If a generation that prides itself on being green is to be defined by its aggressive pursuit of energy efficiency and alternative sources of electricity and fuel, then maybe it‘‘s time we ditched the label "waste" and "garbage", according to the Toronto Star.

Is a used diaper, for example, just a ball of stink destined for a landfill? Or is it a ball of complex molecules that can be busted apart, reorganized and turned into useable energy?

Luciano Piciacchia, vice-president of Quebec operations for global engineering giant AMEC PLC, is in the diaper-buster camp. He‘‘s overseeing the design of a plant in Quebec that, when finished, aims to turn thousands of tonnes of used diapers each year into a synthetic diesel fuel. Used diapers are difficult to reuse or recycle, and while cloth diapers are an alternative, it‘‘s unlikely they‘‘ll ever put a dent in disposable diaper sales.

In Quebec alone, 600 million - or 120,000 tonnes - of used diapers are produced each year, and for the most part they end up in landfills where the plastic that lines them can take 100 years to break down, says Piciacchia. "A baby, from the time it‘‘s born to the time it‘‘s toilet trained, will go through a tonne of diapers," he says, adding that the load will increase as aging boomers turn to adult incontinence products.

The technology for turning diapers into diesel, called pyrolysis, is well understood and has been discussed before in this column. Unlike a dirty process such as incineration, by which a substance is just burned, pyrolysis chemically breaks down organic materials, literally cracking their molecules, by heating them up in an oxygen-starved chamber.

It‘‘s a closed process that doesn‘‘t involve combustion, so emissions are strictly controlled, and three materials emerge at the end of it: a synthetic methane-like gas, a diesel-like oil and carbon-rich char.

"Environmentalists aren‘‘t convinced that it works, but you have to put it in place and see the science of it before you condemn it," says Piciacchia. "The science behind it is solid."

So why focus on diapers? It‘‘s a combination of logistics and consistency. For example, the logistics of garbage collection is easy - municipalities already pay for and have established pickup networks. But turning municipal solid waste into energy can be tricky because of the inconsistency of materials or "feedstock" that must be handled.

The feedstock can range from old clothes to banana peels to yogurt containers to refrigerator doors, and this batch of unpredictable ingredients makes it difficult to control the molecular breakdown of each so that the good molecules can be separated from the bad.

On the other hand, you know that with diapers you‘‘ve got a consistent stream of plastics, resins, fibres, excrement and urine. This consistency of feedstock improves the efficiency of the pyrolysis process and results in a predictable output of gas, oil and char. Another benefit of used diapers is that a large volume is generated daily in hospitals and seniors homes, and a market already exists for the collection and disposal of these diapers. AMEC‘‘s client, a Quebec company that Piciacchia won‘‘t name yet, plans to tap into that collection network by diverting the flow of diapers from landfills to its own processing plant.

The client will get a tipping fee from the diaper disposal company - one source of revenue - and will generate a second source of revenue by converting the diapers into diesel fuel and selling it to generate electricity or heat. The synthetic gas portion will be used to directly power the process and the char could be sold for a variety of uses, including as an additive for fertilizer.
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