United States 

Environmental Protection 

Agency 

Preliminary Study of the 

Metal Finishing Category: 

2015 Status Report 

June 2016 
THIS PAGE INTENTIONALLY LEFT BLANK.
 
 

 

 

U.S. Environmental Protection Agency
 

Office of Water (4303T)
 

1200 Pennsylvania Avenue, NW
 

Washington, DC 20460
 

EPA-821-R-16-004
 
 

 

 

TABLE OF CONTENTS
 

Table of Contents 

Page 

1. INTRODUCTION ................................................................................................................1-1
 

2. EXISTING METAL FINISHING ELGS ...............................................................................2-1
 

2.1 Metal Finishing Industry Profile at Promulgation .................................................2-2
 

2.2 Metal Finishing Process Operations at Promulgation............................................2-3
 

2.3 Treatment of Metal Finishing Wastewater at Promulgation..................................2-7
 

2.3.1	 Common Metals Treatment ................................................................2-10
 

2.3.2	 In-process Cadmium Reduction..........................................................2-10
 

2.3.3	 Treatment of Complexed Metals, Cyanide-Bearing and 

Chromium-Bearing Wastewaters, and Wastewater Containing
 

Oily Wastes.........................................................................................2-11
 

2.3.4	 Control and Treatment of Toxic Organics..........................................2-12
 

2.4 Applicability of the Existing ELGs to Current Operations..................................2-14
 

2.4.1	 Changes to Industry Profile ................................................................2-14
 

2.4.2	 Scope of Metal Finishing Operations .................................................2-14
 

2.4.3	 Process Technology Modifications and Alternative Chemistries.......2-15
 

2.4.4	 Technological Advances in Wastewater Treatment ...........................2-15
 

3. STUDY ACTIVITIES AND PROGRESS ................................................................................3-1
 

3.1 Literature Review...................................................................................................3-1
 

3.2 Technical Conferences...........................................................................................3-2
 

3.3 Industry Experts.....................................................................................................3-2
 

3.3.1	 Metal Finishing Facilities and Technology Vendors............................3-2
 

3.3.2	 Pretreatment Coordinators....................................................................3-3
 

3.3.3	 Other Stakeholders................................................................................3-3
 

3.4 Industry and Trade Organizations..........................................................................3-3
 

3.5 Site Visits to Metal Finishing Facilities.................................................................3-4
 

3.6 Metal Products and Machinery (MP&M) Rulemaking .........................................3-4
 

4. PRELIMINARY STUDY FINDINGS .....................................................................................4-1
 

4.1 Changes in the Metal Finishing Industry Profile ...................................................4-1
 

4.2 Process Technologies.............................................................................................4-2
 

4.2.1	 Cleaning and Rinsing Operations .........................................................4-3
 

4.2.2	 Coating and Plating Processes..............................................................4-7
 

4.2.3	 Polishing ...............................................................................................4-9
 

4.2.4	 Summary of Process Technologies.......................................................4-9
 

4.3 Alternative Chemistries .......................................................................................4-10
 

iii 
 

 

 

 

 

 

Table of Contents 

TABLE OF CONTENTS (Continued) 

Page 

4.3.1	 Cadmium Plating Alternatives............................................................4-10
 

4.3.2	 Hexavalent Chromium Plating, Conversion Coating, Primer, 

Sealer, and Cleaner Alternatives.........................................................4-12
 

4.3.3	 Phosphate Conversion Coating and Cleaning Alternatives................4-17
 

4.3.4	 Cyanide Plating Solution Alternatives................................................4-19
 

4.3.4	 Summary of Alternative Chemistries..................................................4-19
 

4.4 Wastewater Treatment Technologies...................................................................4-20
 

4.4.1	 Technologies Evaluated for the 1983 Metal Finishing ELGs.............4-20
 

4.4.2	 Chemical Precipitation........................................................................4-22
 

4.4.3	 Sorption...............................................................................................4-24
 

4.4.4	 Membrane Filtration ...........................................................................4-34
 

4.4.5	 Flotation ..............................................................................................4-40
 

4.4.6	 Electrochemical Treatment .................................................................4-41
 

4.4.7	 Biological Treatment ..........................................................................4-44
 

4.4.8	 Summary of Wastewater Treatment Technologies.............................4-45
 

4.5 Applicability and Other Regulatory Considerations............................................4-45
 

4.5.1	 Rule Implementation...........................................................................4-45
 

4.5.2	 Applicability of ELGs to New or Modified Metal Finishing
 

Operations...........................................................................................4-46
 

4.5.3	 Considerations for Other Regulations.................................................4-47
 

5. NEXT STEPS .....................................................................................................................5-1
 

5.1 Review Pollutant Discharge and Release Data......................................................5-1
 

5.2 Evaluate Changes to Industry Profile ....................................................................5-2
 

5.3 Review Literature from Conferences and Other Industry Sources........................5-2
 

5.4 Continue Discussions with Industry Experts on Key Topics.................................5-2
 

5.5 Conduct Site Visits to Metal Finishing Facilities..................................................5-3
 

5.6 Investigate the Impacts of Other Regulations on the Industry...............................5-3
 

6. QUALITY ASSURANCE .....................................................................................................6-1
 

6.1 Project Objectives..................................................................................................6-1
 

6.2 Data Sources ..........................................................................................................6-1
 

6.3 Data Quality Objectives and Criteria.....................................................................6-1
 

6.4 Data Quality Evaluation.........................................................................................6-3
 

6.4.1	 Conference Proceedings, Peer-Reviewed Journal Articles, Other
 

Academic Literature .............................................................................6-3
 

6.4.2	 Data and Information Obtained from Industry, Vendors, and 

Trade Associations................................................................................6-4
 

iv 
 

 

Table of Contents 

TABLE OF CONTENTS (Continued) 

Page 

6.4.3 Existing Government Publications and Supporting Information..........6-4
 

7. REFERENCES....................................................................................................................7-1

APPENDIX A: DESCRIPTIONS OF THE 46 UNIT OPERATIONS IN THE METAL FINISHING

 INDUSTRY

APPENDIX B: KEYWORD SEARCH TERMS FOR THE METAL FINISHING INDUSTRY

APPENDIX C: WASTEWATER TREATMENT TECHNOLOGIES EVALUATED FOR METALS

 

 REMOVAL IN THE 1983 METAL FINISHING ELGS

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List of Tables 

LIST OF TABLES
 

Page 

Table 2-1. Unit Operations Regulated by ELGs for the Metal Finishing Category .................... 2-6
 

Table 2-2. Regulated Pollutants and ELG Limits for the Metal Finishing Category .................. 2-8
 

Table 4-1. Process Descriptions of Cadmium-Free Alternative Coatings................................. 4-11
 

Table 4-2. Commercially Available Hard Chrome Plating Alternatives................................... 4-13
 

Table 4-3. Advantages and Disadvantages of Hard Chrome Plating Alternatives .................... 4-14
 

Table 4-4. Chromate Conversion Coating Alternatives............................................................. 4-15
 

Table 4-5. Regulatory Options Considered in the 1983 ELGs and their Daily Maximum, 

Monthly Average, and Long-Term Average Concentrations .................................. 4-21
 

Table 4-6. Chelated Metals Precipitation Treatment Identified in EPA’s Literature 

Review – Summary of Treatment Results ............................................................... 4-25
 

Table 4-7. Low-Cost Adsorbents Identified in EPA’s Literature Review................................. 4-26
 

Table 4-8. Low-Cost Alternatives to Coal-based Activated Carbon Treatment Identified
 

in EPA’s Literature Search – Summary of Treatment Results ................................ 4-29
 

Table 4-9. Biosorbent Treatment Identified in EPA’s Literature Review – Summary of
 

Treatment Results .................................................................................................... 4-31
 

Table 4-10. Nanomaterials Identified in EPA’s Literature Review........................................... 4-32
 

Table 4-11. Ion Exchange Treatment Identified in EPA’s Literature Review – Summary
 

of Treatment Results................................................................................................ 4-33
 

Table 4-12. Ultrafiltration Treatment Identified in EPA’s Literature Review – Summary
 

of Treatment Results................................................................................................ 4-37
 

Table 4-13. Nanofiltration Treatment Identified in EPA’s Literature Review – Summary
 

of Treatment Results................................................................................................ 4-39
 

Table 4-14. RO Treatment Identified in EPA’s Literature Review – Summary of
 

Treatment Results .................................................................................................... 4-39
 

Table 4-15. Electrocoagulation Treatment Identified in EPA’s Literature Review ­

Summary of Treatment Results ............................................................................... 4-42
 

Table 4-16. Electroflotation Treatment Identified in EPA’s Literature Review - Summary
 

of Treatment Results................................................................................................ 4-43
 

Table 6-1. Data Quality Criteria Summary.................................................................................. 6-3
 

Table 6-2. Data Acceptance Criteria for the Preliminary Study of the Metal Finishing
 

Category..................................................................................................................... 6-5
 

vi 
List of Figures 

LIST OF FIGURES 

Page 

Figure 2-1. Metal Finishing Process Application ........................................................................ 2-7
 

Figure 2-2. BPT/BAT/PSES Technology Basis .......................................................................... 2-9
 

Figure 2-3. NSPS/PSNS Technology Basis (Equivalent to BPT/BAT/PSES with 

Additional Cadmium Reduction)............................................................................... 2-9
 

Figure 4-1. Original Process at the Bronze Cyanide Plating Facility.......................................... 4-4
 

Figure 4-2. New Process at the Bronze Cyanide Plating Facility................................................ 4-4
 

Figure 4-3. Potential Rinse Systems in Facility with Metal Finishing Processes........................ 4-6
 

Figure 4-4. Plaforization System for Batch Spraying Equipment ............................................... 4-7
 

Figure 4-5. Traditional Coating Systems................................................................................... 4-17
 

Figure 4-6. Illustration of Membrane Filtration Technologies .................................................. 4-34
 

Figure 4-7. Illustration of Micellar-Enhanced Ultrafiltration.................................................... 4-36
 

vii 
 

Abbreviations 

ABBREVIATIONS 

Acronym	 Definition 

ACS	 American Chemical Society 

ACWA	 Association of Clean Water Administrators 

AFM/AFMmm	 Abrasive Flow Machining/that Incorporates a Movable/Rotatable Mandrel 

APCVD	 Atmospheric Pressure, Chemical Vapor Deposition 

BAT	 Best Available Technology Economically Achievable 

BMR	 Baseline Monitoring Report 

BPT	 Best Practicable Control Technology Currently Available 

CFR	 Code of Federal Regulations 

CIUs	 Categorical Industrial Users 

CPR	 Cleaner Phosphoric Recycling 

CWA	 Clean Water Act 

DAF	 Dissolved Air Flotation 

DCN	 Document Control Number 

DDTC	 Diethyldithiocarbamate 

DMR	 Discharge Monitoring Report 

DoD	 Department of Defense 

DOE	 Department of Energy 

EDTA	 Ethylenediaminetetraacetic Acid 

ELGs	 Effluent Limitations Guidelines and Standards 

ELV	 End of Life Vehicle 

EPA	 Environmental Protection Agency 

ERG	 Eastern Research Group, Inc. 

ESTCP	 Environmental Security Technology Certification Program 

EU	 European Union 

FR	 Federal Register 

GACT	 Generally Available Control Technology 

GBP	 Glass Bead Peening 

gpm	 gallons per minute 

HRS	 Hot Rolled Steel 

HVOF	 High Velocity Oxygen Fuel 

IONMET	 New Ionic Liquid Solvent Technology to Transform Metal Finishing 

Products and Processes 

IP3	 Integrated Profitable Pollution Prevention Technologies 

IPCB	 Independent Printed Circuit Board 

IVD	 Ion Vapor Deposition 

IWC	 International Water Conference 

LDH	 Layered Double Hydroxide 

LTA	 Long-term Average 

MEUF	 Micellar-Enhanced Ultrafiltration 

MF	 Microfiltration 

mg/L	 milligrams per Liter 

viii 
Abbreviations 

ABBREVIATIONS 

Acronym	 Definition 

MP&M	 Metal Products and Machinery 

NACWA	 National Association of Clean Water Agencies 

NAICS	 North American Industry Classification System 

NASF	 National Association for Surface Finishing 

NAVAIR	 Naval Aviation Systems Command 

NESHAP	 National Emission Standards for Hazardous Air Pollutants 

NF	 Nanofiltration 

NPDES	 National Pollutant Discharge Elimination System 

NSPS	 New Source Performance Standards 

OAR	 Office of Air and Radiation 

ORCR	 Office of Resource Conservation and Recovery 

OW	 Office of Water 

PAM	 Polyacrylamide 

PEUF	 Polymer-Enhanced Ultrafiltration 

PFOs	 Perfluorooctane Sulfonate 

POTW	 Publicly Owned Treatment Works 

PPI	 Pollution Prevention Institute 

PQAPP	 Programmatic Quality Assurance Project Plan 

PSES	 Pretreatment Standards for Existing Sources 

PSNS	 Pretreatment Standards for New Sources 

PVD	 Physical Vapor Deposition 

QA	 Quality Assurance 

RCRA	 Resource Conservation and Recovery Act 

RO	 Reverse Osmosis 

RoHS	 Restriction of Hazardous Substances 

SERDP	 Strategic Environmental Research and Development Program 

SIC	 Standard Industrial Classification 

SRB	 Sulfate-Reducing Bacteria 

TDD	 Technical Development Document 

TOC	 Total Organic Compounds 

TOMP	 Toxic Organic Management Plan 

TRI	 Toxic Release Inventory 

TSS	 Total Suspended Solids 

TTO	 Total Toxic Organics 

UF	 Ultrafiltration 

UV	 Ultraviolet 

VOC	 Volatile Organic Compounds 

WAFS	 Wetting Agents/Fume Suppressants 

WEFTEC	 Water Environment Federation’s Annual Technical Exhibition and 

Conference 

ix 
 

 

 

 

 

 

 

Section 1– Introduction 

1.	 INTRODUCTION 

The Clean Water Act (CWA) requires Environmental Protection Agency (EPA) to review 

existing effluent guidelines annually. EPA reviews all point source categories subject to existing 

effluent guidelines and pretreatment standards to identify potential candidates for revision, 

consistent with CWA sections 304(b), 301(d), 304(m)(1)(A), and 304(g). The CWA also requires 

EPA to revise existing Effluent Limitations Guidelines and Standards (ELGs) when appropriate. 

EPA promulgated ELGs for the Metal Finishing Category (Metal Finishing ELGs), 

codified at 40 Code of Federal Regulations (CFR) Part 433, in 1983. EPA revisited the Metal 

Finishing ELGs during the development of the Metal Products and Machinery (MP&M) 

rulemaking in the late 1990s and early 2000s. More recently, EPA conducted a preliminary 

category review of the Metal Finishing Category as part of its annual effluent guideline review 

process. In the Final 2014 Effluent Guidelines Program Plan, EPA announced plans to conduct a 

preliminary study of the Metal Finishing Category to assess the current state of the industry, 

including an updated industry profile, descriptions of new and traditional process technologies 

and techniques, potential new pollutants of concern, advances in wastewater treatment 

technologies, and strategies used to achieve zero liquid discharge (U.S. EPA, 2015a, 2015b). 

This study extends EPA’s efforts beyond the 304(m) annual review to better understand changes 

in metal finishing operations, wastewater characteristics, and wastewater treatment technologies 

since EPA promulgated the 1983 ELGs. The study seeks to answer the following key questions: 

•	 How is the metal finishing industry now different from when EPA first 

promulgated the Metal Finishing ELGs? Specifically: 

—	 What is the distribution of captive facilities and job shops that currently 

make up the industry? 

—	 Which types of facilities are conducting metal finishing operations? 

—	 What products are metal finishing facilities producing? 

•	 Since the promulgation of the Metal Finishing ELGs, what process technology 

changes have been implemented and how have the primary sources of wastewater 

changed? 

•	 Since the promulgation of the Metal Finishing ELGs, what changes to chemical 

formulations have been implemented and how have these changes affected the 

volume of wastewater and the concentrations and types of pollutants generated 

and discharged? 

•	 What are the best available technologies for pollution prevention and wastewater 

treatment, and to what levels do they reduce discharges of pollutions of concern? 

—	 What are the concentrations and loadings of pollutants currently being 

discharged (i.e., baseline concentrations)? 

—	 Which pollutant discharges require additional controls? 

—	 How will industry discharges change if facilities implement these best 

available technologies/practices to control pollutants? 

1-1
 
 

 

 

 

 

 

Section 1– Introduction 

•	 What challenges do metal finishing facilities or regulatory authorities face in 

applying the Metal Finishing ELGs? 

This interim status describes the preliminary study and presents EPA’s findings to date. 

The remainder of the report is organized as follows: 

•	 Section 2 summarizes the existing metal finishing regulations, the state of the 

industry in 1983 when the ELGs were promulgated, and a general discussion of 

changes to the industry since promulgation. 

•	 Section 3 describes activities that EPA plans to conduct as part of the preliminary 

study and the current status of these activities. 

•	 Section 4 details EPA’s study findings (to date) in five general categories: 

industry profile changes, advancements in process technologies, advancements in 

alternative chemistries, advancements in wastewater treatment technologies, and 

existing regulatory issues for consideration. 

•	 Section 5 presents EPA’s next steps for the study. 

•	 Section 6 summarizes EPA’s quality assurance (QA) procedures for reviewing 

existing information presented in this report. 

•	 Section 7 is the list of references cited in the report. 

1-2
 
 

 

 

 

Section 2– Existing Metal Finishing ELGs 

2. EXISTING METAL FINISHING ELGS

This section provides a brief history of the existing ELGs as background and context for

EPA’s continued review of the metal finishing industry. Metal finishing involves changing the 

surface of an object to improve its appearance and/or durability. Wastewater discharges from 

metal finishing operations are regulated primarily under ELGs for the Electroplating Point 

Source Category (40 CFR Part 413) and the Metal Finishing Point Source Category (40 CFR 

Part 433). 40 CFR Part 413 includes pretreatment standards for existing sources (PSES) for the 

Electroplating Category, and 40 CFR Part 433 include effluent limitations based on best 

practicable control technology currently available (BPT) and best available technology 

economically achievable (BAT), new source performance standards (NSPS), pretreatment 

standards for new sources (PSNS), and PSES for the Metal Finishing Category.1

EPA promulgated PSES for the Electroplating Category in 1979; limitations and 

standards for new sources and direct discharges were not established under this rule. The PSES 

apply to facilities that perform one or more of six electroplating operations and that indirectly 

discharge wastewater to surface water via publically owned treatment works (POTW). The 

pretreatment standards differ for discharges less than 10,000 gallons per day (gpd) of wastewater 

compared to discharges greater than 10,000 gpd of wastewater (U.S. EPA, 1979). The National 

Association of Metal Finishers and the Institute of Interconnecting and Packaging Electronic 

Circuits challenged the 1979 rule for the Electroplating Category. On March 7, 1980, EPA 

entered into a settlement agreement with these two organizations, and agreed to amend the final 

electroplating pretreatment standards. These amendments were implemented on January 28, 

1981 (U.S. EPA, 1981). As a result of the agreement, EPA promulgated in 1983 a new regulation 

for the Metal Finishing and Electroplating Categories which established BPT, BAT, NSPS, 

PSNS, and PSES. Following these amendments, the applicability of the Electroplating Category 

ELGs (40 CFR 413) is limited to facilities (both independent (job) platers and captive 

operations) that apply metal coatings via electrodeposition, began operation before July 15, 

1983, and discharge wastes to POTWs. All other facilities performing electroplating or metal 

finishing operations are subject to regulations under the Metal Finishing Category (40 CFR Part 

433).2 

During the development of the MP&M rulemaking (40 CFR Part 438, promulgated in 

2003), EPA evaluated all industries involved in the “manufacture, rebuild or maintenance of 

metal parts, products, or machines,” including facilities regulated under 40 CFR Parts 413 and 

433; however, EPA did not revise the existing limitations and standards for Parts 413 and 433 in 

the final MP&M rule. Therefore, the 1983 regulations continue to be the guidelines set for the 

industry for the indirect and direct discharge of metal finishing wastewater.3

1 Discharges from facilities performing metal finishing operations may also be regulated under other ELGs (e.g., 

Aluminum Forming, Iron and Steel) that take precedence over the Metal Finishing ELGs. 

2 Facilities include electroplaters discharging to surface water, electroplaters that began operation after July 15, 

1983, and metal finishers that do not perform one or more of six electroplating operations. 

3 EPA promulgated the Electroplating Point Source Category regulation in 1974 and amended it in 1977, 1979, 

1981, and 1983. The 1983 amended rule continue to regulate facilities in the Electroplating Point Source Category

in operation prior to July 15, 1983 and that discharge wastes to POTW. Therefore, all other facilities operating on or

after that date that discharge wastewater (indirect and/or direct discharge) are subject to the Metal Finishing Point 

Source Category. 

2-1
 

 

 

 

 

 

 

Section 2– Existing Metal Finishing ELGs 

This remainder of section describes the existing 1983 Metal Finishing ELGs, a profile the 

industry at the time of promulgation (section 2.1), metal finishing process operations (section 

2.2), wastewater treatment of metal finishing wastewater (section 2.3), and the applicability of 

the existing ELGs to current metal finishing operations (section 2.4). 

2.1 Metal Finishing Industry Profile at Promulgation 

The applicability of the Metal Finishing Category is defined by process operations rather 

than by industry sectors; therefore, a facility subject to the Metal Finishing ELGs may belong to 

one or more of a variety of metal processing and metal forming industry classifications. The 

industries covered by the Metal Finishing ELGs perform one of 46 unit operations, discussed in 

section 2.2 below, and are generally included in the following two-digit Standard Industrial 

Classification (SIC) codes (U.S. EPA, 1983a):4

• 34: Fabricated Metal Products, Except Machinery and Transportation.

• 35: Machinery, Except Electrical.

• 36: Electrical and Electronic Machinery, Equipment and Supplies.

• 37: Transportation Equipment.

• 38: Measuring, Analyzing and Controlling Instruments: Photographic, Medical,

and Optical Goods; Watches and Clocks.

• 39: Miscellaneous Manufacturing Industries.

Metal finishing facilities are categorized as either captive facilities or job shops, which 

EPA defined as follows (U.S. EPA, 1984): 

• Captive facility. A facility that in a calendar year owns more than 50 percent (by

surface area) of the materials undergoing metal finishing. Captive facilities were

categorized as integrated or non-integrated to characterize the wastewater

discharges generated. Integrated facilities are those which, prior to treatment,

combine electroplating waste streams with significant process waste streams not

covered by the Electroplating Point Source Category. Non-integrated facilities are

those which have significant wastewater discharges only from operations

addressed by the Electroplating Point Source Category.

• Job shop. A facility that in a calendar year owns less than 50 percent (by surface

area) of the materials undergoing metal finishing. During development of the

regulation, approximately 97 percent of job shops were found to be nonintegrated.

4 Although facilities performing metal finishing operations generally fall under these SIC codes, not all facilities 

under the codes are subject to the Metal Finishing ELGs. For example, the Metal Finishing ELGs are not 

applicable to facilities that do not perform any of the six electroplating operations. Instead, these facilities may be 

subject to other metal ELGs that take precedence over the Metal Finishing ELGs. 

2-2
 

 

 

 

 

 

 

 

Section 2– Existing Metal Finishing ELGs 

At promulgation of the 1983 Metal Finishing ELGs, the Metal Finishing and 

Electroplating Categories included a total of 13,470 facilities, consisting of 10,000 captive 

facilities and 3,470 job shops and independent printed circuit board (IPCB) manufacturers5 (U.S. 

EPA, 1984). The facilities varied greatly in size, age, number of employees, and number and 

type of operations performed, ranging from small shops with less than 10 employees to large 

facilities employing thousands of employees (U.S. EPA, 1983a). 

During the Metal Finishing rulemaking development, EPA identified 10,561 out of 

13,470 facilities (78 percent) that indirectly discharged to surface water via POTWs. These 

facilities were evenly distributed between job shops, non-integrated captive facilities, and 

integrated captive facilities. The remaining 2,909 facilities (22 percent) discharged directly to 

surface water, with captive facilities (both integrated and non-integrated) predominantly 

performing this practice (U.S. EPA, 1983a). The 1983 rule did not capture the number of 

facilities in the industry that reused wastewater. 

2.2 Metal Finishing Process Operations at Promulgation 

Metal finishing is the process of changing the surface of an object by creating a thin layer 

of metal or metal precipitate on its surface to impart the desired surface characteristics to the 

final product, such as corrosion resistance, wear resistance, and hardness. The operations 

performed and the sequence of operations at a metal finishing facility can vary and depend on 

numerous factors (e.g., raw materials used, industry sector, product specifications), and may 

generate significant volumes of wastewater (U.S. EPA, 2000a). 

The Metal Finishing ELGs regulate wastewater discharges from six primary metal 

finishing operations. Additionally, at facilities where at least one of these primary operations is 

being conducted, the ELGs also cover wastewater discharges resulting from 40 additional metal 

finishing operations. If a facility does not perform any of the six primary metal finishing 

operations, it is not subject to the Metal Finishing ELGs (U.S. EPA, 1984). The six primary 

operations and associated waste streams are described below (U.S. EPA, 1983a). 

•	 Electroplating. The application of a thin surface coating of one metal upon 

another by electrodeposition. This surface coating is applied to provide corrosion 

protection, wear or erosion resistance, or anti-frictional characteristics, or for 

decorative purposes. Cathodic surfaces are plated by reducing metal ions in either 

acid, alkaline, or neutral solutions. Metal ions in the plating solution are 

replenished by the dissolution of metal from anodes, small pieces contained in 

inert wire or metal baskets, or metal salts. Hundreds of different electroplating 

solutions have been adopted commercially, but only two or three types are used 

widely for a specific metal or alloy. Electroplating baths contain metal salts, 

acids, alkalines, and various bath control compounds which contribute to the 

wastewater stream through dragout, batch dumping, or floor spills. The waste 

5 Indirect discharging job shops and IPCB manufacturers that existed under Part 413 continued to comply with Part 

413 Electroplating Pretreatment Standards and were exempt from the Part 433 Metal Finishing ELGs (U.S. EPA, 

1984). 

2-3
 
 

 

 

 

 

 

 

Section 2– Existing Metal Finishing ELGs 

from the electroplating process can include common metals, precious metals, 

chromium (hexavalent), and cyanide. 

•	 Electroless plating. A chemical reduction process that depends on the catalytic 

reduction of a metallic ion in an aqueous solution containing a reducing agent and 

the subsequent deposition of metal without the use of external electrical energy. 

Electroless plating has several advantages over electroplating. It provides a 

uniform plating thickness on all areas of a part, and a dense and virtually nonporous plate on properly prepared surfaces. Copper and nickel electroless plating 

are the most common. Electroless plating baths can contain precious metals, 

complexed metals, and cyanide, which can enter the wastewater stream through 

dragout or batch dumping of process baths. The basic ingredients in an electroless 

plating solution are: 

—	 A source of metal, usually a salt. 

—	 A reducer, to reduce the metal to its base state. 

—	 A complexing agent, to hold the metal in solution. 

—	 Various buffers and other chemicals designed to maintain bath stability 

and increase bath life. 

•	 Anodizing. An electrolytic oxidation process that converts the surface of the metal 

to an insoluble oxide. These oxide coatings provide corrosion protection, 

decorative surfaces, a base for painting and other coatings, and special electrical 

and mechanical properties. Aluminum is the most frequently anodized material, 

while some magnesium and limited amounts of zinc and titanium are also treated. 

For aluminum parts, the formation of oxide occurs when the parts are made 

anodic in dilute sulfuric acid or dilute chromic acid solutions. The oxide layer 

begins formation at the extreme outer surface, and as the reaction proceeds, the 

oxide grows into the metal. The last-formed oxide, the boundary layer, is at the 

interface between the base metal and the oxide. The boundary layer is extremely 

thin and nonporous. The wastewater from anodizing processes can contain the 

base material being anodized (typically aluminum or magnesium) and 

constituents of the processing baths (such as sulfuric or chromic acid). It is also 

common to dye or color anodized coatings. Many of the dyes contain chromium 

and other metals which can enter the wastewater stream. 

•	 Coating. The process of chromating, phosphating, metal coloring, and 

passivating. These coatings are applied to previously deposited metal or basis 

material (i.e., the materials onto which metal finishes are applied) for increased 

corrosion protection, lubricity, and preparation of the surface for additional 

coatings or formulation of a special surface appearance. In chromating, a portion 

of the base metal is converted to a component of the film by reaction with 

aqueous solutions containing hexavalent chromium and active organic or 

inorganic compounds. Most coatings are applied by chemical immersion although 

a spray or brush treatment can be used. 

Phosphate coatings are used to provide a good base for paints and other organic 

coatings, to condition the surfaces for cold forming operations by providing a 

2-4
 
 

 

 

 

 

 

Section 2– Existing Metal Finishing ELGs 

base for drawing compounds and lubricants, and to provide corrosion resistance to 

the metal surface (by the coating itself or by providing a suitable base for rustpreventative oils or waxes). Phosphate conversion coatings are formed by the 

immersion of iron, steel, or zinc-plated steel in a dilute solution of phosphoric 

acid plus other reagents. Metal coloring by chemical conversion converts the 

metal surface into an oxide or similar metallic compound, producing a variety of 

decorative finishes. Passivation refers to forming a protective film on metals by 

immersion in an acid solution. Numerous pollutants may enter the wastewater 

through coating operations by rinsing and batch dumping of process baths. The 

baths usually contain metal salts, acids, bases, and dissolved basis materials and 

various additives. 

•	 Chemical Etching and Milling. Methods of producing specific design 

configurations and tolerances on metal parts by controlled dissolution with 

chemical reagents or etchants. This classification includes chemical milling, 

chemical etching, and bright dipping. Chemical etching is the same process as 

chemical milling, but with much lower rates and depths of metal removal. Typical 

solutions for etching and chemical milling include ferric chloride, nitric acid, 

ammonium persulfate, chromic acid, cupric chloride, hydrochloric acid, and 

combinations of these reagents. Bright dipping is a specialized form of etching, 

used to remove oxide and tarnish from ferrous and nonferrous materials, and can 

produce a range of surface appearances from bright clean to brilliant. This unit 

operation also includes the stripping of metallic coatings. The wastewater from 

etching and chemical milling operations mainly contains dissolved basis 

materials, such as stainless steel, aluminum, and copper. Zinc and cadmium, 

frequently subjected to bright dipping, may also be present in wastewater. 

•	 Printed Circuit Board Manufacturing. The formation of a circuit pattern of 

conductive metal (usually copper) on nonconductive board materials such as 

plastic or glass. It usually involves cleaning and surface preparation, catalyst and 

electroless plating, pattern printing and masking, electroplating, and etching. 

There are three main production methods for printed circuit boards: additive, 

which uses pre-sensitized, unclad material as the starting board; semi-additive, 

which uses unclad, unsensitized material as the starting board; and subtractive, 

which begins with copper clad, unsensitized material. Wastewater is generated in 

the manufacturing of printed circuit boards primarily from rinsing and cleaning 

during surface preparation, electroless plating, pattern plating, etching, tab 

plating, and immersion plating. Additionally, rinsing away spills, air scrubbing 

water, equipment washing, and dumping spent process solutions can contribute to 

the wastewater. The most common constituents of the waste streams are 

suspended solids, copper, fluorides, phosphorus, tin, palladium, and chelating 

agents. 

As stated above, if any of the six core electroplating operations is present at a facility, the 

Metal Finishing ELGs also apply to wastewater discharges from 40 additional unit operations 

(listed in Table 2-1). Appendix A further describes the 40 additional metal finishing operations. 

2-5
 
 

Section 2– Existing Metal Finishing ELGs 

Table 2-1. Unit Operations Regulated by ELGs for the Metal Finishing Category 

Six Primary Operations 40 Additional Metal Finishing Unit Operations 

• Electroplating 

• Electroless plating 

• Anodizing 

• Coating 

• Etching and chemical milling 

• Printed circuit board manufacturing 

• Cleaning 

• Machining 

• Grinding 

• Polishing 

• Barrel finishing 

• Burnishing 

• Impact deformation 

• Pressure deformation 

• Shearing 

• Heat treating 

• Thermal cutting 

• Welding 

• Brazing 

• Soldering 

• Flame spraying 

• Sand blasting 

• Abrasive jet machining 

• Electrical discharge machining 

• Electrochemical machining 

• Electron beam machining 

• Laser beam machining 

• Plasma arch machining 

• Ultrasonic machining 

• Sintering 

• Laminating 

• Hot dip coating 

• Sputtering 

• Vapor plating 

• Thermal infusion 

• Salt bath descaling 

• Solvent degreasing 

• Paint stripping 

• Painting 

• Electrostatic painting 

• Electropainting 

• Vacuum metalizing 

• Assembly 

• Calibration 

• Testing 

• Mechanical plating 

Source: 40 CFR Part 433. 

As discussed in supporting documentation for the Metal Finishing ELGs, metal finishing 

operations usually begin with raw stock materials (rods, bars, sheets, castings, forgings, etc.) 

which can progress through the simplest or most sophisticated surface finishing operations. 

Production facilities vary in size and processes, and are custom-tailored to the specific needs of 

each individual plant. Figure 2-1 illustrates the variation in the number of unit operations that can 

be performed in facilities within the metal finishing industry, depending upon the complexity of 

the product. A complex product could require the use of nearly all unit operations, while a simple 

product might require only a single operation (U.S. EPA, 1983a). The Metal Finishing ELGs 

would apply to wastewater discharges from the complex product in Figure 2-1 because at least 

one of the six core electroplating operations is taking place; they would not apply to wastewater 

discharges from the simple product as shown, because none of the six primary operations are 

performed. 

Many different raw materials are used by facilities in the Metal Finishing Category. 

During the development of the 1983 Metal Finishing ELGs, the basis materials were almost 

exclusively metals which range from common copper and steel to extremely expensive high 

grade alloys and precious metals, but may also include glass, plastic, and other non-conductive 

materials. The raw materials used in metal finishing unit operations to coat these basis materials 

can contain acids, bases, cyanide, metals, complexing agents, organic additives, oils, and 

detergents. All of the basis materials and raw materials used in metal finishing can potentially 

enter wastewater streams during production and subsequently be discharged as metal finishing 

wastewater (U.S. EPA, 1983a). 

2-6
 
 

 

Section 2– Existing Metal Finishing ELGs 

Adapted from (U.S. EPA, 1983a) 

Figure 2-1. Metal Finishing Process Application 

2.3 Treatment of Metal Finishing Wastewater at Promulgation 

As described in Section 2.2, Metal Finishing ELGs apply to wastewater discharges from 

the six primary electroplating operations, including any discharges from the additional metal 

finishing unit operations listed in Table 2-1. At promulgation, 78 percent of facilities indirectly 

discharged metal finishing wastewater to receiving water via POTWs and 22 percent directly 

discharged to surface waters (U.S. EPA, 1984). The Metal Finishing ELGs established one set of 

concentration-based discharge limits that apply across a single subpart (Subpart A: Metal 

Finishing), summarized in Table 2-2. Direct dischargers comply with BPT/BAT discharge 

limitations and NSPS, whereas indirect dischargers comply with PSES and PSNS. As the table 

shows, the limitations and standards are the same for new and existing sources of metal finishing 

wastewater discharges, except for cadmium, which has a lower NSPS and PSNS discharge 

standard (U.S. EPA, 1983a). 

