A SEISMIC SHIFT IN LANDFILL management may be under way, based on tests of bioreactor landfills. In one recent example, Intersan, a division of Houston-based Waste Management Inc.'s subsidiary Canadian Waste Services, has implemented a bioreactor operation at the Sainte Sophie Landfill near Montreal to test the environmental and economic benefits of the technology.
Bioreactor landfills use techniques such as recirculating leachate and other liquids to optimize a landfill's natural biodegradation process and to stabilize organic components faster than a dry-tomb landfill, ideally within five to 10 years. Bioreactors aim for a moisture content of approximately 50 percent to 65 percent, compared to a typical landfill's moisture content of only 20 percent to 25 percent. If the project is successful, a typical landfill's waste capacity reportedly can be increased by at least 15 percent to 30 percent, lessening the need for new landfills.
The Sainte Sophie Landfill, which has been operated by Intersan since 1997 and open for 11 years, collects approximately 850,000 metric tonnes (937,000 tons) annually. The bioreactor landfill is located on a 30-acre, double-lined corner of the permitted landfill site.
“We were … developing a new cell at Sainte Sophie, and it was of a size and configuration that worked in terms of developing a bioreactor,” says Hubert Bourque, Intersan vice president. Although Quebec does not need to meet Subtitle D regulations and Sainte Sophie complies with all the current Canada regulations, Intersan was determined to demonstrate the most up-to-date technology and management guidelines.
Meeting the regulations required a more significant investment, according to the company. But “the costs of the new cell were offset by the bioreactor benefits,” Bourque says, noting that the additional capacity will eventually offset the higher Subtitle D costs.
The Sainte Sophie project is one of 10 bioreactor demonstration projects overseen by Waste Management's bioreactor team, says Jim Norstrom, senior director of engineering for the company. “Our overall goal is to evaluate and confirm the environmental and economic benefits of bioreactor technology,” he says. “We evaluate different designs and operating methods in a variety of climates.”
In Sainte Sophie's bioreactor system, leachate is injected into landfilled waste through horizontal, perforated high-density polyethylene (HDPE) pipes lain in gravel trenches at three levels. Trenches are placed 15 meters to 20 meters apart horizontally, and approximately 6 meters apart vertically. Leachate from the existing landfill and the bioreactor cell are collected in a sump on the east side of the new cell and pumped through a main around the north side to the valved recirculation pipes on the west side.
Unlike some bioreactor projects that are retrofitted for existing cells, “this waste system was designed as a bioreactor from the bottom up,” Norstrom says. “We wanted to try out this horizontal system as a method to uniformly distribute the leachate throughout the waste.”
In a system designed by Phillip Smith, a Waste Management senior engineer for landfill gas (LFG), HDPE pipes that control and collect LFG are placed in the same trenches as the leachate recirculation pipes to minimize the cost and impact on existing operations. This system will allow landfill managers to monitor the effect of the bioreactor on LFG generation rates over time. Research already has shown that LFG generation in bioreactors occurs during a much shorter period than in traditional landfills.
Intersan is currently in discussions with a local utility to use the bioreactor's LFG. Bourque estimates that 25 percent of the local community's natural gas needs could be satisfied by the bioreactor. Although Canadian projects would not be affected by the passage of LFG tax credit legislation — still awaiting action in the U.S. Congress — Bourque adds that a strong LFG lobby in Quebec supports these efforts.
“I thought the project fit very well with our provincial objectives on recycling and waste diversion,” Bourque says.
The landfill is currently in the data collection and analysis phase, which will continue for the next few years. Bourque says the company plans to study the impact of leachate temperature and pH levels on biological degradation. “We're learning what conditions will shock the system,” he says. This past winter, the bioreactor team introduced extremely cold leachate, for example. The team also is studying the system's necessary load-rest cycle. For this, operators apply as much leachate as possible until the system will accept no more.
Bourque says that tests such as Sainte Sophie's give politicians and potential critics a better understanding of bioreactor technology. A traditional criticism, for example, is that bioreactors undermine recycling initiatives, but bioreactors actually support recycling, he says. “A bioreactor [won't] take care of everything. Our position is we should maximize recycling. The bioreactor doesn't need the bottles, cans, etc. We should be dealing only with [what cannot be recycled].”
In the meantime, the landfill has applied for a permit to build a 9-million-ton expansion to the landfill to test additional operating modes. The team also recently connected all of its monitors to the company's Intranet site, so that engineers in Houston can examine data from Sainte Sophie in real time.
“We're closing one chapter on sanitary landfills,” Bourque says, “but we're opening a new chapter on bioreactors.”