t
Opportunities for Combined Heat and Power
at Wastewater Treatment Facilities:
Market Analysis and Lessons from the Field
U.S. Environmental Protection Agency
Combined Heat and Power Partnership
October 2011
CHP
IUHTNEHIHP
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The U.S. Environmental Protection Agency (EPA)
CHP Partnership is a voluntary program that seeks to
reduce the environmental impact of power generation
by promoting the use of CHP. CHP is an efficient,
clean, and reliable approach to generating power and
thermal energy from a single fuel source. CHP can
increase operational efficiency and decrease energy
costs while reducing the emissions of greenhouse
gases. The CHP Partnership works closely with
energy users, the CHP industry, state and local
governments, and other stakeholders to support the
development of new CHP projects and promote their
energy, environmental, and economic benefits.
The CHP Partnership provides resources about CHP
technologies, incentives, emission profiles, and other
information on its website at www.epa.gov/chp. For
more information, contact the CHP Partnership
Helpline at chp@epa.qov or (703) 373-8108.
Acknowledgements
The CHP Partnership would like to thank the following people for
their review and comments, which were very helpful in the
development of this report:
Robert Bastian, U.S. EPA Office of Water
John Cuttica, University of Illinois at Chicago
Lauren Fillmore, Water Environment Research Foundation (WERF)
Bruce Hedman, ICF International
Chris Hornback, National Association of Clean Water Agencies
(NACWA)
Dana Levy, New York State Energy Research and Development
Authority (NYSERDA)
JohnMoskal, U.S. EPA Region 1
Report prepared by: Eastern Research Group, Inc. (ERG) and Resource Dynamics Corporation
(RDC) for the U.S. Environmental Protection Agency, Combined Heat and Power Partnership,
October 2011.
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Table of Contents
EXECUTIVE SUMMARY iv
1.0 Introduction 1
2.0 CHP and Its Benefits at Wastewater Treatment Facilities 3
3.0 The Market 5
3.1 Wastewater Treatment Facilities with CHP 5
3.2 Potential CHP Market 7
4.0 Technical and Economic Potential 9
4.1 Technical Potential for CHP at Wastewater Treatment Facilities 9
4.1.1 Methodology 9
4.1.2 Electric and Thermal Generation Potential from CHP Systems at Wastewater
Treatment Facilities 10
4.1.3 National Electric Generation Potential from CHP at Wastewater Treatment
Facilities 12
4.1.4 Potential Carbon Dioxide Emissions Benefits 12
4.2 Economic Potential for CHP at Wastewater Treatment Facilities 13
4.2.1 Methodology 14
4.2.2 Heating Requirements of Wastewater Treatment Facilities 15
4.2.3 Estimated Cost to Generate Electricity 18
4.2.4 National Economic Potential Scenarios 24
5.0 Wastewater Treatment Facility Interviews: CHP Benefits, Challenges, and
Operational Insights 28
5.1 Wastewater Treatment Facilities Interviewed and Interview Format 28
5.2 Drivers and B enefits 30
5.3 Challenges 34
5.4 Operational Insights and Observations 38
Appendix A: Data Sources Used in the Analysis 40
Appendix B: Anaerobic Digester Design Criteria Used for Technical Potential Analysis 42
Appendix C: Space Heating Capability of CHP at Wastewater Treatment Facilities 43
Appendix D: Cost-to-Generate Estimates by State 45
Appendix E: Additional Reference Resources 49
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List of Tables
Table 1: Number of Digester Gas Wastewater CHP Systems and Total Capacity by State 6
Table 2: Number of Sites and Capacity (MW) by CHP Prime Movers 6
Table 3: Number of U.S. Wastewater Treatment Facilities with Anaerobic Digestion 8
Table 4: Wastewater Flow to U.S. Wastewater Treatment Facilities with Anaerobic Digestion and
without CHP 8
Table 5: Prime Mover Performance Specifications for Use in Technical Potential Model 10
Table 6: Electric and Thermal Energy Potential with CHP for Typically Sized Digester 11
Table 7: CHP Technical Potential at Wastewater Treatment Facilities in the United States 12
Table 8: Potential Carbon Dioxide Emissions Displaced with CHP at Wastewater Treatment
Facilities 13
Table 9: Thermal Energy Requirements for Anaerobic Digesters by Climate Zone 17
Table 10: Installed Cost Data Points for Anaerobic Digester Gas CHP Systems 19
Table 11: Prime Mover Price and Performance Specifications for Use in Economic Potential
Model 20
Table 12: Estimated Cost to Generate Anaerobic Digester Gas Electricity (Case 1 - No Natural
Gas Purchases Displaced) 21
Table 13: Estimated Cost to Generate Anaerobic Digester Gas Electricity (Case 2 - CHP Heat
Displaces Natural Gas Space Heating) 22
Table 14: Estimated Cost to Generate Anaerobic Digester Gas Electricity (Case 3 - CHP Heat
Displaces Natural Gas for Both Digester and Space Heating) 23
Table 15: Economic Potential of U. S. Wastewater Treatment Facilities (Scenario 1 - Most
Facilities Do Not Utilize Digester Gas Prior to CHP) 25
Table 16: Economic Potential of U.S. Wastewater Treatment Facilities (Scenario 2 - All Facilities
Use Digester Gas to Heat Digester Prior to CHP) 26
Table 17: Wastewater Treatment Facilities Interviewed 29
Table 18: Interview Results -Drivers and Benefits 31
Table 19: Interview Results - Challenges 35
Table 20: Interview Results - Operational Insights 39
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List of Figures
Figure 1: Map of Five U.S. Climate Zones by State 16
Figure 2: Thermal Energy Requirements for Anaerobic Digesters by Heating Degree Days 17
Figure 3: Wastewater Treatment Facilities with Anaerobic Digesters - Number of Sites with
Economic Potential (Scenario 2) 26
Figure 4: Economic Potential by Wastewater Treatment Facility Size (Scenario 2) 27
in
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EXECUTIVE SUMMARY
Purpose of Report
This report presents the opportunities for combined heat and power (CHP) applications in the
municipal wastewater treatment sector, and it documents the experiences of wastewater
treatment facility (WWTF) operators who have employed CHP. It is intended to be used by CHP
project developers; WWTF operators; state and local government policymakers; and other
parties interested in exploring the opportunities, benefits, and challenges of CHP at WWTFs.
Key Findings
• CHP is a reliable, cost-effective option for WWTFs that have, or are planning to install,
anaerobic digesters.
The biogas flow from the digester can be used as fuel to generate electricity and heat in a
CHP system using a variety of prime movers, such as reciprocating engines,
microturbines, or fuel cells. The thermal energy produced by the CHP system is then
typically used to meet digester heat loads and for space heating. A well-designed CHP
system using biogas offers many benefits for WWTFs because it:
— Produces power at a cost below retail electricity.
— Displaces purchased fuels for thermal needs.
— May qualify as a renewable fuel source under state renewable portfolio standards and
utility green power programs.
— Enhances power reliability for the plant.
— Produces more useful energy than if the WWTF were to use biogas solely to meet
digester heat loads.
— Reduces emissions of greenhouse gases and other air pollutants, primarily by
displacing utility grid power.
• While many WWTFs have implemented CHP, the potential still exists to use more CHP
based on technical and economic benefits.
As of June 2011, CHP systems using biogas were in place at 104 WWTFs, representing
190 megawatts (MW) of capacity. CHP is technically feasible at 1,351 additional sites
and economically attractive (i.e., payback of seven years or less) at between 257 and 662
of those sites.1
• The CHP technical potential is based on the following engineering rules of thumb:
— A typical WWTF processes 100 gallons per day of wastewater for every person
served2, and approximately 1.0 cubic foot (ft3) of digester gas can be produced by an
anaerobic digester per person per day.3
A range is presented due to uncertainties in the data available for WWTFs, making it difficult to support a single,
national economic potential.
2 Great Lakes-Upper Mississippi Board of State and Provincial Public Health and Environmental Managers,
"Recommended Standards for Wastewater Facilities (Ten-State Standards)," 2004.
3 Metcalf & Eddy, "Wastewater Engineering: Treatment and Reuse, 4th Edition," 2003.
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— The composition of anaerobic digester gas from WWTFs is usually 60 to 70 percent
methane with the remainder primarily carbon dioxide (CO2). The lower heating value
(LHV) of digester gas ranges from 550 to 650 British thermal units (Btu)/ft3, and the
higher heating value (HHV) ranges from 610 to 715 Btu/ft3, or about 10 percent
greater than the LHV.4
• Each million gallons per day (MGD) of wastewater flow can produce enough biogas in an
anaerobic digester to produce 26 kilowatts (kW) of electric capacity and 2.4 million Btu per
day (MMBtu/day) of thermal energy in a CHP system.
• The cost to generate electricity using CHP at WWTFs ranges from 1.1 to 8.3 cents per
kilowatt-hour (kWh) depending on the CHP prime mover and other factors.
Current retail electric rates range from 3.9 to over 21 cents per kWh, so CHP can have
clear economic benefits for WWTFs.
• On a national scale, the technical potential for additional CHP at WWTFs is over 400 MW of
biogas-based electricity generating capacity and approximately 38,000 MMBtu/day of
thermal energy.
This capacity could prevent approximately 3 million metric tons of carbon dioxide
emissions annually, equivalent to the emissions of approximately 596,000 passenger
vehicles.
• Also on a national scale, the economic potential ranges from 178 to 260 MW. This represents
43 to 63 percent of the technical potential.5 The vast majority of economic potential comes
from large (>30 MGD) WWTFs that can support larger CHP units.
• Translating CHP potential into actual successes requires an understanding of operational
realities. This report includes interviews of 14 owners/operators of CHP systems at WWTFs
across the country. Key operational observations from these interviews are included in
Section 5.
4 Metcalf & Eddy, "Wastewater Engineering: Treatment and Reuse, ^Edition," 2003. A fuel's LHV does not
include the heat of the water of vaporization.
5 A range is presented due to uncertainties in the data available for WWTFs, making it difficult to support a single,
national economic potential. Economic potential is defined as a payback period of seven years or less.
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1.0 Introduction
In April 2007, the U.S. Environmental Protection Agency's (EPA's) Combined Heat and Power
Partnership (CHPP) released its first report identifying the opportunities for and benefits of
combined heat and power (CHP) at wastewater treatment facilities (WWTFs).6 The primary
purpose of the 2007 report was to provide basic information for assessing the potential technical
fit for CHP at certain WWTFs—specifically, those with influent flow rates greater than 5 million
gallons per day (MGD) that have anaerobic digesters. The 2007 report showed that these larger
facilities produce enough biogas from anaerobic digestion, based on typical practices, to fuel a
CHP system. The report also provided basic information on the cost to generate power and heat
at WWTFs with CHP.
Since the release of the 2007 report, CHPP Partners and other stakeholders have expressed
increased interest in CHP at WWTFs and several additional reports on CHP at WWTFs have
been released.7 This updated report has been prepared in response to the increased interest. The
primary purposes of this update (which is intended to replace the 2007 report) are to:
• Expand the evaluation of technical and economic potential for CHP to include smaller
WWTFs with influent flow rates of 1 to 5 MGD.
• Present operational observations obtained through interviews with WWTF operators who
have employed CHP.
The updated report is intended to be used by CHP project developers; WWTF operators; federal,
state, and local government policymakers; and other parties who are interested in exploring the
opportunities, benefits, and challenges of CHP at WWTFs. The report is organized accordingly:
• Section 2 provides an overview of CHP and its benefits at WWTFs.
• Section 3 describes the existing CHP capacity at WWTFs and the potential market for
additional CHP at WWTFs.
• Section 4 analyzes the technical and economic potential for CHP at WWTFs, presenting
analyses of electric and thermal energy generation potential at WWTFs, as well as cost-
to-generate estimates under three digester gas utilization cases.
• Section 5 presents first-hand observations gathered through interviews of WWTF
operators regarding the benefits and challenges of CHP development and operation.
• Appendix, A lists the data sources and types of data used in the analysis.
• Appendix B provides anaerobic digester design criteria used in the technical potential
analysis.
• Appendix C presents analysis of the space heating capability of CHP at WWTFs.
6 The 2007 report was titled, "The Opportunities for and Benefits of Combined Heat and Power at Wastewater
Treatment Facilities."
7 Recent reports pertaining to CHP at WWTFs include:
• Brown & Caldwell, "Evaluation of Combined Heat and Power Technologies for Wastewater Treatment
Facilities," December 2010. Available at: http://water.epa. gov/scitech/wastetech/publications.cfm.
• Association of State Energy Research & Technology Transfer Institutions, "Strategic CHP Deployment
Assistance for Wastewater Treatment Facilities," October 2009. Available at:
http://www.asertti.org/wastewater/index.html.
• California Energy Commission, "Combined Heat and Power Potential at California's Wastewater
Treatment Plants," September 2009. Available at: http://www.energy.ca.gov/2009publications/CEC-200-
2009-014/CEC-200-2009-014-SF.PDF.
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• Appendix D presents the cost to generate by state for CHP at WWTFs under the three
digester gas utilization cases presented in the economic potential analysis.
• Appendix E lists additional resources available from the CHPP and other organizations.
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2.0 CHP and Its Benefits at Wastewater Treatment Facilities
CHP is the simultaneous production of electricity and heat from a single fuel source, such as
natural gas, biomass, biogas, coal, or oil. CHP is not a single technology, but an energy system
that can be modified depending on the needs of the energy end user. CHP systems consist of a
number of individual components configured into an integrated whole. These components
include the prime mover, generator, heat recovery equipment, and electrical interconnection. The
prime mover that drives the overall system typically identifies the CHP system. Prime movers
for CHP systems include reciprocating engines, combustion turbines, steam turbines,
microturbines, and fuel cells.8
CHP plays an important role in meeting U.S. energy needs as well as in reducing the
environmental impact of power generation. Regardless of sector or application, CHP benefits
include:
• Efficiency benefits. CHP requires less fuel than separate heat and power generation to
produce a given energy output. CHP also avoids transmission and distribution losses that
occur when electricity travels over power lines from central generating units.
• Reliability benefits. CHP can provide high-quality electricity and thermal energy to a
site regardless of what might occur on the power grid, decreasing the impact of outages
and improving power quality for sensitive equipment.
• Environmental benefits. Because less fuel is burned to produce each unit of energy
output, CHP reduces emissions of greenhouse gases and other air pollutants.
• Economic benefits. CHP can save facilities considerable money on their energy bills due
to its high efficiency, and it can provide a hedge against unstable energy costs.
CHP has been successfully implemented in many different sectors, including WWTFs. CHP at
WWTFs can take several forms, including anaerobic digester gas-fueled CHP; non-biogas fueled
CHP (e.g., natural gas); heat recovery from a sludge incinerator that can drive an organic rankine
cycle system; and a combined heat and mechanical power system (e.g., an engine-driven pump
or blower with heat recovery).
The analysis presented in this report is based on CHP fueled by anaerobic digester gas (biogas),
and it focuses on WWTFs that already have, or are planning to install, anaerobic digesters.
Biogas produced by anaerobic digesters can be used as fuel in various prime movers—typically
reciprocating engines, microturbines, and fuel cells—to generate heat and power in a CHP
system. The electric power produced can offset all or most of a WWTF's power demand, and the
thermal energy produced by the CHP system can be used to meet digester heat loads and, in
some cases, for space heating.
It should be noted that CHP is one of several beneficial uses of biogas generated by WWTF
anaerobic digesters, and each WWTF must assess its own site-specific technical, economic, and
environmental considerations to determine the best use of its biogas. Other, non-CHP uses of
biogas include:
• Digester gas for heat. WWTFs can use digester gas in a boiler to provide digester
heating and/or provide space heating for buildings on site.
Information about CHP prime movers, including cost and performance characteristics, can be found in the
''Catalog of CHP Technologies." Available at: http://www.epa.gov/chp^asic/catalog.html.