2-7
 
 

 

 

 

 

 

 

c 

Section 2– Existing Metal Finishing ELGs 

Table 2-2. Regulated Pollutants and ELG Limits for the Metal Finishing Category 

Process Operations Covered Pollutant 

BPT/BAT/PSES

Daily Max

(Monthly Average)

(mg/L) 

NSPS/PSNS 

Daily Max

(Monthly Average)

(mg/L) 

See Table 2-1, for the list of 46 unit operationsa Cadmium (T) 0.69 (0.26) 0.11 (0.07) 

Chromium (T) 2.77 (1.71) 2.77 (1.71) 

Copper (T) 3.38 (2.07) 3.38 (2.07) 

Lead (T) 0.69 (0.43) 0.69 (0.43) 

Nickel (T) 3.98 (2.38) 3.98 (2.38) 

Silver (T) 0.43 (0.24) 0.43 (0.24) 

Zinc (T) 2.61 (1.48) 2.61 (1.48) 

Cyanide (T)b 1.20 (0.65) 1.20 (0.65) 

Total Toxic 

Organics

(TTO)c 

2.13 2.13 

Oil and Greased 52 (26) 52 (26) 

Total 

Suspended 

Solids (TSS)d 

60 (31) 60 (31) 

pHd Within 6.0 to 9.0 Within 6.0 to 9.0 

For industrial facilities with cyanide treatment, and

upon agreement between a source subject to those 

limits and the pollution control authority, the

following amenable cyanide limit may apply in

place of the total cyanide limit. 

Cyanide

amenable to 

alkaline 

chlorination 

0.86 (0.32) 0.86 (0.32) 

Source: 40 CFR Part 433. 

a The provisions of this subpart apply to discharges from six electroplating operations on any basis material: 

electroplating, electroless plating, anodizing, coating (chromating, phosphating, and coloring), chemical etching 

and milling, and printed circuit board manufacturing. If any of these six operations are present, the provisions of 

this subpart also apply to discharges from 40 additional metal finishing operations, listed in Table 2-1. These 

limits do not apply to (1) metallic platemaking and gravure cylinder preparation conducted within or for 

printing and publishing facilities or (2) existing indirect discharging job shops and independent printed circuit 

board manufacturers, which are covered by 40 CFR Part 413. 

b Anti-dilution provisions are stipulated in 40 CFR Part 433, which require self-monitoring for cyanide after 

cyanide treatment and before dilution with other waste streams. In general, the practice of diluting rinse water 

as a partial or total substitute for adequate treatment to achieve compliance with discharge limits is in violation
 

of the National pretreatment standards: Categorical standards (40 CFR Part 403.6(d)).
 

No monthly average TTO limitation.
 

d Parameter is regulated for BPT and NSPS only. 

EPA based BPT, BAT, and PSES on the treatment of metal finishing wastewater using 

hydroxide precipitation, clarification, and sludge dewatering for common metals treatment, with 

pretreatment steps for chromium reduction, cyanide oxidation, complexed metals removal, and 

oil and grease removal, where the wastewater contains these components. This wastewater 

treatment technology is depicted in Figure 2-2 (U.S. EPA, 1983a). 

EPA based NSPS and PSNS on the BPT/BAT/PSES technology, adding in-process 

treatment modifications for controlling the discharge of cadmium, as illustrated in Figure 2-3. 

The modifications for controlling cadmium employ evaporative recovery or ion exchange on 

2-8
 
Section 2– Existing Metal Finishing ELGs 

cadmium-bearing wastewater before it mixes with other wastewater (U.S. EPA, 1983a). The 

following subsections discuss in detail the technology basis for BPT/BAT/PSES and 

NSPS/PSNS. 

Source: (U.S. EPA, 1983a) 

Figure 2-2. BPT/BAT/PSES Technology Basis 

Source: (U.S. EPA, 1983a) 

Figure 2-3. NSPS/PSNS Technology Basis 

(Equivalent to BPT/BAT/PSES with Additional Cadmium Reduction) 

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Section 2– Existing Metal Finishing ELGs 

2.3.1 Common Metals Treatment 

BAT is based on BPT of metal finishing wastewater, which reflects treatment and control 

practices at metal finishing plants of various sizes, ages, and manufacturing processes. Pollutant 

control focuses on end-of-pipe treatment rather than process changes or internal controls, except 

where such are common industry practice. The control technologies for treatment of common 

metals include hydroxide precipitation, clarification, and sludge dewatering, discussed in the 

subsections below. Treatment modifications for controlling the discharges of cadmium (as 

required for NSPS/PSNS), including evaporative recovery and ion exchange, are also discussed. 

2.3.1.1 Hydroxide Precipitation 

Hydroxide precipitation is used to remove dissolved metals and phosphates from metal 

finishing wastewater by converting the dissolved pollutants into solid form (precipitates) and 

coagulating suspended precipitates into larger, faster settling particles. Precipitation is achieved 

by adding lime, caustic, sodium carbonate, or acid to reach a favorable pH (typically 8.8 – 9.3). 

Any recovery of precious metals, reduction of hexavalent chromium, removal of oily wastes, or 

destruction of cyanide must be performed before metals and phosphates are removed via 

hydroxide precipitation. 

2.3.1.2 Clarification 

Following precipitation, the waste streams flow through a clarifier, where solids are 

removed by gravity. Clarifiers are used for sedimentation to reduce space requirements and 

retention time, making solids removal more efficient. Coagulants or flocculants are typically 

added to the waste stream to enhance solids settling (U.S. EPA, 1983a). 

2.3.1.3 Sludge Dewatering 

Precipitation and clarification generate large quantities of sludge requiring disposal. 

These sludges are dewatered prior to disposal to reduce their volume. Sludge dewatering 

techniques include gravity sludge thickening, pressure filtration, vacuum filtration, 

centrifugation, and sludge bed drying. Once the sludge is dewatered, it is generally disposed of at 

an onsite landfill or hauled away by a contractor to an off-site landfill or reclamation facility. 

Other less common disposal options include chemical containment, encapsulation, fixation, and 

thermal conversion, all of which require landfilling, but reduce the potential for groundwater 

contamination (U.S. EPA, 1983a). 

2.3.2 In-process Cadmium Reduction 

In addition to the BPT technology of hydroxide precipitation followed by clarification 

described above, NSPS/PSNS limitations require in-process treatment modifications for 

controlling the discharge of cadmium. The in-process cadmium reduction technologies may 

include ion exchange or evaporative recovery to provide near zero discharge of heavy metals 

from the raw waste stream. Although both ion exchange and evaporation are used in treatment of 

metal finishing wastewaters for removing a variety of precious metals from bath concentrates 

and rinse waters, the technology basis for NSPS and PSNS specifically uses these techniques for 

2-10
 
 

 

 

 

Section 2– Existing Metal Finishing ELGs 

removing of cadmium before mixing with other metal-bearing wastewater for common metals 

treatment (U.S. EPA, 1983a). 

The ion exchange process consists of ions, held by electrostatic forces to charged 

functional groups on the surface of the ion exchange resin, exchanged for ions of similar charge 

from the solution in which the resin is immersed. It is a sorption process because the exchange 

occurs on the surface of the resin. The cadmium is adsorbed onto the resin and exchanged for the 

harmless ions of the resin. Eventually, when the resin cannot exchange any more cadmium ions, 

it must be regenerated. The ion exchange resin is regenerated with regenerant solution containing 

hydrochloric or sulfuric acid. The regenerant flows through the ion exchange resin and replaces 

each cadmium ion with one or more hydrogen ions. The used regenerant solution is then treated, 

reused, and/or disposed. 

Evaporation of water from a solution increases the concentration of solute in the 

remaining solution. Evaporation techniques include atmospheric evaporation (boiling the liquid) 

and vacuum evaporation (the evaporation pressure is lowered to cause the liquid to boil at 

reduced temperature). The vaporized water resulting from these processes humidifies the air in 

the system and is either blown out of the system as hot air or collected, condensed, and reused as 

waste process heat source for the system. The concentrate may be hauled off-site for recovery 

and resale or further processed on site for recovery and reuse. 

2.3.3	 Treatment of Complexed Metals, Cyanide-Bearing and Chromium-Bearing 

Wastewaters, and Wastewater Containing Oily Wastes 

The following subsections discuss additional treatment requirements for facilities 

generating complexed metals, cyanide-bearing, chromium-bearing, or oily wastewaters. 

Complexed metals wastewater requires separate treatment using high pH chemical precipitation. 

Cyanide-bearing, chromium-bearing, or oily wastewaters require pretreatment using cyanide 

oxidation, chromium reduction, or emulsion breaking prior to common metals treatment. These 

constituents in the wastewater may hinder hydroxide precipitation, clarification, and sludge 

dewatering. 

2.3.3.1 High pH Chemical Precipitation 

High pH precipitation is particularly applicable to waste streams containing complexing 

agents (or chelating agents), which hinder conventional precipitation. These agents are used 

during metal finishing operations to maintain heavy metals in solution. The complexing agent 

produces a stable composition of non-metal molecules or ions that are covalently bonded to 

metal atoms or ions, which keeps the metal atoms or ions in solution during metal finishing 

operations, but also hinders their precipitation during wastewater treatment. Waste streams 

containing complexing agents (or complexed metals) are segregated and treated separately. 

Precipitation of complexed metals is characteristically accomplished at a high pH (11.6 – 12.5) 

to induce a shift in the complex dissociation equilibrium. This produces uncomplexed metal ions 

which can then be precipitated out of solution by available hydroxide ions. The pH is adjusted by 

the addition of chemicals such as calcium hydroxide, lime, calcium chloride, or calcium sulfate 

(U.S. EPA, 1983a). 

2-11
 
 

 

 

Section 2– Existing Metal Finishing ELGs 

2.3.3.2 Cyanide Oxidation 

Waste streams containing cyanide are segregated for separate treatment prior to common 

metals treatment. Cyanides are introduced through metal salts for plating and conversion 

coatings, and plating and cleaning baths. Cyanide is generally destroyed by oxidation, and 

chlorine is typically used as the oxidizing agent. If the cyanide is not removed before further 

treatment, it will prevent efficient removal of metals during common metals treatment (U.S. 

EPA, 1983a). 

2.3.3.3 Chromium Reduction 

Waste streams containing hexavalent chromium are segregated for separate treatment 

prior to common metals treatment. Hexavalent chromium-containing wastewaters are generated 

in several ways including chromium electroplating and chromate conversion coatings. Chemical 

reduction requires the addition of a chemical such as sulfur dioxide, sodium bisulfite, sodium 

metabisulfite, and ferrous sulfate, which form strong reducing agents in aqueous solutions that 

reduce hexavalent chromium to trivalent chromium. Trivalent chromium can then be removed 

from wastewater using precipitation in common metals treatment (U.S. EPA, 1983a). 

2.3.3.4 Emulsion Breaking 

Metal finishing wastewater may contain oily wastes from process coolants and lubricants, 

wastes from cleaning operations, wastes from painting processes, and machinery lubricants. If 

oily wastes are generated, they should be separated and pretreated to remove the oils before 

commingling for common metals treatment. Emulsion breaking removes emulsified oils from 

oil/water mixtures. Chemicals such as acids, salts, or polymers are added to the wastewater and 

agitated to break the oil/water emulsion bond. The oily residue rises to the surface where it is 

skimmed off or decanted from the remaining wastewater. The skimmed oily residue is typically 

stored in tanks for further processing or removal by a contractor, and the remaining wastewater is 

sent to common metals treatment (U.S. EPA, 1983a). 

2.3.4 Control and Treatment of Toxic Organics 

The Metal Finishing ELGs also establish discharge limitations and pretreatment standards 

on TTO. EPA defines TTO as the sum of the masses or concentrations of a specific list toxic 

organic compounds detected exist in the industrial user’s process discharge at a concentration 

higher than 0.01 mg/L.6 The primary source of TTO is from waste solvents. Although TTO may 

be present in combined wastewater and concentrated oily wastes generated during metal 

finishing operations, EPA determined that TTO concentrations from these sources were small 

and generally treatable by the technology basis for common metals treatment and the treatment 

of oily wastes (see Sections 2.3.1 and 2.3.3). The established TTO limit in the Metal Finishing 

ELGs was intended to prevent the dumping of concentrated toxic organic wastes from waste 

solvents, such as solvent degreasers and paint strippers. In addition to the TTO limit, EPA also 

established monitoring requirements for TTO in the Metal Finishing ELGs (U.S. EPA, 1983a, 

1983b). 

6 As listed at 40 CFR 433.11. 

2-12
 
 

 

 

 

Section 2– Existing Metal Finishing ELGs 

2.3.4.1 Monitoring Requirements 

Facilities choosing to measure ongoing compliance with the TTO limit via selfmonitoring need to report the results in the baseline monitoring report (BMR) and 90-day 

compliance report, which are submitted to the Control Authority.7 In lieu of self-monitoring for 

TTO, facilities can choose the certification alternative discussed in Section 2.3.4.2. Subsequent 

self-monitoring for TTO is required following the guidelines outlined in the General 

Pretreatment Regulations (40 CFR Part 403) for indirect dischargers and National Pollutant 

Discharge Elimination System (NPDES) permitting requirements for direct dischargers. If selfmonitoring is required to measure compliance with the limit, the facility needs to report 

analytical data only those for pollutants reasonably expected to be present in the wastewater 

(U.S. EPA, 1983b, 1985). Ongoing TTO monitoring is generally performed by those facilities 

that continue to dump waste solvents in the wastewater as a disposal practice. As indicated in the 

1983 Metal Finishing ELGs, EPA anticipated very few facilities with these practices because 

waste solvents have sufficient reclaim value to be recovered, and thus, EPA anticipated few 

facilities that would need to conduct periodic self-monitoring to comply with the regulations 

(U.S. EPA, 1983a). 

2.3.4.2 Toxic Organic Management Plan and Certification Process 

As an alternative option to self-monitoring, a facility may be allowed to comply with the 

requirements through the certification process, which requires that the discharger submit a Toxic 

Organic Management Plan (TOMP).8 Indirect dischargers certify in their semi-annual 

compliance reports to the control authority that they are implementing the TOMP and are not 

dumping toxic organics into the wastewater since the previous filing. For direct dischargers, the 

TOMP is incorporated as a condition of the NPDES permits and is reported in the comment 

section of the Discharge Monitoring Reports (DMRs) (U.S. EPA, 1983b, 1985). 

To determine whether a TOMP is a feasible alternative to TTO monitoring, the facility is 

required to complete a process engineering analysis to identify potential sources of TTO and then 

evaluate pollution control options to reduce or eliminate TTO in wastewater discharge. The 

facility may decide whether a TOMP is a feasible alternative to TTO monitoring after weighing 

the costs for implementing the pollutant control options with those for monitoring. If the TOMP 

is feasible, the facility can make a request to the control or permitting authority to implement the 

TOMP and certification process in lieu of the monitoring requirements. Specifically, the TOMP 

must generally include (U.S. EPA, 1985): 

•	 Identification of all the toxic organic compounds used by the facility.9 

•	 Method of disposal for all wastes associated with TTO (e.g., reclamation, 

incineration, and/or contract hauling). 

7 The Control Authority is considered the POTW, if it has an approved pretreatment program. Otherwise, the reports 

are submitted to the state, if it has an approved state pretreatment program, or to the EPA Region. 

8 Also referred to in the Metal Finishing ELGs as the solvent management plan. 

9 As defined in 40 CFR 433.12. 

2-13
 
 

 

 

 

Section 2– Existing Metal Finishing ELGs 

•	 Procedures followed by facility to assure that toxic organic compounds do not 

routinely spill or leak into any process wastestream that may be discharged. 

The TOMP is submitted to the facility’s control or permitting authority with baseline 

monitoring report to meet the requirements of the certification process (U.S. EPA, 1985). 

2.4 Applicability of the Existing ELGs to Current Operations 

The Metal Finishing ELGs reflect facilities, process operations, and wastewater 

management practices in 1983. Over the ensuing 32 years, process technologies and chemistries 

of metal finishing operations have evolved, and the industry has implemented more advanced 

treatment technologies than those described in Section 2.3. Additionally, many Metal Finishing 

facilities have developed waste minimization techniques leading to zero discharges or to the 

recovery/reuse of metal finishing wastewater. With these changes, stakeholders have raised 

questions regarding the applicability of certain operations to the Metal Finishing ELGs. These 

advances are discussed further in the following subsections. 

2.4.1	 Changes to Industry Profile 

There is uncertainty regarding how the industry profile has changed since 1983. Based on 

a 2008 National Center for Manufacturing Sciences review of the surface finishing industry 

(including metal finishing) and additional discussions with industry representatives, EPA 

believes the industry has moved towards a more global market over the years. In addition, some 

U.S. firms may have more recently attempted to concentrate the industry (i.e., incorporate the 

smaller job shops into larger companies) to achieve economies of scale, expand niche markets, 

and provide a larger range of finishing services in a global market. Many firms may have also 

shifted surfacing operations to non-U.S. locations (such as Asia, India, Mexico, Canada, and 

Europe) to further reduce costs. Outsourcing metal finishing operations has generally been more 

cost effective than operating captive metal finishing facilities; therefore, EPA anticipates a shift 

in the number of captive facilities versus job shops as well as a decrease in the number of 

domestic job shops (ERG, 2016; U.S. EPA, 2015a). 

2.4.2	 Scope of Metal Finishing Operations 

EPA has received comments from the Association of Clean Water Administrators 

(ACWA) urging it to consider the applicability of the Metal Finishing ELGs to current metal 

finishing operations (U.S. EPA, 2015c). Specifically, stakeholders identified a need for clarifying 

descriptions of metal finishing operations listed in the ELGs, including: 

•	 Guidance to distinguish between metal finishing operations in which the same 

acid is used for different functions, such as etching and chemical milling, acid 

cleaning, chemical conversion coating, and similar cases. 

•	 Clarification of how the Metal Finishing ELGs apply to current industry practices, 

including metal finishing processes or chemical alternatives that are not 

specifically identified in the ELGs. 

2-14
 
 

 

Section 2– Existing Metal Finishing ELGs 

•	 Clarification of how the Metal Finishing ELGs apply to newer manufacturing 

operations that use metal finishing processes not identified in the ELGs, such as 

solar panel manufacturing and cell phone manufacturing. 

2.4.3	 Process Technology Modifications and Alternative Chemistries 

Since 1983, numerous modifications and process alternatives have been developed for 

processes conducted at metal finishing facilities such as cleaning and rinsing operations, coating 

and plating processes, and polishing. These modifications may impact the overall wastewater 

volume generated (and subsequently treated) as well as the general wastewater characteristics of 

metal finishing wastewater. Section 4.2 of this report further discusses updates to metal finishing 

process technologies. Additionally, alternatives to traditional chemistries used in the metal 

finishing operations have been developed, primarily alternatives to chemistries using cadmium, 

hexavalent chromium, phosphate, and cyanide. See Section 4.3 of this report for further 

discussion on alternative chemistries. 

2.4.4	 Technological Advances in Wastewater Treatment 

At promulgation, it was evident that other treatment technologies, while not widespread 

in the industry, did exist and could be used to meet the discharge limitations. Since then, 

advanced treatment technologies and zero-discharge or reuse practices have emerged within the 

industry for the treatment and/or recycling of metal finishing wastewater. 

Based on more recent observations from the regional EPA pretreatment coordinators and 

industry sources, emerging technologies are being used to some extent, but are still not 

widespread within the industry (U.S. EPA, 2015a). Some improvements are being applied to the 

technologies identified in the 1983 rule, including new chemical additives for improved 

precipitation and sludge generation, and alternative filtration techniques to replace or supplement 

clarification. Section 4.4 of this report further discusses treatment technologies that have 

emerged in the industry. 

Waste minimization technologies for reuse and zero discharge strategies have a small 

footprint within the metal finishing industry. Vendors have described potential application of 

closed-loop processes for metal finishing operations to collect, treat, and return process 

wastewater for reuse (U.S. EPA, 2015a). Section 4.2 of this report further describes waste 

minimization technologies and practices available to reduce the volume of wastewater 

discharged from metal finishing operations and to recover other process waste streams to be 

reused in the process. 

2-15
 
 

 

 

 

 

 

 

 

Section 3– Study Activities and Progress 

3. STUDY ACTIVITIES AND PROGRESS 

This study seeks to answer the key questions described in Section 1. Historically, EPA 

has used various approaches for collecting information to further inform Agency actions and 

decisions related to effluent guidelines development and revision for select industries. Typically, 

a preliminary study profiles an industry category, gathers information about the hazards posed by 

its wastewater discharges, collects information about availability and cost of treatment and 

pollution prevention technologies, assesses the financial status of the facilities in the category, 

and investigates other factors to determine whether revisions to the current effluent guidelines 

are warranted. As the study evolves, EPA may decide to conduct a more detailed study, which is 

a more rigorous examination of the industry and its practices, and may include primary data 

collection activities (such as industry questionnaires and wastewater sampling and analysis) to 

fill data gaps (U.S. EPA, 2015a). 

As part of this study, EPA is evaluating facilities that make up the metal finishing 

industry, their size, and the major markets they serve; the types of metal finishing operations and 

alternative chemistries used that may potentially introduce new pollutants of concern that are not 

currently regulated; new sources of metal finishing wastewater that contribute to the overall 

wastewater characteristics, such as wet air pollution controls or new operations in metal 

finishing; and advanced technologies that facilities employ for the treatment and subsequent 

recycle or discharge of metal finishing wastewater. The study initially focuses on examining 

existing information that EPA collected or will collect through literature reviews, technical 

conferences, and discussions with industry experts and stakeholders. EPA also plans to conduct 

site visits at metal finishing facilities, analyze current available discharge data, and review 

information collected on the industry during the MP&M Rulemaking development. This section 

describes these activities planned for the preliminary study of the Metal Finishing Category and 

the current status of those planned activities. Section 4 of this report further details EPA’s 

preliminary findings, which will lay the foundation for EPA’s decisions on how to proceed with 

the study. 

3.1 Literature Review 

As an initial step in answering the key study questions, EPA collected and reviewed 

technical literature about the metal finishing industry. Using a defined list of key words, listed in 

Appendix B, EPA identified technical papers and reports, studies, peer-reviewed journal articles, 

and industry publications on metal finishing operations and wastewater management. EPA used 

several research collections and search engines10 to identify over 130 documents that were 

subject to EPA’s quality assurance standards and procedures for inclusion in a literature review 

(these standards are described in Section 6 of this report). EPA categorized the documents into 

three topic areas: 

10 Research collections and search engines used include Kirk-Othmer Encyclopedia of Chemical Technology, 

Google Scholar, Dialog, The Strategic Environmental Research and Development Program (SERDP)-Environmental 

Security Technology Certification Program (ESTCP), Rowan Technology Group, Science Direct, ACS Publications, 

Academic Search, Directory of Open Access Journals, and PLOS One. 

3-1
 
 

 

 

Section 3– Study Activities and Progress 

•	 Process technology documents, addressing improvements in metal finishing 

process techniques and technologies that lower air emissions, reduce chemical 

use, or decrease wastewater pollutant discharges. 

•	 Alternative chemistries documents discuss innovative metal finishing chemistries 

that can be used to reduce toxicity, wastewater volume, and pollutant discharges. 

•	 Wastewater treatment technology documents discuss innovative technologies to 

reduce wastewater pollutant concentrations and strategies to achieve zero liquid 

discharge at metal finishing facilities. 

A significant portion of the preliminary findings of this study to date (presented in 

Section 4 of this report) is based on the data and information gathered from the literature review. 

3.2 Technical Conferences 

EPA attended the Water Environment Federation’s Annual Technical Exhibition and 

Conference (WEFTEC) on September 26-30, 2015. WEFTEC provides water quality education 

and training by offering technical sessions and workshops on a variety of topics and provides 

access to information from exhibitors on water management technologies and services. EPA 

attended presentations and obtained papers from proceedings relevant to the general categories 

listed in Section 3.1. EPA plans to review publications from WEFTEC regarding metal finishing 

wastewater management practices, to support the preliminary study of the industry. 

EPA also attended the Engineers’ Society of Western Pennsylvania’s International Water 

Conference (IWC) on November 15-19, 2015. IWC discusses the most recent scientific advances 

and practical applications for treatment, use, and reuse of water for engineering purposes, 

industry or otherwise. Presenters and attendees of the IWC include researchers, practicing 

engineers, managers, educators, suppliers, contractors, government workers, and end users. EPA 

plans on reviewing IWC presentations and papers relevant to the metal finishing industry in 

support of the preliminary study. 

EPA plans to continue seeking other technical conferences to further inform the Agency 

on current industry practices. 

3.3 Industry Experts 

EPA contacted a variety of experts to improve its understanding of the metal finishing 

industry and to gain different perspectives on the 1983 regulations and current industry 

operations. 

3.3.1	 Metal Finishing Facilities and Technology Vendors 

EPA contacted personnel from metal finishing facilities and technology vendors 

advertising zero discharge systems for the treatment of metal finishing wastewater (ERG, 2016). 

EPA identified and selected facilities and vendors based on: recommendations by other industry 

experts and trade groups; directories and/or marketing databases; information from previous 

EPA data collection efforts; and other publicly available information on metal finishing 

operations and wastewater treatment technologies of interest to the study. Information collected 

3-2
 
 

 

 

 

 

 

Section 3– Study Activities and Progress 

from vendor and facility contacts fulfilled several objectives of the preliminary study: 1) to 

obtain information that helps answer key study questions; 2) to identify potential candidate 

facilities for future EPA site visits; 3) to obtain industry perspectives on the existing 1983 Metal 

Finishing ELGs; and 4) to initiate assessment of the technical and economic feasibility of waste 

minimization practices. EPA plans to continue calling additional metal finishing facilities and 

technology vendors to pursue these objectives further. 

3.3.2 Pretreatment Coordinators 

As discussed in Section 2, the majority of metal finishing facilities are indirect 

dischargers subject to pretreatment standards under the Metal Finishing ELGs. As part of the 

Metal Finishing Category Review under EPA’s annual review process (CWA §304m), EPA had 

discussions with the federal pretreatment coordinator and regional pretreatment coordinators who 

have direct experience with metal finishing wastewater issues at POTWs. These personnel 

provided insight on the applicability of the Metal Finishing ELGs. The coordinators described 

key issues encountered by POTWs receiving metal finishing wastewater, primarily from new or 

modified metal finishing processes. Issues included misapplication of limits in permit 

applications, applicability of the 46 metal finishing unit operations, and new source criteria 

development (U.S. EPA, 2015a). As part of the preliminary study, EPA will continue to have 

discussions with the coordinators to identify metal finishing scenarios for which the applicability 

of the regulations is unclear. 

3.3.3 Other Stakeholders 

EPA held meetings with the Association of Clean Water Administrators (ACWA) and 

several pretreatment coordinators in November 2015 to gather different perspectives on the metal 

finishing category (U.S. EPA, 2015d). EPA also plans to initiate discussions with other 

organizations, such as the National Association of Clean Water Agencies (NACWA), to 

understand their perspective on the implementation of the 1983 regulations. 

3.4 Industry and Trade Organizations 

In response to EPA’s published plans to further review the Metal Finishing Category 

under CWA §304m authority, the National Association for Surface Finishing (NASF) reached 

out to EPA to support EPA’s information gathering efforts for the preliminary study (U.S. EPA, 

2015b, 2015c). NASF is a trade association representing the interests of the North American 

surface finishing industry, including metal finishing. At NASF’s invitation, EPA spoke at the 

NASF Washington Forum on April 14-16, 2015, to discuss the Agency’s plans to review the 

metal finishing industry. EPA also met with NASF in August and November 2015 to discuss the 

preliminary study of the Metal Finishing Category (NASF, 2015; U.S. EPA, 2015e, 2015f). EPA 

and NASF will continue discussions on approaches for collecting information on the industry to 

answer key study questions and to explore potential opportunities to collaborate with industry 

and provide additional outreach activities. 

3-3
 
 

 

 

Section 3– Study Activities and Progress 

3.5 Site Visits to Metal Finishing Facilities 

To date, EPA has accompanied pretreatment coordinators on visits to the Bureau of 

Printing and Engraving (Washington, D.C.), Bethesda (Maryland) Art Metal Works, and Metro 

Plating and Polishing (Kensington, Maryland). 

EPA will continue site visits to metal finishing facilities to observe operations and 

wastewater management practices. EPA may also request information, such as historical data on 

raw and treated wastewater samples, general process design, and typical operating conditions. 

EPA may also obtain information on the wastewater treatment technologies and treatment 

chemicals used on site. EPA will use information gathered through industry experts (as described 

in Section 3.3) to identify potential site visit candidates for the coming year. 

3.6 Metal Products and Machinery (MP&M) Rulemaking 

EPA will continue to review supporting documentation from the MP&M proposed 

rulemaking (proposed in 2000), which evaluated facilities covered under the Metal Finishing 

ELGs in the 1980’s and 1990’s. As part of that proposed rulemaking, EPA extensively reviewed 

the changes to the metal finishing industry, process and wastewater technology improvements 

made by the industry, and metal finishing wastewater characteristics. EPA will evaluate any 

significant changes to the industry since its review during the MP&M proposed rulemaking of 

2000, which will further define the scope of this study. 

3-4
 
 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

4. PRELIMINARY STUDY FINDINGS 

This section describes the information EPA gathered to date for the preliminary study of 

the Metal Finishing Category, which will help answer the key study questions outlined in Section 

1 of this report. EPA summarized the findings into five main categories that are presented in the 

following subsections: 

• Changes in the metal finishing industry profile (Section 4.1), 

• Process technologies (Section 4.2), 

• Alternative chemistries (Section 4.3), 

• Wastewater treatment technologies (Section 4.4), and 

• Applicability and other regulatory considerations (Section 4.5). 

4.1 Changes in the Metal Finishing Industry Profile 

As discussed in Section 2.1, at promulgation of the 1983 Metal Finishing ELGs, the 

Metal Finishing and Electroplating Categories included a total of 13,470 facilities, consisting of 

10,000 captive facilities and 3,470 job shops and IPCB manufacturers. The existing captive 

facilities ultimately fell into the Metal Finishing Category (after the final compliance date) and 

the 3,470 job shops and IPCB manufacturers remained in the Electroplating Category (U.S. EPA, 

1984). EPA has not fully evaluated the changes to the number of facilities in the metal finishing 

industry as part of this preliminary study. However, several EPA efforts have collected recent 

information on this population. 

In the MP&M proposed rulemaking (published in 2000), EPA estimated that 

approximately 12,700 facilities performed metal finishing operations. EPA classified the 

facilities into four subcategories: general metals, metal finishing job shops, non-chromium 

anodizing, and printed wiring boards (U.S. EPA, 2000a). The general metals category may have 

included facilities that did not conduct any of the six primary metal finishing operations that 

define the applicability of the Metal Finishing ELGs and, therefore, the number of facilities may 

be an overestimation of those covered under 40 CFR Part 433. These estimates were primarily 

based on responses to industry surveys sent to MP&M facilities in 1989 and 1996 (U.S. EPA, 

2000a). 

In 2012, EPA revised the National Emission Standards for Hazardous Air Pollutant 

(NESHAP) Emissions: Hard and Decorative Chromium Electroplating and Chromium 

Anodizing Tanks (Subpart N).11 EPA estimated 1,339 existing U.S. facilities performing metal 

finishing operations that involved chromium. Outside California, there were 188 large and 394 

11 EPA also revised the NESHAP for Steel Pickling-HCl Process Facilities and Hydrochloric Acid Regeneration 

Plants (Subpart CCC) in 2012; however, steel pickling facilities (estimated at 100 facilities) are subject to the Iron 

and Steel Category (under 40 CFR Part 420) and therefore, would not be regulated under the Metal Finishing 

Category (40 CFR Part 433). 

4-1
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

small hard chromium electroplating facilities.12 The distribution of large and small facilities was 

unknown in California, but there are approximately 70 additional hard chromium electroplating 

facilities there. There are an estimated 170 chromium anodizing plants and the 517 decorative 

chromium electroplating facilities in the U.S. (77 FR 58220). These estimates are a subset of the 

facilities comprising the metal finishing industry but provide a more recent look at the population 

of chromium electroplaters. 

As part of EPA’s 2014 Annual Effluent Guidelines Review, EPA searched for recent data 

to determine the number of facilities that currently fall into the Metal Finishing Category. The 

2007 Economic Census provides a general industry description for each North American 

Industry Classification System (NAICS) code under which these facilities may fall; however, it 

does not detail facility-specific process operations or wastewater discharge practices, which form 

the basis for determining whether the Metal Finishing ELGs would apply to specific facilities. In 

the 2011 Annual Effluent Guidelines Review, EPA identified 166,356 facilities included in the 

2007 Economic Census for the 200 NAICS codes. However, this number includes establishments 

that are distributors or sales facilities, not just manufacturers (U.S. EPA, 2012a). It may also 

include facilities that do not conduct any of the six primary operations and thus, would not be 

regulated under the Metal Finishing ELGs. In previous annual reviews, EPA has identified the 

number of facilities submitting discharge monitoring reports (DMRs) and reporting to EPA’s 

Toxic Release Inventory (TRI). However, EPA determined that these data sources include only a 

fraction of the facilities that would fall under the Metal Finishing Category ELGs, due to the 

limitations of the data sets. Therefore, these data sources do not adequately provide a complete 

picture of the metal finishing industry (U.S. EPA, 2015a). 

After discussions with regional and state pretreatment coordinators, EPA learned that 

some EPA regions and states have maintained lists of industrial users that discharge metal 

finishing wastewater to POTWs and are subject to pretreatment standards under 40 CFR Part 

433; however, a national inventory of metal finishing facilities does not exist (U.S. EPA, 2015a). 

As discussed in Section 2.4.1, there is uncertainty in how the metal finishing industry profile has 

changed. EPA suspects that the industry has trended toward a wider market since 1983, with 

market share dispersed among many 

companies. Recent discussions with metal Six Primary Metal Finishing Operations 

finishing facilities also suggest some growth 

40 CFR Part 433 applies to discharges from metal of the U.S. metal finishing industry due to finishing facilities conducting any of the six primary increased product quality demands in certain operations: electroplating, electroless plating, markets that cannot be met elsewhere (ERG, anodizing, coating (chromating, phosphating, and 

2016). coloring), chemical etching and milling, and printed 

circuit board manufacturing. If any of these six 

4.2	 Process Technologies operations are conducted at a facility, then the 

provisions also apply to any of the 40 ancillary 

processes (which include cleaning and polishing) EPA identified papers reporting listed in 40 CFR Part 433, if any are also being advances in metal finishing process conducted at the facility. 

12 As defined in the NESHAP, large hard chromium electroplating facilities are any facility with a cumulative 

annual rectifier capacity equal to or greater than 60 million ampere-hours per year (amp-hr/yr). Small hard 

chromium electroplating facilities are defined as any facility with a cumulative annual rectifier capacity less than 60 

million amp-hr/yr. 

4-2
 
 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

techniques and technologies. The papers cover cleaning and rinsing operations, coating and 

plating processes, and polishing. Numerous modifications and process alternatives have been 

developed for these processes since the 1983 Metal Finishing ELGs were promulgated. The 

following subsections discuss the technological advancements in each process category. 

4.2.1	 Cleaning and Rinsing Operations 

Most metal finishing operations require surface preparation including cleaning and 

rinsing. Cleaning and rinsing remove oil and dirt to ensure that the finishes applied during 

coating or plating properly adhere to the surface and meet performance expectations. Surface 

preparation can range from simple mechanical techniques, such as spray cleaning, abrasive 

blasting, buffing, or grinding, to more complex chemical techniques, such as acid washes and 

multi-stage acid/alkaline cleaning processes.13 These techniques may be used alone or in 

combination to remove dust, grease, oils, oxides, base metal, and other materials from the 

surface of the object (U.S. EPA, 1979). 

Acidic or alkaline chemicals are used as cleaning agents. According to studies done at the 

Rochester Institute of Technology and Wayne State University (Fister, 2010; Xiao, et al., 2012), 

cleaning and subsequent rinsing are the primary sources of wastewater from metal finishing 

facilities. However, alternative methods of cleaning and rinsing are increasingly used to reduce 

water use and chemical consumption (Fister, 2010; Xiao & Huang, 2012). In recent discussions 

with industry, EPA learned that cleaning and rinsing operations may be conducted over other 

rinse tanks or plating baths to collect and reuse the wastewater. Facilities have also implemented 

countercurrent rinse cycles to reduce the replacement frequency of the rinsewater used in rinsing 

operations (ERG, 2016). 

