ONTARIO CENTRE FOR MUNICIPAL BEST PRACTICES
393 University Ave., Suite 1701, Toronto, Ontario, M5G 1E6
BEST PRACTICE SUMMARY REPORT
October, 2006
Water and Wastewater
ENERGY MANAGEMENT WITH ALTERNATIVE
SOURCES OF ENERGY
Practice Identification: Water and Wastewater – Alternative Sources of Energy
Case Study Municipality:
 City of Ottawa
Municipal Profile:
Municipality
Population
Water Distribution
Wastewater Collection
Water Treatment Plant
Wastewater Treatment Plants
City of Ottawa1
865,550
2,690 km of watermains with 181,316 service
connections, and 14 pump stations
2,173 km of sanitary sewers, with a total of 181,635
sewer service connections, and 70 pump stations
Britannia has an Average Day Demand (ADD) of 200
ML/day from the Ottawa River
Lemieux has an Average Day Demand (ADD) of 143
ML/day
Ottawa WWTP serves a population of 786,130, with an
Annual Average Flow (AAF) of 422 ML/day
Key Words:
 Energy, Digester Gas, Turbines, Alternative Sources of Energy
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Municipal Profile is 2005 data
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Related National Benchmarking Goal(s):
 Meet Service and Performance Requirements at Sustainable Cost
Related Performance Measures:
 Pump Station Energy Consumed (‘000) kWh / Total Pump Station Horsepower
 Cost of Pump Station Energy / Total HP
 Cost of Energy Purchased / ML Treated
 Energy Consumed in kWh / ML Treated
Related InfraGuide Best Practices:
 None
Description of Case Study
Wastewater:
Currently the Robert O. Pickard Environmental Centre, Ottawa’s wastewater treatment
plant, is categorized as a general commercial user, but it is operating close to the 5000
kW peak demand threshold that would categorize the plant as a large user; this would
mean an increase of $155,000/yr for energy (delivery and administrative costs). To
maintain a purchased peak power demand < 5000kW, Ottawa has implemented an energy
management plan that utilizes and maximizes the output from an alternative source of
energy – Digester Gas. The objective is to optimize the utilization of digester gas as a
fuel, maximizing cogeneration output.
The digester gas produced is utilized in 3 different ways: as a fuel for cogeneration, as
fuel for the boiler plant, and diversion to an open flare.
The first priority for the gas is cogeneration. Ottawa’s Pickard WWTP has three
generators driven by internal combustion reciprocating engines which can produce 2.4
MW of energy for the aeration blowers, gas compressors, pumps, and centrifuges, and 2.9
MW for the plant heating system.
The second priority for the digester gas is to the boiler plant which consists of 4 duel fuel
3000 kW input boilers. The boilers will be fired on digester gas after 1 – it is confirmed
that the heat demand is not being met by cogen, 2 – the cogen output is optimized and 3 –
there is a surplus of digester gas being flared.
Finally, the third priority or option is to divert the digester gas to an open flare.
The Pickard WWTP Supervisory Control & Data Acquisition (SCADA) system is used to
balance the digester gas allocation for the 3 alternatives. If there is excess gas being
flared, the boiler plant will be fired. If the cogeneration is not being optimized, the
digester gas supplied to the boilers will be reduced. The goal is to at all times optimize
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the output of the electro/thermal cogeneration units.
effective maintenance practices.
Output is also maximized by
The cogeneration facility has been operating continuously since October 1997. As
mentioned above, there are three engine/generator sets that run on digester gas or utility
supplied natural gas. The cogeneration units required an initial capital investment of $4.5
million dollars with an estimated annual electricity net cost savings of $1,000,000. An
additional $400,000 per year is saved by using digester gas rather than purchased natural
gas to satisfy process and building space heat demands.
In addition to optimizing digester gas utilization, Ottawa is also currently investigating
using the outfall at the wastewater treatment plant to generate energy.
Water Supply
At the Lemieux Island Water Purification Plant, turbines using the natural head of the
Ottawa River are used as the base load drivers to pump drinking water for high lift
pumping requirements for treated water. This alternative saves the water supply plant
$100,000/month in energy costs. This is a significant component of Ottawa’s distribution
pumping equivalent to 200 ML/d of the 340ML/d average day demand.
A natural gas generator has also been installed at the Britannia Water Purification Plant
and synchronized with the power grid. Beyond providing an emergency back-up power
supply, the operation of the unit is dictated by the price of electrical energy. When the
cost of electricity is greater than $0.12.kW, the lean burn natural gas generator will be
utilized. When in operation the unit generates 3.5 MW, 2.4 MW of which is used for
plant operations and 1 MW for export back to the utility power grid. In 2005, over a four
month period, the unit ran for 672 hours providing over 2,000 MWHs of electricity. This
operation resulted in energy cost savings of over $180,000
Benefits
 Increased operator awareness and involvement in energy management
 Decreased electrical energy consumption
 Efficient use of a by-product from sludge digestion
 Decreased energy costs
Efficiency
By implementing the above mentioned alternative sources of energy Ottawa has seen
significant savings in terms of electricity demand reduction. Maintaining a peak demand
below 5000 kW has a related savings of $155,000/year. The cogeneration facility results
in a savings of $1,000,000/year in elimination of purchased electricity. The utilization of
the of digester gas to meet process and building space heat demands eliminates the need
to purchase 1,000,000 m3 of natural gas annually. At the 2005 price for natural gas this
equates to approximately $400,000/year in additional savings.
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Utilization of the natural head of the Ottawa River for pumping requirements saves the
water treatment plant $100,000/month.
Finally the natural gas generator offset electricity costs by $180,000 in 2005.
Effectiveness
The City of Ottawa has achieved significant energy savings by utilizing alternative
sources of energy. They have also been able to better control their peak demand at the
wastewater treatment plant, preventing them from being classified as large user and
paying a large user rate.
Community or Environmental Outcomes
When considering the purchase and installation of equipment intended for use as
alternative energy sources for power generation, it is important that all aspects of the
environment, especially air and noise emissions, be considered. The City of Ottawa’s
generator was designed, permitted and installed with emissions considerations taken into
account. The selection of natural gas as the energy source and a 'lean burn' engine design
and operating controls allow the City to operate this generator under all atmospheric
conditions, including Smog Days.
The Britannia WPP is situated in a well used public park setting. It was important that
noise controls be designed into the equipment and facility to ensure the lowest noticeable
impact to those enjoying the surrounding green setting. The marginal additional capital
and operating costs of this environmental equipment allow the City the greatest flexibility
to operate the equipment on those days with the highest demand on the provincial utility
power grid.
Statutory Requirements
None
Replication of the Case Study
Utilization of methane gas can be performed at wastewater treatment facilities with
sludge digestion. Other alternative sources of energy are affected by the location and
surroundings of the facility and can be investigated on a case-by-case basis.
Supporting Documentation
None
Other OMBI Members that have implemented this practice:
There are a number of Ontario municipalities that are also utilizing digester gas to
generate heat and/or electricity including: Region of Durham, Region of Halton, Region
of Peel, and City of Toronto. Many municipalities are also in the process of investigating
alternative sources of energy. For example, the Region of Durham, and the Cities of
Windsor and Durham are investigating the potentials of wind power
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Contacts
Dixon Weir
Manager, Drinking Water Services
City of Ottawa
(613) 580-2424
[email protected]
David Robertson
Program Manager, Wastewater Treatment
City of Ottawa
(613) 580-2424
[email protected]
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