3
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• Digester gas purification to pipeline quality. WWTFs can market and sell properly
treated and pressurized biogas to the local natural gas utility.
• Direct biogas sale to industrial user or electric power producer. WWTFs can treat,
deliver, and sell biogas to a local industrial user or power producer where it can be
converted to heat and/or power.
• Biogas to vehicle fuel. WWTFs can treat and compress biogas on site to produce
methane of a quality suitable for use as fleet vehicle fuel.
A well-designed CFtP system using biogas offers many benefits for WWTFs because it:
• Produces power at a cost below retail electricity.
• Displaces purchased fuels for thermal needs.
• May qualify as a renewable fuel source under state renewable portfolio standards and
utility green power programs.
• Enhances power reliability for the plant.
• Produces more useful energy than if the WWTF were to use biogas solely to meet
digester heat loads.
• Reduces emissions of greenhouse gases and other air pollutants, primarily by displacing
utility grid power.
The benefits of CFtP deployment at WWTFs are in addition to those provided by anaerobic
digesters. The typical benefits of anaerobic digesters at WWTFs include enhanced biosolids
management; reduced odors; lower fugitive methane emissions; and additional revenue sources
such as soil fertilizers that can be produced from digester effluent.
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3.0 The Market
This section characterizes the market for CHP at WWTFs. It first presents information about
WWTFs that currently utilize CHP, and then discusses the CHP market potential at WWTFs,
focusing on WWTFs that do not currently utilize CHP but that have anaerobic digesters.
For economic reasons, WWTFs that already operate anaerobic digesters9, or those planning to
implement anaerobic digestion, present the best opportunity for CHP; therefore, the analysis in
this report focuses on WWTFs that have anaerobic digesters. The incorporation of anaerobic
digesters into the wastewater treatment process is typically driven by factors other than power
and heat generation (e.g., enhanced biosolids management or odor control). However, once in
place, anaerobic digesters produce digester gas—or biogas— which is key to CHP feasibility at
WWTFs. Biogas is approximately 60 to 70 percent methane, and can be used to fuel a CHP
system to produce electricity and useful thermal energy. The electricity generated can offset all
or most of a WWTF's electric power demand, and the recovered thermal energy can be used to
meet digester heating loads and facility space heating requirements. However, at this time most
biogas is used to heat digesters or is flared.10
3.1 Wastewater Treatment Facilities with CHP
As of June 2011, wastewater treatment CHP systems were in place at 133 sites in 30 states,
representing 437 megawatts (MW) of capacity.11 Although the majority of facilities with CHP
use digester gas as the primary fuel source, some employ CHP using fuels other than digester
biogas (e.g., natural gas, fuel oil) because they either do not operate anaerobic digesters (so do
not generate biogas), or because biogas is not a viable option due to site-specific technical or
economic conditions. Of the 133 WWTFs using CHP, 104 facilities (78 percent), representing
190 MW of capacity, utilize digester gas as the primary fuel source.12 Table 1 shows the number
of sites and capacity (MW) by state that use digester gas as the primary fuel source for CHP.
9 Anaerobic digestion is a biological process in which biodegradable organic matter is broken down by bacteria in
the absence of oxygen into biogas consisting of methane (CH4), carbon dioxide (CO2), and trace amounts of other
gases.
10 Brown and Caldwell,"Evaluation of Combined Heat and Power Technologies for Wastewater Treatment
Facilities,"December 2010. Available at: http://water.epa.gov/scitech/wastetech/publications.cfm.
11 CHP Installation Database, maintained by ICF International with support from the U.S. Department of Energy and
Oak Ridge National Laboratory. Available at: http://www.eea-inc.com/chpdata/index.html.
12 Some WWTFs blend biogas with natural gas if the volume of biogas from the digesters is not sufficient to meet a
facility's thermal and/or electric requirements (e.g., in the winter when digester heat loads are higher).
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Table 1: Number of Digester Gas Wastewater CHP Systems and Total Capacity by State
State
AR
AZ
CA
CO
CT
FL
IA
ID
IL
IN
MA
MD
Ml
MN
Number
of Sites
1
1
33
2
2
3
2
2
2
1
1
2
1
4
Capacity
(MW)
1.73
0.29
62.67
7.07
0.95
13.50
3.40
0.45
4.58
0.13
18.00
3.33
0.06
7.19
State
MT
NE
NH
NJ
NY
OH
OR
PA
TX
UT
WA
Wl
WY
Total
Number
of Sites
3
3
1
4
6
3
10
3
1
2
5
5
1
104
Capacity
(MW)
1.09
5.40
0.37
8.72
3.01
16.29
6.42
1.99
4.20
2.65
14.18
2.02
0.03
189.8
Source: CHP Installation Database, ICF, June 2011
Table 1 shows that the states with the greatest number of CHP systems utilizing biogas are
California (33), Oregon (10), New York (6), Washington (5), Wisconsin (5), Minnesota (4), and
New Jersey (4). States with the greatest capacity are California (62.67 MW), Ohio (16.29 MW),
Washington (14.18 MW), Florida (13.50 MW), and New Jersey (8.72 MW). These states include
eight of the top 15 largest U.S. cities and six of the 15 most populous U.S. states, and therefore,
tend to support the largest treatment facilities where CHP is most economically beneficial.
Several of these states offer CFtP incentives as well and tend to have higher retail electric rates,
which can make CJTP more attractive economically.
Several types of CHP prime movers can be used to generate electricity and heat at WWTFs.
Table 2 shows the CFIP prime movers currently used at WWTFs that use digester gas as the
primary fuel source.
Table 2: Number of Sites and Capacity (MW) by CHP Prime Movers
13
Prime Mover
Reciprocating engine
Microturbine
Fuel cell
Combustion turbine
Steam turbine
Combined cycle
Total
Number
of Sites
54
29
13
5
1
1
104
Capacity
(MW)
85.8
5.2
7.9
39.9
23.0
28.0
189.8
Source: CHP Installation Database, ICF, June 2011
The most commonly used prime movers at WWTFs are reciprocating engines, microturbines,
and fuel cells. The power capacities of these prime movers most closely match the energy
content of biogas generated by digesters at typically sized WWTFs. Opportunities for using
Information about CHP prime movers, including cost and performance characteristics, can be found in the
"Catalog of CHP Technologies." Available at: http://www.epa.gov/chp^asic/catalog.html.
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combustion turbines, steam turbines, and combined cycle systems are typically found in the few
very large WWTFs (i.e., greater than 100 MOD).
3.2 Potential CHP Market
To estimate the potential market for CHP at WWTFs, the CHPP used the EPA 2008 Clean
Watershed Needs Survey (CWNS) database14 to identify WWTFs that do not already operate
CFIP. As the database was configured to provide a comprehensive assessment of capital needs to
meet water quality goals established under the Clean Water Act, the primary indicators used for
the CHPP's analysis were the number of facilities with anaerobic digestion and the total influent
flow rate to those facilities. The database collection process is voluntary and the data vary in
level of completeness. Since the CHPP 2007 report was released, there have been other state-
specific data sets that have become available. However, the uniform data collection method
applied to the CWNS database introduces a consistency in the data collection methodology. It is
also at this time the primary comprehensive dataset on municipal wastewater treatment activity
at a national scale. These two criteria rendered the data more representative for the CHPP's
national analysis.15
The CHPP's 2007 report about CHP at WWTFs showed that influent flow rates of 5 MOD or
greater were typically required to produce biogas in quantities sufficient for economically
feasible CHP systems. One of the CHPP's goals for this 2011 study, however, was to be
inclusive of all market opportunities for CHP at WWTFs. Recognizing that CHP systems can
and do operate at facilities with influent flow rates less than 5 MOD, this 2011 analysis uses a
lower limit of 1 MGD. Some smaller WWTFs (i.e., between 1 and 5 MGD) can produce
sufficient biogas through conventional means (if biosolid loadings are high enough), or augment
their digestion process to boost the biogas generation rate of the anaerobic digesters (e.g.,
addition of collected fats, oils, and greases to digesters; use of microbial stimulants).
Table 3 presents the total number of WWTFs in the United States and the number with anaerobic
digestion, excluding WWTFs that already utilize CHP. Table 4 shows the wastewater flow to
WWTFs with anaerobic digestion, also excluding those that utilize CHP. Table 3 shows that
1,351 WWTFs greater than 1 MGD utilize anaerobic digesters but do not operate CHP systems.
The data indicate that systems with larger flow rates are more likely to have anaerobic digesters,
and therefore have greater potential for CHP. This finding is corroborated by the data in Table 4,
which indicate that for WWTFs greater than 1 MGD that do not employ CHP, approximately 60
percent of wastewater flow goes to facilities with anaerobic digestion.
14 EPA's Office of Wastewater Management, in partnership with states, territories, and the District of Columbia,
conducts the CWNS every four years in response to Sections 205(a) and 516 of the Clean Water Act and develops a
Report to Congress. The 2008 CWNS is available at: http://water.epa. gov/scitech/datait/databases/cwns/.
15 Water Environment Foundation's Project on the "Preparation of Baseline of the Current and Potential Use of
Biogas from Anaerobic Digestion at Wastewater Plants" was initiated in August 2011 to create a robust consensus
dataset regarding the current and potential production of biogas from anaerobic digestion at Publicly Owned
Treatment Works (POTW) in the United States. EPA is serving on the Advisory Panel for this project, but is not
responsible for its content.
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Table 3: Number of U.S. Wastewater Treatment Facilities with Anaerobic Digestion
and without CHP
WWTFs Flow
Rate Range
(MGD)
>200
100-200
75-100
50-75
20-50
10-20
5-10
1-5
Total
Total
WWTFs
10
18
25
24
137
244
451
2,262
3,171
WWTFs with
Anaerobic
Digestion
7
13
17
17
82
140
230
845
1,351
Percentage of WWTFs
with Anaerobic
Digestion
70%
72%
68%
71%
60%
57%
51%
37%
43%
Source: OWNS, 2008
Table 4: Wastewater Flow to U.S. Wastewater Treatment Facilities with Anaerobic
Digestion and without CHP
WWTFs Flow
Rate Range
(MGD)
>200
100-200
75-100
50-75
20-50
10-20
5-10
1-5
Total
Total Wastewater
Flow (MGD)
3,950
2,705
2,172
1,471
4,133
3,407
3,188
5,124
26,150
Wastewater Flow to
WWTFs with Anaerobic
Digestion (MGD)
3,010
2,076
1,469
1,078
2,491
1,959
1,630
2,082
15,795
Percentage of Flow to
WWTFs with Anaerobic
Digestion
76%
77%
68%
73%
60%
57%
51%
41%
60%
Source: OWNS, 2008
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4.0 Technical and Economic Potential
This section presents the technical and economic potential for CHP at WWTFs. The analyses
focus on WWTFs that operate anaerobic digesters. In the technical potential subsection, this
report presents an estimate of CFIP electric capacity and thermal generation based on WWTF
influent flow. Owners and operators of WWTFs can compare their influent flow to this estimate
to approximate the CHP system size that may be possible at their facility. The economic
potential subsection presents cost-to-generate estimates for various CFIP prime movers under
several digester gas utilization cases. Owners and operators of WWTFs can compare these cost-
to-generate estimates to current electricity rates to determine whether CHP might make sense at
their facility. In addition, the report provides national estimates of both technical and economic
potential based on 2008 CWNS data, as well as an estimate for potential carbon dioxide (CO2)
emissions reductions associated with meeting the national technical potential. The technical and
economic estimates presented in this section serve as indicators of CHP potential at WWTFs, but
every WWTF considering CHP will need to complete its own site-specific technical and
economic analysis to assess the viability of CHP.
4.1 Technical Potential for CHP at Wastewater Treatment Facilities
Section 4.1.1 discusses the assumptions and methodology used in the technical potential
analysis. Section 4.1.2 presents the relationship between influent flow and electric and thermal
generation potential with CHP. Section 4.1.3 presents the national technical potential estimate
for CHP at WWTFs. Section 4.1.4 presents the potential carbon dioxide emissions benefits
associated with meeting the national technical CHP potential.
4.1.1 Methodology
To determine the electric and thermal energy generation technical potential for CHP at WWTFs,
the analysis modeled the fuel produced and heating required by a typically sized digester. The
following assumptions were used to develop the model:
• Digester type. There are two types of conventional anaerobic digestion
processes—mesophilic and thermophilic—and they are distinguished by the temperature
at which they operate. Most anaerobic digesters operate at mesophilic temperatures
between 95 and 100°F. Thermophilic digesters operate at temperatures between 124 and
138°F. The thermophilic process is usually faster due to the higher operating temperature
but is usually more expensive because of higher energy demands.16 Because most
digesters in operation today are mesophilic, the analysis presented here assumes the use
of a mesophilic digester.
• Flow rate. The digester model used in the analysis has an influent flow rate of 9.1 MGD,
which is based on the sludge capacity of a typically sized digester. A wastewater flow
rate of 9.1 MGD produces roughly 91,000 standard cubic feet (ft3) of biogas per day,
which has an energy content of 58.9 million British thermal units per day
(MMBtu/day).17
16 Metcalf & Eddy, "Wastewater Engineering: Treatment and Reuse, 4th Edition," 2003.
17 Biogas generation was calculated based on 100 gallons of wastewater flow per day per capita (Great Lakes-Upper
Mississippi Board of State and Provincial Public Health and Environmental Managers, "Recommended Standards
9
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• Season of operation. The analysis models both summer and winter digester operation.
Appendix B contains the digester design criteria used for the analysis.
The analysis estimates the biogas utilization of the model digester under five possible cases:
• The first case assumes no CHP system, where only the amount of biogas needed for the
digester heat load is utilized and the rest is flared.
• The other four cases assume that a CHP system utilizes the captured biogas to produce
both electricity and thermal energy. The cases differ based on the CHP prime mover
utilized.
The CHP prime movers chosen for analysis are consistent with those currently used at WWTFs
(see Table 2 in Section 3.1).18 The four modeled CHP prime movers include two reciprocating
engines (one rich-burn and one lean-burn),19 a microturbine, and a fuel cell. The analysis uses the
performance characteristics (i.e., electric efficiency and power-to-heat ratio) of commercially
available equipment, as stated by the manufacturers. To develop estimates of electric and thermal
output, the analysis applies CHP prime mover performance characteristics to the produced
biogas (58.9 MMBtu/day). Table 5 presents the performance specifications of the CHP prime
movers used to develop the technical potential estimate.
Table 5: Prime Mover Performance Specifications for Use in Technical Potential Model
Prime Mover
Reciprocating
Engine (Rich-
Burn)
Reciprocating
Engine (Lean-
Burn)
Microturbine
Fuel Cell
Size (kW)
280
335
260
(4 x 65)
300
Thermal
Output
(Btu/kWh)
5,520
3,980
3,860
2,690
Power to
Heat Ratio
0.62
0.86
0.88
1.26
Electric
Efficiency
(%) (HHV)
29.1
32.6
26.0
42.3
CHP
Efficiency
(%) (HHV)
76
71
56
76
4.1.2 Electric and Thermal Generation Potential from CHP Systems at Wastewater
Treatment Facilities
Table 6 presents the results of the modeled CHP systems. The results represent an average of
winter and summer digester operation. The fuel cell CHP system has the highest electric capacity
for Wastewater Facilities (Ten-State Standards)," 2004), and approximately 1.0 cubic foot per day of digester gas
per capita (Metcalf & Eddy, "Wastewater Engineering: Treatment and Reuse, 4th Edition," 2003).
18 Although the prime mover specifications are taken from typical equipment available in the marketplace,
manufacturer names have been removed to avoid implicitly endorsing any manufacturers or products.
