December 2007, Vol. 19, No.12

Plant Profile

Lakeview Wastewater Treatment Plant

lakeview_plantprofile_dec07.jpg Location: Mississauga, Ontario
Startup date: November 1961
Service population: 1 million
Number of employees: 55
Design flow: 118 mgd (447,000 m³/d)
Average flow: 95 mgd (360,000 m³/d)
Peak flow: 335 mgd (1,268,000 m³/d)
Annual operating cost: $22 million Canadian 

In the late 1950s, the Ontario Water Resources Commission spent about $1.7 million to build the Lakeview Wastewater Treatment Plant (WWTP) to serve the Region of Peel, near Toronto. At startup, the average daily flow was about 2 mgd (7600 m³/d).

Jump forward 45 years to December 2006, and Lakeview had just completed a $260 million expansion and upgrade project to meet the community’s needs until 2031. On average, the plant now treats 95 mgd (360,000 m³/d) from about 1 million people, along with industries, commercial facilities, and institutions in the eastern section of Mississauga, Brampton, Bolton, and Caledon East.

Highlights of the upgrade and expansion include a new headworks facility, enhanced nitrification, a new biosolids handling facility, and additional biosolids incinerator capacity. The new headworks facility, designed for future requirements of 137 mgd (518,000 m³/d), is the largest perforated-plate screening facility in North America. Full-scale pilot demonstration of the integrated fixed-film activated sludge process is being evaluated for performance and operability for enhanced nitrification. With one new and three replacement 110-dry-ton/d (100-dry-tonne/d) fluidized-bed incineration units, the Lakeview WWTP is the largest fluidized-bed biosolids incineration facility in the world.

 

Liquid Process
Wastewater enters the treatment plant through the headworks, which consists of mechanical screens, screening grinder washer compactors, and grit chambers. Material caught by the six fine mechanical screens is removed, cleaned, and dewatered before disposal. The four grit chambers remove grit by inducing a vortex pattern in the circular chamber. A drive paddle in the vortex unit maintains circulation under all flow conditions. Grit slurry pumps periodically remove the accumulated grit from the hopper at the bottom of the grit chambers. The
lakeview_01.JPG
With one new and three replacement 110-dry-ton/d (100-dry-tonne/d) fluidized-bed incineration units, the Lakeview WWTP is the largest fluidized-bed biosolids incineration facility in the world. (Photo by Region of Peel.) 

grit is dewatered before being removed to disposal bins.

Eleven primary sedimentation tanks allow suspended solids to settle and floating debris and scum to be skimmed from the surface. The flow then passes into the plant’s 14 aeration tanks, where ferrous chloride is added to mix with the wastewater to flocculate excess phosphorus. Fine-bubble diffusers aerate and mix the wastewater.

After aeration, 16 secondary clarifiers provide a chance for additional suspended solids and flocculated phosphorus to settle out of the water.

Secondary-treated effluent flows over the clarifier weirs. Sodium hypochlorite is added at the beginning of the outfall for disinfection. Sodium bisulfate is added toward the end of the outfall for dechlorination.

The final effluent is discharged to Lake Ontario through a pipe reaching 4100 ft (1250 m) offshore at lake bottom through diffusers. This structure ensures that the effluent is retained long enough to be thoroughly disinfected. The 35 separate ports in this 617-ft-long (188-m-long) pipe discharge the final effluent over a large area to minimize impact to the environment.

Solids Process
Solids handling at the Lakeview WWTP consists of thickening, dewatering, incineration, and ash storage in onsite lagoons. Waste activated sludge (WAS) from the secondary clarifiers is collected in WAS tanks and pumped to centrifuges to be thickened to about 5% to 6% solids. The thickened WAS flows by gravity to blend tanks, where it is mixed with primary sludge from primary treatment tanks. The mixture is between 3% and 4% solids.
  

lakeview_02.jpg
The new headworks facility at the Lakeview Wastewater Treatment Plant in Mississauga, Ontario, was designed for future requirements of 137 mgd (518,000 m³/d). It is the largest perforated-plate screening facility in North America. (Photo by Region of Peel.) 
Next, five dewatering centrifuges and polymer increase the blended solids content to about 26% to 28% in preparation for incineration. Dewatered cake is conveyed by an inclined screw conveyor into collection silos.

