United States
     Environmental Protection
Wastewater Management Fact  Sheet
Energy Conservation
Continual increases in energy costs in the United
States   affect   wastewater   treatment  plants
(WWTPs) just as they do other facilities. Energy
costs can account for 30 percent of the total op-
eration  and  maintenance  (O&M)  costs  of
WWTPs (Cams 2005), and WWTPs account for
approximately 3  percent  of the electric load in
the United  States. Furthermore, as populations
grow  and environmental requirements  become
more  stringent,  demand  for electricity  at such
plants is expected to grow by approximately 20
percent  over the next 15 years (Cams 2005).
Energy conservation is thus an issue of increas-
ing importance  to WWTPs.  This  fact  sheet
describes possible practices that can be imple-
mented to conserve energy at a WWTP.

Evaluating a facility for energy efficiencies and
adopting an energy conservation plan often result
in increased treatment efficiency, along with the
potential  for increased treatment capacity, an
increased ability to meet effluent limitations,
reduced O&M requirements, and reduced energy

The  main  requirement  on  the  part  of the
WWTP staff is a commitment to spend the initial
time needed to  evaluate  the system, to follow
through with the development of an energy con-
servation plan,  and to  implement  the plan's

A number of U.S. facilities, including the Wash-
ington Suburban Sanitary Commission (WSSC)
and the  East  Bay Municipal  Utility  District
(EBMUD) in the San Francisco Bay area, have
developed and implemented energy conservation
and management plans (Taylor 2005, Cohn 2005).
                  These plans typically have the goal of reducing
                  energy costs by a specified percentage.

                  The key components of an effective energy man-
                  agement plan are:

                     Creating a system to track energy usage and
                     Performing energy audits of major operations

                     Upgrading equipment, systems, and controls,
                     including facility and collection system im-
                     provements to increase energy efficiency
                     Developing a cost-effective  electric supply
                     purchasing strategy

                     Optimizing load profiles  by shifting opera-
                     tions where possible
                     Developing in-house energy  management
                     training for operators

                  These  components  are  explained more  fully

                  Tracking and Evaluating Energy  Usage and
                  The first  step in evaluating  energy usage and
                  costs at a treatment  facility is gaining an under-
                  standing of where the energy  is being used. This
                  information allows the  WWTP staff to identify
                  areas for  conservation  and to determine where
                  energy is  being  used  inefficiently.  At  many
                  WWTPs the facility's energy use is recorded at a
                  single recording location. The disadvantage of
                  this method is that it does not allow personnel to
                  see the energy used by each  individual process,
                  and thus operating inefficiencies in these proc-
                  esses might be overlooked.

                  For example, the WSSC commissioned the  es-
                  tablishment of an Energy Information System
                  (EIS) in fiscal year  2002 (Taylor 2005). A Java
                  Web application replaced the spreadsheets that
                  had been used to track energy data. The EIS da-
                  tabase tracks energy consumption,  demand, and

costs  by  major processes at the Blue Plains
WWTP in Washington, DC. With this informa-
tion, an  energy audit  can determine the most
energy-intensive operations.

A facility's energy usage can be compared with
energy usage at similar facilities to identify areas
that should be examined further.  Once the effi-
ciencies  of  different pieces of  equipment and
process operations are  determined, the facility
can begin to develop energy conservation meas-
ures by answering the  following  questions  for
each piece of equipment and process:

  Does the process/equipment  need to run at
  Is it possible to  run the  process/equipment
   for fewer hours?
  Is it possible to shift this activity to off-peak
   hours (for some auxiliary functions)?
  Are energy efficiency process  modifications
   or equipment upgrades practical and possible
   while maintaining equipment efficiency?
  What equipment is  most energy efficient for
   this process?
  Is it possible to run more efficient pumps for
   normal base loads or to use lower-efficiency,
   larger units for only the peak flows?

The answers to these questions will help deter-
mine what processes can be modified or what
equipment can be operated more  efficiently  or
replaced to save energy (Cams 2005).

Performing Facility Energy Audits
A comprehensive energy audit allows a facility to
determine the  largest, most energy-intensive op-
erations. By determining the energy demands  of
the various processes and equipment at a WWTP,
personnel  can look at  improving  the treatment
energy efficiency. The objectives at most facilities
are lower energy consumption, demand, and costs
(Taylor 2005). In some  cases, life-cycle cost ana-
lyses can be used to help assess and optimize the
selection of individual components and systems.

For example,  the WSSC developed an energy
performance project evaluation process to assist
in determining whether to proceed with different
opportunities to upgrade or replace various sys-
tems  (Taylor  2005).  Equipment upgrades and
maintenance were then funded from the energy
savings realized. The  WSSC's Energy Perform-
ance Project  had two phases.  Phase I involved
detailed engineering feasibility studies with as-
sociated evaluation and recommended technical
solutions. Preliminary design work was done and
the scope of the project,  costs,  and financing
were established.