19 Rich-burn engines are characterized by higher fuel-to-air-ratios, whereas lean-burn engines have lower fuel-to-air-
ratios. Lean-burn engines have lower exhaust emissions and achieve higher fuel efficiency due to more complete
fuel combustion. Most of the engines installed at WWTFs today are rich-burn, but these are gradually being phased
out in favor of lean-burn engines with higher efficiencies and lower emissions.
10
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of the modeled systems (304 kilowatts [kW]) due to its high electric efficiency. In many cases,
however, the use of fuel cells at WWTFs is limited because of their high cost and challenges
associated with pre-treating biogas before it can be used in a fuel cell. The two most commonly
used CHP prime movers at WWTFs—reciprocating engines and microturbines— have electric
capacities of 187 to 234 kW and produce 17 to 28 MMBtu of thermal energy based on a flow
rate of 9.1 MOD.
Table 6: Electric and Thermal Energy Potential with CHP for Typically Sized Digester
Total WWTF Flow (MGD)
Heat Requirement for Sludge
(Btu/day)
Wall Heat Transfer (Btu/day)
Floor Heat Transfer (Btu/day)
Roof Heat Transfer (Btu/day)
Total Digester Heat Load
(Btu/day)
Fuel Required for Digester Heat
Load* (Btu/day) (HHV)
Energy Potential of Gas (Btu/day)
(HHV)
% of Gas Used for Digester Heat
Load (Btu/day)
Excess Digester Gas** (Btu/day)
Electric Efficiency (HHV)
Power-to-Heat Ratio
Total CHP Efficiency (HHV)
Electric Production (Btu/day)
Electric Production (kW)
Heat Recovery (Btu/day)
Digester Heat Load (Btu/day)
Additional Heat Available***
(Btu/day)
No CHP
System
9.1
6,693,375
591,725
1,109,484
741,013
9,135,597
11,419,496
58,901,700
19.4%
47,482,204
Reciprocating
Engine CHP/
Rich-Burn
9.1
6,693,375
591,725
1,109,484
741,013
9,135,597
58,901,700
29.1%
0.62
76%
17,140,395
209
27,645,798
9,135,597
18,510,201
Reciprocating
Engine CHP/
Lean-Burn
9.1
6,693,375
591,725
1,109,484
741,013
9,135,597
58,901,700
32.6%
0.86
71%
19,201,954
234
22,327,854
9,135,597
13,192,257
Microturbine
CHP
9.1
6,693,375
591,725
1,109,484
741,013
9,135,597
58,901,700
26.0%
0.88
56%
15,314,442
187
17,402,775
9,135,597
8,267,178
Fuel Cell CHP
9.1
6,693,375
591,725
1,109,484
741,013
9,135,597
58,901,700
42.3%
1.26
76%
24,915,419
304
19,774,142
9,135,597
10,638,545
Note: Analysis assumes 50 percent summer and 50 percent winter digester operation.
*Assumes 80 percent efficient boiler.
"Assumes no other uses except boiler.
"""Available for non-digester heating uses at the facility (e.g., space heating, hot water).
Based on the modeled CHP systems and 9.1 MGD, the analysis developed an engineering rule of
thumb for assessing CHP potential. The analysis shows that 1 MGD of influent flow equates to
26 kW of electric capacity and 2.4 MMBtu/day of thermal energy potential. To develop a
relationship between influent flow rate (i.e., MGD) and CHP capacity, the analysis takes the
average outputs of the four prime movers, yielding the result that an influent flow rate of 9.1
MGD produces 234 kW of electric capacity and approximately 22 MMBtu/day of thermal
energy output. The analysis scaled this result to a per MGD basis to provide a simple relationship
between influent flow and CHP capacity that WWTF operators can use to approximate a CHP
system size at their facilities.
11
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4.1.3 National Electric Generation Potential from CHP at Wastewater Treatment
Facilities
Table 7 summarizes the CHP technical potential at WWTFs in the United States. As shown in
Tables 3 and 4 (see Section 3.2), the 2008 CWNS identified 1,351 WWTFs greater than 1 MOD
that have anaerobic digesters but that do not utilize CHP, representing 15,795 MOD of
wastewater flow. Using the results developed in the technical potential analysis (i.e., 1 MOD of
influent flow can produce 26 kW of electric capacity and 2.4 MMBtu/day of thermal energy),
these 1,351 WWTFs could produce approximately 411 MW of electric capacity and 37,908
MMBtu/day of thermal energy if they all installed and operated CHP.
Table 7: CHP Technical Potential at Wastewater Treatment Facilities in the United States
Facility Type
WWTFs with anaerobic digestion
and no CHP (>1 MGD)
Number of
WWTFs
1,351
Wastewater
Flow (MGD)
15,795
Electric Potential
(MW)*
411
Thermal Potential
(MMBtu/day)*
37,908
*Electric and thermal potential estimates assume that 26 kW of electric capacity and 2.4 MMBtu/day result from a wastewater
influent flow rate of 1 MGD.
Note: An additional 269 MW of electric capacity and 24,852 MMBtu/day of thermal energy is possible at WWTFs greater than 1
MGD that do not currently operate anaerobic digesters. However, as stated earlier, power and heat generation is typically not a
primary driver for installing and operating anaerobic digesters, and because it is unlikely that all these WWTFs will install
anaerobic digesters, this potential is unlikely to be achieved.
4.1.4 Potential Carbon Dioxide Emissions Benefits
As described in Section 4.1.3, 411 MW of CHP technical potential exists at WWTFs that operate
anaerobic digesters. This subsection presents an estimate of the CC>2 emissions that would be
prevented if this potential were to be achieved.
The following assumptions were used to develop the estimate of CC>2 emissions prevented by
CHP at WWTFs with anaerobic digesters:
• Prior to CHP development, WWTFs purchase electricity from the grid and use biogas
from the digesters in on-site boilers to meet digester heat loads and space heating needs,
and flare any excess biogas. (CC>2 emissions reductions therefore arise from displaced
grid electricity only.)
• CC>2 emissions from biogas combustion are emitted regardless of whether or not CHP is
employed, and therefore biogas combustion with CHP yields no net positive CC>2
emissions.
• All of the electricity produced is utilized on site and excess power is not exported to the
grid.
• The CHP system operates year-round.
Since all of the estimated CC>2 emissions reductions are associated with displaced grid-supplied
electricity, the key determinant for estimating total emissions reductions is a grid-based CC>2
emissions factor. The analysis uses the 2010 Emissions & Generation Resource Integrated
12
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Database (eGRID)20 to obtain this factor. eGRID data include total mass emissions and
emissions rates for nitrogen oxides, sulfur dioxide, CC>2, methane, and nitrous oxide; net
generation; and resource mix associated with U.S. electricity generation. This analysis uses the
national all-fossil average CC>2 emissions factor (1,744.81 Ib CCVmegawatt-hour [MWh]
produced), because it most closely approximates the generation mix that is displaced by CHP.21
eGRID CC>2 emissions factors relate pollutant emissions to the amount of electricity generated
and not the amount of electricity delivered. Based on the assumption that all of the electricity
generated by the CHP system is used on site at the WWTF, the eGRID factor is adjusted to
account for transmission and distribution (T&D) losses associated with displaced grid electricity,
since these losses do not occur with CHP. According to eGRID, the U.S. average T&D line loss
percentage is 6.2 percent, meaning that 1 MWh produced results in 0.938 MWh delivered. As a
result, the adjusted all-fossil average CC>2 emission factor is 1,860.14 Ib CO2/MWh delivered.
Multiplying the adjusted CC>2 grid emissions factor by the electric potential estimate yields
avoided CC>2 emissions of 3,040,726 metric tons per year, which is equivalent to the emissions
from 596,052 passenger vehicles.22 Table 8 presents these results.
Table 8: Potential Carbon Dioxide Emissions Displaced with CHP at Wastewater
Treatment Facilities
Input/Output
Electric potential at WWTFs with
anaerobic digesters
Total annual electric production
(assumes year-round operation)
Adjusted all-fossil average C02
emissions factor
Total displaced C02 emissions
Equivalent number of passenger
vehicles
Value
411 MW
3,602,826 MWh
1,860.1 4 lbC02/MWh
3,350,880 tons CCWyear
or
3,040,726 metric tons CCWyear
596,052
4.2 Economic Potential for CHP at Wastewater Treatment Facilities
Section 4.2.1 describes the assumptions and methodology used in the economic potential
analysis. Section 4.2.2 presents a discussion of the heating requirements of WWTFs and
develops estimates for the thermal energy requirements of anaerobic digesters. Section 4.2.3
presents the cost-to-generate estimates for each of the digester gas utilization cases. Section 4.2.4
presents an estimate of national economic potential based on 2008 CWNS data and the cost-to-
generate results.
20 eGRID is the most comprehensive source of data on the environmental characteristics of electricity generated in
the United States. Available at: http://www.epa.gov/cleanenergv/energv-resources/egrid/index.html.
21 For more information on the use and value of eGRID emission data, see
http://www.epa.gov/cleanenergy/documents/egridzips/The Value of eGRID Dec 2009.pdf.
22 Equivalent passenger vehicles are calculated using the EPA Greenhouse Gas Equivalencies Calculator. Available
at: http://www.epa.gov/cleanenergv/energy-resources/calculator.html.
13
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4.2.1 Methodology
To determine the economic potential for CHP at WWTFs, the analysis developed estimates of
the cost to generate electricity on site using digester gas for three digester gas utilization cases.
The following assumptions were used to develop cost-to-generate estimates:
• Digester gas utilization cases. Three cases of different uses of digester gas were
considered in order to evaluate the thermal credit associated with CHP.23 (The thermal
credit represents the avoided fuel costs achieved through CHP heat recovery on a per
kWh basis.)
o Case 1: Assumes digester gas is used for both digester heating and space heating
prior to CHP implementation.
o Case 2: Assumes digester gas is used for digester heating only prior to CHP
implementation and natural gas is used for space heating.
o Case 3: Assumes digester gas is not used for heating, and natural gas is used for
digester and space heating prior to CHP implementation.
Research conducted for this analysis indicates that Case 2 is the most frequent practice
prior to CHP implementation.24'25'26 It is much less common to use digester gas to meet
both digester and space heating needs, or to not use it at all. The cost-to-generate analysis
evaluates all three cases, however, to provide a comprehensive examination of all
possible digester gas utilization options and the benefits of using CHP thermal output.
• Thermal credit. For all thermal credits, the analysis uses the 2010 national average
industrial gas price of $5.40 per thousand cubic feet.27
• WWTFplant size. The plant sizes selected for the analysis are representative of the range
of facility sizes that are applying CHP.
• CHP prime mover. The CHP prime movers chosen for analysis are consistent with those
currently used at WWTFs (see Table 2, Section 3.1). Systems are assumed to be available
95 percent of the time, with 5 percent downtime for maintenance and repairs. For systems
using combustion turbines, however, availability is estimated at 98 percent, based on
Solar Turbines data.
• CHP prime mover size. CHP prime mover size is based on the relationship between
wastewater influent flow and CHP electric capacity as derived in the technical potential
analysis (see Section 4.1), which shows that 1 MGD of flow can produce 26 kW of
electric capacity in a CHP system.
23 The CHPP's 2007 report evaluated these same three cases, with Case 3 providing the highest thermal value
because the CHP thermal output displaces natural gas purchases, and Case 1 providing the lowest thermal value
because the CHP thermal output does not displace any purchased fuel.
24 Fishman, Bullard, Vogt and Lundin, "Beneficial Use of Digester Gas - Seasonal and Lifecycle Cost
Considerations," 2009.
25 Brown and Caldwell (prepared for Town of Fairhaven, Massachusetts, Board of Public Works), "Anaerobic
Digestion and Combined Heat and Power Feasibility Study," December 19, 2008.
26 SEA Consultants, "City of Pittsfield Feasibility Study, Wastewater Treatment Plant," April 2008.
27 Energy Information Administration, Form EIA-857, "Monthly Report of Natural Gas Purchases and Deliveries to
Consumers," Washington, D.C.
14
-------
• Interest rate and project lifespan. The analysis assumes a 5 percent interest rate and a 20-
year lifespan.
The analysis calculates the cost to generate electricity under each of the three digester gas
utilization cases using the thermal energy requirement for anaerobic digesters28 (Table 9) and
CHP prime mover price and performance specifications (Table 11).
4.2.2 Heating Requirements of Wastewater Treatment Facilities
A critical characteristic of any economic CHP application is to use as much CHP thermal output
as possible. For WWTFs, recovered thermal energy from CHP can be used for digester heating
and space heating. This subsection presents a discussion of the heating requirements of WWTFs
and develops estimates of the thermal energy requirements for anaerobic digesters used in the
CHP cost-to-generate estimates. It also presents the results of an analysis of how much CHP
thermal output can be utilized to meet space heating requirements at WWTFs.
Thermal Energy Requirements for Anaerobic Digesters
Climate is the most important factor determining digester heating requirements. When ambient
air and sludge temperatures are low, it takes more energy to heat the digesters. The United States
can be divided into five different climate zones29 based on cooling and heating degree days:
Zone 1 - Cold climate with more than 7,000 heating degree days
Zone 2 - Cold/moderate climate with 5,500 to 7,000 heating degree days
Zone 3 - Moderate/mixed climate with 4,000 to 5,500 heating degree days
Zone 4 - Warm/hot climate with fewer than 4,000 heating degree days and fewer than
2,000 cooling degree days
Zone 5 - Hot climate with fewer than 4,000 heating degree days and more than 2,000
cooling degree days
Figure 1 shows the five U.S. climate zones by state. (States that span more than one zone are
assigned to the zone that covers most of the state.)
Greater thermal energy requirements for anaerobic digesters means that there is less CHP recovered heat available
to displace purchased natural gas for space heating loads, resulting in a smaller thermal credit.
29 U.S. Energy Information Administration, Commercial Buildings Energy Consumption Survey, Washington, DC,
2003.
15
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Figure 1: Map of Five U.S. Climate Zones by State
Recent feasibility studies and technical papers for various anaerobic digester gas projects were
examined to determine how digester heating requirements correlate to climate (see Figure 2).
These feasibility analyses and technical papers assessed digester gas projects in the following
locations: Georgia (Zone 5), North Carolina (Zone 4), Oregon (Zone 3), Massachusetts (Zone 2),
and Maine (Zone 1). Using these locations, the analysis determined the minimum and maximum
energy requirements in terms of heating degree days. In each case, the average energy required
each day (MMBtu/day) was divided by the size of the WWTF, as measured in MOD.
With minimum and maximum bounds for the energy requirements, the average value for
MMBtu/day/MGD was determined. This was accomplished by first plotting the data points and
constructing parallel lines that roughly intersect the two highest and the two lowest data points.
These two lines represent the maximum and minimum heating requirements. The average
heating requirement line was developed by adding a line that divides equally the area between
these two lines. Figure 2 shows the data points used, along with the minimum, maximum, and
average values, according to heating degree days. Table 9 presents the minimum, maximum, and
average values in tabular form. In each case, the average energy required each day (MMBtu/day)
was divided by the size of the WWTF, as measured in MGD. The average values for each zone
were used in the cost-to-generate analysis.
16
-------
Figure 2: Thermal Energy Requirements for Anaerobic Digesters by Heating Degree Days
3.5
Q
(3
2.5
« 2
Q.
ra
•D
5" 1.5-=
00 A
MAX
0.5
Dalles, OR
-Gap-eTear, NC
Pittsfield, MA
Atlanta, GA
Fairhaven, MA ,-^~~". ,
_ „ - - • Auburn,
ME
IN
Zones 4 & 5
Zone 3
Zone 2
Zone 1
1000 2000 3000 4000 5000
Heating Degree Days
6000
7000
8000
Sources:
Atlanta, GA: Hardy, Scott A., AWE A Annual Conference 2011, "Achieving Economic and Environmental
Sustainability Objectives through On-Site Energy Production from Digester Gas," April 11, 2011.
