shows two carbon adsorption systems. In the 

carbon adsorption_process, the wastewater is passed through a stat~onary bed of 

carbon. The ~ntaminants in the wastewater are adsorbed most rapidly and 

effectively by the upper layers of carbon during the initial stages of operation. 

These upper layers are in contact with the wastewater at its highest 

concentrations of contaminants. The small amounts of the contaminants that are 

oot adsorbed in the first few layers of the activated carbon bed are removed from 

solution in the lower or downstream portion of the bed. Initially, none of the 

contaminants escapes from the carbon bed. 

As the wastewater flows down the column (or the location in the column 

where the majority of adsorption is occurring) and the adsorption capacity is 

reached in the top layers, the adsorption zone moves down the column. As the 

adsorption zone approaches the end of the carbon bed, the concentration in the 

effluent rapidly approaches the influent concentration. This point in the 

process is referred to as breakthrough. A breakthrough curve (Figure 14) shows 

the plot of the ratio of effluent to influent concentrations versus time of 

process operation. At breakthrough, the adsorptive capacity of the carbon bed 

!s exhausted, and little additional removal of contaminants occurs. Treated 

wastewater is then either treated further in another carbon adsorption column, 

if necessary, or disposed of. 

Once the carbon bed is spent and can no 1 anger remove contaminants from the 

waste, it is taken off-line. The activated carbon is then either regenerated by 

thermal or chemical methods for further use or treated by incineration and 

disposed of. If carbon adsorption is used to· treat very taxi c or hazardous 

materials, the spent carbon usually is incinerated and disposed of directly. 

Regeneration is accomplished thermally by heating the carbon to a 

temperature (between 1,500 and 1,700•f) at which most of the adsorbed 

contaminants are volatilized and destroyed but which is not high enough to burn 

the surface of the carbon. About 4 to 9 percent of the carbon is lost in this 

process. Steam can also be used to regenerate carbon by volatilizing adsorbed 

f:\document\15254031.01.014 126 
WASTEWATER 

INFLUENt 

DOWHFLOW SERIES ARRAHOEUEHT 

TREATED 

EFFLUENT .ASTEWATER 

lO INFLUENT 

DISPOSAL 

TflEATED 

EFFLUE~T 

TO DISPOSAL 

UPFLOW SERIES ARRANGEMENT 

Figure 13 Carbon Adsorption Systems 

-·-
-

N 

DC) 

WASTEWATER 

INFLUENT 

ADSORPTION I 

ZONE 

Co 

l 

II 

c 

EFFLUENT 

Co 

l 

[XXX1' 

~ 

c 

co co 

.l l 

,l1\. ~ JX)j 'X IXlC :lC 

~ 

t.Dr------------------------y---------,~~.r 

RATIO OF 

EFFLUENT TO INfLUENT 

COHCENTRATIOH8 0.1 

WITH RESPECT TO TIME 

TIME 

Figure 14 Plot of Breakthrough Curve 

"' ,, 

'·' .·~ 

!: 

H 

..... 
organics for subsequent condensation, recovery, and reuse or for treatment and 

disposal. ·Chemica] regeneration involves the use of an acid, alkali, or organic 

solvent to reditsolve contaminants for subsequent recovery and reuse or for 

further treatment and disposal. There is a loss of performance with each 

regeneration of spent carbon because metals (such as calcium, magnesium, and 

fran) plug small pores in the carbon and prevent some organic contaminants from 

being desorbed at the thermal regeneration temperature. In each thermal 

regeneration process, some carbon becomes spent, requiring treatment and 

disposal. As a result, makeup carbon has to be added to the regenerated carbon 

being placed back in service. 

The n!.!mber of times that the carbon r.an be regenerated is detenni ned by the 

extent of its physical erosion and the loss of its adsorptive capacity. Isotherm 

tests can be performed on the rege!'lerated carbon to determine adsorptive 

capacity; such tests can thus aid in predicting the number of times the carbon 

can be regenerated. 

1.4 Waste Characteristics Affecting Performance (WCAPsl 

In determining whether carbon adsorption will achieve the same level of 

performance on an untested waste as it achieved on a previously tested waste and 

whether performance levels can be transferred, EPA examines the following waste 

charac~eristics: (a) the wa:;te type and concentration of adsorbable contaminants 

and (b) the concentrations of suspended solids· and oil and grease. 

1.4.1 Wasta Type and Concentration of Adsorbable Contaminants 

The concentration of adsorbable cont~inants is a measure of the fraction 

of the wastewater constituents that can be expected to be adsorbed by a carbon 

adsorption column. Concentrations of organics in the wastewater greater than 

about 5 percent result in excessive activated carbon consumption requiring 

frequent regeneration. At the higher organic concentrations other treatment 

f:\document\15254031.01.014 129 

, 
technologies, such as wet air oxidation, solvent extraction, or incineration, may 

be more ~propriate. 

t 

Although all organics can be adsorbed to some dearee, activated carbon has 

a greater affinity for aromatic than for aliphatic compounds and for nonpolar 

than for polar compounds. If the type and concentration of adsorbable 

contaminants in an untested waste are significantly less adsorbable and higher, 

respectively, than in the tested waste, the system may not achieve the same 

performance. 

1.4.2 Concentrations of Suspended Solids and Oil and Grease 

Suspended solids and oil and grease can reduce the effectiveness of carbon 

adsorption by clogging and coating the pores, as well as by competing for 

adsorption sites, thereby interfering with the treatment of contaminants of 

concern. EPA has information showing that this treatment interference occurs 

with suspended solids at levels greater than about 50 mg/1 and with oil and 

grease at above 10 mg/1. 

1.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a carbon 

adsorption system, EPA examines the following parameters: (a) the type and pore 

size of the carbon particles, (b) the adsorption temperature, (c) the pH, and 

(d) the hydraulic loading rate. 

For many hazardous organic constituents, analytical methods are not 

available or the constituent cannot be analyzed in the waste matrix. Therefore, 

it would nonaally be impossible to measure the effectiveness of the carbon 

adsorption treatment system. In these cases EPA tries to identify measurable 

parameters or canst i tuents that waul d act as surrogates in order to verify 

treatment. 

f:\document\15254031.01.01• 130 

, 
For organic constituents, each compound contains a measurable amount of 

total organic carbon (TOC). Removal of TOC in the carbon adsorption treatment - system will inc¥_cate removal of organic constituents. Hence, roc analysis is 

likely to be an adequate surrogate analysis where the specific organic 

constituent cannot be measured. 

However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden (i.e., the roc 

analysis may not be sensitive enough to detect changes at the milligrams/liter 

(mg/1) level in matrices where total organic concentrations are hundreds or 

thousands of mg/1). In these cases, other surrogate parameters should be sought. 

For example, if a specific analyzable constituent is expected to be treated as 

well as the unanalyzable constituent, the analyzable constituent concentration 

should be monitored as a surrogate. 

1.5.1 Type and Pore Size of Carbon Particles 

Activated carbon is made from a variety of substances (e.g., coal, wood), 

ground to many different sizes, and manufactured with a number of d1 fferent pore 

sizes. The pore size detenu1nes the surface area available for adsorption and, 

hence, the carbon's adsorptive capacity. The type and -pore size of carbon 

particles exhibit different adsorptive capacities for different contaminants. 

Another property that ·;s. important in assessing the effectiveness of carbon 

particles is the iodine. number; this value is an indicator of the adsorptive 

capacity for low-molecular-weight-organics~ taboratory bench testing is used to 

determine the most effective type and pore size of·carbon particles for treating 

particular wastewaters. EPA examines the type and pore size of the carbon 

particles used to ensure that effective adsorption is achieved. 

1.5.2 Adsorption Ta.parature 

As the temperature increases, the solubility of the contaminants generally 

increases as well, which results in less effective adsorption. EPA monitors the 

f:\document\15254031.01.014 131 
temperature continuously, if possible, to ensure that the system is operating at 

the appropriate d~sign condition and to diagnose operational problems. 

1.5.3 pH 

The pH impacts both the solubility of the various contaminants and the 

potential for chemical bonding to occur. EPA monitors the pH continuously, if 

possible, to ensure that the system is operating at the appropriate design 

condition~ and to diagnose operational problems. 

1.5.4 Hydraulic Loading Rate 

The amount of time that the waste contaminants are in contact with the 

carbon particles (i.e., residence time) impacts the extent to which adsorption 

occurs. Higher residence times generally improve adsorption performance but 

require 1 anger carbon beds to maintain the same overall throughput. Typical 

residence times for GAC adsorption systems range from 30 to 100 minutes. For a 

given size carbon bed, the residence time can be determined by the hydraulic 

loading rate. Typical hydraulic loading rates for downflow adsorption systems 

range from 0.5 to 8.0 gal/min-ft2

, while upflow systems typically operate around 

15 gal/m1n-ft2• EPA monitors the hydraulic loading rate to ensure that 

sufficient time is provided to effectively adsorb contaminants. 

f:\document\15254031.01.014 132 

, 
1. 6 References 

Authur D. Litt'~, Inc. 1977. Physical, chemical and biological treatment 

techniques for industrial wastes. Vol. I., pp. 1-1 to 1-18 and 1-37 to 

1-41. NTIS, PB275-054. 

DeJohn, P. B. 1975. Carbon from lignite or coal: Which is better? Chemical 

Engineering, April 28. 

Eckenfelder, W.W. Jr., Patoczka, J., and Watkins A. 1985. Wastewater treatment. 

Chemical Engineering, September 2, 1985. 

GCA Corp. 1984. Technical assessment of treatment alternatives for wastes 

containing halogenated organics. Prepared for U.S. Environmental Protection Agency, Contract No. 68-01-6871, pp. 150-160. 

Metcalf & Eddy, Inc. 1985. Briefing: Technologies applicable to hazardous 

waste. Prepared for U.S. Environmental Protection Agency, Office of 

Research and Development, Hazardous Waste Engineering Research Laboratory. 

Section 2.13. 

Patterson, J. W. 1985. Industrial wastewater treatment technology, 2nd ed. 

Stoneham, Mass.: Butterworth Publishers. pp. 329-340. 

Touhill, Shuckrow & Assoc. 1981. Concentration technologies for hazardous 

aqueous waste treatment. NTIS, PB81-150583. pp. 53-55. 

USEPA. 1973. U.S. Environmental Protection Agency. Process design manual for 

carbon adsorption. NTIS, PB227-157. pp. 3-21 and 53. 

USEPA. 1982. U.S. Environmental Protection Agency. Development Document for 

the Porcelain Enameling Point Source Category. pp. 172-241. Washington, 9.c.: U.S. Environmental Protection Agency. 

-

USEPA. 1986. U.S. Environmental Protection Agency. Best demonstrated 

available technoloav CBDATl backaround document for F001-F005 Spent 

Solvents, Vol. 1, EPA/530-SW-86-056, p. 4-4. Washington, D.C.: U.S. 

Environmental Protection Agency.·--- --

Versar. 1985 • Versar, Inc. An Overview of Carbon Adsorption. Draft final 

report prepared for U.S. Environmental Protection Agency, Exposure 

Evaluation Division, Office of Toxic Substances. Contract No. 68-02-3968, 

Task No. 58. 

f:\document\15254031.01.014 133 

1 
2. DISTILLATION TECHNOLOGIES 

2.1 Apqlicability 

Distillation is a thermal treatment technology applicable to the treatment 

of wastes containing organics that are volatile enough to be removed by the 

application of heat. Constituents that are not volatilized may be reused or 

incinerated as appropriate. The four most co11111on distillation processes are 

~atcn distillation, fractionation, steam stripping, and thin film evaporation. 

Thermal drying is also included in this section because of its similarity to 

distillation processes. Thermal drying uses heat to volatilize water from 

wastes. 

Batch distillation can be used to treat wastes having a relatively high 

percentage of volatile organics. In general, batch distillation is applied to 

spent solvent wastes where the wastes are highly concentrated in the solvent and 

yield significant amounts of recoverable· materials upon separation. Batch 

distillation is particularly applicable for wastes that have both very volatile 

and very nonvolatile components since the separation of that combination of 

components is amenable to the relatively unsophisticated batch distillation 

equipment. 

Fractionation is typically applied to wastes containing greater than about 

1 percent organics. It is designed to achieve the highest degree of distillate 

purity of the separated components. Fractionation can be operated to produce 

multiple product streams for recovery of more than one organic constituent from 

a waste while generating relatively small amounts of residue to be land disposed. 

In general, this technology is used where recovery of multiple constituents is 

desired and where the waste contains minimal amounts of suspended solids. 

Steam stripping is a form of distillation applicable to the treatment of 

wastewaters containing organics that are volatile enough to be removed by the 

f:\dacument\15254031.01.015 134 
application of heat using steam as the heat source. Typically, steam stripping 

is applied where _the waste contains less than 1 percent volatile organics. 

t 

Thin film evaporation is typically applied to wastes containing greater 

than 40 percent organics. However, the feed stream to the thin film evaporator 

must contain low concentrations of suspended solids. 

Thermal drying is a treatment technology applicable to solid wastes 

typically having a filterable solids content of approximately 40 percent or 

greater. Thermal drying removes water and volatile organics from a solid waste 

through evaporation. Thermal dryers operate in the range of 300 to 700'F and 

usually have mechanical agitation to improve heat transfer. Use of this 

technology results in a smaller volume of waste with reduced concentrations of 

water and volatile organics. 

A thermal dryer or •sludge dryer• is an enclosed device that is typically 

used to dehydrate sludge. The dryer's input (from wastes and auxiliary fuel} 

usually does not exceed 1500 Btu per pound of wastes treated, compared to 3,300 

to 19,000 Btu per pound for incineration. 

2.2 Underlying Principles of Operation 

The basic principle of operation for distillation processes, i.e., batch 

distiTlation, fractionation, thin film evaporation, and steam stripping, is the 

volatilizttion of hazardous components through the application of heat. The 

components that are vol~tilized are then condensed and typically either reused 

or further treated, usually by liquid injection incineration. In thermal drying, 

the basic principle of operation for drying is the removal of a liquid from a 

solid wasta by evaporation. This is similar to distillation in that 

volatilization of organic constituents also occurs. However, the primary purpose 

of thermal drying is to volatilize water. Liquid constituents will vaporize as 

a result of applied heat. In thermal drying, the rate at which liquid 

evaporation occurs depends on the thermal conductivity of the solid waste to be 

f: \doc~~~~ent\15254031. 01.015 135 
dried and the boiling points of the volatile liquid constituents to be 

evaporatad. 

t. 

An integra 1 part of the theory of the d i st i 11 a ti on process is the pri nci p 1 e 

of vapor-liquid equilibrium. When a liquid mixture of two or more components is 

heated, the vapor phase present above the liquid phase becomes more concentrated 

in the more volatile constituents {those having higher vapor pressures). The 

vapor phase above the liquid phase is then removed and cooled to yield a 

condensate that is also more concentrated in the more volatile components. The 

degree of separation of components depends on the relative differences in the 

vapor pressures of the constituents; the larger the difference in the vapor 

pressures, the more easily the separation can be accomplished. 

If the difference between the vapor pressures is extremely large, a single 

separation cycle or a single •equil ibrium stage• of vaporization and condensation 

may achieve a significant separation of the constituents. In such cases, batch 

distillation or thin film evaporation would be used. Typically, batch 

distillation units and thin film evaporation units contain only one equilibrium 

stage and are thus limited in the degree of separation by the relative 

volatilities of the constituents. 

If the difference between the vapor pressures of volatile components is 

small, then multiple equilibrium stages are needed to achieve effective 

-separation. In pr.act..ice·, the' raultiple equilibrium stages are obtained by 

stacking •trays• or placing •packing• into a column. Essentially, each tray 

represents one equilibrium stage. In a packed steam stripping column or 

fractionation column, the individual equilibrium stages are not discer~~ble, but 

the number of equivalent trays can be calculated from mathematical relationships. 

The vapor phase from a tray rises to the tray above it, where it condenses; the 

liquid phase falls to the tray below it, where it 1s again heated and separated. 

The vapor-liquid equilibrium of the waste components can be expressed as 

relative volatility, which is the ratio of the vapor-to-liquid concentrations of 

f:\document\152~031.01.015 136 

, 

I 
a constituent divided by the ratio of the vapor-to-liquid concentrations of 

anJther 'onstitu!nt. The relative volatility is a direct indicator of the ease 

of separation.t_ If the numerical value is 1, then separation is impossible 

because the constituents have the same concentrations in the vapor and liquid 

phases. When the relative volatility is 1, the liquid mixture is called an 

azeotrope. Separation becomes increasingly easier as the value of the relative 

volatility becomes increasingly different from unity. 

2.3 Description of Distillation Processes 

2.3.1 Batch Distillation 

A batch distillation unit usually consists of a steam-jacketed vessel, a 

condenser, and a product receiver. As the name implies, it is a batch process, 

not a cont!nuous process. Figure 15 is a schematic showing the major components 

of a batch distillation unit. The steam jacket provides the heat required to 

vaporize the volatile constituents in the liquid fraction of the waste. The 

rising vapor is collected in the condenser, cooled, and condensed. The liquid 

product stream is then routed to the product receiver. 

It is important to note that this technology treats wastes by vaporizing 

constituents, not destroying them. Accordingly, an integral part of this 

tech~ology is a condensation system to collect the organics, as well as an air 

-emission control system to collect or destroy those organics that are not 

condensed. The cooling load of the condenser is calculated in the design to 

ensure that the product recovery rate is maximized and emissions from condenser 

venting are minimized. The •bottoms,• which are the least volatile constituents 

of the waste, are withdrawn from the bottom of the batch still. Because batch 

distillation is used to remove the volatile organics from wastes, the bottoms are 

reduced in volatile organic content. However, prior to disposal, the bottoms 

generally require additional treatment, such as incineration, for residual, less 

volatile organics. 

f:\doc~nt\15254031.01.015 137 

' I 

{ 
(_ 

WASTE INFLUENT ___ _ 

ST1U. BOTTOMS 

TD FIEUSI OR 

INCINIRA TION 

VENT OF NON·CONCENSEC VAPORS 

TO AIR POUUT10N CONTROL SYSTEM 

AND/OR THE ATMOSPHERE 

"HEATeD 

JACKET 

Figure 15 Batch Dtst111at1on Systea 

138 

CON CENSER 

PRODUCT 

RECEIVER 

RECOVERED 

ORGANICS 

TO REUSE 

OR FURTHER 

lliEATMENT 
2.3.2 Fractionation 

Fraction\~ion is a continuous process conducted in a unit that consists of 

a reboiler, a column containing stripping and rectification sections, a 

condenser, and a nreflux" system. Figure 16 is a schematic showing the major 

components of a fractionation unit. The reboiler is a device that provides the 

heat required to vaporize the liquid fraction of the waste. It supplies enough 

heat to maintain the liquid in the column at its boiling point. The stripping 

and rectifying sections are composed of a set of trays in a vertical column. The 

discrete trays may be replaced by loose packing consisting of plastic, metal, or 

ceramic geometric shapes that provide surface area for the continuous 

boiling/condensing that takes place in the column. In the stripping section, 

vapor rising from the boiler is contacted with the downflowing liquid feed. 

Through this contact, the constituents with lower boiling points (i.e., those 

that are more volatile) are concentrated in the vapor. In the rectification 

section, the vapor rising above the feed tray is contacted with downflowing 

condensed liquid product (reflux). Through this contact, the vapor is further 

enriched in the constituents with lower boiling points (i.e., the more volatile 

constituents}. The rising vapor is collected at the top of the column and 

condensed in a condenser. The liquid product stream, except for the portion 

returned to the column as reflux, is then routed to a product receiver. The 

nbottoms," which are the least volatile components (i.e., those with the highest 

boiling points), are continuously withdrawn from the reboiler. Because the 

.liquid composition varies slightly from one equilibrium stage to the next, it is 

also possible to withdraw streams of differing quality (sometimes called 

nfractions•) from diff~rent locations throughout the c~1umn. This is typically 

done in refining petroleum, resulting in different grades or •cuts• of petroleum 

products. 

2.3.3 Steam Stripping 

Steam stripping is a continuous process conducted in a unit that con$ists 

of a boiler, a stripping column, a condenser, and a collection tank, as shown in 

f: \doc~~~~e~~t\1SZ~031. 01.015 139 

' I 
WASTE 

INFLUENT 

. 

.. 

VENT OF NON•CONOENSED VAPORS 

TO AIR POU.UTlON CONTROL SYSTEM 

ANO/OR THE ATMOSPHERE 

I .. \ 

r- ~_REFLUX 

~---- ·~ 

RECTIFIER 

SECTION 

1f 

t 

STRIPPER 

SECTION 

-----... 

j" 

1f 

~ 

) CONDENS 

,, 

_.. 

ER 

PRODUCT 

RECEIVER 

RECOVERED ORGANICS 

TO REU SE 

REBOIL I 

.. I 

RESOILER 

Figure 16 Fractionation System 

140 

J ' - BOTTOMS 

TC REUSE OR 

INCINERA T10N 
Figure 17. The boiler provides the heat required to vaporize the 1 iquid fraction 

of the waste. The stripping column is composed of a set of trays or packing 

placed in a vertical column. 

The steam stripping process uses multiple equilibrium stages, with the 

initial waste mixture entering at the top, the uppermost equilibrium stage. The 

boiler is located beneath the lowermost equilibrium stage, allowing the vapor to 

move upward in the column, coming into contact with the falling liquid. As the 

vapor comes into contact with the liquid at each stage, the more volatile 

compor.~nts are removed or "stripped" from the liquid by the vapor phase. The 

concentration of the emerging vapor is enriched in the more volatile 

constituents, and the liquid exiting the bottom of the boiler ("bottoms"}, which 

is predominantly water, contains high concentrations of the lower vapor pressure 

constituents. This effluent from the bottom of the stripper is reduced in 

organic content but may still require additional treatment such as carbon 

adsorption or biological treatment. The steam and organic vapors exiting the top 

of the column are condensed. As condensed liquids, the organic components are 

usually immiscible with water. The two immiscible phases are then separated in 

a product receiver. Organics in the organic phase are typically recovered or 

disposed of in a liquid injection incinerator, while the aqueous condensate is 

recycled to the stripper. 

2.3.4 Thin Film Evaporation 

Thin film evaporation is a continuous process conducted in a unit that 

typically consists of. a steam-jacketed cylindrical vessel and a condenser. 

Figure 18 is a schematic showing the major components of a thin film evaporator. 

The steam-heated surface of the cylindrical vessel provides the heat required to 

vaporize the volatile constituents in the waste. The evaporator walls are heated 

from the outside as the feed trickles down the inside walls in a thin film. 

Unique to this form of distillation is the distribution device that spreads the 

thin film over the heated surface. The feed rate of waste is controlled to allow 

the more volatile ~aterial adequate time to vaporize. The heat transfer from the 

f:\document\15254031.01.015 141 

. 

'l 
WASiEWATER _ __, 

INFl.UENT 

t. VENT OF NOH•CQNOEHS&D VAPORS 

TO AIR POU.UT10H C:ONmOL SYSTEM 

AND/OR THI! A TMCSPHEAI! 

STEAM 

I OILER 

--

CONDENSER 

RECOVERED 

.___. ORGANICS 

TO REUSE 

QR TREA T'MENT 

TAUT!t2 EFFt.UENT 

1----~- TO ~ATHER TAEATl.CEHT 

AND/OR DISPOSAl. 