The Wayne State study reviewed the growing use of “integrated profitable pollution 

prevention” (IP3) techniques by metal finishers to reduce water use and chemical consumption 

(Xiao & Huang, 2012). That study identified the following five IP3 technologies: 

•	 A cleaning and rinse process control method that uses a two-layered hierarchical 

dynamic optimization technology to conserve chemical and water use. The lower 

layer adjusts local control variables, such as chemical concentration and water 

flow rate, to optimal settings. The upper layer uses the optimal processing time in 

all the cleaning and rinse tanks to achieve the desired surface characteristics. The 

two layers, when used together, maximize cleaning and rinsing efficiency, thereby 

minimizing chemical use and conserving water. 

•	 Re-designing water flow patterns through a rinsing system to optimize flow rates. 

The water flow patterns can be switched during operation (based on current use) 

to maximize water reuse while maintaining rinse water quality. 

•	 A sludge reduction method to classify sludge as avoidable or unavoidable. The 

method determines the amount of avoidable sludge and reduces it by altering the 

chemical use and identifying unnecessarily long cleaning times. 

13 Acid washes are subject to Metal Finishing ELGs (U.S. EPA, 2004). 

4-3
 
 

 

 

 

Section 4 – Preliminary Study Findings 

•	 A model-based design and operation strategy to derive an optimal reversed dragout network system to recover chemical losses from cleaning and plating systems. 

•	 A dynamic hoist scheduling algorithm to generate a production schedule based on 

waste generation, chemical consumption, and energy use. 

To demonstrate the effectiveness of IP3 technologies, the researchers also described a 

manually operated bronze cyanide plating line at a facility that implemented a near-zero 

chemical and metal discharge system, intended to reduce chemical consumption and water use 

(Xiao & Huang, 2012). Figure 4-1 presents the original configuration of the bronze cyanide 

plating line. Each rack of parts is first cleaned (soak cleaning and electro cleaning or de-rusting) 

and then rinsed. As shown in the diagram, the initial cleaning and rinsing are followed by an acid 

clean step, followed by another rinse before the actual copper and tin plating (Xiao & Huang, 

2012). 

Source: (Xiao & Huang, 2012) 

Figure 4-1. Original Process at the Bronze Cyanide Plating Facility 

Figure 4-2 presents a revised rinsing configuration. The facility installed a new rinse tank 

(Tank 11) so chemical solvents from the soak clean and electro clean steps, accumulated in Rinse 

Tank 3, could be recovered and reused. The tank before New Rinse Tank 11 is charged for static 

rinse, and New Rinse Tank 11 is for flow rinse. Rinse Tank 8 is also charged for static rinse, 

while Rinse Tanks 9 and 10 are countercurrent rinse tanks. Two pumps are added to the system, 

one to pump the solution from Rinse Tank 3 to the electrocleaning tank, and one to pump water 

back to the plating tank from Rinse Tank 8 (Xiao & Huang, 2012). 

Source: (Xiao & Huang, 2012) 

Figure 4-2. New Process at the Bronze Cyanide Plating Facility 

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Section 4 – Preliminary Study Findings 

After making these changes, the facility reduced use of the derusting chemicals (used in 

the electroclean and acid clean steps) by 40 percent, the soak cleaners by 100 percent, and the 

acid by 8 percent. Rinse water costs were reduced by 40 percent and wastewater treatment costs 

were reduced by 70 percent. According to the study authors, implementation of profitable 

pollution prevention techniques typically involve slight modifications of processes, which 

require little capital investment but can increase efficiency and reduce waste (Xiao & Huang, 

2012). 

Traditional rinsing methods include independent rinse tanks, with rinse water flowing in 

and out of each tank, and countercurrent rinsing, with relatively clean rinse water flowing from 

the second rinse tank to the more contaminated primary rinse tank. The top diagram in Figure 

4-3 shows a typical rinse system with four independent rinse tanks; and the bottom diagram 

depicts a reduced flow rinse scheme (Fister, 2010). 

The study done by the Pollution Prevention Institute (PPI) at the Rochester Institute of 

Technology (Fister, 2010) indicates that reactive rinsing can be used to reduce water use in 

rinsing processes that include both acid and alkaline rinse tanks. In a reactive rinse system, as 

shown in the bottom diagram of Figure 4-3, the acid from the acid rinse is sent to a preceding 

alkaline rinse tank where it neutralizes residual alkalinity in the water. In traditional rinsing 

methods, the acid contained in the rinse water is sent to be treated. Reactive rinsing allows any 

rinse water from the alkaline rinse that is dragged out by parts to the acid tank to now contain 

acid that would have otherwise been wasted (Fister, 2010). According to Fister (2010), the total 

water use for a rinse system with four independent rinse tanks is 12 gallons per minute (gpm) 

(top diagram, Figure 4-3). By incorporating reactive rinsing into a reduced flow rinsing scheme 

(bottom diagram, Figure 4-3), the water use is 3 gpm. This results in a savings of $5,400 per year 

in water costs (at a rate of $5 per 1,000 gallons for a 2,000 hours-per-year operation) (Fister, 

2010). 

Powder coating facilities commonly use phosphate-based cleaning and rinsing systems 

before painting large fabricated products. Conventional cleaning and rinsing systems are 

generally separate and use large amounts of water and chemicals to clean, degrease, and apply a 

pretreatment chemical to products (Guidetti, et al., 2009). EPA identified two alternatives to 

conventional phosphate-based cleaning and rinsing systems: the Cleaner Phosphoric Recycling 

(CPR) System and the plaforization process. 

From reviewing vendor literature and a facility case study, EPA found that CPR Systems, 

a division of T. George Podell & Co, Inc., has developed the CPR System primarily for 

companies that manufacture large fabricated steel and aluminum products. The CPR System 

incorporates non-rinse cleaning, degreasing, and pretreatment in one-step. PhosBite 101, a 

combined cleaning and coating chemical, is used in the wash water to surface clean and generate 

a conversion coating on the metal substrate to improve paint adhesion. Water and chemicals used 

in the system are recycled, greatly reducing water and chemical use compared to conventional 

systems. The CPR system was introduced in 1989. According to CPR Systems, over 100 

facilities in the United States have installed the CPR System (ERG, 2016; Tucker, 2013). 

4-5
 
 

 

Section 4 – Preliminary Study Findings 

Source: (Fister, 2010) 

Figure 4-3. Potential Rinse Systems in Facility with Metal Finishing Processes 

A powder coating facility in Pennsylvania installed the CPR System in 2013 to clean and 

pretreat large hydraulic dump trailers, while also decreasing water and chemical use. Facility 

contacts reported that after learning to use the new process, they were able to reduce chemical 

and water consumption by 70 percent, primarily through recycling (Tucker, 2013). 

From reviewing industry literature, EPA identified the plaforization process, a second 

alternative to conventional phosphate-based cleaning and rinsing systems. The technology was 

first introduced in the European market by PAI-KOR S.r.l, in Italy, in the late 1960s. As of 2009, 

approximately 500 industrial facilities in more than 25 countries had incorporated plaforization 

processes. Plaforization is a one-step process with no rinse; it does not use water and creates no 

wastewater, sludge, or other contaminants (Guidetti, et al., 2009). 

The chemistry is based on organic high-boiling-point fluids and an organic polymeric 

resin modified by phosphating groups. Several different processes occur almost simultaneously: 

organic fluids dissolve oily contaminants, solid particles are washed off and taken into the 

solution, the phosphating acid part of the organic resin attacks the metal surface to clean and 

pretreat the metal. Finally, an organic polymeric resin is applied to the part with a thickness of 

about one micron (Guidetti, et al., 2009). 

According to the developer of plaforization, the process eliminates the need for 

continuous chemical analysis, dumping tanks, chemical replenishment, and sludge removal, all 

4-6
 
 

 

 

 

Section 4 – Preliminary Study Findings 

of which are required with conventional phosphate-based cleaning and rinsing systems (Guidetti, 

et al., 2009). Plaforization also allows many metals, such as steel, aluminum, and cast iron, to be 

treated with the same chemistry (Guidetti, et al., 2009). Figure 4-4 shows an example of a 

plaforization system installed for batch spraying equipment. In this system, parts are manually 

hung in the washer; the unit is equipped with three risers with nozzles that move during 

treatment to completely bathe all the part surfaces. 

Source: (Guidetti, et al., 2009) 

Figure 4-4. Plaforization System for Batch Spraying Equipment 

4.2.2 Coating and Plating Processes 

Numerous coating types are used in metal finishing, including transition metal coatings, 

hexavalent and trivalent chromium coatings, and graphene nanocomposite coatings. In 2008, the 

Strategic Environmental Research and Development Program (SERDP), an environmental 

research program under the Department of Defense (DoD),14 completed a study on ultraviolet 

(UV)-curable, corrosion-inhibiting primers and high-performance topcoats that protect aluminum 

substrates, specifically for aircraft interiors. Conventional coatings used for DoD vehicles release 

volatile organic compounds (VOC) during application and curing. Additionally, while the 

equipment is in use, flaking and chipping of the coating can cause hazardous substances, such as 

hexavalent chromium, to enter the environment. The goal of DoD’s study was to test a 

combination of chromate-free and VOC-free substrate preparation and coating systems to 

identify a coating system that eases compliance with current and anticipated environmental 

regulations, and at the same time makes coating application simpler and faster. Results from the 

study indicated that all tested coating systems provided good adhesion, fluid resistance, impact 

and solvent resistance, and low-temperature flexibility, making them viable alternatives to 

conventional coatings. These coating systems do not release VOCs during application or curing, 

and minimize flaking and chipping, thereby reducing hazardous materials (such as hexavalent 

chromium) in the environment. The process tested can be used in many industries and products, 

14 Two environmental research programs exist under the DoD: the Strategic Environmental Research and 

Development Program (SERDP), and the Environmental Security Technology Certification Program (ESTCP). 

4-7
 
 

 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

including aircraft and spacecraft, ground and marine vehicles and equipment for all military 

branches, and industrial coatings in chemical and mechanical plants (Phely-Bobin, 2010). 

A study performed at the University of Ulster investigated the corrosive response of hot 

rolled steel (HRS) after exposure to various pre-powder-coating surface treatments (Tepe, et al., 

2008). Powder-coated HRS is used extensively in the automotive, agricultural, and appliance 

industries, among others. The study reviewed conventional pre-powder coating treatments, 

including iron and zinc phosphate, as well as newer nano-structured conversion coatings (such as 

zirconium-based coatings). The study reported that the nano-structured conversion coatings 

perform as well as or better than the conventional coatings, and can enhance the corrosion 

resistance of powder coated HRS. However, researchers determined that achieving the optimally 

effective corrosion barrier with zirconium-based nano-scaled conversion coatings requires the 

removal of oxide scale from the substrate before any pre-powder-coating treatments (Tepe & 

Gunay, 2008). Zirconium-based coatings are further discussed in Section 4.3. 

According to a study on the use of ionic liquids in metal finishing practices, conventional 

coating and plating processes based on aqueous technologies such as cyanide or hexavalent 

chromium are well established in the metal finishing industry (Smith, et al., 2010).15 However, 

many companies are feeling pressure to develop new coating and plating processes in order to 

increase process efficiency, decrease energy use and wastewater discharges, and reduce the use 

of toxic chemicals (Smith, et al., 2010). Due to this pressure, the New Ionic Liquid Solvent 

Technology to Transform Metal Finishing Products and Processes (IONMET) consortium was 

developed in Europe. The IONMET project consists of 33 partners, including industrial 

companies, trade associations, and research institutions. The overall objective of the project is to 

introduce breakthrough ionic liquid technology into metal finishing processes. Ionic liquids are 

ionic materials that are liquid below 100 degrees Celsius and have properties that make them 

well-suited for metal finishing, such as high solubility of metal salts, high conductivity, and 

unique metal ion coordination chemistry (Smith, et al., 2010). 

The IONMET consortium scaled up five room temperature ionic liquid metal deposition 

processes: 

• Electropolishing; 

• Hard chromium electroplating; 

• Aluminum plating; 

• Immersion silver displacement; and 

• Zinc-tin barrel plating. 

The IONMET consortium found that in all five processes, ionic liquids could be 

considered drop-in replacements for existing aqueous solutions composed of strong inorganic 

acids and toxic reagents (i.e., all five processes are effective metal coating processes). Ionic 

liquids are easy to handle, inexpensive, and have low toxicity, making them attractive 

alternatives to conventional coating and plating solutions. The IONMET consortium stated that 

15 Ionic liquids are salts in the liquid state, which act as powerful solvents or electrically conducting fluids. 

4-8
 
 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

further research is necessary, but that ionic liquids have a high potential to be incorporated into 

metal finishing processes (Smith, et al., 2010). 

In the United States, SERDP is researching the application of ionic liquids. The DoD 

expects this research to illuminate key mechanisms and process variables for using ionic liquids 

in electroplating aluminum, specifically related to weapon systems. The project is expected to be 

completed in 2016 (Dai, 2014). 

According to industry experts, brush plating, also known as spot plating, is an 

electroplating process in which a pad is used to apply aqueous coatings, such as nickel, hard 

chromium, silver, etc., to a substrate (Chaix, et al., 2013). Advantages of brush plating include 

low costs, limited need for extensive air handling or scrubbing, and portability. However, it can 

be messy, with drips and splatters, and is best used for small areas. An alternative to brush 

plating is brush electrofinishing, which features a computerized non-drip stylus. According to 

industry experts, brush electrofinishing can be performed in any orientation, including overhead, 

and it eliminates drips, splashes, and most of the fumes associated with brush plating (Chaix, et 

al., 2013). The brush electrofinishing technique can reduce air emissions and replace toxic 

materials with less toxic alternatives, while still maintaining process control (Chaix, et al., 2013). 

4.2.3 Polishing 

Polishing (i.e., smoothing out surface defects) is typically one of the final steps in metal 

finishing. According to industry literature, some polishing is traditionally done by hand, making 

it one of the most time-consuming and expensive steps in metal finishing (Pusavec, et al., 2014). 

An alternative to hand polishing is abrasive flow machining (AFM), in which the flow of a 

pressurized abrasive polymer medium removes excess material from part surfaces. Pusavec and 

Kenda (2014) researched the performance and energy efficiency of AFM, focusing on an 

upgrade of AFM that incorporates a movable/rotatable mandrel (AFMmm). Their study looked 

at a computer simulation of AFMmm in the finishing of gear injection molds and performed 

fatigue and performance tests. They concluded that the AFMmm finishing system uses less 

polishing fluid and energy compared to the traditional AFM system and hand polishing, which 

improves the efficiency and environmental impact of the technology (Pusavec & Kenda, 2014). 

4.2.4 Summary of Process Technologies 

Based on recent literature and industry discussions, there are a few reasons for which 

industry would consider process technology advances: 1) to improve the efficiency of the 

coating/finishing operation; 2) to implement pollution prevention strategies that would reduce 

the impact of the pollutants generated and discharged; and 3) to reduce the operating costs 

associated with chemical usage, wastewater treatment, and hazardous solid waste disposal. 

Industry discussions have suggested that wastewater management and solid waste 

disposal generally play a significant role in the overall operating costs at metal finishing 

facilities. Recycling generated wastewater and chemicals back to the process minimize the need 

for the facility to replenish with a separate water source or with new chemicals. Minimizing the 

chemical usage can also reduce the volume of sludge generated and disposed during wastewater 

treatment. EPA learned that several facilities are implementing pollution prevention practices to 

minimize the volume of wastewater discharged, including a countercurrent rinsing system and 

4-9
 
 

 

 

 

Section 4 – Preliminary Study Findings 

replenishing plating baths that have evaporative losses with both untreated and treated rinsewater 

(ERG, 2016). To date, EPA has not found information that suggest that the primary sources of 

wastewater has changed. A significant portion of the wastewater generated continues to originate 

from rinsing and cleaning operations. Improvements to coating and plating processes have not 

shown to generate additional waste streams and generally aim to minimize the amount of process 

losses associated with the technology. Several facilities and vendors suggest that chemical 

recovery operations do occur at metal finishing facilities to minimize the need to treat and 

dispose of process losses containing valuable plating chemicals as waste (see Section 4.4 for 

information of technologies used for this purpose). 

4.3 Alternative Chemistries 

At the promulgation of the 1983 Metal Finishing ELGs, facilities covered by the ELGs 

operated one of six primary operations, including electroplating, electroless plating, anodizing, 

coating, etching and chemical milling, and printed circuit board manufacturing. Generally, these 

six operations produce a coating on the surface of the base materials that consist of a metal or 

metal oxide. See Section 2 for detailed descriptions of the traditional chemistries used in these 

six metal finishing operations, as well as the 40 additional unit operations regulated by the ELGs. 

EPA’s literature review identified papers reporting on alternatives to the traditional 

chemistries used in metal finishing operations, primarily alternatives to chemistries using 

cadmium, hexavalent chromium16, phosphate, and cyanide. Exposure to these materials may 

result in adverse health and/or environmental impacts. In addition, solid waste and wastewater 

generated from these materials result in high costs for hazardous waste disposal. The following 

subsections discuss alternatives to the most common metal finishing chemistries: cadmium 

plating, the use of hexavalent chromium in plating, conversion coating, primers, sealers, and 

cleaners, phosphate conversion coatings and cleaners, and cyanide in plating baths. 

4.3.1 Cadmium Plating Alternatives 

Cadmium is widely used in electroplating and electroless plating operations to provide 

corrosion protection in applications for the aerospace, military, and aviation fields. Cadmiumplated high-strength steel is used in aircraft, spacecraft, and components of weapon systems. 

According to Keith Legg of Rowan Technology Group, the aerospace and military industries 

have successfully replaced most cadmium coatings used on nuts and bolts with a safer zincnickel plating alternative (K. Legg, 2012a). However, industry has not identified replacements 

for cadmium plating on structural materials because of the strict requirements for high corrosion 

resistance and a narrow margin for material fatigue (Berman, et al., 2009). According to the 

literature, the aerospace and military industries are considering potential cadmium alternatives 

16 Chromium is a naturally occurring element, and primarily occurs in the environment in two valence states: 

trivalent chromium (Cr III) and hexavalent chromium (Cr VI). Trivalent chromium occurs naturally, is an essential 

nutrient, and is much less toxic than hexavalent chromium. Hexavalent chromium and metallic chromium are most 

commonly produced by industrial processes. 

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Section 4 – Preliminary Study Findings 

for protective shells on electrical connectors and steel fasteners, as well as for brush plating 

repair solutions.17 

Table 4-1 presents the cadmium-free alternatives reported in literature and the processes 

used to apply them. Aluminum deposition uses glass bead peening (GBP) (Aguero, et al., 2012), 

atmospheric pressure, chemical vapor deposition (APCVD) (Berman & Brooman, 2009), and the 

ion vapor deposition (IVD) (K. Legg, 2012a). Electroplating processes use tin-zinc alloys and 

zinc-nickel alloys as alternatives to cadmium, and etching electroless plating processes use 

nickel alloys (R. Mason, et al., 2010; Orduz, 2008)). According to one industry representative, 

commercially available coating systems use 20 to 30 percent zinc in tin-zinc alloys, and 5 to 15 

percent nickel in zinc-nickel alloys, to provide the best performance (R. Mason, et al., 2010). 

Table 4-1. Process Descriptions of Cadmium-Free Alternative Coatings 

Cadmium 

Alternative Coating Process Process Description Source 

Glass bead 

peening (GBP) 

Parts are sand-blasted and vapor-degreased prior to coating. 

The coating slurry is applied by brush, immersion, or spray 

gun and cured using a proprietary curing process under air, 

followed by glass bead peening. 

(Aguero, et 

al., 2012) 

Aluminum 

Atmospheric 

pressure 

chemical vapor 

deposition 

(APCVD) 

Parts are cleaned, subjected to a tri-isobutyl-aluminum 

coating in a deposition chamber, using nitrogen as the carrier 

gas and an induction heater to deposit aluminum at 

temperatures between 275 and 300 degrees Celsius. After 

removing from the chamber the surface may or may not be 

treated with a conversion coating. 

(Berman & 

Brooman, 

2009) 

Ion vapor 

deposition (IVD) 

Parts are placed in a vacuum chamber and subjected to 

ionized gas (typically argon), which generates a glow 

discharge and acts as a cleaning process prior to coating. 

Pure aluminum is added to the chamber and deposited onto 

the surface. As the coating is formed, ions from the glow 

discharge attract to the aluminum and increase the coating’s 

density. 

(R. Mason, 

et al., 2010) 

Tin-Zinc 

Alloy Electroplating 

Parts are electroplated in a bath of an aqueous solution 

containing a tin-zinc alloy composed of 20 to 30 percent 

zinc. 

(R. Mason, 

et al., 2010) 

Zinc-Nickel 

Alloy Electroplating 

Parts are electroplated in a bath of an aqueous solution 

containing a zinc-nickel alloy composed of 5 to 15 percent 

nickel. 

(R. Mason, 

et al., 2010) 

Nickel 

Etching 

Electroless 

plating 

Parts are soaked in an acid cleaner, and acid etched. Parts are 

submerged in a nitric acid solution, then a zincate 

(Zn(OH)4

2−) solution, then placed in each solution once more 

before plating in an electroless nickel bath. Parts are rinsed 

between each step. 

(Orduz, 2008) 

When tested against a cadmium coating, the GBP aluminum coating demonstrated 

comparable or better performance, exhibiting higher fatigue strength and equal corrosion 

resistance. According to the study, the coating process produces significantly less process waste 

compared to electroplating, and is therefore more cost-effective (Aguero, et al., 2012). A study 

17 Brush plating is a portable process where an electroplated or anodized coating is applied locally to a metal part, 

focusing only on the specific areas that require the coating. 

4-11
 
 

 

 

 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

on APCVD aluminum coatings by the Air Force Research Laboratory presented several 

advantages. The study found that no vacuum chamber, pumps, or ancillary control equipment are 

needed for coating. The process allows for higher throughput due to short processing times and 

provides consistent and even coating thickness across the part. However, drawbacks to APCVD 

aluminum coatings include susceptibility to embrittlement when exposed to hydrogen gas, 

unacceptable performance in handling fatigue, and less lubricity than traditional coatings, which 

allow parts to operate more smoothly (Berman & Brooman, 2009). The aircraft industry has used 

IVD aluminum for years on high-strength steels; however, the vacuum deposition method is 

significantly more expensive than cadmium plating (K. Legg, 2012a). An ongoing project by the 

Environmental Security Technology Certification Program found that high purity aluminum 

plating applied to high strength steel fasteners combined with an electrocoated topcoat was 

comparable to cadmium plating in corrosion resistance. Aluminum coating is potentially costlier 

than cadmium plating (Scott, 2013). 

Non-aluminum alloy coatings are primarily made from tin-zinc and zinc-nickel alloys, of 

varying composition. A tin-zinc alloy coating, specifically tin-20 wt. percent zinc, provided 

efficient electrochemical protection and superior corrosion protection compared to both cadmium 

and zinc-nickel coatings, but also has a slightly higher friction coefficient (Dubent, et al., 2010). 

Zinc-nickel coating exhibited sufficient adhesion after bending, adhesion to paint, long-term 

corrosion resistance, and resistance to embrittlement when exposed to hydrogen gas; however, 

the coatings only performed marginally better when tested for environmentally induced cracking. 

Boeing determined that zinc-nickel plating is a commercially acceptable cadmium replacement 

for use on component parts made of low strength steel, stainless steel, aluminum, and copper 

alloys (Indumathi, et al., 2011; R. Mason, et al., 2010). A zinc coating consisting of an inorganic 

metal flake dip-spin coating offered high corrosion resistance with an equal or lower cost than 

cadmium (Scott, 2013). A zinc-nickel brush plated coating for repairing weapon systems was 

found to have several advantages compared to cadmium, mainly in cost savings – the plating 

solution is recycled and reused in a closed-loop process (Slife, 2014). 

Lastly, Uyemura Corporation developed a cadmium- and lead-free electroless nickel 

coating system that provides a long bath life, corrosion resistance, and passed bend testing 

without blistering or flaking the plated aluminum sheet (Orduz, 2008). 

Although the chemistries reviewed eliminate the use of cadmium coatings, some may 

require post-treatment conversion coatings to improve corrosion resistance and paint adhesion. 

For example, the APCVD process described in Table 4-1 may use a hexavalent chromium-based 

conversion coating (i.e., chromate conversion coating), which would also present health and 

environmental concerns (Berman & Brooman, 2009). 

4.3.2	 Hexavalent Chromium Plating, Conversion Coating, Primer, Sealer, and Cleaner 

Alternatives 

Hexavalent chromium finishing processes provide self-healing corrosion protection and 

improve adhesion between the paint and metal surface. Hexavalent chromium is applied in hard 

chrome plating conversion coating, in primers and paint, and with anodizing processes (K. Legg, 

2012b). Hexavalent chromium is hazardous to human health and the environment, and therefore, 

4-12
 
 

 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

researchers are exploring and developing alternatives that would reduce human and 

environmental exposure to the chemical during use and disposal. 

Hexavalent chromium may be present in wastewater generated by a facility and when 

further treated, may end up in wastewater discharged to POTWs or surface waters and 

wastewater sludge. Hexavalent chromium is also volatile and likely present in the air emissions 

surrounding open tank baths. The Office of the Secretary of Defense in 2009 issued a 

memorandum restricting the use of hexavalent chromium unless no cost-effective alternatives 

that provide satisfactory performance are available (K. Legg, 2009). These actions pushed 

defense and other industries to identify and adopt alternatives to hexavalent chromium. 

According to Paul Wynn of MacDermid, for chromium-free alternatives to be widely adopted, 

cooperation is required along the entire metal finishing supply chain to achieve low operating 

costs, high performance, and best practice techniques (Morose, 2013; Wynn, 2006). 

In EPA’s review, EPA identified alternatives to hexavalent chromium that replace it with 

a less toxic metal or that substitute a mechanical treatment step that imparts similar surface 

characteristics, or a combination of both. The following sections discuss hard chrome plating 

alternatives, chromate conversion coating alternatives, and alternatives for chromium-based 

primers, sealers, and cleaners. 

4.3.2.1 Hard Chrome Plating Alternatives 

Hard chrome plating applies a thin layer of chromium metal to a base metal by 

electroplating in a chromic acid solution. Hard chrome plating18 is used to make industrial 

equipment and automobile parts wear- and corrosion-resistant. Since chromic acid contains 

hexavalent chromium, researchers are testing alternative treatments for a variety of applications. 

Table 4-2 presents examples of commercially available alternatives to hard chrome plating, their 

market applications, and descriptions of the chemistries of each method. Commercially available 

alternatives include thermal spraying with high velocity oxygen fuel (HVOF), which can replace 

hard chrome plating of parts for commercial and military aircraft, off-road vehicles, and 

hydraulic systems. The Air Force began implementing HVOF coatings on landing gear 

components in 2003. HVOF sprays provide high performance, but according to industry experts, 

the spray process is not as forgiving as hard chrome plating and requires more preparation, 

training, and process control (K. Legg, 2008; K. Legg, 2010, 2012b; Sartwell, et al., 2004). 

Table 4-2. Commercially Available Hard Chrome Plating Alternatives 

Alternative 

Methods 

Typical 

Applications Description of Alternative Chemistries Sources 

Thermal spray 

(high velocity 

oxygen fuel, 

etc.) 

Aircraft landing 

gear, hydraulic 

rods, industrial 

rolls 

Thermal spraying can be performed with a wider range of 

coating materials than hard chrome plating, including materials 

that incorporate non-hexavalent chromium. The most common 

materials used in thermal sprays are chrome carbide-nickel 

chrome (Cr3C2-NiCr) and tungsten carbide-cobalt (WC-Co or 

WC-CoCr). The chromium in these coating materials is not in 

hexavalent form. 

(K. Legg, 

2012c) 

18 Hard chrome plating is used as a protective layer for increased corrosion resistance, while decorative chrome 

plating is used to provide metal parts with a bright and shiny finish. 

4-13
 
 

 

 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

Table 4-2. Commercially Available Hard Chrome Plating Alternatives 

Alternative 

Methods 

Typical 

Applications Description of Alternative Chemistries Sources 

Electroplating 

and electroless 

plating 

Aircraft 

engines, 

internals 

(especially 

electroless Ni) 

The most common chromium-free electroplates are based on 

nickel; other available materials are based on nickel-tungsten, 

nickel-tungsten-boron, and nickel-tungsten-boron combined 

with silicon carbide. Cobalt-based electroplates are also used, 

including a nanocrystalline cobalt phosphorous alloy plating. 

Electroless nickel plating alternatives to chromium include 

nickel-phosphorous and nickel-boron. 

(K. Legg, 

2012c; 

Prado, et 

al., 2010) 

Heat treating Hydraulic rods, 

gears, bearings 

Heat treating puts metal through cycles of high temperatures 

and cooling in a controlled atmosphere. Processes include 

nitriding, carburizing, and nitrocarburizing, which add 

nitrogen, carbon, and both, respectively, to the surface of the 

metal. The controlled heating and cooling cycles harden the 

surface. 

(K. Legg, 

2012c) 

Vacuum 

coatings 

Typically small, 

high value 

items, molds, 

and dies 

Physical vapor deposition (PVD) vacuum coating most 

commonly uses titanium nitride, chromium nitride, and various 

diamond-like coatings. Chromium nitride contains chromium 

in trivalent form. 

(K. Legg, 

2012c) 

Welding 

methods 

Rebuild of worn 

or corroded 

items 

Welding involves melting the surface of the treated material; 

hence, only materials that can withstand the required heating 

can be welded successfully. Welding replaces chromium 

application with a mechanical method, instead of chemical 

alternatives, to impart similar properties (e.g., wear resistance). 

(K. Legg, 

2012c) 

The hard chrome plating alternatives presented in Table 4-2 have advantages and 

disadvantages, described below in Table 4-3. 

Table 4-3. Advantages and Disadvantages of Hard Chrome Plating Alternatives 

Alternative 

Methods Advantages Disadvantages Sources 

Thermal spray 

(high velocity 

oxygen fuel, etc.) 

Harder and more wear resistant; can 

rebuild; spraying is faster than hard 

chrome plating. 

Require more careful process 

control; spraying requires constant 

attention. 

(K. Legg, 

2012c) 

Electroplating and 

electroless plating 

Drop-in chrome replacement due to 

similar bath process; cobaltphosphorous plating exhibited good 

wear and corrosion resistance in a labscale study; electroless nickel is a very 

flexible process and can apply uniform 

coatings to complex parts. 

Generally no better than chrome; 

nickel electroplating baths 

periodically require complete 

replacement; alternatives may be 

based on alloys that are usually 

more complicated than elemental 

coatings. 

(K. Legg, 

2012c; 

Prado, et 

al., 2010) 

Heat treats 

Almost any size and shape; not a 

coating process and therefore cannot 

come off as coatings can. 

Cannot be used for rebuild or for 

heat-sensitive materials. (K. Legg, 

2012c) 

Vacuum coatings 

Extremely hard and wear resistant, can 

be cost effective on small components. 

Complex and expensive; cannot be 

used for rebuild; highly sensitive to 

contaminants. 

(K. Legg, 

2012c) 

Welding methods 

Good for thick coatings, mostly on 

externals, can be highly controlled and 

automated. 

Not for heat sensitive materials, 

must be refinished. (K. Legg, 

2012c) 

4-14
 
 

 

 

 

 

Section 4 – Preliminary Study Findings 

4.3.2.2 Chromate Conversion Coating Alternatives 

The metal finishing industry is developing alternatives to hexavalent chromium-based 

conversion coatings, also referred to as chromate conversion coatings. Chromate conversion 

coatings are widely used in the aircraft and defense industries, on large components as well as on 

screws, nuts, and bolts, to provide corrosion resistance and self-healing properties (K. Legg, 

2009). Several alternatives are undergoing laboratory testing and some are commercially 

available. Table 4-4 lists chromate conversion coating alternatives and descriptions of their 

performance. 

Table 4-4. Chromate Conversion Coating Alternatives 

Alternatives 

Materials 

Coated Description Sources 

Trivalent 

chromium 

coatings 

Aluminum 

alloys and 

magnesium 

alloys 

A trivalent chromium process can replace hexavalent 

chromium on aluminum alloys with comparable properties 

and costs. Tests of a trivalent chromium conversion coating 

applied to magnesium alloys displayed better corrosion 

resistance than hexavalent chromium. 

(Bhatt, et al., 

2009; La Scala, 

2009; 

Manavbasi, et al., 

2012; Nickerson, 

et al., 2012) 

Silicate-based 

ceramic 

coatings 

Steel 

screws, 

nuts, and 

bolts 

Elisha Technologies researched and tested a passivation 

system that replaces chromium with silicates, which form a 

ceramic, glass-like layer on the finished parts. In a lab-scale 

salt spray performance test, the ceramic surface treatment 

combined with a zinc plate and aluminum-rich epoxy 

coating displayed great corrosion resistance. 

(Winn, et al., 

2008) 

Polymer-based 

coatings 

Aluminum 

alloys and 

magnesium 

alloys 

NEI Corporation’s NANOMYTE® PT-60 is commercially 

available hexavalent chromium conversion coating 

replacement for use on magnesium alloys. Another coating 

comprised of zeolites provides a universal solution and 

process that can coat several types of aluminum alloys. 

(Bhargava, et al., 

2012; Lew, et al., 

2010; NEI 

Corporation, 

2014; Yan, 2009) 

Permanganatebased coatings Zinc and 

zinc alloys 

John Bibber with Sanchem, Inc. explored alternatives to 

chromium-based conversion coatings and found that 

permanganate-based coatings duplicate chromium’s 

chemical and physically properties without heavy metals. 

(Bibber, 2008) 

Phytic acid 

coatings Zinc alloys 

Phytic acid is a non-toxic acid requiring no hazardous waste 

treatment. A phytic acid conversion coating and chromate 

conversion coating were applied to a zinc-cobalt alloy and 

tested for corrosion. According to the study, the phytic acid 

with a 15-minute deposition time resulted in superior 

corrosion resistance compared to the chromate coating. 

(Bikulcius, et al., 

2010) 

Cerium 

conversion 

coating 

Aluminum 

alloys 

A system using a cerium conversion coating and a 

multifunctional UV curable coating with inorganic 

corrosion inhibitors resulted in aluminum alloys exhibiting 

good flexibility, adhesion, and fluid resistance. The coating 

system met most aerospace metal finishing requirements. 

(O’Keefe, 2010) 

According to Keith Legg of Rowan Technology Group, most industries have already 

adopted hexavalent chromium-free conversion coatings for aluminum, however hexavalent 

chromium is still used in the aerospace and defense industries due to the increased importance of 

high performance corrosion resistance in these industries (Eichinger, et al., 1997; K. Legg, 

2011). Out of several non-chromate conversion coatings laboratory tested by the Naval Aviation 

4-15
 
 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

Systems Command (NAVAIR), the only coatings based on trivalent chromium were comparable 

to hexavalent chromium conversion coatings (Nickerson & Matzdorf, 2012). NAVAIR’s 

trivalent chromium process requires no additional equipment or operator training when changing 

from hexavalent chromium processes (La Scala, 2009). During testing, NAVAIR found that 

process parameters, such as coating time, temperature, and chemical concentration required 

adjustment for each specific aluminum alloy. Due to trivalent chromium’s increased dependence 

on process parameters, some facilities may be discouraged to change from conventional 

hexavalent chromium processes (Bhatt, et al., 2009). In recent discussions with metal finishing 

facilities, EPA learned that some facilities that conduct hexavalent chromium plating operations 

may have also installed trivalent chromium plating operations in response to increasing demand 

for safer alternatives. However, this practice is not widespread. Trivalent chromium generally 

presents a less durable product which can lead to product performance issues. Its use also 

requires higher operating costs to maintain the plating baths and equipment used, although 

facilities incur less costs for wastewater treatment (ERG, 2016). 