Auburn, ME: CDM, Lewiston Auburn Water Pollution Control Authority, "Maine: Anaerobic Digestion
and Energy Recovery Project, Conceptual Design Report," October 2009.
Cape Fear, NC: Fishman, Bullard, Vogt and Lundin, "Beneficial Use of Digester Gas - Seasonal and
Lifecycle Cost Considerations," 2009.
Dalles, OR: Carollo, "The Dalles Wastewater Treatment Plant Cogeneration Feasibility Study," September
2009.
Fairhaven, MA: Brown and Caldwell (prepared for Town of Fairhaven, Massachusetts, Board of Public
Works), "Anaerobic Digestion and Combined Heat and Power Feasibility Study," December 19, 2008.
Pittsfield, MA: SEA Consultants, "Feasibility Study - Wastewater Treatment Plant: City of Pittsfield,"
April 2008.
Table 9: Thermal Energy Requirements for Anaerobic Digesters by Climate Zone
Climate Zone
Zone 1 (Cold)
Zone 2 (Moderate/Cold)
Zone 3 (Moderate/Mixed)
Zone 4 (Warm/Hot)
Zone 5 (Hot)
Average MMBtu/day/MGD
Minimum
1.8
1.6
1.4
1.2
1.0
Maximum
3.7
3.4
3.0
2.8
2.6
Average
2.8
2.5
2.3
2.0
1.8
Space Heating Capability of CUP at Wastewater Treatment Facilities
In addition to estimating the thermal energy requirements for anaerobic digesters, the analysis
also developed estimates of how much CHP thermal output is available for space heating after
17
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digester heating requirements are met. The estimates of surplus thermal output for space heating
were taken into consideration when developing the value of the thermal credit used in the cost-
to-generate analysis.
The analysis revealed that a substantial amount of surplus heat for space heating is available only
in warm and hot climates, where demand for space heating is minimal, except in cold winter
months. In these warm and hot climates, up to 25 percent of the CHP thermal output is available
for space heating. In cold climates, where more energy is required to heat the digester, surplus
thermal energy for space heating is generally not available. In these cooler climates, the analysis
estimated that less than 10 percent of the CHP thermal output is available, and in many cases
there is none left for space heating.
While the data suggest that surplus heat may not be available in colder climates after the digester
heating needs have been met, some facilities in these climates do in fact have surplus heating.
For example, one of the WWTFs interviewed by the CHPP, the town of Lewiston, NY (see
Section 5), has enough thermal output to heat one building in the summer and to meet 95 percent
of that building's winter heating requirement. This discrepancy between estimated and realized
thermal surplus can be attributed to a number of factors:
• Digester heating requirements depend on many different factors, and design and
construction of the digester can influence the heat loss due to factors such as insulation.
• Certain methods for increasing digester gas production can allow for a larger CHP system
and more surplus thermal output for space heating. These methods include mixing of the
contents of the digester tank, or incorporating fats, oils, and greases (FOG) into the
digester.
• WWTFs can also increase the size of the CHP system and incorporate natural gas in their
fuel usage to increase the amount of CHP thermal output available for space heating.
Further details about the analysis of space heating capability of CHP can be found in Appendix
C.
4.2.3 Estimated Cost to Generate Electricity
This subsection presents estimates of the cost to generate electricity with CHP using digester gas
for each of the three digester gas utilization cases. The cost-to-generate calculation involves
calculating the investment cost (CHP system and gas pretreatment equipment) on a per-kWh
generated basis; adding in maintenance costs; and applying a thermal credit, as appropriate, to
derive the full cost per kWh to own and operate a CHP system. WWTF operators can compare
the cost-to-generate estimates to the current retail electric rate that they pay to help them evaluate
if a more detailed analysis of CHP makes sense for their facility.
Based on the results of the analysis, the following observations can be made:
• The cost to generate electricity using CHP at WWTFs ranges from 1.1 to 8.3 cents per
kWh depending on the CHP prime mover and other factors. Current retail electric rates
range from 3.9 to more than 21 cents per kWh, so CHP can have clear economic benefits
for WWTFs.
• Cost to generate tends to decrease as the prime mover increases in size.
18
-------
• The more thermal energy a WWTF can use throughout the year, the lower the cost to
generate.
Table 10 presents installed cost data for digester gas-fueled CHP systems. Gas pretreatment
equipment is typically required for digester gas generators, so these costs are included. Data were
obtained from case studies and feasibility studies for digester gas reciprocating engines,
microturbines, fuel cells, and combustion turbines.
Table 10: Installed Cost Data Points for Anaerobic Digester Gas CHP Systems
Facility Name
Essex Junction Wastewater Treatment Facility1
Lewiston Wastewater Treatment Facility2
Chiquita Water Reclamation Plant1
Albert Lea Wastewater Treatment Facility1
Columbia Blvd. Wastewater Treatment Plant3
Fairfield Wastewater Treatment Facility4
Wildcat Hill2
Vander Haak Dairy Farm3
Gresham Wastewater Treatment Plant5
Janesville Wastewater Treatment Facility1
King County South Treatment Plant6
Salt Lake City Water Reclamation Plant7
Rochester Wastewater Reclamation Plant1
Southside Wastewater Treatment Plant8
Del Rio Wastewater Treatment Plant8
Generic Site9
State
VT
NY
CA
MN
OR
CT
AZ
WA
OR
Wl
WA
UT
NY
TX
TX
USA
Prime Mover
Microturbine
Microturbine
Microturbine
Microturbine
Microturbine
Fuel Cell
Reciprocating
Engine
Reciprocating
Engine
Reciprocating
Engine
Reciprocating
Engine
Fuel Cell
Reciprocating
Engine
Reciprocating
Engine
Combustion
Turbine
Combustion
Turbine
Combustion
Turbine
Size (kW)
60
60
60
120
120
200
292
300
395
400
1,000
1,400
2,000
4,200
4,200
4,910
Total Installed
Cost
$303,000
$300,000
$275,000
$500,000
$346,000
$1,200,000
$1,750,000
$1,200,000
$1,352,000
$910,000
$5,000,000
$3,500,000
$4,000,000
$10,500,000
$9,400,000
$8,758,000
Cost per kW
$5,000
$5,000
$4,600
$4,200
$2,900
$6,000
$6,000
$4,000
$3,400
$2,300
$5,000
$2,500
$2,000
$2,500
$2,200
$1,800
1 Midwest CHP Application Center: RAC Project Profiles, http://www.chpcentermw.orq/15-00 profiles.html
2 Project Interview, 9/14/2010
3 Northwest CHP Application Center: Case Studies, http://chpcenternw.org/ProiectProfilesCaseStudies.aspx
4 Project Interview, 9/22/2010, installation uses natural gas and not digester gas
5 http://files.harc.edu/Sites/GulfCoastCHP/CaseStudies/GreshamORWastewaterServices.pdf
6 Estimate from Greg Bush, King County Project Manager on new MCFC Installation
7 http://www.slcgov.com/utilities/NewsEvents/news2003/news552003.htm
8 Estimate by COM (2005)
9 Estimate by Solar Turbines (2010) for landfill site
Based on data from Table 10:
Microturbine CHP systems range from $3,000/kW to $5,000/kW.
30
1 Microturbine CHP systems can be the most versatile option for smaller (i.e., <10 MOD) WWTFs.
19
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• Reciprocating engine CHP systems in the 300 kW to 1 MW size range typically cost
between $2,500/kW and $4,000/kW. Larger engine systems over 1 MW in size tend to
range from $2,000/kW to $3,000/kW.31
• Combustion turbine CHP systems are generally the least expensive option on a per-kW
basis, ranging between $l,800/kW and $2,800/kW.32
• In general, fuel cell systems are the highest cost option, at $5,000/kW to $6,000/kW,
even for large gensets greater than 1 MW.33
Using the cost data points shown in Table 10, the analysis developed size ranges and costs for
the different prime movers for use in the cost-to-generate estimates. Specifications for the prime
movers, such as maintenance costs, efficiencies, and system availability (used to estimate down
time), were also estimated based on manufacturer data. The results are presented in Table 11.
Table 11: Prime Mover Price and Performance Specifications for Use in Economic
Potential Model
Prime Mover
Small Rich-Burn
Engine
Microturbine
Rich-Burn
Engine
Fuel Cell
Small Lean-
Burn Engine
Lean-Burn
Engine
Combustion
Turbine
Min Size
(kW)
30
30
100
200
300
1,000
4,000
Max Size
(kW)
100
250
300
2,000
900
4,800
16,000
Modeled
Installed Cost
($/kW)
4,500
4,000
3,600
5,500
3,200
2,500
2,100
Maintenance
($/kWh)*
0.03
0.025
0.025
0.03
0.02
0.016
0.012
Thermal
Output
(Btu/kWh)
5,800
3,900
5,500
2,700
4,000
3,400
3,900
Electric
Efficiency
(%)
28
26
29
42
32
38
35
CHP
Efficiency
(%)
76
55
76
76
71
75
75
Note: All equipment and maintenance costs include gas pretreatment. Electric and CHP efficiencies are based on HHV of the
digester gas supplied.
* Maintenance costs for WWTFs using CHP can vary considerably. During the interviews of WWTF operators with CHP
installations (see Section 5), it was found that some facilities have maintenance costs as high as 7 cents per kWh, primarily due
to excessive contaminants in the digester gas leading to very high fuel treatment costs. Other sites were able to keep
maintenance costs down due to cleaner digester gas and ideal maintenance strategies. As a result, the maintenance costs in
Table 11 should be seen as estimates and are not intended to indicate what any individual site will experience.
The analysis used the CHP prime mover price and performance specification data in Table 11
and the thermal energy requirement for anaerobic digesters data in Table 9 to develop cost-to-
generate estimates for CHP at WWTFs. Tables 12 through 14 present the cost-to-generate
estimates for the three digester gas utilization cases:
• Table 12 presents the cost-to-generate results for Case 1. This case assumes the site uses
digester gas in its boiler to provide digester and space heating prior to CHP; therefore, no
31 Some smaller rich-burn engine systems have been employed at smaller WWTFs, but they tend to be costly and do
not offer the benefits of lean-burn technology in this smaller (under 300 kW) size. Rich-burn engines tend to
produce more emissions and have lower electric efficiencies than their lean-burn counterparts, so deployment of
rich-burn engines has declined in recent years as lean-burn engines have been produced at increasingly smaller sizes.
32 Combustion turbines are mostly limited to WWTF applications 4 MW or larger in size.
33 Some states (e.g., Connecticut) offer incentives for fuel cell installations, which can help lower costs.
20
-------
value is given to the thermal output of the CHP because it does not displace any natural
gas purchases. As a result, there is no variation in the value of thermal output by climate
zone, and the cost to generate is estimated to be constant for each climate zone. Of the
three cases modeled, Case 1 results in the highest cost to generate, although in areas with
high retail electric rates, CHP projects can have an acceptable payback period.
• Table 13 presents the cost-to-generate results for Case 2. This case assumes the site uses
digester gas in its boiler to provide digester heating and purchases natural gas for space
heating (when needed) prior to CHP, resulting in a thermal credit for reductions in natural
gas purchases used for space heating. To account for the fact that space heating
requirements are highest during cold winter periods when digester heating loads are also
at their peak, the analysis employed a seasonal digester load factor to adjust for peak
loads.34 For most climate zones and WWTF capacities, the thermal credit was very small
and had minimal impact on the cost to generate. The thermal credit for space heating
results in a lower cost to generate only in warmer climates, where less energy is required
to heat the digester.
• Table 14 presents the cost-to-generate results for Case 3. This case assumes the site uses
natural gas to provide all digester and space heating, resulting in a full thermal credit. In
this case, the thermal credit is much more substantial and reduces the cost to generate by
several cents in all climates for all WWTF sizes as compared to Case 2. The research
conducted for this analysis indicates, however, that Case 3 is atypical and that Case 2
represents the most frequently observed practice.
Appendix D provides state-by-state cost-to-generate estimates for Case 1, Case 2, and Case 3 for
each type of CHP system.
Table 12: Estimated Cost to Generate Anaerobic Digester Gas Electricity (Case 1 - No
Natural Gas Purchases Displaced)
Climate Zone
1-5
(All Zones)
WWTF Plant Size
(MGD)
1-5
5-10
10-20
20-40
40-150
>150
Corresponding
CHP System
Size (kW)
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
Estimated Cost to Generate ($/kWh)
Micro-
turbine
0.064
0.064
0.064
—
—
...
Rich-
Burn
Engine
0.073
0.060
0.060
—
—
...
Fuel
Cell
—
0.083
0.083
0.083
0.083
...
Lean-
Burn
Engine
—
—
0.051
0.051
0.040
0.040
Turbine
—
—
—
—
—
0.032
34 Average digester loads are lower than winter digester loads, and subtracting average digester loads from CHP
thermal output leaves more thermal output for space heating than actually is available during winter period. Using
seasonal loads is necessary to avoid overstating the amount of surplus heat available for space heating, and the size
of the thermal credit. The seasonal digester load factor is the ratio of the winter digester heat load to the average
monthly digester heat load. The seasonal digester load factor chosen for the analysis was 1.36 which is based on data
from the Cape Fear, NC, and Pittsfield, MA, feasibility analyses (these two analyses provided seasonal data whereas
the other analyses cited in Figure 2 did not).
21
-------
Table 13: Estimated Cost to Generate Anaerobic Digester Gas Electricity (Case 2 - CHP
Heat Displaces Natural Gas Space Heating)
Climate Zone
A P«|~|
1 - Gold
2 - Cold/
Moderate
3 - Moderate/
Mixed
4 -Warm/
Hot
5i_i_i
- Hot
WWTF Plant Size
(MGD)
-
5-10
10-20
20-40
40-150
>150
1-5
5-10
10-20
20-40
40-150
>150
1-5
5-10
10-20
20-40
40-150
>150
1-5
5-10
10-20
20-40
40-150
>150
1-5
5-10
10-20
20-40
40-150
>150
Corresponding
CHP System
Size (kW)
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
30-130
130-260
260 - 520
520-1,040
1,040-3,900
>3,900
Estimated Net Cost to Generate ($/kWh)
Micro-
turbine
0.064
0.064
0.064
—
—
0.064
0.064
0.064
—
—
—
0.064
0.064
0.064
—
—
—
0.064
0.064
0.064
—
—
—
0.064
0.064
0.064
—
—
...
Rich-
Burn
Engine
0.073
0.060
0.060
—
—
0.073
0.060
0.060
—
—
—
0.073
0.059
0.059
—
—
—
0.073
0.058
0.058
—
—
—
0.072
0.058
0.058
—
—
...
Fuel
Cell
—
0.083
0.083
0.083
0.083
—
—
0.083
0.083
0.083
0.083
—
—
0.083
0.083
0.083
0.083
—
—
0.083
0.083
0.083
0.083
—
—
0.083
0.083
0.083
0.083
...
Lean-
Burn
Engine
—
0.051
0.051
0.040
0.040
—
—
0.051
0.051
0.040
0.040
—
—
0.051
0.051
0.040
0.040
—
—
0.051
0.051
0.040
0.040
—
—
0.051
0.051
0.040
0.040
Turbine
—
—
—
0.032
—
—
—
—
—
0.032
—
—
—
—
—
0.032
—
—
—
—
0.032
—
—
—
—
—
0.031
22
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Table 14: Estimated Cost to Generate Anaerobic Digester Gas Electricity (Case 3 - CHP
Heat Displaces Natural Gas for Both Digester and Space Heating)
Climate Zone
A P«|~|
1 - Gold
2 - Cold/
Moderate
3 - Moderate/
Mixed
- Warm/Hot
5i_i_i
- Hot
WWTF Plant Size
(MGD)
1-5
5-10
10-20
20-40
40-150
>150
1-5
5-10
10-20
20-40
40-150
>150
1-5
5-10
10-20
20-40
40-150
>150
1-5
5-10
10-20
20-40
40-150
>150
1-5
5-10
10-20
20-40
40-150
>150
Corresponding
CHP System
Size (kW)
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
30-130
130-260
260-520
520-1,040
1,040-3,900
>3,900
Estimated Net Cost to Generate ($/kWh)
Micro-
turbine
0.043
0.043
0.043
—
—
0.043
0.043
0.043
—
—
—
0.043
0.043
0.043
—
—
—
0.043
0.043
0.043
—
—
—
0.045
0.045
0.045
—
—
...
