Solid Waste & Recycling

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Mechanical-Biological Treatment – Part II

Our June/July, 2007 issue carried an article by Andy Wilson of the European company of Golder Associates, an international environmental and geotechnical consultancy, indicating what is happening rega...


Our June/July, 2007 issue carried an article by Andy Wilson of the European company of Golder Associates, an international environmental and geotechnical consultancy, indicating what is happening regarding mechanical-biological treatment (MBT) in Europe. This article gives a perspective on the potential for MBT in Canada.

Difficulties in obtaining permits for new or expanded landfills and waste-to-energy (WTE) facilities and higher diversion targets could force municipalities to take a closer look at mechanical biological treatment (MBT) as a means of managing Canada’s municipal solid waste.

MBT is a generic term for a range of processes used to treat residual waste (i.e. post-curbside collection of source-separated recyclables and organics) using a combination of mechanical separation and biological treatment. This usually involves mechanical size reduction, biological drying to further reduce volume and bio-stabilize the organic fraction of the waste, and material separation to recover recyclable materials not source separated by waste generators.

The resulting end product is more stabilized so it has less chance of producing methane when placed in a landfill than untreated solid waste. Treated residue also has lower moisture content and higher energy (BTU) value, so it offers a good potential fuel for energy facilities.

One reason MBT’s future may be bright in Canada is found in the growing forest of high-rise condominium towers and apartments in many of our major cities. Recycling rates from residential-tower residents are notoriously low, and MBT represents one way to boost these recoveries. (See article, page 14.) There’s room for improvement throughout the country; however, the average capture rate for recyclables and organics is only 24 percent for Canada as a whole, leaving 73 percent for MBT to help divert additional recyclables and stabilize the residuals. This will keep our landfills functioning longer and cleaner.

On the other hand, Canada does not face the same sense of urgency, or legislative imperative, that drives MBT growth in Europe. Particularly on the Prairies, wide-open spaces leave plenty of land for conventional landfills. Even in much of British Columbia where topography makes habitable land scarce, and the more densely populated areas of Central and Eastern Canada, there has been limited assessment of the viability of MBT.

This is changing. There’s growing public awareness of the need to manage municipal solid waste in a more environmentally sustainable way, in some cases with politicians scrambling to get in front of the public, to deal with the problem. Conventional landfill alone is not always a popular long-term solution. A larger role for WTE is being explored by a number of municipalities in Canada, but is still considered by many just a “disposal” option.

So, MBT. It’s reasonable to argue that MBT will be accepted as a viable component of an integrated waste management system, particularly in highly urbanized centres. It’s likely to be instrumental in attaining the 60 percent and higher waste diversion goals that some jurisdictions seek.

There are other ways to boost recovery, such as better public education about what materials can be recycled. It may also be possible to apply social pressure to get people to take more care about what goes in their garbage bag and what they put out for recycling. However, MBT can go a long way toward boosting diversion rates by further pulling off recyclable materials and utilizing the residual organic fraction for energy production or alternative composting uses (with further back-end curing).

MBT is not viable in every municipality, partly because (given current technology) the optimal size of an MBT facility ranges from 60,000 to 200,000 tonnes of waste per year. This makes it economically accessible to communities of some 100,000 or higher. Other communities, of course, could truck their waste to a larger community’s MBT facility.

Currently, it appears two forays into MBT facilities have been made in Canada: the Otter Lake facility near Halifax and the Edmonton Waste Management Centre. Clearly, there’s room to grow and opportunities for municipalities and operators interested in implementing this technology.

As municipalities begin to assess the advantages and disadvantages of different waste treatment technologies, the incorporation of life-cycle analysis (LCA) tools will become more critical in the decision making process. With the growing concern over climate change and provinces across the country developing climate change policies, we need to begin assessing waste systems using an LCA approach. MBT technologies should be added to the mix of available waste treatment for consideration during the municipal planning process.

Michael Cant is a senior solid waste planner and Ontario Region waste sector leader with Golder Associates Ltd., based in the company’s Whitby, Ontario office. Contact Michael at mcant@golder.com


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