vvEPA
United States
Environmental Protection
Agency
United States Environmental Protection Agency
August 2013
Renewable Energy Fact Sheet
Viable Sources
INTRODUCTION
This fact sheet describes the use of auxiliary and
supplemental powers sources (ASPSs), which can
provide wastewater treatment plants
(WWTPs) with a secondary power source in
the case of a blackout or other problem
resulting in a loss of power. Wastewater
utilities can also use this power to supplement
other sources of power on a continuous basis.
In order to be effective, these ASPSs should
provide the power necessary to run the
WWTP efficiently and effectively, and also
have a short start-up time if they are to be used
in an emergency.
Most WWTPs have electric power
connections to at least two independent
power substations, such that if power from
one substation fails (i.e., due to a localized
storm or the downing of a local power line),
the WWTP could receive power from the
other substation. However, if the entire grid
fails (such as it did for much of the northeast
and the Great Lakes states in August 2003),
having power feeds from separate substations
that are all connected to the same main grid will
not meet the auxiliary power needs to keep
many WWTPs operating during such a
failure. Without an adequate reliable auxiliary
power source, many WWTPs will discharge
untreated sewage into the receiving waters.
There are a number of different types of ASPSs
that can provide reliable power to WWTPs on either
a continuous or emergency basis. These include:
• Internal Combustion Engine
Driven Generators (diesel, natural
gas, or bio-gas)
• Microturbines
• Fuel Cells
• Solar Cells
• Wind Turbines
• Low Head Hydro Power
• Wastewater Heat Recovery
Some of these technologies can also be used by
the wastewater utilities to supplement their
commercial power sources. Technologies such
as fuel cells, solar cells, wind turbines, and bio-
gas driven generators can provide renewable
energy on a continuous basis, while diesel or
natural gas power generators have been used to
reduce peak energy demands on a short-term
basis.
Planning for auxiliary power must take into
account the expected flow rates at the WWTP
during the time of the power failure in order to
ensure that sufficient auxiliary power will be
available to meet the normal operating needs
of the WWTP. Planners should also consider
other factors that could affect the amount of
power required by the WWTP to remain
operational, such as potential weather conditions
(wet weather can increase stormwater flow to the
WWTP in combined systems), collection system
pump station operation, and whether drinking
water is distributed during the power failure (this
function requires increased pump capacity, and
could be a factor for combined water/wastewater
utilities). If the technology is planned to
supplement commercial power, other
considerations, such as continuous operating costs,
energy market trends, and long-range fuel price
projections, may need to be factored in.
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In addition to general considerations related to
evaluating auxiliary and supplemental power
sources, there are also technology specific
considerations that must be evaluated. These
include:
• Reliability: ASPSs must provide reliable
auxiliary power under adverse conditions. ASPSs
should be available for immediate service
(i.e., warm up quickly) and be available for the
time period for which they are needed without
interruption. In some case, auxiliary power may
be needed for extended periods of time (i.e., 48
hours or more), and sufficient fuel must be available
for long-term operation.
• Cost: ASPS technologies range widely in costs
which will be a major factor in a utility's
selection of the best options for providing
auxiliary or supplemental power. Costs should be
weighed against many other factors, including the
expected life, annual maintenance, and reliability of
the technology, as well as potential economic and
environmental costs associated with an extended
power failure at the POTW.
• Appropriateness: ASPSs should have
sufficient capacity to operate primary treatment
and disinfection for all wastewater flows for
at least 24 hours after a power interruption. For
discharges to sensitive water bodies, capacity to
operate additional unit processes (i.e., advanced
treatment) may be required by state regulatory
authorities.
• Security: When possible, ASPSs should be
located on-site, because it is easier for most
wastewater utilities to protect on-site power
supplies than it is to protect transmission
lines and substations that feed the plant or remote
pumping stations.
• Environmental Factors: The goal of
insuring an adequate auxiliary power supply is
to protect human health and the environment i n
the event of a power interruption. An
auxiliary power supply should be adequate to
prevent raw sewage from coming in contact with
the public or discharging to sensitive receiving
waters. However, spills or leaks from underground
fuel tanks used to store fuel for ASPSs can create a
risk to the ground water and the environment. In
addition, some of the older gas or diesel engine
driven generators produce air emissions that are
harmful to public health.
• Safety: One significant ob stacle to the
installation of on-site electricity generation at
WWTPs is the safety risk associated with the
operation of such equipment. Operators must be
trained to safely operate and maintain the
equipment. There may also be concerns with
fuel storage and handling. For example, large
above-ground fuel or gas storage may pose a
risk to public health from an accident or terrorist
attack.
INTERNAL COMBUSTION ENGINE
DRIVEN GENERATORS
Electric generators can be furnished with engines
that can run on diesel fuel, natural gas, or bio-gas.
In many cases the engine can be provided with
duel fuel capability. All of the engines currently
being manufactured are required to meet Clean
Air Act emissions requirements as stated in
sections 89-90, Chapter 40 of the Code of
Federal Regulations. Some states have
additional requirements that restrict the use of
some auxiliary or supplemental power sources.