Figure 17 Stem~ Stripping Systa~ 

142 
LIQUID 

FILM 

VENT OF 

NON·CONOENSED VAPORS TO 

AlA POL.L.UT10N CONTROL. SYSTSM 

ANCIOA 1ltE ATUOSPHERE 

t 

CONDENSER 

r-..--- HEATED 

JACKET 

BOTTOMS TO 

'-------..,REUSE OR 

INCINERATION 

F1gure 18 Thin Film Evaporation Syst81 

143 

PRODUCT 

RECeiVER 

RECOVERED 

ORGANICS 

TO REUSE 

, 

t 
heating medium (steam) to the waste is determined by their relative temperatures, 

the heat transfer:.rate of the vessel materials, and the thermal properties of the 

waste stream farming the film. The rising vapor is collected at the top of the 

column, cooled, and condensed in a condenser. The condensed liquid product 

stream is then routed to a product receiver. The "bottoms," which are the least 

volatile components of the waste, are continuously withdrawn from the bottom of 

the thin film evaporator. Because thin film evaporation is used to remove the 

volatile organics from wastes, the bottoms are reduced in volatile organic 

content. However, prior to disposal, the bottoms usually require additional 

treatment, such as incineration, for residual, less volatile organics. 

2.3.5 Thermal Drying 

A wide range of batch and continuous dryers is available. One commonly 

used continuous type is the screw-flight dryer, the major components of which are 

shown in Figure 19. The screw-flight dryer consists of a screw surrounding a 

hollow shaft enclosed in a trough. Heat transfer fluid is heated to temperatures 

as high as 7so•F and circulated, usually countercurrent to the flow of waste, 

through the hollow shaft. Heat transfers from the shaft to the screw blades, and 

then into the feed material, causing water and organics to be driven off in a 

vapor form. The dried cake is discharged from the dryer . 

. The dryer is designed to create good contact between the screw and feed 

material. The screw h usually equipped with breaker bars to ensure proper 

shearing ~f the input materials and to prevent the screw surfaces from fouling . .._. -.,: ,· I L ~ 

.- .... -0... .~ .... .; 

Vapors emerging frJm this system are managed in one of two ways, depending 

on their composition. If the vapors. contain only water, they are usually 

directly vented to the atmosphere. However, if the vapors contain volatile 

organics, they are generally passed through a water-cooled condenser system. The 

recovered organic liquids from the condenser unit are then forwarded to another 

process for treatment or recovery. 

f: \dac~~~~ent\15Z~031. 01.015 144 

, 
FEED fl IIIIEAIIER BARS ~ .... 

~ 

- - Sl£.ALf IN 

=t ...... SCREWS HOllOW DRIED ..... 

U1 SHAFT UAlERIAL 

Figure 19 Screw Flight Dryer 

...... 
2.4 Waste Charact~ristics Affecting Performance (WCAPs} 

In determt_ning whether distillation technologies will achieve the same 

level of performance on an untested waste as on a previously tested waste and 

whether performance levels can be transferred, EPA examines the following waste 

characteristics: (a) the component boiling points, (b) the thermal conductivity, 

(c) the concentration of volatiles, (d) the concentration of suspended solids, 

{e) the surface tension, and (f) the oil and grease content. The above-mentioned 

waste characteristics affecting performance vary for each distillation 

technology. 

The WCAPs for each specific distillation process are as follows: 

• Batch distillation: thermal conductivity, component boiling points, and 

conc~ntration of volatiles. 

• Fractionation, steam stripping, and thin film evaporation: concentration of suspended solids, component boiling points, concentration of 

volatiles, surface tension, and oil and grease content. 

• Thermal drying: thermal conductivity and component boiling points. 

2.4.1 Component Bo111ng Points 

As noted earlier., the greater the ratio of volatility of the waste 

constituents, the more easily the separation of these constituents can proceed. 

This ratio is called relative volatility. EPA recognizes, however, that relative 

volatilities cannot be measured or calculated directly for the types of wastes 

generally treated by distillation processes because such ••~tes usually consist 

of a myriad of components, all with different vapor pressure-versus-temperature 

relationships. However, because the volatility of components is usually 

inversely proportional to their boiling points (i.e., the higher the boiling 

f:\document\1525403l.Ol.Ql5 146 

, 

1 

i 
point, the lower the volat1l1ty), EPA uses the boiling point of waste components 

as a surrogate was~e characteristic for relative volatility. If the differences 

in boiling poin~s between the more volatile and less volatile constituents are 

significantly smaller in the untested waste than in the tested waste, the system 

may not achieve the same performance and more rigorous operating conditions or 

other, more applicable treatment technologies may need to b·e considered for 

treatment of the untested waste. 

2.4.2 Thermal Conductivity of the Waste 

A major factor determining whether a particular constituent will volatilize 

is the potential for transfer of heat through the waste. For batch distillation, 

heat transfer is accomplished principally by conduction from the external source 

of heat (with some convection within the waste). For thermal drying, heat 

transfer is _accompli shed primarily by conduction rather than convection si nee the 

wastes are usually not liquids. Thermal conductivity is not as critical a 

consideration with other forms of di st illation because tile wastes are broken up 

into thin films, which conduct heat relatively rapidly. 

Heat flow by conduction is proportional to the temperature gradient across 

the material. The proportionality constant, referred to as the thermal 

conductivity, is a property of the material to be distilled (or dried in the case 

of th~rmal drying). With regard to convection, EPA believes that the amount of 

~eat transferred by convection is not de~endent on the waste's thermal 

conductivity. Convection will usually be more a function of the system design 

than of the waste itself (f.e., how well the waste can be mixed during the 

process). 

Thermal conductivity measurements, as part of a treatability comparison for 

two different wastes to be treated by a single batch distillation unit, are most 

meaningful when applied to wastes that are homogeneous (i.e., uniform 

throughout). As wastes exhibit greater degrees of nonhomogeneity, thermal 

conductivity becomes less accurate in predicting treatability because the 

f:\document\1SZ54031.01.015 147 

l 
conductivity becomes less accurate in predicting treatability because the 

measurement esse~tially reflects heat flow through regions having the greatest 

conductivity ('~e., the path of least resistance) and not heat flow through all 

parts of the waste. Nevertheless, EPA believes that thermal conductivity may 

provide the best measure of performance of heat transfer. If the therma 1 

conductivity of an untested waste is significantly lower than that of the tested 

waste, the system may not achieve the same performance, and other, more 

applicable treatment technologies may need to be considered for treatment of the 

untested waste. 

2.4.3 Concentration of Volatile Components 

The concentration of volatile components is a measure of the maximum 

fraction of the waste that can be expected to volatilize during a distillation 

process. A relatively low concentration of volatile components implies that most 

of the waste may become bottoms (i.e., relatively nonvolatile). If the 

concentration of relatively volatile components in the untested waste is 

significantly lower than that in the tested waste, the untested system may not 

perfonn adequately. Hare rigorous operating conditions, such as higher 

temperatures, higher residence times, etc., may be required to volatilize less 

volatile components and achieve the same treatment performance, or other, more 

applicable treatment technologies may need to be considered for treatment of the 

ur.tested waste. 

2.4.4 Concentration of Suspended Solids 

Wastes containing 1 arge amounts of suspended sol ids--organic or 

inorganic--may have an adverse effect on distillation treatment systems. For 

example, in thin film evaporation, large amounts of suspended solids may coat 

heat transfer surfaces, thereby disturbing the uniform film and inhibiting 

volatilization of constituents. In fractionation and steam stripping, large 

amounts of suspended solids may clog column internals and coat heat tranfer 

surfaces, thereby inhibiting heat transfer and mass transfer of constituents 

f:\document\15254031.01.015 148 

, 
between the vapor and 1 iqufd phases. If the concentration of suspended solids 

in the untested ~aste is significantly higher than that in the tested waste, the 

system may nott_achieve the same performance. Filtration may be required prior 

to distillation processes to reduce the concentr~tion of suspended solids and 

achieve the same treatment performance, or other, more applicable treatment 

technologies may need to be considered for treatment of the untested waste. 

2.4.5 Surface Tension 

The surface tens ion of the waste is a measure of the tendency of the waste 

to foam and to "wet" the heat and mass transfer surfaces. The higher the surface 

tension of the liquid, the higher its tendency to foam. Also, higher surface 

tcr.s ions wi 11 not a 11 ow a film of the waste to coat heat and mass transfer 

surfaces as well as 1 ow surface tens f ons wi 11 . The 1 ike 11 hood of foaming 

requires special column design or the incorporation of de foaming compounds. 

Packed columns are usually less susceptible to foaming than are tray columns. 

Waste with high surface tensions that cannot effectively wet column packing or 

evaporator walls will not form the thin films that enhance heat and mass 

transfer. If the surface tension of the untested waste is significantly higher 

than that of the tested waste, the system may not achieve the same performance. 

Defoaming compounds and/or the use of a packed column may be required to reduce 

foaming and achieve the same treatment perfonmance, or other, more applicable 

treatment technologies may need to be considered for treatment of the untested . -waste. 

2.4.6 Concentration of 011 and Grease 

High concentrations of oil and grease may clog steam stripping and 

fractionation equipment, thereby reducing their effectiveness. In thin film 

evaporation, high concentrations of oil and grease may result in the waste 

coating the evaporator walls, preventing a uniform film from forming and 

inhibiting volatilization of waste components. If the concentration of oil and 

grease in the untested waste is significantly higher than that in the tested 

f:\document\15254031.01-015 149 
applicable treatment technologies may need to be considered for treatment of the 

untested waste. 

{_ 

2.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of distill at ion 

technologies, EPA may examine the following parameters: (a) the temperature and 

pressure, (b) the differential pressure, (c) the liquid and vapor flow rates, 

(d) the internal column design, (e) the number of separation stages, (f) the 

residence time, (g) the surface area, and (h) the mechanical system design. 

The above-mentioned design and operating parameters vary for each 

distillation technology. The design and operating conditions for each specific 

distillation process are as follows: 

• Batch distillation: temperature and pressure, and residence time. 

• Fractionation: number of separation stages, liquid and vapor flow 

rates, temperature and pressure, differential pressure, and internal 

column design. 

e Steam stripping: number of separation stages, liquid and vapor flow 

rates, temperature and pressure, and intern~l column design. 

• Thin film evaporation: evaporator surface area, temperature and 

pressure, resi.dence time, and the speed and design of the waste disposal 

mechanism. 

• Thennal ~ryer: temperature and pressure, residence time, and the design 

and speed of the screw mechanism. 

f:\document\1525403l.Ol.Ol5 150 
To evaluate the effectiveness of design and operating variables, it is 

necessary to measure the concentrations of the components to be separated in both 

the feed syste"\and the process residuals (e.g., overheads and bottoms). For 

many hazardous organic constituents, analytical methods are not available or the 

constituent cannot be analyzed in the waste matrix. Therefore, it would normally 

be impossible to measure the effectiveness of treatment of distillation systems. 

In these cases EPA tries to identify measurable parameters or constituents that 

would act as surrogates to verify treatment. 

For organic constituents, each compound contains a measurable amount of 

total organic carbon (TOC). Removal of TOC in the distillation treatment system 

will indicate removal of organic constituents. Hence, TOC analysis is likely to 

be an adequate surrogate analysis where the specific organic constituent cannot 

be measured. 

However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden; that is, the TOC 

analysis may not be sensitive enough to detect changes at the milligrams per 

liter (mg/1) level in matrices where total organic concentrations are hundreds 

or thousands of mg/1. In these cases other surrogate parameters should be 

sought. For example, if a specific analyzable constituent is expected to be 

treated as well as the unanalyzable constituent, the analyzable constituent 

concentration might be monitored as a surrogate. 

2.5.1 Temperature and Pressure 

These parameters are integrally related to the vapor-liquid equilibrium 

conditions. In steam stripping and fractionation, tr.e temperature at any point 

in the column is an indicator of the constituent concentrations at that point, 

thus revealing whether the separation of components is taking place as expected. 

Overall column pressure influences the boiling point of the liquid at any 

location in the column. For example, through application of a partial vacuum to 

the column, the temperatures required to achieve the desired separation can be 

f:\document\15254031.01.015 151 
reduced because liquids volatilize at lower temperatures when pressures are 

reduced. ·EPA monitors the temperature and pressure of a steam stripping column 

and a fractionation column continuously, if possible, to ensure that the system 

is operating at the appropriate design conditions and tc diagnose operational 

problems. 

In thin film evaporation, to achieve the desired volatilization, the 

evaporator may be oper~ted at pressures below atmospheric (slight vacuum). At 

vacuum conditions, lower temperatures can be used, requiring less heat input, 

because boiling points decrease as pressure decreases. EPA monitors the thir. 

film evaporator temperature as well as the pressure (if pressures other than 

atmospheric are used) continuously, if possible, to ensure that the system is 

operating at the appropriate design condition and to diagnose operational 

problems. 

In batch distillation and in thermal drying, temperature provides an 

indirect measure of the energy available {i.e., Btu/hr) to vaporize the waste 

constituents. As the design temperatm·e 1 ncreases, more constituents with 1 ower 

volatilities will be removed from the waste. Pressure is integrally related to 

the boiling point of the waste and the subsequent vaporization of the organic 

constituents. As the pressure is lowered below atmospheric (i.e., as vacuum is 

increased), the boiling point of the waste will also be lowered, thereby 

requiring less heat input to ~olatilize waste constituents. EPA monitors the 

-distillation temperature as well as the pressure (if pressures other than 

atmospheric are used) to ensure that the system is operating at the appropriate 

design conditions and to diagnose operational problems~ 

2.5.2 Differential Pressure 

In fractionation, measuring the differential pressure between the top and 

bottom of the column indicates whether the flow rate of either the liquid or the 

vapor phase is excessive. For instance, a high pressure drop across the column 

may indicate a condition of •flooding,• in which the liquid phase cannot flow 

f:\document\15254031.01.015 152 
down through ths column as fast as feed is entering, causing backing up or 

"flooding" to OCfur. EPA monitors the pressure drop across the fractionation 

column continuausly, if possible, to ensure that the system is operating at the 

appropriate design condition and to diagnose operational problems. 

2.5.3 Liquid and Vapor Flow Rates 

For steam stripping and fractionation, the vapor-liquid equilibrium data 

are also used to determine the liquid and vapor flow rates that provide 

sufficient contact and residence time between the liquid and vapor streams. The 

appropriate flow rates are affected by the column diameter. EPA monitors the 

liquid and vapor flow rates to ensure that sufficient contact time between the 

liquid and vapor streams is provided to effectively separate the organics from 

the wastewater, and to ensure that the column does not "flood" {i.e., the vapor 

or liquid flow is so high that the vapor cannot exit the top of the column as 

rapidly as it is generated and/or the liquid cannot run out the bottom as rapidly 

as it is fed into the column). Also see Differential Pressure, above. 

2.5.4 Internal Column Design 

In steam stripping and fractionation, column internals are designed to 

accormnodate the physical and chemical properties of the waste to be fractionated. 

Two types of internals may be used in steam stripping and fractionation: trays 

.and picking. Tray types include bubble cap, sieve, valve, and turbo-grid. Trays 

have several advantages over packing. They are less susceptible to blockage by 

solids, they have a l~wer capital cost for large-d4ameter columns {more than 

approximately 3 feet), and they accommodate a wider range of liquid and vapor 

flow rates. Compared to trays, packing has the advantages of having a lower 

pressure drop per theoretical stage, being more resistant to corrosive materials, 

having a lower capital cost for small-diameter columns (less than approximately 

3 feet), and being less susceptible to foaming because of a more uniform flaw 

distribution (i.e., lower local variations in flow rates). EPA examines the 

internal column design of a steam stripping or fractionation column to ensure 

f:\document\1SZS4031.01.015 153 
that the system is designed to handle potential operational problems (e.g., 

corrosion, foaming, channeling). 

{_ 

2.5.5 Number of Separation Stages 

The number of separation stages in a steam stripping or fractionation 

column required to achieve the desired separation of the more volatile 

constituents from the less volatile constituents is calculated from vapor-liquid 

equilibrium data, which are determined empirically. Using the theoretical number 

of stages, one can determine the actua 1 number of stages through the use of 

empirical tray efficiency data, typically supplied by equipment manufacturers. 

EPA examines the actual number of stages in the steam stripping or fractionation 

column to ensure that the system is designed to achieve an effective degree of 

separation of organics from the wastewater stream. 

2.5.6 Residence Time 

The residence time determines the necessary energy input into the system 

as well as the degree of volatilization achieved for organic constituer.ts. The 

residence time requirement is dependent on the distillation or evaporation 

temperature (or dryer temperature in the case of thermal drying} and the thermal 

conductivity of the waste. EPA observes the residence time to ensure that 

sufficient time is provided to effectively volatilize organic constituents from 

-the waste. In the case of thermal drying, the residence time must be sufficient 

to effectively evaporate the volatile liquid constituents and, hence, to dry the 

waste. 

2.5.7 Evaporator Sur1ace Area 

In th1n film evaporation, the evaporator surface area required to achieve 

the desired volatilization of organic components from the waste is calculated 

from the vapor-liquid equilibrium data, which are determined empirically, and 

from waste liquid flow rates. EPA examines the surface area of the evaporator 

f: \doc~~~~ent\1525~031. 01.015 154 
to ensure that sufficient surface area is provided to achieve effective 

volatili~ation of the more volatile organic components. 

t 

2.5.8 Mechanical System Design 

Both thin film evaporation and thermal drying have rotating parts. For the 

evaporator, the speed and design of the feed distributor will help determine how 

well the feed will coat the evaporator surfaces. For the dryer, the size, screw 

flight, spacing, and speed of the screw mechanism will affect residence time and 

heat transfer. Typically, higher rotational speed will distribute feed more 

effectively in an evaporator and will provide more mixing turbulence in a dryer 

(for improved heat transfer). However, increased speed will reduce residence 

time in the dryer and will cause earlier mechanical failure in both evaporators 

and dryers (i.e., the bearings and shafts will wear more rapidly). 

f:\document\15254031.01.015 155 
2.6 References 

DeRenzo, D.J., td. 1978. Unit operation for treatment of hazardous industrial 

wastes. Park Ridge, N.J.: Noyes Data Corporation, 

Kirk-Othmer. 1965. Encyclopedia oF chemical technology. 2nd ed., vol. 7, pp. 204-248. New York: John Wiley and Sons. 

McCabe, W.L., Smith, J.C., and Harriet, P. 1985. Unit operations of chemical 

engineering. pp. 533-606. New York: McGraw-Hill Book Co. 

Perry, R.H. and Chilton, C.H. 1973. Chemical engineers' handbook. 5th ed., pp. 13-1 to 13-60. New York: McGraw-Hill Book Co. 

Rose, L.M. 1985. Distillation design in practice. pp. 1-307. New York: 

Elsevier. 

Van Winkle, M. 1967. Distillation. pp. 1-684. New York: McGraw-Hi"ll Book Co. 

Water Chemical Corporation. 1984. Process design manual for stripping of 

organics. PB84-232628. pp. 1-1 to F4. Prepared for the Industrial 

Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency. 

156 
3. EXTRACTION TECHNOLOGIES 

3.1 ApPiicability 

Extraction technologies (i.e., solvent extraction and critical fluid 

extraction) are used to treat wastes containing a variety of organic constituents 

and a broad range of total organic content. Extraction technologies have been 

demonstrated for treatment of API separator sludges and other hydrocarbon-bearing 

wastes generated by the petroleum and petrochemicals industries. In theory, 

these technologies are also applicable to wastes ot similar composition generated 

by other industries such as the organic chemicals industry. 

In solvent extraction, the selection of an extraction fluid (solvent) is 

dependent on the solubility of the organic waste constituents in the extraction 

fluid. 

Critical fluid extraction is applicable to wastes containing organics that 

are soluble in pressurized fluids such as carbon dioxide, propane, butane, or 

pentane (extraction fluids). Compounds that have been successfully extracted 

from wastes by this process include aliphatic hydrocarbons, alkenes, simple 

aromatics such as benzene and toluene, polynuclear aromatics, and phenols. 

3.2 Underlying Principles of Operation 

The basic principle of operation in extraction technologies is that 

constituents are removed fr011 a waste by llixing the waste with an extraction 

fluid (solvent) that will preferentially dissolve the waste constituents of 

concern from the waste. In the simplest extraction systems, two components are 

mixed: (a) the waste stream to be extracted and (b) extraction fluid. The 

extraction fluid and waste stream are mixed to allow mass transfer of the 

constituent (the solute) from the waste stream to the extraction fluid. 

f:\document\15254031.01.016 157 
Except for the waste constituents that are to be extracted, the waste must 

be immis~ible in the extracted fluid, so that after mixing, the two immiscible 

phases can phy~~cally separate by gravity. Separation of the extraction fluid 

phase and the waste stream phase occurs under quiescent conditions, relying on 

tne density differences between the two phases. 

The extraction fluid, which now contains the extracted contaminants, is 

called the extract; the extracted waste stream from which the contaminants have 

been removed is cal lea the raffinate. The extract can be either the heavy (more 

dense) phase or the light (less dense) phase. In theory, the maximum degree of 

separation that can be achieved is provided by the selectivity value, which is 

the ratio of the equilibrium concentration of the contaminants in the extraction 

fluid to the equilibrium concentration of the contaminants in the waste. The 

solvent extraction process can be either batch or continuous. 

In critical fluid extraction, the extraction fluids used are compounds 

that are usually gases at ambient conditions. Since the extraction fluid being 

used is a gas, it is first pressurized, which converts it to a liquid. As a 

liquid, it leaches (dissolves) the organic constituents out of the complex wast~ 

with which it is mixed. The enhanced solubilities of variousorganiccompounds 

in hydrocarbons and other extraction fluids at high pressure aid in their removal 

from a waste. The process is usually carried out at or near the extraction 

fluid's "critical pressure," which is the pressure above which the liquid form 

.of the extraction fluid cannot be gasified, no matter how much the fluid is 

heated. (In fact, above the critical pressure liquid and gas phases become 

physically indistingui~hable, in that two phases do not really exist.) 

3.3 Description of Extraction Process 

3.3.1 Solvent Extraction 

The simplest, least effective solvent extraction unit is a single-stage 

sy3tem (mixer-settler system). The solvent and the 1 iquid waste stream are mixed 

f:\documant\1SZ54031.01.016 158 
together; the raffinate and extract are separated by settling w:~~~Jt further 

extractiop. 

t. 

The more effective multistage contact extraction is basically a series of 

batch mixer-settler units. The waste stream is contacted with solvent in a 

series of successive steps or stages. Raffinate from the first extraction stage 

is contacted with fresh solvent in a second stage, and so on. 

In countercurrent, multistage extraction columns, fresh solvent and the 

waste stream continuously enter at opposite ends of a column consisting of a 

series of extraction stages. Extract and raffinate layers pass continuously and 

countercurrently from stage to stage through the system. 

Several types of extraction systems are used for contact and separation. 

Three of the most common systems--mixer-settler systems, extraction columns, and 

centrifugal contactors--are discussed below. 

3.3.2 Mixer-Settler Systems 

Single-stage mixer-settler systems are extraction systems composed of a 

mixing chamber for phase dispersion, followed by a settling chamber for phase 

separation. Mixer-settler systems are typically used to treat solids or highly 

viscous wastes and can handle difficult-to-mix components. The vessels may be 

either vertical or horizontal. Dispersion in the mixing chamber occurs by pump 

circulation, nonmechanical in-line mixing, air agitation, or mechanical 

stirring. In a two-s~age mixer-settler system (a simple multistage contact 

extractor), as shown in Figure 20, the extract from the first stage is sent to 

a recovery unit to separate the solvent from the remaining extract containing the 

organic constituents of concern. The recovered solvent is used, and the 

remaining extract is either reused or further treated in an ir.cineration unit. 