Rich-
Burn
Engine
0.044
0.035
0.035
—
—
0.047
0.037
0.037
—
—
—
0.050
0.039
0.039
—
—
—
0.052
0.040
0.040
—
—
—
0.053
0.042
0.042
—
—
...
Fuel
Cell
—
0.068
0.068
0.068
0.068
—
—
0.068
0.068
0.068
0.068
—
—
0.068
0.068
0.068
0.068
—
—
0.068
0.068
0.068
0.068
—
—
0.068
0.068
0.068
0.068
...
Lean-
Burn
Engine
—
0.029
0.029
0.022
0.022
—
—
0.029
0.029
0.022
0.022
—
—
0.030
0.030
0.022
0.022
—
—
0.033
0.033
0.022
0.022
—
—
0.034
0.034
0.024
0.024
Turbine
—
—
—
0.011
—
—
—
—
—
0.011
—
—
—
—
—
0.012
—
—
—
—
0.014
—
—
—
—
—
0.016
23
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4.2.4 National Economic Potential Scenarios
Using the cost-to-generate results presented in the previous subsection and the 2008 CWNS data,
national economic potential estimates were developed. Two scenarios were evaluated due to
uncertainties in 2008 CWNS data:
• Scenario 1: Most Facilities Do Not Use Digester Gas Prior to CHP. This scenario
assumes that the 2008 CWNS data on how WWTFs use their digester gas are completely
accurate, meaning that most WWTFs with anaerobic digesters do not use their biogas in
any way. As mentioned in Section 3.2, however, there are limitations to using CWNS
data, and the CWNS finding that biogas is used minimally is inconsistent with research
and interviews conducted as part of this report.
• Scenario 2: All Facilities Use Digester Gas to Heat Digester Prior to CHP. This
scenario assumes that the research conducted in preparing this report is correct, and that
most WWTFs use their digester gas to heat the digester. For the purposes of the analysis,
Scenario 2 assumes that all WWTFs use their digester gas to heat the digester only and
use natural gas for any additional space heating needs prior to CHP implementation.
For both scenarios, the analysis estimates the national economic potential by estimating the
simple payback period for each WWTF and summing all CHP system sizes (MW) that have a
payback period of seven years or less. The analysis was done for each WWTF in the United
States greater than 1 MOD that has an anaerobic digester but does not have CHP installed.
Payback period was determined by dividing the total capital investment for CHP by the total
annual savings achieved through CHP use.35
The results show an economic potential range for CHP of 178 to 260 MW at WWTFs greater
than 1 MGD with anaerobic digesters, with Scenario 1 providing an upper bound and Scenario 2
the lower bound.
Details concerning each of the scenario analyses are discussed below.
Scenario 1: Most Facilities Do Not Use Digester Gas Prior to CHP
Scenario 1 assumes that the 2008 CWNS data are completely accurate, indicating that most
WWTFs with anaerobic digesters do not use their biogas in any way. Based on research and
through the facility interviews conducted as part of this report, however, the authors believe that
most WWTFs use at least some of their digester gas. The CWNS data suggest otherwise—that
1,148 of the 1,351 facilities evaluated do not use their digester gas. As a result of this
discrepancy, the analysis of the CWNS is presented here as a scenario of what the economic
potential could be if the CWNS data were fully accurate, and the scenario is meant to serve as an
upper bound of CHP economic potential.
35 Total annual cost savings were calculated by adding the annual electric and natural gas bill savings and
subtracting the annual maintenance costs. Annual electric bill savings were derived from annual CHP electrical
output multiplied by state average industrial electricity prices from 2010 (EIA). Annual natural gas bill savings were
estimated using the thermal credit calculation described in Section 4.2.3 on cost to generate that were based on
annual avoided gas purchases for each potential project, using 2010 state industrial natural gas prices (EIA). Annual
maintenance costs were derived from the maintenance costs as shown in Table 12, multiplied by the CHP annual
electric output.
24
-------
Table 15 presents the number of WWTFs and the total capacity for each digester gas utilization
case, with an estimated payback period of less than seven years (see Section 4.2.1 for an
explanation of the three digester gas utilization cases).
Table 15: Economic Potential of U. S. Wastewater Treatment Facilities (Scenario 1 - Most
Facilities Do Not Utilize Digester Gas Prior to CHP)
Digester Gas Utilization
Case Prior to CHP
Case 1 : Digester Gas Used
for both Digester Heating
and Space Heating
Case 2: Digester Gas Used
for Digester Heating Only
Case 3: Digester Gas Not
Used
WWTFs
Analyzed
Those Utilizing Digester Gas
(not for CHP)
Those Utilizing Digester Gas
(not for CHP)
Those Not Utilizing Digester
Gas
Total
Number of Facilities
Evaluated
203
203
1,148
1,351
Facilities with
Economic
Potential
88
\J\J
88
574
662
Potential
Capacity (MW)
74
74
186
260
The analysis revealed no difference in economic potential between Case 1 (i.e., no natural gas
purchases displaced) and Case 2 (i.e., CHP heat displaces natural gas space heating). This is
because most of the heat recovered from CHP units is required for digester heating, leaving little
(if any) thermal output for space heating, For Case 3 (i.e., CHP heat displaces natural gas for
both digester and space heating), full thermal credit is given for recovered CHP heat, assuming
that natural gas is used to heat the digester and provide space heating prior to CHP.
Scenario 1 shows economically feasible CHP potential at 662 WWTFs across the country, with a
national potential capacity of 260 MW. Since Case 1 and Case 2 draw from the same pool of
WWTFs (i.e., those that are currently using their digester gas), their potentials are not additive.
The estimated economic potential of 260 MW represents approximately 63 percent of the 411
MW of national technical potential presented in Section 4.1.3.
Scenario 2: All Facilities Use Digester Gas to Heat Digester
Scenario 2 assumes that all of the WWTFs larger than 1 MGD that do not already employ CHP
use their digester gas for heating the digester and use natural gas for any additional space heating
needs prior to CHP implementation; therefore, all facilities evaluated under this scenario fall
under Case 2 (i.e., using digester gas to heat only the digester prior to CHP implementation). As
mentioned previously, Case 2 is the most common situation for a WWTF that has not already
implemented CHP.
Table 16 presents the number of WWTFs with economic potential and the total capacity under
Scenario 2.
25
-------
Table 16: Economic Potential of U.S. Wastewater Treatment Facilities (Scenario 2 - All
Facilities Use Digester Gas to Heat Digester Prior to CHP)
Digester Gas Utilization
Case Prior to CHP
Case 2: Digester Gas Heats
Digester
WWTFs Analyzed
Those with Digesters
>1 MW not using CHP
Total
Number of
Facilities in Data
Pool
1,351
1,351
Facilities with
Economic
Potential
257
257
Potential Capacity
(MW)
178
178
Scenario 2 shows economic CHP potential at 257 sites across the country, with a national
potential capacity of 178 MW. The estimated economic potential of 178 MW represents
approximately 43 percent of the 411 MW of national technical potential presented in Section
4.1.3. These data are graphically presented in Figure 3 below.
Figure 3: Wastewater Treatment Facilities with Anaerobic Digesters - Number of Sites
with Economic Potential (Scenario 2)
104 Sites with
CHP Already
Installed
257 Sites with
Economic
Potential
1,094 Sites
with No
Current
Economic
Potential
Under Scenario 2, the vast majority of potential comes from large WWTFs (i.e., >30 MOD) that
can support larger CHP units. At smaller facilities using digester gas for digester heating prior to
CHP implementation, it is difficult to support CHP unless the facility is located in an area with
extremely high electricity prices, or the facility is willing to accept a longer payback period.
Figure 4 shows economic potential broken down by WWTF size.
26
-------
Figure 4: Economic Potential by Wastewater Treatment Facility Size (Scenario 2)
160
140-
1-10 MGD
10-20 MGD 20-30 MGD
WWTF Size Range
>30MGD
27
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5.0 Wastewater Treatment Facility Interviews: CHP Benefits, Challenges, and
Operational Insights
The previous sections of this report demonstrate that there is both technical and economic
potential for increased CHP use at WWTFs in the United States. Translating potential into actual
successes, however, requires an understanding of operational realities. This section builds on the
previous sections by presenting operational experiences from WWTFs that have already
implemented CHP. To assess operational experiences with CHP at WWTFs, interviews of a
number of WWTFs that utilize CHP were conducted. The focus of these conversations was to
gain a better understanding of their decision to utilize CHP, the benefits they have realized from
CHP to date, and the challenges/barriers of operating and maintaining CHP systems. Much of the
information obtained through the interviews affirms common elements reported in other recent
studies on CHP at WWTFs,36 but new operational insights were also discovered.
This section first provides an overview of the WWTFs interviewed by the CHPP and explains
how they were chosen. It also provides descriptions of the interview format used and the
questions asked. Subsequent subsections summarize the information obtained through the
interviews and are organized by:
• Drivers for installing CHP and operational benefits
• Challenges to CHP project development and operation/maintenance (O&M)
• Operational insights and observations
5.1 Wastewater Treatment Facilities Interviewed and Interview Format
When selecting WWTFs to interview, the objective was to build a representative pool of
WWTFs so that the results were indicative of the sector. WWTFs selected to be interviewed,
therefore, represent operational, geographical, and technological diversity. Thirty WWTFs were
initially identified, and 14 were ultimately interviewed. Table 17 provides a summary of the 14
WWTFs interviewed.
Of the 14 CHP systems represented, the prime mover breakdown matches closely with what is
seen in the marketplace (see Table 2, Section 3.1), with nine operating reciprocating engines,
four operating microturbines, and one operating a fuel cell system. CHP system sizes range from
60 kW to 3.075 MW, and WWTF flow capacities range from 2 MOD to 75 MOD. The earliest
CHP system was installed in 1987 and the most recent in 2009. The 14 WWTFs are also located
across the country, with four operating in the East, one operating in the Southeast, five operating
in the Midwest, and four operating in the West.
36 Association of State Energy Research & Technology Transfer Institutions, "Strategic CHP Deployment
Assistance for Wastewater Treatment Facilities," October 2009. Available at:
http://www.asertti.org/wastewater/index.html: Brown & Caldwell, "Evaluation of Combined Heat and Power
Technologies for Wastewater Treatment Facilities," December 2010. Available at:
http://water.epa.gov/scitech/wastetech/publications.cfm.
28
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Table 17: Wastewater Treatment Facilities Interviewed
Wastewater Treatment
Facility Name
Albert Lea Wastewater
Treatment Plant
Allentown Wastewater
Treatment Plant
Bergen County Utilities
Authority
Chippewa Falls Wastewater
Treatment Plant
City of Great Falls
Wastewater Treatment Plant
City of Santa Maria
Wastewater Treatment Plant
Columbia Boulevard
Wastewater Treatment Plant
Des Moines Metro
Wastewater Reclamation
Facility
Fairfield Water Pollution
Control Authority
Fourche Creek Treatment
Plant
Rock River Water
Reclamation Plant
Theresa Street Wastewater
Treatment Facility
Town of Lewiston Water
Pollution Control Center
Wildcat Hill Wastewater
Treatment Plant
Location
Albert Lea, MN
Allentown, PA
Little Ferry, NJ
Chippewa Falls, Wl
Great Falls, MT
Santa Maria, CA
Portland, OR
Des Moines, IA
Fairfield, CT
Little Rock, AR
Rockford, IL
Lincoln, NE
Lewiston, NY
Flagstaff, AZ
Average Flow
Rate (MGD)
5.0
31.0
75.0
2.0
21.0
7.8
60.0
70.0
9.0
15.0
31.0
19.5
2.0
3.5
CHP Prime
Mover
Microturbine
Microturbine
Reciprocating
Engine
Microturbine
Reciprocating
Engine
Reciprocating
Engine
Reciprocating
Engine
Reciprocating
Engine
Fuel Cell (Natural
Gas)
Reciprocating
Engine
Reciprocating
Engine
Reciprocating
Engine
Microturbine
Reciprocating
Engine
CHP
Capacity
(MW)
0.120
0.360
2.812
0.060
0.540
0.300
1.700
1.800
0.200
1.100
3.075
0.900
0.060
0.292
CHP
Installation
Date
2004
2001
2008
2003
2008
2009
2008
1987
2005
2009
2004
1992
2001
2008
Phone interviews were conducted with the facility operators over a two-month period in August
and September 2010. The interviews were conducted in an unstructured format and sought to
gain information on specific CHP drivers, benefits, and challenges/barriers. The interviews
covered the following operational areas:
• The key operational characteristics of the CHP system (e.g., prime mover type and heat
recovery equipment; heat recovery use; CHP sizing relative to facility demand; biogas
treatment method; system start-up date).
• The key drivers for installing CHP.
• Degree of local support the WWTF received in installing the CHP system.
• Whether the WWTF received financial incentives for the CHP system, and if incentives
were critical to project viability.
• The primary challenges and barriers encountered with CHP development and operation,
and how they were overcome.
• The WWTF's experience working with the local utility.
• The benefits achieved to date, and the benefits the WWTF expects to achieve in the
future.
• Going forward, whether the WWTF would consider CHP as part of any anticipated
facility expansions; if not, what would make a difference in considering CHP.
• Lessons the WWTF can impart to other facilities considering CHP.
29
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5.2 Drivers and Benefits
WWTFs can experience efficiency, reliability, environmental, and economic benefits with CHP.
Table 18 presents the primary drivers and benefits reported by the WWTFs, which specifically
include the following:
• Energy cost savings
• Federal, state, local, and utility incentives
• Energy/sustainability plans and emissions reductions
• Enhanced reliability
• Facility upgrades
• Increased biogas production
• Enhanced biosolid management
• "Green" publicity/positive public relations
• Utility load shedding
The interview results clearly show strong benefits from operating CFtP at WWTFs and suggest
that CFIP is a proven method of utilizing digester gas to both produce and conserve energy.
30
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Table 18: Interview Results - Drivers and Benefits
Driver/Benefit
Summary
Examples
Energy Cost Savings
Each WWTF interviewed utilizes their biogas in
a CHP system to displace electricity and/or fuel
for digester heat loads that they would otherwise
have to purchase, leading to significant energy
cost savings for the facility. Some facilities said
they use the savings generated from CHP to
invest in other infrastructure upgrades needed
at the facility, and some of the facilities
mentioned that the use of CHP makes them
more conscious of the energy they use,
resulting in additional projects that improve
energy efficiency and reduce costs. Several
facilities also noted the desire to hedge against
possible energy price increases as a driver for
CHP.
The 120 kW microturbine CHP system at Albert Lea Wastewater Treatment Plant
generates approximately $100,000 in annual energy savings. Approximately 70 percent
of the savings derives from reduced electricity and fuel purchases and 30 percent from
reduced maintenance costs. The facility noted that CHP made the facility more
conscious of its energy use, leading to a number of other energy-efficiency
improvements, which resulted in further cost savings.
The 1.7 MW reciprocating engine CHP system at the Columbia Boulevard Wastewater
Treatment Plant operates at an overall efficiency of 82 percent and generates
approximately $700,000 in annual energy savings. The system offsets approximately 40
percent of the facility's electric power demand.
The 900 kW reciprocating engine CHP system at Theresa Street Wastewater Treatment
Facility generates $50,000 to $100,000 in annual energy savings out of an operational
budget of $4.5 million.