States are required to be as strict in environmental
regulations as the federal government, but can
be stricter if needed to meet local air quality
restrictions (like emissions in California). While
older engines can contribute to air pollution
problems, today high-efficiency, low- emission
engines are available for most generators.
MICROTURBINES
Microturbines are a new, innovative technology
based on jet engines (more specifically the turbo
charger equipment found in jet engines) that use
rotational energy to generate power.
Microturbines can run on bio-gas, natural gas,
propane, diesel, kerosene, methane, and other fuel
sources, making them suitable for a variety of
applications. From an environmental standpoint,
these new machines take up less space, have higher
efficiencies, and generate lower emissions than
reciprocating engines. If operated from a natural
gas pipeline, no on-site gas storage is needed,
thus reducing safety concerns.
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Based on estimates by the Gas Research Institute
and National Renewable Energy Laboratory, the
total plant cost varies from about $2,600 per
kilowatt (kW) for a 30 kW system to around
$1,800 per kW for a 100 kW system. The 18.4
MGD Sheboygan Regional WWTP in Wisconsin
has installed 10, 30 kW Capstone microturbines
that provide an annual savings of close to
$140,000.
SOLAR CELLS
Solar cells, also known as photovoltaic (PV) cells,
convert sunlight directly into electricity. They are
often assembled into flat plate systems that can be
mounted on rooftops or other open areas. Solar
cells require only sunlight (a renewable energy
source) as fuel, and have no emissions. They
generate electricity with no moving parts and
require little maintenance, making them ideal for
remote locations. However, solar cells are
dependent on weather. If there is no sun there is no
energy generated. If used as an auxiliary source of
power, some type of storage system (i.e., batteries)
must be provided. In 2007, the cost of
implementing a solar power project was $8 per
watt. Currently, solar power companies offer a
"Power Purchase Agreement" model wherein the
wastewater treatment plants do not have to incur
expenditure on implementing a solar power project.
The project costs are borne by the solar power
company which would then sell the solar power to
the wastewater treatment plant. An ideal example
would be the City of Madera's WWTP in
California. It has a solar installation that can
produce 1.158 megawatts (MW) of electricity. This
project would lower the WWTP's energy costs by
$250,000 annually.
FUEL CELLS
A fuel cell is an electrochemical device similar to a
battery. While both batteries and fuel cells generate
power through an internal chemical reaction, a fuel
cell differs from a battery in that it uses an external
supply that continuously replenishes the reactants
in the fuel supply of reactants. The fuel cell can
supply power cell. A battery, on the other hand, has
a fixed internal continuously as long as the
reactants are replenished, while the battery can
only generate limited power before it must be
recharged or replaced. Most types of fuel cells can
operate on a wide variety of fuels including
hydrogen, digester gas, natural gas, propane, and
landfill gas, diesel, or other combustible gas. In
some cases such, as in a WWTP, methane
(sludge gas) from anaerobic digesters can be
reused in the fuel cell instead of flaring off the
excess gas. Other advantages of fuel cells include
few moving parts, modular design and negligible
emission of pollutants. Palmdale Water
Reclamation Facility in Los Angeles County,
California, installed a 250 kW molten carbonate
fuel cell at a cost of $1.9 million. The reduction
in the energy expenditure for the facility was
calculated to be $227,000 annually.
WIND TURBINES
Wind turbines convert wind into mechanical
energy and electricity. A generator is equipped
with fan blades and placed at the top of a tall
tower. The tower must be tall in order to harness
the wind at a greater velocity, free of turbulence
caused by interference from ground obstacles
such as trees, hills, and buildings. Generally,
individual wind turbines are grouped into wind
farms containing several turbines. The power
generated from wind farms can be inexpensive
when compared to other traditional power
production methods. The cost to generate the
electricity from wind farms decreases as the size
of the farm increases.
Wind turbines do not produce any harmful
emissions nor do they require any fuel product
for operation. However, wind turbines do require
periodic maintenance, which can present a safety
problem, since most turbines are mounted on tall
towers. There is also concern about construction
and other activities below each turbine, although
the land can generally still be used for animal
grazing or farming. Problems with birds flying
into the turbine propellers have been reported,
However, newer designs have reduced this
problem. The costs of implementing a wind
power project vary with the size of the project.
The WWTP in Evansville, Indiana, installed a
100 kW wind turbine at a cost of $594,000,
which translates to $5,940 per kW.
The Jersey Atlantic Wind Farm owned by the
Atlantic County Utilities Authority in Atlantic
City, New Jersey, has an installed capacity of 7.5
MW and the cost per kW is $1,667. The Cost of
wind generated at this facility is $0.076 per
kilowatt hour (kWh) with an annual energy cost
saving is around $350,000.
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LOW-HEAD HYDROPOWER
The electric energy that is harnessed from the force
of moving water is termed as hydroelectric power.
The two types of systems used for this purpose are
the run-of-the-river system and storage system. In
either system, water is channeled through a
pipeline to a turbine and the pressure at the end of
the pipeline constitutes the net head. Hydroelectric
power is renewable, clean, and the largest source of
renewable energy in the United States. According
to the U.S. Energy Information Administration,
about 60% of the renewable energy produced in the
United States in 2010 was from hydroelectric
projects.
