### Materials Characterization Paper In Support of the Proposed Rulemaking: Identification of Nonhazardous Secondary Materials That Are So lid Waste Wastewater Treatment Sludge

March 18, 2010



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1. Definition of Wastewater Treatment Sludge

The suspended and dissolved solids generated in the wastewater treatment process are called sludges or sewage sludge. Sludge may also be defined as any solid, semisolid or liquid material generated from a wastewater treatment proce ss. This sludge is also commonly known as

biosolids. Wastewater treatmen t operations require careful mana gement of sludge, not only after removal from the treatment process, but also duri ng the treatment process: sludge is a critical biologically active mix of water, organic matter (derived from hu man wastes, food wastes, etc.), inorganic solids (including trace elements), dead and alive micro-organisms (including pathogens), and trace contaminants (e.g., chemicals). Some sludge is routinely recycled within the treatment facility process to optimize operations. However, as sludge builds up, batches of it are regularly removed from effluent treatment opera tions. This “raw” sludge is typically two to three percent solids and 97 to 98 percent water and must be further treated to be utilized in a beneficial manner. Most sludge comes from primary settling tanks (“clarifiers”) and/or secondary settling tanks and, in mo st cases, is a slig htly thick, gray-bo ttom liquid. In this analysis, wastewater treatment sludge include s materials generated after both primary and secondary treatment stages.

Sludges generated from the pulp and paper industry are discusse d in the Materials Characterization Paper entitled, “Forest-Derive d Biomass and Pulp and Paper Residues.”

2. Annual Quantities of Wastewater Tr eatment Sludge Generated and Used:

(1) Sectors that generate Wastewater Treatment Sludge: The NAICS code for sewage treatment facilities is 221320.

(2) Quantities and Prices of Waste water Treatment Sludge Generated:

• Data sources for the 2002-2003 period differ in their assessment of the generation of wastewater treatment sludge in the U.S. Based on th e range of values reported by these sources, an estimated 5 to 7 milli on tons were generated annually in the U.S. during this period. (City of Tor onto 2003; WEF 2002; NBP 2005, p. 19-1).

• Nationwide data on the market value of wastewater treatment sludge are not readily available. On a lo cal scale, a 1996 article by BioCycle magazine estimated that biosolids produced by the Hampton Roads Sanitation District in Virginia was worth approximately $20 per dry ton of biosolids (or $95 per acre for land application) (NBP 2005). More recent estimates of the economic value of biosolids were not readily available.Wastewater Treatment Sludge



### (3) Trends in Generation of Wastewater Treatment Sludge:

• The readily available data do not show a clear tr end in the generation of wastewater treatment sludge.

3. Uses of Wastewater Treatment Sludge

(1) Fuel uses:

• Wastewater treatment sludge may be used as a fuel in cement kilns (NAICS 327310 cement industry). The available data do not indicate how widespread this practice is.

• Various sources indicate that between 15 and 22 percent of wastewater treatment sludge is incinerated (WEF 2002; City of Toronto 2003; UNE P). Approximately 150 municipalities in the U.S. - repres enting approximately 250 installations - engage in this practice (City of Tor onto 2003). However, when wastewater treatment sludge is burned in dedicated wa stewater treatment sludge incinerators, it is most likely not used as a substi tute for conventional fossil fuels that incinerators may burn to maintain efficient combustion. 1



### • There are two fundamental options for rec overy of energy from dried biosolids: 1) utilize an existing offsite “host” pr ocess in which the biosolids replace a portion of the prime fuel; and 2) constr uct a dedicated plant onsite to produce energy for either onsite use or export (ENERGOs, 2007).