Phase  II involved more detailed design work,
including   construction,   commissioning,  and
training, along with operation  and maintenance.
Phase II also  included monitoring and verifica-
tion of the performance of the improved systems
and the savings that resulted (Taylor 2005).

Upgrading Equipment, Systems, and Controls
Numerous processes can be upgraded to improve
the energy efficiency of WWTPs. Some of these
were  demonstrated when EBMUD instituted  an
aggressive energy management program in 2001
(Cohn 2005). EBMUD  serves  approximately
600,000 people in the San  Francisco Bay area of
California.  Its Energy Management  (EM)  pro-
gram  included energy demand reduction, on-site
energy generation, and modifications to the way
electricity was purchased. Energy usage was ex-
amined, and a variety  of processes were targeted
for energy demand reductions. EBMUD modified
some  traditional  processes, and the result was
large savings in energy usage. For example, in the
initial  stage of the activated-sludge process,  a
100-horsepower surface aerator was replaced with
a 25-horsepower subsurface aerator. In addition,
an aerated grit chamber that used approximately
2,900 megawatts  per  year was replaced with a
vortex system, resulting in energy  savings  of
approximately 70 percent per year (Cohn 2005).

EBMUD also implemented additional improve-
ments, including the following:

  Installing high-efficiency influent and efflu-
   ent  pumps,   high-efficiency  motors,  and
   variable-frequency drives
  Discontinuing second-stage activated-sludge

  Adding plastic balls to prevent heat loss and
   evaporation losses in the oxygen production
   vaporizer pit
  Tying in pipes on gas recirculation blowers
   to allow one  blower to service two mixing

These energy-efficient strategies  and modifica-
tions, along with others, resulted in an estimated
annual savings of $2,796,000 (California Energy
Commission, EBMUD Case Study, 2003).

In addition to  the upgrades  and  modifications
mentioned above, there are numerous other proc-
ess  changes  that  can  contribute  to  energy
savings. High  rate diffusers are capable of sup-
plying large quantities of air or oxygen with low
pressure drop and small bubble size (approx. 1-4
mm). Fine bubble diffusion is  inherently  more
effective than coarse bubble diffusers in improv-
ing oxygen transfer efficiency.  Systems can be
purchased  that incorporate many of the  tech-
nologies  mentioned in  this fact  sheet into an
efficient  aeration system. Aeration systems can
incorporate  high-efficiency  motors, variable-
frequency drives (VFDs), and dissolved oxygen
monitoring. This,  in  conjunction with energy
efficient  aeration systems,  can provide energy
savings of 10 to 25 percent over traditional aera-
tion   processes  (Pacific  Gas   and  Electric
Company, 2006).

VFD motors are becoming increasingly popular.
A VFD is an electronic controller that adjusts the
speed of  an electric motor by modulating the
power being delivered  (California Energy Com-
mission,  Variable Frequency  Drive,  2003). For
applications involving  varying  flow require-
ments, mechanical devices such  as  valves  are
often used to control  flow. This process  uses
excessive energy and can create  less-than-ideal
conditions for the mechanical  equipment  in-
volved.  VFDs  enable  pumps  to  accommodate
fluctuating demand, resulting  in operating  at
lower speeds and conserving energy while still
meeting pumping needs. According to the Cali-
fornia Energy  Commission, VFDs can result in
significant energy savings: a VFD can reduce  a
pump's  energy use by  as much  as 50 percent.
Because the benefit of a VFD  is dependent on
system variables like pump size, static head, fric-
tion, and flow variability, it is imperative to fully
examine each  application before  specifying  a
VFD. For example, the Onondaga County (NY)
Department of Water Environment Protection
retrofitted VFDs on the  activated sludge  pump
motors. Combined with  other savings  from re-
ducing aeration basin blowing and improving the
efficiency of some pumps, the plant saved 2.8
million kW-hrs per year, an  annual cost savings
of over $200,000. Since the cost for implementa-
tion of the program was just over $230,000, the
project payback period was 13 months for the 80
million gallons per  day facility  (U.S.  DOE,

Another technology readily available to plants is
the use of high-efficiency motors. Since  pump
and blower motors can account for more than 80
percent of a WWTP's  energy  costs and  high-
efficiency motors are up to 8 percent more effi-
cient than standard motors, it is readily apparent
that   high-efficiency  motors  can  contribute
greatly to reducing facility energy costs.

