The City of Edmonton touts its new co-composting facility as the largest and most sophisticated of its kind in North America. Along with claims about high municipal recycling rates (81 per cent participation), officials say composting efforts will help divert approximately 70 per cent of waste from landfill. This is a dramatically higher diversion rate than any other major Canadian city and exceeds the national target of 50 per cent.
According to Bud Latta, director of processing and disposal for the city, the facility represents 35 per cent of Canada’s total composting capacity.
The Edmonton Co-Composting Facility — which began operations on March 15, 2000 — is a public-private 30-year partnership between the city and TransAlta Energy Corporation based in Calgary, Alberta. It operates in conjunction with an adjacent MRF built by BFI that opened on March 30, 1999. (See article in the August/September 1999 edition.) The facility handles approximately 180,000 tonnes of residential waste and 22,500 dry tonnes of biosolids per year.
“With the new facility, we’ll produce approximately 125,000 tonnes of compost a year,” says Mr. Latta. Composting in Edmonton will initially cost more than landfill disposal but the facility is expected to stabilize disposal costs.
The city (population one million) pays $62 per tonne for processing. Comparatively, the City of Toronto, which produces more than one million tonnes of waste annually and does not compost, pays $72 per tonne. In fact, Toronto Mayor Mel Lastman recently visited Edmonton to explore the feasibility of building an Edmonton-style plant for the Ontario city. (See article, page 16.)
Residents separate cans and bottles, paper, glass and plastics through a Blue Bag recycling system. All waste that is not set out for recycling is hauled to the co-composting facility. No wet waste sorting is required.
Municipal waste and sewage sludge (biosolids) are delivered to the facility for processing at two locations: the waste to the tipping floor and the biosolids to a storage lagoon. The biosolids are recovered from the lagoon by an extraction barge, then pumped to the composting facility for processing.
Reg Belyea, P.Eng., manager of business development of Edmonton-based GKO Engineering (the principal engineers and contractor of the facility), says priority is placed on convenience for citizens and waste handlers without compromising the low cost maintenance strategy.
Approximately 70 per cent of the material brought to the facility is organic and is suitable for composting. The remaining 30 per cent is separated and either recycled or sent to landfill.
Centrifuges dewater the biosolids (that arrive as 2 to 6 per cent solids) to a solid content of between 28 and 32 per cent. The biosolids and waste organic feedstocks are then mixed together to obtain a carbon to nitrogen ratio of 30:1, a moisture content of 48 per cent, a pH of 5.5 to 6 and a particle size no greater than 80 mm.
To achieve this, the MSW is pushed by front-end loaders and the biosolids by hydraulic equipment into five mixing drums where they’re slowly mixed for 24 hours. The drums are rotary steel vessels, 74 metres (240 feet) long and 4.9 metres (16 feet) in diameter — about the size of six buses.
After mixing, the material is transported by conveyors (which move at approximately 4.3 km/hour) to one of two trommel screens (each has 3,400 holes). Materials less than 80 mm are transported to one of three aeration bays; materials greater than 80 mm are landfilled.
Variables such as porosity, temperature, oxygen and moisture content are maintained within specified levels to effectively compost the feedstock. Up to 96 samples are collected around the facility each day.
The material is held in the stainless steel aeration building, which is 23,355 m2 — the equivalent of 14 NHL hockey rinks. The aeration bays supply a negative aeration system that draws air down through the feedstock to supply oxygen and remove heat. A compost-turning system restores pile porosity, adds make-up water as necessary and transports the feedstock through the bay during the 28-day detention period. The entire process takes 30 days. The compost then needs to cure for two to three months before it is sold.
Air that passes through the composting feedstocks contains odours. A proven odour treatment system mitigates these concerns. The system captures and transports process air from the entire facility and treats it by cooling, scrubbing and biofiltration.
Oversized material, synthetic inerts and sharps are removed. The facility utilizes a trommel screen and various separation methods: ballistic (air), eddy current (for non-ferrous metals) and magnetic (for ferrous metals).
As of August 2001, all residential waste is going to the facility, which produces an average of 300 tonnes of compost each day — enough to fill 330 pick-up trucks. Dwayne Simmons, facility plant manager, says, “We are amazed at the number of potential markets showing up at our door. Many in the oil and gas sector have discovered beneficial uses for compost to help clean soils.”
Critics say that the compost will never be a high quality product due to the two-stream mixed waste processing system. The compost meets federal and provincial standards, which distinguish between two types of compost: Grade A (which has no restrictions for use) and Grade B. Due to high levels of copper and zinc, Edmonton produces Grade B, which is limited to use in land reclamation, commercial landscaping and agricultural applications.
Connie Vitello is editor of this magazine.