The City of Toronto’s previous biosolids management strategy included incinerating sewage sludge at the 818 ML Ashbridges Bay Treatment Plant. To lower operations costs and to address environmental constraints, it was determined that other biosolids management practices should be employed. R.V. Anderson Associates Limited (RVA) was retained to lead the development of a diverse beneficial biosolids use program that would allow shut down of the plant’s sewage sludge incinerators. The program resulted in the implementation of three major design/build projects, including the $23-million Pelletizer Facility, $40-million New Truck Loading and Odour Control Facilities, and the $34.6 million New Plant-Wide Heating System.
The scope of this $90+ million program was to prepare the proposal call documents for contractors to bid on the provision of beneficial use options for approximately 50,000 dry tonnes per year of biosolids. Contractors were selected for a direct land application of biosolids in a cake form, as well as marketing of the biosolids pellets.
RVA also assisted the City of Toronto in evaluation of the related design/build proposals, contractor selection, site inspection and contract administration services for all three projects. The work also included participation in commissioning of the projects and operator training activities.
For the New Truck Loading and Odour Control Facilities, and the New Plant-Wide Heating System, RVA completed 20% design to assist in limiting risk to the City of Toronto—the expanded design criteria set enhanced quality and performance standards for the contractors to bid on. This approach better managed risks related to the quality of the final product.
The project included construction of the Dryer Pelletization facility with a total capacity of 25,000 dry tonnes/year of 90% dry pellets. The process transforms anaerobically digested material into a useable fertilizer product. The facility utilizes the Seghers indirect drying system (referred to as the Pelletech® Process), and comprises two individual process trains, each with a capacity of 1.85 t/hr.
The pelletized fertilizer product is clean, odorless, easy to handle and store, and is sold as a fertilizer or soil conditioner. The facility minimizes environmental impact by controlling noise and odor to surrounding areas.
The City was able to reduce the number of trucks on the roads, further minimizing the facility’s environmental footprint and the costs associated with transportation.
The project included a 1,200 m3 sludge cake storage facility; a high-pressure sludge cake pumping and pipe lubrication systems; a fully automated truck loading facility with an additional 800 m3 sludge cake storage; and an odour control system, consisting of two-stage chemical scrubbing and four biological filters.
The new facilities are capable of pumping approximately 30% dry sludge cake over a distance of 185 m with or without use of a polymer-type lubricant. Truck loading operations are carried out by truck drivers. The facility is capable of loading a large truck in 15 minutes, which equals to 20 trucks in a six hour work day.
The odour control system, which in addition to a chemical scrubber, employs one of largest bio-filters in Canada. It has a capacity of 20 m3/s (units consistency) of odourous air containing 100,000 odour units/m3, and was designed to meet a stringent 1 ou/m3 at the nearest point of impingement.
The overall project comprised converting the plant’s old steam heating system to a hot water heating system. The first phase of the Plant Wide Heating System project converted a portion of the loads previously heated through the steam heating system by connecting them through secondary loops to a hot water primary loop reservoir. The primary loop reservoir was constructed throughout the plant. Four gas-fired hot water boilers and related circulation pumps were added to supply the hot water.
During Phase 2, the remaining steam heating system, with steam currently provided by a number of steam boilers, was replaced. Additional secondary heat loops were constructed and connected to the existing hot water primary distribution loop or extended through the existing secondary heat loops. All the existing buildings and area loads previously heated with steam were converted to hot water heating.
The heating system also provided additional heating units within areas that were identified as requiring additional heat, as well as provided the heating requirements for Digestors 1-4. Redundant steam piping and equipment was removed.