The 3.075 MW reciprocating engine CHP system at the Rock River Water Reclamation
Plant saves the facility approximately 50 percent on its energy bill, an annual savings of
approximately $250,000.
The business case for CHP clearly drove CHP installation for the Santa Maria
Wastewater Treatment Plant. Prior to installing its 300 kW reciprocating engine CHP
system, the facility was paying 13 to 15 cents per kWh, but with CHP, the facility is now
only paying the equivalent of 8 cents per kWh.37
The 1.8 MW reciprocating engine CHP system at the Des Moines Metro Wastewater
Reclamation Facility has reduced the electrical bill by $500,000/year since 2002.
Federal, State, Local, and
Utility Incentives38
A number of the facilities interviewed received
financial incentives that helped pay for the cost
of installing CHP, with some describing the
incentives as a key component to project
viability. Incentive examples include government
grants or payments for the "green" attributes of
power generated at WWTFs using biogas, and
utility programs targeted at expanding clean
energy or energy efficiency. In addition, some
facilities can sell excess power to the grid
through power purchase agreements, which has
enhanced CHP project economics at those
sites.
Fairfield Water Pollution Control Authority cited availability of public funding as a key
driver for installing their 200 kW fuel cell CHP system. Their system is fueled with
natural gas; the site previously had biogas-fueled microturbines but had challenges with
gas treatment. The facility received $880,000 in funding from the Connecticut Clean
Energy Fund, approximately two-thirds of the total $1.2 million CHP system cost.
For the Town of Lewiston Water Pollution Control Center, state and utility funding
provided 100 percent of the $300,000 project cost of the 60 kW microturbine CHP
system.
Allentown Wastewater Treatment Plant developed its 360 kW microturbine CHP system
under a Master Energy Savings agreement with its local utility. Under the arrangement,
installation of the system was funded through a 10-year lease/purchase agreement, and
an O&M agreement with the utility provides for fixed O&M costs (with an escalator)
through 2014. In exchange, the facility receives guaranteed energy savings achieved
The costs of purchasing backup power when the CHP system is down have made the total costs about the same as prior to CHP, but this has been attributed to
the contract with the third party not covering expected hours of operation or backup charges.
38 National and state level incentives applicable to CHP and biogas can be found in the CHPP Funding Database (http://www.epa.gov/chp/funding/funding.html)
and the Database of State Incentives for Renewable Energy (DSIRE) (http://www.dsireusa.org/).
31
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Driver/Benefit
Summary
Examples
through the operation of the CHP system and other Energy Conservation Measures
constructed throughout the plant. The arrangement was a direct result of the
Guaranteed Energy Savings Act passed by the Pennsylvania legislature.
Albert Lea Wastewater Treatment Plant developed its CHP system through an
innovative relationship with its local utility. Under the agreement, the utility helped pay
for the CHP system and agreed to maintain it for the first five years of operation. In
exchange, the utility received clean energy credits for use under Minnesota's
Conservation Improvement Program.
The Columbia Boulevard Wastewater Treatment Plant took advantage of the Oregon
Business Energy Tax Credit and received money from the Oregon Energy Trust in
exchange for the clean energy credits generated from the CHP system. The Business
Energy Tax Credit provided 33.5 percent of the total CHP system cost. Although the
WWTF is not a tax-paying entity, the tax credit rules allow public entities to sell the
credit to entities that are subject to state tax.
Energy/Sustainability
Plans and Emissions
Reductions
Many states, localities, and facilities have
implemented energy and sustainability plans
aimed at increasing energy efficiency and clean
sources of energy. Several facilities noted that
CHP at their WWTF was a driver for helping to
meet a state/local/facility sustainability plan. In
addition, some of the facilities noted that, as
environmental organizations, their goal is to
enhance the health and welfare of their
communities. These facilities see CHP as a
means to help further fulfill this goal because of
CHP's ability to displace grid-based electricity
with clean, renewably fueled electricity-
decreasing emissions of pollutants such as
nitrogen oxide, sulfur dioxide, and C02.
The Wildcat Hill Wastewater Treatment Plant, the Great Falls Wastewater Treatment
Plant, the Des Moines Metro Wastewater Reclamation Facility, and the Bergen County
Utilities Authority cited sustainability plans as a driver/benefit of CHP installation. Both
the Wildcat Hill and Great Falls facilities cited sustainability plans as the primary driver
for CHP installation.
The Columbia Boulevard Wastewater Treatment Plant's CHP system helps the city of
Portland meet its sustainability plan, but the plan was not a driver for the CHP
installation. The facility is considering expanding the CHP system, however, and sees
the city's sustainability plan as a driver for the expansion.
Prior to CHP installation, the Allentown Wastewater Treatment Plant fired a small
portion of its biogas in boilers for heat, flared the remaining biogas, and purchased all of
its electricity. The facility cited the desire to reduce C02 emissions associated with
purchased electricity to be more in line with its environmental mission as a driver for
CHP installation.
Enhanced Reliability
If interconnected in a way that also allows grid-
independent operation, CHP systems can
enable WWTFs to sustain operations in case of
a grid outage. Some facilities stated that the
ability to operate independently from the grid
was a key driver for CHP. Most of the facilities,
however, said they are designed to shut down
when the grid goes down, to satisfy local utility
requirements.
The Rock River Reclamation Plant first installed a 2 MW reciprocating engine CHP
system in mid-2004. In the spring of 2010, the facility expanded the CHP system to
include three reciprocating engines with a total capacity of 3.075 MW. The main driver
cited for the CHP system upgrade was the desire to fully meet the facility's electric
demand on site, allowing the facility to operate independently from the grid if needed.
The facility has a total electric demand of 2.2 MW, and with the new CHP system, the
facility has plenty of excess capacity. In addition to having the ability to operate
independently from the grid, the facility's excess capacity also enables it to take one
engine off line at a time for maintenance while still maintaining the ability to fully meet
the facility's electric demand.
Facility Upgrades
A portion of the facilities incorporated CHP as
part of a scheduled facility equipment and
process upgrade. Some of these facilities
operated CHP for a number of years and noted
In 1988, the Des Moines Metro Wastewater Reclamation Facility underwent a complete
facility redesign, which included installing anaerobic digesters and a 1.8 MW
reciprocating engine CHP system. In 1997, the facility started to experiment with taking
industrial waste and fats, oils, and greases (FOG) to boost biogas production, and
~32
-------
Driver/Benefit
Summary
Examples
that the scheduled facility upgrade allowed them
to install a newer CHP system that would help
simplify O&M, increase system reliability, and
offer increased efficiencies.
today, approximately 70 percent of the biogas produced at the facility is derived from
hauled waste. The facility plans to take in additional hauled waste and is upgrading its
anaerobic digesters to accommodate the increased load. To take advantage of the
resulting increased biogas production, the facility plans to install four additional
reciprocating engines, two of which will be incorporated with the CHP system. The other
two will be used as standby power.
Increased Biogas
Production
Some facilities noted that they are taking on
additional waste streams that will boost their
biogas production, and CHP was a natural fit to
capitalize on the increased fuel availability.
Additional waste streams include wastes from
other nearby treatment facilities, additional
industrial wastes, or FOG.
The Des Moines Metro Wastewater Reclamation Facility noted that it is upgrading its
anaerobic digesters to handle additional hauled wastes, and that expanding its existing
CHP system will give the facility the ability to make efficient use of the increased biogas
generation.
Little Rock, Arkansas, currently has a program in place for pretreatment of FOG to
which participants must adhere. The Fourche Creek Treatment Plant is interested in
how it might adapt one of its existing digesters to handle FOG, which is a possibility for
future expansion. The facility would consider CHP expansion to handle any increases in
biogas generation.
Enhanced Biosolid
Management
Once the decision was made to incorporate
anaerobic digesters into the treatment process,
all facilities recognized that utilizing the resulting
biogas in a CHP system made sense. Treating
biosolids in anaerobic digesters reduces biosolid
mass, decreasing the burdens associated with
drying biosolids on site and/or shipping them to
landfills, while also producing biogas that can be
used to generate power and heat on site.
The Theresa Street Wastewater Treatment Facility described keeping raw sludge out of
landfills through better biosolids management as a key driver for installing anaerobic
digesters on site. With the digesters in place, CHP allowed the facility to generate clean
power and heat with the resulting biogas.
"Green" Publicity/Positive
Public Relations
A couple of facilities noted that the "green"
attributes of CHP at WWTFs (i.e., increased
efficiency and reduced emissions through the
use of renewable biogas), and the myriad other
benefits offered by CHP, generated public
interest and positive awareness for the facility.
Although not a driver for initial installation,
WWTFs see the positive response from the
public as a benefit and a driver for continued
operation.
Both the Allentown Wastewater Treatment Plant and the Columbia Boulevard
Wastewater Treatment Plant reported that their CHP systems were very well received
by their communities and generated a lot of positive buzz.
Utility Load Shedding
On-site generation of power at WWTFs can help
utilities that operate in constrained areas shed
load rather than invest in new generation
infrastructure or add additional burden to
existing transmission and distribution systems.
The Fairfield Water Pollution Control Authority noted that its CHP system not only helps
the local utility avoid installing new capacity, but also enables the facility to avoid the
premium price paid for electricity during high demand periods. The Fairfield facility is
located in Southwestern Connecticut, a highly constrained electric area.
33
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5.3 Challenges
Despite the benefits associated with CHP, there are several key challenges to CHP development
and operation, regardless of sector or application. These include regulated fees and tariffs,
interconnection issues, environmental permitting, and technical barriers. All of the WWTFs
interviewed noted these as challenges to CHP development and operation to some degree, but
also reported others specific to CHP operation at WWTFs, including:
• Staff education/training with CHP
• Gas pretreatment
• Utility issues
• Lack of adequate biosolid supply
• Permitting issues
Although not discussed in detail by the interviewed WWTFs, it should also be noted that
obtaining the capital needed for a CHP system at a WWTF can pose a significant challenge for a
WWTF and should not be overlooked. There are also specific challenges associated with
utilizing biogas beyond gas pretreatment. A more detailed investigation of biogas utilization
challenges is currently being undertaken by the Water Environment Research Foundation
(WERF) in a report titled, "Barrier to Biogas Utilization Survey" (WERF Project Number
OWSO11C10).
The interviewed WWTFs all successfully implemented CHP, so all challenges encountered were
overcome in various ways, though they were not insignificant. Table 19 presents the key
challenges reported by the interviewed WWTFs along with relevant examples. A key finding is
that WWTFs need to recognize that CHP is a separate function beyond traditional wastewater
treatment, and therefore, it is important to dedicate O&M staff time or contract with a third party
to operate and maintain the CHP system.
34
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Table 19: Interview Results - Challenges
Challenge
Summary
Examples
Staff Education/Training
with CHP
Most facilities interviewed identified the training
of staff in O&M of CHP and its components
(e.g., gensets, heat recovery, gas pretreatment,
anaerobic digesters) as a key challenge to CHP
implementation. These facilities noted that on-
site energy production was a new experience for
them, and the process of transitioning from a
wastewater treatment-only facility to one that
also produces on-site power and heat was a
hurdle for staff to overcome. Some facilities,
however, entered into O&M contracts with
service providers, so they did not have to take
on the responsibility of training/hiring staff.
Some also required CHP equipment
manufacturers to provide the requisite training.
The Rock River Water Reclamation Plant stated that it had to overcome the process of
transitioning from a wastewater treatment-only utility to one that also generated power
and heat. This process required the training of its staff, which it did by hiring an
engineering firm. The CHP system requires at least a half-time employee equivalent,
which the facility absorbed into its existing staff.
Under the arrangement between Albert Lea Wastewater Treatment Plant and its local
utility, the local utility installed, maintained, and operated the CHP system for five years;
2010 was the first year in which the facility operated and maintained the CHP system
itself. The facility noted that the five years of O&M provided by the local utility essentially
constituted an extended training period for the facility's staff.
Under the Master Energy Savings agreement between the Allentown Wastewater
Treatment Plant and its local utility, the facility is paying the local utility a fee to maintain
and operate the CHP system until 2014.
The Des Moines Metro Wastewater Reclamation Facility noted that operating and
maintaining its reciprocating engines has been a challenge. The environment is noisy,
oily, and physically demanding. The facility described the importance of not only training
its staff to maintain and operate the CHP system, but also getting them to take
ownership of the equipment. The facility plans to expand its CHP system in the coming
years and said that it plans to require the engine manufacturer to provide training.
The Columbia Boulevard Wastewater Treatment Plant purchased a maintenance
contract from its engine manufacturer. The bulk of the maintenance for the CHP system
is supplied through this contract, but the facility still relies on staff to help maintain the
system. The biggest challenge reported by the facility is sometimes inadequate
response time under the maintenance contract.
Gas Pretreatment
Many facilities noted that understanding the
importance of gas pretreatment and developing
a gas pretreatment strategy was a key
challenge. Digester gas at WWTFs contains
contaminants such as hydrogen sulfide,
siloxanes, and excess moisture that can impair
CHP equipment if not properly pretreated. Gas
pretreatment is more of a concern for some
CHP prime movers than others (e.g.,
microturbines are more sensitive to
contaminants than some reciprocating engines).
The Chippewa Falls Wastewater Treatment Plant reported biogas conditioning as the
number one challenge to developing its microturbine CHP system. Despite some early
struggles and setbacks getting the conditioning system to work properly, with the help
of an experienced engineering consultant, the facility no longer experiences any
significant gas cleanup issues.
The Great Falls Wastewater Treatment Plant reported dealing with high hydrogen
sulfide levels, which leads to frequent replacement of its iron sponge and considerable
maintenance costs.
The Town of Lewiston Water Pollution Control Center initially had much higher moisture
levels than planned and had to incorporate better moisture removal equipment.
Allentown Wastewater Treatment Plant's CHP system did not initially include a gas
conditioning system, which led to significant downtime. Hydrogen sulfide and siloxanes
in the digester gas damaged the compressors and microturbines. The utility
subsequently installed a gas conditioning system but noted that the facility still
experiences a significant amount of downtime as a result of the lack of redundancy in
35
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Challenge
Summary
Examples
the glycol chiller and digester gas compressor.
Utility Issues
A number of facilities indicated that burdensome
interconnection requirements or high tariff and
standby rates were significant challenges to
developing CHP. Some mentioned that their
utility restricts sales of excess power to the grid,
impairing project economics. However,
opportunities may exist for WWTFs to partner
with their local utility to help move a CHP project
forward.
The Des Moines Metro Wastewater Reclamation Facility stated that working with the
local utility on interconnection was a challenge. It took the facility one to two years to
negotiate an interconnection agreement, creating great expense in terms of both money
and staff time.
The Rock River Water Reclamation Plant reported that working with the local utility on
interconnection was very difficult, time consuming, and expensive. Of note, the facility
stated that the cost of interconnection represented 10 percent of the total cost
associated with CHP implementation.
Fourche Creek Treatment Plant initially experienced problems with grid interruptions. To
remedy this, the facility installed a fiber interlock between the plant and the electric
substation that allows the facility to completely disconnect from the grid when there are
interruptions. This is mainly a safety feature that helps protect the CHP system
equipment and helps to ensure smooth operation of the system.
The Columbia Boulevard Wastewater Treatment Plant experienced resistance from the
local utility concerning selling power back to the utility under a contract. The utility was
not opposed to the facility operating CHP, but it forced the facility to install reverse
power relays to prevent any power export back to the grid. The facility would have
preferred the option of selling excess power.
The Theresa Street Wastewater Treatment Facility did not experience any problems
working with the local utility on interconnection. However, although the facility is able to
sell excess power, it feels it does not receive enough credit for the power it supplies.
The facility buys power at 5.5 cents per kWh but receives only 2.5 cents per kWh for
power sold back to the grid.
