By David Jess,Bonnybrook Wastewater Treatment Plant
First spray with puck holder/nozzle.
Top view of the chlorine header.
The City of Calgary owns and
operates the Fish Creek
Wastewater Treatment Plant, a
72,000 m3/d oxygen activated
sludge (UNOX) plant. The Fish Creek
Wastewater Treatment Plant went into
service in 1960. It doubled in size in
1968, followed by the addition of secondary
treatment in 1980. Phosphorous
removal was introduced in 1982 and
ultra violet disinfection in 1997.
The Fish Creek Wastewater
Treatment Plant started using the
UNOX system for secondary treatment
in 1980. Since 1980, the plant has
experienced severe foam in the secondary
clarifiers due to Nocardia
growing in the bio-reactor.
Nocardia is a member of the family
Actinomycetalesand, filamentous
branching bacteria and is strictly aerobic.
High levels of fats, oils and greases
or hydrocarbons and phenols (compounds
in which a hydroxyl group is
bonded to an aromatic ring) usually
cause its presence in wastewater. One
of the cost-effective ways to eliminate
foam-causing Nocardia is with chlorine.
With the Fish Creek Plant located
in the middle of a residential area, the
capital cost of implementing a one
tonne chlorinating system with a
scrubber system was over $280,000.
Testing Chlorine Pucks
One day the chief operator, Wayne
Harris, mentioned that, when foaming
started in his swimming pool, he controlled
it with chlorine pucks. So we
bought some chlorine pucks and threw
them in the clarifier scum pits. This
helped lower the level of the foam in
the anaerobic digesters, but did not
stop the foam-causing Nocardia in the
clarifiers.
The next step was to locate the
chlorine pucks in the centre wells of
the secondary clarifiers. After the
pucks were placed in floating holders
(the same type you see in a hot tub), we
noticed the foam was turning a lighter
colour of brown. Also the pucks did
not work that well in cold weather.
Our Senior Process Engineer, Paul
Do, informed us that the only way to
kill Nocardia with chlorine is to spray
it from the top! Since we had no capital
for this project we built a prototype
puck holder/nozzle from parts that we
had in the plant and put it into service
using disinfected effluent water to mix
with the chlorine pucks. The foam
changed to a light brown colour and
migrated into the main area of the clarifier.
The new puck holder/nozzle
worked well, but the water was not
atomized well enough and this caused
more foam in the centre well due to
heavy droplets.
In order to better atomize the water,
we installed two showerheads onto the
puck holder/nozzle. Not only did this
reduce the foam, it reduced the amount
of chlorine pucks used to two pucks in
three days (or $0.45 per day).
The New Design
There are only two headers in the
centre well of the clarifier, one set with
water only with the showerheads and
the other with chlorine pucks with the
showerheads. The spray on both bars
must be able to reach from the very
centre to the outer ring. That way no
foam will be untouched.
The chlorine puck system was
removed for three days while we built
the new system. The clarifier foam
returned. This showed us that the foam
reduction was from the chlorine not
the weather.
On December 8, 2003, the new system
with eight showerheads on a chlorine
header and eight water nozzles
was put into service.
By December 16, the only foam left
in the clarifier was in the centre well.
By December 22, there were no
traces of foam in the clarifier. We also
added heat tape and insulation to the
system.
The Final Results
In 14 days we used 38 chlorine
pucks for a total of $51.68. The total
cost of the project was $3,100.00. This
method is safe to use in residential
areas as well as non-hazardous when
handling. Continual testing for residual
chlorine showed 0 at the outfall of
the plant.
David Jess is Operations &
Maintenance Supervisor, Bonnybrook
Wastewater Treatment Plant, Calgary,
Alberta.
Contact e-mail: djess@calgary.ca.
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