NEI Corporation developed and tested NANOMYTE® PT-60, a chromium-free, selfhealing, polymer-based nanocomposite conversion coating, consisting of organic, inorganic, 

and/or both polymer types. According to NEI Corporation, the alternative coating applied by 

immersion into a bath of PT-60 solution displayed uniform distribution and consistent thickness, 

higher electrochemical resistance compared to chromate coatings, and excellent corrosion 

resistance and self-healing properties after salt-fog exposure when applied to magnesium alloy 

during a laboratory-scale test (Bhargava & Allen, 2012). 

The University of California conducted laboratory-scale research on a zeolite coating 

developed to replace military chromium-based coatings. Zeolites are inexpensive, non-toxic, 

crystalline inorganic polymers containing silica and aluminum. Zeolite coatings were tested on 

hundreds of 1 by 2 inch and 3 by 6 inch metal panels and 99 percent passed corrosion resistance 

tests including adhesion, impact, bending, salt-fog, and UV testing. The researchers were able to 

develop a universal solution composition and deposition procedure that produces high quality 

coatings on several different aluminum alloys, which involved immersing the metal panels into 

the solution and then heating in a convection oven at 175 degrees Celsius for 12 to 16 hours. 

This results in significant cost savings because no adjustments are needed for coating different 

types of alloys (Lew, et al., 2010; Yan, 2009). 

An experiment examining several types of conversion coatings concluded that while 

some coatings work well in certain areas, none of them compare against hexavalent chromium. 

Trivalent chromium had better heat resistance but less corrosion resistance. Permanganate-based 

coatings had equal corrosion resistance but was unable to regenerate (Pommiers, et al., 2014). 

4.3.2.3 Alternatives for Chromium-based Primers, Sealers, and Cleaners 

Most research for replacing hexavalent chromium has focused on alternatives to hard 

chrome plating and chromate conversion coatings; however, researchers are also exploring 

alternatives for chromium-based primers, sealers, and cleaning solutions. Primers provide 

additional adhesion between the surface and topcoat paint. Sealers are mainly used to prevent the 

surface from absorbing paint, but may also act as a primer. Figure 4-5 illustrates traditional steel 

4-16
 
 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

and aluminum coating systems. As shown, traditional coating systems also use primers 

containing hexavalent chromium on top of a chromate conversion coating. 

Source: (K. Legg, 2009) 

Figure 4-5. Traditional Coating Systems 

Researchers at an Air Force facility that anodizes aluminum landing gear investigated 

alternatives to their sodium dichromate sealer. They identified two: a commercial off-the-shelf 

nickel-based sealer and permanganate-based sealer. The nickel-based sealer is applied at a lower 

temperature than the sodium dichromate but seals at a slower rate. Researchers found that the 

permanganate-based sealer had exceptional corrosion resistance but exhibited less adhesion than 

the sodium dichromate (R. Mason, et al., 2011). In addition to the nickel- and permanganatebased sealers, the aerospace industry tested a magnesium-rich primer to replace chromate-based 

primers used on aluminum alloys. They found this primer was the only chromium-free 

alternative that provides equal or superior corrosion protection to conventional chromate 

systems, and does not require any pretreatment other than a good cleaning (Bierwagen, et al., 

2010). 

Along with sealers and primers, hexavalent chromium is a constituent of acidic cleaning 

solutions used to remove impurities and inorganic contaminants from metals before plating. Acid 

treatments are also known as pickling. Researchers tested a pickling solution consisting of 

phosphoric acid and sodium molybdate and found it produced a more uniform film and less 

corrosion when compared to a pickling bath of chromium trioxide and nitric acid (Lei, et al., 

2011). 

4.3.3 Phosphate Conversion Coating and Cleaning Alternatives 

Phosphate conversion coatings are used to provide a good base for paints and other 

organic coatings, to condition the surfaces for cold forming operations by providing a base for 

drawing compounds and lubricants, and to impart corrosion resistance to the metal surface by the 

coating itself or by providing a suitable base for rust-preventative oils or waxes (U.S. EPA, 

1979). Along with phosphate conversion coatings, phosphate cleaners may also be used in order 

to remove grease and other contaminants from metal substrates prior to coating (List, et al., 

4-17
 
 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

2012). Note that phosphate cleaners or other alkaline cleaners are also subject to the Metal 

Finishing ELGs (U.S. EPA, 2004). 

Phosphorous is an essential nutrient for plants and animals. Increased phosphorous levels 

in water bodies from the discharge of phosphate-containing wastewater can impact aquatic 

ecosystems and lead to fish kill by lowering dissolved oxygen levels in the water (U.S. EPA, 

2012b; USGS, 2015). In recent years, metal finishing companies have converted to phosphatefree processes to address strict environmental regulations on phosphorus discharges in some 

localities and high operating costs associated with phosphate sludge removal (List, et al., 2012). 

Kaluzny (2012) noted several benefits to alternative phosphorus-free conversion coating 

processes, mainly in cost savings by avoiding POTW surcharges due to phosphate restrictions, 

eliminating onsite wastewater treatment, minimizing heat required during the surface treatment 

process, and significantly reducing the amount of sludge produced. They also identified several 

disadvantages of phosphorous-free processes, including the need for additional rinsing and 

cleaning between each process step (Kaluzny, 2012). 

One alternative to phosphate conversion coatings is the use of ionic liquids containing 

ethylene glycol and choline chloride for electropolishing steel in a process that incorporates a 

recycling protocol for the liquid waste. Researchers found the ionic liquids were as effective as 

aqueous solutions using phosphoric acid mixtures. Additionally, metals are highly soluble in 

ionic liquids, so such liquids are suitable for electrodepositing tin, zinc, and zinc alloys. The 

study shows the ionic liquid surface finishes for the electropolishing process were at least as 

good as conventional aqueous solutions and incorporated a recycling system that allowed for full 

metal recovery (Abbott, et al., 2007). 

Zirconium-based conversion coatings are an alternative to phosphate conversion coatings. 

Klingenberg and Jones (2007) tested zirconium and zirconium-vanadium coatings against iron 

phosphate coatings and found several benefits in the zirconium-based alternatives. The 

phosphate-free process involved immersing metals into a bath of the zirconium-based solution. 

When compared to traditional phosphate conversion coating processes, this process requires less 

heat, shorter contact time, and lower coating bath volume. The process also provided thinner 

surfaces, produced much less process waste, and exhibited better corrosion-resistance 

(Klingenberg, et al., 2007). 

Researchers found that phosphorous-free coatings that use ZirconizationTM provide 

similar benefits. Zirconization eliminates the need for a conditioning step, which further reduces 

required chemicals and water use (Moore, et al., 2008). David Schmipff of DuBois Chemicals 

was reported to have said that in two years of testing ZirconizationTM and iron phosphate 

coatings, “less than 5% of results favor an iron phosphate over ZirconizationTM or other nonphosphate technology” (Dunham, 2012). 

Atotech provides phosphorous-free cleaners and conversion coatings. According to 

Atotech, after a metal finishing company changed to these products, the company reduced costs 

by 22 percent and reduced their defect rate from 25 to 11 percent. The phosphorous-free 

chemistries improved the company’s process by lowering the operating temperatures of the 

4-18
 
 

 

 

 

Section 4 – Preliminary Study Findings 

cleaning and coating stages and eliminating the build-up of significant sludge on their spray line 

(List, et al., 2012). 

4.3.4 Cyanide Plating Solution Alternatives 

Plating operations use cyanide with copper, zinc, brass, cadmium, silver, and gold. 

Cyanide is also in chromate and phosphate coatings and etching operations. Cyanide is used as 

an additive in plating baths due to its ability to form more fine grained metal deposits and 

increase the bath’s tolerance to impurities and contaminants. Many cyanide compounds are 

highly toxic and can be readily absorbed through the skin and lungs. Some compounds are highly 

stable, making them difficult to break down during wastewater treatment processes (U.S. EPA, 

2000b). According to industry experts, replacing cyanide in metal finishing operations has 

become increasingly popular due to the health and environmental concerns associated with 

cyanide (Abdel-Hamid, et al., 2009; Lei, et al., 2010). The literature presents cyanide-free 

alternatives for coatings on stainless steel and magnesium alloy surfaces. 

Researchers tested non-cyanide alkaline baths on stainless steel and demonstrated 

successful electroplating of a copper layer using an alkaline electrolyte (Abdel-Hamid & AbdelAal, 2009). The presence of sorbitol in the plating bath improved efficiency and helped form a 

dense copper layer, even in the absence of cyanide (Abdel-Hamid & Abdel-Aal, 2009). 

Researchers also studied cyanide-free coating processes for magnesium alloys (Lei, et al., 

2010). Magnesium alloys are widely used in the aerospace, automotive, electronic, and 

communication industries due to their low weight; however, their use generally requires a metal 

plating finish to improve corrosion resistance, and the plating solutions usually contain cyanide 

(Lei, et al., 2010). The study showed successful coating applications on magnesium alloys 

without the use of cyanide for the following metal finishes (Lei, et al., 2010): 

• Electroless nickel plating 

• Electrodeposited nickel 

• Electroplated copper 

• Electroplated copper/nickel/chromium composite layer plating 

The copper/nickel/chromium composite was obtained through multi-electrodeposition. 

The magnesium alloys were electroplated in three bath compositions of acid copper, bright 

nickel, and chromium, each with different operating conditions (Lei, et al., 2010). Researchers 

found nickel and copper-based processes are the most viable alternatives to cyanide-containing 

plating solutions (Abdel-Hamid & Abdel-Aal, 2009; Lei, et al., 2010). 

4.3.5 Summary of Alternative Chemistries 

Another key research focus for the industry is finding and applying less toxic alternatives 

than those commonly used in metal finishing operations. In practice, this proves a challenge to 

industries that have more stringent product quality specifications that cannot be achieved by 

those alternatives to date. There is evidence that these alternatives have been applied 

commercially in the metal finishing industry for products with less stringent specifications. The 

alternative chemistries show that there may be emerging pollutants of interest because 1) the 

4-19
 
 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

industry has introduced new chemicals that were not identified in metal finishing wastewater 

during the 1983 regulations (e.g., zirconium, platinum, tungsten) or 2) increased use of chemicals 

that may have been identified in the 1983 regulations may have increased presence in metal 

finishing wastewater (e.g., magnesium, manganese, boron). This may also be evident for other 

chemicals that are used in plating processes; however, EPA did not identify in literature any 

specific chemicals used outside of the primary plating chemicals. 

Alternative chemistries may also require a change to commonly used metal finishing 

operations. In recent literature, many of the alternative chemistries that have been commercially 

applied use different operations than the typical plating operations, such as thermal spray and 

vapor deposition applications. As a result of changes to plating chemistries, new finishing 

operations may require EPA to further evaluate them in the context of the existing six primary 

metal finishing operations that subject facilities to the Metal Finishing ELGs. 

4.4 Wastewater Treatment Technologies 

As part of its preliminary study, EPA reviewed literature describing recent technological 

advances in removing metals from wastewaters (e.g., metal finishing wastewater). This section 

first presents the heavy metals removal technologies that EPA evaluated while promulgating the 

1983 Metal Finishing ELGs, and then compares them with the performance of treatment 

technologies that EPA identified in its recent literature search. 

4.4.1 Technologies Evaluated for the 1983 Metal Finishing ELGs 

Metal finishing operations generate wastewater primarily from rinsing the surfaces of 

metals (often several times) during cleaning and preparation, and again after coating or plating is 

completed. Other sources of metal finishing wastewater include spills, spent process fluids, wash 

or quench water from auxiliary operations, and water from air pollution control devices. The 

wastewater may include inorganic wastes (primarily heavy metals) and organic wastes (including 

cyanide, oils, and toxic organics). As such, the 1983 Metal Finishing ELGs regulate the direct 

and indirect discharge of metal finishing wastewater containing heavy metals, cyanide, and TTO 

to surface waters of the United States (see Section 2 of this report) (U.S. EPA, 1983a). 

In setting the pretreatment standards and discharge limitations for metal finishing 

wastewater in the 1983 regulations, EPA evaluated several wastewater treatment technologies for 

removal of heavy metals, cyanide, and other organic waste. Table 4-5 summarizes these 

treatment technologies and their calculated daily maximum, monthly average, and long-term 

average concentrations. Ultimately, EPA selected hydroxide precipitation followed by 

sedimentation (regulatory option 1) as both the BPT and the BAT. Hydroxide precipitation 

followed by sedimentation with in-plant cadmium controls (regulatory option 3) was selected as 

the NSPS/PSNS technology for the ELGs. (See Section 2.3 of this report for a more detailed 

description of these technologies). Although the technology considered in regulatory option 2 

demonstrated better treatment performance, EPA did not select this option because filtration 

presented a very high incremental cost to the industry (U.S. EPA, 1983a). 

In identifying these regulatory options, EPA evaluated the performance of individual 

treatment technologies for heavy metals removal. Table C-1 in Appendix C presents additional 

treatment technologies that EPA identified in the 1983 regulations as being used to remove 

4-20
 
 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

Table 4-5. Regulatory Options Considered in the 1983 ELGs and their Daily Maximum, 

Monthly Average, and Long-Term Average Concentrations
 

Regulatory Option Technology Description Pollutant 

Daily Maximum 

Concentration 

(mg/L) 

Monthly Average 

Concentration 

(mg/L) 

Long-term Average 

(LTA) Concentration 

(mg/L)a 

1: Hydroxide precipitation A precipitation technique to form insoluble TSS 60b 31b 16.7b 

followed by sedimentation metal hydroxides and phosphates that are Cadmium 0.69 0.26 0.13 

removed by gravity settling techniques Chromium 2.77 1.71 0.572 

(the BPT technology basis in including sedimentation basins or circular Copper 3.38 2.07 0.815 

the 1983 ELGs) clarifier. May require pretreatment of Lead 0.69 0.43 0.2 

wastewater containing cyanide, precious Nickel 3.98 2.38 0.942 

metals, hexavalent chromium and oily Zinc 2.61 1.48 0.549 

wastes. Wastewater containing complexed Silver 0.43 0.24 0.096 

metals are also segregated and treated Cyanide 1.20 0.65 0.18 

separately using this treatment technology. TTO 2.13 NA 0.434 

Oil and Grease 52b 26b 12b 

2: Hydroxide precipitation In addition to Regulatory Option 1, a TSS 46 24 12.8 

followed by sedimentation filtration device is placed after the primary Cadmium 0.42 0.16 0.08 

and filtration solids removal to remove metal hydroxides Chromium 1.55 0.95 0.32 

that did not settle out via gravity settling. Copper 1.52 0.93 0.37 

(not selected as a technology Filtration devices include granular bed or Lead 0.14 0.09 0.04 

basis in the 1983 ELGs)c diatomaceous earth. Nickel 1.94 1.16 0.46 

Zinc 1.13 0.67 0.25 

3: Hydroxide precipitation In addition to Regulatory Option 1, in-plant TSS 60b 31b 16.7b 

followed by sedimentation controls to nearly eliminate cadmium from Cadmium 0.114 0.066 0.058 

with in-plant cadmium the wastewater. Controls can include Chromium 2.77 1.71 0.572 

controls evaporative recovery, ion exchange, and Copper 3.38 2.07 0.815 

recovery rinses. Lead 0.69 0.43 0.2 

(the NSPS/PSNS technology Nickel 3.98 2.38 0.942 

basis in the 1983 ELGs) Zinc 2.61 1.48 0.549 

Silver 0.43 0.24 0.096 

Cyanide 1.20 0.65 0.18 

TTO 2.13 NA 0.434 

Oil and Grease 52b 26b 12b 

TSS – Total suspended solids; TTO – Total toxic organics; NA – Not applicable a Based on Table 3.4 of the Guidance Manual for Electroplating and Metal Finishing Pretreatment Standards, unless otherwise noted (U.S. EPA, 1984). b LTA is based on the daily variability factor of 3.59 mg/L for TSS and 4.36 mg/L for Oil and Grease (U.S. EPA, 1983a). c Regulatory option 2 was based on Table 7-32 of the Development Document for Effluent Limitations Guidelines New Source Performance Standards for the 

Metal Finishing Point Source Category (U.S. EPA, 1983a). 

4-21
 
 

 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

heavy metals. The table also includes performance data for each technology used to treat metal 

finishing wastewater. 

4.4.2 Chemical Precipitation 

Chemical precipitation has been used to remove heavy metals from metal finishing 

wastewater for many years. In general, chemical precipitation involves the conversion of soluble 

heavy metals into insoluble compounds (i.e., precipitates) that are then physically separated from 

the water using any of several removal techniques, such as clarification, sedimentation, or 

membrane filtration (WEF, 2008). Precipitation techniques commonly used to remove heavy 

metals include hydroxide precipitation and sulfide precipitation; complex metals precipitation 

and electrochemical precipitation have also been used to remove heavy metals. All of these 

precipitation techniques were evaluated during the 1983 rulemaking. Electrochemical 

precipitation is further discussed in the electrochemical treatment methods section below (see 

Section 4.4.5). 

4.4.2.1 Hydroxide Precipitation 

As discussed in Section 2.3, hydroxide precipitation is widely used to treat metal 

finishing wastewater and is part of the technology basis for the Metal Finishing ELGs (see Table 

4-1). The BPT for the Metal Finishing ELGs includes hydroxide precipitation, followed by 

clarification and a sludge dewatering step. BPT also includes pretreatment steps for cyanides, 

hexavalent chromium, and oil and grease prior to hydroxide precipitation (U.S. EPA, 1983a). 

Hydroxide precipitation relies on the solubility curves of targeted heavy metals and uses 

hydroxide compounds to manipulate this characteristic in the wastewater. Although lime (CaO) 

and caustic (NaOH) are common treatment chemicals, calcium hydroxide (Ca(OH2)) and 

magnesium hydroxide (Mg(OH2)) are also effective for treating metal finishing wastewater (Fu, 

et al., 2011; U.S. EPA, 1983a). 

A disadvantage of hydroxide precipitation is that the process generates large volumes of 

low-density sludge that can be difficult and costly to dewater and dispose of. Optimization of 

single stage hydroxide precipitation for wastewater containing multiple metals may also be 

difficult to attain because metal hydroxides can have dissimilar solubility ranges and pH 

adjustment may return metals back into solution. Moreover, complexing agents (which are used 

in metal finishing processes) are also present in the wastewater and can inhibit hydroxide 

precipitation, thereby making it difficult to remove heavy metals completely (Fu & Wang, 2011; 

Islamoglu, et al., 2006). EPA did not identify literature indicating any advances in hydroxide 

precipitation treatment of metal finishing wastewater. 

4.4.2.2 Sulfide Precipitation 

Sulfide precipitation uses treatment chemicals such as sodium hydrogen sulfide (NaSH), 

sodium sulfide (Na2S), calcium sulfide (CaS), and iron sulfide (FeS) to precipitate heavy metals 

from wastewater. Ferrous and ferric sulfate may also be used in this process (Huisman, et al., 

2006; U.S. EPA, 1983a). Like hydroxide precipitation, sulfide precipitation relies on the 

solubility of metals in wastewater; however, metal sulfide precipitates have a much lower 

solubility, and therefore, more metal is removed over a broader pH range than metal hydroxide 

precipitates. This characteristic of sulfide precipitation allows metal precipitation to be more 

4-22
 
 

 

 

 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

selective, particularly for divalent soluble metals, such as cadmium, copper, zinc, and lead 

(WEF, 2008). 

During the development of the 1983 Metal Finishing ELGs, EPA identified a few 

facilities treating metal finishing wastewater by sulfide precipitation in conjunction with 

hydroxide precipitation. EPA’s literature search indicates that the chemistry employed by sulfide 

precipitation systems remains relatively unchanged; however, the use of multi-stage 

precipitation, applying multiple precipitation techniques, was a relatively new approach for metal 

finishing wastewater treatment at the time of the 1983 regulations. This approach may be more 

widely used now. Sulfide precipitation combined with hydroxide precipitation can improve 

removal of several metals over a wide pH range (Fu & Wang, 2011; Huisman, et al., 2006). 

Compared to hydroxide precipitation, sulfide precipitation generates a more dense sludge 

that is more amenable to thickening and dewatering for disposal. The pH of the system must also 

be maintained at a neutral to basic medium because sulfide precipitates in an acidic medium can 

generate toxic hydrogen sulfide gas (H2S) (WEF, 2008). 

4.4.2.3 Chelated Metals Precipitation 

Complexing (or chelating) agents in industrial wastewater can hinder conventional 

precipitation techniques, such as hydroxide precipitation. Complexing agents are used in 

chemical processes to help maintain metals in solution, and these metals are present in the 

wastewater as complexed metals (or chelated metals). Commonly used complexing agents in 

metal finishing include phosphates, tartrates, ethylenediaminetetraacetic acid (EDTA), cyanide, 

and ammonia. Successful removal of complexed metals in wastewater require adjusting the pH 

of the wastewater to very low or very high levels. The technology basis for the 1983 regulations 

includes the separate treatment of wastewaters using hydroxide precipitation (lime) to drive up 

the pH of the system to disassociate the complexed metals and free the metal ions to allow 

hydroxide precipitates to form. Wastewater containing complexed metals can also be treated by 

adding chemicals to lower the pH of the wastewater and followed by chemical reduction and 

precipitation. In the acidic environment, the complexed metals disassociate and subsequently, a 

reducing agent added to reduce the free metal ions to an oxidation state which can then be removed 

using hydroxide precipitation. In this process, a suitable cation (e.g., calcium, iron) may be added 

to tie up the complexing agents and allow for effective precipitation of the targeted metal using 

hydroxide precipitation techniques (U.S. EPA, 1983a; WEF, 2008). 

Another approach to treating wastewater containing complexed metals that EPA 

identified in the 1983 regulations uses sulfide precipitation (through addition of ferrous or ferric 

sulfate) to facilitate metals removal. Similar to the chemical reduction process, the approach 

introduces a suitable cation (i.e., iron) into the wastewater, which frees the metal ions targeted 

for removal (U.S. EPA, 1983a; WEF, 2008). Recent studies focus on the synthesis of precipitants 

that effectively remove heavy metals even in the presence of complexed metals (Fu & Wang, 

2011; Li, et al., 2003). The treatment effectiveness of the precipitants in forming metal 

precipitates depends on the complexing agents present in the wastewater. In addition to ferrous 

and ferric sulfate, three other commercially available precipitants used in treating wastewater 

containing complexed metals are trimercaptotriazine, potassium or sodium thiocarbonate, and 

sodium dimethyldithiocarbamate. All three are known pesticides, but are effective at removing 

4-23
 
 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

complexed metals from the wastewater. Experimental xanthates, thiol-based compounds, and 

dithiocarbamate compounds have also been studied for treating electroplating wastewater 

containing complexing agents (Fu & Wang, 2011; Li, et al., 2003). Some of these precipitants, 

particularly the pesticides, present their own environmental risks when discharged into surface 

waters (U.S. EPA, 2000a). Table 4-6 summarizes the effectiveness of precipitants used in 

chelated metals precipitation that EPA identified in recent literature. According to Li et al. 

(2003), the concentration of complexed metals can have an impact on the overall metal removal 

observed and additional adjustments to the precipitant doses would need to be considered to 

optimize the removal by the system. On a bench scale, several precipitants demonstrate the 

ability to remove heavy metals to concentrations that are lower than the LTAs for the BPT 

technology basis, specifically for copper. 

In addition to hydroxide precipitation, EPA also identified chemical reduction and sulfide 

precipitation as alternative methods for treating wastewater containing complexed metals in the 

1983 regulations, although chemical reduction was much less prevalent in the industry at that 

time. Treatment performance data at that time indicated that sulfide precipitation effectively 

treated wastewater containing cyanide complexes using ferrous sulfate as the precipitant (see 

Appendix C). EPA did not identify recent literature describing treatment performance for 

chemical reduction or sulfide precipitation. 

4.4.3 Sorption 

Recent literature shows increased research interest in sorption technologies for heavy 

metals removal. The most common sorption technologies studied involve adsorption and ion 

exchange processes. The literature reviewed to date did not identify absorption processes for 

heavy metal removal. This section discusses the advances in adsorption and ion exchange 

processes in the metal finishing industry. 

4.4.3.1 Adsorption 

Adsorption involves the physical or chemical binding of a substance that exists in a liquid 

solution (e.g., metals in wastewater) onto the surface of a solid resin or adsorbent, thereby 

removing the substance from the liquid solution (Kurniawan, et al., 2006; WEF, 2008). The 

effectiveness of adsorption (i.e., adsorptive capacity) relies on the number of binding sites 

available on the adsorbent and can be greatly affected by how the adsorbent is synthesized. Some 

adsorption processes are reversible, which allows for the recovery of metals via desorption 

processes. In the 1983 regulations, EPA identified several adsorption technologies as polishing 

steps (tertiary treatment steps) for removing organics, dissolved metals, and trace metals. These 

technologies included carbon adsorption, integrated adsorption, peat adsorption, and synthetic 

resin adsorption. However, the adsorption technologies were relatively new at the time and no 

metals removal data were available (U.S. EPA, 1983a). Recent studies apparently continue to 

evaluate adsorption as a tertiary treatment step, rather than as a primary technology for heavy 

metals removal (Kurniawan, et al., 2006). Adsorbents that have been identified in literature for 

the removal of heavy metals from wastewater include activated carbon and low-cost alternatives 

to activated carbon, described below. 

4-24
 
 

 c 

Section 4 – Preliminary Study Findings 

Table 4-6. Chelated Metals Precipitation Treatment Identified in EPA’s Literature Review – Summary of Treatment Results 

Scale of 

Study Type of Wastewater Precipitant 

Targeted 

Metal 

LTA 

Concentration 

(mg/L)a 

Final Metal 

Concentration 

(mg/L)b 

Percent 

Removal 

(%) Source 

Bench scale, 

batch 

operation 

Synthetic (without 

complexing agents) 

Sodium diethyldithiocarbamate 

(DDTC), Ferric sulfate 

(Fe2(SO4)3); polyacrylamide 

(PAM) 

Copper 0.815 0.08 99.6 (Li, et al., 2003) 

Synthetic (with 

complexing agents)c 

0.38 92.3 

0.40 96.0 

0.41 98.0 

5.35 73.3 

10.3 48.6 

Uncertain Uncertain (synthetic 

or industrial) 

Potassium ethyl xanthate Copper 0.815 3 94.0 – 99.7 (Chang et al., 2002)d 

Uncertain Uncertain (synthetic 

or industrial) 

Dipropyl dithiophosphate Lead 0.2 1 99.5 (Xu and Zhang, 

2006)

d

Cadmium 0.13 0.1 100 

Copper 0.815 0.5 99.8 

Mercury NA 0.05 100 

Uncertain Uncertain (synthetic 

or industrial) 

1,3,5­

hexahydrotriazinedithiocarbamate 

Copper 0.815 0.25 99.0 (Fu et al., 2007)d 

0.35 99.3 

0.4 99.6 

NA – Not applicable 

a	 Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory option 1 in Table 4-1). 

b Concentrations in bold text indicate lower treatment results than the long-term average concentration for the BPT technology basis. 

The results represent the total copper removal observed for multiple scenarios of complexed copper and total copper concentrations in the sample. Total 

copper removals of 73.3 and 48.6 percent present scenarios in which the complexed copper represents at least half of the total copper concentrations. 

d As cited in (Fu & Wang, 2011). 

4-25
 
 

 

 

 

Section 4 – Preliminary Study Findings 

Activated carbon is a widely used adsorbent made from carbonaceous materials such as 

coal, wood, lignite, peat, coconut husks, or nutshells. A majority of commercially available 

activated carbon is made from coal. Generally, activated carbon is an effective adsorbent because 

its microporosity offers a large surface area to which substances can adhere. In EPA’s review of 

the literature, several articles noted its effectiveness in heavy metal removals (Fu & Wang, 2011; 

Haynes, 2014); however, there were limited quantitative results showing the treatment 

effectiveness of these adsorbents for heavy metals removal. Sancey et al. (2011) suggested that 

the high cost of activated carbon adsorption as a tertiary treatment technology makes it less 

desirable for heavy metals treatment. According to the Water Environment Federation, the 

effectiveness of activated carbon adsorption for treating inorganic compounds such as metals has 

not been well demonstrated (WEF, 2008). 

The primary focus of many of the adsorption studies EPA reviewed was the adsorptive 

capacities of activated carbon derived from inexpensive alternatives to coal. These alternatives 

include agricultural wastes, industrial by-products, natural materials, and many other 

carbonaceous materials that can be converted to activated carbon and used for adsorbing 

polyvalent metals such as zinc, nickel, cadmium, copper, lead, mercury, and arsenic. Table 4-7 

lists low-cost activated carbon alternatives that EPA identified in recent literature. 

Table 4-7. Low-Cost Adsorbents Identified in EPA’s Literature Review 

Adsorbent Source 

Agricultural Byproducts and Natural Materials 

Eucalyptus bark (Kongsuwan et al., 2009)

a 

Dried plants (Chiban, et al., 2011) 

Hulls (peanut, soybean) (Periasamy & Namasivayam, 1995)

b

; (Marshall et al., 1999)

b 

Husks (corn, rice, almond, black gram, coffee) 

(Ahmaruzzaman, et al., 2011; Ajmal, et al., 2003; Hegazi, 2013; 

Wong, et al., 2003) (Oliveira et al., 2008)

a

; (Saeed et al., 2005)

a

; 

(Hasar, 2003)

b 

Peels (orange, banana, potato) (Ahmen-Basha, et al., 2008; Ajmal, et al., 2000) (Annadurai et 

al., 2002)

b 

Piths (coconut, sugar cane) (Namasivayam, et al., 2008); (Khan et al., 2001)

c

; (Tan et al., 

1993)

c 

Shells (pecan, hazelnut, almond, seed, egg) 

(Jai et al., 2007)

a

; (Amudaa et al., 2009)

a

; (Bansode et 

al., 2003)

b

; (Demirbas ̧ et al., 2002)

b

; (Kobya, 2004)

b

; (Dakiky 

et al., 2002)

b 

Corn cobs (Ahmaruzzaman & Gupta, 2011) 

Poultry litter (Guo et al., 2010)

a 

Sawdust (Agoubordea & Navia, 2009)

a 

Modified starch (flour) (Sancey, et al., 2011) 

Industrial Byproducts 

Pulp and paper byproducts (Sthiannopkao, et al., 2009) 

Fly ash (Ahmaruzzaman & Gupta, 2011; Haynes, 2014; Hegazi, 2013) 

Slag (blast furnace, iron or steel) (Haynes, 2014) 

Lignin (Betancur et al., 2009)

a

; (Reyes et al., 2009)

a 

Lignite, diatomite, clino-pyrrhotite, kyanite (Mohan & Chander, 2006)

a

; (Sheng et al., 2009)

a 

; (Lu et al., 

2006)

a

; (Ajmal, et al., 2001) 

4-26
 
 

 

 

 

 

 

 

c 

Section 4 – Preliminary Study Findings 

Table 4-7. Low-Cost Adsorbents Identified in EPA’s Literature Review 

Adsorbent Source 

Clays (Clinoptilolite, kaolinite, 

montmorillonite) (Fu & Wang, 2011); (Bhattacharyya & Gupta, 2008)

a 

Zeolites, vermiculite, bentonite (Alvarez-Ayuso, et al., 2003); (Apiratikul & Pavasant, 2008)

a 

Aragonite shells (Kohler et al., 2007)

a 

Peat (Liu et al., 2008)

a 

Natural Materials 

Sodium alginate (natural polymer) (Abdel-Halima, et al., 2011) 

Olive (stone, cake) (Dakiky et al., 2002)

b 

Pine needles, cactus (Dakiky et al., 2002)

b 

Synthetic Materials 

Activated alumina (Bishnoi et al., 2004)

d 

Synthesized Layered Double Hydroxide 

(LDH) (Lv, et al., 2013) 

Silicates (Fu & Wang, 2011) 

a As cited in (Fu & Wang, 2011). 

b As cited in (Kurniawan, et al., 2006). 

As cited in (Hegazi, 2013). 

d As cited in (Ahmaruzzaman & Gupta, 2011). 

The literature describes methods to optimize heavy metals removal by adjusting 

adsorbent dose and pH levels (Kurniawan, et al., 2006). Table 4-8 summarizes the optimal 

percent removals for heavy metals using various adsorbents and determined by using optimal 

adsorbent dose and operating pH ranges. Adsorption of heavy metals was not well demonstrated 

at the time of the 1983 regulations. Many of the alternative adsorbents demonstrate at bench 

scale the capability to achieve effluent concentrations equal to or lower than the LTAs for the 

BPT technology basis. 

Another form of adsorption is biosorption (or bioadsorption), which uses inexpensive 

biomass adsorbents (e.g., non-living, algal, and microbial biomasses) to remove toxic heavy 

copper, zinc, cadmium, lead, etc. from water. These low-cost alternatives can be available in 

large quantities, relative to more common adsorption media, such as coal-based activated carbon 

(Ahluwalia, et al., 2007; Fu & Wang, 2011; Lesmana, et al., 2009). Table 4-9 summarizes the 

treatment effectiveness of biosorbents in heavy metals removal identified in EPA’s literature 

review. Many of the studies are bench scale and hence, do not firmly establish applicability of 

the treatment to full scale operations. EPA did not identify biosorbents in the 1983 regulations; 

however, most of the results show final treated effluent concentrations that do not yet meet the 

LTAs for chromium, nickel, or zinc. 

Research on nanomaterials is relatively new. None of the studies reviewed to date 

investigated the technology for treating metal finishing wastewater. Most of the studies focus on 

the adsorption capacities achieved for heavy metals, such as lead, copper, chromium, cadmium, 

zinc, and nickel, but few studies presented removal data. Table 4-10 lists the nanomaterials EPA 

identified in recent literature. Because the nanomaterials are usually present in fine or ultrafine 

particles, their treatment effectiveness can be improved by using structural supports, such as 

4-27
Section 4 – Preliminary Study Findings 

those incorporating natural materials, metal oxides, or manufactured polymers (Hua, et al., 

2012). 

