Treating cooling pond water for Wabamun Lake level mitigation project in Alberta
TransAlta, Canada’s largest nonregulated
electricity generation
and marketing company, operates
three power plants in the
Wabamun Lake area, west of
Edmonton, Alberta. For the past 25
years, two of these plants have used
water from the lake to feed their cooling
towers. The level of the lake has
decreased significantly, not only from
power plant intake, but also from lack
of rainfall, surface runoff, and natural
evaporation. The challenge was to
recharge Wabamum lake by treating
nearby cooling pond water, fed by the
North Saskatchewan River, and returning
it to the lake.
In 1997, TransAlta built a water
treatment plant next to its 2,020-
megawatt Sundance power plant to
mitigate TransAlta’s historical and
ongoing effect on the lake’s water
level. The treatment plant treats cooling
pond water so that it can fill the
lake. Water taken from the cooling
pond is replaced by water from the
North Saskatchewan River.
Subsequently, and based on input
from local stakeholders, TransAlta
expanded the output of water to the
lake with the construction of an additional
plant. It began operating in June
2002 to ensure the company would
meet its license requirements. The two
treatment plants comprise the
Wabamun Lake Water Treatment
Facility. The second plant had to meet
stringent effluent water quality
requirements of 0.10 NTU turbidity
and no more than 1/100 mL of living
zooplankton. It also had to produce 8
million cubic metres of treated water
per year.
Table 1 - Water Treatment System Final Effluent Quality Requirements as specified
by Alberta Environment.
In June 2001, TransAlta awarded
John Meunier Inc. of Montreal,
Quebec, a $10.7 million contract to
provide a water treatment system,
including a mechanical and process
guarantee.
“The project was a real challenge,”
says Gilles Filion, president and general
manager, John Meunier Inc.,
“because of the very tight schedule and
the strict process warranty. The contract
was awarded to us on June 28,
2001. The installation had to be complete
by March 20, 2002, with
mechanical and process testing from
the end of March to the beginning of
June. Actual system startup was scheduled
for the end of June 2002.”
Says Filion, “TransAlta was working
with our local sales representative
on a request for a clarifier package
plant. John Meunier met with the
client, and after evaluating their needs,
offered them a complete turnkey system,
which included two Actiflo®
microsand-ballasted clarifier package
plants and three Dusenflo® gravity filter
package plants.”
Installation of the Actiflo clarifier.
The turnkey contract includes: site
preparation; water supply; drainage;
interior and exterior fire protection
systems; pumping station and underground
piping; reservoirs; building
and services rooms and concrete foundations;
walkways and stairways; electrical
supply and services; emergency
lighting; and heating and ventilation.
Besides the Actiflo and Dusenflo
package plants, the mechanical
process equipment includes chemical
dosing systems, an ozonation unit and
two cooling towers.
At the Wabamun Lake Water
Treatment Facility, the water to be
treated is first chlorinated to kill zooplankton,
algae and bacteria. Next, the
pH is adjusted using sulfuric acid.
Alum coagulant is used to destabilize
colour, particles and colloids before
the water is fed to the Actiflo clarifiers.
The Actiflo process uses microsand
as a seed for floc formation. The
microsand provides increased surface
area for floc attachment, and acts as a
ballast or weight. The resulting sandballasted
flocs have higher settling
velocities than do flocs produced in
conventional clarifiers. This allows
much higher clarifier overflow rates,
which translate into reduced clarification
retention time, reduced system
footprint and reduced total cost. The
Actiflo is able to produce settled water
with turbidity less than 1.0 NTU.
Clarified water from the Actiflo
systems is fed to the Dusenflo filters,
remaining anthracite and sand to remove the largest suspended
solids. The water then flows through the finer sand
media at the bottom of the filtration bed, where the remaining
turbidity, color and bacteria are removed.
The ozonation system inactivates any remaining bacteria,
algae and zooplankton in the filtered water. Thiosulfate
is used to remove chlorine and ozone in the treated water
before it is discharged to the lake.
The cooling towers ensure that the treated water discharged
to Wabamun Lake is kept at a constant temperature,
as the discharged water must not vary more than 3°C
from the lake water temperature.
In addition to the mechanical process equipment, John
Meunier Inc. also supplied all instrumentation and controls,
start-up and commissioning services, performance
testing and a full-time, onsite technical advisor until final
acceptance by the client.
With commissioning completed at the end of June 2002,
the project met the schedule requirements
with no delays. The water treatment
system is meeting the effluent
quality requirements as requested by
Alberta Environment. Contact Jean-François Beaudet who is
field Service Supervisor, ACTIFLO®
Process for John Meunier Inc.
E-mail: jfbeaudet@johnmeunier.com.
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