The raffinate from the first stage is sent to the second-stage unit for 

additional extraction. Recycled solvent from recovery of the first-stage extract 

and/or fresh solvent makeup is added to the first-stage raffinate before it is 

f:\document\15254031.01.016 159 
-

0\ 

C) 

EXTRACT 

RECYCLED SOLVENT FROM 

RECOVERY/FRESH SOLVENT 

.MAKEUP 

MIXER 

RECYCLED 

SOLVENT 

EXTRACT TO RECOVERY 

RECYCLED 

TO PROCESS 

EXTRACT 

SOLIDS 

BEPARA 1;oiON 

I 

EXTRACT TO ._ __ RECYCLE OR 

DISPOSAL 

Figure 20 Two-Stage Mixer-Settler Solve.nt Extraction System 

TO 

DISPOSAL 
mixed and sent to the second stage. The extract from the second stage, 

containing mainly solvent, is recycled to the first-stage unit as the solvent 

stream. The reeulting raffinate from the second stage may require filtering to 

remove solids before it is sent to further treatment (if required). If solids 

collected during filtration contain treatable levels of hazardous constituents, 

they will require further treatment, such as stabilization (for metals) and/or 

incineration (for organics) prior to disposal. 

Parameters such ~s the density or specific constituent concentrations in 

the extract may be monitored to determine when the second-stage extract must be 

sent to solvent recovery and when fresh or recycled solvent must be added to the 

first-stage u~it. 

3.3.3 Extraction Columns 

Extraction columns are continuous flow, countercurrent, multistage contact 

systems. Two types of extraction columns are packed extractors and sieve-tray 

extractors. Figure 21 presents schematics of these two types of extraction 

columns. A packed extractor contains plastic or ceramic materials in various 

geomP.tric shapes or structured packings of wire gauze or mesh. Mass transfer of 

the contaminants from the waste to the extract is promoted because of breakup and 

distortion of both phases as they contact th& packing, resulting in the intimate 

mixing of the waste and the solvent. 

The sieve-tray extractor is similar to the sieve-tray column used in 

fractionation distillation. Tray perforations cause the formation of liquid 

droplets that aid the mass transfer process by allowing for more intimate contact 

between the solute and the solvent. 

3.3.4 Certr1fuga1 Cantactors 

Centrifugal contactors are based on the application of centrifugal force 

to increase rates of countercurrent flow and enhance separation of the phases. 

f:\doc~nt\15254031.01.016 161 
-

"' N 

RAFFINATE TO 

r----t~ TREATMENT AN RAFFINATE TO 

DISPOSAL 

SOLVENT----~·~~----r-~--,--, 

WA 8 TE ----t~ 1------....__...___. 

INFLUENT PACKING 

SUPORT 

EXTRACT AND SOLVENT 

TO SEPARATOR 

AND RECOVERY UNIT 

A. PACKED EXTRACTOR 

0/0R -:- TREATMENT 

DISPOSAL 

SOLVENT~ 

'- - ---

-- - -

- - - ._ 

-

-- ----

:....... -- .A - .._.------

EXTRACT AND SOLVENT 

TO SEPARATOR 

~ AND RECOVER'/ UNIT 

B. SIEVE TRAY EXTRACTOR 

F1gura 21 Packed and Steve Tray Solvent Extraction Columns 

AND/OR 
Centrifugal units are used when short contact times are required, such as when 

unstable. materi ~ s are being processed. One type of centrifugal contactor 

consists of a ~um that rotates around a shaft equipped with annular passages at 

each end for feed and raffinate. The light phase is injected under pressure 

through a shaft and is then routed to the periphery of the drum through 

perforations. The heavy phase is also charged through the shaft, but it is 

channe 1 ed to the center of the drum through perforations. Centrifuga 1 force 

acting on the phase-density difference pr~~otes dispersion as the phases are 

forced through the perforations. Centrifugal extractors provide short contact 

time, have minimal space requirements, and easily handle emulsified materials and 

fluids with small density differences. 

3.3.5 Critical Fluid Extraction 

A critical fluid extraction system consists of a blending tank, one or more 

extraction vessels, one or more decanters, one or more filters, and an 

evaporation unit. Organic wastes such as oil refinery sludges are first combined 

in a blending t~nk and mixed well to yield a homogeneous, pumpable mixture. This 

mixture is then pumped under pres sure to an extraction vesse 1 fi 11 ed with a 

liquified gas such as carbon dioxide, propane, butane, or pentane and is mixed 

under pressure to extract (dissolve) hydrocarbon components from the waste into 

the liquified gas extraction fluid. After the hydrocarbon components of the 

waste dissolve in the pressurized liqui"d, the resulting solution is 

·gravity-separated in a decanter into a wastewater (or waste solids) stream and 

an extraction fluid-rich stream. The wastewater stream, containing inorganic 

solids, is sometime~ filtered under pressure to remove the insoluble components. 

The extraction fluid-rich stream is fed to a pressurized evaporation unit. The 

extraction fluid (carbon dioxide, propane, butane, or pentane) is evaporated by 

dropping the pressure and is subsequently recovered, repressurized, and 

recondensed for reuse. The residue from the evaporation, consisting of a liquid 

hydrocarbon mixture, is then reprocessed or reused, blended with fuels for heat 

recovery, or incinerated. If the extracted waste stream still exceeds treatment 

f:\document\15254031.01.016 163 
requirements, it may be extracted again ~ith fresh extraction fluid at the high 

pressure.conditions. 

t 

If inorganic residuals {or waste solids) filtered from the waste/solvent 

mixture contain treatable levels of hazardous constituents such as certain metals 

(e.g., chromium, lead) or organics, they will require further treatment such as 

stabilization or incineration prior to disposal. 

3.4 Waste Characteristics Affecting Performance (WCAPs) 

In determining whether extraction processes will achieve the same level of 

performance on an untested waste as on a previously tested \iJste and whether 

performance levels can be transferred, EPA examines the following waste 

characteristics: {a) the concentration of extractable hydrocarbons, (b) the 

solubility of the waste constituents of concern in the extraction fluid, {c) the 

surface tension, and {d) the alkalinity of the waste. 

3.4.1 Concentration of Extractable Hydrocarbons 

The concentration of extractable hydrocarbons in the waste feed is a 

measure of the maximum fraction of the waste that can be expected to be extracted 

in the process. A relatively low concentration of extractable hydrocarbons 

implies that most of the wasta may become wastewater or waste solids (i.e., is 

- nonextractabl e). Total extractable hydrocarbon content can be estimated by 

measurement of the total organic carbon {TOC) content. If the TOC of an untested 

waste is significantlY. lower than that of the tested waste, the untested system 

may not remove as much hydrocarbon as the tested system. More rigorous 

extraction conditions such as higher temperatures and pressures, additional 

mixing, and longer settling times may be required to extract less extractable 

components and achieve the same treatment performance, or other, more applicable 

treatment technologies may need to be considered for treatment of the untested 

waste. 

f:\document\15254031.01.016 164 
Critical fluid extraction processes are designed to extract hydrocarbon 

component. from m2xed oi1y and organic waste liquids and sludges. For critical 

fluid extracti~ to be economically applied, the waste should contain at least 

a few percent by weight of extractable hydrocarbons. This process has been 

demonstrated on wastes containing from 5 to 34 percent hydrocarbons. For lower 

concentrations, batch distillation or conventional solvent extraction may be more 

economical. Also, critical fluid extraction is not economical for wastes 

containing high concentrations of extractable hydrocarbons (higher than 

95 percent). These wastes are more amenable to fractionation treatment. 

3.4.2 Solubility of the Waste Constituents of Concern in the 

Extraction Fluid 

The constituents in the waste feed that are to be extracted determine the 

type of extraction fluid that is best suited for the process. For example, polar 

organic molecules (e.g., phenol} in an organic feed can be extracted with an 

aqueous solvent. Organic constituents in aqueous feeds can be extracted with 

various organic solvents. Hetal-contain~ng wastes can be extracted with acids 

{e.g., trialkylphosphoric and carboxylic acids) or amine solvents. If the 

solubility of the waste constituents of concern in the extraction fluid in the 

untested waste is significantly lower than that in the tested waste, the untested 

system may not achieve adequatP- performance. Use of another extraction fluid may 

be required to increase the solubility of the waste constituents of concern and 

achieve the same treatment performance, or other, more applicable treatlilent 

technologies may need to be considered for treatment of the untested waste. 

3.4.3 Surface Te"sion 

The surface tension of the waste is a measure of the tendency of the waste 

to foam. The higher the surface tension of the liquid, the higher its tendency 

to foam. If foaming is likely, the system design must be modified or defoaming 

compounds may be required. For column extractors, packed columns are less 

susceptible to foaming than are tray columns. If the surface tension of the 

untested waste is significantly higher than that of the tested waste, the 

f:\document\15254031.0! .016 165 
untested system may not achieve adequate performance. Defoaming compounds and/or 

the use of a packed column may be required to reduce foaming and achieve the same 

treatment perfo~ance, or other, more applicable treatment technologies may need 

to be considered for treatment of the untested waste. Foaming has not been found 

to affect the performance of critical fluid extraction processes. 

3.4.4 Alkalinity of the Waste 

In critical fluid extraction, when carbon dioxide is used as the extraction 

fluid, high alkalinity will interfere with the process because carbon dioxide 

will react to form carbonates and bicarbonates. This will result in excessive 

carbon dioxide consumption. For wastes having high alkalinity levels, ar. 

extraction fluid other than carbon dioxide should be used in the critical fluid 

extraction process. The same problem does not arise if a hydrocarbon fluid 

(propane, butane, or pentane} is used. If carbon dioxide was the extraction 

fluid used on a tested waste and the alkalinity of the untested waste is 

significantly higher than that of the tested waste, the system may not achieve 

the same performance. Use of another extraction fluid may be required to achieve 

the s arne treatment performance, or other, more app 1 i cab 1 e treatment techno 1 og; es 

may need to be considered for treatment of the untested waste. Alkalinity of the 

waste has not been found to affect the performance of conventional solvent 

extraction processes. 

3.5 Design and Operating Parameters 

In assessing the ~ffectiveness of the design and operation of extraction 

systems, EPA examines the following parameters: (a) the number of separation 

stages, (b) the extraction temperature and pH, (c) the degree of mixing, (d) the 

residence time, (e) the settling time, and (f) the extraction pressure. 

For many hazardous organic constituents, analytical methods are not 

available or the constituent cannot be analyzed in the waste matrix. Therefore, 

it would normally be impossible to measure the effectiveness of the extraction 

f:\document\15254031.01.016 166 
treatment system. In these cases, EPA tries to identify measurable parameters 

or consti~ents t~at would act as surrogates to verify treatment. 

t.. 

For organic constituents, each compound contains a measurable amount of 

total organic carbon (TOC). Removal of TOC in the extraction treatment system 

implies removal of organic constituents. Hence, TOC analysis is likely to be an 

adequate surrogate analysis where the specific organic constituent cannot be 

measured. 

However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden; that is, the TOC 

anaiysis may not be sensitive enough to detect changes at the milligrams per 

liter (mg/1) level in matrices where total organic concentrations are hundred~ 

or thousands of mg/1. In these cases, other surrogate parameters should be 

sought. For example, if a specific analyzable constituent is expected to be 

treated as well as the unanalyzable constituent, the analyzable constituent 

concentration should be monitored as a surrogate. 

3.5.1 Number of Separation Stages 

For solvent extraction columns, the number of theoretical stages required 

to achieve the desired separation of hazardous constituents from a liquid waste 

into the selected extraction fluid is calculated from solvent equilibrium data, 

which are detennined empirically. Using the theoretical number of stages, one 

can then determine the actual number of stages through the use of empirical tray 

efficiency data typicallY supplied by equipment manufacturers. EPA examines the 

actual number of stages in a solvent extraction column system to ensure that the 

system is designed to achieve an effective degree of extraction. 

3.5.2 Extraction Ta.perature and pH 

Temperature and pH changes can affect equilibrium conditions (pH will 

affect equilibrium when the waste or the extraction fluid 1s aqueous) and, 

f:\document\15254031.01.016 167 
consequently, the performance of the solvent extraction system. Critical fluid 

extraction is nor~ally performed at ambient temperature although it is possible 

to use higher t~~peratures when necessary. In all cases, temperatures used must 

be below the critical temperature* of the extraction fluid used to ensure that 

the fluid is present in the extraction vessel in the 1 iquid phase (so that 

maximum contact with the waste can be achieved). EPA monitors the temperature 

and pH (as applicable) continuously, if possible, to ensure that the system is 

operating at the appropriate design conditions and to diagnose operational 

problems. 

3.5.3 Degree of Mixing 

For mixer-settler sol vent extractors, mixing determines the amount of 

contact between the two immiscible phases and, accordingly, affects the degree 

of mass transfer of the constituents to be extracted. Intense agitation to . provide high rates of mass transfer, however, can produce sol vent waste 

dispersions that are difficult to separate into distinct phases. The waste must 

be premixed before introduction into the critical fluid extraction system to 

ensure a uniform, pumpable blend of material. The waste is normally mixed in 

tanks or other vessels. Any well-designed and well-operated system should have 

such waste blending equipment. The quantifiable degree of mixing is a complex 

assessment that includes, among other things, the amount of mhing energy 

supplied, the length of time the material is mixed, and the related turbulence 

effects of the specific size and shape of the tank vessel. This is beyond the 

scope of simple measurement. During the fluid extraction, the extraction fluid 

and waste need to be mi~ed to ensure maximum contact and, hence, efficiency of 

extraction. Any well-designed system should include a pressurized extraction 

vessel that is equipped with an operable mixing system. EPA, however, evaluates 

the degree of mixing qualitatively by considering whether the type of mixing 

*The critical temperature of a substance is that temperature above which the 

the substance cannot be liquified, no matter how high the operating pressures. 

f:\document\15254031.01.016 168 
device pr~vided is one that could be expected to achieve adequate uniform mixing 

of the waste. 

~ 

3.5.4 Residence Time 

The residence time in the extraction vessel impacts the extent of 

extraction of organic contaminants from the waste. Residence time will vary with 

the so 1 ubil i ty of the organic contaminants in the sol vent and the degree of 

mixing. For a batch solvent extraction system, the residence time is controlled 

directly by adjusting the treatment time in the extraction vessel. For a 

continuous solvent extraction system, the waste feed rate is controlled to ensure 

that the system is operating at the appropriate design residence time. In 

critical fluid extraction, as with conventional solvent extraction, the residence 

time in the extraction vessel impacts the extent of extraction of organic 

contaminants from the waste. EPA monitors the residence time to ensure that 

sufficient time is provided to effectively extract the organic contaminants from 

the waste. 

3.5.5 Settling Time 

For mixer-settler solvent extractors and critical fluid extractors, 

adequate settling time must be provided to make sure that separation of the 

phases has been effectively completed. EPA monitors the settling time to ensure 

-effective phase separation. 

3.5.6 Extract1on.Pressure 

Critical fluid extraction systems operate at pressures at which the 

extraction fluids will be liquids at ambient temperatures. Pressure is normally 

monitored by means of gauges and recorders attached to the extraction vessel. 

EPA monitors the extraction pressure continuously, if possible, to ensure that 

the system is operating at the appropriate design condition and to diagnose 

operational problems. 

f: \dcclllll!nt\15254031.01.016 169 
3.6 References 

CF Systems Corporation. 1988. CF Systems units to render refinery wastes 

non-hazart:fous. 

DeRenzo, O.J., ed. 1978. Unit operations for treatment of hazardous industrial 

wastes. Park Ridge, N.J.: Noyes Data Corporation. 

Gallacher, L.V. 1981. Liquid ion exchange in metal recovery and recycling. 

Third Conference on Advanced Pollution Control for the Metal Finishing 

Industry. USEPA 600/2-81-028. pp. 39-41. 

Hackman, E. 1978. 

pp. 109-111. 

Toxic organic chemicals, destruction and waste treatment. 

Park Ridge, N.J.: Noyes Data Corporation. 

Hanson, C. 1968. Solvent extraction theory, equipment, commercial operations, 

and economics. Chemical Engineering, August 26, 1968, p. 81. 

Humphrey, J.L., Rocha, J.A., and Fair, J.R. 1984. The essentials of extraction. 

Chemical Engineering, September 17, 1984, pp. 76-95. 

Johnston, K. 1978. Supercritical fluids. In Kirk·Othmer encyclopedia of 

chemical technology. Supplement Vol. I, pp. 872-983. New York: 

Wiley-Interscience. 

Lo, Teh C., Baird, H.H.I., and Hanson, C., eds. 1983. Handbook of solvent 

extraction. pp. 53-89. New York: John Wiley and Sons. 

Perry, R.H., and Chilton, C.H. 1973. Chemical engineer's handboolc, 5th ed., 

pp. 15-1 to 15-24. New York: McGraw-Hill Book Company. 

Weast, R.C., ed. 1978. Handbook of chemistry and ohysics. 58th ed. Cleveland, 

Ohio: CRC Press. 

f:\document\1SZ54031.01.016 170 
4. FUEL SUBSTITUTION 

Fuel subsJ:i1ution involves using hazardous waste as a fuel in industrial 

furnaces or in bo i 1 ers. The hazardous waste may be b 1 ended with other 

nonhazardous wastes (e.g., municipal sewer sludge) and/or fossil fuels. 

On December 31, 1990, EPA promulgated regulations to control emissions from 

industria 1 furnaces and boilers from treatment of hazardous waste. Permit 

requirements are similar to those for incineration, in that controls limit the 

emissions of total organic carbons, toxic metals, HCl, and wastewaters. Like the 

in~inerator regulations (40 CFR 264, Subpart 0), the boiler and furnace 

regulations (40 CFR 266, Subpart H) require 99.99 percent destruction and removal 

efficiency of principal organic hazardous constituents (POHCs). These 

regulations will also minimize products of incomplete combustion (PICs), 

including carbon monoxide (CO). These regulations will also minimize particulate . . 

emissions by regulating the metal emissions. 

4.1 Applicability 

Fuel substitution has been used with industrial waste solvents, refinery 

wastes, synthetic fibers/petrochemicai wastes, and waste oils. It can also be 

used when combust i ng other waste types produced during the manufacture of 

pharmaceuticals, pulp and paper, and pesticides. These wastes can be handled in 

a solid, liquid, or gaseous form. 

Industrial furnac~s include a variety of industrial processes that produce 

heat and/or products by burning fuels. They include blast furnaces, electric arc 

smelting furnaces, cement kilns, lime kilns, smelters, coke ovens, and halogen 

acid furnaces (HAFs). Industrial boilers are units wherein fuel is used to 

produce steam for process and plant use. Industrial boilers typically use coal, 

oil, or gas as the primary fuel source. 

f:\document\15254031.01.017 171 
The parameters that affect the applicability of fuel substitution are the 

fo 11 owing:. 

t. 

• Halogen content of the waste; 

• Inorganic solids content (ash content} of the waste, particularly heavy metals; 

• Heating value of the waste; 

• Viscosity of the waste (for liquids}; 

• Filterable solids concentration (for liquids}; and 

• Sulfur content. 

4.1.1 Halogen Content of the Waste 

If halogenated organics are burned, halogenated acids and free halogen are 

among the products of combustion. These released corrosive gases may require 

subsequent treatment prior to venting to the atmosphere. Also, halogens and 

halogenated acids formed during combustion are likely to severely corrode boiler 

tubes and other process equipment. To minimize such problems, halogenated wastes 

are blended into fuels only at very low concentrations. High chlorine content 

can also lead to the incidental production (at very low concentrations} of other 

hazardous compounds such as polychlorinated biphenyls (PCBs}, chlorinated 

dibenZQ-p-dioxins {COOs), chlorinated dibenzofurans (COFs), and chlorinated 

phenols. 

4.1.2 Inorganic Solids Content of the Waste 

High inorganic solids content (i .er, ash content) of wastes may cause two 

problems: (1) scaling in the boiler and (2) particulate air emissions. Scaling 

results from deposition of inorganic solids on the walls of the boiler. 

Particulate emissions are produced by noncombustible inorganic constituents that 

flow out of the boiler with the gaseous combustion products. Because of these 

f:\document\15254031.01.017 172 
problems, wastes with significant concentrations of inorganic materials are not 

usually handled in boilers unless the boilers have an air pollution control 

system. ( 

Industrial furnaces vary in their tolerance to inorganic constituents. 

Heavy metal concentrations, found in both halogenated and nonhalogenated wastes 

used as fuel, can cause environmental concern because they may be emitted in the 

gaseous emissions from the combustion process, in the dSh residues, or in a~y 

produced solids. The partitioning of the heavy metals to these residual streams 

primarily depends on the val ati 1 ity of the metal, waste matrix, and furnace 

design. 

4.1.3 Heating Value of the Waste 

The heating value of the waste must be high enough (either alone or in 

combinat·lon with other fuels) to maintain combustion temperatures consistent with 

efficient waste destruction and operation of the boiler or furnace. For many 

applications, only supplemental fuels having minimum heating values of 4,400 to 

5,600 kcal/kg (8,000 to 10,000 Btu/lb) are considered to be feasible. Below this 

value, the unblended fuel would not be likely to maintain a stable flame, and its 

combustion would release insufficient energy to provide oeeded steam generation 

potential in the boiler or the necessary heat for an industrial furnace. Some 

wastes with heating values of less than 4,400 kcal/kg (8,000 Btu/lb) can be used 

}f sufficient auxiliary fuel is used to support combustion or if special designs 

are incorporated into the combustion device. Occasionally, for wastes with 

heating values higher than virgin fuels; blending with auxiliary fuel may be 

required to prevent overheating or overcharging of the combustion device. 

4.1.4 Viscosity of the Waste 

In combustion devices designed to burn liquid fuels, the viscosity of the 

liquid waste must be low enough that it can be atol!lized in the combustion 

chamber. If the viscosity is too high, heat; ng the storage tanks may be required 

f:\document\15254031.01.017 173 
prior to combustion. For atomization of liquids. a viscosity of 165 centistokes 

(750 SaybQlt Universal Seconds (Sus)) or lP~s is typically required. 

(_ 

4.1.5 Filterable Solids Concentration 

Filterable materials suspended in the liquid fuel may prevent or hinder 

pumping or atomization and if so other technologies may need to be considered. 

4.1.6 Sulfur Content 

A waste's sulfur content may affect whether it can be burned or not because 

the waste may emit sulfur oxide into the atmosphere. For instance, the EPA has 

promulgated sulfur oxide emission regulations for certain new source industrial 

boilers (40 CFR 266, Subpart H). Air pollution control devices are available to 

remove sulfur oxides from the stack gases. 

4.2 Underlying Principles of Operation 

For a boiler and most industrial furnaces there are two distinct principles 

of operation. Initially, anergy in the form of heat is transferred to the waste 

to achieve volatilization of the various waste constituents. For liquids, 

volatilization energy may also be supplied by using pressurized atomization. The 

energy used to pressurize the liquid waste allows the atomized waste to break 

into smaller particles, thus enhancing its rate of volatilization. The 

volatilized constituents then require additional energy to destabilize the 

chemical bonds, allowin~ the constituents to react with oxygen to form carbon 

dioxide and water vapor. The energy needed to destabilize the chemical bonds is 

referred to as the energy of activation. 

4.3 Description of Fuel Substitution Process 

Since a number of industrial applications can use fuel substitution, there 

is no one process description that will fit all of these applications. The 

f:\document\1525403l.O:.Ol7 174 
following section, however, provides a general description of industrial kilns 

(one form·of indu~trial furnace) ana industrial boilers. 

t 

4.3.1 Kilns 

Combustible wastes have the potential to be used as fuel in kilns and, for 

waste liquids, are often used with oil to co-fire kilns. Coal-fired kilns are 

capable of handling some solid wastes. In the case of cement kilns, there are 

usually no residuals requiring land disposal since any ash formed becomes part 

of the product or is removed by particulate collection systems and recycled back 

to the kiln. The only residuals may be low levels of unburned gases that escape 

with combustion products. If this is the case, air pollution control devices may 

be required. 

Three types of k1lns are particularly applicable: cement kilns, lime kilns, 

and lightweight aggregate kilns. 