The dewatered solids are pumped from the collection silos to four fluid-bed incinerators. Additional dewatered cake is received by truck from the nearby Clarkson Wastewater Treatment Facility.

Combustion air is fed into the windbox at the base of the incinerator. Dewatered cake and supplementary fuel, fuel oil or natural gas, is pumped into the fluidized sand bed. (No supplementary fuel is

needed if the solids are dewatered to about 27% and volatiles of 70%.) 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 temperatures between 700°C and 900°C.

The incinerator exhaust is treated to protect air quality. 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.

The ash slurry from the air pollution control system is pumped to ash lagoons for onsite storage.

Job Well Done
KMK Consultants Ltd. (Brampton, Ontario) and Black & Veatch (Kansas City, Mo.), the consulting engineering firms that planned and designed the upgrade project, received the 2007 Willis Chapman Award from the Consulting Engineers of Ontario (Toronto). The award is the highest distinction in Ontario’s consulting engineering community. It recognizes the project that best demonstrates the valuable contribution that consulting engineers make to the social, economic, and environmental quality of life in the province.

“This project and the planning that preceded it have brought out the best in everyone,” said Mark Schiller, Peel Region director for water and wastewater treatment. “Best project management and wastewater treatment practices came together in the Lakeview WWTP expansion and upgrade to improve the performance and operations of the wastewater treatment plant and quality of life for the people in this region.”

 

grit is dewatered before being removed to disposal bins.Eleven primary sedimentation tanks allow suspended solids to settle and floating debris and scum to be skimmed from the surface. The flow then passes into the plant’s 14 aeration tanks, where ferrous chloride is added to mix with the wastewater to flocculate excess phosphorus. Fine-bubble diffusers aerate and mix the wastewater.After aeration, 16 secondary clarifiers provide a chance for additional suspended solids and flocculated phosphorus to settle out of the water.Secondary-treated effluent flows over the clarifier weirs. Sodium hypochlorite is added at the beginning of the outfall for disinfection. Sodium bisulfate is added toward the end of the outfall for dechlorination.The final effluent is discharged to Lake Ontario through a pipe reaching 4100 ft (1250 m) offshore at lake bottom through diffusers. This structure ensures that the effluent is retained long enough to be thoroughly disinfected. The 35 separate ports in this 617-ft-long (188-m-long) pipe discharge the final effluent over a large area to minimize impact to the environment.Solids handling at the Lakeview WWTP consists of thickening, dewatering, incineration, and ash storage in onsite lagoons. Waste activated sludge (WAS) from the secondary clarifiers is collected in WAS tanks and pumped to centrifuges to be thickened to about 5% to 6% solids. The thickened WAS flows by gravity to blend tanks, where it is mixed with primary sludge from primary treatment tanks. The mixture is between 3% and 4% solids.needed if the solids are dewatered to about 27% and volatiles of 70%.) 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 temperatures between 700°C and 900°C.The incinerator exhaust is treated to protect air quality. 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.The ash slurry from the air pollution control system is pumped to ash lagoons for onsite storage.KMK Consultants Ltd. (Brampton, Ontario) and Black & Veatch (Kansas City, Mo.), the consulting engineering firms that planned and designed the upgrade project, received the 2007 Willis Chapman Award from the Consulting Engineers of Ontario (Toronto). The award is the highest distinction in Ontario’s consulting engineering community. It recognizes the project that best demonstrates the valuable contribution that consulting engineers make to the social, economic, and environmental quality of life in the province.“This project and the planning that preceded it have brought out the best in everyone,” said Mark Schiller, Peel Region director for water and wastewater treatment. “Best project management and wastewater treatment practices came together in the Lakeview WWTP expansion and upgrade to improve the performance and operations of the wastewater treatment plant and quality of life for the people in this region.”