Exhaust from the biofilter exits through a stack. The easiest way we found to detect when to change the biofilter is to monitor the air that flows through. In eight experiments done over about one year in 1996, Lambert Otten and Lindsay Dennison of the University of Guelph concluded that there was very little risk of odor problems from this facility. It was believed that after release from the stack, atmospheric dilution would reduce the risk of nuisance odors. Leachate is drained from the bottom of the biocells and recirculated by being sprayed onto the top of the compost.
Excess moisture is evaporated by the heat of the compost and exits with the exhaust air.
The ideal moisture level within the composting units is 45 to 60 percent. A three-day cooling and drying stage follows composting, during which the reactors are continually flushed with ambient air. Following that step, the compost is removed and placed in windrows for 35 days of curing. The piles rest on about two meters of clay soil at the peak of closed cells at the landfill so that leachate filters through the garbage instead of the ground, says Larry Conrad, manager of landfill operations for Peel. Weather permitting, the windrows are turned weekly.