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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