4-28
 
 

 

Section 4 – Preliminary Study Findings 

Table 4-8. Low-Cost Alternatives to Coal-based Activated Carbon Treatment Identified in EPA’s Literature Search –
 

Summary of Treatment Results
 

Scale of 

Study 

Type of 

Wastewater Adsorbent Material Targeted Metal 

LTA 

Concentration 

(mg/L)a 

Final Metal 

Concentration 

(mg/L)b 

Percent 

Removal 

(%) Source 

Pilot scale, 

batch 

operation 

Electroplating Synthesized LDH Chromium (VI) 0.572 <0.5 >99.9 (Lv, et al., 2013) 

Bench scale, 

continuous 

operation 

(column) 

Synthetic Rice husk (tartartic 

acid treated) 

Copper 0.815 0.007 – 32.0 46.9 – 

100.0 

(Wong, et al., 2003) 

Lead 0.2 0.007 – 35.5 49.4 – 100.0 

Electroplating Orange peels Nickel (II) 0.942 1.5 89 (Ajmal, et al., 2000) 

Bench scale, 

batch 

operation 

Metal finishing Lime mud (pulp and 

paper byproduct) 

Chromium 0.572 2.16 – 4.06 89.7 – 93.7 (Sthiannopkao & 

Copper Sreesai, 2009) 0.815 0.11 – 3.08 95.4 – 99.8 

Lead 0.2 0.10 – 0.17 93.3 – 97.1 

Zinc 0.549 0.059 – 12.33 56.4 – 99.8 

Metal finishing Recovery boiler ash 

(pulp and paper) 

Chromium 0.572 2.93 – 36.6 6.61 – 92.5 

Copper 0.815 5.90 -62.24 6.85 – 91.2 

Lead 0.2 0.327 – 1.46 22.9 – 90.8 

Zinc 0.549 0.736 – 29.4 -0.789 – 

97.6 

Electroplating Coconut coir pith Chromium 0.572 2.46 80 (Namasivayam & 

Sureshkumar, 2008) 

Electroplating Kyanite (commercial 

mineral) 

Copper (II) 0.815 1.50 81.3 (Ajmal, et al., 2001) 

Zinc (II) 0.549 2.70 15.6 

Nickel (II) 0.942 4.06 71 

Chromium (VI) 0.572 39.7 5.5 

Acid zinc 

electroplating 

Synthetic zeolite Zinc 0.549 42.5 66 (Alvarez-Ayuso, et 

al., 2003) 

Nickel 

electroplating 

Nickel 0.942 7.0 86 

Chromium 

electroplating 

Chromium 0.572 9.0 91 

Zinc 0.549 0.08 – 4.77 44.2 – 97.2 

4-29
 
 

 

Section 4 – Preliminary Study Findings 

Table 4-8. Low-Cost Alternatives to Coal-based Activated Carbon Treatment Identified in EPA’s Literature Search –
 

Summary of Treatment Results
 

Scale of 

Study 

Type of 

Wastewater Adsorbent Material Targeted Metal 

LTA 

Concentration 

(mg/L)a 

Final Metal 

Concentration 

(mg/L)b 

Percent 

Removal 

(%) Source 

Treated surface 

finishing 

Modified starch 

(flour) 

Iron NA 0.04 – 0.66 53.5 – 95.4 (Sancey, et al., 

Copper 2011) 0.815 0 – 0.076 66.7 – 100 

Lead 0.2 1.03 – 5.01 40.3 – 77.6 

Cadmium 0.13 0.071 – 2.18 38.3 – 91.7 

Nickel 0.942 87.2 - 503 41.8 – 85.9 

Industrial Dried plants Cadmium 0.13 0.004 94.1 (Chiban, et al., 

Copper 2011) 0.815 0.163 - 0.338 84.1 – 92.4 

Lead 0.2 0.008 - 0.051 99.2 – 99.9 

Zinc 0.549 0.44 - 2.75 84.1 – 97.5 

Synthetic Eucalyptus bark Chromium (VI) 0.572 2 99 (Sarin, et al., 2006) 

Rice husk Iron NA 0.09 – 3.71 68.6 - 99.3 (Hegazi, 2013) 

Lead 0.2 0.15 – 0.93 22.2 - 87.2 

Cadmium 0.13 0.15 – 0.36 26.0 - 67.9 

Copper 0.815 0.1 – 4.1 24.5 - 98.2 

Fly ash Iron NA 1.56 – 6.34 46.2 - 86.8 

Lead 0.2 0.28 – 0.92 21.79 - 76.1 

Cadmium 0.13 0.13 – 0.36 25.2 - 73.5 

Copper 0.815 0.08 – 3.40 37.4 - 98.5 

Uncertain Clinoptilolite Lead (II) 0.2 466 55 (Inglezakis et al., 

2007)c 

Nickel (II) 0.942 1.6 93.6 (Argun, 2008)c 

Zinc 0.549 Negligible 100 (Athanasiadis & 

Helmreich, 2005)c 

NA – Not applicable 

a Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory option 1 in Table 4-1). 

b Concentrations in bold text indicate lower treatment results than the long-term average concentration for the BPT technology basis. 

c As cited in Fu & Wang, 2011. 

4-30
 
 

 

 

Section 4 – Preliminary Study Findings 

Table 4-9. Biosorbent Treatment Identified in EPA’s Literature Review – Summary of Treatment Results 

Scale of Study 

Type of 

Wastewater Biosorbent Material Targeted Metal 

LTA 

Concentration 

(mg/L)a 

Final Metal 

Concentration 

(mg/L)b 

Percent 

Removal 

(%) Source 

Pilot scale, 

continuous 

operation 

(column) 

Chromium 

plating 

Dry yeast (Saccharomyces 

cervisiae) 

Chromium (VI) 0.572 154 61.5 (Colica, et al., 

2012) 

Bench scale, 

batch operation 

Electroplating Dead fungal biomass (A. 

niger) 

Chromium (VI) 0.572 8.65 71.2 (Kumar, et al., 

2008) 

Dead fungal biomass (A. 

sydoni) 

Chromium (VI) 0.572 10.4 65.3 

Dead fungal biomass (P. 

janthinellum) 

Chromium (VI) 0.572 11.2 62.6 

Bacterial strains isolated from 

electroplating effluent (B. 

cereus) 

Chromium (VI) 0.572 239 76 (Naik, et al., 2012) 

Brown seaweed (Ecklonia sp.) Zinc 0.549 0.1 97.6 (Park, et al., 2006) 

Chromium (VI) 0.572 Negligible 100 

Chromium (III) 1 33.3 

Synthetic Brown seaweed (F. 

vesiculosus) 

Chromium (VI) 0.572 795 18.7 (Murphy, et al., 

2009) Chromium (III) 831 NAc 

Green seaweed (Ulva spp.) Chromium (VI) 0.572 1117 14.7 

Chromium (III) 590 NAc 

Red seaweed (P. palmata) Chromium (VI) 0.572 930 18.4 

Chromium (III) 702 NAc 

NA – Not applicable 

a Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory option 1 in Table 4-1). 

b Concentrations in bold text indicate lower treatment results than the long-term average concentration for the BPT technology basis. 

c Chromium (III) was not present in the untreated wastewater; it was generated through the reduction of chromium (VI) and subsequently biosorbed. 

4-31
 
 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

Table 4-10. Nanomaterials Identified in EPA’s Literature Review 

Nanosized ferric oxides Nanosized aluminum oxides 

Goethite (α-FeOOH) 

Hematite (α-Fe2O3) Nanosized titanium oxides 

Hydrous ferric oxide 

Maghemite (γ-Fe2O3) Nanosized zinc oxides 

Magnetite (Fe2O3) 

Polymer-modified (Fe3O4) magnetic nanoparticles Nanosized magnesium oxides 

Nanosized manganese oxides Nanosized cerium oxides 

Hydrous manganese oxide 

Mixed-valence manganese oxides Single- or multi-walled carbon nanotubes 

Source: (Fu & Wang, 2011; Ge, et al., 2012; Hua, et al., 2012). 

4.4.3.2 Ion Exchange 

Ion exchange technology has been used successfully in industry for removing heavy 

metals from wastewater, including metal finishing wastewater. It is also effective at treating 

wastewater containing complexed metals (WEF, 2008). Ion exchange is a process in which ions, 

held by electrostatic forces within charged functional groups on the surface of the ion exchange 

resin, are exchanged for ions of similar charge from the solution in which the resin is immersed. 

This is classified as a sorption process because the exchange occurs on the surface of the resin, 

and the exchanging ion undergoes a phase transfer from solution phase to solid phase (i.e., from 

wastewater to the ion exchange resin). Resin performance declines with continued use and 

requires regeneration to remove the impurities removed from the wastewater (U.S. EPA, 2000a). 

EPA identified ion exchange in the 1983 regulations for the in-process treatment of cadmiumbearing wastewaters, but the technology was not included as part of the BPT technology basis 

(U.S. EPA, 1983a). During the MP&M rulemaking, EPA found that ion exchange technologies 

were used as a polishing step to remove trace metals from electroplating wastewater (U.S. EPA, 

2000a). 

Ion exchange systems have been demonstrated in recovery operations at metal finishing 

facilities, particularly to concentrate and purify plating baths; however, they are only part of the 

technology basis in the 1983 ELGs for new sources to control cadmium (see Appendix C). Table 

4-11 summarizes the results of ion exchange treatment for removing hexavalent chromium—the 

only metal identified by EPA in the recent literature on ion exchange. Treatment performance 

data EPA collected in 1983 from metal finishing plants operating this technology have 

comparable concentrations for hexavalent chromium, as well as effective removals for a number 

of other heavy metals including aluminum, cadmium, copper, iron, manganese, nickel, silver, tin, 

and zinc. Recent studies in adsorption and ion exchange technologies focus on alternative 

sorbents and tend to overlap because sorption processes can include surface interactions 

involving both adsorption and ion exchange. Many of the low-cost adsorbents identified 

previously in Table 4-3, such as zeolites and silicate materials, have been identified as potentially 

effective adsorbents as well as ion exchange resins. 

4-32
 
 

 

c 

Section 4 – Preliminary Study Findings 

Table 4-11. Ion Exchange Treatment Identified in EPA’s Literature Review – Summary of Treatment Results 

Scale of Study 

Type of 

Wastewater Resin Material 

Targeted 

Metal 

LTA 

Concentration 

(mg/L)a 

Final Metal 

Concentration 

(mg/L)b 

Percent 

Removal 

(%) Source 

Bench scale, 

continuous 

operation 

Electroplating Strongly basic resin ( with 

trimethylbenzyl ammonium) 

Chromium 

(VI) 

0.572 Negligible 100 (Sapari et al., 1996)c 

Synthetic Strongly basic resin (with 

electrodialysis) 

Chromium 

(VI) 

0.572 3.67 – 4.09 98.7 – 

98.8 

(Ahmen-Basha, et 

al., 2008) 

Bench scale, 

batch operation 

Synthetic Acidic resin (based on 

hydrophilic polymer) 

Chromium 

(VI) 

0.572 0.0005 99.5 (Kabay et al., 2003)c 

a Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory option 1 in Table 4-1). 

b Concentrations in bold text indicate lower treatment results than the long-term average concentration for the BPT technology basis. 

As cited in (Owlad, et al., 2009). 

4-33
 
 

 

 

 

 

Section 4 – Preliminary Study Findings 

Based on the studies, ion exchange performance is sensitive to pH, temperature, and 

initial metal concentrations (Ahluwalia & Goyal, 2007; Fu & Wang, 2011; Owlad, et al., 2009). 

In recent discussions with industry, EPA also learned that penetration of this technology for 

treating metal finishing wastewater has been hindered by costs related to resin regeneration and 

solids disposal (ERG, 2016). 

4.4.4 Membrane Filtration 

The 1983 Metal Finishing rulemaking identified a total of 20 membrane filtration systems 

used to remove solids from industrial wastewater, including metal finishing wastewater. At that 

time, EPA identified seven metal finishing plants using these systems, although the types of 

membrane filtration systems were not specified. The research at the time also showed effective 

treatment of wastewater containing specific complexing agents on a pilot scale. By 1996, EPA 

identified nearly 700 MP&M facilities that used membrane filtration systems, a subset of which 

likely comprised metal finishing facilities. The 1983 regulations did not identify filtration 

technologies as part of the technology basis (U.S. EPA, 1983a, 2000b). 

Membrane filtration technologies are basically physical sieves that separate contaminants 

such as metals and oils from the wastewater. They are widely used as a solids removal step due 

to their high removal efficiency, easy operation, and minimal space requirements. As a solids 

removal step, this technology is preceded by a treatment technique, such as chemical 

precipitation, to prepare the wastewater for solids removal (Fu & Wang, 2011; U.S. EPA, 

1983a). Commercially available membranes offer a variety of pore sizes to achieve the desired 

level of filtration, and each type of membrane can tolerate a range of operating pressures. Figure 

4-6 illustrates typical membrane pore sizes and operating pressures used to filter selected 

contaminants. 

Figure 4-6. Illustration of Membrane Filtration Technologies 

4-34
 
 

 

 

 

 

Section 4 – Preliminary Study Findings 

From the literature, EPA identified the following membrane processes used to remove 

metals from wastewater: microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and 

reverse osmosis (RO). These processes differ by the pore size and the differential pressure 

required across the membrane for filtration to occur (Fu & Wang, 2011; U.S. EPA, 2000a). 

4.4.4.1 Microfiltration 

Microfiltration technologies use membranes that reject particle sizes ranging from 0.1 to 

5 microns. Microfiltration is an alternative to gravity clarification after chemical precipitation 

and has been used to remove precipitates from metal-bearing industrial wastewater, such as 

metal finishing wastewater. Microfiltration membranes primarily consist of homogeneous 

polymer material and operate between 0.1 and 3 bar, depending on membrane pore size, to drive 

the separation of the contaminants across the membrane (U.S. EPA, 2000a). EPA observed use 

of microfiltration for solids separation following chemical precipitation at metal finishing 

facilities visited as part of the MP&M rulemaking development. Based on these visits, EPA 

determined that well-operated chemical precipitation systems followed by microfiltration 

removed 99.6 percent of targeted metals, compared to 96.7 percent for chemical precipitation 

systems followed by gravity clarification. Absent a preceding chemical precipitation step, 

microfiltration does not achieve high removal efficiencies of dissolved heavy metals, due to its 

large membrane pore size. 

Similar to clarification (which is part of the BPT), microfiltration generates a 

concentrated, suspended-solid slurry that requires dewatering. Microfiltration is more expensive 

than conventional gravity clarification because it requires periodic membrane regeneration to 

maintain treatment effectiveness (U.S. EPA, 2000a). 

4.4.4.2 Ultrafiltration 

Ultrafiltration technologies reject particles ranging from 0.02 to 0.1 microns (or 20 nm to 

100 nm). Ultrafiltration membranes also operate between 2 to 10 bar to drive the separation of 

contaminants, particularly dissolved and colloidal material, across the membrane. The pore size 

of the membrane does not prevent dissolved metals or some metal complexes from passing 

through, but has been shown to remove oil and grease (Fu & Wang, 2011; U.S. EPA, 2000a). 

The technology was not well demonstrated for metals removal during the 1983 Metal Finishing 

or the 2000 MP&M rulemakings. 

Recent literature reports that micellar-enhanced ultrafiltration (MEUF) and polymerenhanced ultrafiltration (PEUF) use surfactants and complexing agents, respectively, to aid in the 

aggregation of micelles or polymers that bind with metal ions to form a macro-structure that is 

large enough to be rejected by ultrafiltration membranes (as illustrated in Figure 4-7 for MEUF) 

(Fu & Wang, 2011). In the last decade, researchers have identified several surfactants and 

complexing agents that form macromolecules with heavy metals (e.g., copper, chromium, nickel, 

cadmium), which are susceptible to this level of filtration. 

4-35
 
 

 

 

Section 4 – Preliminary Study Findings 

Figure 4-7. Illustration of Micellar-Enhanced Ultrafiltration 

The metal removal efficiency of MEUF depends on the characteristics and concentrations 

of the metals and surfactants used, as well as membrane operating parameters (Fu & Wang, 

2011). The effectiveness of PEUF membranes also relies on membrane operating parameters, in 

addition to the polymer used to selectively remove the metal, the targeted metal to polymer ratio, 

and the presence of other metals in solution (Bakarat, et al., 2010; Fu & Wang, 2011; Owlad, et 

al., 2009). Table 4-12 summarizes the treatment effectiveness of ultrafiltration membranes at 

optimal conditions in bench scale experiments that EPA identified in recent literature. Several 

MEUF and PEUF systems demonstrate at bench scale the capability to achieve effluent 

concentrations equal to or lower than the LTAs for the BPT technology basis. 

4-36
 
 

 

 

 

 

Section 4 – Preliminary Study Findings 

Table 4-12. Ultrafiltration Treatment Identified in EPA’s Literature Review – Summary of Treatment Results 

Scale of Study 

Type of 

Wastewater Ultrafiltration Membrane 

Targeted 

Metal 

LTA 

Concentration 

(mg/L)a 

Final Metal 

Concentration 

(mg/L)b 

Percent 

Removal 

(%) Source 

Ultrafiltration Membranes 

Bench scale, 

batch operation Synthetic 

Carbon Chromium (VI) 0.572 40 96 (Pugazhenthi et 

al., 2005) Nitrated carbon Chromium (VI) 0.572 160 84 c

Aminated carbon Chromium (VI) 0.572 120 88 

Bench scale, 

continuous 

operation 

Synthetic Polyamide thin-film Chromium (VI) 0.572 Not reported 77 (Hafiane, 2000)c 

MEUF and PEUF Systems 

Bench scale, 

continuous 

operation 

Synthetic 

Ceramic 

(Dodecylbenzenesulfonic 

acid, dodecylamine) 

Lead (II) 0.2 0.044 - 0.076 >99 (Ferella et al., 

2007)

d Arsenate NA 3.56 – 6.16 19 

Polysulfone (Sodium dodecyl 

sulfate) 

Cadmium (II) 0.13 1 – 4 92-98 (Huang et al., 

2010)

d Zinc (II) 0.549 1 – 4 92-98 

Polyethersulfone 

(polyethyleneimine) 

Copper (II) 0.815 3 94 (Molinari et al., 

2008)

d Nickel (II) 0.942 Negligible 100 

Polyethersulfone (Carboxy 

methyl cellulose) 

Copper (II) 0.815 0.24 97.6 (Bakarat & 

Schmidt, 2010) Chromium (III) 0.572 0.05 99.5 

Nickel (II) 0.942 0.09 99.1 

Amicon 8400 Chromium (III) 0.572 <0.9 82-100 (Korus & Loska, 

2009)

d Chromium (VI) 0.572 <9 82-100 

Ceramic (Poly(acrylic acid) 

sodium) Copper (II) 0.815 0.8 99.5 (Camarilloa et al., 2010)

d 

Polysulfone (Poly(ammonium 

acrylate)) Cadmium (II) 0.13 1.12 99 (Ennigrou et al., 2009)

d 

Polysulfone (chitosan, 

polyethylenimine, or pectin) Chromium (VI) 0.572 7 30 (Aroua et al., 2007)

c 

Ground water Polyacrylnitrile fibre 

(hexadecylpyridine chloride) Chromium (VI) 0.572 0.02 90 (Bohdziewicz, 2000)c 

NA – Not applicable
 a Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory option 1 in Table 4-1).
 b Concentrations in bold text indicate lower treatment results than the long-term average concentration for the BPT technology basis.
 

As cited in (Owlad, et al., 2009). d As cited in (Fu & Wang, 2011). 

4-37
 

c 
 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

In the 1983 ELGs, EPA identified ultrafiltration as an effective technology for treating 

oily wastes, not as a metals removal technology. These results show the potential of enhanced 

membrane filtration systems to treat heavy metals to concentrations lower than those established 

in the 1983 ELGs for cadmium, chromium, copper, lead, nickel, and zinc. A disadvantage of this 

technology is that surfactants and complexing agents account for a large portion of operating 

costs and can become less cost effective if not recovered and reused (Fu & Wang, 2011). 

4.4.4.3 Nanofiltration 

Nanofiltration membranes retain particle sizes greater than 0.001 microns, which 

approach the size of dissolved multivalent metals, such as nickel, chromium, copper, and arsenic. 

Similar to microfiltration and ultrafiltration, nanofiltration is a pressure driven process, with 

operating pressures typically ranging between 5 and 30 bar (Fu & Wang, 2011). Nanofiltration 

membranes are commercially available. Summarizes the information EPA identified on the 

treatment effectiveness of nanonfiltration membranes. Nanofiltration membranes are relatively 

new; EPA did not identify nanofiltration during the development of the 1983 regulations and 

further, did not find recent literature on the use of nanofiltration for treating metal finishing 

wastewater. 

One disadvantage of nanofiltration membranes is that, because of the small pores, the 

membranes are more prone to fouling and may require frequent regeneration to remove 

contaminants that impact membrane performance. Frequent regeneration adds to the total 

operating costs of the system (Fu & Wang, 2011). 

4.4.4.4 Reverse Osmosis (RO) 

RO uses a semi-permeable membrane and a pressure differential to drive the wastewater 

across the membrane. The membrane rejects contaminants, including particulates and dissolved 

contaminants, from passing across the membrane (WEF, 2008). The rejection rate for specific 

contaminants is dependent on several operating factors. The feed rate, temperature, pH, as well 

as the operating pressure across the membrane, can all impact overall treatment performance 

(Qin, et al., 2002; WEF, 2008). 

The 1983 ELGs evaluated the performance of RO units for treating oily wastes at several 

metal finishing facilities. During the MP&M rulemaking, EPA found that RO applications for 

metal recovery in cadmium, copper, nickel, and zinc plating operations rejected 99 percent of 

multivalent ions and 90 to 96 percent of monovalent ions. Similar to ion exchange, RO is not 

sensitive to the presence of chelating agents in the wastewater. The permeate stream is usually of 

sufficient quality to be reused as rinsewater (U.S. EPA, 2000a). As reported by Fu & Wang 

(2011) and summarized in Table 4-13, several studies evaluated the performance of RO under 

various conditions and found heavy metal removal rates up to 99.5 percent. Fu & Wang (2011) 

did not identify whether the treatment performance represented metal finishing wastewater; 

however, in a separate study by Qin et al. (2002), RO successfully removed greater than 99.8 

percent nickel concentrations from nickel plating wastewater. 

4-38
 
 

 

 

c 

Section 4 – Preliminary Study Findings 

Table 4-13. Nanofiltration Treatment Identified in EPA’s Literature Review – Summary of Treatment Results 

LTA Final Metal Percent 

Type of Nanofiltration Concentration Concentration Removal 

Scale of Study Wastewater Membrane Targeted Metal (mg/L)a (mg/L)b (%) Source 

Composite polyamide Chromium (VI) 0.572 10 99 (Muthukrishnan 

& Guha, 2008)c 

Bench scale, 

continuous 

operation 

Synthetic 

Chromium (VI) 0.572 60 94 

Polyamide thin-film Nickel (II) 0.942 0.1 98 

(Murthy & 

Chaudhari, 

2008)d 

Nickel (II) 0.942 20 92 

Commercial 

Nickel 0.942 0.05 98.9 

Cadmium 0.13 0.87 82.7 

a Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory option 1 in Table 4-1). 

b Concentrations in bold text indicate lower treatment results than the long-term average concentration for the BPT technology basis. 

As cited in (Owlad, et al., 2009). 

d As cited in (Fu & Wang, 2011). 

Table 4-14. RO Treatment Identified in EPA’s Literature Review – Summary of Treatment Results 

Scale of Study 

Type of 

Wastewater Targeted Metal 

LTA 

Concentration 

(mg/L)a 

Final Metal 

Concentration 

(mg/L)b 

Percent 

Removal 

(%) Source 

Bench scale, continuous 

operation Uncertain 

Copper (II) 0.815 2.5 99.5 (Mohsen-Nia et al., 

2007)c Nickel (II) 0.942 2.5 99.5 

Copper (II) 0.815 1 – 30 70 - 95 (Zhang et al., 2009)c 

Arsenic (V) NA 0.005 - 0.045 91 - 99 (Chan & Dudeney, 

2008)c Arsenic (III) NA 0.4 - 0.225 20 - 55 

Nickel (II) 0.942 0.31 - 1.18 99.3 

(Ipek, 2005)c 

Zinc (II) 0.549 0.70 - 1.87 98.9 

Bench scale, continuous 

operation Nickel plating Nickel 0.942 <0.009 >99.8 (Qin, et al., 2002) 

NA – Not applicable 

a Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory option 1 in Table 4-1). 

b Concentrations in bold text indicate lower treatment results than the long-term average concentration for the BPT technology basis. 

c As cited in (Fu & Wang, 2011). 

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Section 4 – Preliminary Study Findings 

The metal plating industry has a growing interest in RO for recovering and reusing 

rinsewater (Qin, et al., 2002). Qin, et al. (2002) evaluated RO treatment of spent rinse water for 

reuse as alkaline rinsewater. Their study investigated the performance of four different 

commercial RO membranes in treating four variations of metal plating rinsewater containing 

cyanide and heavy metals such as chromium, copper, zinc, lead, nickel, and iron, among other 

contaminants from metal plating. They observed reduced fouling when ultrafiltration preceded 

RO; therefore, in the treatability experiments, they pretreated nickel plating wastewater with an 

ultrafiltration membrane prior to RO, which resulted in greater than 99 percent removal of nickel 

(Qin, et al., 2002). Cséfalvay et al. (2009) and Sudilovskiy (2008) also reported greater than 95 

percent copper removals, as cited in Fu & Wang (2011), using sequential RO and nanofiltration 

technologies. 

Due to the operational costs of this technology—particularly costs of high power 

consumption, regenerating the membranes, and potential need for softening pretreatment—RO is 

not a widely applied technology in the metal plating industry (Fu & Wang, 2011). 

4.4.5 Flotation 

Since the 1990s, studies have investigated flotation technologies to separate heavy metal 

precipitates from wastewater. Common flotation technologies include dissolved air flotation 

(DAF), ion flotation, and precipitation flotation (Fu & Wang, 2011). 

DAF relies on the physical interaction between bubbles of air introduced to the 

wastewater and the suspended particles in the wastewater. The interaction creates agglomerates 

of particles that float to the surface of the water and are skimmed off and removed (Fu & Wang, 

2011; WEF, 2008). The DAF technology is well demonstrated for treating oily wastes in the 

metal finishing industry, and was identified as part of the technology basis for the separate 

treatment of oily wastes in the 1983 regulations. The review of metal finishing facilities during 

the MP&M rulemaking suggests that this technology is still prevalent in the industry for oily 

waste treatment (U.S. EPA, 1983a, 2000b). EPA did not find recent literature describing the 

effectiveness of DAF systems in heavy metals removal. 

Ion flotation uses surfactants to make the ionic metal species in the wastewater 

hydrophobic, and subsequently separates the hydrophobic species from the wastewater using air 

bubbles. The wastes are then skimmed off the surface of the water. Several studies investigated 

the effectiveness of ion flotation for treating lead, copper, cadmium, silver, zinc, and trivalent 

chromium. Yuan et al. (2008), as cited in Fu & Wang (2011), reported use of tea saponin, 

sodium dodecyl sulfate, and hexadecyltrimethyl ammonium bromide as complexing agents. Tea 

saponin demonstrated bench scale removal of lead (II), copper (II), and cadmium (II) at 90.0, 

81.1, and 71.2 percent, respectively. Also reported in Fu & Wang (2011), Polat & Erdogan 

(2007) indicated optimal removals of copper (II), zinc (II), chromium (III), and silver reached 

approximately 74 percent under acidic conditions and 90 percent under basic conditions (with 

the aid of secondary hydroxide precipitation in the high pH range). Fu and Wang (2011) pointed 

out that that study did not report treated effluent concentrations (Fu & Wang, 2011). 

Precipitate flotation applies the flotation method to remove metal precipitates formed 

through common precipitation techniques. Air bubbles introduced into the wastewater carry the 

precipitates to the surface of the water, where they are skimmed off. Capponi et al. (2006), as 

4-40
 
 

 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

cited in Fu and Wang (2011), conducted a bench scale study which showed 96.2 percent removal 

of trivalent chromium by precipitate flotation of dilute aqueous solutions. The study did not 

report treated effluent concentrations (Fu & Wang, 2011). EPA did not identify these 

technologies in the 1983 regulations or the MP&M regulations for the treatment of heavy metals. 

4.4.6 Electrochemical Treatment 

Electrochemical treatment involves the application of an electric potential across a 

cathode and anode to facilitate the recovery or precipitation of heavy metals in wastewater (Fu & 

Wang, 2011). As part of the 1983 ELGs, EPA identified electrochemical oxidation, reduction, 

and regeneration as alternative treatments for chromium and cyanide-bearing wastewaters. EPA 

identified several treatment methods using this electrochemical approach, including 

electrodialysis, electrocoagulation, electroflotation, and electrodeposition, which are further 

described in this section. Electrochemical treatment methods have not found application on a 

large industrial scale due to high initial costs and potentially high energy costs (Fu & Wang, 

2011). 

4.4.6.1 Electrodialysis 

Electrodialysis is the process of separating metal ions across a charged membrane, 

typically an ion exchange membrane. The use of ion exchange membranes in this process is also 

referred to as electrochemical ion exchange. Electrodialysis uses an electric field as the driving 

force across the membrane, rather than the typical pressure driven process described for 

membranes above, and the literature shows effective treatment of several metals, including 

hexavalent chromium and lead, as well as copper and iron from copper electrowinning 

operations. In a pilot study, electrodialysis treated hexavalent chromium down to levels as low as 

0.1 milligrams per liter, which is lower than chromium limits in the 1983 regulations (Fu & 

Wang, 2011; U.S. EPA, 1983a). One study observed the recovery of chromium from plating 

rinsewater using a combination of ion exchange and electrodialysis units, which effectively 

recovered nearly 99 percent of chromium on a bench scale. The treated effluent had sufficient 

quality to be reused in the process. The study did not describe disposal considerations for the 

reject stream (Ahmen-Basha, et al., 2008). Further investigations also determined that increasing 

voltage and temperature improved the performance of electrodialysis; however, the treatment 

effectiveness may be reduced with greater flow rates and concentrations (i.e., conditions that 

would apply to a full scale operation) (Fu & Wang, 2011). 

4.4.6.2 Electrocoagulation 

Electrocoagulation incorporates electric potential into conventional chemical 

precipitation processes to improve heavy metals removal from wastewater. The process may also 

be referred to as electrochemical precipitation, which involves an electrolytic cell containing 

steel plates (one cathode and one anode) submerged in water and between which an electric 

current is applied. By applying an electric potential between the cathode and anode, the charges 

that hold the heavy metals in solution destabilize and coagulate to form a mass, which can be 

easily removed. Additional chemicals are generally not required to facilitate precipitation, just 

the anode and cathode. The effectiveness of the process has been found to rely on the electrical 

potential, hydraulic retention time, and solution pH. According to Fu & Wang (2011), 

electrocoagulation applications have grown over the past two decades. At the promulgation of 

4-41
 
 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

the 1983 Metal Finishing regulations, its application was evaluated for treating chromiumcontaining wastewater; however electrocoagulation could also be effective in removing other 

heavy metals from wastewater (U.S. EPA, 1983a). Table 4-15 provides a summary of available 

electrocoagulation treatment results that EPA identified in recent literature. 

Table 4-15. Electrocoagulation Treatment Identified in EPA’s Literature Review -

Summary of Treatment Results
 

Scale of 

Study 

Type of 

Wastewater 

Targeted 

Metal 

LTA 

Concentration 

(mg/L)a 

Final Metal 

Concentration 

(mg/L) 

Percent 

Removal 

(%) Source 

Bench 

scale, 

unknown 

operation 

Electroplating Chromium 

(VI) 

0.572 0.12 98.5 (Owlad, et al., 

2009) 0.52 99.6 

Not reported 77.0 – 

100 

312.9 85.1 

Uncertain Uncertain Manganes 

e (II) 

NA 21.8 78.2 (Shafaei et al., 

2010)c 

Nickel (II) 0.942 Negligible 100 (Kabdaşli et 

al, 2009)c Zinc (II) 0.549 Negligible 100 

Arsenic 

(III) 

NA <0.022 >99 (Parga et al., 

2005)c 

Arsenic 

(V) 

NA <0.022 >99 

Chromium 

(VI) 

0.572 Negligible 100 (Olmez, 2009) 

Bench 

scale, 

batch 

operation 

Synthetic Copper, 

Nickel, 

Zinc, 

Cadmium, 

Lead, Iron 

0.815, 0.942, 

0.549, 0.13, 0.2, 

NA 

0.5 - 40 90 – 99 (Merzouk, et 

al., 2009) 

NA – Not applicable 

a 

b 

c 

Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory 

option 1 in Table 4-1). 

Concentrations in bold text indicate lower treatment results than the long-term average concentration for the 

BPT technology basis. 

As cited in (Fu & Wang, 2011). 

Electrocoagulation studies involving the removal of zinc, copper, chromium, nickel, 

silver, lead and dichromate show effective and consistent removals across a broad concentration 

range (Akbal, et al., 2011; Fu & Wang, 2011; Merzouk, et al., 2009). Kabdasli et al. (2009) also 

investigated the treatability of complexed metals in nickel and zinc plating wastewater using 

electrocoagulation. In the study, both zinc and nickel were completely removed using this 

process (Fu & Wang, 2011; Kabdasli, et al., 2009). In Kobya et al. (2010) reported that 

electrocoagulation showed effective removal (greater than 99 percent) of cadmium, nickel, and 

cyanide at optimal conditions. Electrocoagulation may be an alternative treatment option for 

removing cyanide by first dissociating the metal complexes in electroplating wastewater, 

removing the freed cadmium and nickel ions, and generating a new metal complex with the 

metal ions generated by the electrodes (Kobya, et al., 2010). During an electrocoagulation 

4-42
 
 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

process, no additional chemicals are added to the wastewater, in contrast to conventional 

precipitation methods. Therefore, this process generates a more compact sludge, which can 

significantly reduce disposal costs (Akbal & Camci, 2011). 

The studies indicate that for electrocoagulation, optimization of metals removal relies on 

the electrode positions, electrical potential, and pH of the solution. According to Senturk (2013), 

iron electrodes are more effective than aluminum in treating electroplating wastewater 

containing zinc and cyanide; however, in a separate study, Akbal & Camci (2011) noted ironaluminum electrode pairs to be equally efficient in electroplating wastewater containing nickel, 

copper, and chromium (Akbal & Camci, 2011; Senturk, 2013). Olmer (2009) noted stainless 

steel electrodes for use in hexavalent chromium removals in hard chrome plating rinsewater. 

Several studies have focused on optimization schemes for different types of wastewater 

characteristics and suggest that conditions for optimal removal should be identified on a case-bycase basis. EPA did not identify any full-scale application of electrocoagulation processes for 

metal finishing wastewater during the literature review. 

4.4.6.3 Electroflotation 

Similar to conventional flotation techniques, electroflotation relies on the use of air 

bubbles to bind with and transport metal precipitates to the surface of the water. Bubbles 

consisting of hydrogen and oxygen gases are generated through the electrolysis of the water on 

the surface of the electrodes as an electric potential is applied. These hydrogen and oxygen gases 

become the transport media for metal ions. Multiple studies have been reported to show potential 

uses in the metal finishing industry for treating iron, nickel, copper, zinc, lead, and cadmium at 

up to 99 percent removal efficiency (Fu & Wang, 2011). In a separate study, copper and nickel 

removals under optimal conditions reached 98 to 99 percent (Khelifa, et al., 2005). Table 4-16 

summarizes the removals of electroflotation that EPA identified in recent literature. 

Table 4-16. Electroflotation Treatment Identified in EPA’s Literature Review -

Summary of Treatment Results 

Scale of Study 

Type of 

Wastewater 

Targeted 

Metal 

LTA 

Concentrati 

on 

(mg/L)a 

Final Metal 

Concentrati 

on (mg/L) 

Percent 

Removal 

(%) Source 

Bench scale, 

batch operation 

Synthetic Zinc (II) 0.549 0.8 96 (Casqueira et 

al., 2006)b 

Nickel (II) 0.942 2 98-99 (Khelifa et al., 

2005)b Copper (II) 0.815 1 99-99 

a Long-term average concentrations represent total metal concentrations for the BPT technology basis (regulatory 

option 1 in Table 4-1). 

b As cited in (Fu & Wang, 2011). 

4.4.6.4 Electrodeposition 

Electrodeposition (or electrophoretic deposition) is a general term used for a process 

using an applied current across electrodes to deposit metals onto an electrode. Electrodeposition 

can refer to an electroplating process; however, it also covers a number of processes to recover 

4-43
 
 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

metals from wastewater. Terms such as ‘electrolytic recovery’ and ‘electrowinning’ are also 

common terms for recovery processes using electrodeposition (Kirk-Othmer, 2004; U.S. EPA, 

1983a). Oztekin & Yazicigil (2006) and Chang et al. (2006), as cited in Fu & Wang (2011) 

investigated the recovery of metals from complex wastewaters, which effectively removed up to 

90 percent and nearly 96 percent, respectively, of copper from complex wastewater (Fu & Wang, 

2011). A disadvantage of electrodeposition—and of other electrochemical methods discussed in 

this section—is the high energy requirement (resulting in high operating costs). 

4.4.7 Biological Treatment 

The literature suggests that biological treatment of metal-bearing wastewater is an 

expanding area of research. EPA identified a few biological treatment systems during the 1983 

rulemaking; however, biological treatment was not part of the technology basis for the 1983 

Metal Finishing ELGs. 

Researchers have evaluated the use of biological processes to reduce hexavalent 

chromium (Cr (VI)) to trivalent chromium (Cr (III)) in industrial electroplating wastewater prior 

to conventional chemical precipitation. A pilot study conducted on the ChromeBacTM biological 

system in Malaysia showed successful reduction of Cr (VI) down to less than 0.05 milligrams per 

liter (or greater than 99.8 percent removal). Total chromium was reduced to 0.7 mg/L (or 98.6 

percent removal) (Ahmad, et al., 2010). Chromium removal (as Cr (III)) was completed using 

conventional chemical precipitation. 

