Taking out the Trash

Where I live, I have to pay for each bag of household waste picked up by the trash man. Each bag gets a sticker, and every so often I purchase a sheet of stickers for a not inconsiderable amount of money.

Abengoa's municipal-waste to biofuel plant in Spain

Abengoa’s municipal-waste to biofuel plant in Spain. Credit: Abengoa

Luckily, I recycle and compost, and so my actual trash output is minimal.

Still, whatever volume of garbage I produce is a liability on the household balance sheet. Meanwhile, in the biobased/renewables economy, any source of unused carbon can be an asset if handled properly. And so I’m a bit surprised that I did not take note of one important cleantech project that came online in 2013: Abengoa‘s municipal solid waste-to-ethanol plant in Salamanca, Spain.

Thanks go to Jim Lane from Biofuels Digest for describing the facility in his Bioeconomy Achievement Awards post. In my defense, I have heard of  and followed the other projects that made his list.

The biofuel facility was inaugurated in June – and judging from the press release I imagine that Abengoa workers are busy adjusting it and scaling it up. It has an eventual capacity to take in 25,000 tons of municipal solid waste and produce about 400,000 gal of ethanol per year. That is a great deal of ethanol – much closer in output to a Midwestern corn ethanol plant than any advanced biofuel plant I’ve come across.

The secondary benefit of course, besides fuel, is that the amount of waste is reduced by 80%, with only the remainder going to a landfill.

In addition to scale, the other striking feature of the plant is that it uses a fermentation and enzymatic hydrolysis process to get at the carbon inside the cellulose and hemicellulose fraction of waste. Other waste to fuels plants (like Enerkem’s in Alberta) use more physical/chemical processes such as gasification or pyrolysis and inorganic catalysts.

Generally the stated benefits of the thermo-chemical routes are that all carbon-based inputs (i.e., old tires, plastics – you name it) are converted. But whether this distinction is important is questionable. For example, even gasification projects require upfront sorting and shredding of trash.

Perhaps someday when I put out my trash, rather than paying for the privilege, I’ll get paid instead.

Author: Melody Bomgardner

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