Solid Waste & Recycling


Aerobic Technology

Ontario's Township of Laurentian Valley, in partnership with the Town of Petawawa, the City of Pembroke, the Township of North Algona-Wilberforce, and the Township of Bonnechre Valley (combined popul...

Ontario’s Township of Laurentian Valley, in partnership with the Town of Petawawa, the City of Pembroke, the Township of North Algona-Wilberforce, and the Township of Bonnechre Valley (combined population of 40,000) has committed to the implementation of new diversion facilities to reduce the disposal of solid waste through landfilling. With assistance from consultants J.L. Richards & Associates Limited and Golder Associates Ltd., the new waste management system is expected to increase the diversion rate of this combined urban/ rural service area to approximately 65 per cent after source separated collection begins in 2002 — well above the 50 per cent provincial objective.

A major component of the system is the recently built Central Composting Facility. A 750 m3 (8,000 sq. ft) building with a tip floor receives the source-separated waste collected from municipal curbside organic collection and from some ICI sector generators. Westeinde Construction Ltd. designed and built this facility in conjunction with WCI Waste Conversion Inc. For the purpose of odour control, the facility is negatively pressured, and a biofilter vents the building exhaust.

Non-organic waste is separated mechanically and manually before the organic waste is loaded into a mixer with various amendments for blending to achieve an optimal mix. This feedstock is tested to ensure critical parameters — including carbon to nitrogen ratio, moisture content, structure and particle size, and pH –fall within established ranges. The feedstock is then loaded via conveyor directly into the modular composting containers.

Eleven insulated CompTainer modular vessels, developed by Engineered Composting Systems and distributed in Ontario by WCI Waste Conversion Inc., are used to process approximately 4,500 tonnes per year of the source-separated organic waste. Each of these containers holds approximately 32 m3, and is insulated with 75 mm and 50 mm of high-density rigid insulation on the sides and top, respectively.

The interior is stainless steel, and the raised, perforated floor facilitates uniform distribution of airflow and the collection of leachate. When connected to the distribution system, the airflow can be reversed to minimize temperature gradients within the biomass to help ensure complete decomposition. Heat sensors located in the container indicate areas of active decomposition. The exhaust from the container ventilation system passes through the biofilter for odour control.

The biofilter, made by AMBIO Biofiltration Inc., is a low-maintenance, open-bed style filter, with a one-metre thick layer of shredded root-wood growth medium. Exhaust air is forced upwards through the biofilter. A bacteriological biofilm on the growth medium absorbs and metabolizes organic compounds in the exhaust air. The biofilm is maintained by controlling the humidity within the biofilter using an array of soaker hoses in the lower third of the filter medium.

The loaded containers are then transported to an exterior pad and connected to an aeration and control system. Aeration piping is connected to each container to provide complete control over process air and odour emissions. The leachate is collected, stored, and reused to increase the moisture content of the feedstock in the mixing phase.

After the biomass undergoes thermophilic decomposition (for three days at or above 55C) pathogens are effectively killed. When a minimum of 14 days passes, the containers are moved and then dumped onto a curing area pad, where the biomass is windrowed for a 50 to 60 day curing period to stabilize and mature.

The length of time to stabilize may vary with the time of year, as the seasonal variation of outside temperature is substantial in Renfrew County (about two hours north-west of Ottawa). Daytime temperatures in February are -25C, but the initial 14-day decomposition cycle generally doesn’t change due to the insulation on the containers and the regulated air supply.

Regular testing of the biomass during the different stages of its transformation to compost will aid the staff in maintaining control over the process. The compost will be then be stored for final market preparation, which includes screening, to produce high-value finished compost. Tests of the final product are expected to ensure regulatory compliance as Class A compost.

The facility, including the eleven modular containers, cost $2.5-million. The organic carts used for residential curbside collection cost $840,000. This facility is part of an $11-million expansion program at the Alice & Fraser Landfill, which is entirely funded by the municipal partnership.

Richard Cox, P. Eng. is a civil project engineer with J.L. Richards & Associates Limited in Kingston, Ontario.

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