• Atlanta-based EnerTech Environmental recently developed the “Slurry-CarbTM” process that converts biosolids into a re newable fuel called E-Fuel. The E-Fuel product derived from the Slurry-C arbTM process is suitable for gasification, cofiring, use in cement kilns or utilization in industrial and utility boilers 

### (PWM 2007; EnerTech 2008). The cost of the Slu rry-Carb process is approximately $72 per ton (PWM 2007). The first Sl urry-Carb facility is sche duled to open in the Los Angeles area in 2008 and will convert 675 wet tons of sludge per day into approximately 145 tons per day of E-fuel , which will be sold to a local cement kiln as a substitute for coal (PWM 2007).

• Incineration of wastewater treatmen t sludge is regulated under 40 CFR 503 Subpart E. These regulations cover pollutant limits; general management practices; and monitoring, reporting, and recordkeeping requirements (EPA 2004).

(2) Non-Fuel Uses of Wastewater Treatment Sludge

• According to EPA data summarized by the Water Environment Federation, more than 60 percent of wastewater treatment sludge produced in the United States is beneficially used on land following trea tment, frequently by alkaline addition (WEF 2002). Similarly, another data source indicates that 63 pe rcent of biosolids

1 We note, however, that a public comment submitted to EPA in response to the Advanced Notice of Proposed Rulemaking (ANPRM) for the Identification of No n-hazardous Materials That Are Solid Waste indicated that a sanitary district in California would require additional natural gas if it were unable to incinerate waste water treatment sludge for energy recovery (Craig 2009).

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### in the U.S. were land applied in 1998, w ith this figure e xpected to reach 66 percent in 2005 and 70 per cent in 2010 (Oleszkiewi cz and Mavinic 2002).

• Nearly 42 percent of all U.S. wastewat er treatment solids are land applied as fertilizer (Clackamas County 2006). Based on the figures presented in the previous bullet, this represents approximately two-thirds of the total percentage land applied.

• Data published by the United Nations Envi ronment Program (UNEP) suggest that approximately 36 percent of wastewater treatment sludge generated in the mid1990s was beneficially used for agricultu ral applications (land applied) and 10 percent was managed through other methods (UNEP). Examples of land application uses include:

o Agricultural cropland application, through liquid injection, or surface spreading followed by incor poration into the soil;

o Commercial sale as a fertil izer or soil conditioning material, particularly for horticultural and landscaping applications;

o Rangeland and pasture application to improve available grazing;

o Remediation of contaminated areas such as mine sites;

o Soil amendment and recovery of marginal land; and

o Land application in refo rested areas (UNEP).

• A potential future use of wa stewater treatment sludge is as an anaer obic agent to optimize the natural degradation of waste in municipal solid waste landfills. (NBP 2005, p 19-1).

• Land application of wastewater treatmen t sludge is regulated under 40 CFR 503. These regulations cover pollutant limits ; general management practices; and monitoring, reporting, and recordkeeping requirements (EPA 2004). The pollutant limits are listed below in Exhibit 4.

(3) Quantities of Wastewater Treatment Sludge Landfilled

• Based on EPA estimates from the 2000-2002 period, approximately 14 to 17 percent of wastewater treatment sludge is landfilled, and, of this, approximately 3 percent is used as daily or final cover in landfills (EPA as cited in WEF 2002 and NBP 2005, p. 19-1).

• Data published by UNEP suggest that 38 pe rcent of wastewater treatment sludge was disposed in landfills in the mid-1990s (Chang, Pang and Asano 1996).

(4) Quantities Wastewater Treatme nt Sludge Stockpiled/Stored

• The available information sources do not suggest that wastewater treatment sludge is stockpiled or stored.

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### Exhibit 1: Overview of Generation an d Use - Wastewater Treatment Sludge

Beneficial Use
Annual Quantity

Generated Fuel (cement

kiln) Land Applied Annual Quantity

Landfilled Annual Quantity

Incinerated Annual Quantity in

Other Uses

(landfill cover) Commodity



### --------------------------------- Short Tons --------------------------------

Biosolids (Wastewater Treatment Sludge) 5 to 7 million dry

tons Quantity

data

unavailable 60%+ 14 to 17% 15 to 22% Quantity

data

unavailable

Sources: City of Toronto 2003, NBP 2005, Oleszkiewicz and Mavinic 2002, UNEP, and WEF 2002



### 4. Management and Combustion processes

(1) Types of Units

• Fluidized Bed Incineration (FBI)

• Multiple Hearth Furnace (MHF)

• Cement Kilns

(2) Sourcing information

• Municipal and food wastewater treatment plants.