Design improvements and more accurate manu-
facturing tolerances are  keys to  the improved
efficiencies with these motors. In addition, these
motors  typically  have   greater  bearing  lives,
lower heat output, and less vibration than stan-
dard motors. While high efficiency motors have
a  10-15 percent higher  initial  cost, with their
lower  energy  consumption  and  lower failure
rates, these motors  should be considered for all
new purchases and replacements (California  En-
ergy  Commission,  Energy-Efficient   Motors,

An example of an emerging technology with po-
tential  application  to  WWTPs  is  fuel  cells
(Figure 1). Like a conventional battery, a fuel  cell
uses two reacting chemicals separated by an elec-
trolyte to produce an electric current.  Unlike  a
conventional battery, however, a fuel cell  is not
charged prior to use. The chemical reactants in a
fuel cell are fed continuously to the cell to provide
constant power output. The reaction involves no
combustion and no moving parts, and it  produces
little pollution. Heat generated in the process can
be recovered and used in the facility.

                                                                                from air
                                                               Cathode Catalyst
          Figure 1. Fuel Cell Schematic
Although fuel cells are costly to install, they have
distinct advantages  over the combustion  power
sources at  WWTPs,  such  as  diesel generators.
One advantage  of the fuel cells is lower harmful
emissions. Using diesel driven generators, espe-
cially for continued use  as a supplemental  power
source,  can  lead to air  quality problems.  Many
states  (including California)  have  established
strict emissions limits on all diesel engines.  While
most older diesel engines can not meet the new air
restrictions,  newer  high-efficient, low emission
engine driven generators are now available.

As  a fuel source, fuel cells use hydrogen,  which
can  be derived from methane, natural gas, or
anaerobic digester  gas.  Digester  gas must be
scrubbed before use to  remove compounds  that
can  be problematic for fuel  cells  (U.S.  EPA
1995). Fuel  cell emissions are so clean that they
are  exempt from many Clean Air Act permitting
requirements (California  Energy  Commission,
Fuel Cells, 2003).

Energy conservation might  also include the in-
vestment in Auxiliary and Supplemental Power
Sources (ASPS) or energy recovery equipment,
which will allow energy to  be produced on-site
(EPA, 2006). This energy could then be used to
run  processes or power buildings on-site,  par-
tially or fully, or could  be sold to other users if
there  is an  appropriate delivery system to the
electric grid.  Possible  ASPS  include  bio-gas-
fueled internal  combustion  engines, microtur-
bines  (Figure  2), wind  turbines,  fuel cells, and
solar  cells.  Some ASPS available  do not con-
serve  energy but replace off-site generation with
on-site generation.

The city of Pacifica,  California,  recently began
operating  1,800  solar panels to supply a portion
of the Calera Creek Water Recycling Plant's
electric needs. The solar panels provide  10 to 15
percent of the treatment plant's energy needs.
The facility estimates $100,000 per year in en-
ergy savings (Manekin, 2006).

Making improvements to the wastewater treat-
ment  plant  and  the  collection system  has also
been found  to result in energy savings. In par-
ticular,  installation  of an  equalization basin
allows the plant  to even out pumping needs, and
so allows  for "peak shaving" by running pumps
during off-peak  hours (Fuller,  2003). Reducing
infiltration and inflow in  the collection system
also can pay for itself in energy savings. By re-
habilitating  damaged or deteriorated sewer lines
and eliminating improper connections to the sys-
tem, the overall  flow to the WWTP is  reduced,
thus reducing  the amount of energy required to
treat the flows.

                                                                     Turbine Exhaust
                               System Exhaust
                               (Heat Recovery)
          Figure 2. Microturbine Schematic
Another improvement to a wastewater treatment
plant that can result in large energy savings is a
Supervisory  Control  and   Data  Acquisition
(SCADA) system. These systems use  computers
to automate process monitoring and operational
control. Because such systems  monitor energy
usage,  cost savings can be realized, along with
the savings associated with enhanced process
control  (Fuller  2003).  SCADA  systems  can
monitor and  control the activity of wastewater
systems from a single location. Immediate detec-
tion  of problems through  diagnostic  displays
enables quick intervention  for  fast  resolution.
Operators can easily  compensate for  seasonal
flow and wet weather by automatically adjusting
set points. Centralized  control and monitoring of
distribution and collection systems provides data
for water modeling and energy use optimization,
as well as predictive maintenance of  distributed

In addition  to monitoring treatment  processes,
SCADA  systems can provide continuous moni-
toring and control of plant operations such as:
                            Pump stations
                            Sewer diversion
                          Wet weather
                          overflow protection
   collection systems
   Water distribution
Remote operations
Programmable logic
Creating the most efficient electric supply
purchasing strategy, optimizing load profiles,
and reducing costs
At  many  facilities,  the  administrators  are  un-
aware of the rate structures of their electric bills.
Electricity is typically billed in two ways:  (1) by
the amount of energy used over a specific period,
measured in kilowatt-hours and  (2) by demand,
the rate of the flow of energy, measured in kilo-
watts.  Electric  utilities  structure their rates  on
the basis of the user's  required voltage  level,
the electricity  usage at different hours  of the
day, and the peak demand. A WWTP might be
operating equipment when electricity is at peak
rates,  resulting in unnecessary costs. Plant per-
sonnel should become familiar with the energy
rate structure to determine whether they can op-
erate  equipment  at off-peak hours or  reduce
energy consumption during peak-demand hours.

