Field Data and Experience Summary from Ashbridges Bay Treatment Plant Biosolids Loadout Facility Expansion in Toronto, Canada

The City of Toronto's Ashbridges Bay Treatment Plant (ABTP) currently treats an average of 180 mgd and produces around 55,000 dry tons per year of digested sludge cake at about 30 percent solids concentration. Until 1996, all sludge was incinerated in multiple-hearth incinerators. In 1996 the City began a small biosolids beneficial use demonstration program.In January 1998, the City Council directed staff to shut down the incinerators by December 31, 2000 and introduce a full-scale beneficial use program. After a series of staff reports, Council accepted an implementation plan, which would implement the 100 percent beneficial use program by January 1, 2001.A consulting team made up of R. V. Anderson and Associates, Ltd. and Brown and Caldwell was hired to oversee the fast track implementation of the conversion from incineration to beneficial use. As part of the program, the City issued the following bid requests and subsequent contracts:A land application contract (Land Application Contract) to expand the demonstration program's beneficial reuse of dewatered biosolids produced by the plant.A design build contract (Loadout Contract) to construct 2,000 cubic meters of dewatered biosolids storage, cake conveyance systems, truck loading and odor control facilities.A design build contract (Dryer Contract) to identify a recommended process and construct a Class A biosolids treatment technology. This contract resulted in construction of sludge drying facilities.A design build contract (Plant Wide Heating Contract) to replace the existing incinerator heat-recovery system with a system of digester gas driven boilers to maintain the plant's hot water system in service.This paper provides details on the Loadout Contract that started operation in March 2001 and presents operational information from that facility. The facility includes three 400- cubic-meter bulk storage silos and four 200-cubic-meter loading hoppers that load biosolids hauling trucks. Previously existing cake pumps deliver dewatered cake to the storage silos through a combination of new and existing pipe. New cake pumps then transfer the stored biosolids to the loading hoppers through runs of pipe that are as long as 180 m (580 ft). The piping system is carbon steel with provisions for friction-reducing lubrication.Due to the existing site layout and the potential length of the pipe runs, there were several concerns regarding the friction pressures that would develop in the cake pumping system. This paper briefly discusses the options considered during the conceptual development of the cake pumping system from the existing cake dewatering facility, the selection of a preferred location for the new loading facility and the requirements for, and location of, intermediate storage.Data are presented on the observed relationship of pressure, pipe station, use or lack of use of pipeline lubrication, flow rate, and the observed pressure drop for this particular sludge.