Sulfide precipitation processes have used sulfate-reducing bacteria (SRB) to generate 

sulfide on-site. The SRB oxidizes simple organic compounds and reduces sulfates under 

anaerobic conditions to form biogenic hydrogen sulfide. Hydrogen sulfide is subsequently used 

to precipitate metals. The process was tested on zinc-bearing wastewater (containing 400 mg/L 

of Zn) and proved effective at completely removing soluble zinc as well as sulfate and total 

organic compounds (TOC) (Fu & Wang, 2011). According to Huisman et al. (2006), Paques BV, 

a Netherlands company, is operating full-scale Sulfateq® technology using SRB for wastewater 

treatment. They have implemented nearly 500 industrial installations for several industries. The 

technology reliably removes sulfate, nitrate, heavy metals, selenium, and fluoride from metal and 

mining industry wastewater. Another Pacques BV technology, the Pacques Thioteq process, was 

also developed to aid in the on-site generation of biogenic hydrogen sulfide when wastewater 

characteristics inhibit its production (Huisman, et al., 2006). EPA did not identify application of 

these technologies in metal finishing wastewater. 

In another study, Park et al. (2005) evaluated the use of iron-oxidizing bacteria to reduce 

iron levels from electroplating wastewater. The researchers used a biological treatment step to 

remove iron from the wastewater without removing other heavy metals such as zinc or nickel. 

After biological pretreatment, wastewater was treated by sodium hydroxide precipitation to 

generate sludge with high concentrations of zinc or nickel. The iron-removal pretreatment 

reduced the volume of the hydroxide sludge generated, allowing for more economical recovery 

of higher value metals (Park, et al., 2005). 

4-44
 
 

 

Section 4 – Preliminary Study Findings 

4.4.8 Summary of Wastewater Treatment Technologies 

Thus far, EPA’s literature review on wastewater treatment has primarily focused on 

articles from academic journals, which identified numerous wastewater treatment technologies 

for removing heavy metals; however, many are not new technologies or new applications for 

metal finishing wastewater treatment. In fact, EPA identified many of these technologies during 

the development of the 1983 Metal Finishing ELGs (as summarized in Table 4-5 and in 

Appendix C). Although these technologies effectively removed metals from wastewater at 

sampled metal finishing facilities, many were relatively new applications for the industry and 

likely cost more than the treatment technologies that industry used at the time. In particular, EPA 

had considered granular bed and diatomaceous earth filtration, or similar media filtration 

technologies, as part of regulatory option 2 (see Table 4-5); however, EPA ultimately did not 

select these alternatives because they were not economically feasible at the time. 

There were additional technologies that EPA also considered in the 1983 ELGs, 

specifically for treating oily wastes and toxic organics, which are now finding application in 

heavy metals removal. These included sorption, advanced membrane filtration, flotation, and 

electrochemical methods. Advances in heavy metals removal have also included research into 

better-performing or more cost-effective chemical additives or materials. Based on the number of 

articles EPA identified, sorption and membrane filtration seem to be the focus of recent research 

for heavy metals removal. The articles present bench-scale results that suggest promising 

advances in treating heavy metals; however, EPA has not determined whether any of these 

promising technologies have been implemented at full-scale within the metal finishing industry. 

From discussions with pretreatment coordinators and with industry representatives, EPA 

learned that most metal finishing facilities continue to use conventional chemical precipitation 

technologies, although some facilities have added a polishing step such as membrane filtration or 

sorption technologies. EPA also learned that advances in wastewater treatment technologies in 

the industry have been slow, and most likely inhibited by the costs of installing and operating 

more advanced technologies. However, EPA has not fully evaluated the extent to which the 

metal finishing industry is applying technologies beyond the BPT technology basis (ERG, 2016; 

U.S. EPA, 2015a). 

4.5 Applicability and Other Regulatory Considerations 

EPA expects that in the 32 years that have passed since the promulgation of the Metal 

Finishing ELGs, metal finishing process technologies and chemistries have evolved and 

advanced wastewater treatment technologies have become available for metal finishing 

wastewater treatment. EPA has often received requests for official EPA determinations on the 

applicability of the ELGs to specific operations or to provide clarification on metal finishing 

operations described in the rule. Additionally, stakeholders have also urged EPA to consider 

other regulations that may also have a bearing on the industry. This section outlines the key 

considerations that have been identified thus far in the Metal Finishing Preliminary Study. 

4.5.1 Rule Implementation 

Pretreatment coordinators noted that POTWs are still implementing 40 CFR Part 413 

(Electroplating) pretreatment standards for some metal finishing facilities. Most metal finishing 

4-45
 
 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

facilities should be covered by 40 CFR Part 433 pretreatment standards, and not 40 CFR Part 

413 standards. The scope of facilities still regulated under 40 CFR Part 413 is technically limited 

to job shops and IPCB manufacturers that were considered existing sources at the time of the 

promulgation of the 1983 Metal Finishing ELGs. In a public comment on EPA’s 2014 Effluent 

Guidelines Program Plan, the Association of Clean Water Administrators (ACWA) urged EPA 

to consider merging the facilities still operating under 40 CFR Part 413 regulations into the 

Metal Finishing ELGs (U.S. EPA, 2015c). 

Unlike wastewater regulations for other metal-related industries (e.g., aluminum forming, 

iron and steel), which include production-based limits, the Metal Finishing ELGs are 

concentration-based which can make them easier to apply in wastewater permits. Due to 

potential overlap of Metal Finishing regulations with other metal related regulations that make 

take precedence, pretreatment coordinators suspect that there is confusion on when Metal 

Finishing ELGs versus other metals related ELGs may apply at POTWs. 

4.5.2	 Applicability of ELGs to New or Modified Metal Finishing Operations 

EPA and regional pretreatment coordinators have received questions from stakeholders 

on a number of topics related to the 46 metal finishing operations that are listed in the 1983 

Metal Finishing ELGs. In particular, stakeholders asked for clarification on: 

•	 Whether a newly designed metal finishing operation would fall under the six 

primary metal finishing operations that would subject them to the Metal Finishing 

ELGs (e.g., revivation, zirconization, citric acid passivation); 

•	 Whether modifications to the metal finishing operation over time (e.g., increasing 

the number of finishing lines, expanding plant operations, changing plating 

process) would subject them to new source standards (NSPS and PSNS) under 40 

CFR Part 433 (instead of BAT and PSES or 40 CFR Part 413 electroplating 

standards); 

•	 Whether newer manufacturing industries (e.g., solar panel manufacturing, cell 

phone manufacturing) that were not considered during development of the 1983 

rule would be subject to the Metal Finishing ELGs. 

•	 How to define current industry practices to determine whether they are subject to 

the Metal Finishing ELGs. For example, 

—	 Clarification of the distinction between “cleaning” and “etching” 

operations. 

—	 Use of phosphoric acid, chromic acid, or citric acid in “cleaning” versus 

“conversion coating” or “etching” operations. 

—	 Use of brighteners during “acid cleaning” vs “bright dipping” operations 

where “bright dipping” is mentioned as an example “etching” core process 

in the Technical Development Document (TDD) and “cleaning” is not a 

core process. 

—	 Clarification on whether facilities performing “powder coating” are 

subject to the Metal Finishing ELGs. 

4-46
 
 

 

 

 

 

 

 

 

 

Section 4 – Preliminary Study Findings 

Regional pretreatment coordinators have fielded questions from industry on a case-bycase basis related to these topics. When necessary, EPA plans to develop policy memoranda to 

address questions on the applicability of the Metal Finishing ELGs. 

4.5.3	 Considerations for Other Regulations 

Based on discussions with stakeholders and EPA’s review of the literature, EPA 

identified the following regulations that may impact the characteristics of wastewater generated 

from metal finishing operations or inhibit the implementation of advanced wastewater treatment 

technologies for the industry. 

4.5.3.1	 National Emission Standards for Hazardous Air Pollutants (NESHAPs), Office of 

Air and Radiation (OAR) 

EPA identified the following air regulations that have been promulgated since the 1983 

Metal Finishing ELGs. These regulations can impact the overall characteristics of process 

wastewater generated from metal finishing operations. 

•	 NESHAP for Chromium Emissions from Hard and Decorative Chromium (40 

CFR Part 63, Subpart N), 1995 and 2012. EPA promulgated the original 

NESHAP in 1995 affecting all facilities using chromium electroplating tanks. In 

2012, EPA amended the rule to tighten emission standards for chromium 

electroplating and anodizing operations, which included revised emission limits 

and a ban on the use of perfluorooctane sulfonate (PFOS)-based fume 

suppressants in air pollution control devices. Based on discussions ith some metal 

finishing facilities, EPA learned that wastewater generated from emission control 

devices used to control chromium emissions can be commingled with metal 

finishing wastewater prior to wastewater treatment. 

•	 NESHAP for Plating and Polishing Operations (40 CFR Part 63, Subpart 

WWWWWW), 2008. EPA published the NESHAP in 2008 requiring use of 

generally available control technology (GACT) standards at facilities with plating, 

polishing or thermal spray processes that contain cadmium, nickel, lead, 

manganese and/or chromium (excluding chromium electroplating and 

anodizing operations). The rule does not establish emission limits for these 

operations. Facilities have several compliance alternatives including use of 

wetting agents/fume suppressants (WAFS), air pollution control devices or tank 

covers. Platers also need to implement management practices that reduce the 

generation of airborne chemicals. These modifications may introduce pollutants to 

metal finishing wastewater that are not commonly used in metal finishing 

operations. 

•	 NESHAP for Metal Fabrication and Finishing Area Source (40 CFR Part 63, 

Subpart XXXXXX), 2008. In 2008, EPA promulgated requirements to reduce air 

pollution of compounds of metals such as cadmium, chromium, lead, manganese 

and nickel from nine metal fabrication and finishing source categories. This rule 

applies to facilities primarily engaged in these nine source categories and covers 

the following operations: dry abrasive blasting, dry grinding and dry polishing 

4-47
 
 

 

 

 

 

Section 4 – Preliminary Study Findings 

with machines, dry machining, spray painting, and welding. The NESHAP may 

require the use of wet emission control devices for some operations, which may 

introduce pollutants that impact metal finishing wastewater characteristics. 

4.5.3.2	 Resource Conservation and Recovery Act (RCRA) Hazardous Waste Regulations, 

Office of Resource Conservation and Recovery (ORCR) 

Based on discussions with wastewater treatment technology vendors, EPA also learned 

that hazardous waste regulations can inhibit the advancement of wastewater treatment 

technologies for the industry. Specifically, vendors noted the difficulty of applying more 

advanced technologies such as ion exchange or RO due to the costs to the facilities for offsite 

resin or membrane reclamation and/or disposal. As defined under RCRA, the resins and 

membranes may be classified as hazardous waste (most commonly under F006 – wastewater 

treatment sludges from electroplating operations). Technologies such as ion exchange and RO 

can treat wastewaters to a quality that can be reused in the process, which can significantly 

reduce the amount of wastewater discharged; however, the added cost of managing the 

hazardous wastes generated by these technologies may have rendered them economically 

infeasible for many of metal finishing facilities (particularly, job shops). On January 13, 2015, 

EPA published in the Federal Register (FR) a revised definition of solid waste (80 FR 1694). 

EPA recently revised the definition of solid waste in 2015 with the objective of encouraging 

reclamation of hazardous secondary materials without increasing risk to human health and the 

environment from discarded hazardous secondary material. This new definition may pave a way 

for the advancement of wastewater treatment and reuse for the metal finishing industry. 

4.5.3.3	 European Union (EU) End of Life Vehicle (ELV) and Restriction of Hazardous 

Substances (RoHS) Directives 

The EU issued the End of Life Vehicles Directive in 2000 to address the issue of the 

recycling and/or disposal of automobiles at the end of their useful lives to limit waste containing 

lead, mercury, cadmium, and hexavalent chromium. The directive bans lead, mercury, and 

cadmium and limits hexavalent chromium to 2.0 grams per vehicle for the purpose of corrosion 

protection only. Similarly, in 2006, the EU also issued the RoHS Directive banning lead, 

mercury, cadmium, and hexavalent chromium, as well as two additional flame retardants, from 

electronic products, thereby reducing the amount of these substances disposed at the end of their 

useful lives. Based on discussions with the metal finishing industry, these directives may impact 

the metal finishes used in the U.S. on products that are then sold abroad. 

4-48
 
 

 

 

Section 5 – Next Steps 

5.	 NEXT STEPS 

As discussed in Section 1 of this report, EPA plans to gather sufficient information to 

answer the following key questions for the study: 

•	 How is the current metal finishing industry different from the industry as 

regulated by the Metal Finishing ELGs? 

—	 What is the current distribution of captive facilities and job shops within 

the industry? 

—	 Which types of facilities are conducting metal finishing operations? 

•	 Since the promulgation of the Metal Finishing ELGs, what process technology 

changes have been implemented and how have the primary sources of wastewater 

changed? 

•	 Since the promulgation of the Metal Finishing ELGs, what chemical formulation 

changes have been implemented and how have these changes affected the 

characteristics of the raw wastewater, i.e., pollutants, concentrations, flow 

rates/volume? 

•	 What are the best available technologies for pollution prevention and wastewater 

treatment and to what levels do they reduce pollutants of concern? 

—	 What are the concentrations and loadings of pollutants currently being 

discharged (i.e., baseline concentrations)? 

—	 Which pollutant discharges require additional control? 

—	 How will industry discharges change if facilities implement these best 

available technologies and practices? 

•	 What challenges do metal finishing facilities face in applying the Metal Finishing 

ELGs? 

EPA plans to continue gathering and analyzing information relevant to these questions 

over the next year, after which it will determine whether additional data collection efforts are 

needed and how to proceed with updating the 1983 Metal Finishing ELGs. The information that 

EPA has compiled to date identifies the key topics for further investigation, as described in the 

subsections below. 

5.1 Review Pollutant Discharge and Release Data 

EPA plans to review existing industry discharge data to further evaluate and characterize 

both direct and indirect metal finishing wastewater discharges. EPA will evaluate discharge 

monitoring report (DMR) and Toxics Release Inventory (TRI) data to identify metal finishing 

facilities with wastewater discharges, the location of facilities reporting to DMR and TRI, the 

pollutants being generated and discharged, and their respective prevalence, magnitude, and 

relative toxicity in wastewaters that are not currently regulated by the Metal Finishing ELGs. 

5-1
 
 

 

 

 

 

 

Section 5 – Next Steps 

5.2 Evaluate Changes to Industry Profile 

Currently, EPA does not have a complete understanding of how the industry profile has 

changed since the promulgation of the 1983 regulations. Particularly, EPA is seeking to 

understand any changes in metal finishing operations and markets, in wastewater treatment and 

discharge practices, and in the number, size, and types of facilities generating and discharging 

wastewater. To date, EPA’s review of the industry suggests that there have been changes in the 

industry since 1983 that would affect wastewater characteristics and discharges from metal 

finishing facilities. However, EPA cannot yet adequately define the extent of those changes or 

their impacts. 

EPA will evaluate options for developing a current profile of metal finishing facilities. 

These options may include using a marketing database, reviewing more recent data collected 

during the MP&M regulatory development, reviewing TRI and DMR data, and identifying other 

data collection efforts that may have been conducted by other EPA offices, such as the Office of 

Air and Radiation (OAR) and the Office of Resource Conservation and Recovery (ORCR), 

which may have already compiled these types of information. EPA will also collaborate with 

EPA regional offices, state and local agencies, and POTW control authorities to obtain POTW 

pretreatment reports, which identify categorical industrial users (CIUs) in the POTW’s 

catchment area. 

5.3 Review Literature from Conferences and Other Industry Sources 

EPA has conducted an extensive literature review of metal finishing process 

technologies, alternative chemistries, and wastewater treatment using industry keywords on 

several research collections and search engines.19 In addition, EPA collected and will review 

literature on wastewater treatment from the 2015 WEFTEC and 2015 IWC. EPA does not plan to 

conduct another extensive literature search on technical papers and reports, studies, peerreviewed journal articles, and industry publications on metal finishing operations and wastewater 

management; however, EPA will review literature that it identifies from other EPA activities and 

industry sources described in this section. 

5.4 Continue Discussions with Industry Experts on Key Topics 

EPA will continue conversations with federal and regional pretreatment coordinators. 

These personnel often have on-site experience at POTWs that receive metal finishing 

wastewater. Such discussions will help EPA identify and explore issues with the implementation 

of the Metal Finishing ELGs, and to understand the effects of these issues on POTW operations. 

EPA held meetings with the ACWA and several pretreatment coordinators in November 2015 to 

gather different perspectives on the metal finishing category (U.S. EPA, 2015d). EPA also plans 

to initiate discussions with other organizations, such as NACWA and NASF, to understand their 

perspective on the implementation of the 1983 regulations. 

EPA will also continue to reach out to personnel from metal finishing facilities and 

wastewater treatment technology vendors to: 1) obtain information that will help answer key 

19EPA used specific industry keywords for the metal finishing category, listed in Appendix B. 

5-2
 
 

 

 

 

Section 5 – Next Steps 

study questions, 2) identify potential candidate facilities for future EPA site visits, 3) gain 

industry perspective on the 1983 Metal Finishing ELGs, and 4) generally assess the technical and 

economic feasibility of implementing more advanced wastewater treatment technologies and 

waste minimization practices at metal finishing facilities. EPA will identify additional facilities 

to contact, based on discussion with these industry experts, and based on its review of available 

annual pretreatment reports or other sources listing metal finishing facilities that indirectly 

discharge wastewater. 

5.5 Conduct Site Visits to Metal Finishing Facilities 

EPA will visit metal finishing facilities to observe operations and wastewater 

management practices first-hand. EPA will seek to visit facilities representing a range of 

operational approaches, including facilities that are: 

•	 Operating new or modified finishing processes. 

•	 Using alternative chemicals in metal finishing operations. 

•	 Using pollution prevention practices to maximize the reuse and minimize the 

generation and/or discharge of pollutants in wastewater. 

•	 Operating advanced wastewater treatment technologies (aside from conventional 

hydroxide precipitation and clarification). 

During these visits, EPA may request data on wastewater treatment effectiveness, general 

process design, typical operating conditions, market demands, and other topics. EPA may also 

request information on the wastewater treatment technologies and treatment chemicals used on 

site. 

5.6 Investigate the Impacts of Other Regulations on the Industry 

EPA will further investigate how other EPA regulations may be affecting the metal 

finishing industry. Possible examples of such regulations include NESHAPs (described in 

Section 4.5), RCRA hazardous waste disposal regulations, and other EPA efforts. As part of this 

investigation, EPA will collaborate with other EPA offices and analyze information regarding 

regulatory impacts that the Agency has already collected from the industry. 

5-3
 
 

 

 

 

Section 6 – Quality Assurance 

6.	 QUALITY ASSURANCE 

In gathering information to support EPA’s preliminary study of the Metal Finishing 

Category. EPA evaluated and documented the usefulness and quality of the data collected to date 

in accordance with the criteria specified in The Environmental Engineering Support for Clean 

Water Regulations Programmatic Quality Assurance Project Plan (PQAPP) (ERG, 2013). 

EPA’s review of the data sources for this interim study also followed the quality assurance 

procedures specified in the PQAPP, with the addition of specific criteria discussed in Section 

6.3, below. This section provides detailed information on the data sources used and data quality 

evaluation performed. 

6.1 Project Objectives 

As discussed in Section 1 one of EPA’s primary objectives for the preliminary study of 

the Metal Finishing Category is to assess the current state of the industry to better understand 

how metal finishing operations, wastewater characteristics, and wastewater treatment 

technologies have changed since EPA promulgated the 1983 ELGs. This assessment will help 

EPA to determine whether additional data collection efforts are needed and how best to address 

the 1983 Metal Finishing ELGs. Specifically, the study seeks to answer the key questions listed 

in Section 1 and reiterated in Section 5 of this report. 

6.2 Data Sources 

To date, EPA has used the following types of data sources to support its preliminary 

study of the Metal Finishing Category: 

•	 Conference proceedings, peer-reviewed journals, other academic literature. 

•	 Interviews with industry personnel, vendors, trade association representatives, and 

pretreatment coordinators. 

•	 Existing government publications and supporting information. 

6.3 Data Quality Objectives and Criteria 

As described in the PQAPP, EPA ensures that the data collection, processing, and 

analyses performed for the preliminary study will meet the data quality objectives of objectivity, 

integrity, and utility, as described below: 

•	 Objectivity. The information must be accurate, reliable, and unbiased, and the 

manner in which the information is presented must be accurate, clear, complete, 

and unbiased. 

•	 Integrity. The information may not be compromised through corruption or 

falsification, either by accident, or by unauthorized access or revision. 

•	 Utility. The information must be useful for the intended users. 

The sources of the data used will also be made transparent. As the study progresses and 

EPA analyzes the data, EPA will also provide information on the various assumptions, analytical 

6-1
 
 

 

 

 

 

 

 

Section 6 – Quality Assurance 

methods, and statistical procedures applied throughout the study. EPA prioritized the review of 

the data sources described in Section 6.2 to address the key study questions listed in Section 1 of 

this report. The criteria that EPA will use to evaluate the quality of literature are accuracy, 

reliability, and representativeness, as described in Section 4.3.1 and in Table 4-2 of the PQAPP 

(ERG, 2013), and summarized below: 

Accuracy. EPA assumed that the underlying data and information contained in state and 

federal reports, peer-reviewed journal articles, and industry publications are accurate. Although 

industry publications are not usually peer-reviewed, this resource provides useful information for 

understanding metal finishing processes and wastes generated. 

Relevance. Selected articles must describe process operations, pollutants, or wastestreams 

that are representative of the metal finishing industry. Articles that most closely provide answers 

to the key questions listed in Section 1 are the most relevant. 

Reliability. EPA considered the following factors when evaluating reliability of the data 

sources used to support the study: (1) data sources that have been generated by governmental 

agencies or are otherwise subject to peer review and assessment are considered to be the most 

reliable and useful for understanding industry process operations, quantitatively characterizing 

wastewater discharges, and demonstrating treatment system performance; (2) data sources from 

entities with established knowledge in the topic area (e.g. studies conducted by industry experts, 

academic researchers, data generated by an industrial facility using documented and approved 

methods) are also considered to be reliable and useful for understanding industry process 

operations, quantitatively characterizing wastewater discharges, demonstrating treatment system 

performance, and understanding applicability of the regulations; and (3) data sources that use 

unknown collection and data review procedures are less reliable, but may be generally useful for 

qualitative understanding of industry process operations and waste streams. In general, EPA 

evaluated reliability based on the degree to which sources met the following criteria: 

•	 Scientific work is clearly written, so that all assumptions and methodologies can 

be identified. 

•	 Variability and uncertainty (quantitative and qualitative) in the information or in 

the procedures, measures, methods, or models are evaluated and characterized. 

•	 Assumptions and methodologies are consistently applied throughout the analysis 

as reported in the source. 

Representativeness. EPA evaluated whether selected data sources described process 

operations, pollutants, or waste streams that are representative of the metal finishing industry. 

For the purposes of this study, EPA expanded upon the general criteria set forth in the PQAPP by 

establishing data quality acceptance criteria related to the geographic scope and age of the data 

(described below): 

•	 Geographic Scope. Data sources must describe the wastewater characteristics for 

the metal finishing industry in the United States. EPA also collected additional 

information from the data sources to describe the generation of the data, such as 

the source of the wastewater, sample collection procedures, analytical methods, 

6-2
 
 

 

 

 

 

 

 

Section 6 – Quality Assurance 

units, and relevant data qualifiers to further evaluate its quantitative use in future 

analyses. EPA included some international data sources that were relevant for 

their descriptions of other potential wastewater treatment technologies or 

chemical processes used in metal finishing. 

•	 Age. EPA prioritized data sources published in 2000 or later, as they reflect more 

recent industry changes. However, information published prior to 2000 (e.g., 1983 

Metal Finishing Technical Development Document, supporting documentation for 

the MP&M rulemaking) can provide useful qualitative information regarding the 

status of the industry then and the nature of any changes in the years following 

promulgation. In addition, EPA notes the year of the data source referenced in the 

preliminary study to clearly document the time period. 

Table 6-1 summarizes the data quality criteria discussed above. 

Table 6-1. Data Quality Criteria Summary 

Data Quality Criterion Description 

Accuracy Underlying data in state and federal reports, peer-reviewed journal articles, 

and industry publications are accurate. 

Clearly written, assumptions and methodologies identified. 

Reliability Variability and uncertainty in the information are evaluated and characterized. 

Assumptions and methodologies are consistently applied. 

Process operations, pollutants, or waste streams that are representative of the 

metal finishing industry are described. 

Representativeness 

Wastewater characteristics of the U.S. metal finishing industry are described. 

Data sources addressing industry outside of the United States were also 

included for descriptions of potential wastewater treatment technologies or 

chemical processes. 

Data sources published in 2000 or later are prioritized; data sources prior to 

2000 were used qualitatively. 

6.4 Data Quality Evaluation 

This section describes the data sources in detail and how they met the evaluation criteria 

listed in Section 6.3. Table 6-2, at the end of this section, summarizes the data sources and 

acceptance criteria evaluated. EPA recognizes data sets contain different levels of information 

and limitations, therefore, EPA evaluates each type of data set and will apply appropriate 

acceptance criteria based on the purpose of each analysis. Table 6-2 presents the applied 

acceptance criteria EPA used to evaluate data for the Preliminary Study. 

6.4.1	 Conference Proceedings, Peer-Reviewed Journal Articles, Other Academic Literature 

EPA reviewed selected conference proceedings,20 peer-reviewed journal articles, and 

other academic literature in support of its preliminary study of the Metal Finishing Category. 

EPA used a list of key words (see Appendix B) to identify peer-reviewed journal articles and 

20 For the preliminary study, EPA focused its literature review on peer-reviewed journal articles and other academic 

literature, but not on conference proceedings. EPA intends to review conference proceedings and collect additional 

industry data. 

6-3
 
 

 

 

 

Section 6 – Quality Assurance 

other academic literature. EPA collected over 130 documents from the literature search, recorded 

them on a quality evaluation tracking spreadsheet, and documented how each data source met (or 

did not meet) the quality criteria described in Section 6.3 (ERG, 2015). EPA applied the data 

quality criteria established in the Environmental Engineering Support for Clean Water 

Regulations PQAPP (ERG, 2013) and determined that the data and information obtained from 

conference proceedings, peer-reviewed journals, and other academic literature were sufficiently 

accurate, reliable, and relevant for characterizing metal finishing process operations, chemistries, 

wastewater, and treatment technology performance. 

6.4.2 Data and Information Obtained from Industry, Vendors, and Trade Associations 

EPA obtained information from direct email or telephone communications with industry 

personnel, wastewater treatment technology vendors, and trade association representatives to 

support its preliminary study of the Metal Finishing Category. This included contacting specific 

facilities, vendors, and trade associations to gather information regarding facility-specific process 

operations and waste streams. EPA also obtained information from the web sites of metal 

finishing facilities, vendors, and trade associations. Web site information included descriptions 

of process operations and company profiles, including, for example, the types of products and 

services performed. EPA applied the criteria established in the Environmental Engineering 

Support for Clean Water Regulations PQAPP (ERG, 2013) and determined this information was 

sufficiently accurate, reliable, and representative of the facilities of interest for use in 

characterizing industry sector trends and qualitative understanding of process operations and 

treatment technologies used. 

6.4.3 Existing Government Publications and Supporting Information 

EPA obtained information from government publications and supporting documents, 

specifically documents supporting the Metal Finishing ELGs and the MP&M proposed 

rulemaking. During the MP&M proposed rulemaking, EPA evaluated facilities covered under 

the Metal Finishing ELGs in the 1980’s and 1990’s. EPA applied the criteria established in the 

Environmental Engineering Support for Clean Water Regulations PQAPP (ERG, 2013) and 

determined this information was sufficiently accurate and reliable for characterizing metal 

finishing process operations, chemistries, wastewater characteristics, and wastewater treatment 

technologies. However, due to the age of the data, EPA determined that the information may not 

be representative of current industry practices, and only used the information qualitatively to 

establish a timeline for changes within the industry. 

6-4
 
 

 

 

 

 

Section 6 – Quality Assurance 

Table 6-2. Data Acceptance Criteria for the Preliminary Study of the Metal Finishing Category 

Type of Data Data Not Usable 

Data Usable to 

Profile Operations 

and Wastewater 

Treatment 

Technologies 

Data Usable to 

Characterize InProcess Waste 

Streams 

Data Usable to Demonstrate Wastewater 

Treatment Performance/Efficiency 

Conference Proceedings, 

Peer-Reviewed Journal 

Articles, Other Academic 

Literature 

Article/paper not peerreviewed or otherwise 

deemed sufficient for 

limited purposes such as 

identifying incidental and 

qualitative data. 

Current and relevant 

to the specific 

facilities/industry 

operations of 

interest. 

Waste stream 

identified and 

analytes, units, 

analytical methods, 

and detection limits 

identified. 

Geographic scope is 

within the United 

States. 

(1) Represents full-scale system operated at 

applicable metal finishing facility. 

(2) Influent and effluent data show that 

treatment system is well designed and operated. 

(3) Detailed description of the treatment system 

and operating conditions. 

(4) Analytes identified; units, analytical 

methods and detection limits included. 

Data and Information 

Obtained from Industry, 

Vendors, and Trade 

Associations (e.g., direct 

email or telephone 

communications with 

industry, wastewater treatment 

technology vendors, and trade 

associations) 

(1) The plant has since 

changed operations (e.g., 

installed a new treatment 

system) since the data 

were collected. 

(2) Data collected during 

upset conditions. 

(3) Represents a process 

that is not of interest (e.g., 

sanitary wastewater). 

Process operations 

clearly described. 

Waste stream 

identified and 

analytes, units, 

analytical methods, 

and detection limits 

identified. 

(1) Represent full-scale system operated at 

applicable metal finishing facility. 

(2) Influent and effluent data or percent removal 

identified and show that treatment system is 

well designed and operated. 

(3) Detailed description of the treatment system 

and operating conditions. 

(4) Analytes identified; units, analytical 

methods and detection limits included. 

Government Publications and (1) Data collected by an Process operations Waste stream (1) Represents full-scale system operated at 

Supporting Information (e.g., unknown method or units clearly described. identified and applicable metal finishing facility. 

documents supporting the undefined. analytes, units, (2) Influent and effluent data show that 

Metal Finishing ELGs, data (2) Data collected during analytical methods, treatment system is well designed and operated. 

collected during the MP&M upset conditions. and detection limits (3) Detailed description of the treatment system 

Rulemaking, DMR and TRI (3) Represents a process identified. and operating conditions. 

databases, other governmental that is not of interest (e.g., (4) Analytes identified; units, analytical 

agency databases/lists) sanitary wastewater). methods and detection limits included. 

6-5
 
 

 

 

 

Section 7 – References 

7. REFERENCES

1. Abbott, A., et al. (2007). Electropolishing and Electroplating of Metals Using

Ionic Liquids Based on Choline Chloride. Ionic Liquids IV, Chapter 13, 186-197.

doi:10.1021/bk-2007-0975.ch013. EPA-HQ-OW-2015-0665. DCN MF00002.

2. Abdel-Halima, E. S., & Al-Deyab, S. S. (2011). Removal of Heavy Metals from

Their Aqueous Solutions through Adsorption onto Natural Polymers.

Carbohydrate Polymers, 84(1), 454-458. doi:10.1016/j.carbpol.2010.12.001.

EPA-HQ-OW-2015-0665. DCN MF00003.

3. Abdel-Hamid, Z., & Abdel-Aal, A. (2009). New Environmentally Friendly

Noncyanide Alkaline Electrolyte for Copper Electroplating. Surface and Coatings

Technology, 203(10-11), 1360-1365. doi:10.1016/j.surfcoat.2008.11.001. EPAHQ-OW-2015-0665. DCN MF00004.

4. Aguero, A., et al. (2012). Aluminum Slurry Coatings to Replace Cadmium for

Aeronautic Applications. Surface & Coatings Technology, 213, 229-238.

doi:10.1016/j.surfcoat.2012.10.052. EPA-HQ-OW-2015-0665. DCN MF00005.

5. Ahluwalia, S. S., & Goyal, D. (2007). Microbial and Plant Derived Biomass for

Removal of Heavy Metals from Wastewater. Bioresource Technology, 98(12),

2243-2257. doi:10.1016/j.biortech.2005.12.006. EPA-HQ-OW-2015-0665. DCN

MF00006.

6. Ahmad, W. A., et al. (2010). Pilot-scale Removal of Chromium from Industrial

Wastewater Using the ChromeBac System. Bioresource Technology, 101(12),

4371- 4378. doi:10.1016/j.biortech.2010.01.106. EPA-HQ-OW-2015-0665. DCN

MF00007.

7. Ahmaruzzaman, M., & Gupta, V. K. (2011). Rice Husk and Its Ash as Low-Cost

Adsorbents in Water and Wastewater Treatment. Industrial & Engineering

Chemistry Research, 50(24), 13589- 13613. doi:10.1021/ie201477c. EPA-HQOW-2015-0665. DCN MF00008.

8. Ahmen-Basha, C., et al. (2008). Management of Chromium Plating Rinsewater

Using Electrochemical Ion Exchange. Inudstrial & Engineering Chemistry

Research, 47(7), 2279-2286. doi:10.1021/ie070163x. EPA-HQ-OW-2015-0665.

DCN MF00009.

9. Ajmal, M., et al. (2000). Adsorption Studies on Citrus reticulata (fruit peel of

orange): Removal and Recovery of Ni(II) from Electroplating Wastewater.

Journal of Hazardous Materials, 79(1-2), 117- 131. doi:10.1016/S0304­

3894(00)00234-X. EPA-HQ-OW-2015-0665. DCN MF00010.

10. Ajmal, M., et al. (2001). Removal and Recovery of Heavy Metals from

Electroplating Wastewater by using Kyanite as an Adsorbent. Journal of

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Section 7 –References 

Hazardous Materials, 87(1- 3), 127- 137. doi:10.1016/S0304-3894(01)00234-5. 

EPA-HQ-OW-2015-0665. DCN MF00011. 

11.	 Ajmal, M., et al. (2003). Adsorption Studies on Rice Husk: Removal and 

Recovery of Cd(II) from Wastewater. Bioresource Technology, 86(2), 147- 149. 

doi:10.1016/S0960-8524(02)00159-1. EPA-HQ-OW-2015-0665. DCN MF00012. 

12.	 Akbal, F., & Camci, S. (2011). Copper, Chromium, and Nickel Removal from 

Metal Plating Wastewater by Electrocoagulation. Desalination, 269(1- 3), 214­

222. doi:10.1016/j.desal.2010.11.001. EPA-HQ-OW-2015-0665. DCN MF00013. 

13.	 Alvarez-Ayuso, E., et al. (2003). Purification of Metal Electroplating Waste 

Waters Using Zeolites. Water Research, 37(20), 4855- 4862. 

doi:10.1016/j.watres.2003.08.009. EPA-HQ-OW-2015-0665. DCN MF00014. 

14.	 Bakarat, M. A., & Schmidt, E. (2010). Polymer-enhanced Ultrafiltration Process 

for Heavy Metals Removal from Inudstrial Wastewaer. Desalination., 256(1- 3), 

90- 93. doi:10.1016/j.desal.2010.02.008. EPA-HQ-OW-2015-0665. DCN 

MF00015. 

15.	 Berman, E. S., & Brooman, E. W. (2009). Evaluation of APCVD Aluminum 

Coatings as an Environmentally Acceptable Alternative to Electroplated 

Cadmium Coatings. Metal Finishing, 107(2), 35- 43. doi:10.1016/S0026­

0576(09)80029-9. EPA-HQ-OW-2015-0665. DCN MF00016. 

16.	 Bhargava, G., & Allen, F. (2012). Self-Healing, Chromate-free Conversion 

Coating for Magnesium Alloys. Metal Finishing, 110(4), 32- 38. 

doi:10.1016/S0026-0576(13)70127-2. EPA-HQ-OW-2015-0665. DCN MF00017. 