4.3.1.1 Cement Kilns 

The cement k1ln is a rotary furnace, which is a refractory-lined steel 

shell used to calcine a mixture of calcium, silicon, aluminum, iron, and 

magnesium-containing minerals. The kiln is normally fired by coal or oil. 

liquid and solid combustible wastes may then serve as auxiliary fuel. 

Temperatures within the kiln are typically between 1,380 and 1,540•c (2,500 to 

2,Soo•F). To date, only 1 iquid hazardous wastes have been burned in cement 

kilns. 

Most cement kilns have a dry particulate collection device (i.e., either 

an electrostatic precipitator or a baghouse), with the fly ash collected and 

recycled back to the kiln. Buildup of metals or other noncombustibles is 

prevented through their incorporation into the product cement. Many types of 

cement require a source of chloride so that most halogenated liquid hazardous 

f:\document\15254031.01.017 175 
wastes currently can be burned in cement kilns. Available information shows that 

scrubbers.are not used. 

t. 

4.3.1.2 Lime Kilns 

Quick lime (CaO} is manufactured in a calcination process using limestone 

(CaC03) or dolomite (CaC03 and MgC03). These raw materials are also heated in 

a refractory-lined rotary kiln, typically to temperatures of 980 to 1,260'C 

(1,800 to 2,300'F). Lime kilns are less likely to burn hazardous wastes than are 

cement kilns because product lime is often added to potable water systems. Only 

one 1 ime kiln in the United States currently burns hazardous waste. That 

particular facility sells its product lime for use as flux or as refractory in 

b 1 ast furnaces. 

As with cement kilns, any fly ash collected is recycled back to the lime 

kiln; thus, no residual streams are produced by the kiln. Available information 

shows that scrubbers are not used. 

4.3.1.3 Lightweight Aggregate Kilns 

Lightweight aggregate kilns heat clay to produce an expanded lightweight 

inorganic material used in Portland cement formulations and other applications. 

The kiln has a normal temperature range of 1,100 to 1,1SO•c (2,000 to 2,1oo·F). 

Lightweight aggregate kilns are less amenable to combustion of hazardous wastes 

as fuels than are the other kilns described above because these k i1 ns lack 

material to adsorb halogens. As a result, burning of halogenated organics in 

these kilns would likely require afterburners to ensure complete destruction of 

the halogenated organics and scrubbers to control acid gas production. Such 

controls would produce a wastewater residual stream subject to treatment 

standards. 

f:\document\15254031.01.017 176 
4.3.2 Industrial Boilers 

A boiler is a closed vessel in which water is transformed into steam by the 

application of heat. Normally, heat is supplied by the combustion of pulverized 

coal, fuel oil, or gas. These fuels are fired into a combustion chamber with 

nozzles and burners that provide mixing with air. liquid wastes, and granulated 

solid wastes in the case of grate-fired boilers, can be burned as auxiliary fuel 

in a boiler. However, few grate-fired boilers burn hazardous wastes. For 

liquid-fired boilers, residuals requiring land disposal are generated only when 

the bo"l1ci" is shut down and cleaned. This is generally done once or twice per 

year. Other residuals from liquid-fired boilers would be the gas emission . 

stream, which would consist of any products of incomplete combust;~n, along with 

the normal combustion products. For example, chlorinated wastes would produce 

acid gases. If this is the case, air pollution control devices may be required. 

For solid-fired boilers, an ash normally is generated. This ash may contain 

residual amounts of organics from the blended waste/fuels, as well as 

noncombustible materials. land disposal of this ash would require compliance 

with applicable BOAT treatment standards. 

4.4 Waste Characteristics Affe~ting Performance CWCAPsl 

In determining whether fuel substitution will achieve the same level of 

perfo~ance on an untested waste as on a previously tested waste and whether 

performance levels can be transferred, EPA examines the following waste 

characteristics: (a) the component boiling points, (b) the thermal conductivity 

of the waste, and (c) the component bond dissociation energies. 

4.4.1 Component Boiling Points 

The term relative volatil-Ity refers to the ease with which a substance 

present in a solid or liquid waste will vaporize from that waste upon application 

of heat from an external source. Hence, it bears a relationship to the 

equilibrium vapor pressure of the substance. 

f:\document\15254031.01.017 177 
EPA recognizes that the relative volatilities canna~ be measured or 

calculated directlY for the types of wastes generally treated in an industrial 

boiler or furn"=e. The Agency believes that the best measure of relative 

volatility is the boiling point of the various hazardous constituents and wi11, 

therefore, use this parameter in assessing volatility of the organic 

constituents. 

4.4.2 Thermal Conductivity of the Waste 

Consistent with t~e underlying principles of combustion in aggregate kilns 

or boilers, a major factor with regard to whether a particular constituent will 

volatilize is the transfer of heat through the waste. In the case of industrial 

boilers burning solid fuels, heat is transferred through the waste by three 

mechanisms: radiation, convection, and conduction. For a given boiler, it can 

be assumed. that the type of waste will have a minimal impact on the heat 

transferred from radiation. With regard to convection, EPA believes that the 

range of wastes treated would exhibit similar properties with regard to the 

amount of heat transferred by convection. Therefore, EPA will not evaluate the 

radiation or convection heat transfer properties of wastes in determining similar 

treatability. For solids, the third heat transfer mechanism, conductivity, is 

the one principally operative and most likely to change between wastes. 

Using thermal conductivity measurements as part of a treatability 

comparison for two different wastes through a given boiler or furnace is most 

meaningful when applied to wastes that are homogeneous. As wastes exhibit 

greater degrees of nonhomogeneity, thermal conductivity becomes less accurate in 

predicting treatability because the measurement essentially reflects heat flow 

through regions having the greatest conductivity (i.e., the path of least 

resistance) and not heat flow through all parts of the waste. Nevertheless, EPA 

has not identified a better alternative to thermal conductivity, even for ~astes 

that are nonhomogeneous. 

f: \doCIIIII!nt\15254031.01.017 178 
4.4.3 Component Bond Dissociation Energies 

Given an txcess of oxygen, an organic waste in an industrial furnace or 

boiler would be expected to convert to carbon dioxide and water vapor provided 

that the activation energy is achieved. Activation energy is the quantity of 

heat (energy} needed to destabilize molecular bonds so that the oxidation 

(combustion) reaction will proceed to completion. As a measure of activation 

energy, EPA is using bond dissociation energies. In theory, the bond 

dissociation energy would be equal to the activation energy; in practice, 

however, this is not al~~ys the case because of molecular interaction bonds. In 

some instances, bond dissociation energies will not be available and will have 

to be estimated, or other energy effects will have a significant 1nf1uence on 

activation energy. 

4.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a fuel 

substitution system, EPA examines the following parameters: (a} the combustion 

temperature, (b) the residence time, (c) the degree of mixing, (d) the air feed 

rate, (e) the fuel feed rate, and (f) the steam pressure/rate of production. 

For many hazardous organic canst ituents, ana 1 yt i ca 1 methods are not 

available or the constituent cannot be analyzed in the waste matrix. Therefore, 

it ;;;~uld normally be impossible to measure ·the effectiveness of the fuel 

substitution treatment system. In these cases, EPA tries to identify measurable 

parameters or constituents that would act as surrogates to verify treatment. 

For organ1~ constituents, each compound contains a measurable amount of 

total organic cart,on (TOC}. Removal of TOC in the fuel substitution treatment 

system will indic,,te removal of organic constituents. Hence, TOC analysis is 

likely to be an adequate surrogate analysis where the specific organic 

constituent cannot be measured. 

f:\document\15254031.01.017 179 
However, TOC analysis may not be able to adequately detect treatment of 

specific organics in matrices that are heavily organic-laden (i.e., the TOC 

analysis may no\ be sensitive enough to detect changes at the milligrams/liter 

(mg/1) level in matrices where total organic concentrations are hundreds or 

thousands of mg/1). In these cases, other surrogate parameters should be sought. 

For example, if a specific analyzable constituent is expected to be treated as 

well as the unanalyzable constituent, the analyzable constituent concentration 

should be monitored as a surrogate. 

4.5.1 Combustion Temperature 

Industrial boilers are generally designed based on their steam generation 

potential {Btu output). This factor is related to the design combustion 

temperature, which, in turn, depends on the amount of fuel burned and its Btu 

value. The fuel feed rates and combustion temperatures of industrial boilers are 

generally fixed based on the Btu values of fuels normally handled (e.g., No. 2 

versus No. 6 fuel oils). When wastes are to be blended with fossil fuels for 

combustion, the blending, based on Btu values, must be such that the resulting 

Btu value of the mixture is close to that of the fuel value used in the design 

of the boiler. Industrial furnaces also are designed to operate at specific 

ranges of temperature to produce the desired product (e.g., lightweight 

aggregate). The blended waste/fuel mixture should be capable of maintaining the 

design temper~ture r~nge. 

4.5.2 Residence Time 

A sufficient residence time of combustion products is normally necessary 

to ensure that the hazardous substances being combusted (or formed during 

combustion) are completely oxidized. Residence times on the order of a few 

seconds are generally needed at normal operating conditions. For industrial 

furnaces as well as boilers, the residence time is a function of the size of the 

furnace and the fuel feed rates. For most boilers and furnaces, the residence 

time usually exceeds a few seconds. 

f:\docunent\15254031.01.017 180 
4.5.3 Degree of Mixing 

- Boilers ar~ designed so that fuel and air are intimately mixed. This helps 

to ensure that complete combustion takes place. The shape of the boiler and the 

method of fuel and air feed influence the turbulence required for good mixing. 

Ind~strial furnaces also are designed for turbulent mixing where fuel and air are 

mixed. 

4.5.4 Air Feed Rate 

An important operating parameter in boilers and many industrial furnaces 

is the oxygen content in the flue gas, which is a function of the air feed rate. 

Stable combustion of a fuel generally occurs within a specific range of 

air-to-fuel ratios. An oxygen analyzer in the combustion gases can be used to 

control the_feed ratio of air to fuel to ensure complete thermal destruction of 

the waste and efficient operation of the boiler. When necessary, the air feed 

rate can be increased or decreased to maintain proper fuel-to-oxygen ratios. 

Some industrial furnaces do not completely combust fuels (e.g., coke ovens and 

blast furnaces); hence, oxygen concentration in the flue gas is a meaningless 

variable. 

4.5.5 Fuel Feed Rata 

The rate at which fuel is injected into the boiler or industrial furnace 

will determine the thermal output of the system per unit of time (Btu/hr). If 

steam is produced, ste~ pressure monitoring will indirectly determine whether 

the fuel feed rate is adequate. However, various velocity and mass measurement 

devices can be used to monitor fuel flow directly. 

4.5.6 Stall Pressure or Rata of Production 

Steam pressure in boilers pr~~ides a direct measure of the thermal output 

of the system and is directly monitored by use of in-system pressure gauges. 

f:\document\15254031.01.017 181 
Increases or decreases in steam pressure can be effected by increasing or 

decreasin9 the fuel and air feed rates within certain operating design limits. 

Most industrial~FUrnaces do not produce steam; instead they produce a product 

(e.g., cement, aggregate} and monitor the rate of production. 

f:\document\15254031.01.017 182 
4.6 References 

Bonner, T.A., rt al. 1981. Engineering handbook for hazardous waste 

incinerat1on. Prepared by Monsanto Research Corporation for U.S. 

Environmental Protection Agency PB 81-248163. 

Castaldini C., et al. 1986. Disposal of hazardous wastes in industrial boilers 

or furnaces, Park Ridge, N.J.: Noyes Publications. 

USEPA. 1990. Office of Solid W1ste. Standards for owners and operators of 

hazardous wastes in boilers and industrial furnaces; proposed and 

supplemental proposed rule, technical corrections, and request for 

convnents. 55 FR 17862, April 27, 1990. 

Versar. 1984. Estimating PMN incineration results. EPA Contract No. 

68-01-6271, Task No. 66. Draft report for Exposure Evaluation Division, 

Office of Toxic Substances. Washington, D.C.: U.S. Environmenta1 

Protection Agency. 

f: \docl.llllnt\15254031.01. 017 183 
l 

II. REMOVAL TECHNOLOGIES (CONTINUED) 

B. RECOVERY AND/OR SEPARATION TECHNOLOGIES 

FOR METALS 
1. ACID LEACHING 

1.1 ApPlicability 

( 

Acid leaching is a treatment technology used to treat wastes in solid or 

slurry form containing metal constituents that are soluble in a strong acid 

solution or can be conv~rted by reaction with a strong acid to a soluble fonn. 

This process has been used to recover metals such as mercury, copper, nickel, 

silver, and cadmium from inorganic wastes generated in the primary metals and 

inorganic chemicals industries. 

The acid leaching process is most effective with wastes having high (over 

1,000 ppm) levels of metal constituents. Wastes containing lower levels of such 

contaminants are more difficult to process because the low metal concentrations 

require longer contact times. 

Acid leaching can also be used to extract heavy metals or radionuclides 

from mixed wastes, principally soils, separating the material into its hazardous 

and radioactive components. This process has greater utility when combined with 

unit operations such as ion exchange, solvent extraction, chemical precipitation, 

and filtration. 

Another type of leaching process, alkaline 1 eaching, is used to treat 

~astes· containing metal constituents that are soluble in a strong caustic or 

alkaline solution. This process is mainly useful in recovering aluminum from 

bauxite ore. Generally, the. following information on acid leaching would be 

applicable to alkaline leaching. 

1.2 UnderlYing Principles of Operation 

The basic principle of operation for acid leaching is that ~nlubilities of 

various metals in acid solutions aid in their removal from a waste. The process 

concentrates the constituent(s) leached by the acid solutions. These 

constituents can then be filtered to remove residual solids and neutralized to 

f:\document\15254031.01.018 184 
precipitate solids containing high concentrations of the constituents of 

interest, which _can be further treated in metals recovery processes. 

Alternatively, the acid solutions can be electrolyzed to recover pure metals. 

An acid leaching system usually consists of a solid/liquid contacting unit 

followed by a solid/liquid separator. The most frequently used acids include 

sulfuric (H2

S04), hydrochloric (HCl), and nitric (HN03). Although any acidic pH 

can theoretically be used, acid leaching processes are normally run at a pH from 

1 to 4. 

1.3 Description of Acid Leaching Process 

Acid leaching processes can be categorized into two major types: 

(a) treatment by percolation of the acid through the solids or (b) treatment by 

dispersion of the solids within the acid solution. Both treatments are followed 

by subseque_nt separation of the solids from the liquid. In both types of 

systems, sufficient acid must be supplied to keep the pH at the level needed to 

effectively leach the metals from the waste. 

1.3.1 Percolation Processes 

Percolation is typically conducted in batch tanks. Batch percolators are 

large tanks ranging in size up to 50,000 gallons. First, the solids are placed 

in the tank, and then acid is added. The acid percolates through the solids and 

drains out through screens or a porous medium in the tank bottom. Following 

treatment, the sol ids are removed and further treated using stabilization, and/or 

they are land disposed~. 

1.3.2 Dispersed-Solids Processes 

Acid leaching by dispersion of fine solids into the acid is performed in 

batch tanks. The untreated waste and the acid are mixed in the reaction tank to 

ensure effective contact between the solids and the acid. Following mixing, the 

suspension may be p~mped to stirred holding tanks, where the leaching is allowed 

f:\document\15254031.01.018 185 
to proceed to completion. The treated solids are then usually separated from the 

acid by filtration and further treated using stabilization, and/or they are land 

disposed. t 

1.4 Waste Characteristics Affecting Performance (WCAPs) 

In determining whether acid leaching will achieve the same level of 

performance on an untested waste that it achieved on a previously tested waste 

and whether performance levels can be transferred, EPA examines the following 

waste characteristics: (a) the solid waste particle size, (b) the alkalinity of 

the waste, (c) the solubility of metal constituent~ in the acid, and (d) the 

concentration of leachable metals. 

1.4.1 Solid Waste Particle Size 

Both the solubility reaction rate of the acid with the hazardous metal 

c~nstituents in the waste and the rate of transport of acid to and from the site 

of the hazardous constituents are affected by the size of the solid waste 

particles. The smaller the particles, the more rapidly they will leach because 

of the increased surface area of the waste that is exposed to the acid. If the 

particle size of the untested waste is greater than that of the tested waste, the 

system may not achieve the same performance. Grinding the untested waste may be 

required to reduce the particle size and achieve the same treatment performance, 

or it may be necessary to consider other, more applicable treatment technologies 

for treatment of the untested waste. 

1.4.2 Alkalinity of the Waste 

The neutralizing capacity (or alkalinity) of the waste solids affects the 

amount of acid that must be added to the waste ta achieve and/or maintain the 

desired reactor pH. In addition to dissolving the waste contaminants, the acid 

will also dissolve some of the alkaline bulk solids; therefore, highly alkaline 

wastes require more acid or a stronger acid to maintain pH during treatment. If 

f:\document\15254031.01.018 !86 
the alkalinity in an untested waste is greater than that in a tested waste, the 

system may not a_chieve the same performance. Use of additional acid or a 

stronger acid ~Y be required to compensate for the increased alkalinity and 

achieve the same treatment performance, or other, more applicable treatment 

technologies may need to be considered for treatment of the untested waste. 

1.4.3 Solubility of the Metal Constituents in the Acid 

The metal constituents must dissolve in the acid to form soluble salts for 

the process to be effective. Thus, the acid selected should be one that forms 

soluble salts for all of the constituents to be removed. If the solubility of 

a metal constituent(s) of concern in an untested waste is less than that of 

another constituent(s) of concern in a previously tested waste in the same acid,_ 

or less than the solubility of the same metal(s) tested with a different acid, 

the system may n.:)t achieve the same performance. Use of another acid may be 

required to increase the solubilities of the metal constituent(s) of concern and 

achieve the same treatment performance, or other, more appl;cable treatment 

technologies may need to be considered for treatment of the untested waste. 

1.4.4 Concentration of Leachable Metals 

The amount of leachable metals is a measure of the maximum fraction of the 

waste that can be expected to leach in the acid leaching system. A relatively 

low concentration of leachable metals implies that most of the waste will remain 

in the solid or slurry waste residues (i.e., it is nonleachable). If the 

concentration of leach~ble metals in the untested waste is significantly less 

than that in the tested waste, the system may not achieve the same performance. 

Use of a higher concentration of acid or a stronger acid may be required to leach 

less leachable components and achieve the same treatment performance, or other, 

more applicable treatment technologies may need to be considered for treatment 

of the untested waste. 

f:\document\15254031.01.018 187 
1.5 Design and Operating Parameters 

- In asses~ng the effectiveness of the design and operation of an acid 

leaching system, EPA examines the following parameters: (a) the residence time, 

(b) the type and concentration of acid used, (c) the pH, and (d) the degree of 

mixing. 

1.5.1 Residence Time 

The extent of reaction and dissa1ution of the contaminants in the acid is 

directly r~lated to the contact time. EPA monitors the residence time to ensure 

that sufficient time is provided to effectively leach the metal contaminants from 

the waste. 

1.5.2 _Type and Concentration of Acid Used 

If the hazardous constituents to be removed in the acid leaching system are 

already present in the waste in soluble form, or are solubilized by pH reduction, 

then any acid that will reduce the pH to the desired value may be used. However, 

if chemical reaction is necessary to form soluble species, then the appropriate 

acid, as well as the appropriate concentration of the acid, must be used to 

ensure effective leaching of the metal constituents. EPA examines the type and 

concentration of acid used to ensure that the acid solution select~d is capable 

of effectively leaching the metal constituents from the waste. 

1.5.3 pH 

For dispersed solids systems, the feed of acid to the leaching reactor is 

based on pH 1110nitoring and control because the reaction rate is highly pH 

dependent. Therefore, a pH should be determined, based on the residence time and 

amount of hazardous metal constituents in the waste, that provides for complete 

dissolution of metal constituents. For percolation systems, pH monitoring of the 

acid percolating through the tank (i.e., leaving the system) should ensure that 

f:\document\15Z54031.01.018 188 
enough acid is being added. EPA monitors the pH to ensure that the system is 

operating· at the_ appropriate design conditions and to diagnose operational 

problems. t. 

1.5.4 Degree of Mixing 

Mixing provides greater contact between the acid and the solid waste 

particles, ensuring more rapid leaching of metal contaminants from the waste. 

The quantifiable degree of mixing is ~ complex assessment that includes, among 

other factors, the amount of energy supplied, the length of time the material is 

mixed, and the related turbulence effects of the specific size and shape of the 

tank. Although the exact degree of mixing is beyond simple measurement, EPA 

evaluates it by considering whether mixing is provided and whether the type of 

mixing device is one that could be expected to achieve uniform mixing of the 

waste solution. 

f:\document\15254031.01.018 189 
1.6 References 

Kirk-Othmer. 1~78. Encyclopedia of chemical technology. Vol. 2, pp. 140-144. 

New York: John Wiley and Sons. 

McCabe, L., and Smith, J. 1976. Unit operations of chemical engineering. 3rd 

ed., pp. 607-610. New York: McGraw-Hill Book Co. 

Perry, R.H., and Chilton, C.H. 1973. Chemical engineers' handbook. 5th ed., 

pp. 19-41 to 19-43. New York: McGraw-Hill Book Co. 

f:\document\15254031.01.018 190 
2. FILTRATION TECHNOLOGIES 

2.1 APPlicability 

Filtration technologies (i.e., polishing filtration and sludge filtration} 

are used to remove particles from waste streams that are predominantly water or 

to remove water from wet solids and sludges. 

Polishing filtration is a treatment technology applicable to wastewaters 

containing relatively low concentrations of solids (usually less than 

1,000 mg/1). This type of filtration is typically used as a polishing step for 

the supernatant 1 iquid following chemical precipitation and settling/ 

clarification of wastewaters containing metal and other inorganic precipitates. 

Polishing filtration removes particles that are difficult to settle because of 

their size and/or density, as well as precipitated particles from an 

underdesigned settling system. 

Sludge filtration, also known as sludge dewatering or cake-formation 

filtration, is a technology used on wastes that contain high concentrations of 

suspended solids, usually higher than 1 percent (10,000 mg/1). Sludge filtration 

is commonly applied to waste sludges, such as clarifier solids, for dewatering. 

Typically, these sludges can be dewatered to 19 to 50 percent solids 

concentration using this technology. 

2.2 UnderlYing Principles of Operation 

The basic principle of operation for sludge and polishing filtration is the 

removal/separation of particles from a mixture of fluid and particles by a medium 

that permits the flow of the fluid but retains the particles. Usually, the 

larger the particles, the easier they are to remove from the fluid. 

Extremely small particles, in the colloidal size range, may not be removed 

or filtered effectively in a sludge or polishing filtration system and thus may 

f:\document\1SZS4031.01.0!9 191 
appear in the wastewater passing through the filter. To mitigate this problem, 

the wastewater can be treated prior to filtration to modify the particle size 

distribution ~d/or particle electrostatic charge by using appropriate 

precipitants, coagulants, flocculants, and filter aids. The selection of the 

appropriate precipitant and coagulant is important because they affect the type 

of waste particles formed. For example, lime (calcium hydroxide) precipitation 

usually produces larger, less gelatinous particles (which are easier to remove 

from aqueous wastes by using filtration) than does caustic soda (sodium 

hydroxide) precipitation. For particles that become too small or too highly 

charged to remove effectively, the use of coagulants and flocculants both 

decreases particle charge and increases the size of the particles. Also, if 

pumps are used, shear can be minimized by lowering the pump speed or using a 

low-shear type of pump. Excessive shea:" breaks up agglomerated particles, making 

them smaller and more difficult to filter. Filter aids such as diatomaceous 

earth are used to precoat cloth-type filter media and to provide an initial 

filter cake onto which additional solids can be deposited during the filtration 

process. The presence of the precoat aids in the removal of small particles from 

the solution being filtered. These particles adhere to, and are actually 

filtered by, the precoat solids during the filtration process. 