Hydroelectric power systems that operate with a
head or water level of less than 66 feet are termed
low-head hydropower systems. In most cases, low-
head hydropower systems are built as a run-of-the-
river system, and the power generation is
dependent on having perennial flow in the river.
Loss of head due to build up of debris is also an
issue. When implemented in a WWTP, the low-
head hydro- power system will not encounter the
same problems as a run-of-the-river system
because of the constant supply of debris-free water.
Figure 1 shows different types of turbines and their
operating criteria.
The power that can be potentially produced at a site
is roughly given by the following equation:
n ™ Head (feet) x Flow (cfs) v ,,. .
Power (kW) = X efficiency
11.8
Where H is available head in feet; F is the flow
in cubic feet per second (cfs); efficiency is overall
system efficiency as a fraction; and 11.8 is a
constant that converts the equation to kilowatts.
By harnessing the potential energy of effluent
water contained in a 4.5 mile long outfall, Point
Loma Wastewater Treatment Plant of San Diego,
California, is able to produce 1.35 MW of
electricity. A hydroelectric turbine is operated by
the effluent water before being discharged to the
ocean. The head available from the plant to the
outfall is 88.5 feet. The total cost of this project is
$1.7 million, out of which $419,000 was provided
by a California Energy Commission grant.
Make
Energy
Systems
Power
Pal
Canyon
Hydro-
Kaplan
Hydro-
e-kid
Very
Low
Head
Head
(feet)
10
5
30-50
Varies
6.6-11
Flow
(cfs)
2
5
100-
400
Varie
s
Varie
s
Power
(kW)
1
1
Varies
2-200
486-
496
Figure 1: Types of Low-Head Hydropower
Turbines
WASTEWATER HEAT RECOVERY An
estimated 350 billion kWh of energy stored in hot
water is drained annually from households and
most of it is recoverable. Using municipal
wastewater as a heat source in the winter and as a
heat sink in the summer, considerable savings in
heating, ventilation, and air conditioning
(HVAC) costs can be achieved. Wastewater heat
recovery systems use a heat exchanger to transfer
heat from the municipal wastewater to a
conveyance medium, which is then pumped to
individual buildings. Heat pumps located at these
buildings then extract heat from the conveyance
medium and deliver energy for space heating and
cooling. The conveyance medium is sent back
into the loop where it exchanges heat with the
municipal wastewater again. The first project of
this kind was announced jointly by the East
Division Reclamation Plant, Renton,
Washington, and The Boeing Company in 1992.
Wastewater was pumped to one of Boeing's
training facilities and used for space cooling
purposes. The annual savings in energy costs,
from this project was estimated to be $120,000.
On a commercial scale, this system has been
implemented at the Whistler Athletes'
Village, British Columbia at a cost of $4.1
million. The incoming wastewater has an
annual temperature range of 50° F to 64° F.
The installed system is capable of generating
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up to 11,000 megawatt hours (MWh) per year of
heating energy for an occupied space of 85,000
square meters. Kent County, Delaware, is
implementing this system to provide a heating and
cooling solution for two buildings located at the
Kent County Regional Wastewater Treatment
Facility. Sustainability and flexibility are among
the key benefits of implementing this system.
REFERENCES
1. Renewable Energy Fact Sheet: Solar Cells, EPA
832-F-13-019, US EPA, Office of Wastewater
Management, August 2013.
2. Renewable Energy Fact Sheet: Fuel Cells,
EPA 832-F-13-014, US EPA, Office of
Wastewater Management, August 2013...
3. Renewable Energy Fact Sheet: Wind Turbines,
EPA 832-F-13-017, US EPA, Office of
Wastewater Management, August 2013.
4. Renewable Energy Fact Sheet: Microturbines,
EPA 832-F-13-012, US EPA, Office of
Wastewater management, August 2013.
5. Small Hydro and Low-Head Hydro
Power Technologies and Prospects, Congressional
Research Service, March 2010.
6. Using Wastewater Energy to Heat an Olympic
Village for the 2010 Winter Olympics and Beyond,
Neil Godfrey, John Hart, William Vaughan and
Wayne Wong, WEFTEC 2009.
7. Atlantic County Utilities Authority
(ACUA). Atlantic City Wind Farm Project.
(http://www. acua. com/alternative/
a_projects dsply.cfm?id=214 and http:/
/www. acua. com/file s/windfacts6o 7.pdf.)
8. Nova-Thermal Energy, LLC.
http://www.novathermalenergy.com/index.html
9. Renewable Energy Fact Sheet: Low-head
Hydropower for Wastewater (EPA 832-F-13-
018), Office of Wastewater Management,
August 2013.
Some of the information
presented in this fact sheet was
provided by the manufacturer or
vendor and could not be verified
by the EPA.
The mention of trade names,
specific vendors, or products
does not represent an actual or
presumed endorsement,
preference, or acceptance by the
EPA or federal government.
Stated results, conclusions,
usage, or practices do not
necessarily represent the
views or policies of the EPA.
Environmental Protection Agency
Office of Wastewater Management
EPA 832-F-13-015
August 2013
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