(3) Processing Information:

• Most often, wastewater treatment sludge is treated in either an aerobic or anaerobic digester to stabilize the materi al and reduce pathogen concentrations (disease-causing organisms). A variety of other treatment options may be used to ensure that sludge meets federal and state requirements for beneficial use. Upon satisfying these requirements, the sludge is considered a “biosolid” (NEBRA 2005).

• The Slurry-CarbTM technology converts bios olids to fuel using the following

processes:

o Biosolids are subjected to pressure and heat;

o Upon reaching the desired reaction temper ature, the biosolids break down into carbon and light gases;

o The result is a slurry with molecules th at are much smaller than the original biosolids and very high in energy;

o The slurry is dewatered to 50 percent total solids through ce ntrifugation rather than evaporation, allowing it to dry using approximately two-thirds less energy than conventional drying methods;

o The end product, a renewable fuel called E-Fuel, is an alte rnative to fossil fuels (EnerTech 2008).

• Energy recovery technologies can be classi fied into sludge-to- biogas processes, sludge-to-syngas processes, sludge-to-o il processes, and sludge-to-liquid processes. The technologies available for resource recovery include those to recover phosphorus, building materials, nitrogen, volatile acids, etc (WERF, 2008a).

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### (4) Changes in Technology to improve use as a fuel:

• Information is not readily available on specific technological developments to improve the use of wastewater treatment sludge in combustion applications. The Lehigh Cement Company, however, began performing tests in 2004 on the use of dried sewage pellets from two Baltimore treatment plants to replace some of the coal burned by Lehigh’s kiln near Union Bridge. Lehigh’s parent corporation, Heidelberger Zement, and other cement make rs have been using sludge pellets for about 20 years in Europe. Approximately 55 dry tons of pellets are produced each day at the Back River and the Patapsco wastewater treatment plants in Baltimore (Hand-Smith 2007, p5).

(5) State status of Combustion as beneficial use:

• At this stage, we have not identified any states that have approved use of wastewater treatment sludge as fuel, but we have not performed an exhaustive investigation of state ac tivities and regulations.

5. Wastewater Treatment Sludge Composition and Impacts

(1) Composition of Commodity

• The Slurry-CarbTM process recently developed by EnerTech Environmental, produces a final product called “E-Fuel” fr om biosolids that can be sold as a renewable fuel with approximately 7,000 BTU per pound (EnerTech 2008)

.



### • According to the Water Environment Founda tion, the energy value of biosolids is approximately 5,500 kcal/kg (10,000 Btu pe r pound) of dry volatile solids or 2,500 to 3,000 kcal/kg (4,500 to 5,500 Btu pe r pound) of total dry matter (WEF 2000). Exhibit 2 presents separate Btu va lues for different types of wastewater treatment sludge.

Exhibit 2: Btu Value of Different Types of Wast ewater Treatment Sludge

Wastewater Treatment Sludge

Material Heating Value (Btu per pound of dry solids) Fine Screenings 9,000

Grit 4,000

Grease and Scum 16,700

Dewatered Raw Biosolids 10,300 Chemical Precipitated Biosolids 7,500 Dewatered Digested Biosolids 5,300

