Landfill Gas Utilization

BFI Canada’s Lachenaie landfill is the nearest landfill facility serving the waste disposal needs of Montreal, Quebec — a community of 3.5 million people. The Lachenaie landfill site is located on the north shore adjacent to the extreme east of Montreal Island, crossed by highways 40 and 640. The annual capacity of the landfill handles about a third of Montreal’s waste; the city disposes approximately 3.8 millions tonnes of non-hazardous solid waste annually.



In 1994, BFI designed and built a landfill gas extraction system at the landfill. The following year it constructed a power plant that features a 4-megawatt (MW) reciprocating Waukesha 7042 GL engine plant to produce electricity. This power plant benefited from the company’s experience designing and building seven such installations in the United States.



The company established a 25-year agreement with Hydro-Quebec for the purchase of the electricity generated by the landfill biogas — the first such operation in Quebec. The plant generates enough electricity to power approximately 2,500 homes.



An important side benefit of the energy project is that it reduces greenhouse gas emissions. The reduction (approximately 600,000 tonnes of carbon dioxide equivalent) is roughly equal to the amount of carbon dioxide emitted by 160,000 cars in a year.



The idea for the project grew in tandem with an aggressive action plan from the Quebec government that decided in 1998 to recycle waste at a rate of 67 per cent by 2008. (This included municipal waste, as well as industrial, commercial and institutional [IC&I] waste and construction/demolition [C&D] debris.) By 2001 the City of Montreal achieved a recycling rate of 17 per cent for its municipal solid waste stream. The annual quantity of biogas generated from waste buried in the landfill was projected with estimates that used the recycling rate objectives of the Quebec government. The calculations determined the total airspace that is likely to be available in the landfill (which will be used up in 40 years).



According to the company, around 50 per cent of the total waste received at the Lachenaie landfill is municipal solid waste, 43 per cent is IC&I and the remainder is C&D debris and sludge from municipal wastewater treatment plants.



Landfill design and gas collection



The Lachenaie landfill cell is built like a vault in clay. The design leaves at least 10 meters of clay under the bottom of the cell, exceeding proposed provincial regulations that require a minimum six meters of clay. A state-of-the-art system collects leachate and the bottom of the cells is covered with sand that filters solid particles from the leachate.



The leachate is pumped through a treatment system comprised of three lagoons. The first pond acts as an anaerobic system; the other two use aerators to reduce organic pollutants before discharge to the municipal wastewater treatment facility (owned by the Townships of Terrebonne and Mascouche).



Eventually the maximum height allowed by the facility’s certificate of approval issued by the Quebec Ministry of the Environment is reached for each cell. Clay excavated from a new cell is then used to cap each completed cell. This occurs after the final drainage cap is installed over the last layer of buried solid waste. To complete the structure, topsoil is added above the clay cap and seeded.



Landfill gas is extracted via a number of wells drilled into the waste. The wells extend to approximately two meters above the bottom of the waste. Well installation is an ongoing process with new wells added to the gas collection system as landfill cells are filled and capped. Currently, about 250 wells are in place. The well risers are constructed of high-density polyethylene (HDPE) pipe. Each wellhead is equipped with sampling ports and a valve to allow measurement, to control extraction vacuum and to limit oxygen ingress into the waste (to av