october 2009 issue
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The SUmmit Series
Making Landfills Last Longer
Reducing the waste that gets tossed away in the first place is one way to extend a landfill’s life. Another way, the City of Calgary believes, is biocell technology, which has the added benefit of increasing the production of recoverable methane
BY CHRISTINE COTTRELL
Editorial Assistant
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PROJECT PREPARATION |
Garbage — it’s one of Planet Earth’s biggest problems. Where do we put it? How can we reduce its impact on the environment? How can we handle it without shredding public budgets?
The City of Calgary has come up with a new approach to meet these challenges. Alberta’s largest city is using biocell technology developed by Dr. Patrick Hettiarachi, P.Eng., of the Schulich School of Engineering.
Biocells improve decomposition while increasing methane production. That means more of a resource to tap and a less rapid use of land. As waste decomposes, leachate collected from the bottom of the cell is recycled to the top. This added moisture increases biological activity.
Earlier this year, the Calgary Biocell Pilot Project won the Environment and Sustainabity Award in the APEGGA Summit Awards. But the project’s origins go back to 2003, after the city recognized a need to reduce its dependence on landfill waste disposal.
“The current practice is to construct dry-tomb type sanitary landfills, in which the waste is contained and stabilized over a long period of time,” explains Dr. Hettiaratchi. “One of the critical problems with this approach is that every few years you have to find new space to put the waste. Most big cities are facing a space crunch when it comes to waste. In addition, waste is considered a liability rather than a resource.”
The Burial Mentality
With funding from the Natural Sciences and Engineering Research Council of Canada, Dr. Hettiarachi set about reducing the amount of garbage in the Calgary landfill. It’s a bit like teaching an old dog a new trick — landfills, and before them dumps, have been around for a long, long time.
Disposal by burial, in fact, is the oldest and most common form of solid waste management and remains so in most of the world. But landfills are unsustainable, because new locations are required every few years.
Few people want to live next door to a landfill. Combine that with understandably tight environmental restrictions on design, soil type, the location of water tables and much more, and the entire picture takes shape. We may need landfills, but we’re running out of places to put them.
The three Rs — reduce, reuse, recycling — help extend the lives of existing landfill sites. Municipalities in Canada and elsewhere have a variety of recycling programs in their communities, covering plastic, paper, metals, yard waste for composting and more. Some municipalities are able to go further and provide eco-stations. These collect paints and corrosive materials, and computers and other electronic equipment, for safe disposal or recycling.
The landfills in Calgary are expected to last roughly another 30 to 40 years. The implementation of biocell technology, however, could increase their lifespan to more than 100 years, while enhancing methane production and resource extraction. Seventy per cent of the waste could be processed using biocell technology, leaving a much reduced need for long-term disposal.
The Calgary biocell is a full-scale pilot project. It is an isolated, one-hectare pit within the Shepard landfill southeast of Calgary. It is lined with clay and plastic, filled with 65,000 tonnes of waste and sealed with a geomembrane.
Garbage Into Gas
Day and night, that special pit is turning garbage into a resource. Or make that two resources — gas and compost or refuse-derived fuel, or RDF as its known.
By 2007 the project was producing enough gas to feed an on-site generator. When methane production decreases to a point where gas extraction is no longer cost effective, air will be injected into the biocell to convert it into a large, in-ground composter. This will produce a stable organic material, which is used as low quality compost or RDF.
The biocell is not yet failsafe. Problems that still need to be resolved include moisture distribution within the cell, gas emissions during cell filling and the problems with rapid settlement of the cell.
Gas can be extracted from most landfills, but usually not in an economically feasible way. If a landfill is not designed for energy recovery or is too small, there’s just not enough gas available to make recovery viable.
Researchers hope to use what they learn at the Calgary site to recreate it, but on a much larger scale. “Our long-term goal is to set up a national and international biocell network,” says Dr. Hettiaratchi.
Worldwide Solution?
If the technology is applied across the globe, conversion of future landfills to biocells will minimize reliance on municipal energy grids. Biocells will also decrease the lifecycle greenhouse gas emissions associated with waste management and energy consumption.
That’s why Dr. Hettiaratchi travels the world to speak about the biocell technology. “Different countries have different waste disposal needs, dependent on the local climate,” he notes.
“Places like Bangkok have a high level of rainfall, whereas Melbourne does not. Sometimes the wastes could be similar, but the climates are very different. Therefore, modifications are needed in the construction and operation of biocells depending on the climatic conditions.”
What all countries have in common is the need to extend the lives of their landfills. The Calgary project may prove to be exactly what they’ve been looking for.
The Environment and Sustainability Award recognizes excellence in the application of engineering, geological and geophysical methods to preserving the environment and practicing sustainable development.