Source: NBP 2005, p 15-10



### • Exhibit 3 compares the results of two surveys of the chemical composition of biosolids, and, for comparison, also in cludes the composition of coal. The 40- City Study, which was conducted in 1979 and 1980, examined the solids generated at 40 publicly-owned wastewater treatment facilities, while the National Sewage Sludge Survey conducted in 1989 summarizes the results of testing

conducted at over 200 wastewater treatment facilities (NBP 2005, pp. 3-1 to 3-2). While dated, the results of the two surveys indicate that, in almost every case, the

observed concentrations in the National Sewage Sludge Survey are less than those

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### in the 40-city study, suggesting that concentrations fell during the 1980s (NBP 2005, p.3-2). Copper and mercury concentr ations, however, appear to have increased during this period. The increase in copper concentrations most likely reflects increased use of copper plumbi ng in new homes. There is no clear explanation for the increas e in the average mercur y concentration (NBP 2005, p.3-2).

• Public comments submitted by the Nationa l Association of Clean Water Agencies (NACWA) to EPA in response to th e ANPRM suggest that contaminant concentrations continued to decline in the 1990s and 2000s. In particular, NACWA notes that mercury and beryll ium concentrations for wastewater treatment sludge at two Ohio wastewater plants tested in 2004 were below 1.0 mg/dry kg and 0.3 mg/dry kg, respectively (Hornback 2009).

Exhibit 3: Composition of Munici pal Wastewater Treatment Sludges

Wastewater Treatment Sludge

Element 40-City Study (1980) mg/kg dry weight National Sewage Sludge Study (1989) mg/kg dry weight Coal (mg/kg)

Arsenic 9.9 6.7 10

Cadmium 69 6.9 0.5

Chromium 429 119 20 Copper 602 741 Not available

Lead 369 134.4 40 Mercury 2.8 5.2 0.1 Molybdenum 17.7 9.2 Not available

Nickel 135.1 42.7 20

Selenium 7.3 5.2 1

Zinc 1,594 1,202 Not available

Sources: NBP 2005, pp. 3-1 to 3-2 and EPA 1998, p. 1-5

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### • In accordance with Part 503, a ll biosolids applied to the land must be within the

limits listed in Exhibit 4.

Exhibit 4: Pollutant Limits for Biosolids Applied to the Land

Pollutant Ceiling Concentration Limits for All Biosolids Applied to Land (milligrams per kilogram) a

Arsenic 75

Cadmium 85

Chromium 3000 Copper 4300

Lead 840 Mercury 57 Molybdenum b 75

Nickel 420

Selenium 100

Zinc 7500 Applies to: All biosolids that are land applied

From Part 503 Table 1, Section 503.13

Source:

EPA 2004

Notes:

a Dry-weight basis

b As a result of the February 25, 1994, Amendment to the rule, the limits for molybdenum were deleted from the Part 503 rule pending EPA reconsideration.



### (2) Impact Information

• Cost Impacts: The net cost impacts associated with the beneficial use of wastewater treatment sludge as a fuel in cement kilns depends on the value of the fuel that this material replaces and the co st of processing the material prior to its use as a fuel. Information on these proces sing costs is not readily available, but we estimate that the fuel savings associ ated with using wastewater treatment sludge as a substitute for conventional fuels would be $2.23 per MMBtu, assuming that the wastewater treatment sludge would replace coal (EIA 2007, Table ES1). 2

, 3



### • Emissions Impacts of Using Wastewater Tr eatment Sludge as a Fuel in Cement

Kilns: As indicated above, an unknown quantity of wastewater treatment sludge may be beneficially used as a fuel in cement kilns. Information is not available on

the emissions associated with this act ivity, but we were able to identify

information on the emissions associated with the incineration of wastewater

2 To express this value as dollars per MMBtu, we assu med 22,473,000 Btu per short ton of coal (EIA 2005, Table A5).

3 In a comment submitted to EPA following the release of the ANPRM, a sanitary district in California indicated that the cost of incinerating its waste treatment sludge is, on an annual basis, $4.3 million less than the cost of landfilling this material. Additionally, incineration of this wastewater treatment sludge reportedly saves the district $320,000 per year in energy costs, assuming the dist rict would use natural gas in place of the sludge (Craig 2009).

