Organics as Hazardous Wastes

When folks load up their garbage cans with food scraps, yard wastes and paper, they may feel a vague sense of guilt, but they don't usually think that they are sending away hazardous materials for disposal in a landfill. These materials look so innocent, not a bit like those bottles with stern warnings on the side.

It is true of course, that these common organic materials are not particularly dangerous when they leave our homes and businesses. If we send them off to a landfill, however, their biodegradabliltiy creates some problems.

Materials biodegrade when they are slowly disassembled by other living creatures, usually tiny ones like bacteria and fungi. Bacteria tend to be most active in compost piles and landfills and their action depends, in both places, on the availability of air and moisture.

Ideally, landfills are dry and compacted, thus airless. In a relatively dry landfill, only the organic items that went in wet will break down. If moisture is present, and the materials are not frozen, then considerable breakdown will occur. The airless nature of the landfill causes the bacteria to use the type of processes available to them when no oxygen is present. This is called anaerobic decomposition and it leads to some predictable by-products: methane gas, carbon dioxide gas, water, organic acids and hydrogen sulphide (rotten egg gas). Moisture in a landfill becomes a complex mix of substances called leachate. Methane, leachate and hydrogen sulfide gas are all substances that need to be handled carefully.

Methane, like so many other things, can either be a problem or a resource. It causes problems at or near landfill sites by building up to concentrations that can ignite and cause explosions. If methane is released into the air, it acts as a greenhouse gas. Methane is actually 21 times more 'effective' than carbon dioxide as a greenhouse gas.

There are a couple of strategies used at large landfill sites to better manage methane emissions. The simpler solution sees the gas collected and flared, which turns the methane to carbon dioxide thus eliminating the problem with explosions and reducing the greenhouse gas load.

The alternative is to put the collected methane to use. The City of Edmonton is a near-by example. EPCOR Technologies Inc. is capturing and purifying landfill gas from Edmonton's Clover Bar Landfill and providing it as a secondary fuel to the natural gas-fired Clover Bar Generating Station.

There are 33 landfills in Canada that have active landfill gas recovery systems; 70% is used to generate electricity with the reminder used directly as fuel for industrial processes. This collection is certainly sensible where the materials have already been landfilled and decayed, but it is also making some municipalities consider leaving the organics in the waste stream. When the whole picture is looked at, this will probably not be a wise course of action.

There are two problems with encouraging methane production in landfills. The first is a stewardship issue. The nutrients in food and yard waste belong back in the soil system not in a landfill, where they are difficult if not impossible to reclaim.

The second consideration is that methane is not the sole by-product of anaerobic decay. The water that organic materials use to break down leads to leachate. Generally speaking, the moister the materials, the faster the decay and the greater the volume of methane that will be produced until the organic materials are all decayed. There is an obvious trade-off between desired methane and unwanted leachate. The exact nature of the leachate soup depends on the materials in the garbage mix, but it should always be prevented from contaminating surface or ground water. Leachate monitoring and containment is an expensive part of modern landfill construction and operation.

Hydrogen sulfide, better known as rotten egg gas, is another by-product of anaerobic breakdown. In small concentrations, it smells bad. At higher concentrations, there is no odour but it is quite toxic. In 1999 Saskatchewan residents had a sharp reminder about its toxicity when several people died trying to fix a liquid manure tank. Hydrogen sulfide is a minor gas at landfills but it does cause odour and occupational health problems.

Food scraps and yard waste (including tree trimmings) make up about 1/3 of the household waste stream. These materials are usually considered non-hazardous, but as was just outlined, that is only true until they begin to break down under landfill conditions. Keeping moisture levels down in a landfill means that little breakdown will occur, but these materials take up a lot of space and therefore reduce the working life of the site.

This discussion of organics in landfills leads us inevitably back to the importance of the three Rs: reduce, reuse, recycle. The organization of many new regional waste authorities in Saskatchewan should provide better reduction incentives and recycling services.

Over the next few years, with consistent pressure, industries are likely to offer more complete product stewardship^* which will assist with the cost and logistics of managing many materials. Compostables are the category that will not likely find industrial support. This view is reinforced by Ontario's Waste Diversion Organization's June/00 report.

Fortunately there are many tactics for recycling these orphans locally to make useful products. This is an area of considerable interest to SWRC. If you have ideas or stories to share, please let us know.

* For a discussion of product stewardship, visit Environment Canada's page on Extended Producer Responsibility & Stewardship

(Source: September 2000 WasteWatch)

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