The Wildcat Hill Wastewater Treatment Plant ultimately partnered with the local utility to
provide renewable energy credits (RECs) and motivate the utility to help move the
project forward.
Lack of Adequate
Biosolid Supply
Some WWTFs do not treat enough wastewater
to generate sufficient biogas to make CHP
economically feasible. In many cases, this holds
true for facilities with flow rates less than 5
MGD. However, smaller facilities can make CHP
viable by hauling additional waste such as FOG
or taking on industrial waste streams that are
high in biological oxygen demand (BOD)39.
Larger facilities can also expand their
opportunities for CHP by increasing their biogas
generation potential through processing of FOG
or other industrial waste streams.
The Chippewa Falls Wastewater Treatment Plant was one of three facilities interviewed
with an influent flow rate less than 5 MGD. Prior to installing a 60 kW microturbine CHP
system, the facility operated gas-powered blowers with the biogas they produced and
captured the waste heat off the blowers to help meet digester heat loads. Although the
facility only treats an average of 2 MGD, approximately 50 percent of the BOD treated
by the facility comes from a local brewer. This enhanced BOD content allows the facility
to generate enough biogas to power its CHP system.
BOD is the amount of oxygen required by aerobic microorganisms to decompose the organic matter in a sample of water. It is a common measure of the
biosolid loading in wastewater treatment streams and an indicator of biogas generation potential.
36
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Challenge
Summary
Examples
Permitting Issues
A couple of facilities noted that obtaining the
correct permits for their CHP system was
burdensome and time-consuming. Installing on-
site energy production requires facilities to
obtain the necessary permits, which can be a
new challenge for WWTFs, especially if a Title V
Clean Air Act (CM) permit is needed.
The Bergen County Utilities Authority reported that its CHP system required careful
negotiation of changes to their existing Title V CAA permit.
The Des Moines Metro Wastewater Reclamation Facility reported that the installation of
its reciprocating engine CHP system required the facility to obtain a Title V CAA permit.
The process of obtaining a Title V permit was somewhat unfamiliar to the facility, and it
is still learning about all of the issues involved.
37
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5.4 Operational Insights and Observations
Based on the benefits achieved and challenges encountered, several common operational insights
became apparent at the conclusion of the interviews. These insights were considered by all
WWTFs as important to any facility considering CHP. Table 20 presents the key CHP
operational insights gathered from WWTFs across the following topic areas: organizational
acceptance, utility relationship, system design, and O&M.
In general, the insights show that CFIP is an added element to a WWTF, beyond traditional
treatment of wastewater, and that it requires appropriate planning and attention. To this end,
high-level buy-in from facility management is very important to project success. In addition,
WWTFs need to be closely involved with the design of the CUP system, including all of its
components (e.g., fuel pretreatment), and understand how the system operates and its
maintenance requirements.
Coordination with the local utility was also seen as extremely important for developing and
operating a successful CUP system. From the beginning, immediate and continuing coordination
with the utility is needed to ensure that all components of the CHP system are in line with utility
requirements. This process often requires close negotiations over topics such as interconnection,
sale of excess power, and potential changes in utility rates. Several of the WWTFs encountered
utilities unwilling to buy excess power or allow operation independent of the grid. These
restrictions eliminated a potential source of revenue and also one of the primary benefits of CHP,
enhanced reliability of the WWTF's power supply.
38
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Table 20: Interview Results - Operational Insights
Topic
Organizational
Acceptance
Utility Relationship
System Design
Operations and
Maintenance
Key Insights
High-level buy-in for CHP can greatly facilitate project approval. A CHP champion is needed to get the
project off the ground and for continual successful operation.
Aligning the project with community goals for renewable energy/energy efficiency can serve as a great
justification for the project.
Immediate and continuing coordination with the local utility is highly recommended. Issues such as
interconnection, sales of excess power, and potential changes in utility rates all require close
communication with the local utility and can require significant time to resolve.
Identifying opportunities for collaboration or partnership with the local utility can be highly beneficial
(e.g., master energy savings agreement, sale of RECs, other ownership/O&M agreements).
CHP projects require due diligence from design through O&M. It is important for facilities to ensure
that any consultants or project developers hired are fully versed in all aspects of design, installation,
and O&M of CHP systems at WWTFs. WWTFs want to avoid "problem fatigue" that can arise from a
poorly designed system and can lead to system shutdown.
WWTFs should ensure that the fuel treatment and compression systems have been designed to
satisfy the CHP manufacturer specifications. A rigorous gas pretreatment approach is needed for
certain applications— thorough gas analysis and possible gas treatment may be required.
In some cases, blending digester gas with natural gas may help maintain desired heat content and
composition.
WWTFs should familiarize themselves with CHP equipment and processes and see what fits best with
their plant and staff experience. A comprehensive review of leading facilities that operate CHP is a
good idea.
WWTFs should consider outside waste streams and sludge pre-treatment to improve quantity and
quality of digester biogas, but also consider the facility requirements to receive and process these
wastes during the design process.
Specific training for O&M personnel is important for successful operation of a CHP system. Having
staff that is well trained regarding mechanical and electrical equipment is extremely beneficial.
WWTFs should ensure that agreements with CHP developers or suppliers include proper O&M
training.
WWTFs need to recognize that CHP is a separate function beyond traditional wastewater treatment
and should dedicate O&M staff time or contract with a third party to operate and maintain the CHP
system. It takes more effort for a WWTF to operate CHP in addition to typical wastewater treatment
operations.
WWTFs should institute a preventive maintenance schedule instead of reactive maintenance.
WWTFs need to be aware of the maintenance issues related to fuel treatment, including siloxane
deposits on CHP equipment. Improper maintenance will lead to more frequent maintenance intervals.
A comprehensive design/build/operation/maintenance agreement can greatly simplify the process of
installing and operating CHP for WWTFs. Even if the maintenance agreement expires after a certain
number of years, a facility can gain valuable training experience over that time.
39
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Appendix A: Data Sources Used in the Analysis
To develop an overview of the wastewater treatment sector and the potential for CHP, the CHPP
used publicly available information contained in the 2008 CWNS Databases,40 the Combined
Heat and Power Installation Database,41 EPA's 2010 eGRID,42 and U.S. Energy Information
Administration (EIA) electricity and natural gas prices.43 The CHPP also conducted WWTF
interviews and performed independent research. The following describes each type of data used
in the CHPP's analysis.
2008 Clean Watersheds Needs Survey
EPA's Office of Wastewater Management, in partnership with states, territories, and the District
of Columbia, conducts the CWNS every four years in response to Sections 205(a) and 516 of the
Clean Water Act and develops a Report to Congress. The CWNS is a comprehensive assessment
of the capital needs to meet the water quality goals set in the Clean Water Act. Every four years,
the states and EPA collect information about:
• Publicly owned wastewater collection and treatment facilities.
• Stormwater and combined sewer overflow (CSO) control facilities.
• Nonpoint source (NFS) pollution control projects.
• Decentralized wastewater management.
Information collected about these facilities and projects includes:
• Estimated needs to address water quality or water quality-related public health problems.
• Location and contact information for facilities and projects.
• Facility populations served and flow, effluent, and unit process information.
• NFS best management practices.
CHP Installation Database
The CHP Installation Database is maintained by ICF with support from the U.S. Department of
Energy and Oak Ridge National Laboratory. The database lists all CHP systems in operation in
the United States. Information is gathered in real time and originates from industry literature,
manufacturer contacts, and regional CHP centers. The database is continually updated.
2010 eGRID
eGRID is a comprehensive source of data on the environmental characteristics of almost all
electric power generated in the United States. These environmental characteristics include air
emissions for nitrogen oxides, sulfur dioxide, carbon dioxide, methane, and nitrous oxide;
emission rates; net generation; resource mix; and many other attributes.
40 The 2008 CWNS is available through EPA's Office of Wastewater Management and can be accessed at:
http://water.epa.gov/scitech/datait/databases/cwns/index.cfm.
41 The CHP Installation Database is available at: http://www.eea-inc.com/chpdata/index.html.
42 eGRID is available at: http://www.epa.gov/cleanenergv/energv-resources/egrid/index.html.
43 Average industrial electricity prices taken from Energy Information Administration (EIA), "Monthly Electric
Sales and Revenue Report with State Distributions Report," year to date through December 2010. Natural gas price
data can be found at: http://www.eia.gov/dnav/ng/ngjri sum dcunusm.htm.
40
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U.S. EIA Electricity and Natural Gas Prices
Electric Power Monthly is a report prepared by the EIA that summarizes the average price paid
by industrial customers purchasing electricity on a state-by-state basis. WWTFs are treated as
industrial customers because they are fairly large electricity consumers and they consume power
throughout the day and night, as do other industrial facilities. Data are collected from a multitude
of EIA forms, as well as from other federal sources.
Wastewater Treatment Facility Interviews
The CHPP attempted to contact 30 WWTFs that have operational CUP systems and ultimately
spoke with 14 facilities. The WWTFs chosen for contact and those ultimately interviewed
represent operational, geographical, and technological diversity. Information obtained from
interviews included operational insights and addressed drivers and benefits of CUP; barriers and
challenges encountered; and lessons learned.
Independent Research
The CHPP also conducted independent research, which included reviewing reports, studies, and
case studies of WWTFs that employ CUP, and utilizing the extensive CUP resources and
contacts available to the CHPP.
41
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Appendix B: Anaerobic Digester Design Criteria Used for Technical Potential Analysis
The following anaerobic digester design criteria were used to estimate the total wastewater
influent flow rate that a typically sized digester can treat, as well as the biogas generation rate
and the heat load of a typically sized digester. All criteria are based on a typically sized
mesophilic digester.
System Design Parameter
Reactor Type1
Reactor Shape1
Organic Load2 (Ibs/day VS)
Percent Solids in Flow2 (% w/w)
Sludge Density2 (Ibs/gal)
Flow to Reactor (Ibs/day)
Flow to Reactor (gal/day)
Flow to Reactor (ft3/day)
Reactor Depth3 (ft)
Design Load1 (Ibs VS/ft3/day)
Total Reactor Volume (ft3)
Reactor Area (ft)
Reactor Diameter1 (ft)
Retention Time (days)
Influent Temp- Winter (°F)
Air Temp- Winter (°F)
Earth Around Wall Temp - Winter (°F)
Earth Below Floor Temp - Winter (°F)
Reactor Temp (°F)
Influent Temp - Summer (°F)
Air Temp - Summer (°F)
Earth Around Wall Temp - Summer (°F)
Earth Below Floor Temp - Summer (°F)
Sp. Heat Sludge1 (Btu/lb*°F)
Area Walls (ft2)
Area Roof (ft2)
Area Floor (ft2)
U Walls - Concrete1 (Btu/hr*ft2*°F)
U Roof -Concrete1 (Btu/hr*ft2*°F)
U Floor- Concrete1 (Btu/hr*ft2*°F)
Gas Generation1 (ft3/lbVS)
Gas Heat Content1 (Btu/ft3) (HHV)
VS Removal Percent at 20 days2 (%)
VS Removed (Ibs/day)
Gas Generation (ft3/day)
Heat Potential of Gas (Btu/day)
Gas Generation per Capita1 (ft3/day/person)
Population Served by POTW (persons)
Flow per Capita3 (gal/day/person)
Total POTW Flow (MGD)
Value
Complete Mix
Circular
13,730
8
8.5
171,625
20,191
2,699
20
0.25
54,920
2,746
60
20
40
40
40
40
98
78
78
47
47
1.0
3,769.9
2,827.4
2,827.4
0.12
0.28
0.30
12
650
55
7,552
90,618
58,901,700
1
90,618
100
9.1
Sources:
1. Metcalf and Eddy, "Wastewater Engineering and Design, 4th Edition", 2003.
2. Eckenfelder, "Principals of Water Quality Management," 1980.
3. Great Lakes-Upper Mississippi Board of State and Provincial Public Health and Environmental Managers,
"Recommended Standards for Wastewater Facilities (Ten-State Standards)," 2004.
42
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Appendix C: Space Heating Capability of CHP at Wastewater Treatment Facilities
As discussed in Section 4.2.2, the analysis estimated the space heating capability of CHP at
WWTFs, demonstrating that after digester loads are met, there is little CHP recovered heat
available for space heating in most climates. Based on the results shown in Figure 2 and Table 9
(both in Section 4.2.2), the analysis estimated the amount of heat available for space heating after
digester heating is met. By subtracting the average values for digester heating requirements (see
Table 9) from the thermal output of representative CHP systems, the amount of heat available for
space heating was estimated for three different sizes of WWTFs (i.e., 3,16, and 40 MGD) for
each of the five climate zones. The CHP systems chosen represent typical prime mover types and
sizes used at WWTFs, and the WWTF sizes are representative of the range of facility sizes that
are applying CHP. The following table presents the results.
Estimated Space Heating Capability for CHP Units in Different Climate Zones
Climate Zone
1 - Cold
2 - Cold/
Moderate
3 - Moderate/
Mixed
4 -Warm/Hot
5 -Hot
WWTF Plant
Size (MGD)
3
16
40
3
16
40
3
16
40
3
16
40
3
16
40
Representative CHP
System
65 kW Microturbine
400 kW Engine
1 MW Engine
65 kW Microturbine
400 kW Engine
1 MW Engine
65 kW Microturbine
400 kW Engine
1 MW Engine
65 kW Microturbine
400 kW Engine
1 MW Engine
65 kW Microturbine
400 kW Engine
1 MW Engine
Thermal Output/Load (MMBtu/day)
Estimated CHP
Thermal Output
5.9
38.4
81.6
5.9
38.4
81.6
5.9
38.4
81.6
5.9
38.4
81.6
5.9
38.4
81.6
Average
Digester
Load
8.4
44.8
112.0
7.5
40.0
100.0
6.9
36.8
92.0
6.0
32.0
80.0
5.4
28.8
72.0
Surplus Thermal
Output for Space
Heating
0.0
0.0
0.0
0.0
4.0
0.0
0.0
1.6
0.0
0.0
6.4
1.6
0.5
9.6
9.6
The data in the table above reveal that a substantial amount of surplus heat for space heating is
available only in warm and hot climates, where demand for space heating is minimal (except in
cold winter months). In cold climates, where more energy is required to heat the digester, surplus
thermal energy for space heating is generally not available.
CHP provides for much higher gas utilization than if the digester were heated directly with
boilers, since the use of digester gas is much higher in the summer months when heating loads
are minimal. Gas utilization by baseloaded CHP systems is fairly constant throughout the year,
other than during periods of maintenance, whereas gas utilization for boilers drops significantly
during summer periods when some digester heating may be needed but little or no space heating
43
-------
is needed. A WWTF in North Carolina44 indicated that 63 to 66 percent of available digester gas
can be beneficially used with CHP, whereas use of digester gas-fueled boilers would consume
only 33 to 38 percent of the gas, with the balance either stack losses or flared gas. This
experience is consistent with the interviews of WWTFs conducted for this report, in which a
number of facilities indicated that using CHP results in more beneficial use of the digester gas.
For example, the Town of Lewiston, NY, indicated that prior to implementing CHP, its boiler
used only 40 to 50 percent of the gas, whereas with the CHP system, gas utilization reached 98
percent. Future trends45 also indicate that more facilities are likely to build gas storage into their
digester system, which should result in improved gas utilization. Storing digester gas during
periods of low demand and drawing from storage when demand for heat is high minimizes the
need for gas flaring. For many WWTFs, improving gas utilization while at the same time
eliminating or minimizing flaring is a key driver for implementing CHP.
44 Fishman, Bullard, Vogt and Lundin, "Beneficial Use of Digester Gas - Seasonal and Lifecycle Cost
Considerations," 2009.
45 Based on a number of recent installations and feasibility studies that included gas storage (City of Riverside, CA;
Cape Fear, NC; Ithaca, NY; Rochester NY; and Gloversville-Johnstown, NY).