2.3 Description of Filtration Processes 

2.3.1 Polishing Filtration Processes 

During polishing filtration, wastewater may flow by gravity or under 

pressure to the filter .. The two most common polishin~ filtration processes are 

cartridge and granular bed filtration. Both processes remove particles that are 

much smaller than the pore size of the filter medium by straining, adsorption, 

and coagulation/flocculation mechanisms; these processes are also capable of 

producing an effluent with a low level of solids (typically less than 10 mg/1). 

f:\document\15254031.01.019 192 
2.3.1.1 Cartridge Filtration 

Cartridgetfilters can be used for relatively low waste feed flows. In this 

process, a hollow, cylindrically shaped cartridge with a matted cloth-type filter 

medium is placed within a sealed vessel. Wastewater is pumped through the 

cartridge wall until the flow drops excessively or until the pumping pressure 

becomes too high because of plugging of the filter medium. The sealed vessel is 

then opened, and the plugged cartridge is removed and replaced with a new 

cartridge. The plugged cartridge is then cleaned and/or disposed of. Cartridge 

filters can be assembled in a parallel arrangement to increase the overall system 

flow. 

2.3.1.2 Granular Bed Filtration 

For relatively large volume flows, granulated media such as sand, garnet, 

or anthracite coal are used singly or in combination to trap suspended solids 

within the pore spaces of the media. Dual· and multimedia filter arrangements 

allow higher flow rates and efficiencies. Typical hydraulic loading rates range 

from 2 to 5 gal/sq ft-min for single-medium filters and from 4 to 8 gal/sq ft-min 

for multimedia filters. 

In this process, wastewater is either gravity-fed or pumped through the 

granular bed media and filtered until either the flow drops excessively or the 

pumping pressure becomes too high because of plugging of the granular filter 

media. Granular media filters are usually cleaned by backwashing with previously 

filtered water in an upflow manner to expand the bed, loosen the media granules, 

and resuspend the entrapped filtered solids. The backwash water, which may be 

as much as 10 percent of the volume of the filtered wastewater, is then returned 

to the head of the wastewater treatment system so that the filtered solids in the 

backwash-water can be settled out of solution and the water refiltered prior to 

discharge. 

f:\docunent\1SZ~031.01.019 193 
2.3.2 Sludge Filtration Process 

For sludg~_ filtration, waste is pumped through a cloth-type filter medium 

(also known as pressure filtration, such as that performed with a plate-and-frame 

filter); drawn bt vacuum through the cloth or metal mesh medium (also known as 

vacuum filtration, such as that performed with a vacuum drum filter); or 

gravity-drained and mechanically pressed through two continuous fabric belts 

(also known as belt filtration, such as that performed with a belt filter press). 

In all cases, the solids "cake" builds up on the filter medium and acts as a 

filter for subsequent solids removal. 

For a plate-and-frame filter, removal of the solids is accomplished by 

taking the unit off-line, ~pening the filter, and using mechanical or manual 

methods to scrape off the solids (a batch process). For the vacuum filter, cake 

is removed continuously by using an adjustable knife mechanism to scrape the 

sludge from the vacuum drum as the drum rotates. For the belt filter, the cake 

is continuously removed by a discharge roller and blade, which dislodge the cake 

from the belt. For a specific sludge, the plate-and-frame filter will usually 

produce the driest cake (highest percentage of sol ids). The belt filter produces 

a drier cake than does a vacuum filter, but usually not as dry as that produced 

by a plate-and-frame filter. Dewatered solids are further treated in processes 

such as slu~g~ diying, incineration, solvent extraction (if treatable levels of 

organics are present), stc:bfltzation (if treatable levels of leachable metals are 

present), and/or disposal. The liquid filtrate that penPtrates the filter medium 

is further treated in processes such as polishing filtration, carbon adsorption, 

and biological treatment, and/or it is disposed of. 

2.4 Waste Characteristics Affecting Performance (WCAPs) 

In determining whether polishing and sludge filtration will achieve the 

same level of performance on an untested waste as on a previously tested waste 

and whether performance levels can be transferred, EPA examines the following 

f:\doc~nt\15254031.01.019 194 
waste characteristics: (a) the solid waste particle size and (b) the type of 

solid waste particles. 

(_ 

2.4.1 Solid Waste Particle Size 

Extremely small particles, in the colloidal range, may not be filtered 

effectively in a polishing filter and thus may appear in the filtrate. 

In sludge filtration, the smaller the particle size, the more the particles 

tend to go through the filter media. This is especially true for a vavJum 

filter. For a pressure filter (such as a plate and frame), smaller particles may 

require higher pr~ssures for equivalent fluid throughput because the smaller pore 

spaces between particles collected on the filter medium create resistance to 

flow. If the solid waste particle size distribution of an untested waste is 

significantly lower than that of the tested waste, the system may not achieve the 

same performance. Ir. practice, it is usually aifficult to measure particle size 

accurately and representatively. Ho~ever, it can be said that individual 

particles formed by chemical precipitati<!n are typically much smaller than 

particles formed mechanically (e.g., by erosion, grinding, or abrasion). 

Pretreatment of the waste with coagulants and flocculants may be required to 

increase the particle sizes and achieve the same treatment performance, or other, 

more applicable treatment technologies may need to be considered for treatment 

of the untested waste. 

2.4.2 Type of Solid Waste Particles 

Some solids formed during metal precipitation are gelatinous in nature 

because of high levels of electrostatic charge. Such solids are difficult to 

filter by polisning filtration and may be impossible to dewater effectively by 

sludge filtration. In most cases, solids can be made less gelatinous by use of 

the appropriate coagulants and coagulant dosage prior to settling/clarification, 

or after settling/clarification but prior to filtration. In addition, the use 

or 11me instead of caustic in chemical precipitation of metals reduces the 

f: \doc~ment\15254031.01. Ol9 195 
formation of gelatinous solids. Aiso, in the case of sludge filtration, adding 

filter ai"s, such~s 1 ime or diatomaceous earth, to a gelatinous sludge increases 

its filterabilt_ty significantly. Finally, precoating filter media with 

diatomaceous earth prior to sludge filtration assists in dewatering gelatinous 

sludges. If solids in an untested waste are significantly more gelatinous than 

those in the tested waste, the system may not achieve adequate performance. 

Pretreatment of the waste with t:oagul ants may be required to decrease the· 

gelatinous nature of the waste and achieve the same treatment performance, or 

other, more applicable treatment technologies may need to be considered for 

treatment of the untested waste. 

2.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of a polishing 

filtration system, EPA examines the following parameters: (a) the type and size 

of the filter; (b) the filtration pressure; (c) the amount and type of 

coagulants, flocculants, and filter aids used; (d) the hydraulic loading rate; 

and (e) the pore size of the filter media. 

2.5.1 Type and Size of Filter 

The type and size of the filtration system used is dependent on the rate 

of feed, the nature of the particles to be removed/separated, the desired solids 

concentration in the filtrate (usually just for polishing filtration) and in the 

filter cake (in sludge filtration), the amount and concentration of solids in the 

feed, and the required downtime for solids removal and maintenance. As noted 

earlier, with polishing filtration, cartridge filtration is limited to lower 

volume wastewaters and those with lower solids concentrations as compared to 

granular bed filtration. For granular bed filtration, when more than one medium 

is used (dual and multimedia filter arrangements such as sand, garnet, and 

anthracite co a 1) , a higher capacity can be expected for the same size filter bed. 

f:\document\15254031.01.019 196 
In sludge filtration, typically a pressure filter (such as a plate and 

frame) will yield a drier cake than a belt or vacuum filter and will also be more 

tolerant of vatiations in influent sludge characteristics. Pressure filters, 

however, are characterized by batch processes requiring downtime for so 1 ids 

removal. When cake is built up to the maximum depth physically possible 

(constrained by f~lter geometry) or to the maximum design pressure, the 

filtration system is taken off-line while the cake is removed. (An alternate 

unit can be put on-line while the other is being cleaned.) Belt and vacuum 

filters are continuous systems (i.e., cake discharges continuously), but each of 

these filters is usually much 12rger than a pressure filter with the same 

capacity. 

For all filtration processes, the 1 arger the filter, the greater its 

hydraulic capacity (overall throughput) and the longer the filter runs between 

solids remoyal. EPA examines the type and size of the filter chosen to ensure 

that it is capable of achieving effective filtration of the wastewater. 

2.5.2 Filtration Pressure 

Pressure impacts both the design pore size of the filter media and the 

design feed flow rate (hydraulic loading rate). The higher the feed pressure, 

the longer the run will be prior to solids removal in polishing filtration. In 

sludg~ filtration, at higher pressures the cake will be drier and the runs will 

usually be longer prior to cake discharge. However, for gelatinous solids, such 

as some metal hydroxides, excessive pressure may cause the solids to clog the 

filter pores and prevent additional polishing or sludge fiitration. Also, high 

pressures may force particles through the filter medium, especially early in a 

filter run, resulting 1n ineffective filtration. In vacuum sludge filtration, 

the maximum amount of vacuum typically applied ranges from 20 to 25 inches of 

mercury. (The absolute maximum amount of vacuum that can theoretically be 

applied is 29.9 inches of mercury, or atmospheric pressure.) For belt filters, 

neither hydraulic pressure nor vacuum is applied to the waste feed (although 

mechanical pressure is applied). For plate-and-frame and vacuum filtration 

f: \doclllll!nt\15254031. 01.019 19 7 
systems, EPA monitors the filtration pressure (or vacuum) applied to the waste 

feed continuouslYT if possible, to ensure that the system is operating at the 

appropriate des~gn condition and to diagnose operational problems. 

2.5.3 Amount and Type of Coagulants, Flocculants, and Filter Aids 

Coagulants, flocculants, and filter aids may be mixed with the waste feed 

prior to filtration. Coagulants and flocculants affect the type and size of the 

particles in the waste and, hence, their ease of removal. In vacuum filtration 

their effect is particularly significant since they may make the difference 

between no cake formation and the forming of a relatively dry cake. In a 

pressure filter, coagulants, flocculants, and filter- ~ids can significantly 

improve overall throughput and cake dryness. Filter aids, such as diatomaceous 

earth, can be precoated on all sludge filters for particularly difficult-tofilter sludges (those containing a high concentration of gelatinous solids). The 

precoat layer acts somewhat like a filter in that sludge solids are trapped in 

the precoat pore spac~s. In polishing filtration, filter aids both improve the 

effectiveness of filtering gelatinous particles and increase the time that the 

filter can stay on-line. 

Coagulants, flocculants, and filter aids are particularly useful when the 

sludge (in the case of sludge filters) and wastewater {in the case of polishing 

filtr~tion) have a high percentage of very small particles or when the 

·concentration of solids in the waste feed or wastewater is low. Inorganic 

coagulants include alum, ferric sulfate, and lime. Organic flocculants, which 

are called polyelectralytes, are anionic, cationic, or nonionic in nature. 

Diatomaceous earth is the most commonly used filter aid. The use of coagulants, 

flocculants, and filter aids increases the amount of solids requiring disposal. 

Polyelectrolyte flocculant usage, however, usually does not increase the solids 

volume significantly because the required dosage is relatively low. If the 

addition of coagulants, flocculants, and filter aids is required, EPA examines 

the amount and type added to the waste, along with their method of addition, to 

ensure effective dewatering and filtration. 

f:\document\15254031.01.019 198 
2.5.4 Hydraulic Loading Rate 

Lower hyd(aulic loading rates generally improve filtration pe~formance. 

For sludge filtration, higher hydraulic loading rates for a given size filter 

yield greater overall throughput but result in the formation of wetter cakes 

(lower percent solids) and, for plate-and-frame filters, shorter cycle times. 

For polishing filtration, higher hydraulic loading rates yield greater throughput 

but result tn shorter cycle times. EPA monitors the hydraulic loading rate to 

ensure effective dewatering and filtration of waste sludge and effective 

filtration of wastewater. 

2.5.5 Pore Size of the Filter Media 

For polishing filtration systems, the pore size of the filter media 

determines the particle size that will be effectively removed from the 

wastewater. EPA examines the pore size of the filter media to ensure effective 

filtration of wastewater. For sludge filters, the pore size and type relate to 

resistance to abrasion and corrosion. 

f:\document\15254031.01.019 199 
2.6 References 

Anonymous. 19d5. Feature report. Wastewater treatment. Chemical Engineering 92(18):71-72. 

Crain, R.W. 1981. Solids removal and concentration. In Third Conference on 

Advanced Pollution Control for the Metal Finishing Industry, pp. 56-62. 

Cincinnati, Ohio: U.S. Environmental Protection Agency. 

Eckenfelder, W.W., Jr., Patoczka, J., and Watkins, A. 1985. Wastewater 

treatment. Chemical Engineering, September 2, 1985. 

Kirk-Othmer. 1980. Encyclopedia of chemical technology. 3rd ed. Vol. 10. New 

York: John Wiley and Sons. 

Perry, R.H., and Chilton, C.H. 1973. Chemical engineers' handbook. 5th ed., 

Section 19. New York: McGraw Hill Book Co. 

f:\dacument\15254031.01.019 200 
3. HIGH TEMPERATURE METALS RECOVERY 

3.1 Ap~lfcability 

High temperature metals recovery (HTMR} is a technology applicable to 

wastes containing metal oxides and metal salts (including cadmium, chromium, 

lead, nickel, and zinc compounds} at concentrations ranging from 10 percent to 

over 70 percent with low levels (i.e., below 5 percent} of organics and water in 

the wastes. There are a number of different types of nigh temperature metals 

recovery systems, which generally differ from one another in the source of energy 

used and the method of recovery. These HTMR systems include the rotary kiln 

process, the plasma arc reactor, the rotary hearth electric furnace system, the 

molten slag reactor, and the flame reactor. 

HTMR is generally not used for mercury-containing wastes even though 

mercury will volatilize readily at the process temperatures present in the high 

temperature units. The retorting process is normally used for mercury recovery 

because mercury is very volatile and lower operating temperatures can be used. 

Thus, the retorting process is more economical than HTMR for mercury-bearing 

wastes. Retorting is discussed in Section II.S.S. 

The HTHR process has been demonstrated on wastes such as baghouse dusts and 

dewatered scrubber sludge from the production of steels and ferroalloys. Zinc, 

cadmium, and lead are the metals most frequently recovered. The process has not 

been extensively evaluated for use with metal sulfides. The sulfides are 

chemically identical t9 natural minerals ordinarily present in ores used as 

feedstocks by primary smelters. Some sulfide-bearing wastes from the chrome 

pigments industry have been sent to such primary smelters. However, with 

sulfides, a possibility exists for formation of either carbon disulfide from 

reaction with carbon or sulfur dioxide from reaction with oxygen in the HTMR 

processes. 

f:\document\15254031.01.020 201 

, 
Metal halide salts are also not directly used in HTMR processes. They, 

however,. may be converted to oxides or hydroxides, which are acceptable 

feedstocks for HTMR processes. (_ 

3.2 Underlying Principles of Operation 

The basic principle of operation for HTMR is that metal oxides and salts 

are separated from a waste through a high temperature thermal reduction process 

that uses carbon, limestone, and silica (sand) as raw materials. The carbon acts 

as a reducing agent and reacts with metal oxides to generate carbon dioxide and 

free metal. The silica and limestone serve as fluxing agents. This process 

yields a metal product for reuse and reduces the concentration of metals in the 

residuals and, hence, the amount of waste that needs to be land disposed. An 

example HTMR reaction is the recovery of zinc, which proceeds as follows: 

2 ZnO + C • 2 Zn + C02 

3.3 Description of High Temperature Metals ~eco•ery Process 

The HTHR process consists of a mixing unit, a high temperature processing 

unit (kiln, furnace, etc.), a product collection system, and a residual treatment 

system. A schematic diagram for a high temperature metals recovery system is 

shown in Figure 22. 

The mixing unit homogenizes metal-bearing wastes, thus minimizing feed 

variations to the high temperature processing unit. Before the wastes are fed 

into the high temperature processing unit, fluxing agents and carbon can be added 

to the mixing unit and mixed with the wastes. The fluxes used (sand and 

1 in1estone) are often added to react with certain meta 1 components, preventing 

their volatilization and resulting in an enhanceapurity of the desired volatile 

metals removed. 

f:\document\15254031.01.020 202 
WASTE INFLUENT ... -

CARBON - MIXING 

CREDUCIHO AGENT) ... UNIT . FLUXES - ... 

CLIMES TONE, BAND)-

I 

.. -

. 

,. 

. . 

l 

.. 

! 

., 

,. 

j 

' ., 

It 

HIGH 

TEMPERATURE 

PROCESSINO 

UNIT 

• • 

RESIDUAL 

COLLECTION 

CQUENCH TANk) 

-

--

EXHAUST AIR OR GAS 

TO THE 

ATMOSPHERE 

PRODUCT 

COLLECTION 

UNIT 

(CONDEHSOH on 

COHDENSOR 

AND BAGttOUSEt 

NON-VOLATILE IIETAL PRODUCTS TO REUSE. 

FURJIIER RECOVERY IN A FURNACE, 

STABILIZ~TION FOLLOWED BY LAND OIPO:IAL1 

OR DIRECTLY TO LAND DISPOSAL 

Figure 22 High Temperature Metals Recovery Syste• 

--

VQt.ATILE 

IIET~L 

PRODUCTS 

TO REUSE 

OR FUHTttER 

REFINEMENT 

PRIOR TO 

REUSE 

.... -----
The blended waste materials are fed to a furnace, where they are heated to 

temperatures rangjng from 1100 to 1400"C (2012 to 2552"F), resulting in the 

reduction and Glolatilization of the desirad metals. The combination of 

temperature, residence time, and turbulence provided by rotation of the unit or 

addition of an air or oxygen stream helps ensure the maximum reduction and 

volatilization of metal constituents. 

The product collection system can consist of either a condenser or a 

combination condenser and baghouse. The choice of a particular system depends 

on whether the metal is to be collected in the metallic form or as an oxide. 

Recovery and collection are accomplished for the metallic form by condensation 

alone, and for the oxide by reoxidation, condensation, and subsequent collection 

of the metal oxide particulates in a baghouse. There is no difference in these 

two types of metal recovery and collection systems relative to the kinds of waste 

that can be treated; the use of one system or the other simply reflects the 

facility's preference relative to product purity. In the former case, the direct 

condensation of metals allows for the separation and collection of individual 

metals in a relatively uncontaminated form; in the latter case, the metals are 

collected as a combination of several metal oxides. 

The treated waste residual slag, containing higher concentrations of the 

less-volatile metals than the untreated waste, is sometimes cooled in a quench 

tank and (a) reused directly as a product (e.g., a waste residual cont~ining 

-mostly iron can be reused ~-n steelmaking); (b) reused a~:ter further orocessing 

(e.g., a waste residual containing oxides of iron, chromium, and nicke 1 :Jn be 

reduced to metallic fprm and then recovered for use in the manufacture of 

stainless steel); (c) stabilized (material has no recoverable value) to 

immobilize any remaining metal constituents and then land disposed; or 

(d) directly land disposed as a slag. 

f:\document\15254031.01.020 204 

f 
3.4 Waste Characteristics Affecting Performance (WCAPs) 

In determtning whether high temperature metals recovery will achieve the 

same level of performance on an untested waste that it achieved on a previously 

tested waste and whether performance levels can be transferred, EPA examines the 

following waste characteristics: (a) the concentrations of undesirable volatile 

metals, (b) the metal constituent boiling points, and (c) the thermal 

conductivity of the waste. 

3.4.1 Concentration of Undesirable Volatile Metals 

Because HTMR is a recovery process, the product must meet certain purity 

requirements prior to reuse. If the waste contains other volatile metals, such 

as arsenic or antimony, which are difficult to separat~ from the desired metal 

products and whose presence may affect the ability to reuse the product or refine 

it for subsequent reusf:, HTMR may not be an appropriate techno 1 ogy. If the 

concentration of undesirable volatile metals in the untested waste is 

significantly higher than that in the tested waste, the system may not achieve 

the same performance, and other, more applicable treatment technologies may need 

to be considered for treatment of the untested waste. 

3.4.2 Metal Constituent Bailing Points 

The greater the ratio of volatjlity of the waste·constjtuents, the more 

easily the separation.of these constituents can proceed. This ratio is called 

relative volatility •. ~PA retognizes, hC*ever, that~the relative volatilities 

cannot be measured or calculated directly for the types of wastes generally 

treated by high temperature metals recovery. This is because the wastes usually 

consist of a myriad of components, all with different vapor pressure-versustemperature relationships. However, because the volatility of components is 

usually inversely proportional to their boiling points (i.e., the higher the 

boiling point, the lower the volatility), EPA uses the boiling point of waste 

components as a surrogate waste characteristic for relative volatility. If the 

f: \doc~~n~nt \15254031.01.020 205 
differences in boiling points between the more volatile and less volatile 

constituents are significantly smaller in the untested waste than in the tested 

waste, the syst~ may not achieve the same performance and other, more applicable 

treatment technologies may need to be considered for tr2atment of the untested 

waste. 

3.4.3 Thermal Conductivity of the Waste 

The ability to heat constituents within an HTMR process feed matrix is a 

function of the heat transfer characteristics of the individual feed components 

(coke, limestone, untreated waste, etc.). The constituents being recovered from 

the waste must be heated to near or above their boiling points in order for them 

to be volatilized and recovered. The rate at which heat will be transferred to 

the feed mixture is dependent on the mixture's thermal conductivity, which is the 

ratio of t~e conductive heat flow to the temperature gradient across the 

material. Thermal conductivity measurements, as part of a treatability 

comparison of two different wastes to be treated by a single HTHR system, are 

most meaningful when applied to wastes that are homogeneous (i.e., uniform 

throughout). As wastes exhibit greater degrees of nonhomogeneity, therma 1 

conductivity becomes less accurate in predicting treatability because the 

measurement reflects heat flow through regions having the greatest conductivity 

(i.e., the path of least resistance) and not heat flow through all parts of the 

waste. Nevertheless, EPA believes that thermal conductivity may provide the best . measure of performance of heat transfer. If the thermal conductivity of the 

untested waste is significantly lower than that of the tested waste, the system 

may not achieve the same performance and other, more applicable treatment 

technologies may need to be considered for treatment of the untested waste. 

3.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of an HTMR 

system, EPA examines the following parameters: (a) the HTMR temperature, (b) the 

f:\dcc~nt\15254031.01.020 206 

, 
residence time, (c} the degree of mixing, (d) the carbon content of the feed, and 

(e) the calcium-to-silica ratio of the feed. 

{_ 

3.5.1 HTMR Temperature 

Temperature provides an indirect measure of the energy available (i.e., 

Btu/hr} to volatilize the metal waste constituents. The higher the temperature 

in the high temperature processor, the more likely it is that the constituents 

will react with carbon to form free metals and volatilize. The temperature must 

be equal to or greater than the boiling point of the metals being volatilized for 

recovery. However, excessive temperatures could volatilize less-volatile, 

undesirable metals into th~ product, possibly inhibiting the potential for reuse 

of the product. EPA monitors the HTMR processor temperature continuously, if 

possible, to ensure that the system is operating at the appropriate design 

condition (at or above the boiling point(s} of the metal or metals being 

recovered, but not so high that it volatilizes other unwanted constituents} and 

to diagnose operational problems. 

3.5.2 Residence Time 

The residence time affects the amount of volatile metals volatilized and 

recovered. It is dependent on the HTHR processor temperature and the thermal 

condu~tivity of the feed ~tend. EPA monitors the residence time to ensure that 

~ufficient time is provfded t~effectfvely volat111ze the volatile constituents 

for recovery. 