For example, the WSSC revised its  power pur-
chasing to optimize  energy costs  at WWTPs. The
WSSC purchases blocks of power supply (kilo-
watt-hours)  at  a  wholesale,  competitive  level.
This provides for a predictable baseload cost.
The WSSC purchases  its remaining kilowatt-

hours on the spot market. The WSSC also pur-
chases  energy  (kilowatt-hours)  and capacity
(kilowatts) separately. As market prices shift, the
electric utility shifts the WWTP's load accord-
ingly (Taylor 2005).  An  example  of shifting
loads is the  use of  system  storage to  store
wastewater during periods of highest load rather
than operating pumps. The stored wastewater can
then be pumped and treated  during  periods of
low demand.

Another example, EBMUD has also changed the
way it  purchases electricity.  EBMUD used to
buy electricity solely from Pacific Gas and Elec-
tric at an average cost of $0.11 per kilowatt-hour.
Now EBMUD  purchases  electricity from the
Western Area  Power Administration,   which
markets hydroelectric power, at an average cost
of  $0.06 per  kilowatt-hour  (Cohn  2005).  It
should be noted that there  are risks  associated
with purchasing electricity on the spot market.
Correct  market  forecasts  are essential,  and
WWTPs must deal with price volatility  in the

A technology often used to  supplement energy
usage at WWTPs is cogenerating electricity and
thermal energy on-site, capturing and using an-
aerobic digester gas (or bio-gas). For example,
EBMUD generates  enough  energy for approxi-
mately 50 percent of its energy needs. EBMUD
is considering a digester cover that would store
gas at night, creating  a temporary  reserve that
could be used during peak-demand periods. The
Encina Wastewater Authority also uses digester
gas (bio-gas) to  generate electricity on-site. En-
cina has also adopted  seasonally  adjusted time-
of-use rates from its electric company. By shift-
ing treatment process times, Encina has been
able to reduce peak-demand rates. By using the
time-of-use  rates and cogeneration,  Encina esti-
mates annual savings of $350,000 per year.  At
EBMUD, cogeneration of electricity and thermal
energy has resulted in cost savings  estimated at
$1.7 million annually  (California Energy Com-
mission, Encina  Case Study, 2003).

Energy Management Education
Energy conservation includes monitoring  and
maintaining each process  in  the plant.  Proper
maintenance  and upkeep of the equipment and
processes in a facility are an integral component
of a complete energy conservation plan. Em-
ployee training and awareness of the energy plan
and procedures need  to be continually updated
to ensure that the  goals and energy savings are

Training for  plant personnel is essential as is
educating the public  on  energy, efficiency  and
conservation.  A good option for conserving energy
at a WWTP is the possibility of reducing flows
to the  plant by reducing water use in  the com-
munity. As less  water flows into the plant,  less
volume is treated  and thus less energy is con-
sumed. An  aggressive  Infiltration and  Inflow
program can also reduce flows to the plant.

Ideas for promoting water conservation  include

  Educating residents  about  high-efficiency
   appliances, plumbing fixtures and  water-
   saving habits
  Educating residents to reduce peak  water
   demands  to avoid the  extra costs associated
   with operating additional  pumps and equip-
   ment during peak-flow periods

Many WWTPs are beginning to identify a range
of approaches for setting  their rate  structures
based  on full-cost recognition.  Under full-cost
pricing, utilities recognize their actual cost of pro-
viding  service over the long term and implement
pricing structures that recover costs and promote
economically efficient and environmentally sound
water use decisions by  customers.  WWTPs are
encouraged to factor in the full spectrum of capi-
tal  and  O&M  costs, including   energy  usage
(i.e., life cycle costing), in accordance  with full
cost pricing concepts (U.S. EPA 2006).

Energy conservation costs depend  on the equip-
ment  purchased  and  the  plans  implemented.
There  are costs associated with tracking energy
usage,  equipment  efficiency, and  with gaining
knowledge about the  distribution of  energy

Cost savings are expected as energy use de-
creases. According  to the California  Energy
Commission's Electric Load Management study
(2003), the Encina WWTP (36 mgd) altered the
operation of certain processes  to off-peak hours
and realized cost savings of $50,000 per  year.
The study also  found that the Moulton Niguel
Water  District,  which  serves 160,000  people,
eliminated peak  operations at several pumping
stations and reduced costs by $320,000 per year.
The study concluded  that cost savings from im-
plementing an  energy  management system to
track energy for a WWTP treating an average
daily flow of 15 million to 30 million gallons per
day is estimated to be  up to $25,000 per year.

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