17.	 Bhatt, H., et al. (2009). Trivalent Chromium for Enhanced Corrosion Protection 

on Aluminum Surfaces. Metal Finishing, 107(6), 39- 47. doi:10.1016/S0026­

0576(09)80292-4. EPA-HQ-OW-2015-0665. DCN MF00018. 

18.	 Bibber, J. (2008). Non-chrome-containing Conversion Coatings for Zinc and Zinc 

Alloys: Environmentally Friendly Alternatives Provide Equal or Better Adhesion 

and Corrosion Resistance as Conventional Methods. Metal Finishing, 106(4), 41­

46. doi:10.1016/S0026-0576(08)80091-8. EPA-HQ-OW-2015-0665. DCN 

MF00019. 

19.	 Bierwagen, G., et al. (2010). Active Metal-based Corrosion Protective Coating 

Systems for Aircraft Requiring No-Chromate Pretreatment. Progress in Organic 

Coatings, 68(1- 2), 48-61. doi:10.1016/j.porgcoat.2009.10.031. EPA-HQ-OW2015-0665. DCN MF00020. 

20.	 Bikulcius, G., et al. (2010). Ecologically Green Conversion Coating for ZincCobalt Alloy. Transactions of the Institute of Metal Finishing, 88(3), 163- 165. 

doi:10.1179/174591910X12692576434699. EPA-HQ-OW-2015-0665. DCN 

MF00021. 

7-2
 
 

 

 

 

Section 7 –References 

21.	 Chaix, J. P., et al. (2013). Thinking Outside the Bucket with Non-Drip 

Electrochemical Processing. Retrieved from 

http://www.rowantechnology.com/wpcontent/uploads/2014/02/SURFIN%202013%20Dalistick%20for%20web.pdf. 

EPA-HQ-OW-2015-0665. DCN MF00022. 

22.	 Chiban, M., et al. (2011). Characterization and Application of Dried Plants to 

Remove Heavy Metals, Nitrate, and Phosphate Ions from Industrial Wastewaters. 

Clean – Soil, Air, Water, 39(4), 376-383. doi:10.1002/clen.201000127. EPA-HQOW-2015-0665. DCN MF00023. 

23.	 Colica, G., et al. (2012). Biosorption and Recovery of Chromium from Industrial 

Wastewaters By Using Saccharomyces cerevisiae in a Flow-Through System. 

Industrial & Engineering Chemistry Research, 51(11), 4452-4457. 

doi:10.1021/ie202584k. EPA-HQ-OW-2015-0665. DCN MF00024. 

24.	 Dai, S. (2014). Alternative Plating for Metal Electorplating using Ionic Liquids. 

Retrieved from U.S. DOE Strategic Environmental Research and Development 

Program (SERDP) website: https://www.serdp-estcp.org/ProgramAreas/Weapons-Systems-and-Platforms/Surface-Engineering-and-StructuralMaterials/Coatings/WP-2316. EPA-HQ-OW-2015-0665. DCN MF00025. 

25.	 Dubent, S., et al. (2010). Electrodeposition, Characterization and Corrosion 

Behaviour of Tin–20 wt.% Zinc Coatings Electroplated from a Non-Cyanide 

Alkaline Bath. Materials Chemistry and Physics, 120(2-3), 371-380. 

doi:10.1016/j.matchemphys.2009.11.017. EPA-HQ-OW-2015-0665. DCN 

MF00026. 

26.	 Dunham, B. (2012). Zirconium Pretreatments: Not Just for Early Adopters 

Anymore. Metal Finishing, 110(6), 18-21. doi:10.1016/S0026-0576(13)70215-0. 

EPA-HQ-OW-2015-0665. DCN MF00027. 

27.	 Eichinger, E., et al. (1997). Hexavalent Chromium Elimination: An Aerospace 

Industry Progress Report. Metal Finishing, 95 (3), 36, 38, 40-41. 

doi:10.1016/S0026-0576(97)86771-2. EPA-HQ-OW-2015-0665. DCN MF00028. 

28.	 ERG. (2013). Eastern Research Group, Inc. Environmental Engineering Support 

for Clean Water Regulations Programmatic Quality Assurance Project Plan 

(PQAPP). Chantilly, VA. (October). EPA-HQ-OW-2010-0824-0229. 

29.	 ERG. (2015). Eastern Research Group, Inc. Quality Evaluation Tracking 

Spreadsheet for the 2015 Literature Review. Chantilly, VA. (August). EPA-HQOW-2015-0665. DCN MF00030. 

30.	 ERG. (2016). Eastern Research Group, Inc. Summary of Metal Finishing 

Facilities and Vendors Contacted During Preliminary Study Activities in 2015. 

Chantilly, VA. (August). EPA-HQ-OW-2015-0665. DCN MF00029. 

7-3
 
 

 

 

Section 7 –References 

31.	 Fister, D. (2010). Reducing Operational Costs, Environmental Impact Via 

Rigorous Plating/Finishing Analyses. Metal Finishing, 108(6), 39-46. 

doi:10.1016/S0026-0576(10)80032-7. EPA-HQ-OW-2015-0665. DCN MF00031. 

32.	 Fu, F., & Wang, Q. (2011). Removal of heavy metal ions from wastewaters: A 

review. Journal of Environmental Management, 93(3), 407-418. 

doi:10.1016/j.jenvman.2010.11.011. EPA-HQ-OW-2015-0665. DCN MF00032. 

33.	 Ge, F., et al. (2012). Effective removal of heavy metal ions Cd2+, Zn2+, Pb2+, 

Cu2+ from aqueous solution by polymer-modified magnetic nanoparticles. 

Journal of Hazardous Materials, 211-212, 366-372. 

doi:10.1016/j.jhazmat.2011.12.013. EPA-HQ-OW-2015-0665. DCN MF00033. 

34.	 Guidetti, G., et al. (2009). Plaforization Process for Cleaning, Degreasing, and 

Phosphating. Metal Finishing, 107(3), 39-43. doi:10.1016/S0026-0576(09)80050­

0. EPA-HQ-OW-2015-0665. DCN MF00034. 

35.	 Haynes, R. J. (2014). Use of Industrial Wastes as Media in Constructed Wetlands 

and Filter Beds – Prospects for Removal of Phosphate and Metals from 

Wastewater Streams. Critical Reviews in Environmental Science and Technology, 

45(10), 1041-1103. doi:10.1080/10643389.2014.924183. EPA-HQ-OW-2015­

0665. DCN MF00035. 

36.	 Hegazi, H. A. (2013). Removal of heavy metals from wastewater using 

agricultural and industrial wastes as absorbents. HBRC Journal, 9(3), 276-282. 

doi:10.1016/j.hbrcj.2013.08.004. EPA-HQ-OW-2015-0665. DCN MF00036. 

37.	 Hua, M., et al. (2012). Heavy metal removal from water/wastewater by nanosized 

metal oxides: A review. Journal of Hazardous Materials, 211-212, 317-331. 

doi:10.1016/j.jhazmat.2011.10.016. EPA-HQ-OW-2015-0665. DCN MF00037. 

38.	 Huisman, J., et al. (2006). Biologically produced sulphide for purification of 

process streams, effluent treatment and recovery of metals in the metal and 

mining industry. Hydrometallurgy, 83(1-4), 106-113. 

doi:10.1016/j.hydromet.2006.03.017. EPA-HQ-OW-2015-0665. DCN MF00038. 

39.	 Indumathi, S. N., et al. (2011). Cadmium- and Chromate-Free Coating Schemes 

for Corrosion Protection of 15CDV6 Steel. Metal Finishing, 109(3), 15-21. 

doi:10.1016/S0026-0576(11)00010-9. EPA-HQ-OW-2015-0665. DCN MF00039. 

40.	 Islamoglu, S., et al. (2006). Development of a Precipitation Based Separation 

Scheme for Selective Removal and Recovery of Heavy Metals from Cadmium 

Rich Electroplating Industry Effluents. Separation Science and Technology, 

41(15), 3367-3385. doi:10.1080/01496390600851665. EPA-HQ-OW-2015-0665. 

DCN MF00040. 

41.	 Kabdasli, L., et al. (2009). Complexing agent and heavy metal removals from 

metal plating effluent by electrocoagulation with stainless steel electrodes. 

7-4
 
Section 7 – References 

Journal of Hazardous Materials, 165(1-3), 838-845. 

doi:10.1016/j.jhazmat.2008.10.065. EPA-HQ-OW-2015-0665. DCN MF00041. 

42.	 Kaluzny, K. (2012). Roll with the Changes. Metal Finishing, 110(4), 43-46. 

doi:10.1016/S0026-0576(13)70130-2. EPA-HQ-OW-2015-0665. DCN MF00042. 

43.	 Khelifa, A., et al. (2005). Treatment of metal finishing effluents by the 

electroflotation technique. Desalination, 181(1-3), 27-33. 

doi:10.1016/j.desal.2005.01.011. EPA-HQ-OW-2015-0665. DCN MF00043. 

44.	 Kirk-Othmer. (2004). Electroplating. Krik-Othmer Encyclopedia of Chemical 

Technology, 5th Edition, 9, 759-838. EPA-HQ-OW-2015-0665. DCN MF00044. 

45.	 Klingenberg, C., & Jones, D. (2007). Low-Temperature, Phosphate-Free 

Conversion Coatings. Metal Finishing, 28-30. EPA-HQ-OW-2015-0665. DCN 

MF00045. 

46.	 Kobya, M., et al. (2010). Treatment of cadmium and nickel electroplating rinse 

water by electrocoagulation. Environmental Technology, 31(13), 1471-1481. 

doi:10.1080/09593331003713693. EPA-HQ-OW-2015-0665. DCN MF00046. 

47.	 Kumar, R., et al. (2008). Biosorption of chromium(VI) from aqueous solution and 

electroplating wastewater using fungal biomass. Chemical Engineering Journal, 

135(3), 202-208. doi:10.1016/j.cej.2007.03.004. EPA-HQ-OW-2015-0665. DCN 

MF00047. 

48.	 Kurniawan, T. A., et al. (2006). Comparisons of low-cost absorbents for treating 

wastewaters laden with heavy metals. Science of The Total Environment, 366(2­

3), 409-426. doi:10.1016/j.scitotenv.2005.10.001. EPA-HQ-OW-2015-0665. 

DCN MF00048. 

49.	 La Scala, J. (2009). Non-Chromate/No VOC Coating System for DoD 

Applications. WP-1521. Retrieved from http://www.dtic.mil/cgibin/GetTRDoc?AD=ADA608406. EPA-HQ-OW-2015-0665. DCN MF00049. 

50.	 Legg, K. (2008). Rowan Technology Group. Greening DoD Surface Finishing 

Operations. Paper presented at the Washington Forum. 

http://www.rowantechnology.com/wp-content/uploads/2012/06/Greening-DoDsurface-finishing-operations1.pdf. EPA-HQ-OW-2015-0665. DCN MF00050. 

51.	 Legg, K. (2009). Rowan Technology Group. Hexavalent Chrome Issues and 

Options. Paper presented at the DLA Shelf Life Symposium. 

http://www.rowantechnology.com/wp-content/uploads/2012/06/Legg-Hexavalentchrome-issues-and-options.pdf. EPA-HQ-OW-2015-0665. DCN MF00051. 

52.	 Legg, K. (2010). Rowan Technology Group. Eliminating Cr6+, Cd, and Other 

Hazardous Materials without Compromising Performance. Paper presented at the 

Army Corrosion Summit. http://www.rowantechnology.com/wp7-5
 
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content/uploads/2012/06/Eliminating_Cr6_Cd_etc.pdf. EPA-HQ-OW-2015-0665. 

DCN MF00052. 

53.	 Legg, K. (2011). Rowan Technology Group. Overview of Development and 

Implementation of Non-Chromate Treatments for Aluminum in the U.S. . Paper 

presented at the A3TS, Paris. http://www.rowantechnology.com/wpcontent/uploads/2012/06/Legg-A3TS-Paris-overview.pdf. EPA-HQ-OW-2015­

0665. DCN MF00053. 

54.	 Legg, K. (2012a). Rowan Technology Group. Choosing a Cadmium Plate 

Alternative. Retrieved from http://www.rowantechnology.com/wpcontent/uploads/2012/06/Cd-Plating-Alternatives.pdf. EPA-HQ-OW-2015-0665. 

DCN MF00054. 

55.	 Legg, K. (2012b). Rowan Technology Group. Choosing a Chromate Alternative. 

Retrieved from http://www.rowantechnology.com/wpcontent/uploads/2012/06/Chromate-Alternatives2.pdf. EPA-HQ-OW-2015-0665. 

DCN MF00055. 

56.	 Legg, K. (2012c). Rowan Technology Group. Choosing a Hard Chrome 

Alternative. Retrieved from http://www.rowantechnology.com/wpcontent/uploads/2012/06/Hard-Chrome-Plating-Alternatives.pdf. EPA-HQ-OW2015-0665. DCN MF00056. 

57.	 Lei, X., et al. (2010). Successful Cyanide Free Plating Protocols on Magnesium 

Alloys. Transactions of the Institute of Metal Finishing, 88(2), 75-80. 

doi:10.1179/174591910X12646055765330. EPA-HQ-OW-2015-0665. DCN 

MF00057. 

58.	 Lei, X., et al. (2011). A Study of Chromium-free Pickling Process before 

Elecroless Ni-P Plating on Magnesium Alloys. Surface and Coatings Technology, 

205(16), 4058-4063. doi:10.1016/j.surfcoat.2011.02.051. EPA-HQ-OW-2015­

0665. DCN MF00058. 

59.	 Lesmana, S. O., et al. (2009). Studies on potential applications of biomass for the 

separation of heavy metals from water and wastewater. Biochemical Engineering 

Journal, 44(1), 19-41. doi:10.1016/j.bej.2008.12.009. EPA-HQ-OW-2015-0665. 

DCN MF00059. 

60.	 Lew, C. M., et al. (2010). Zeolite Thin Films: From Computer Chips to Space 

Stations. Accounts of Chemical Research, 43(2), 210-219. 

doi:10.1021/ar900146w. EPA-HQ-OW-2015-0665. DCN MF00060. 

61.	 Li, Y., et al. (2003). Study on the treatment of copper-electroplating wastewater 

by chemical trapping and flocculation. Separation and Purification Technology, 

31(1), 91-95. doi:10.1016/S1383-5866(02)00162-4. EPA-HQ-OW-2015-0665. 

DCN MF00061. 

7-6
 
 

 

 

Section 7 –References 

62.	 List, B., et al. (2012). Transitioning to Phosphorous-Free Paint Pretreatment 

Processes: A Comprehensive View. Metal Finishing, 110(6), 12-16. 

doi:10.1016/S0026-0576(13)70214-9. EPA-HQ-OW-2015-0665. DCN MF00062. 

63.	 Lv, X., et al. (2013). Use of high-pressure CO2 for concentrating CrVI from 

electroplating wastewater by Mg-Al layered double hydroxide. ACS Applied 

Materials & Interfaces, 5(21), 11271-11275. doi:10.1021/am4035009. EPA-HQOW-2015-0665. DCN MF00063. 

64.	 Manavbasi, A., et al. (2012). New Pretreatments and Non-Chromated Chemfilm 

for Magnesium Alloys. Metal Finishing, 110(8), 17-22. doi:10.1016/S0026­

0576(13)70144-2. EPA-HQ-OW-2015-0665. DCN MF00064. 

65.	 Mason, R., et al. (2010). Update on Alternatives for Cadmium Coatings on 

Military Electrical Connectors. Metal Finishing, 108(3), 12-20. 

doi:10.1016/S0026-0576(10)00012-7. EPA-HQ-OW-2015-0665. DCN MF00065. 

66.	 Mason, R., et al. (2011). Alternatives to dichromate sealer in anodizing 

operations. Metal Finishing, 109(4-5), 25-32. doi:10.1016/S0026-0576(11)80065­

6. EPA-HQ-OW-2015-0665. DCN MF00066. 

67.	 Merzouk, B., et al. (2009). Removal turbidity and separation of heavy metals 

using electrocoagulation-electroflotation technique: A case study. Journal of 

Hazardous Materials, 164(1), 215-222. doi:10.1016/j.jhazmat.2008.07.144. EPAHQ-OW-2015-0665. DCN MF00067. 

68.	 Moore, R., & Dunham, B. (2008). ZicronizationTM: The Future of Coating 

Pretreatment Processes: Alternative, phosphate-free, eco-friendly pretreatment 

procedure addresses energy and chemical consumption while improving product 

quality. Metal Finishing, 106(7-8), 46-55. doi:10.1016/S0026-0576(08)80259-0. 

EPA-HQ-OW-2015-0665. DCN MF00068. 

69.	 Morose, G. (2013). Evaluation for Alternatives to Hexavalent Chromium 

Sealants. Metal Finishing, 111(3), 32-37, 63. doi:10.1016/S0026-0576(13)70232­

0. EPA-HQ-OW-2015-0665. DCN MF00069. 

70.	 Murphy, V., et al. (2009). A novel study of hexavalent chromium detoxification 

by selected seaweed species using SEM-EDX and XPS analysis. Chemical 

Engineering Journal, 148(2-3), 425- 433. doi:10.1016/j.cej.2008.09.029. EPAHQ-OW-2015-0665. DCN MF00070. 

71.	 Naik, U. C., et al. (2012). Isolation and characterization of Bacillus cereus IST105 

from electroplating effluent for detoxification of hexavalent chromium. 

Environmental Science and Pollution Research, 19(7), 3005-3014. 

doi:10.1007/s11356-012-0811-6. EPA-HQ-OW-2015-0665. DCN MF00071. 

72.	 Namasivayam, C., & Sureshkumar, M. V. (2008). Removal of chromium(VI) 

from water and wastewater using surfactant modified coconut coir pith as a 

7-7
 
 

 

Section 7 –References 

biosorbent. Bioresource Technology, 99(7), 2218-2225. 

doi:10.1016/j.biortech.2007.05.023. EPA-HQ-OW-2015-0665. DCN MF00072. 

73.	 NASF. (2015). Preliminary Response to EPA's Metal Finishing Study Questions 

from November 23, 2015 Meeting. EPA-HQ-OW-2015-0665. DCN MF00102. 

74.	 NEI Corporation. (2014). Nanomyte® PT-60, Chromate-Free Self-Healing 

Pretreatment for Magnesium. Retrieved from 

http://www.neicorporation.com/specs/Nanomyte_PT-60.pdf. EPA-HQ-OW-2015­

0665. DCN MF00073. 

75.	 Nickerson, W., & Matzdorf, C. (2012). Non-Chromate Aluminum Pretreatments. 

ESTCP Project WP-200025. Retrieved from https://www.serdpestcp.org/Program-Areas/Weapons-Systems-and-Platforms/Surface-Engineeringand-Structural-Materials/Coatings/WP-200025. EPA-HQ-OW-2015-0665. DCN 

MF00074. 

76.	 O’Keefe, M. (2010). Missouri University of Science and Technology. Corrosion 

Finishing/Coating Systems for DoD Metallic Substrates Based on Non-Chromate 

Inhibitors and UV Curable, Zero Valent Materials. SERDP Project WP-1519. 

Retrieved from https://www.serdp-estcp.org/Program-Areas/Weapons-Systemsand-Platforms/Surface-Engineering-and-Structural-Materials/Coatings/WP-1519 

EPA-HQ-OW-2015-0665. DCN MF00075. 

77.	 Olmez, T. (2009). The optimization of Cr(VI) reduction and removal by 

electrocoagulation using response surface methodology. Journal of Hazardous 

Materials, 162(2-3), 1371-1378. doi:10.1016/j.jhazmat.2008.06.017. EPA-HQOW-2015-0665. DCN MF00076. 

78.	 Orduz, M. (2008). High-Performance Characteristics of Lead- and Cadmium-Free 

Electroless Nickel. Metal Finishing, 106(1), 22-26. doi:10.1016/S0026­

0576(08)80004-9. EPA-HQ-OW-2015-0665. DCN MF00077. 

79.	 Owlad, M., et al. (2009). Removal of Hexavalent Chromium-Contaminated Water 

and Wastewater: A Review. Water, Air, & Soil Pollution, 200(1), 59-77. 

doi:10.1007/s11270-008-9893-7. EPA-HQ-OW-2015-0665. DCN MF00078. 

80.	 Park, D., et al. (2005). Metal Recovery from Electroplating Wastewater Using 

Acidophilic Iron Oxidizing Bacteria: Pilot-Scale Feasibility Test. Industrial & 

Engineering Chemistry Research, 44(6), 1854-1859. doi:10.1021/ie049015m. 

EPA-HQ-OW-2015-0665. DCN MF00079. 

81.	 Park, D., et al. (2006). Biosorption Process for Treatment for Electroplating 

Wastewater Containing Cr(VI): Laboratory-Scale Feasibility Test. Industrial & 

Engineering Chemistry Research, 45(14), 5059-5065. doi:10.1021/ie060002d. 

EPA-HQ-OW-2015-0665. DCN MF00080. 

7-8
 
 

 

Section 7 –References 

82.	 Phely-Bobin, T. (2010). U.S. DOE Strategic Environmental Research and 

Development Program (SERDP). UV Curable Non-Chrome Primer and Advanced 

Topcoat System. EPA-HQ-OW-2015-0665. DCN MF00081. 

83.	 Pommiers, S., et al. (2014). Alternative Conversion Coatings to Chromate for the 

Protection of Magnesium Alloys. Corrosion Science, 84, 135-146. 

doi:10.1016/j.corsci.2014.03.021. EPA-HQ-OW-2015-0665. DCN MF00082. 

84.	 Prado, R., et al. (2010). Optimized Deposition Parameters & Coating Properties of 

Cobalt Phosphorus Alloy Electroplating for Technology Insertion Risk Reduction. 

Retrieved from https://www.serdpestcp.org/content/download/11913/144973/file/WP200411_Supplemental_Work_Report.pdf. EPA-HQ-OW-2015-0665. DCN 

MF00083. 

85.	 Pusavec, F., & Kenda, J. (2014). The Transition to a Clean, Dry, and Energy 

Efficient Polishing Process: An Innovative Upgrade of Abrasive Flow Machining 

for Simultaneous Generation of Micro-Geometry and Polishing in the Tolling 

Industry. Journal of Cleaner Production, 76, 180-189. 

doi:10.1016/j.jclepro.2014.03.071. EPA-HQ-OW-2015-0665. DCN MF00084. 

86.	 Qin, J. J., et al. (2002). A feasibility study on the treatment and recycling of a 

wastewater from metal plating. Journal of Membrane Science, 208(1-2), 213­

221. doi:10.1016/S0376-7388(02)00263-6. EPA-HQ-OW-2015-0665. DCN 

MF00085. 

87.	 Sancey, B., et al. (2011). Heavy metal removal from industrial effluents by 

sorption on cross-linked starch: chemical study and impact on water toxicity. 

Journal of Environmental Management, 92(3), 765- 772. 

doi:10.1016/j.jenvman.2010.10.033. EPA-HQ-OW-2015-0665. DCN MF00086. 

88.	 Sarin, V., & Pant, K. K. (2006). Removal of chromium from industrial waste by 

using eucalyptus bark. Bioresource Technology, 97(1), 15- 20. 

doi:10.1016/j.biortech.2005.02.010. EPA-HQ-OW-2015-0665. DCN MF00087. 

89.	 Sartwell, B., et al. (2004). Naval Research Laboratory. Validation of HVOF 

WC/Co Thermal Spray Coatings as a Replacement for Hard Chrome Plating on 

Aircraft Landing Gear. EPA-HQ-OW-2015-0665. DCN MF00088. 

90.	 Scott, M. (2013). PPG Industries Inc. Environmentally Friendly Fastener Coating 

Demonstartion. ESTCP Project WP-201315. Retrieved from https://www.serdpestcp.org/Program-Areas/Weapons-Systems-and-Platforms/Surface-Engineeringand-Structural-Materials/Coatings/WP-201315. EPA-HQ-OW-2015-0665. DCN 

MF00089. 

91.	 Senturk, E. (2013). The treatment of zinc-cyanide electroplating rinse water using 

an electrocoagulation process. Water Science and Technology, 68(10), 2220­

2227. doi:10.2166/wst.2013.481. EPA-HQ-OW-2015-0665. DCN MF00090. 

7-9
 
 

 

Section 7 –References 

92.	 Slife, R. (2014). Air Force Materiel Command. Cadmium-Free Alternatives for 

Brush Plating Repair Operations. ESTCP Project WP-201412. Retrieved from 

https://serdp-estcp.org/Program-Areas/Weapons-Systems-and-Platforms/SurfaceEngineering-and-Structural-Materials/Coatings/WP-201412/WP-201412. EPAHQ-OW-2015-0665. DCN MF00091. 

93.	 Smith, E. L., et al. (2010). Metal Finishing with Ionic Liquids: Scale-up and Pilot 

Plants from IONMET Consortium. Transactions of the Institute of Metal 

Finishing, 88(6), 285-293. doi:10.1179/174591910X12856686485734. EPA-HQOW-2015-0665. DCN MF00092. 

94.	 Sthiannopkao, S., & Sreesai, S. (2009). Utilization of pulp and paper industrial 

wastes to remove heavy metals from metal finishing wastewater. Journal of 

Environmental Management, 90(11), 3283-3289. 

doi:10.1016/j.jenvman.2009.05.006. EPA-HQ-OW-2015-0665. DCN MF00093. 

95.	 Tepe, B., & Gunay, B. (2008). Evaluation of Pre-Treatment Processes for Hot 

Rolled Steel in Powder Coating. Progress in Organic Coatings, 62(2), 134-144. 

doi:10.1016/j.porgcoat.2007.10.004. EPA-HQ-OW-2015-0665. DCN MF00094. 

96.	 Tucker, R. (2013). One Step, Zero Discharge. Metal Finishing, 111(4), 16-17. 

doi:10.1016/S0026-0576(13)70249-6. EPA-HQ-OW-2015-0665. DCN MF00095. 

97.	 U.S. EPA. (1979). Development Document for Existing Source Pretreatment 

Standards for the Electroplating Point Source Category. Washington, D.C. EPAHQ-OW-2014-0170-0007. 

98.	 U.S. EPA. (1981). Federal Register Notice: Effluent Guidelines and Standards; 

Electroplating Point Source Category Pretreatment Standards for Existing 

Sources. Washington, D.C. . EPA-HQ-OW-2014-0170-0138. 

99.	 U.S. EPA. (1983a). Development Document for Effluent Limitations Guidelines 

and New Source Performance Standards for the Metal Finishing Point Source 

Category. Washington, D.C. EPA-HQ-OW-2004-0032-0110. 

100.	 U.S. EPA. (1983b). Federal Register Notice: Electroplating and Metal Finishing 

Point Source Categories; Effluent Limitations Guidelines, Pretreatment 

Standards, and New Source Performance Standards. Washington, D.C. EPA-HQOW-2014-0170-0004. 

101.	 U.S. EPA. (1984). Guidance Manual for Electroplating and Metal Finishing 

Pretreatment Standards. Washington, D.C. EPA-HQ-OW-2014-0170-0139. 

102.	 U.S. EPA. (1985). Guidance Manual for Implementing Total Toxic Organics 

(TTO) Pretreatment Standards. Washington, D.C. EPA-HQ-OW-2015-0665. 

DCN MF00107. 

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Section 7 –References 

103.	 U.S. EPA. (2000a). Development Document for the Proposed Effluent Limitations 

Guidelines and Standards for the Metal Products & Machinery Point Source 

Category. Washington, D.C. EPA-HQ-OW-2014-0170-0005. 

104.	 U.S. EPA. (2000b). Capsule Report: Managing Cyanide in Metal Finishing. . 

(EPA/625/R-99/009). Washington, D.C. Retrieved from 

http://nepis.epa.gov/Exe/ZyPDF.cgi/30004TAD.PDF?Dockey=30004TAD.PDF. 

EPA-HQ-OW-2015-0665. DCN MF00108. 

105.	 U.S. EPA. (2004). “Chemical Etching” Metal Finishing Option. . Retrieved from 

https://www.epa.gov/sites/production/files/2015-10/documents/chemicaletching_metal-finishing_air-products_epa-letter_2004-06-04.pdf. EPA-HQ-OW2015-0665. DCN MF00106. 

106.	 U.S. EPA. (2012a). The 2011 Annual Effluent Guidelines Review Report. (EPA821-R-12-001). Washington, D.C. EPA-HQ-OW-2010-0824-0195. 

107.	 U.S. EPA. (2012b). 5.6 Phosphorous. Water: Monitoring & Assessment. 

Retrieved from http://water.epa.gov/type/rsl/monitoring/vms56.cfm. EPA-HQOW-2015-0665. DCN MF00109. 

108.	 U.S. EPA. (2015a). The 2014 Annual Effluent Guidelines Review Report. (EPA821-R-15-001). Washington, D.C. EPA-HQ-OW-2014-0170-0209. 

109.	 U.S. EPA. (2015b). Final 2014 Effluent Guidelines Program Plan. (EPA-821-R15-002). Washington, D.C. EPA-HQ-OW-2014-0170-0210. 

110.	 U.S. EPA. (2015c). Response to Comments for the Preliminary 2014 Effluent 

Guidelines Program Plan. Washington, D.C. EPA-HQ-OW-2015-0665-0208. 

111.	 U.S. EPA. (2015d). Meeting notes with Association of Clean Water 

Administrators (ACWA) on November 9, 2015. EPA-HQ-OW-2015-0665. DCN 

MF00105. 

112.	 U.S. EPA. (2015e). Meeting Notes with National Association of Surface Finishers 

(NASF) on November 23, 2015. EPA-HQ-OW-2015-0665. DCN MF00103. 

113.	 U.S. EPA. (2015f). Meeting Notes with National Association of Surface Finishers 

(NASF) on August 19, 2015. EPA-HQ-OW-2015-0665. DCN MF00104. 

114.	 USGS. (2015). The USGS Water Science School: Water Questions & Answers, 

What Causes Fish Kills. Retrieved from http://water.usgs.gov/edu/qa-chemicalfishkills.html. EPA-HQ-OW-2015-0665. DCN MF00110. 

115.	 WEF. (2008). Water Environment Federation. Industrial Wastewater 

Management, Treatment, and Disposal, Manual of Practice No. FD-3 (Third ed.). 

Alexandria, VA: McGraw-Hill. EPA-HQ-OW-2015-0665. DCN MF00096. 

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Section 7 –References 

116.	 Winn, D., & Dalton, W. (2008). Chromium-free Corrosion Solutions: Silica-based 

Electrolytic Method Offers Viable Alternative to Both Hex- and TrivalentChromate Passivates. Metal Finishing, 106(6), 70-74. EPA-HQ-OW-2015-0665. 

DCN MF00097. 

117.	 Wong, K. K., et al. (2003). Removal of Cu and Pb from electroplating wastewater 

using tartaric acid modified rice husk. Process Biochemistry, 39(4), 437-445. 

doi:10.1016/S0032-9592(03)00094-3. EPA-HQ-OW-2015-0665. DCN MF00098. 

118.	 Wynn, P. (2006). Managing the Transition to Hexavalent Chromium Free AntiCorrosion Coatings. Transactions of the Institute of Metal Finishing, 84(6), 280­

285. doi:10.1179/174591906X130266. EPA-HQ-OW-2015-0665. DCN 

MF00099. 

119.	 Xiao, J., & Huang, Y. (2012). Technology Integration for Sustainable 

Manufacturing: An Applied Study on Integrated Profitable Pollution Prevention 

in Surface Finishing Systems. Industrial & Engineering Chemistry Research, 

51(35), 11434-11444. doi:10.1021/ie300154n. EPA-HQ-OW-2015-0665. DCN 

MF00100. 

120.	 Yan, Y. (2009). Zerolite Coating System for Corrosion Control to Eliminate 

Hexavalent Chromium from DoD Applications. SERDP Project WP-1342. 

Retrieved from http://www.dtic.mil/dtic/tr/fulltext/u2/a554408.pdf. EPA-HQOW-2015-0665. DCN MF00101. 

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Electroplating is the production of a thin surface coating of one metal upon another by electrodeposition. This 

surface coating is applied to provide corrosion protection, wear or erosion resistance, anti-frictional 

characteristics, or for decorative purposes. The electroplating of common metals includes the processes in which 

ferrous or nonferrous basis material is electroplated with copper, nickel, chromium, brass, bronze, zinc, tin, lead, 

cadmium, iron, aluminum or combinations thereof. Precious metals electroplating includes the processes in which 

a ferrous or nonferrous basis material is plated with gold, silver, palladium, platinum, rhodium, indium, 

ruthenium, iridium, osmium, or combinations thereof. 

In electroplating, metal ions in either acid, alkaline, or neutral solutions are reduced on cathodic surfaces. The 

cathodic surfaces are the workpieces being plated. The metal ions in solution are usually replenished by the 

dissolution of metal from anodes or small pieces contained in inert wire or metal baskets. Replenishment with 

metal salts is also practiced, especially for chromium plating. In this case, an inert material must be selected for 

the anodes. Hundreds of different electroplating solutions have been adopted commercially but only two or three 

types are utilized widely for a particular metal or alloy. For example, cyanide solutions are popular for copper, 

zinc, brass, cadmium, silver, and gold. However, non-cyanide alkaline solutions containing pyrophosphate have 

come into use recently for zinc and copper. Zinc, copper, tin and nickel are plated with acid sulfate solutions, 

especially for plating relatively simple shapes. Cadmium and zinc are sometimes electroplated from neutral or 

slightly acidic chloride solutions. The most common methods of plating are in barrels, on racks, and continuously 

from a spool or coil. 

Electroless Plating is a chemical reduction process which depends upon the catalytic reduction of a metallic ion in 

an aqueous solution containing a reducing agent and the subsequent deposition of metal without the use of 

external electrical energy. It has found widespread use in industry due to several unique advantages over 

conventional electroplating. Electroless plating provides a uniform plating thickness on all areas of the part 

regardless of the configuration or geometry of the part. An electroless plate on a properly prepared surface is 

dense and virtually non-porous. Copper and nickel electroless plating are the most common. The basic 

ingredients in an electroless plating solution are: 

1. A source of metal, usually a salt. 

2. A reducer to reduce the metal to its base state. 

3. A complexing agent to hold the metal in solution (so the metal will not plate out indiscriminately). 

4. Various buffers and other chemicals designed to maintain bath stability and increase bath life. 

Electroless plating is autocatalytic, i.e., catalysis is promoted from one of the products of a chemical reaction. 

The chemistry of electroless plating is best exemplified by examining electroless nickel plating. The source of 

nickel is a salt, such as nickel chloride or nickel sulfate, and the reducer is sodium hypophosphite. The most 

commonly used complexing agents are citric and glycolic acid. Hypophosphite anions in the presence of water 

are dehydrogenated by the solid catalytic surface provided by nickel to form acid orthophosphite anions. Active 

hydrogen atoms are bonded on the catalyst forming a hydride. Nickel ions are reduced to metallic nickel by the 

active hydrogen atoms, which are in turn oxidized to hydrogen ions. Simultaneously, a portion of the 

hypophosphite anions are reduced by the active hydrogen and adsorbed on the catalytic surface, producing 

elemental phosphorus, water and hydroxyl ions. Elemental phosphorus is bonded to or dissolved in the nickel 

making the reaction irreversible. At the same time hypophosphite anions are catalytically oxidized to acid 

orthophosphite anions, evolving gaseous hydrogen. The basic plating reactions proceed as follows: 

The nickel salt is ionized in water 

NiS04 = Ni+2 + SO4

- 2 

There is then a reduction-oxidation reaction with nickel and sodium hypophosphite. 

Ni+2 + SO4

- 2 + 2NaH2PO2 + 2 H20 = Ni + 2NaH2PO3 + H2 + H2SO4 

The sodium hypophosphite also reacts in the following manner: 

2NaH2PO2 + H2 = 2P + 2NaOH + 2H2O 

As can be seen in the equations above, both nickel and phosphorus are produced, and the actual metal deposited 

is a nickel-phosphorus alloy. The phosphorus content can be varied to produce different characteristics in the 

nickel plate. 