3.5.3 Degree of Mixing 

Effective mixing of the waste with coke, silica, and limestone 1s necessary 

to produce a uniform feed blend to the system. The quantifiable degree of mixing 

is a complex assessment that includes, among other things, the amount of energy 

supplied, the length of time the material is mixed, and the related turbulence 

effects of the specific size and shape of the tank or vessel. This is beyond the 

f: \doc~m~nt\152S.C031.01.020 207 
scope of simple measurement. EPA, however, evaluates the degree of m1X1ng 

qualitatiyely by considering whether mixing is provided and whether the type of 

mixing device is-one that could be expected to achieve uniform mixing of the 

(_ 

waste. 

3.5.4 Carbon Content of the Feed 

The amount of carbon added to the waste must be sufficient to ensure 

complete reduction of the volatile metals being recovered. EPA examines the 

basis for calculation of the amount of carbon added to the waste to ensure that 

sufficient carbon is being used in the feed blend to effectively reduce metal 

compounds. 

3.5.5 Calcium-to-Silica Ratio of tha Feed 

The calcium-to-silica ratio in the feed blend must be controlled to limit 

precipitation of metallic iron in the high temperature processor. The iron forms 

as solid calcium iron silicate, which is very difficult to subsequently process 

into any useful material. Aluminum oxide will also undergo reactions with lime 

and silica to form calcium aluminosilicates, which will lower the density and 

increase the volume of slag generated. 

Precipitates and modified slags affect the reduction, volatilization, and 

recovery of volatile metals by changing heat flow characteristics in the system 

and by undergoing secondary, high temperature chemical reactions with metal 

oxides in the feed, conv_ert i ng them to the previously notec1 inert metal s il i cates 

or silicoaluminates. The ratio of calcium to silica to be used is dependent on 

the waste composition. Generally, a one-to-one silica-to-calcium oxide ratio is 

highly desired, so amounts of limestone and sand need to be adjusted based on the 

calcium and silica content of the waste to achieve this ratio. 

Excess lime may also be added to fix sulfur in the feed as calcium sulfate. 

This will preve~t the volatile metals from rP.acting with sulfur to form metal 

f:\document\1SZS40Jl.Ol.OZO 208 
sulfides, thereby lowering the recovery of metals or oxides. EPA monitors the 

amounts .of limestone and sand added to the waste to ensure that the 

calcium-to-siltca ratio selected to maximize metal or oxide recovery is 

maintained during treatment. 

f:\dccument\15254031.01.020 209 
3.6 References 

- Center for Het~]s Production. 1985. Electric arc- furnace dust--disoosal, 

recvcle and recovery. Pittsburgh, Pa. 

Duby, P. 1980. Extractive metallurgy. In Kirk~Othmer encyclopedia of chemical 

technology. 3rd ed. Vol. 9, p. 741. New York: John Wiley and Sons. 

Lloyd, T. 1980. Zinc compounds. In Kirk~Othmer encyclopedia of chemical 

technology. 3r~ ed. Vol. 24, p. 824. New York: John Wiley and Sons. 

Haczek, H., and Kola, R. 1980. Recovery of zinc and lead from electric furnace 

steelmaking dust at Berzelius. Journal of Metals 32:53-58. 

Price, L. 1986. Tensions mount in EAF dust bowl. Metal Producing. February 

1986. 

f:\docuaent\152~031.01.020 210 

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! 
4 • I ON EXCHANGE 

4.1 Appl'fcability 

Ion exchange is a treatment technology applicable to (a) metals in 

wastewaters where the metals are present as soluble ionic species (e.g., cr·3 and 

Cr04-

2); (b) nonmetallic anions such as halides, sulfates, nitrates, and 

cyanides; and (c) water-soluble, ionic organic compounds including (1) acids such 

as carboxylics, sulfonics, and some phenols, at a pH sufficiently alkaline to 

yield ionic species, (2) amines, when the solution acicil~i is suffici~ntly acid 

to form the corresponding acid salt, and (3) quaternary amines and alkysulfates. 

4.2 Underlying Principle~ ~f Operation 

Ion e~change, when used in hazardous waste treatment, is a reversible 

process in which hazardous cations and/or anions are removed from an aqueous 

solution and are replaced by nonhazardous cations and/or anions such as sodium, 

hydrogen, chloride, or hydroxyl ions. Ion exchange resins are cationic if they 

exchange positive ions (cations) and anionic if they exchange negative ions 

(anions). When the waste stream to be treated is brought into contact with a bed 

of resin beads (usually in a packed column), an exchange of hazardous ions for 

nonhazardous ions occurs on the surface of the resin beads. Inithlly, a 

nonhaz~rdous ton is loos~ly bound to the surface of the resin. When a hazardous 

1on is near the resin, it is preferentially adsorbed to the surface of the resin 

(based on the differences in ionic potential), releasing the nonhazardous ion. 

Cation exchange resins contain mobile positive ions, such as hydrogen (H.) 

or sodium (Na•), which are attached to immobile functional acid groups, such as 

sulfonic (501-) and carboxylic (COO-) groups. Anion exchange resins have 

immobile basic ions, such as amine (NH2-), to which the mobile anions, such as 

hydroxyl {OH-) or chloride {Cl-), are attached. 

f:\document\15254031.01.021 211 
Ion exchange material is contacted with the solution containing the ion to 

be removed until jhe active sites in the exchange material are partially or 

completely used ~p ("exhausted") by that ion. For example, a cation exchange 

resin (designated R-) to which a mobile positive ion (N+) is attached reacts with 

a solution of electrolyte (H•x-) as shown below: 

After exhaustion, the resin is then contacted with a relatively low volume of a 

very concentrated solution of the exchange ion to convert ("regeneraten) it back 

to its original form. The regeneration reaction may be written as follows: 

For instance, in the case of a sodium-based resin, a strong solution of sodium 

chloride is typically the regenerant solution. The regenerant solution forces 

the previously removed ions back into solution. This relatively low volume 

solution, now highly concentrated with the contaminant ions, must then be treated 

prior to disposal for recovery or removal of the hazardous cation or anion 

contaminants. There will continue to be a high concentration of the regenerant 

ion (sodium in the above example) in the used regenerant solution because excess 

regenerant ion is necessary to force the contaminant ions back into solution. 

The direction and extent of the completion of th~ ~~ch;~;a reaction deptdd upon • It . 

the equilibrium that is established between the ions in the solution (H•x-) and 

those in the exchange naterial (R_N.). 

4.3 Description of Ion Exchange Process 

Host ion exchange operations are conducted in packea columns. The aqueous 

solution to be treated is continuously fed to either the top or the bottom of the 

column. A typical fixed-bed ion exchange column consists of a vertical 

cylindrical pressure vessel with corrosion-resistant linings. If appropriate, 

a filter is installed at the inlet of the column to reu~ve suspended particles 

f:\document\15254031.01.021 212 

1 

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I 

' 

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because they may plug the exchange resin. Spargers are provided at the top and 

bottom of. the cQ_lumn to distribute waste flow. Frequently, a separate 

distributor is 1sed for the regenerant solution to ensure an even flow. The 

resin bed, usually cons~sting of several feet of ion exchange resin beads, is 

supported by a screen near the bottom distributor or by a support bed of inert 

granular material. Externally, the unit has a valve manifold to permit downflow 

operation, upflow backwashing (to remove any suspended material), injection of 

the regenerant solution, and rinsing of any excess regenerant. 

A typical process schematic for a basic two-step cation/anion ion exchange 

system is presented in Figure 23. The ion exchange system shown in this 

schematic includes a series treatment with separate cation and anion exchange 

systems. Some systems contain both anion and cation exchange resins in the same 

vessel. The pressure vessels used for ion exchange generally range in size from 

2 to 6 feet in diameter for prepackaged modular systems, which typically handle 

25- to 300-gpm flow rates, to a maximum custom size of 12 feet in diameter, which 

can handle flow rates up to 1,150 gpm. The height of these vessels varies 

between 6 and 10 feet to provide adequate resin storage, distribution nozzle 

layout, and freeboard capacity for bed expansion during backwashing. The nominal 

surface loading area of the ion exchange vessels ranges from 8 to 10 gpm per 

square foot. 

4.4 Waste Characteristics Affecting Performance (WCAPs) 

In determining whether ion exchange will achieve the same level of 

performance on an untested waste as on a previously tested waste and whether 

performance levels can be transferred, EPA examines the following waste 

characteristics: (a) the concentration and valence of the contaminant, (b) the 

concentration of competing ionic species, (c) the concentration of interfering 

inorganics and organics, (d) the concentrations of dissolved and suspended sol ids 

and oil and grease, and (e) the corrosiveness relative to the resin material. 

f: \doc1111ent \15254031. 0 1. 021 213 

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N 

-... 

USED BACKFLUSH WATER 

TO THEA TIIENT 

BACKFLUSH WATER 

CATION 

EXCHANGE 

SYSTEM 

USED REOENERANT 

SOLUTION AND HINSJ:S 

TO RECOVERY . 

ANDIOR TREATMENT 

RINSE WATER 

ACID REOENERANT 

USED BACKFLUSH WATER 

TO 1REATMEN1 

RINSE WATER 

CAUSTIC 

HEOENERANT 

TREATED 

EFFI.UENT 

"----.TO L=URTffER 

ANION 

EXCttANGE 

SYSTEM 

USED REGENERANT 

SOLUTION AND RINSES 

TO RECOVERY 

ANOIOR TREATMENT 

TREATMENT 

. AND/OR DISPOSAL 

Ft gure 23 Two-Step Cat ton/Anton Jon Exchangct SJ•:c;tem 
4.4.1 Concentration and Valence of the Contaminant 

As the cancentration and valence of adsorbable ions in the wastewater 

increase, the size of the resin bed required will increase as well, or, 

alternatively, the bed will become exhausted more rapidly. This is because a 

~iven amount of ion exchange resin has a 1 imited number of sites to adsorb 

charged ions. If, for example, the valence is doubled or the concentration of 

the adsorbed ions is doubled, the sites will be exhausted twice as quickly. 

Hence, very high concentrations of the waste may be inappropriate for ion 

exchange because of rapid site exhaustion, which could conceivably require 

regenerant volumes to be essentialiy equal to waste flow volumes. If the 

concentration and/or the valence of the contaminant in an untested waste is 

significantly higher than that of the tested waste, the system may not achieve 

the same performance. A larger exchange bed or more frequent regeneration may 

be required to exchange higher concentrations and/or higher valences of the 

contaminar.t and achieve the same treatment performance,. or other, more applicable 

treatment technologies may need to be considered for treatment of the untested 

waste. 

4.4.2 Concentration of Competing Ionic Species 

The presence of other contaminants or ions in the wastewater can affect the 

perforynance of the. ion exchange unit in removing the hazardous contaminant of 

-concern. Other ion.t -inr.the wastewater wit~ the s-ame charge· as the contaminant 

of concern will compete for exchange sites on the resin. .~1so, ions with a 

higher valence will be preferentially adsorbed., While a low-concentration of the 

contaminant of concern may be readily removed from a solution with a low 

concentration of other similarly charged ionic species, the contaminant may not 

be removed as efficiently from s~1utions where high concentrations of similarly 

charged ions exist, especially if those ions have a higher valence than that of 

the contaminants. If the ions of concern are removed from a solution with high 

concentrations of other ~imilarly charged ions, the resin will become exhausted 

more rapidly because most resins cannot selectively adsorb one contaminant in a 

f:\document\l525403l.Ol.021 215 
solution containing other similarly charged ionic species. If the concentration 

of competing ionic_species in an untested waste is significantly higher than that 

in the tested watte, the system may not achieve the same performance. A larger 

exchange bed or more frequent regeneration may be required to exchange higher 

concentrations of competing ionic species and achieve the same treatment 

performance, or other, more applicable treatment technologies may need to be 

considered for treatment of the untested waste. 

4.4.3 Concentration of Interfering Inorganics and Organics 

Interfering inorganics, such as iron precipitates, can accumulate in the 

pores of aninn exchangers; these ir.organics will physically break down or block 

the rasin particles. Some organic compounds, particularly aromatics, can be 

irreversibly adsorbed by the exchange resins. Also, some ions tend to oxidize 

after they are removed from solution. For instance, Mn•Z (manganese) may oxidize 

to the insoluble Mn~ state, thereby permanently fouling the exchange sites and 

requiring the premature replacement of the resin. If the concentration of 

interfering inorganics and organics in an untested waste is significantly higher 

than that in the tested waste, the system may not achieve the same performance 

and other, more applicable treatment technologies may need to be considered for 

treatment of the untested waste. 

4.4.4 Concentrations of Dissolved and Suspended Solids and Oil and 

Grease 

High concentrations of dissolved and suspended solids and oil and grease 

can affect the performance of ion exchange sites. Convention a 1 1 on exchange 

systems are usually downflow; i.e., the wastewater flows down through the resin 

bed. Regeneration is accomplished in either the downflow or upflow mode. If 

excessive concentrations of dissolved and suspended solids and/or oil and grease 

are present in the wastewater, the bed may clog and require backwashing prior to 

exhausting its exchange capacity. Backwashi ng may prove ineffective in the 

removal of some solids or oils. If the concentration of dissolved and suspended 

solids and/or oil and grease in an untested waste is significantly higher than 

f:\document\15254031.01.021 216 

1 
that in the tested waste, the system may not achieve the same performance and 

other, mare app 1 i cable treatment techno 1 ogi es may need to be considered for 

treatment of thf_ untested waste. 

4.4.5 Corrosiveness 

Some wastewaters are extremely corrosive to ion exchange resin materials, 

reducing efficiency or increasing downtime for maintenance and repair. For 

instance, strong solutions of chromates may oxidize many resins, requiring 

premature replacement. If the corrosiveness of the untested waste is 

significantly higher than that of the tested waste, the system may not achieve 

the same performance and other, more applicable treatment technologies may need 

to be considered for treatm~nt of the untested waste. 

4.5 Design and Operating Parameters 

In assessing the effectiveness of the design and operation of an ion 

exchange system, EPA examines the following parameters: (a) the amount and type 

of resin, (b) the amount and type of regenerant solution, (c) the hydraulic 

loading, and (d) the exchange temperature. 

For many hazardous organic constituents, ana lyti ca 1 methods are not 

available or the constituent cannot be analyzed in the waste matrix. Therefore, 

;t would nonmally be impossible to measure the effectiveness of the ion exchange 

system. In these cases EPA tries to identify measurable parameters or 

canst i tuents that would. act as. surrogates to verify treatment. 

For organic constituents, each compound contiins a measurable amount of 

total organic carbon (TOC). Removal of TOC in the ion exchange system will 

indicate· removal of organic constituents. Hence, TOC analysis is likely to be 

an adequate surrogate anilysis where the specific organic constituent cannot be 

measured. However, TOC analysis may not be able to adequately detect treatment 

of specific organics in matrices that are heavily organic-laden (i.e., the TOC 

f:\docUQtnt\15254031.01.021 217 

, 
analysis may not be sensitive enough to detect changes at the milligrams/liter 

(mg/1} le¥el in J!atrices where total organic concentrations are hundreds or 

thousands of mg/d}. In these cases other surrogate parameters should be sought. 

For example, if a specific analyzable constituent is expected to be treated as 

well as the unanalyzable constituent, the analyzable constituent concentration 

should be monitored as a surrogate. 

4.5.1 Amount and Type of Resin 

The main design parameter that affects the performance of ion exchange 

systems is the amount and type of resin used. Numerous cationic and anionic 

resins are conmercially available. The selection of a resin is based on a 

variety of factors. Different resins have different exchange capacities, and 

some have greater affinity than others for specific ions. Certain resins are 

designed to tolerate corrosive, oxidizing, or high temperature solutions, so 

their exchange capacity does not degrade as rapidly with use. Most <esins will 

effectively remove contaminant ions from solution until they become exhausted. 

However, if resin bed exhaustion occurs too frequently, or if regeneration 

requires excessive volumes of the regenerant, the type and/or amount of resin 

might need to be changed. In some instances, pretreatment technologies may be 

required prior to ion exchange. For most metals removal, cation resins are 

usually required. However, some metal complexes, such as copper cyanide 

(Cu(C~) ), chromates (Cr04

-

2

), and arsenates (As04

-

3}, are anionic and require 

"the use of ~nion exchange resins. EPA examines the amount and type of ion 

exchange resin in the treatment system to ensure that a sufficient amount of ion 

exchange resin is provided to effectively exchange the metal ions of concern. 

4.5.2 Amount and Type of Regenerant Solution 

For hydrogen-based cation exchangers, acid regenerant solutions are used 

(e.g., sulfuric, nitric, or hydrochloric ;;cids). For sodium-based cation resins, 

sodium chloride is generally used. For anion exchange resins, al~:~i (commonly 

sodium hydroxide) is used to regenerate hydroxide-based resins. Sodium chloride 

f:\document\15254031.01.021 218 

• 
is used for chloride-based anion resins. EPA examines the amount and type of 

regeneraAt solution used to ensure that it is compatible with the resin and waste 

treated and thtt effective removal of the contaminant ions from the exchange 

resin is achieved. 

4.5.3 Hydraulic loading Rate 

The amount of time that the wastewater contaminants are in contact in the 

ion exchange resin (i.e., residence time} impacts the extent to which ion 

exchange occurs. Higher residence times generally improve exchange performance, 

but require larger ion exchange beds to maintain the same overall throughput. 

For a given size ion exchange bed, the residence time can be determined by the 

hydraulic loading rate. Typical hydraulic loading rates for ion exchange systems 

range from 600 to 15,000 gal/day-ftz. EPA monitors the hydraulic loading rate 

to ensure that sufficient time is provided to effectively exchange contaminants. 

4.5.4 Exchange Temperature 

High temperatures reduce resin life, requiring premature replacement. EPA 

monitors the temperature in an ion exchange column continuously, if possible, to 

ensure that the system is operating at the appropriate design condition and to 

diagnose operational problems. EPA has information showing that the high 

temperature limit for anionic resins may be approximately 60°C. 

f:\document\15254031.01.021 219 
4.6 References 

DeRenzo, D.J.,~d. 1978. Unit operations for treatment of hazardous industrial 

wastes. Park Ridge, N.J.: Noyes Data Corporation. 

Dorfner, K. 1972. Ion exchangers: properties and applications. Ann Arbor, 

Mich.: Ann Arbor Science Publishers, Inc. 

Metcalf & Eddy, Inc. 1979. Wastewater engineering: treatment disposal reuse. 

2nd ed. New York: McGraw-Hill Book Co. 

Patterson, J.W. 1985. Industrial waste treatment technology. 2nd ed. Stoneham, 

Mass.: Butterworth Publishers. 

Perry, R.H., and Chilton, C.H. 1973. Chemical engineers' handbook. 5th ed. 

New York: McGraw-Hill Book Co. 

Sundstrom, D.W., and Klei, H.E. 1979. Wastewater treatment. Englewood Cliffs, 

N.J.: Prentice-Hall, Inc. 

USEPA. 1982. U.S. Environmental Protection Agency. Development document for 

the porcelain enameling point source category. pp. 172-241. Washington, D.C.: U.S. Environmental Protection Agency. 

USEPA. 1983. U.S. Environmental Protection Agency. Treatability manual: ~ol. III. Technology for control/removal of pollutants. EPA-600/ 

2·82-001c. Washington, D.C.: U.S. Environmental Protection Agency. 

Wheaton, R.H. 1978. Kirk-Othmer encyclopedia of chemical technology. 3rd ed. 

Vol. 13. New York: John Wiley and Sons. 

f:\documant\15254031.01.021 220 

, 
5. RETORTING 

5.1 Apli icab11ity 

Retorting is a treatment technology applicable to wastes containing 

elemental mercury, as well as mercury present in the oxide, hydroxide, and 

sulfide forms, at 1 evels above 100 parts per mill ion, provided that the waste has 

a low total organic content (i.e., below 1 percent). Fo~ metals other than 

mercury, the typica·, retort operating temperatures (700 to 1000.F) are not high 

enough to decompose the meta 1 compounds. High temperature meta 1s recovery (HTMR} 

processes must be used to recover most other metals when they are not present in 

the pure metal form. 

For most retorting processes, there is an additional requirement that the 

waste have ~ low water content, preferably below 20 percent. Dewatering reduces 

energy consumption by minimizing the amount of water evaporated and precludes 

problems involving the separation of recovered metals from large quantities of 

water. 

5.2 Unde~lyinq Principles of Operation 

The basic principle of operation for retorting is a process similar to that 

for high temperature metals recovery in that it provides for recovery of metals 

from wastes primarily by volatilization and subsequent collection and 

condensation of the volatilized components. Retorting yields a metal product for 

reuse and significantly reduces the concentration of- metals in the waste 

residual, and, hence, the amount of treated waste that needs to be land disposed. 

This technology 1s different from HTHR in that HTMR includes a reduction reaction 

i nvo 1 vi ng the use of carbon, while retorting does not use a reducing agent. 

Additionally, this process differs with regard to the form and, possibly, the 

leachability of the residue generated; HTHR generates a slag, while retorting 

generates a granular solid residue that may have lower leachability than a slag 

if mercury is the only constituent of concern present in the untreated waste. 

f:\docuroent\15254031.01.022 221 
The basic principle of operation of retorting is that sufficient heat must 

be transf~rred to the waste to cause elemental metals to vaporize. In the case 

of mercury prestnt as an oxide, hydroxide, or sulfide compound, sufficient heat 

must be transferred to the waste to first decompose the compounds to the 

elemental form and then volatilize the mercury. In mercury wastes that are 

wastewater treatment sludges, mercury is most often present in the forrn of the 

sulfide (HgS) as a result of the use of sodium hydrosulfide treatment of 

mercury-bearing wastewaters. In a few instances, hydrazine is used to treat 

these same wastewaters; in such instances, a mercurous hydroxide s1iiC:;•.! is 

generated. This latter compound can be more easily treated to yield elemental 

mercury because this reaction occurs more readily than the sulfide decomposition 

at·the temperatures at ~hich the process is normally operated. Preheated air is 

provided to the retort to supply the oxygen necessary for the sulfide 

decomposition and to enhance the heat transfer to the waste. 

The equations for decomposition of both forms of mercury are presented 

below: 

(a} HgS + 02 • Hg + 502 

5.3 Description of Retorting Process 

The retorting process generally consists of a retort (typically an oven, 

i.e., mu1tiple hearth furnace or rotary kiln} fn which the waste is heated to 

volatilize the metal constituents, a condenser, a metals collection system, and 

an air pollution control system. Figures 24 and 25 show a retort system without 

and with a scrubber-type air pollution control system. 

Trays of wastes are placed in the retort, where they are heated, and 

decomposition of mercury compounds and volatilization of the metallic mercury and 

f:\document\15254031.01.022 222 
PREHEATED 

AIR 

RETORT 

COOLING 

WATER 

-------------... -• ..__ wAs·re 

INFLUENT 

TRE~TED RESIDUAL WASTE TO 8JABJLIZATION 

AHPIOH LAND DISPOSAL 

... 

AIR POLlUTION...__-.&... __ 

CONTROL 

SYSTEM 

METAL 

COLLECTION 

VOLATILE UI::T ALS 

TO REUSE 

EXHAUST AIR 

TO THE ATMOSPHERE 

r 

-4--STACK 

Ftgure 24 Retorttnv Process (Vtthout a Scrubber and Subsequent Wastewater Dtscharge) 

.. , 
EXttAUST AIR 

TO THE ATMOSPHERE 

t 

WATER 

._STACK 

PREHEATED 

AIR 

DECANTER 1---t~ WASTEWATER TO TREATMENT 

u RETORT 

r-------7.i::l-- WASTE 

INFLUENT 

TREATED RESIDUAL WASTE TO STABILIZATION 

AND/OR LAND DISPOSAL 

VOLATILE 

L----.t~ METALS 

TO REUSE 

F1 gure 25 Retort 1 ng Process (M1 th a Scrub bur and Subsequent Wastewater Dt scharge) 
other volatile elemental metals occur. Although most commonly carried out in an 

oven, retOrting can also be performed in a multiple hearth furnace. 

t_ 

The vapor stream from the retort is cooled in a condenser. If a scrubber 

is not used as an air pollution control device, an electrostatic precipitator is 

provided after the condenser to remove any residual metal in the exhaust vapor 

stream, as well as to control other potential emissions such as sulfur dioxide 

(S02), fly ash, and hydrogen chloride (HCl) vapors. Condensed metal is collected 

for reuse before the electrostatic precipitator. 

