SWITCHING FROM INCINERATION OF THE HEAT TREATED SLUDGE TO INCINERATION OF THE UNTREATED SLUDGE – EXPERIENCE AT THE REGION OF PEEL LAKEVIEW WWTP, ONTARIO

The Lakeview wastewater treatment plant (WWTP) in Mississauga, Ontario, is owned by the Region of Peel and is operated by the Ontario Clean Water Agency (OCWA). The plant is equipped with fluid bed incineration (FBI) systems as their disposal option for almost thirty years. The facility is located on the shore of Lake Ontario, just west of the Metropolitan Toronto and serves Mississauga, Brampton and the Town of Caledon. It has a design capacity of 118 mgd on an annual average. For the last several decades, sludge generated at the plant and imported sludge from Clarkson WWTP (The second WWTP in the Western part of Mississauga in the Region of Peel) were heat-treated by the Zimmerman Process (or Zimpro), decanted, dewatered up to 38%TS and burned in three cold-wind-box (CWB) fluidized beds.Due to the high maintenance and the odor generated by Zimpro, in 2003 The Region of Peel decided to eliminate the heat-treated system and to replace the three existing CWB fluid beds by four hot-windbox (HWB) fluid beds, each dispose of 110 US tons of dry sludge per day. Today the untreated sludge at Lakeview is dewatered to about 27% dry solids by centrifuge decanters and combusted autogenously in the HWB fluid bed incinerator. The untreated sludge is about 60/40 mix of primary and activated sludge. Sludge is primarily municipal with at least 30% from industrial sources.The initial two CWB fluid beds at the plant began operation in 1982. In 1994, an additional third CWB system was put on-line. All threes systems were of type push-pull and equipped with waste heat boiler and venturi scrubber. The steam generated from the plant was used in the Zimpro heat-treated system. In February 2006, the first of four hot-windbox systems was on-lined and commissioned. The new system is equipped with external shell and tube heat exchanger for preheating the combustion air to 1230 oF to hugely reducing the auxiliary fuel consumption, and a venturi scrubber of type multiple venturi scrubber as air pollution control device.Since it went operational in February 2006, the new hot wind-box system ran around the clock, 24 hours a day, 7 days a week with very little requirement for auxiliary fuel nor for makeup sand. The system satisfied the design emission requirements by a wide margin upon initial performance testing. The paper discusses the detailed transition period during the replacement of the Zimpro system. The text provides technical and economical differences between incineration of the treated and the untreated sludge.With all four fluid beds in operation by mid 2009, the Lakeview plant will be the largest sludge incineration plant in the world.The Region of Peel has shown the HWB fluid bed incineration system to be an economical, environmentally acceptable sludge disposal method satisfactory to the Authority, the permitting agencies and the general public.