Solid Waste & Recycling

Feature

Toronto Anaerobic Digestion Plant

Enwave District Energy Ltd. has formally proposed to the City of Toronto that it enter into a contract to divert as much as half the city's garbage from landfill and treat it in a large-scale anaerobi...


Enwave District Energy Ltd. has formally proposed to the City of Toronto that it enter into a contract to divert as much as half the city’s garbage from landfill and treat it in a large-scale anaerobic digestion plant. The plant would turn organic waste into usable compost and methane gas that would fuel a vast existing network of district heating steam pipes. Toronto’s proposed deal to send its garbage for disposal in the Adam’s Mine 600 kilometres away is not a “put or pay” contract and this kind of waste diversion is allowed under the city’s “new and emerging technologies” program.

Background

Enwave currently supplies district steam heating services to 110 buildings in downtown Toronto. The organization was recently restructured from a user co-operative to a share-capital corporation owned 50 per cent by the OMERS municipal pension fund and 50 per cent by the City of Toronto. This was done primarily so that it could finance and build a unique project to take cold water from deep in Lake Ontario and use it to air condition buildings in the Enwave service area. This creative endeavour is in line with Enwave’s corporate “innovative energy solutions” theme. The company is North America’s second largest district energy system after New York and, in 1999, won the International District Energy Association’s “System of the Year” award.

“Toronto’s public works committee has recommended that the city develop one or more facilities of this kind to divert up to 450,000 tonnes of the city’s garbage (roughly half of the total).”

On the heating side of its business, Enwave relies on boilers fired by natural gas (and backed up by No. 2 fuel oil when the gas supply is interrupted). It has three heating plants with a total of 16 boilers and a steam distribution system consisting of 18 kilometres of underground pipes. The inherent business principle of district energy is that the central plants can be operated more efficiently than small in-house boilers — about 75 per cent versus 60 per cent — and the district energy system draws on more diverse sources of heat energy.

The price of natural gas in Ontario has tripled over the past three years along with a commensurate increase in Enwave’s steam prices and this is becoming a business concern. Under customer pressure, Enwave has searched for new solutions on the heating side that, like the lake water cooling project, are economically and environmentally sound.

Anaerobic digestion appears to be just what Enwave and its customers are looking for.

The process

Anaerobic digestion uses special bacteria that thrive in the absence of oxygen to turn waste into energy. The process occurs naturally landfills and produces methane, which can in turn be used to generate power. Many facilities do this; but it takes years for the biogas to form. (This is in addition to the challenge of containing and treating leachate and various contaminants.) Anaerobic digestion produces the same methane but in the controlled environment of a digester plant; and does it in days rather than years.

The technology is sophisticated but not unproven. More than 50 anaerobic digester plants operate in Europe and two pilot plants exist in Ontario. Enwave intends to build such a plant to supply a portion of its steam. The scale of the plant will be determined by the land required; preliminary studies indicate that a plant using about 150,000 tons annually of mixed solid waste would be economical. (This would consume about 10 per cent of Toronto’s mixed waste.)

When organic waste can be diverted, the process is even more effective. Toronto has told Enwave that such a waste stream will be available. The plant will be located in an industrial area near downtown, with a steam line connected to Enwave’s existing distribution loop. If the plant can be built at a larger scale, it can be designed to generate both heat and electric power (i.e., co-generation). Encouraging discussions have been held with Toronto Hydro about this possibility. Toronto’s public works committee has recommended that the city develop one or more facilities of this kind to divert up to 450,000 tonnes of the city’s garbage (roughly half of the total). The city is assisting in finding a site and an anaerobic digestor plant could be up and running in 2003 — the same year that the deep lake water cooling project becomes operational.

Written by Guy Crittenden, editor-in-chief of this magazine.


Print this page

Related Posts



Have your say:

Your email address will not be published. Required fields are marked *

*