44
-------
Appendix D: Cost-to-Generate Estimates by State
To estimate the cost to generate for CHP at WWTFs, the analysis considered three digester gas
utilization cases for each WWTF greater than 1 MOD that operates anaerobic digesters.
• Case 1: Assumes digester gas is used for both digester heating and space heating prior to
CHP implementation.
• Case 2: Assumes digester gas is used for digester heating only prior to CHP
implementation and natural gas is used for space heating.
• Case 3: Assumes digester gas is not used for heating, and natural gas is used for digester
and space heating prior to CHP implementation.
45
-------
Cost to Generate Electricity with Digester Gas (Case 1 - No Thermal Credit)
State
Alaska
Alabama
Arkans as
Arizona
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Iowa
Idaho
Illinois
Indiana
Kansas
Kentucky
Louisiana
Massachusetts
Maryland
Maine
Michigan
Minnesota
Missouri
Mississippi
Montana
North Carolina
North Dakota
Nebraska
New Hampshire
New Jers ey
New Mexico
Nevada
New York
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Virginia
Vermont
Washington
Wisconsin
West Virginia
Wyoming
Average
Industrial
FJectricity
Price
(cents/kWh)
14.1
6.1
5.4
6.7
10.9
6.9
14.4
9.6
8.9
6.2
21.9
5.4
5.1
6.7
6.0
6.2
5.1
5.8
13.2
9.5
8.8
7.2
6.3
5.5
6.4
5.6
6.1
5.7
5.9
12.8
11.6
6.0
7.4
9.7
6.3
5.2
5.5
7.6
12.8
5.7
5.9
6.7
6.3
4.9
6.7
9.5
4.0
6.8
5.9
5.0
Average
Industrial
Natural Gas
Price
(S/1000 scf)
4.2
6.4
7.6
8.2
7.0
5.8
9.6
14.0
9.4
6.7
24.2
6.1
6.4
7.3
5.5
5.3
5.3
4.6
12.1
8.6
9.1
9.2
5.7
9.6
5.9
9.1
8.1
5.2
5.7
12.1
9.7
6.0
10.5
9.5
8.9
12.6
7.3
10.2
12.6
6.1
5.9
6.2
4.6
5.5
7.1
6.6
9.4
7.6
5.4
5.4
Cost to Generate (cents /kWh)
Small Rich-
Burn FJigine
(1-5 MGD)
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
7.3
Microturbine
(1-10 MGD)
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
Rich-Burn
Fjigine
(5-15 MGD)
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
Fuel Cell
(10-80 MGD)
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
Small Lean-
Burn Fjigine
(12-40 MGD)
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
Lean-Burn
Fjigine
(40-160 MGD)
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
Combustion
Turbine
(>160 MGD)
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
Average industrial electricity prices taken from Energy Information Administration (EIA), "Monthly Electric Sales
and Revenue Report with State Distributions Report," year to date through December 2010.
Average industrial natural gas prices taken from EIA, available at:
http://www.eia.gov/dnav/ng/ng pri sum dcu nus m.htm.
46
-------
Net Cost to Generate Electricity with Digester Gas (Case 2 - Thermal Credit for Space
Heating)
State
Alaska
Alabama
Arkans as
Arizona
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Iowa
Idaho
Illinois
Indiana
Kansas
Kentucky
Louisiana
Massachusetts
Maryland
Maine
Michigan
Minnesota
Missouri
Mississippi
Montana
North Carolina
North Dakota
Nebraska
New Hampshire
New Jersey
New Mexico
Nevada
New York
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Is land
South Carolina
South Dakota
Tennessee
Texas
Utah
Virginia
Vermont
Washington
Wisconsin
West Virginia
Wyoming
Average
Industrial
FJectricity
Price
(cents/kWh)
14.1
6.1
5.4
6.7
10.9
6.9
14.4
9.6
8.9
6.2
21.9
5.4
5.1
6.7
6.0
6.2
5.1
5.8
13.2
9.5
8.8
7.2
6.3
5.5
6.4
5.6
6.1
5.7
5.9
12.8
11.6
6.0
7.4
9.7
6.3
5.2
5.5
7.6
12.8
5.7
5.9
6.7
6.3
4.9
6.7
9.5
4.0
6.8
5.9
5.0
Average
Industrial
Natural Gas
Price
(S/1000 scf)
4.2
6.4
7.6
8.2
7.0
5.8
9.6
14.0
9.4
6.7
24.2
6.1
6.4
7.3
5.5
5.3
5.3
4.6
12.1
8.6
9.1
9.2
5.7
9.6
5.9
9.1
8.1
5.2
5.7
12.1
9.7
6.0
10.5
9.5
8.9
12.6
7.3
10.2
12.6
6.1
5.9
6.2
4.6
5.5
7.1
6.6
9.4
7.6
5.4
5.4
Cost to Generate (cents /kWh)
Small Rich-
Burn FJigine
(1-5 MGD)
7.3
7.1
7.2
7.2
7.2
7.3
7.3
7.3
7.0
7.0
6.8
7.3
7.3
7.3
7.3
7.3
7.3
7.2
7.3
7.3
7.3
7.3
7.3
7.3
7.1
7.3
7.2
7.3
7.3
7.3
7.3
7.2
7.3
7.3
7.3
7.2
7.3
7.3
7.3
7.2
7.3
7.2
7.2
7.3
7.3
7.3
7.3
7.3
7.3
7.3
Microturbine
(1-10 MGD)
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
Rich-Burn
Fjigine
(5-15 MGD)
6.0
5.8
5.8
5.8
5.8
5.9
6.0
5.9
5.7
5.6
5.3
6.0
6.0
6.0
6.0
6.0
6.0
5.8
6.0
5.9
6.0
6.0
6.0
5.9
5.8
6.0
5.8
6.0
6.0
6.0
6.0
5.9
6.0
6.0
6.0
5.8
5.9
6.0
6.0
5.8
6.0
5.8
5.8
6.0
5.9
6.0
6.0
6.0
6.0
6.0
Fuel Cell
(10-80 MGD)
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
8.3
Small Lean-
Burn Fjigine
(12-40 MGD)
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.0
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
5.1
Lean-Burn
Fjigine
(40-160 MGD)
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
Combustion
Turbine
(>160 MGD)
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
*Includes thermal credit as described in Section 4.2.3
Average industrial electricity prices taken from Energy Information Administration (EIA), "Monthly Electric Sales
and Revenue Report with State Distributions Report," year to date through December 2010.
Average industrial natural gas prices taken from EIA, available at:
http://www.eia.gov/dnav/ng/ng pri sum dcu nus m.htm.
47
-------
Net Cost to Generate Electricity with Digester Gas (Case 3 - Full Thermal Credit)
State
Alaska
Alabama
Arkansas
Arizona
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Iowa
Idaho
Illinois
Indiana
Kansas
Kentucky
Louisiana
Massachusetts
Maryland
Maine
Michigan
Minnes ota
Missouri
Mississippi
Montana
North Carolina
North Dakota
Nebraska
New Hampshire
New Jersey
New Mexico
Nevada
New York
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Is land
South Carolina
South Dakota
Tennessee
Texas
Utah
Virginia
Vermont
Washington
Wisconsin
West Virginia
Wyoming
Average
Industrial
Electricity
Price
(cents/kWh)
14.1
6.1
5.4
6.7
10.9
6.9
14.4
9.6
8.9
6.2
21.9
5.4
5.1
6.7
6.0
6.2
5.1
5.8
13.2
9.5
8.8
7.2
6.3
5.5
6.4
5.6
6.1
5.7
5.9
12.8
11.6
6.0
7.4
9.7
6.3
5.2
5.5
7.6
12.8
5.7
5.9
6.7
6.3
4.9
6.7
9.5
4.0
6.8
5.9
5.0
Average
Industrial
Natural Gas
Price
(S/1000 scf)
4.2
6.4
7.6
8.2
7.0
5.8
9.6
14.0
9.4
6.7
24.2
6.1
6.4
7.3
5.5
5.3
5.3
4.6
12.1
8.6
9.1
9.2
5.7
9.6
5.9
9.1
8.1
5.2
5.7
12.1
9.7
6.0
10.5
9.5
8.9
12.6
7.3
10.2
12.6
6.1
5.9
6.2
4.6
5.5
7.1
6.6
9.4
7.6
5.4
5.4
Cost to Generate (cents /kWh)
Small Rich-
Burn FJigine
(1-5 MGD)
5.0
4.9
3.9
4.0
4.7
4.0
3.2
1.9
4.0
4.8
0.2
4.4
3.5
3.8
4.3
5.4
4.8
5.7
0.0
2.6
0.5
2.1
4.2
3.1
4.9
2.4
4.0
4.5
4.4
0.0
3.0
5.3
1.9
1.5
2.6
3.5
3.7
1.9
1.3
4.7
4.1
4.3
5.4
4.5
4.3
3.5
3.1
3.1
4.7
4.7
Microturbine
(1-10 MGD)
4.8
4.2
3.1
3.3
3.9
3.5
3.1
1.6
3.3
4.2
0.0
4.1
3.7
3.6
4.0
4.8
4.2
4.9
0.1
2.2
1.5
2.6
4.2
2.7
4.2
2.9
3.2
4.4
4.1
0.3
2.9
4.4
2.0
2.2
2.5
2.8
3.2
2.0
1.5
3.9
4.1
3.5
4.6
4.1
3.7
3.7
3.0
3.4
4.1
4.5
Rich-Burn
FJigine
(5-15 MGD)
4.0
3.9
3.0
3.1
3.7
3.1
2.5
1.2
3.0
3.7
0.0
3.5
2.7
3.0
3.4
4.4
3.8
4.5
0.0
1.8
0.1
1.5
3.3
2.3
3.9
1.8
3.0
3.6
3.5
0.0
2.3
4.2
1.3
1.0
1.9
2.6
2.8
1.3
0.8
3.7
3.2
3.3
4.3
3.5
3.3
2.7
2.3
2.4
3.7
3.8
Fuel Cell
(10-80 MGD)
7.2
6.6
6.0
6.1
6.5
6.3
6.0
5.0
5.9
6.4
3.2
6.7
6.4
6.3
6.6
7.2
6.8
7.1
3.9
5.4
4.9
5.7
6.8
5.7
6.6
5.9
6.1
6.9
6.7
4.0
5.9
6.9
5.3
5.4
5.6
5.8
6.1
5.3
4.9
6.6
6.7
6.3
6.9
6.7
6.5
6.4
5.9
6.2
6.7
7.0
Small Lean-
Burn FJigine
(12-40 MGD)
3.5
3.2
2.3
2.4
2.9
2.3
1.7
0.4
2.5
3.1
0.0
2.7
2.3
2.2
2.6
3.5
2.9
3.8
0.0
1.0
0.0
1.2
2.8
1.5
3.2
1.5
2.3
3.0
2.7
0.0
1.6
3.4
0.6
0.8
1.1
2.0
2.0
0.6
0.1
2.9
2.7
2.6
3.6
2.7
2.5
2.3
1.6
2.0
2.8
3.2
Lean-Burn
Fhgine
(40-160 MGD)
2.6
2.1
1.2
1.3
1.8
1.5
1.1
0.0
1.4
2.1
0.0
2.0
1.6
1.5
1.9
2.6
2.1
2.7
0.0
0.4
0.0
0.7
2.1
0.8
2.1
0.9
1.2
2.2
2.0
0.0
1.0
2.3
0.2
0.3
0.6
0.9
1.2
0.2
0.0
1.8
2.0
1.5
2.5
2.0
1.7
1.6
1.0
1.4
2.0
2.4
Combustion
Turbine
(>160MGD)
1.6
1.3
0.4
0.5
1.0
0.4
0.0
0.0
0.6
1.2
0.0
0.9
0.5
0.4
0.8
1.6
1.0
1.9
0.0
0.0
0.0
0.0
1.0
0.0
1.3
0.0
0.4
1.2
0.9
0.0
0.0
1.5
0.0
0.0
0.0
0.1
0.1
0.0
0.0
1.0
0.9
0.7
1.7
0.9
0.6
0.5
0.0
0.2
0.9
1.3
*Includes thermal credit as described in Section 4.2.3
Average industrial electricity prices taken from Energy Information Administration (EIA), "Monthly Electric Sales
and Revenue Report with State Distributions Report," year to date through December 2010.
Average industrial natural gas prices taken from EIA, available at:
http://www.eia.gov/dnav/ng/ng pri sum dcu nus m.htm.
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Appendix E: Additional Reference Resources
EPA Combined Heat and Power Partnership (CHPP)
The CHPP is a voluntary program that seeks to reduce the environmental impact of power
generation by promoting the use of CHP. The CHPP works closely with energy users, the CHP
industry, state and local governments, and other stakeholders to support the development of new
projects and promote their energy, environmental, and economic benefits.
Website: www.epa.gov/chp/
The CHPP offers a number of tools and resources that can help a WWTF implement a CHP
system. These include:
• Description of the CHP project development process, including information on key
questions for each stage of the process along with specific tools and resources.
Website: www.epa.gov/chp/project-development/index.html.
• The CHP funding database with bi-weekly updates of new state and federal incentive
opportunities.
Website: www.epa.gov/chp/funding/funding.html.
• The CHP Catalog of Technologies, which describes performance and cost characteristics
of CHP technologies.
Website: www.epa.gov/chp/basic/catalog.html.
• The Biomass CHP Catalog of Technologies, which provides detailed technology
characterization of biomass CHP systems.
Website: www.epa.gov/chp/basic/catalog.html.
Reports
The following reports about CHP at WWTFs are available for download:
Brown & Caldwell, "Evaluation of Combined Heat and Power Technologies for Wastewater
Treatment Facilities," December 2010. Available at:
http ://water. epa. gov/scitech/wastetech/publications. cfm.
Association of State Energy Research & Technology Transfer Institutions, "Strategic CHP
Deployment Assistance for Wastewater Treatment Facilities," October 2009. Available at:
http ://www. asertti.org/wastewater/index. html.
California Energy Commission, "Combined Heat and Power Potential at California's
Wastewater Treatment Plants," September 2009. Available at:
http://www.energv.ca.gov/2009publications/CEC-200-2009-014/CEC-200-2009-014-SF.PDF.
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Organizations
The following organizations work closely with the wastewater treatment industry and offer a
wealth of knowledge concerning wastewater treatment and the use of anaerobic digestion.
EPA Office of Wastewater Management (OWM) - The OWM oversees a range of
programs contributing to the well-being of the nation's waters and watersheds.
Website: www.epa.gov/owm/
National Association of Clean Water Agencies (NACWA) - NACWA represents the
interests of more than 300 public agencies and organizations. NACWA members serve
the majority of the sewered population in the United States and collectively treat and
reclaim more than 18 billion gallons of wastewater daily.
Website: www.nacwa.org/
Water Environment Federation (WEF) - Founded in 1928, the WEF is a not-for-profit
technical and educational organization with members from varied disciplines who work
toward the organization's vision of preserving and enhancing the global water
environment.
Website: www.wef.org/Home
Water Environment Research Foundation (WERF) - WERF helps improve the water
environment and protect human health by providing sound, reliable science and
innovative, effective, cost-saving technologies for improved management of water
resources.
Website: www.werf.org
Air and Waste Management Association (A&WMA) - A&WMA is a not-for-profit,
non-partisan professional organization that provides training, information, and
networking opportunities to thousands of environmental professionals in 65 countries.
Website: www.awma.org/
Other
Database of State Incentives for Renewables and Efficiency (DSIRE) - DSIRE is a
comprehensive source of information on federal, state, local, and utility incentives and
policies that promote renewable energy and energy efficiency.
Website: http://www.dsireusa.org/
&EPA
United States Environmental Protection Agency
Office of Air and Radiation (6202 J)
430R11018
October 2011
www.epa.gov/chp
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