Waste & Recycling

Feature

In-Vessel Processing

Waste managers across Canada stand to benefit from a process under way in the City of Toronto that is examining "new and emerging technologies" for disposal of the portion of municipal solid waste that can't easily be recycled via the blue box and...


Waste managers across Canada stand to benefit from a process under way in the City of Toronto that is examining “new and emerging technologies” for disposal of the portion of municipal solid waste that can’t easily be recycled via the blue box and curbside diversion schemes for organics.

A technology from Germany that has been tried out in Caledon — a small municipality just northwest of Toronto — is interesting in this regard. (See News item, pg. 7.)

Germany is often considered an environmental leader. It’s the one democratic country that has had the Green Party as part of the coalition government. It established the Ordinance to the Avoidance of Packaging Waste (commonly called the “Green Dot program”) that requires manufacturers to take back packaging, and it led the charge for the European End-of-Life Vehicle Directive. Germany is also home to the Herhof method for the treatment of municipal solid waste that was implemented as a pilot plant in Caledon.

Herhof (Dry-Stabilate) method

The Herhof method effectively separates municipal solid waste into glass, a mineral fraction, metals (ferrous and non-ferrous), batteries and fuel pellets (referred to a stabilate). According to its proponents, what makes the system unique is its ability to separate waste into recyclable/re-useable components and fuel, without the need for pre-sorting. Another key feature of the method is that it leaves virtually no residue for landfill.

There are six major steps to the Herhof method. At the first step, waste is accepted in bunkers as either as ICI or domestic. The second step, preconditioning, involves the crushing, shredding and mixing of waste. This results in a material that is homogeneous. The shredded waste is then transferred to composting boxes for batch treatment.

During the fourth step, drying, the water content of the waste is reduced to below 15 per cent and aerobic decomposition is allowed to occur for six days. At the end of this process, cranes carry the waste to the mechanical separation step.

Mechanical separation results in “stabilate” — a clean “industrial fuel” that can be used in cement kilns or power plants and materials for recycling (mixed plastics, ferrous and non-ferrous metals, glass ceramics and batteries). Separation is so effective that there is no residual material to be disposed of in landfill. The inerts that are left over can be cleaned and sent to an aggregate plant to be used as road bed material but this is expensive and likely not attractive in current economic conditions.

The complete stabilate system commenced production in Europe in 1997 and currently treats the waste of approximately two million people in Germany and Italy. The approximate cost for treatment of the waste is the equivalent of CDN $100 per tonne. The market for the stabilate fuel has yet to be established, but operations in Europe are working with industry to prove its potential as a clean industrial fuel.

Application in Canada

There is no Herhof stabilate technology in Canada, but the composting method is utilized at two sites in Canada, one in Ontario and another in B.C. The B.C. plant has been the subject of recent litigation. The Ontario installation is located at the Region of Peel’s Caledon landfill and has been in operation since 1995.

The Caledon operation consists of eight air-tight concrete reactors, each with a capacity of 32 tonnes. Each reactor is loaded with shredded organic material and cycles through four phases over a seven-day period.

The key to the process is the measurement and control of the temperature and carbon dioxide concentration throughout the entire process. Recycled or ambient air is forced through the organic waste and to control the carbon dioxide concentration and temperature.

There are four stages to the Herhof composting process. In stage I (initial warm-up), the temperature inside the bioreactor is allowed to rise to 40C. During Stage II, the temperature is maintained at a minimum of 45C for 48 hours. During this time, aerobic digestion occurs. Phase III is the sterilization stage whereby the temperature is allowed to rise up to 55C and held for 72 hours so that all pathogens are destroyed. During the final stage — cool down/drying — the reactor is allowed is flushed with ambient air.

In my conversation with operations staff, they noted that on only one occasion did they have a batch go anaerobic (the result of a plugged line). The advantage of the air-tight batch system is that exhaust air can be treated. Biofilters are used to remove potentially noxious odors. (See Composting Matters, page 34.)

Leachate collected from the compost is collected in a pit and recirculated into the reactor by overhead spray nozzles. Once every two months the accumulated sludge in the leachate collection pits are pumped out and sent to the sewage treatment plant.

Currently the compost is sold for $35 per tonne and meets the unrestricted use guidelines of the Ontario Ministry of the Environment.

The Region of Peel is expanding its composting capabilities and the public works department is recommending that more Herhof composting units be purchased.

“The Herhoff composting process is an exceptionally good process,” says Larry Conrad, manager of landfill Operations for the Region of Peel. “It really works.”

John Nicholson is a management consultant with Environmental Business consultants based in Toronto, Ontario. E-mail John at john.nicholson@ebccanada.com


Print this page

Related Posts



Have your say:

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

*