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When electroless plating is done on a plastic basis material, catalyst application and acceleration steps are 

necessary as surface preparation operations. These steps are considered part of the electroless plating unit 

operation. 

Immersion plating is a chemical plating process in which a thin metal deposit is obtained by chemical 

displacement of the basis metal. Unlike electroless plating, it is not an autocatalytic process. In immersion 

plating, a metal will displace from solution any other metal that is below it in the electromotive series of 

elements. 

The lower (more noble) metal will be deposited from solution while the more active metal (higher in the series) 

will be dissolved. A common example of immersion plating is the deposition of copper on steel from an acid 

copper solution. Because of the similarity of the wastes generated and the materials involved, immersion plating 

is considered part of the electroless plating unit operation. 

Anodizing is an electrolytic oxidation process which converts the surface of the metal to an insoluble oxide. 

These oxide coatings provide corrosion protection, decorative surfaces, a base for painting and other coating 

processes, and special electrical and mechanical properties. Aluminum is the most frequently anodized material, 

while some magnesium and limited amounts of zinc and titanium are also treated. 

Although most anodizing involves immersion of racked parts in tanks, continuous anodizing is done on large 

coils of aluminum in a manner similar to continuous electroplating. For aluminum parts, the formation of the 

oxide occurs when the parts are made anodic in dilute sulfuric acid or dilute chromic acid solutions. The oxide 

layer begins formation at the extreme outer surface, and as the reaction proceeds, the oxide grows into the metal. 

The last formed oxide, known as the boundary layer, is located at the interface between the base metal and the 

oxide. The boundary is extremely thin and nonporous. The sulfuric acid process is typically used for all parts 

fabricated from aluminum alloys except for parts subject to stress or containing recesses in which the sulfuric 

acid solution may be retained and attack the aluminum. Chromic acid anodic coatings are more protective than 

sulfuric acid coatings and have a relatively thick boundary layer. For these reasons, a chromic acid bath is used if 

a complete rinsing of the part cannot be achieved. 

Coating – This manufacturing operation includes chromating, phosphating, metal coloring, and passivating. 

These coatings are applied to previously deposited metal or basis material for increased corrosion protection, 

lubricity, and preparation of the surface for additional coatings or formulation of a special surface appearance. In 

chromating, a portion of the base metal is converted to one of the components of the protective film formed by 

the coating solution. This occurs by reaction with aqueous solutions containing hexavalent chromium and active 

organic or inorganic compounds. Chromate coatings are most frequently applied to zinc, cadmium, aluminum, 

magnesium, copper, brass, bronze, and silver. Most of the coatings are applied by chemical immersion, although 

a spray or brush treatment can be used. Changes in the solutions can impart a wide range of colors to the coatings 

from colorless to iridescent yellow, brass, brown, and olive drab. Additional coloring of the coatings can be 

achieved by dipping the parts in organic dye baths to produce red, green, blue, and other colors. 

Phosphate coatings are used to provide a good base for paints and other organic coatings, to condition the 

surfaces for cold forming operations by providing a base for drawing compounds and lubricants, and to impart 

corrosion resistance to the metal surface by the coating itself or by providing a suitable base for rust-preventative 

oils or waxes. Phosphate conversion coatings are formed by the immersion of iron, steel, or zinc plated steel in a 

dilute solution of phosphoric acid plus other reagents. The method of applying the phosphate coating is dependent 

upon the size and shape of the part to be coated. Small parts are coated in barrels immersed in the phosphating 

solution. Large parts, such as steel sheet and strip, are spray coated or continuously passed through the 

phosphating solution. Supplemental oil or wax coatings are usually applied after phosphating unless the part is to 

be painted. 

Metal coloring by chemical conversion methods produces a large group of decorative finishes. This operation 

covers only chemical methods of coloring in which the metal surface is converted into an oxide or similar 

metallic compound. The most common colored finishes are used on copper, steel, zinc, and cadmium. 

Application of the color to the cleaned basis metal involves only a brief immersion in a dilute aqueous solution. 

The colored films produced on the metal surface are extremely thin and delicate. Consequently, they lack 

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resistance to handling and the atmosphere. A clear lacquer is often used to protect the colored metal surface. A 

large quantity of copper and brass is colored to yield a wide variety of shades and colors. Shades of black, brown, 

gray, green and patina can be obtained on copper and brass by use of appropriate coloring solutions. The most 

widely-used colors for ferrous metals are based on oxides which yield black, brown, or blue colors. A number of 

colors can be developed on zinc depending on the length of immersion in the coloring solution. Yellow, bronze, 

dark green, black and brown colors can be produced on cadmium. Silver, tin, and aluminum are also colored 

commercially. Silver is given a gray color by immersion in a polysulfide solution such as ammonium polysulfide. 

Tin can be darkened to produce an antique finish of pewter by immersion in a solution of nitric acid and copper 

sulfate. 

Passivation refers to forming a protective film on metals, particularly stainless steel and copper, by immersion in 

an acid solution. Stainless steel is passivated to dissolve any imbedded iron particles and to form a thin oxide film 

on the surface of the metal. Typical solutions for passivating stainless steel include nitric acid and nitric acid with 

sodium dichromate. Copper is passivated with a solution of ammonium sulfate and copper sulfate forming a bluegreen patina on the surface of the metal. 

Etching and Chemical Milling - These processes are used to produce specific design configurations and 

tolerances or surface appearances on parts (or metal-clad plastic in the case of printed circuit boards)-by 

controlled dissolution with chemical reagents or etchants. Included in this classification are chemical milling, 

chemical etching, and bright dipping. Chemical etching is the same process as chemical milling except the rates 

and depths of metal removal are usually much greater in chemical milling. Typical solutions for chemical milling 

and etching include ferric chloride, nitric acid, ammonium persulfate, chromic acid, cupric chloride, hydrochloric 

acid, and combinations of these reagents. Bright dipping is a specialized form of etching and is used to remove 

oxide and tarnish from ferrous and nonferrous materials and is frequently performed just prior to anodizing. 

Bright dipping can produce a range of surface appearances from bright clean to brilliant, depending on the surface 

smoothness desired for the finished part. Bright dipping solutions usually involve mixtures of sulfuric, chromic, 

phosphoric, nitric, or hydrochloric acids. This unit operation also includes the stripping of metallic coatings. 

Printed Circuit Board Manufacturing involves the formation of a circuit pattern of conductive metal (usually 

copper) on nonconductive board materials such as plastic or glass. There are five basic steps involved in the 

manufacture of printed circuit boards: cleaning and surface preparation, catalyst and electroless plating, pattern 

printing and masking, electroplating, and etching. 

After the initial cutting, drilling and sanding of the boards, the board surface is prepared for plating electroless 

copper. This surface preparation involves an etchback (removal of built-up plastic around holes) and an acid and 

alkaline cleaning to remove grime, oils, and fingerprints. The board is then etched and rinsed. Following etching, 

the catalyst is applied and rinsing operations following catalyst application. The entire board is then electroless 

copper plated and rinsed. 

Following electroless copper plating, a plating resist is applied in non-circuit areas. Following application of a 

resist, a series of electroplates are applied. First the circuit is copper plated. A solder electroplate is applied next 

followed by a rinse. For copper removal in non-circuit areas, an etch step is next. After the etch operation, a 

variety of tab plating processes can be utilized depending on the board design requirements. These include nickel 

electroplating, gold electroplating, rhodium electroplating, and tin immersion plating. There are presently three 

main production methods for printed circuit boards: additive, semi-additive, and subtractive. The additive method 

uses pre-sensitized, unclad material as the starting board; the semi-additive method uses unclad, unsensitized 

material as the starting board; and the subtractive method begins with copper clad, unsensitized material. 

Cleaning involves the removal of oil, grease, and dirt from the surface of the basis material using water, with or 

without a detergent or other dispersing agent. Alkaline cleaning (both electrolytic and non-electrolytic) and acid 

cleaning are both included. 

Alkaline cleaning is used to remove oily dirt or solid soils from workpieces. The detergent nature of the cleaning 

solution provides most of the cleaning action; agitation of the solution and movement of the workpiece are 

secondary. There are three types of alkaline cleaners: soak, spray, and electrolytic. Soak cleaners are used on 

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easily removed soil; they are less efficient than spray or electrolytic cleaners. Spray cleaners combine the 

detergent properties of the solution with the impact force of the spray, which mechanically loosens the soil. The 

most effective conventional alkaline cleaning method is electrolytic cleaning. The strong agitation of the solution 

by gas evolution, and oxidation-reduction reactions that occur during electrolysis produce the cleanest surface of 

the three methods. Also, certain dirt particles become electrically charged and are repelled from the surface. 

Direct current (cathodic) cleaning uses the workpiece as the cathode; reverse current (anodic) cleaning uses the 

workpiece as the anode. In periodic reverse current cleaning, the current is periodically reversed from direct 

current to reverse current. Periodic reverse cleaning gives improved smut removal, accelerated cleaning, and a 

more active surface for any subsequent surface finishing operation. 

Acid cleaning employs a combination of a wetting agent or detergent with a solution of an inorganic (mineral) 

acid, organic acid, or an acid salt to remove oil, dirt, or oxide from metal surfaces. Depending on the acid 

concentration, acid cleaning may be referred to as pickling, acid dipping, descaling, or desmutting. The solution 

may or may not be heated and can be an immersion or spray operation. Agitation is normally required with 

soaking, and spray is usually used with complex shapes. An acid dip operation may also follow alkaline cleaning 

prior to plating. Phosphoric acid mixtures are also commonly used to remove oils and light rust while leaving a 

phosphate coating that provides a paint base or temporary resistance to rusting. Strong acid solutions are used to 

remove rust and scale prior to surface finishing. 

Machining removes stock from a workpiece by forcing a cutting tool through the workpiece and removing a chip 

of basis material. Machining operations such as turning, milling, drilling, boring, tapping, planing, broaching, 

sawing and cutoff, shaving, threading, reaming, shaping, slotting, bobbing, filing, and chamfering are included in 

this definition. 

Grinding removes stock from a workpiece with abrasive grains held by a rigid or semirigid binder. The grinding 

tool is usually in the form of a disk (the basic shape of grinding wheels), but may also be in the form of a 

cylinder, ring, cup, stick, strip, or belt. The most commonly used abrasives are aluminum oxide, silicon carbide, 

and diamond. The processes included in this unit operation are sanding (or cleaning to remove rough edges or 

excess material), surface finishing, and separating (as in cut-off or slicing operations). 

Polishing is an abrading operation used to remove or smooth out surface defects (scratches, pits, tool marks, etc.) 

that adversely affect the appearance or function of a part. Polishing is usually performed with either a belt or 

wheel to which an abrasive, such as aluminum oxide or silicon carbide, is bonded. Both wheels and belts are 

flexible and will conform to irregular or rounded areas where necessary. The operation usually referred to as 

buffing is included in the polishing operation. 

Barrel Finishing or tumbling is a controlled method of processing parts to remove burrs, scale, flash, and oxides 

to improve surface finish. Widely used as a finishing operation for many parts, it obtains a uniformity of surface 

finish not possible by hand finishing. For large quantities of small parts it is generally the most economical 

method of cleaning and surface conditioning. Parts to be finished are placed in a rotating barrel or vibrating unit 

with an abrasive medium, water, or oil, and usually some chemical compound to assist in the operation. As the 

barrel rotates slowly, the upper layer of the work is given a sliding movement toward the lower side of the barrel, 

causing the abrading or polishing action. The same results may also be accomplished in a vibrating unit, in which 

the entire contents of the container are in constant motion. 

Burnishing is the process of finish sizing or smooth finishing a workpiece (previously machined or ground) by 

displacement, rather than removal, of minute surface irregularities. It is accomplished with a smooth point or linecontact and fixed or rotating tools. 

Impact Deformation is the process of applying an impact force to a workpiece such that the workpiece is 

permanently deformed or shaped. Impact deformation operations include shot peening, peening, forging, high 

energy forming, heading, and stamping. 

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Pressure Deformation is the process of applying force (at a slower rate than an impact force) to permanently 

deform or shape a workpiece. Pressure deformation includes operations such as rolling, drawing, bending, 

embossing, coining, swaging, sizing, extruding, squeezing, spinning, seaming, staking, piercing, necking, 

reducing, forming, crimping, coiling, twisting, winding, flaring, or weaving. 

Shearing is the process of severing or cutting a workpiece by forcing a sharp edge or opposed sharp edges into 

the workpiece, stressing the material to the point of shear failure and separation. 

Heat Treating is the modification of the physical properties of a workpiece through the application of controlled 

heating and cooling cycles. Such operations as tempering, carburizing, cyaniding, nitriding, annealing, 

normalizing, austenizing, quenching, austempering, siliconizing, martempering, and malleabilizing are included 

in this definition. 

Thermal Cutting comprises cutting, slotting, or piercing a workpiece with an oxyacetylene oxygen lance or 

electric arc cutting tool. 

Welding refers to joining two or more pieces of material by applying heat, pressure, or both, with or without filler 

material, to produce a localized union through fusion or recrystallization across the interface. Included are gas 

welding, resistance welding, arc welding, cold welding, electron beam welding, and laser beam welding. 

Brazing joins metals by filling a thin (capillary thickness) layer of nonferrous filler metal into the space between 

them. Bonding results from the intimate contact produced by the dissolution of a small amount of base metal in 

the molten filler metal, without fusion of the base metal. The term brazing is used when the temperature exceeds 

425°C (800°F). 

Soldering is the process of joining metals by filling a thin (capillary thickness) layer of nonferrous filler metal 

into the space between them. Bonding results from the intimate contact produced by the dissolution of a small 

amount of base metal in the molten filler metal, without fusion of the base metal. The term soldering is used 

when the temperature range falls below 425°C (800°F). 

Flame Spraying is the application of a metallic coating to a workpiece using finely powdered fragments of wire, 

together with suitable fluxes, projected through a cone of flame onto the workpiece. 

Sand Blasting removes stock, including surface f1lms, from a workpiece by the use of abrasive grains 

pneumatically impinged against the workpiece. The abrasive grains used include sand, metal shot, slag, silica, 

pumice, or natural materials such as walnut shells. 

Abrasive Jet Machining is a mechanical process for cutting hard brittle materials. It is similar to sand 

blasting, but uses much finer abrasives carried at high velocities (500-3,000 fps) by a liquid or gas stream. Uses 

include frosting glass, removing metal oxides, deburring, and drilling and cutting thin sections of metal. 

Electrical Discharge Machining is a process which can remove metal with good dimensional control from any 

metal. It cannot be used for machining glass, ceramics, or other nonconducting materials. The machining action is 

caused by the formation of an electrical spark between an electrode, shaped to the required contour, and the 

workpiece. Since the cutting tool has no contact with the workpiece, it can be made from a soft, easily worked 

material such as brass. The tool works in conjunction with a fluid such as mineral oil or kerosene, which is fed to 

the work under pressure. The function of this coolant is to serve as a dielectric, to wash away particles of eroded 

metal from the workpiece or tool, and to maintain a uniform resistance to flow of current. 

Electrical discharge machining is also known as spark machining or electronic erosion. The operation was 

developed primarily for machining carbides, hard nonferrous alloys, and other hard-to-machine materials. 

Electrochemical Machining is a process based on the same pr1nc1ples used 1n electroplating except the 

workpiece is the anode and the tool is the cathode. Electrolyte is pumped between the electrodes and a potential 

applied with the result that metal is rapidly removed. 

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In this process, electrode accuracy is important since the surface finish of the electrode tool will be reproduced in 

the surface of the workpiece. While copper is frequently used as the electrode, brass, graphite, and coppertungsten are also used. The tool must be an electrical conductor, easy to machine, corrosion resistant, and able to 

conduct the quantity of current needed. Although there is no standard electrolyte, sodium chloride is more 

generally used than others. 

Electron Beam Machining is a thermoelectric process. In electron beam machining, heat is generated by high 

velocity electrons impinging on part of the workpiece. At the point where the energy of the electrons is focused, it 

is transformed into sufficient thermal energy to vaporize the material locally. The process is generally carried out 

in a vacuum. While the metal-removal rate of electron beam machining is approximately 0.01 milligrams per 

second, the tool is accurate and is especially adapted for micro-machining. There is no heat affected zone or 

pressure on the workpiece and extremely close tolerances can be maintained. The process results in X-ray 

emission which requires that the work area be shielded to absorb radiation. At present the process is used for 

drilling holes as small as 0.0508 mm (0.002 in.) in any known material, cutting slots, shaping small parts, and 

machining sapphire jewel bearings. 

Laser Beam Machining uses a highly focused monochromatic collimated beam of light is to remove material 

from a workpiece at the point of impingement. Laser beam machining is a thermoelectric process, and material 

removal is largely accomplished by evaporation, although some material is removed in the liquid state at high 

velocity. Since the metal removal rate is very small, they are used for such jobs as drilling microscopic holes in 

carbides or diamond wire drawing dies, and for removing metal in the balancing of high-speed rotating 

machinery. 

Lasers can vaporize any known material. They have small heat-affected zones and work easily with nonmetallic 

hard materials. 

Plasma Arc Machining is the process of material removal or shaping of a workpiece by a high velocity jet of high 

temperature ionized gas. A gas (nitrogen, argon, or hydrogen) is passed through an electric arc causing it to 

become ionized and raised to temperatures in excess of 16,649°C (30,000°F). The relatively narrow plasma jet 

melts and displaces the workpiece material in its path. Because plasma machining does not depend on a chemical 

reaction between the gas and the work material and because plasma temperatures are extremely high, the process 

can be used on almost any metal, including those that are resistant to oxygen-fuel gas cutting. The method is of 

commercial importance mainly for profile cutting of stainless steel and aluminum alloys. 

Ultrasonic Machining is a mechanical process designed to effectively machine hard, brittle materials. It removes 

material by the use of abrasive grains which are carried in a liquid between the tool and the work and which 

bombard the work surface at high velocity. This action gradually chips away minute particles of material in a 

pattern controlled by the tool shape and contour. A transducer causes an attached tool to oscillate linearly at a 

frequency of 20,000 to 30,000 times per second at an amplitude of 0.0254 to 0.127 mm (0.001 to 0.005 in.). The 

tool motion is produced by being part of a sound wave energy transmission line which causes the tool material to 

change its normal length by contraction and expansion. The tool holder is threaded to the transducer and 

oscillates linearly at ultrasonic frequencies, thus driving the grit particles into the workpiece. The cutting 

particles, boron carbide and similar materials, are of a 280-mesh size or finer, depending upon the accuracy and 

the finish desired. Operations that can be performed include drilling, tapping, coining, and the making of 

openings in all types of dies. Ultrasonic machining is used principally on materials such as carbides, tool steels, 

ceramics, glass, gem stones, and synthetic crystals. 

Sintering is the process of forming a mechanical part from a powdered metal by fusing the particles together 

under pressure and heat. The temperature is maintained below the melting point of the basis metal. 

Laminating is adhesive bonding of layers of metal, plastic, or wood to form a part. 

Hot Dip Coating is defined by coating a metallic workpiece with another metal by immersion in a molten bath to 

provide a protective film. Galvanizing (hot dip zinc) is the most common hot dip coating. 

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Sputtering covers a metallic or nonmetallic workpiece with thin films of metal. The surface to be coated is 

bombarded with positive ions in a gas discharge tube, which is evacuated to a low pressure. 

Vapor Plating is the decomposition of a metal or compound upon a heated surface by reduction or decomposition 

of a volatile compound at a temperature below the melting point of either the deposit or the basis material. 

Thermal Infusion applies a fused zinc, cadmium, or other metal coating to a ferrous workpiece by imbuing the 

surface of the workpiece with metal powder or dust in the presence of heat. 

Salt Bath Descaling is the process of removing surface oxides or scale from a workpiece by immersion of the 

workpiece in a molten salt bath or a hot salt solution. Molten salt baths are used in a salt bath—water quench— 

acid dip sequence to clean hard-to-remove oxides from stainless steels and other corrosion-resistant alloys. The 

work is immersed in the molten salt (temperatures range from 400 to 540 degrees C), quenched with water, and 

then dipped in acid. Oxidizing, reducing, and electrolytic baths are available, and the particular type needed 

depends on the oxide to be removed. 

Solvent Degreasing removes oils and grease from the surfaces of a workpiece by the use of organic solvents, such 

as aliphatic petroleums (e.g., kerosene, naptha), aromatics (e.g., benzene, toluene), oxygenated hydrocarbons 

(e.g., ketones, alcohol, ether), halogenated hydrocarbons (e.g., 1,1,1-trichloroethane, trichloroethylene, methylene 

chloride), and combinations of these classes of solvents. Solvent cleaning can be accomplished by either the 

liquid or vapor phase of these solvents. Solvent vapor degreasing is normally quicker than solvent liquid 

degreasing. However, ultrasonic vibration is sometimes used with liquid solvent so as to decrease the immersion 

time required with complex shapes. Solvent cleaning is often used as a precleaning operation, e.g., prior to the 

alkaline cleaning that precedes plating, as a final cleaning of precision parts, or as a surface preparation for some 

painting operations. 

Emulsion cleaning is a type of solvent degreasing that uses common organic solvents (e.g., kerosene, mineral oil, 

glycols, and benzene) dispersed in an aqueous medium with the aid of an emulsifying agent. Depending on the 

solvent used, cleaning is done at temperatures from room temperature to 82°C (180°F). This operation uses less 

chemical than solvent degreasing because a lower solvent concentration is employed. The process is used for 

rapid superficial cleaning and is usually performed as emulsion spray cleaning. 

Paint Stripping is the removal of an organic coating from a workpiece. The stripping of such coatings is usually 

performed with caustic, acid, solvent, or molten salt. 

Painting refers to the application of an organic coating to a workpiece. The application of coatings such as paint, 

varnish, lacquer, shellac, and plastics by spraying, dipping, brushing, roll coating, lithographing, and wiping are 

included. Spray painting is by far the most common and can be used with nearly all varieties of paint. The paint 

can be sprayed manually or automatically, hot or cold, and it may be atomized with or without compressed air to 

force the paint through an orifice. Other processes included under this unit operation are printing, silk screening, 

and stenciling. 

Electrostatic Painting is the application of electrostatically charged paint particles to an oppositely charged 

workpiece followed by thermal fusing of the paint particles to form a cohesive paint film. Usually the paint is 

applied in spray form and may be applied manually or automatically, hot or cold, and with or without compressed 

air atomization. Both waterborne and solvent-borne coatings can be sprayed electrostatically. 

Electropainting is the process of coating a workpiece by making it either anodic or cathodic in a bath that is 

generally an aqueous emulsion of the coating material. The electrodeposition bath contains stabilized resin, 

dispersed pigment, surfactants, and sometimes organic solvents in water. Electropainting is used primarily for 

primer coats because it gives a fairly thick, highly uniform, corrosion resistant coating in relatively little time. 

Vacuum Metalizing coats a workpiece with metal by flash heating metal vapor in a high-vacuum chamber 

containing the workpiece. The vapor condenses on all exposed surfaces. 

A-7
 
Appendix A

Appendix A:
 

Descriptions of the 46 Unit Operations in the Metal Finishing Industry
 

Assembly is the fitting together of previously manufactured parts or components into a complete machine, unit of 

a machine, or structure. 

Calibration is the application of thermal, electrical, or mechanical energy to set or establish reference points for a 

component or complete assembly. 

Testing is the application of thermal, electrical, or mechanical energy to determine the suitability or functionality 

of a component or complete assembly. 

Mechanical Plating is the process of depositing metal coatings on a workpiece using a tumbling barrel, metal 

powder, and usually glass beads for the impaction media. The operation is subject to the same cleaning and 

rinsing operations that are applied before and after the electroplating operation. 

Source: U.S. EPA, 1983a 

A-8
 
Appendix B 

Appendix B
 

Keyword Search Terms for the Metal Finishing Industry
 
Appendix B 

Appendix B: Keyword Search Terms for the Metal Finishing Industry 

Master Terms 

Metal Finishing 

Industrial Wastewater 

Industrial Wastewater Treatment 

Metals Removal 

General Terms 

Case study 

Effluent 

Elimination 

Green 

Pilot (scale) 

Full/Field (scale) 

Improvement 

Influent 

Nano 

Percent (%) 

Performance 

Pollution Prevention 

Recovery/recycle 

Reduce/Reduction 

Removal 

Rinse Water 

Replacement 

6 Primary Metal Finishing Operations 

Electroplating 

Electroless Plating 

Anodizing 

Coating 

Chromating 

Phosphating 

Coloring 

Chemical Etching and Milling 

Printed Circuit Board Manufacture 

Pollutants 

Cadmium 

Chromium 

Hexavalent Chromium 

Phosphate 

Trivalent Chromium 

Cyanide 

B-1
 
 

Appendix B 

Process Operations 

Aluminum Coating 

Bright Dipping 

Brighteners 

Cadmium Free Technologies 

Cell Phone Screen Manufacturing 

Chemical Etching and Milling 

Dry Technologies 

Hexavalent Chromium Free Technologies 

New Wastewater Treatment Technologies 

Nickel Fluorocarbon 

Phosphate free technologies 

Phosphoric Acid 

Powder Coating 

Reuse 

Replacement for Phosphating 

Solar Panel Manufacturing 

Transition Metal Coatings 

Transportation equipment cleaning 

Zero Liquid Discharge 

Zinc-Nickel Alloy Coating 

Zirconization 

B-2
 
Appendix C 

Appendix C
 

Wastewater Treatment Technologies Evaluated
 

for Metals Removal in the 1983 Metal Finishing ELGs
 
 

 

 

Appendix C 

Appendix C:
 

Wastewater Treatment Technologies Evaluated
 

for Metals Removal in the 1983 Metal Finishing ELGs
 

Treatment 

Technology Technology Description Main Treatment Purpose 

Type of 

Wastewater Pollutant 

Average 

Effluent 

Concentration 

(mg/L) 

Average 

Percent 

Removal 

(%) 

Sulfide 

precipitation 

A precipitation technique using 

hydrogen sulfide or soluble sulfide salts 

to precipitate metal sulfides. May also 

use ferrous or ferric sulfates to 

precipitate metals, specifically for 

Inorganics Removal; 

Complex Metals Removal 

Aluminum 

anodizing 

wastewater 

Aluminum 

Chromium 

(VI) 

Chromium 

0.112 

Non-detect 

Non-detect 

97.3 

100 

100 

Metal finishing Chromium <0.01 >99.9 

complex wastewater. wastewater (VI) <0.04 >99.9 

Chromium 0.1 80.8 

Full-scale application in metal finishing. Iron <0.07 >99.8 

Zinc 

Metal finishing Chromium <0.005 >99.9 

wastewater (VI) <0.005 >99.9 

Chromium 0.003 89.7 

Copper 0.009 85 

Zinc 

Industrial Chromium <0.02 >9.1 

wastewater (VI) <0.1 >95.8 

Chromium, 0.6 99.4 

total <0.1 >85.3 

Iron 

Nickel 

Zinc 

<0.1 >99.7 

Metal finishing 

wastewater 

(cyanide bearing) 

Cyanide, total 0.024 99.2 

High pH Precipitation technique operating at high Complex Metals Removal No data available 

precipitation pH levels for complex wastewater 

treatment. 

Full-scale application in metal finishing. 

Chemical 

reduction 

Precipitation technique operating at low 

pH levels for complex wastewater 

Inorganics Removal; 

Complex Metals Removal 

No data available 

C-1
 
 

 

 

 

Appendix C 

Appendix C:
 

Wastewater Treatment Technologies Evaluated
 

for Metals Removal in the 1983 Metal Finishing ELGs
 

Treatment 

Technology Technology Description Main Treatment Purpose 

Type of 

Wastewater Pollutant 

Average 

Effluent 

Concentration 

(mg/L) 

Average 

Percent 

Removal 

(%) 

treatment. Addition of reducing agent to 

reduce metals oxidation state to allow 

precipitation at high pH. Commonly 

used for hexavalent chromium reduction. 

Full-scale application in metal finishing 

for chromium reduction. 

Electrochemical 

Chromium 

Reduction 

Selective reduction of hexavalent 

chromium by applying an electric current 

across iron electrodes to free ferrous ions 

that further react with chromate in 

solution to form chromic and ferrous 

hydroxides. Also effective with zinc. 

Full-scale application in metal finishing. 

Inorganics Removal Metal finishing 

wastewater 

Chromium 

(VI) 

Zinc 

0.05 

0.1 

99.5 

96.7 

Oxidation by 

Chlorination 

Addition of chlorine in an alkaline 

environment to convert cyanide into 

carbon dioxide and nitrogen. 

Inorganics Removal; 

Complex Metals Removal 

Metal finishing 

wastewater 

Cyanide Non-detect >99 

Oxidation by 

Ozonation 

The generation of ozone via an electrical 

discharge process that is dissolved in the 

wastewater to convert cyanide 

compounds into cyanates that are 

subsequently decomposed by other 

methods. 

Full-scale application in metal finishing. 

Inorganics Removal Cyanide bearing 

wastewater 

Cyanide, total 

Cyanide, 

amenable 

0.083 

0.082 

91.6 

91.7 

Oxidation by 

Ozonation with 

UV Radiation 

In addition to oxidation by ozone, 

simultaneous application of ultraviolet 

light. Commonly used to treat complex 

cyanide salts. 

Inorganics Removal; 

Complex Metals Removal 

No data available. 

C-2
 
 

 

 

 

Appendix C 

Appendix C:
 

Wastewater Treatment Technologies Evaluated
 

for Metals Removal in the 1983 Metal Finishing ELGs
 

Treatment 

Technology Technology Description Main Treatment Purpose 

Type of 

Wastewater Pollutant 

Average 

Effluent 

Concentration 

(mg/L) 

Average 

Percent 

Removal 

(%) 

Full-scale application in metal finishing. 

Oxidation by 

Hydrogen 

Peroxide 

Addition of peroxides to convert 

cyanides to cyanates. Applicable to 

cyanide-bearing wastewater containing 

zinc or cadmium. 

Full-scale application in metal finishing 

for cyanide destruction and metal 

recovery. 

Inorganics Removal; 

Metal/Chemical Recovery 

No data available. 

Electrochemical 

Cyanide 

Oxidation 

Conversion of cyanides to cyanates by 

applying an electric current across iron 

electrodes to generate ions that further 

react with cyanide via ozonation and 

direct oxidation. 

No full-scale application for metal 

finishing in 1983. 

Inorganics Removal No data available. 

Flotation Solids removal process using air bubbles 

to carry suspended solids to the surface 

where they are skimmed off and 

disposed. Commonly used to treat 

wastewaters with suspended solids near 

the specific gravity of 1.0, which make 

gravity settling difficult. Also used for 

oily waste treatment. 

Full-scale application in oily waste 

removal. Bench scale studies in heavy 

metals removal. 

Inorganics Removal No data available. 

Membrane 

Filtration 

Solids removal process by recirculating 

wastewater through a tubular membrane 

Complex Metals Removal; 

Polishing 

Metal finishing 

wastewater 

Chromium 

(VI) 

0.008 

0.038 

98.9 

99.8 

C-3
 
 

 

 

Appendix C 

Appendix C:
 

Wastewater Treatment Technologies Evaluated
 

for Metals Removal in the 1983 Metal Finishing ELGs
 

Treatment 

Technology Technology Description Main Treatment Purpose 

Type of 

Wastewater Pollutant 

Average 

Effluent 

Concentration 

(mg/L) 

Average 

Percent 

Removal 

(%) 

filter to enhance removal of heavy Chromium 0.13 98.5 

metals. May also be used to treat Copper 0.28 99.3 

complex wastewater. Iron 0.01 97.5 

Lead 0.18 99.8 

Full-scale application in metal finishing. Nickel 0.05 98.4 

Zinc 

TSS 

4.05 69.2 

Diatomaceous Solids separation device to further Polishing Unclarified TSS 35.6 94.2 

Earth Filtration enhance suspended solids removal. chemical Cadmium 0.01 59.1 

Equipment includes multiple leaf screens precipitation Chromium 0.19 97.4 

coated with diatomaceous earth, filter effluent (metal Copper 1.39 94.4 

housing, and pumps. finishing) Lead 0.06 70.9 

Nickel 0.20 87.1 

Full-scale application in metal finishing. Tin 0.08 87.1 

Zinc 1.68 89.0 

Peat Adsorption Solids removal through chemical Polishing Industrial Antimony 0.9 64.0 

bonding between naturally occurring wastewater Chromium <0.04 >99.9 

functional groups in peat moss and (VI) 0.24 99.9 

transition metals and polar organic Copper 0.7 98.1 

molecules in wastewater. Cyanide 0.025 99.9 

Lead 0.02 >98.0 

Pilot scale studies in metal finishing. Mercury 0.07 97.2 

Full-scale application in textile, Nickel 0.05 >95.0 

newsprint, and metal reclamation 

industries. 

Silver 

Zinc 

0.25 83.3 

Insoluble 

Starch Xanthate 

Ion exchange resin material that can treat 

wastewater in a batch or continuous 

process or as a filter precoat. 

Polishing; Metal/Chemical 

Recovery 

Treated metal 

finishing effluent 

All metals 0.02 98.0 

Metal finishing Copper 0.26 3.9 

rinse water Iron 0.13 31.6 

Full-scale application in metal finishing. Lead 0.27 5.4 

Nickel 273.5 0.9 

C-4
 
 

 

Appendix C 

Appendix C:
 

Wastewater Treatment Technologies Evaluated
 

for Metals Removal in the 1983 Metal Finishing ELGs
 

Treatment 

Technology Technology Description Main Treatment Purpose 

Type of 

Wastewater Pollutant 

Average 

Effluent 

Concentration 

(mg/L) 

Average 

Percent 

Removal 

(%) 

Tin 

Zinc 

0.75 

0.063 

25.0 

16.4 

Electrolytic Selective reduction of a metal by Metal/Chemical Recovery Photographic Silver 21 95.6 

Recovery applying an electric current across 

electrodes and allowing a plating process 

to occur to recover the metal. 

Full-scale application in metal finishing. 

processing 

wastewater 

Evaporation Concentration process where water 

evaporates from solution and increases 

concentration of solute in remaining 

solution. May also involve a 

condensation process. 

Full-scale application in metal finishing. 

Metal/Chemical Recovery; 

In-plant Controls 

No data available 

Ion Exchange Exchange of ionic contaminants in 

wastewater with ions of the resin. 

Commonly used to recover process 

chemicals and metals from rinsewater to 

allow reuse. Many metal finishers use 

the technology to concentrate and purify 

plating baths. 

Full-scale application in metal finishing. 

Metal/Chemical Recovery; 

In-plant Controls 

Electroplating 

rinse water 

Aluminum 

Cadmium 

Chromium 

(III) 

Chromium 

(VI) 

Copper 

Cyanide 

Iron 

Manganese 

Nickel 

Silver 

Tin 

Zinc 

0.2 

0.00 

0.01 

0.01 

0.09 

0.04 

0.01 

0.00 

0.00 

0.00 

0.00 

0.4 

96.4 

100 

99.7 

99.9 

98.0 

99.6 

99.9 

100 

100 

100 

100 

97.3 

Printed circuit 

board 

Copper 

Cyanide 

0.1 

0.09 

99.8 

97.4 

C-5
 
Appendix C 

Appendix C:
 

Wastewater Treatment Technologies Evaluated
 

for Metals Removal in the 1983 Metal Finishing ELGs
 

Treatment 

Technology Technology Description Main Treatment Purpose 

Type of 

Wastewater Pollutant 

Average 

Effluent 

Concentration 

(mg/L) 

Average 

Percent 

Removal 

(%) 

manufacturing 

rinse water 

Gold 

Lead 

Nickel 

Silver 

Sulfate 

Tin 

0.1 

0.01 

0.01 

0.01 

2 

0.1 

95.7 

99.4 

99.4 

99.9 

99.0 

90.9 

Metal finishing 

rinse water 

Chromium 

Copper 

Nickel 

0.03 

0.16 

0.003 

76.9 

99.8 

89.6 

Photographic 

processing 

wastewater 

Silver 0.093 90.3 

C-6