Materials Characterization Paper

In Support of the

Advanced Notice of Proposed Rulemaking –

Identification of Nonhazardous Materials That Are Solid Waste

Wastewater Treatment Sludge

December 16, 2008

====================================================================

1.	Definition of Wastewater Treatment Sludge

The suspended and dissolved solids generated in the wastewater treatment
process are called sludges or sewage sludge.  This sludge is also
commonly known as biosolids.  Wastewater treatment operations require
careful management of sludge, not only after removal from the treatment
process, but also during the treatment process:  sludge is a critical
biologically active mix of water, organic matter (derived from human
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 operations.  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 most cases, is a slightly thick, gray-bottom liquid.  In this
analysis, wastewater treatment sludge includes materials generated after
both primary and secondary treatment stages.

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

2.	Annual Quantities of Wastewater Treatment Sludge Generated and Used:

Sectors that generate Wastewater Treatment Sludge:   

The NAICS code for sewage treatment facilities is 221320.

Quantities and Prices of Wastewater 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 the
range of values reported by these sources, an estimated 5 to 7 million
tons were generated annually in the U.S. during this period. (City of
Toronto 2003; WEF 2002;  NBP 2005, p. 19-1).  

Nationwide data on the market value of wastewater treatment sludge are
not readily available.  On a local 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.

 

Trends in Generation of Wastewater Treatment Sludge:  

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

3.	Uses of Wastewater Treatment Sludge

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; UNEP).
Approximately 150 municipalities in the U.S. - representing
approximately 250 installations - engage in this practice (City of
Toronto 2003).  However, when wastewater treatment sludge is burned in
dedicated wastewater treatment sludge incinerators, it is most likely
not used as a substitute for conventional fossil fuels that incinerators
may burn to maintain efficient combustion. 

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

“Slurry-Carb™” process that converts biosolids into a renewable
fuel called E-Fuel.  The E-Fuel product derived from the Slurry-Carb™
process is suitable for gasification, co-firing, use in cement kilns or
utilization in industrial and utility boilers (PWM 2007; EnerTech 2008).
 The cost of the Slurry-Carb process is approximately $72 per ton (PWM
2007).  The first Slurry-Carb facility is scheduled 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 treatment 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).

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 treatment,
frequently by alkaline addition (WEF 2002).  Similarly, another data
source indicates that 63 percent of biosolids in the U.S. were land
applied in 1998, with this figure expected to reach 66 percent in 2005
and 70 percent in 2010 (Oleszkiewicz and Mavinic 2002).  

Nearly 42 percent of all U.S. wastewater 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 Environment Program (UNEP) suggest
that approximately 36 percent of wastewater treatment sludge generated
in the mid-1990s was beneficially used for agricultural applications
(land applied) and 10 percent was managed through other methods (UNEP). 
Examples of land application uses include:

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

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

Rangeland and pasture application to improve available grazing;

Remediation of contaminated areas such as mine sites;

Soil amendment and recovery of marginal land; and

Land application in reforested areas (UNEP).

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

Land application of wastewater treatment 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.

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 percent of wastewater treatment
sludge was disposed in landfills in the mid-1990s (Chang, Pang and Asano
1996).

Quantities Wastewater Treatment Sludge Stockpiled/Stored

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

Exhibit 1:  Overview of Generation and Use - Wastewater Treatment Sludge

Commodity	Annual Quantity Generated

	Beneficial Use	Annual Quantity Landfilled	Annual Quantity Incinerated
Annual Quantity in Other Uses (landfill cover) 



Fuel

(cement kiln)	Land Applied





--------------------------------- 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

Types of Units

Fluidized Bed Incineration (FBI)

Multiple Hearth Furnace (MHF) 

Cement Kilns 

Sourcing information

Municipal and food wastewater treatment plants.  

Processing Information: 

Most often, wastewater treatment sludge is treated in either an aerobic
or anaerobic digester to stabilize the material 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
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The Slurry-Carb™ technology converts biosolids to fuel using the
following processes:

Biosolids are subjected to pressure and heat;

Upon reaching the desired reaction temperature, the biosolids break down
into carbon and light gases;

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

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

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

Energy recovery technologies can be classified into sludge-to-biogas
processes, sludge-to-syngas processes, sludge-to-oil 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).

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 makers 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). 

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 activities and regulations.

5.	Wastewater Treatment Sludge Composition and Impacts

Composition of Commodity

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

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

Exhibit 2:  Btu Value of Different Types of Wastewater 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 includes 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 in the 40-city study, suggesting that concentrations
fell during the 1980s.  Copper and mercury concentrations, however,
appear to have increased during this period.  The increase in copper
concentrations most likely reflects increased use of copper plumbing in
new homes. There is no clear explanation for the increase in the average
mercury concentration (NBP 2005, p.3-2).

Exhibit 3:  Composition of Municipal Wastewater Treatment Sludges

Element	Wastewater Treatment Sludge	Coal (mg/kg)

	40-City Study (1980)

mg/kg dry weight	National Sewage Sludge Study (1989)

mg/kg dry weight

	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



In accordance with Part 503, all 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

Molybdenumb	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:

aDry-weight basis

bAs 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.



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 cost of processing
the material prior to its use as a fuel.  Information on these
processing costs is not readily available, but we estimate that the fuel
savings associated 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).  