Residual solids remaining in the retort, stripped of volatile metal 

contaminants, are collected and may be either directly land disposed or 

stabilized, to i11111obilize any remaining metal constituents, and then land 

disposed. 

5.4 Waste Characteristics Affect~nq Performance CWCAPsl 

In determining whether retorting will achieve the same level of performance 

on an untested waste that it achieved on a previously tested waste and whether 

performance levels can be transferred, EPA examines the following waste 

characteristics: (a) the concentration of undesirable volatile constituents in 

the waste and (b) the thennal conductivity of the waste. 

5.4.1 Concentration of Undesirabl~Yolatile Constituents 

Because retorting is a recovery process, its product must meet certain 

purity requirements prfor· to, reuse. · If the waste contains other volatile 

constituents with boiling points equal to or below that of the metal(s) to be 

recovered, they will be volatilized and condensed a 1 ong with the desired meta 1 ( s) 

present in the waste. These constituents may be difficult to separate from the 

recovered product and may affect the ability to reuse the product metal or refine 

it for subsequent reuse. Undesirable volatile constituents sometimes present in 

mercury-bearing wastes include (a) mercury chlorides, which distill unchanged in 

f:\document\15254031.01.022 225 
I 

I 

I 

I 

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I 

the retorting process, and other volatile metal halides; (b) arsenic oxide and 

arsenic trichloride; and (c) organomercury compounds, such as phenylmercuric 

acetate, which \~e not decomposed to elemental mercury by the retorting process. 

For wastes containing significant levels (i.e., above 1 percent) of these 

contaminants, retorting may not be an appropriate technology. If the 

concentration of undesirable volatile constituents in the untested waste is 

significantly higher than that in the tested waste, the system may not achieve 

the same performance. ·chemical pretreatment may be required to convert mercury 

chiorides and organomercury compounds to mercuric sulfide and/or elemental 

mercury and achieve the same treatment performance, or other, more applicable 

treatment technologies may need to be considered for treatment of the untested 

waste. 

5.4.2 Thermal Conductivity of the Waste 

The ability to heat canst ituents within a waste matrix is a function of the 

heat transfer characteristics of the waste material. Mercury and other 

recoverable metals in the waste must be heated to near or above their boiling 

points in order to be volatilized and recovered. The rate at which heat will be 

transferred to the waste materia 1 is dependent on the materia 1 's therma 1 

conductivity, which is the ratio of the conductive heat flow to the temperature 

gradient across the material. Thermal conductivity measurements, as part of a 

treatability comparison of two different wastes to be treated by a single retort 

system, are most meaningfui when applied to wastes that are homogeneous (i.e., 

uniform throughout). As wastes exhibit greater degrees of nonhomogeneity, 

thermal conductivity becoiiM!s less accurate in predicting treatability because the 

measurement reflects heat flow through regions having the greatest conductivity 

(i.e., the path of least resistance) and not through all parts of the waste. 

Nevertheless, EPA believes that thermal conduct1v.1ty may provide the best measure 

of performance of heat transfer. If the thermal conductivity of the untested 

waste is significantly lower than that of the tested waste, the system may not 

f: \docunent\1525-4031. 01.022 226 

, 
achieve the same performance and other, more applicable treatment technologies 

may need to be considered for treatment of the untested waste. 

t 

5.5 Design and Operating Parame~~~! 

In assessing the effectiveness of the design and operation of a retort 

system, EPA examines the following parameters: (a) the retorting temperature and 

(b) the residence time. 

5.5.1 Retorting Temperature 

Temperature provides an indirect measure of the energy available (i.e., 

Btu/hr} to vaporize the metal of concern. The higher the temperature in the 

retort, the more likely it is that the metal will volatilize. The temperature 

must be equal to or greater than the boning point of the metal. However, 

excessive tem~eratures could volatilize undesirable constituents into the 

product, possibly inhibiting its potential reuse, and also could cause sintering 

of the feed material. For mercury retorting, EPA monitors the retort temperature 

to ensure that the system is operating at the appropriate design condition (a 

temperature at least equal to the boiling point of mercury (674.F) but below 

lOOO.F) and to diagnose operationa1 problems. 

5.5.2 Residence i1me 

The residence time impacts the amount of volatile metal volatilized and 

recovered. It is dependent on the retort temperature and the thermal 

conductivity of the waste. Typical residence times in retort systems for mercury 

range from 4 hours to 20 hours. EPA monitors the residence time to ensure that 

sufficient time is provided to effectively volatilize all of the mercury and/or 

other metals to be removed from the waste. 

f:\document\1SZS403l.Ol.OZ2 227 
5.6 References 

Occidental Chem~al Corp. 1987. Oelisting petition, chloralkali plant, Muscle 

Shoals, Alabama. Submitted to U.S. En vi ronmenta 1 Protection Agency, July 20, 1987. 

Perry, R.A. 1984. Mercury recovery fr:= contaminated wastewaters and sludges. 

PB 238 600. 

Sittig, M. 1975. Resource recovery and recycling handbook of industrial 

wastes. Park Ridge, N.J.: Noyes Publications. 

Versar. 1987. Waste minimization audit report - case studies of minimization 

of mercury bearing wastes from chloralkali plants. Prepared for U.S. 

Environmental Protection Ag::ncy, Office of Research and Developmer.t, Hazardous Waste Engineering Research Laboratory by Versar Inc., Contract 

No. 68-01-7053. 

f:\document\15254031.01.022 228 

, 

i 
t 

III. TECHNOLOGIES APPLICABLE TO MIXED WASTE (RADIOACTIVE~RDOUS) 

, 
Introduction 

This sectiun describes the treatment technologies applicable to mixed waste 

(i.e., waste that is both radioactive and hazardous). This introduction explains 

what mixed wastes are and how they are classified, where they are likely to be 

generated, and how they are regulated. Following this introduction are sections 

discussing (a) technologies for treating mixed wastes containing organics and 

in(jrganics other than metals, (b) technologies for treating mixed wastes 

containing metals, and (c) technologies for treating mixed wastes that cannot be 

treated by technologies d2termined to be BOAT for the corresponding 

nonradioactive wastes (i.e., special mixed wastes treatability group). Each of 

these three sections includes subsections describing applicable treatment 

technologies. 

Mixed-wastes are those wastes that satisfy the definition of radioactive 

wa~te subject to the Atomic Energy Act (AEA) and that also contain waste that 

either is 1 i sted as a hazardous waste in Subpart 0 of 40 Code of Federal 

Regulations (CFR) Part 261 or exhibits any of the hazardous waste characteristics 

identified in Subpart C of 40 CFR Part 261. Because they are hazardous, mixed 

wastes are subject to the Resource Conservation and Recovery Act (RCRA) Land 

Disposal Restrictions. All promulgated treatment standards for RCRA listed and 

characteristic wastes apply to the RCRA mixed wastes unless EPA has specifically 

estabLished a separate treatability group for a specific category of mixed waste 

(see following Section C). Although mixed wastes are regulated by EPA under 

RCRA, the specific standards for radioactive material management developed under 

the AEA are administered by the Department of Energy (DOE) for government-owned 

facilities and by the Nuclear Regulatory Commission (NRC) for commercially owned 

facilities. The majority of mixed wastes can be divided into the following three 

categories based on the radioactive component of the waste: (a) 1 ow-level 

wastes, (b) transuranic (TRU} wastes, and (c) high-level wastes. Low-level 

wastes include radioactive waste that is not classified as spent fuel from 

commercial nuclear power plants or as defense high-level radioactive waste from 

the production of weapons. TRU wastes are those wastes containing elements with 

f:\document\15254031.01.023 229 
an atomic number greater than 92 (the atomic number for uranium). TRU wastes 

generally.pose greater radioactivity hazards than low-level wastes because they 

contain long-lited alpha radiation emitters. However, commercial transuranic 

waste is included as low-level radioactive waste. High-level mixed wastes havP. 

high levels of radioactivity and are extremely dangerous to handle. High-level 

mixed wastes are generated from the reprocessing of irradiated fuel rods from 

commercial and military nuclear reactors. 

Mixed low-level wastes are generated principally from nuclear power plants, 

the Department of Energy (DOE), and academic and medical institutions. Some 

examples of low-level mixed wastes include spent solvents containing suspended - or dissolved radionuclides, scintillation cocktails from diagnostic procedures, 

spent Freon used for cleaning protective garments, acetone or solvents used for 

cl~aning pipes or other equipment, and still bottoms from the distillation of 

chlorofluorocarbon solvents (CFCs). Other wastes in this category include a wide 

range of solid materials such as spent ion-exchange resins (contaminated with 

various metals), filters used in reclaiming CFCs, adsorbents, residues from the 

cleanup of spills, lead shields, lead-lined containers, welding rods, and 

batteries. Also, the production of military weapons produces large amounts of 

wastes that fall into the low-level and TRU categories of mixed waste. 

f:\document\15254031.01.023 230 

, 

. 
A. TECHNOLOGIES FOR MIXED WASTES CONTAINING ORGANICS 

AND INORGANICS OTHER THAN METALS 

The following technologies have been determined to be applicable for 

treating mixed waste. These technologies were described in detail in previous 

sections in this document for hazardous wastes that are not mixed. Technologies 

for mixed waste operate under the same principles of operation used for treating 

nonmixed waste. However, with mixed waste these technologies ~ypically separate 

the hazardous waste components from the radioactive components, thereby reducing 

the volume of the radioactive component requiring treatment, or immobilize the 

waste {in the case of stabilization technologies}. If the hazardous component 

is also radioactive (e.g., a hazardous solvent whose structure contains 

radioactive carbon}, that component may sometimes be removed from the waste; 

leaving a less hazardous, less radioactive residual. 

1. Carbon Adsorption 

For organic low-level mixed wastes, carbon adsorption may be used to remove 

organics in wastewaters. If the organic component is not radioactive, then this 

treatment reduces the quantity of the hazardous waste component in the mixed 

waste. 

2. Distillation Technologies 

A distillation technology such as batch distillation, steam stripping, 

fractionation, thin film evaporation, or thermal drying may be applied to a mixed 

waste in that it can be used to separate the mixed waste into the hazardous and 

radioactive waste components, as long as the hazardous component is not also 

radioactive. The separation can be made where the volatility of the hazardous 

components is significantly different from the volatility of the radioactive 

components. The distillation process will remove the more volatile organic 

components, leaving the less volatile constituents in the still bottoms. 

f: \doc1111ent \15254031.01.023 231 

, 
.. 

3. Extraction Technologies 

As with d{.stillation, extraction technologies {i.e., solvent extraction and 

critical fluid extraction} may be used to separate a mixed waste into its 

radioactive and hazardous components if either the hazardous or the radioactive 

components can be selectively extracted by the extracting solvent. 

f:\document\15254031.01.023 232 
B. TECHNOLOGIES FOR MIXED WASTES CONTAINING METALS 

1. Ac~d Leaching 

Acid leaching may be used to extract hazardous metals (regardless of 

whether the metals are radioactive) from mixed wastes, principally soils, 

separating the material into its hazardous and radioactive components or removing 

the hazardous and radioactive component from the rest of the waste. This process 

may have greater utility when combined with unit operations such as ion exchange, 

solvent extraction, chemical precipitation, and filtration. 

2. Chemical Precipitation 

Chemical precipitation may be applicable to mixed wastes for separating 

hazardous metals and/or hazardous metal radionuclides from other constituents in 

wastewaters. Specific conditions of pH, temperature, and precipitating reagent 

addition are required to selectively remove part or all of the radioactive 

components ~c a precipitate. 

3. Filtration 

Filtration technologies may be used following precipitation and settling 

proce.sses to separate low-level mixed waste from high-level mixed waste. Hence, 

-filtration may concentrate the high-level waste components in the filter cake, 

leaving a relatively low-level filtrate. 

4. Hfgh Teuperature Metals Recovery 

The hfgh temperature metals recovery (HtMR) process may be applicable to 

mixed wastes if the volatility of the radioactive metal component is 

significantly different from that of the nonradioactive portion. This technology 

is similar to distillation of organics, but instead •distills• more volatile 

inorganic components from less volatile ones. 

f:\document\15254031.01.023 233 

, 

I 
5. Ion Exchange 

Ion exclfilnge treatment may be used to separate a mixed waste into its 

radioactive and hazardous constituents if the radioactive components are ionic. 

It will also concentrate the radioactive ionic species into a small volume, 

leaving a nonradioactive aqueous phase. The principal mixed waste application 

of this process is to recover metallic radionuclides from wastewaters or acid 

leach liquors. If more than one radionuclide exists in solution, it may be 

necessary to use either a mixed bed ion exchange unit or different types of ion 

exchange resins to recover all the radionuclides. 

6. Stabilization of Metals 

Stabilization refers to a broad class of treatment processes that 

immobi1 izs hazardous constituents in a waste. For treatment of metals in 

low-level mixed wastes and for some TRU wastes containing low-level radioactive 

components, stabilization technologies will reduce the leachability of the 

hazardous metal constituents (regardless of whether the metals are radioactive) 

in nonwastewater matrices. However, EPA does not believe that stabilization 

using cementitious binders is an appropriate treatment for high-level radioactive 

mixed wastes generated during the reprocessing of fuel rods. It does not 

adequately immobilize the high-level radioactive portion of the mixed wastes. 

f:\doc~nt\1SZ5403l.Ol.OZ3 234 
C. TECHNOLOGIES FOR MIXED WASTES IN SPECIAL TREATABILITY GROUPS 

1. AmaJsamati on 

Amalgamation is applicable to radioactive wastes containing mercury and 

particularly to wastes containing radioactive mercury isotopes. Mercury 

compounds are converted into a solid mercury-zinc alloy, which is more easily 

managed and less mobile than solutions containing radioactive mercury. The 

process can be used directly with radioactive wastes provided that additional 

precautions are t~ken to prevent release of radioactive materials and to protect 

operations from radioactive emissions. 

The Agency has established amalgamation as a method of treatment for mixed 

wastes containing elemental mercury. These types of wastes are typically found 

in vacuum pumps and related manometers. In the nuclear industry, this form of 

mercury has been contaminated with radioactive tritium (a radioisotope of 

hydrogen). 

EPA has determined that amalgamation not only provides a significant 

reduction in air emissions of mercury but also provides a change in mobility from 

liquid mercury to a paste-like solid, potentially reducing leachability. The 

required method of treatment, i.e., amalgamation, may be performed using any of 

the following elements: zinc, copper, nickel, gold, and sulfur. Further 

~formation on the amalgamation process may be found in Section I.B.l. 

2. Encapsulation 

Encapsulation processes such as plastic and asphalt encapsulation may be 

used for the management of mixed wastes. However, the equipment used for mi!ing 

of the wastes with molten encapsulating agents must be of special design to 

prct~ct workers from radioactive hazards. Additional precautions may be neaded 

to prevent generation of airborne particulates or vapors of radioactive material 

f:\document\152~031.01.023 235 

, 
during the processing. More information on encapsulation may be found in the 

encapsulation se~tion (see Section 1.8.3). 

{. 

The Agency has established a treatment standard of macroencapsulation 

(encapsulating an entire mass, rather than microencapsulation, which coats 

individual particles of a waste) as a method of treatment for radi~active lead 

solids. This treatment standard applies to all forms of radioactive mixed waste 

containing _elemental lead (including discarded equipment containing elemental 

lead that served as personnel or equipment shielding prior to becoming a RCRA 

hazardous waste). These lead sol ids do not include treatment residuals such as , 

hydroxide sludges, other wastewater treatment residuals, or incinerator ash, 

which are usually amenable to cu.wentional pozzolanic stabilization, nor do they 

include organolead materials that can be incinerated and then stabili:ed as ash. 

3. Vitrification 

Vitrification is a treatment technology tnat will provide effective 

inunobilization of the inorganic constituents (i.e., both radioactive and 

hazardous components) of a mixed waste. Vitrification has been demonstrated to 

be an effective treatment technology for high-level mixed waste generated during 

the reprocessing of fuel rods. Since vitrification is a high-temperature 

process, small quantities of organics that may be present will be volatilized 

dur;ng the vitrification process. If there are gaiJitla-emitting radionuclides 

.present, the ga11111a dose rate will be reduced as a result of the increase in 

density of the vitrif;ed matrix (go;ng from the density of soil or other solids 

to the density of glas~). If rad;um is present, the radon flux rate wnl also 

be reduced because of the change in the dens;ty. Both alpha and beta emitters 

will be sealed in the glass matrix. More information on the vitrification 

process may be found in the vitrif;cation section (see Section I.B.S). 

f:\document\15Z5403l.Ol.OZ3 236 

~ I 

f 
4. Incineration 

Incineration is a technology applicable to nonradioactive elemental mercury 

(i.e., retorting) waste containing high 1 evel s of organics. The Agency has 

determined that incineration is also an applicable technology for 

mercury-containing hydraulic oil contaminated with radioactive material 

(low-level mixed waste) and has set incineration as the standard (method of 

treatment) for that waste. Incineration of radioactive mercury and other 

volatile mixed waste components is likely to cause the mercury or other volatile 

components to volatilize. Therefore, incinerator~ ::u:t be equipped with air 

poll uti on control devices to ensure that any volatilized hazardous and/or 

radioactive components are not re 1 eased to the atmo5phP-re above permitted 1 eve 1 s. 

Incineration of organic wastes containing concentrations of the radionuclides 

tritium and carbon 14 will cause the esr.ape of radioactive compounds since the 

combustion products of tritium (radioactive hydrogen) and carbon 14 are steam and 

carbon dioxide, respectively, both of which will usually escape conventional air 

pollution control devices. 

f:\document\15254031.01.023 237 
References 

U.S. Congress, ~ffi ce of Technology Assessment. 1989. Partnerships under 

pressure: managing conunercial low-level radioactive waste. Washington, D.C.: U.S. Government Printing Office. OTA-0-426. 

USEPA. 1990. U.S. Environmental Protection Agency. Federal Register Notice, 

55 FR 22626, June 1, 1990. 

U.S. General Accounting Office. 1989. Fact sheet for the Chairman, Environment, 

Energy, and Natural Resources Subcommittee, Committee on Government 

Operations, House of Representatives; Nuclear Waste, DOE's program to 

prepare high-level radioactive waste for final disposal. Washington, D.C.: U.S. General Accounting Office. 

U.S. General Accounting Office. 1989. Report to the Chairman, Committee on 

Governmental Affairs, U.S. Senate; Nuclear Regulation, the military would 

benefit from a comprehensive waste disposal program. 

Westinghouse Electric Corp. 1983. Waste technology reprints: Nuclear waste 

management in the United States. 

f:\document\15254031.01.023 238 
t 

APPEND!~ A 

LIST OF BEST DEMONSTRATED AVAILABLE TECHNOLOGY (BDAT) BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S) 

f:\document\15254031.01.024 
This appendix contains a list of BOAT background documents prepared for 

EPA's Office of Solid Waste, Waste Treatment Branch, in support of the Land 

Disposal Restrtctions. (The specific Third under which each document was 

prepared is a 1 so noted.) This appendix is meant to be a quick reference, 

however, for details on a specific waste code see the relevant background 

document for that waste code. In summary, this appendix presents the following: 

• The waste codes, industries, or sources of the waste associated with 

each background document. 

• The treatment technologies on which the treatment standards were based 

i.e., BOAT. The BOAT associated with each background document is also 

identified. (Note that BOAT(s) may vary for individual waste codes. 

contained in a background document. Fllr specific information on the 

BOAT applicable to a certain waste code, see the applicable background 

document.) 

• The source of the treatment data used to set the treatment standard and 

whethsr the data were collected or submitted to EPA (actual data) or 

transferred from existing data. 

• The category of waste treated ( 1 . e., organics, i norg.an i cs, meta 1 s). 

A-1 

f:\document\15254031.01.024 
,J:>o 

I 

N 

Yaate Code/ 

Third CBackgrotnJ Doc~.~~~ent) 

1/l f001·f005 (revlud for .. thyl~ chloride) 

1/] f006 

1/l K001 

1/l K01S 

1/l 1(016, K018, K019, 

IC020, IC030 

1/] IC022 

1/3 IC024 

1/3 1(0]7 

1/l IC044, K04S, IC047 

1/3 IC046 (nonreactlves) 

LIST bF BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S) 

Industry or Source of Yaate 

f'tla,...ceut I cal 

Industry 

Electroplating 

operatlona 

Wood preaervlng Industry 

Distillation of benzyl 

chloride 

Chlorinated organics 

produc: t I on 

Phenol/acetone 

produc: t I on 

Phthalic anhydride 

produc: t I on 

Olaulfoton production 

"anufacturlng end 

proceBSinQ of 

explosives 

Lead-based lnltlatlns c~ proc1Jct ion 

BOAT( a) 

Ste .. stripping (waatewatera) 

Stabilization (nonM8atewatera) 

Rotary kiln Incineration, 

Stabilization (nonwaatewatera, 

wastewaters): chealcal precl~ltatlon 

( .. tala In waatewatora) 

Ll~ld InJection lnclfMiratlon 

(nonwaatewatera); che.lcal 

precipitation (wastewaters) 

Rotary kiln Incineration 

(nonwaatewatera, waat~tera) 

fuel substitution, atablllzatlon 

(nonwaatewatera) 

Rotary kllfl Incineration 

<~•stCNatera, waatewatera) 

Rotary kiln Incineration 

(nonwaatewaters, wastewaters) 

Open burning/Open detonation, 

Incineration (nonwaatewatera) 

Stabilization (nonwastewatera) 

Actual Data or Transferred 

and 

ortaln of Data 

Data/lndustry·a~ltted 

Oata/lndustry·a~ltted 

Data/EPA test, 

tranafer/F006 

Tranafer/K019 

Data/EPA test 

Data/lndustry·a~ltted, 

tranafer/F006 

Data/EPA test 

Oata/fPA test 

Data/DOD 

Data/EPA test 

Types of ' 

Yastes Regulated 

Methylene ch~orlde 

Metals, cyanides 

Organics, metals 

organics, metals 

Organics 

Orsanlcs, metals 

Phthalic a!;ld 

Disutfoton, toluene 

Reactive waste from 

IC044, IC04S, K047 

Leac;l Cnaetals) 

---
LIST Of aDAT BACKGROUND DOCUHfNTS AND ASSOCIATED BDAl(S) 

Actual Data or Transferred 

Waate Code/ l~try or and Types of 

Third (BackgrCUld Doc..-ent) Source of Waste IOAT(II) origin of Data Uastea Regulated 

..... 

1/l l048·l052 Petrol refining Solvent extractloni fluidized bed Data/Industry-submitted Organlc.s, ~tala, 

lnc1Jatry lnclneretlon, ateb llzetlon Inorganic& 

(nonMasteMatera); lnclneretlon, 

chr011IU1 racbctlon, ch•lcal 

precipitation, lind filtering (WaSteMatera) 

1/] IC061 Prl•ry at .. l High te.perature -tala recovery for D"ta/£PA teat "ctols 

production l~try hlih zinc aubcategory, atablllzatlon 

for low zinc atJJcateaorv 

1/] l062 Steel finishing fru. Chru.IUI re<b:tlon, ch•t.:al Data/EPA test "etals 

Iron and ateel precipitation, aettllng, filtering procb:tlon (nonwaatewatera, wastewaters) 

);:a. 

