Diagram
of Wastewater Treatment Process
(PDF 1 page, 399 KB)
Solids handling at the Lakeview WWTF consists of thickening, dewatering, incineration and ash storage in onsite lagoons.
Thickening Process:
Thickening increases the solids content of the sludge in
preparation for dewatering. Waste Activated Sludge (WAS) is
collected in WAS tanks and pumped to thickening centrifuges,
which 
separate the liquid content of the sludge in a similar
way to how the spin cycle of a washing machine removes water
from clothes. Thickened WAS (TWAS) flows by gravity to blend
tanks, where it is mixed with the raw sludge from primary
treatment tanks. Centrate (the liquid removed from thickened
sludge) is recycled back to the primary tanks. Polymer may
be added to further thicken the sludge.
Dewatering Process:
Dewatering increases the sludge's solids content to about
28 per cent total solids in preparation for incineration.
TWAS and 
primary sludge are collected in the blend tanks and
pumped to dewatering centrifuges. Dewatered cake is conveyed
by an inclined screw conveyor into collection silos. Centrate
flows by gravity to centrate tanks and is pumped back to the
head of the plant for treatment. Polymer is added to the blended
sludge feed to increase efficiency.
Fluid Bed Incinerators:
The dewatered solids are pumped from the collection silos to the fluid bed incinerators. Dewatered cake is received by truck from Clarkson WWTF.
Combustion air is fed into the windbox at the base of the
incinerator. Dewatered cake and supplementary fuel (fuel oil
or natural gas), if necessary, is pumped into the fluidized
sand bed. Water is evaporated and most of the solids combustion
is processed within the sand bed. Final combustion occurs
above the bed in the freeboard section with exhaust gases
exiting at 700 - 900 degrees Celsius.
No supplementary fuel is needed if the dewatered solids are about 28 per cent.
(Above photo: Image shows incinerator under construction)
Air Pollution Control:
The air pollution control system consists of a quenching
unit, impingement 
scrubber and a multiple, fixed venturi scrubber.
The quenching unit reduces the exhaust gas temperature and
most of the ash and gaseous pollutants are collected in a
slurry and flow by gravity to the ash tanks. The impingement
scrubber and fixed venturi further reduce the temperature
of the exhaust gas and remove the rest of the ash and gaseous
pollutants. Cleaned and cooled exhaust is discharged to the
atmosphere. Dedicated emissions monitoring systems provide
a continuous check on emissions levels.
Ash Lagoons:
The ash slurry from the air pollution control system is pumped to ash lagoons for onsite storage.
