Three waste-to-energy solutions

This post originally appeared on TriplePundit and is part of a series on biofuel sponsored by Novozymes.

What is this stuff we call waste?

We all add to the waste stream every day – probably without thinking much about it. According to Webster, waste is “damaged, defective, or superfluous material,” also considered, “an unwanted by-product,” or refuse, which is defined as “a worthless or useless part of something.” In other words, it is something that was created that no longer has any use for anyone. In a given day an individual’s waste stream might include packaging from a new purchase, discarded coffee cups, take-out food containers or used up toothpaste tubes – just to name a few once-valuable items that become waste every day.

So if we have a waste problem, which we do, (Americans generate some 200 million tons of waste per year) it appears that there are two ways to address it. First, stop creating the waste in the first place, or, second, find a way to to turn that waste back into something useful. In other words, turn it into a raw material for some other process.

Janine Benyus, author of Biomimicry, explains that nature merges waste and raw materials – fallen leaves turn into fertilizer for new saplings in the forest, for example. Benyus calls this “waste equals food.” If we are to become sustainable, she suggests we need to follow nature’s lead.

I don’t expect we’ll ever find ourselves eating municipal waste, but since we also have an energy problem, converting that waste into energy would certainly be the next best thing. Besides, what is food after all, if not a source of energy?

Waste-to-energy is already happening today and there are many technologies to make the process cleaner and more efficient. Let’s have a look.

1) Waste incineration

The simplest approach is to just burn the stuff directly. These basic incinerators are in operation in over 1000 plants around the world, mostly in Europe and Asia. After some presorting, the municipal solid waste (MSW) is dumped into a bunker where it is burned. The heat is used to create steam, which generates electricity, and the exhaust is processed by an extensive air pollution control system (here’s a video).

Many waste items contain mixed materials (e.g. metal and plastic), which are difficult to separate and can’t be economically recycled. So the only disposal options for these items are incineration or landfill. At least with incineration, some value is extracted in the form of energy. However, there are questions about the resulting emissions from incineration plants. Greenpeace and other groups have long fought these plants, raising concerns over heavy metals, as well as dioxin and furans, and new pollutants formed during the incineration process. They also give off CO2 and other greenhouse gases that contribute to climate change – so emissions capture systems must be very robust.

Waste incineration also produces a waste product of its own – ash – which must be treated as hazardous waste. However, as the capture technology improves, these risks are being mitigated and managed. In super-green Denmark, incineration plants are very popular and effective – only 4 percent of all trash ends up in landfills, compared with 54 percent in the U.S.

Should waste incineration be considered a renewable energy source? While the generation of MSW seems endless, incineration is first and foremost an attempt to manage the waste problem and reduce landfills, rather than a truly renewable fuel, since it does create some waste of its own. And while these plants produce cheap energy and reduce the volume of waste sent to landfills, both good things, ultimately it would be better for society to produce less trash in the first place.