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### treatment sludge, as summarized in Exhibit 5. The exhibit also summarizes the combustion-related emissions for coal, distil late oil, residual oil, and natural gas.

• 

### Upstream Emissions Impacts: Use of wastewater treatment sludge as a replacement for traditional primary fuels in cement kilns eliminates the environmental impacts associated with ex traction and processing of the traditional fuels. Exhibit 5 lists the quantities of cradle-to-gate (i.e., combustion plus upstream) emissions for coal, the fuel typically used by cement kilns, and other fossil fuels based on typical processes in the United States in the late 1990s.Wastewater Treatment Sludge9Exhibit 5: Comparative Impacts of SludgeIncineration versus Alternative Primary FuelsSludgeIncinerationCoalDistillate Fuel OilResidual Fuel OilNatural GasPollutantCombustion(Incineration)CombustionCombustionplusUpstreamCombustionCombustionplusUpstreamCombustionCombustionplusUpstreamCombustionCombustionplusUpstream-------------------------------------------------------lb./MMBtu------------------------------------------------Criteria PollutantsPM2.50.025--------PM100.0430.0540.0540.0110.0110.0930.0930.0090.009PM,unspecified0.010-0.246-0.012-0.012-0.004NOx0.2010.4820.5040.1730.2340.3670.4280.3010.417VOCs0.0080.0060.0140.0010.3630.0020.3670.0090.524SOx0.281.4461.4690.2090.3941.5931.7810.0731.985CO0.80.0680.0850.0360.0820.0330.0790.0580.282Pb3.1x10-38.93x10-69.19x10-64.60x10-65.61x10-65.80x10-55.90x10-5-2.72x10-7Hg-2.05x10-62.14x10-61.58x10-61.77x10-68.67x10-68.85x10-6-7.18x10-8Greenhouse GasesCO2-210.7214.7161.2180.1173.3192.5114.6129.8CH43.023x10-40.0070.4583.74x10-40.030.0070.0360.0030.372N2O-0.0030.003-2.01x10-5-2.07x10-5-1.17x10-5MTCO2E/MMBtu0.0960.1020.0730.0820.0790.0880.0520.062Source:Franklin Associates 1998.Notes:“-” signifies data not available; may equal zero.The sludge incineration numbers are based on a combination of averages, including the average controlled emissions rates from 12 sources and three differentincineration technologies (multiple hearth, fluidized bed, and electric). Additionally, a midpoint value of 10,350 BTUs/lb heating value for wastewatertreatment sludge was used (heating values ranged from 4,000 btu/lb to 16,700 btu/lb).The emission information presented in this table is derived from Life Cycle Inventory (LCI) data, as compiled by Franklin Associates. LCI data identifies andquantifies resource inputs, energyrequirements, and releases to the air, water,and land for each step in the manufacture of aproduct or process, from theextraction of the raw materials to ultimate disposal. The LCI canbe used to identify those systemcomponents or life cycle steps that are the main contributorsto environmental burdens such as energy use, solid waste, and atmospheric and waterborne emissions. Uncertainty in an LCI is due to the cumulative effects ofinput uncertainties and data variability.There are several life cycle inventory databases available in the U.S. and Europe. For this paper, we applied the most readilyavailable LCI database that wasmost consistent with the materials and uses examined. These LCI data rely on system boundaries as defined by Franklin Associates, as described in thedocumentation for this database, available at:http://www.pre.nl/download/manuals/DatabaseManualFranklinUS98.pdf.Wastewater Treatment Sludge



### References

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Clackamas County Oregon, 2006. “A Beneficial Product of Wastewater Treatment,” fact sheet, June 2006.

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of Non-Hazardous Material s That Are Solid Waste, EPA docket EPA-HQ-RCRA-2008-0 329, submitted on behalf of Central Contra Costa Sanitary District, January 30, 2009.

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20Practice

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2245

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