Secondary 1 ead Recycling (noncalclu. aulfate Data/lnduatry·s~ltted "eta Is • 1/l K069 w ... ltlna oporatlona category); (nonwaatewatera) 

1/3 K071 Chlorine procb:tlon Acid leaching, ch•lcal oxldat ion Oata/lndustry·submftted "ercury 

fr011 the •rcurv aludue dewatering/acid washing 

cell process (nonwesteMatera), ch•lcal 

preclphat I on end f II terlng (wastewater•) 

1/l IC081 Dlatlllatlon botta.s Liquid Injection lnclneretlon Date/Industry-submitted Organics 

fr011 aniline prcOictlon (nonwasteMaters, wastewaters) 

1/l 11:086 Solvent washea end Liquid Injection Incineration Data/EPA test, Organics, metals 

sludges fro:~ the cnonwastewatera, wastewaters); tranafer/IC062 

procb:t ion of I nita, chr011ha recb:tlon, cheilllcol 

pluments, soaps, end precipitation, settling, stablllzera filtering (wastewaters) 
·-----------

LIST Of BOAT BACKGROUND OOOUMfNTS AND ASSOCIATED BDAl(S) 

Actual Pate or Transferred 

Waste Codef II'OJitry or and Types cU 

Third (8ac:kgr0t.nd Doc~t) Source of Waste BOAT( a) Origin of Date Wastes Regulated 

II'\ 

I 

113 KOll7 Tar aludge fr0111 , Rotary kiln Incineration Data/EPA test, Organics, metals 

coking operatlooa (nonwaatewatera); transfer/K06Z 

chrcxaha re<1ittion, thtllltal 

prccipitatton, aettllna, 

filtering (w.atewatera) 

\/3 1(099 2,4·Didhlorophenoxy· Chetalce\ oxidation (nonwastewatera, Data/EPA collected Z,4·Dichlorophenoxy· 

.cetlc .cld (2,4·D) Waatwetera) aoet ic acid, dllorireted 

procb:tlon dibenzo·p·dioxins, 

dllcrlrated dii:Jcnrof\.nm 

1/1 K1D1, IC1D2 Pradctlon of Rotary kiln Incineration Data/EPA test, Organics, metals 

v.terlnery (nonwaatwetera); ch.,.lcal tranafertK06Z 

pha.-..ceut I ula trcxa precipitation, aettllne, 

ereenlc fllterlna (wastewaters) 

):a liS l10:S, l104 Aniline/nitrobenzene solvent extr.ctlon, ate .. atrlpplng, DatatEPA teat Organics, inorganlcs I 

.$» procb:tlon end activated carbon ed$orptlon (cyanides) 

followed~ Incineration of the 

aolvent atre .. fr0111 extraction 

cnonwaatewatera, waatewatera) 

\/:S 1(106 Sludges fr~ the Therwal recovery (retorting) Date/Industry-submitted Mercury 

-rcury cell process (nonwastewatera) 

In chlorine procb:tlon 

1/3 1(0(\ft·ICDOa, IC021 Plg.enta, fluoro· Chra.lus r.m.:tlon, carbon Datatlndustry·sua.ltted Metals, organics 

1(025, K036, K060, -th-, nitrobenzene, edsorptlon; chetalcel oxidation 

l100 (no doc~aent dlaulfoton, coking end •t•l precipitation 

prepared) end lead pr~tlon (nonwastewetera, wastewaters) 

2/'S f006·f012, f019 Electroplating, heat Alkaline chlorination, Deta/lndustry·submltted Cyanides, metals 

treating operations stabilization (nonuaatewaters), 

alkaline chlorination, chemical 

precipitation, settling, 

filtering (wastewaters) 

l.\docoun-.1111i21i40l1.01.021i 
::J:a 

I 

Ul 

waate Code/ 

ThIrd C Background Doc..-nt) 

2/l K011, K013, k014 

2/3 Cyenlde P wastes 

(P013, P021, P029 

POlO, P063, P074, P09B, 

P099, P104, P106, P1l1) 

2/l f024 

2/l Inorganic pl~tl 

(k002-k008) 

2/3 k009, k010 

2/l K02], K093, K094 

U028, U069, U088, 

U102, U107, U190 

2/3 k027, K111, K112 

K11l, k114, K115, 

K116, K221, UZ23 

2/l k028, kOZ9, K09S 

IC096 

I ,...,~•~n•nr\lb1b40l1 01 02b 

LIST Of BOAT BACKGROUND I)()(UtfNTS AND ASSOCI . .TED BDAf(S) 

lnct.Jstry or Source of Waate 

Acrylonitrile 

procb:tlon 

Cyanide P wutea 

. 

Chlorinated allphatlca 

procb:tlon 

PI g11e0t1 procb: t I ()t'. 

Acetaldehyde product!~ 

Phthalic anhydride procb:tlon 

Toluene dllaocyanate production 

1,1,1,-trichloroethane 

F>f oduc: t I on 

BOAT( a) 

Rotary kiln lnctneratlon 

(MonNUt-tara) 

Electrolytic oxidation, alkaline 

chlorination, atablllzatlon 

(nonwaatewatera), alkaltne chlorination, 

chealcal precipitation, settling and 

filtration (waatewetera) 

Rotary kiln Incineration 

(nonwaatewatera); rotary kiln 

IC1Cineratlon, U• and aultlde 

precipitation, vac:LUI filtering 

(weat-tera) 

Not eatabl llhed U'lder Z/l 

rule; ae!l l/3 

Rotary kiln Incineration c~·t-tera); at~ .. atrlpplnu, biological treet.ent (waatewatera) 

Rotary kiln Incineration 

(nonwaatewatera and wastewater&) 

Incineration or fuel a~tltutlon 

cnonwaatewatera); dlrec:t lnciner.at ion, or carbon edsorptlon followed by 

Incineration or fuel substitution, 

stabilization (wastewaters) 

Incineration, ateblllzatlon 

(nonwastewatera); ll• and sulfide 

precipitation (waatewatera) 

Actual Data or Tr1101ferred 

and 

Origin of Data 

Data/EPA t::.at 

Data/lndustry·s~ltted, 

tranafer/F006-f012, f019 

Data/lndustry·a~itted, 

tranafer/K062 

See 3/l 

Tranafer/K.019, 

Transfer/data tr~ 

Ott Ice of Water 

Tran~~fer/IC024 

Transter/11:015, IC086, 

f006 

Tranafer/IC019, 

Transfer/IC062 

Typea of 

\laatea Regulated 

Acryta11t r II es, qllllidcs 

Cyanides, .etala 

Organics, ~tala 

See 3/3 

Organics 

Organics 

Organics, -.rats 

Organics, ~tala 

'> 

I 

I 

i 

__ _j 
;J:a 

I 

0'1 

Waste Code/ 

Third (Beclt"rcxm Doc~t) 

2/l KOl6, K038, K039, 

K040, P0l9, P040, 

P041, P043, P044, 

P062, P07, PD85, 

P089, P094, P097, 

P109, P111, uose, uoa7, U2ls 

l./l K04l 

2/l K069 (Calclu. 

aul fate) 

l/] DOOI 

ltl DOOZ 

l/l DOOl 

1.~1116264031.01.026 

LIS~ Of RDAJ BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S) 

lnduatry or Source of Waate 

Organophoaphorous 

peatlcldo product,on, a.11., dlaulfoton, 

phoratea, .and othr• 

P end U wastes 

J 

2,4-Dic:hlorophenol 

procb:tlon 

secondary a .. ct 

-ltlng ·~try 

Waatea having the 

charecterlatlc of 

lenlteblllty 

Waatea having the 

characterlatlc of 

corroalvlty 

Uutea having the 

dlaracterlatlc 

of reactivity 

BOAT( a) 

Rotary ltlln Incineration 

Cnonwastewatera); biological 

lneration Cwaatewetera) ~ • ...,,. '"'"'" .... ,p,loo 

Incinerator (nonweatewetera, 

-tewetera) I 

Stabilization (nonweateNatera); 

c:hra.tu. reclJctlon, c:h•lcal 

preclpl tatlon, t•ttllng, and/or 

filtering (Maatewatera) 

Deactivation" to re.we 181\ltablllty, 

~Incineration/fuel albstltutlon, 

ovary for hlah roc 0001 

DfKtlvatlon" to r..ave corroalvlty 

Deactivation" of cyanides; albtlne 

except for cyanides; alkaline 

chlorination (clanldea) 

I 

Actual Data or Transferred 

and 

oriSIIn of Data 

Transfer/IC037, 

Data/lndustry·s~ltted 

Data/lndustry·aubaltted 

Jransfer/f006 

and K062 

lnfo~tlon referencea 

lnfor.-tlon references 

lnfor.etlon references, 

Industry a~itted data, 

transfer/Office of Water 

. Types of 

Wastes Regulated 

Organ f cs, org3llQJilos-

,tau; cx:npa.rd;, dil»>illi 

and furans 

Phenols, dioxins, 

and furans 

Metals 

~astu having the 

characteristic 

of fgnltablll ty 

~aste having the 

character 1st lc 

of corror.lvl ty 

~estes having the 

charactc-rf st fcs 

of reactivity 

. _ __......, 
LIST qF BOAT BACICGRll.IHD DOCUMENTS AND ASSOCIATED l'OAT(S) 

Actual Data or Tr-ferred 

Waste Code/ lrnatry or and Types of" 

Third (lackgrcxnd DocU~mt) Source of Waste BDAT(s) llrlgln of Data Wastes Regulated 

.... I 

3/3 Arsenic, selenlua, (DOD4, characteristic and VItrification (nonwaatewaters); beta/Industry-submitted Arsenic, ~tats, 

OD1D, K031, K084, K101, P&u wastes I k wastes cheatcal precipitation (wastewaters) trtnsfer/Offlce of Water lnorganlcs 

IC102, P010, ~011, P012, for arsenic and 

P036, P038, P103, P114, aelenlu. and waatea 

P204, P205, U136) fra. veterinary pf'lar.Keut fcala 

proclJCtfon 

3/3 Bartua (0005, P01J) Characteristic and Stabilization Cnonwastewaters); Data/Office of Uater, Barha 

P wasta for berlua ch•lcal precipitation Data/lrO.Atry·a~ltted 

settling, filtration (wastewaters) 

J/J c..-lua (0006) Characteristic wasta 5tablltzatton, then.al recovery Data/lrO.Atry-submltted, CIKhlllll 

for c..-lua (c~tua bettert .. ) (nonwastewaters); transfer FOD6, ICD62 

ch .. lcal precipitation, filtration 

(wast .... tara) 

:P 

I 3/3 Chro.h.- (0007, U032) Char.cterlallc .nd Chr0111l._ r~\ I on, ChCIIIUl Transfer/l062 Chrllnlh.a -.... U wastes for chra.lu. precipitation, settling, filtration, 

dewatering of ao\tda (nonwaatewatera 

and wastewatara) 

J/3 lead (0008, IC069, Characteristic and Stabilization/vitrification (non· Data/lnduatry·submltted Lead, organometallic 

K100, P110, U144·U146) u&P wast .. for le8d, wastewater•>; ch•lcal precipitation, c~ 

Mld K waate fro. flocculation, clarification, filtration, 

leMi .. ttlne Md sludge thlckenlne (wastewaters) 

operations 

3/J Mercury (0009, IC071, Characteristic and Therael proceastng, Incineration Data/lndustry·subml\ted, Ptetals, Of"9ii'UII!Ialllc 

K106, P065, P092, u&P waatea for acid leaching, roasting, retorting trans fer /IC071 c:~ 

U151) .. rcury and K waste -lg-tlon, stablllzat I on fro. chlorine (nonwastewaters); ch .. lcal 

procb:tlon precipitation, filtration, 

Incineration, ion exchange, 

carbon adsorption (wastewaters) 

3/l Silver (0011, P099, Characteristic wastes Recovery, stabilization Data/Industry-submitted, He tala 

P104) for silver, and P (nonwastewater .. >; and transfer/F006/ 

allver wastes chemical preclflltat ion, fit trat ion Of fl ce of Water 

(wastewaters) 

l.\doc..,_,l\lb2b40JI 01.026 

.. ..-..A 
:J::o 

I 

Ol 

U.ate Code/ 

Third C&.ckground Docu.ent) 

]/] Thalllu. (P11l, P114, 

P115, U214, U215, 

U216, U217) 

]/] Venadlua (P119, P120) 

]/] f002, fOOS 

]/] f006 

]/] f019 

]/] F024 

]/] f0Z5 

:s,;s f039 and associated 

u&P wastes (Vol. A-E) 

liST OF BDAT BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S) 

lncbltry or Source of W.ate 

UI.P thallua .... t .. 

u&P venwtlua .... t .. 

' 

Spent hal ogene ted W1d 

..-ilal ogan~~tad 

solvents 

S l udiea f rCfl 

electroplatlna 

operation I 

Sludges frflfl tha 

c:h•fcal c~ralon coating of ah•l,.... 

I 

Productton of 

c:hlnrlnatad allphst lc hyd·oca~ 

Wsatn frflfl ~cdJctfon 

of chlorinated 

aliphatic hydrocsrbonll 

having can-t chain 

linkage 

Kultfsource leachate 

and u&P wastes 

IOAT(a) 

Recovery, stabilization 

(nonwastewatera); 

cha.lcal oxidation chealcal 

precipitation .. ttllne, filtration 

( .... twatera) 

Sttblllzatlon (nonwaatewatera); 

recovery. ch•lcal precipitation (NIIat .... tera) 

Incineration (ncwwutwatera); 

biological treat.-nt, ate-. atrlpplne • carbon adsorption • -t air 

o111ldat lonlc:h•lcal olllldatlon 

liquid e111trac:tlon (waatwaters) 

Stabilization (nonwaat~tera); 

a~lne chlorination, ct\rOMI.,. r tlon. ch .. tcal ~ec:lpltatlon 

,.,...t .... ter-) 

Alkaline chlorination. stabilization 

(nonwastewatars); alkaline 

chlorination. c"ro.h• rocNt:tlon, 

chealcal precipitation ( .... tewaters) 

stabilization, Incineration 

(nonwastewatera) 

Incineration (,__Uewatera) 

blotrest.ent, are-. stripping, 

carbon adtorptlon, liquid extraction (wastewaters) 

See Footnote b. 

ActUIIl Data or rr-ferred 

IIHld 

Origin .Jf Data 

Data/lndustry-suaaltted 

Data/lnduatry-aubmitt~ 

Transfer/EPA dots tron~ 

various aourLes 

Transfer/JCD62 

Transfer/F006-F012 

Data/EPA test 

Jranater/K019. K001, 

F039 (Vol. A) 

Data/transfer/EPA data 

f r0111 veri ous sources and 

EPA test 

Types ·of 

Wastes Regulated 

Metals 

Metals 

Organics 

Hetels, cyanides 

Metals. cyanides 

Metals, organics 

Organics 

Metals, lnorganlcs, organics 

~ jf 

,, 

'I 

,, 

---
Waate Code/ 

Thl rd CBac:kgrOU'ld Doc"*fft) 

3/3 K001, U051 ( addendull) 

3/3 KOOZ·KODa 

l/3 ICOU, IC013, IC014 

3/3 IC015 

3/3 K017 

:P 

I 

o.D 3/3 K021 

3/3 IC073 

3/3 KOZ2 

3/3 K025 

3/3 ICOZ6 

l.~l\ll>2b40.ll.01.021> 

LIST Of BOAY BACKGROUND DOtUMENTS AND ASSOCIATED BDAT(S) 

lnct.atry or 

~GurU of Weate 

Wood pre.ervlng II'Qatry 

PI s-ent I rQ. try 

...... 

Acrylonitrile, 

prcdlctlon 

Still botta.a froa 

dlattllatlon of 

benzyl chloride 

Procbctlon of 

eplchloroflrdrln 

Aqueoua ant I~ 

catalyst froa 

fluoroaethprocbctlon 

Chlorine product I on 

BottOIIB, tara 

froa production of phenol/acetone 

Dlatlll•tlon 

bottar.a fr~ the 

product!::., of nitro· 

benzfalla froa the produc:· 

tlon of ~thyt ethyl pyridine• 

BOAT( a) 

Incineration 

(norwastctwatera, wastewaters) 

Che~~lcal prcclpltetlon, atabltlzetlon 

Cnonwastewatera); alkaline 

chlorination followed by chr011ha 

rec1Jctlon (waatewatera) 

Wet air oxidation (weatcwatera) 

Incineration, atablllzatlon 

( nonwaa tewatera) 

Incineration cnonwaatewatera); 

blotraat..nt (waatewatera) 

Incineration (nonwaatewatera); blotreat.ent, ate .. atrlpplng, 

ll• conditioning, aedl.entatlon, 

Filtration (waatewatera) 

Incineration Cnonwastewatera); blotreat~t. ate .. atrlpplng, 

filtration (waatewatera) 

Cha~lcal preclplt11tlon, vaclUI 

filtration (wastewater•) 

Incineration (nonwaatewatera); 

llquld·llquld extraction, 

ate .. atrlpplng, carbon adsorption, 

Incineration of apent carbon 

(wastewatera) 

Incineration Cnonwaatewatera, 

wastewaters) 

Actual Data or Transferred 

.,.. 

Origin c,f Date 

Data/EPA test 

Data/transfer/Industry, 

Ka62, trensfer/F006 

Deta/lndustry·submltted 

Transfer/K048·5Z, K087, 

trenafer/F039 (VolURe A) 

Tranafer/F039, 

(Vol. A and C) 

Tranafer/K019, K048·52, 

F039 (Vol. A) 

Tranafer/K019, 

tranafer/F039 (Vol. A) 

Tranafer/F039 (Vol. A), 

Ktl6l 

Transfer/previous EPA 

Incineration tests, 

tranafer/K103·K104 

Transfer/prevlcua 

Incineration tests 

. Types of 

U&stea Regulated 

Organics, metals 

Metals, lnorgonlcs 

Metals, organics 

Organics, ~tala 

Organics 

Metals, organics 

Organics 

Metala, organics 

Organics 

Organics 
JP> 

I 

...... 

0 

Waste Code/ 

Third (Backl!rot.nd Doc~t) 

3/3 IC028, IC029, 

1(()95 • 1(096 

K03Z·K034, K041·K042, 

K005 I K091 I K09DI 

K105, DD12·DD17 

3/3 IC035 

3/3 IC036 

l/3 IC037 

3/3 IC044, IC045, K047 

3/3 K046 (re.ctlves) 

I.~I\H•21>4<l31 .01.025 

LISt OF BOAT BACKGROUND DOCUMENTS AND ASSOCIATED BDAT(S) 

l,.._try or 

5ourca of W.sta 

Wastes fra. 

procb:tlon of 

1,1,1-trlchloroethene 

Halogenated pesticides 

Md chlorabenlene · .... c. 

wast~ter treat.ent 

sludges fra. the 

prod;JC t I on of 

creoaota 

Stitt botta.s fra. 

toluene recl ... tlon 

distillation In the 

procb:tlon of 

dlsulfoton 

W.at~ter treat.-nt 

Sludges fra. the 

Procb:tlon of 

Dlaulfoton 

Manuf.cturlng 

axptoalvea .,-d teed· 

based lnltl~tlng 

cOIIpO'nia 

Lead·baaed Initiating 

cOIIIpOUOda 

BDAT(s) 

Stabilization (nonwastewaters); 

blotreatmeot, -tea. stripping carbon adsorption, 

filtration c~•tewatera) 

Incineration (nonMaatewatera) 

btotreat..nt, atea. stripping, • carbon adsorption, l lq.ald 

extr.ctlon Incineration/wet 

air oxldatlon/ch~lcal 

CIOJIIdatlon c ... stW~~ters) 

Incineration (nonwaatewaters); 

blotreat-.nt (wastewaters) 

Incineration (nonwastewaters for 

dlsulfoton) 

Biological treet.ent (wastewaters) 

De.ctlvatlon, settling and flltratlo~. 

alkaline precipitation (wastewaters) 

Deactivation by cha.lcat tre~t~t or special hed Incineration followed 

by stabilization (nonwastewaters); ch~lcal deactivation followed by alkaline precipitation, settling, 

and filtrating (Nastewaters) 

Actual Data or Transferred 

Mld 

Origin of Data 

Transfer/FD39 (Vol. A), 

transfer/FD24 

Transfer/EPA data 

Transfer/IC087 

Transfer/K037 

Data/Industry-submitted, 

EPA 

Data/Industry-submitted 

Transfer/K062 

Types of 

Wastes Regulated 

Organics, metals 

Various halogenated 

pestlcl'*=s, dllorin~~tocl 

norbornane der Iva· 

tlves, other organics 

Organics 

Organics 

Organics.· >rgano· 

phosphorL's 

pesticides 

Reactive wastes 

Lead 

-
:bo 

I 

,_. 

..... 

-,, 

LIST 0~ BOAT BACKGROUND DOOUM[NTS AND ASSOCIATED BDAT(S) 

Actual Data or Transferred 

Waste Code/ lrQ,atry or and Types of Third CS.ckgrOlnt Doc llri'nt) lource of W.ate BDATCI) Origin of Data Uastes Re;ulated 

""' I 

l/l IC~IHC052 Petrol~ raflnlng Incineration, solvent extraction Oata/lndustry·aua.ltted Organics, ~netala, 

( ecidenc!ull) lrQ,atry (nunwaatewatera) inorganlcs 

3/3 K060 ~Ia atll\ ll• Incineration (nonwastuwaters) Transfer/Office of Water, Organics, lnorganlcs aludge fro. c:oltlng biological treatllent ,· wastewa(era) transfer/K087 

operatlona 

3/l IC061 E•laalon control Cha.lcal rect.ct I on, che.lcal Transfer/IC062, Metals 

duat/aludge fra. the 

prl•ry procb:tlon of 

precipitation (Meatewatera) Industry ciata 

steel In electric 

furn.ucn 

3/3 I( Oil) Dlatlllatlon botta.a Incineration, atablllzatlon Transfer/previous EPA Organics, .etals 

fro. the pro4,c;tlon (nonwaatewatera); llquld·llquld Incineration test, Transfer/ 

of llf'lll lne extraction, ate .. stripping, f039 (Vol. A) 

carbon adSorption, biological 

treat.ent (waatewatera) 

3/3 KOM Waates fra. cleaning Incineration, chra.lu. rect..ctlon, Data/EPA test, Organics, cyanides ~lpRflt used In cha.lcal precipitation, filtration, transfer/f006·f01Z, (Inorganic) 

fonaulatlon of I~ at alii I hat I on (nonwautewatera), tranafer/f039 (Vol. A) 

fra. pls-enta, drlcra, Incineration, Net air oxidation or ao.p~, and atablllzera cha.lcal oxidation, cerbon 

containing c:hra.l~ adsorption, biological treatment, 

and lead or ate .. atrlpplng 

~h: Agency haa pra.ulaated a treatllent atand.rd of Deactivation for weatea exhibiting the cha~acterlatlc of lgnltablllty (D001), Corroslvlty (D002), or 

Reactivity (D003). AI pert of the lllnd dlaposal reatrlctlona, treatera of thne ebove·.antloned wastes are r~lred to use a deactivation technology that 

will re.ov, the charac:terlatlc for which the waste Ia hazardous. Technologlea that are applicable and detloonstrated for treating these characteristic wastes are llated In 40 CfR Part 268, Appendix 6. 

"The f039 background doc:..-nt (V·•lu.ea A through E) contains trear.ant perfo~e data fra. various oourcea auch as the BOAT progr-, rhe Office of Warer•a 

Industrial Technology Division, the National Pollutant Discharge Ell•lnatlon Syst._, the Hazardous Waste Engineering Resource laboratories, and orher aources. The f039 bec:ltgrOlnt doc..-nt presents ,._roua technologies as BOAT. for further lnfor11111t I on, refer to the FO:S9 background doc:~t, VoluneK A 

through E. 

l.lclooun-.l\112fi40JII.01.02tl