Emissions Impacts of Using Wastewater Treatment 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
activity, but we were able to identify information on the emissions
associated with the incineration of wastewater treatment sludge, as
summarized in Exhibit 5.  The exhibit also summarizes the
combustion-related emissions for coal, distillate 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 extraction 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.  

Exhibit 5:  Comparative Impacts of Sludge Incineration versus
Alternative Primary Fuels

Pollutant	Sludge Incineration	Coal	Distillate Fuel Oil	Residual Fuel Oil
Natural Gas

	Combustion (Incineration)	Combustion	Combustion plus Upstream
Combustion	Combustion plus Upstream	Combustion	Combustion plus Upstream
Combustion	Combustion plus Upstream

	------------------------------------------------------- lb./MMBtu
------------------------------------------------

Criteria Pollutants

PM2.5	0.025	-	-	-	-	-	-	-	-

PM10	0.043	0.054	0.054	0.011	0.011	0.093	0.093	0.009	0.009

PM, unspecified	0.010	-	0.246	-	0.012	-	0.012	-	0.004

NOx	0.201	0.482	0.504	0.173	0.234	0.367	0.428	0.301	0.417

VOCs	0.008	0.006	0.014	0.001	0.363	0.002	0.367	0.009	0.524

SOx	0.28	1.446	1.469	0.209	0.394	1.593	1.781	0.073	1.985

CO	0.8	0.068	0.085	0.036	0.082	0.033	0.079	0.058	0.282

Pb	3.1x10-3	8.93x10-6	9.19x10-6	4.60x10-6	5.61x10-6	5.80x10-5	5.90x10-5
-	2.72x10-7

Hg	-	2.05x10-6	2.14x10-6	1.58x10-6	1.77x10-6	8.67x10-6	8.85x10-6	-
7.18x10-8

Source:

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 different incineration technologies (multiple hearth, fluidized
bed, and electric).  Additionally, a midpoint value of 10,350 BTUs/lb
heating value for wastewater treatment 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 and quantifies resource inputs, energy requirements, and
releases to the air, water, and land for each step in the manufacture of
a product or process, from the extraction of the raw materials to
ultimate disposal. The LCI can be used to identify those system
components or life cycle steps that are the main contributors to
environmental burdens such as energy use, solid waste, and atmospheric
and waterborne emissions.  Uncertainty in an LCI is due to the
cumulative effects of input 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 readily available LCI
database that was most consistent with the materials and uses examined.
These LCI data rely on system boundaries as defined by Franklin
Associates, as described in the documentation for this database,
available at:   HYPERLINK
"http://www.pre.nl/download/manuals/DatabaseManualFranklinUS98.pdf" 
http://www.pre.nl/download/manuals/DatabaseManualFranklinUS98.pdf .  



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

Energos (UK), 2007.  “Energy from Waste, Biosolids as an Energy
Source,” powerpoint presentation, February 

2007.

EnerTech Environmental, 2008.  “The Slurry-Carb™ Process, Renewable
Energy from Biosolids,” powerpoint presentation, 2008, accessed on
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http://www.enertech.com/downloads/SlurryCarbOverview.pdf 

Franklin Associates, 1998.  “Franklin US LCI 98 Library,” 1998.

Hand-Smith, Gillian, 2007.   “The Future of International High Tech
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Australia,” 2007, accessed on August 21, 2008, at:  

http://www.mwhglobal.com.au/technical-paperspost-2006.

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  HYPERLINK
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Management,” J. Environ. Eng. Sci. 1:75-88.

Public Works Magazine, 2007.  “From Sludge to Fuel, California is the
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instead of coal,” August 1, 2007, accesses on September 30, 2008, at: 
http://www.pwmag.com/industry-news.asp?sectionID=760&articleID=547650

United Nations Environment Programme (UNEP), Division of Technology,
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Management:  An Environmentally Sound Approach for Managing Sewage
Treatment Plant Sludge, Practices in Europe and North America:  Waste
Disposal Versus Resource Utilisation,” Newsletter and Technical
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"http://www.unep.or.jp/ietc/Publications/Freshwater/FMS1/3.asp" 
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Water Environment Federation, “A Guide to Understanding Biosolids
Issues,” 2002.

Water Environment Research Foundation, 2008a.  “State of Science
Report:  Energy and Resource Recovery from Sludge,” Executive Summary,
May 2008, accessed on September 30, 2008, at: 
http://www.werf.org/AM/Template.cfm?Section=Search_Research_and_Knowledg
e_Areas&Template=/CustomSource/Research/ResearchProfile.cfm&ReportId=OWS
O3R07&CFID=1651559&CFTOKEN=63512245

Water Environment Research Foundation, 2008b.  “Wastewater Sludge:  A
New Resource for Alternative Energy and Resource Recovery,” Factsheet,
June 11, 2008, accessed on September 30, 2008, at:    HYPERLINK
"http://www.werf.org/am/template.cfm?section=Search_Research_and_Knowled
ge_Areas&template=/cm/ContentDisplay.cfm&ContentID=7008" 
http://www.werf.org/am/template.cfm?section=Search_Research_and_Knowledg
e_Areas&template=/cm/ContentDisplay.cfm&ContentID=7008 

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

 PAGE   

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Wastewater Treatment Sludge

