I’d been thinking about the potential for the last few days, ever since I heard about Growing Power heating their greenhouses with compost – the heaps get very hot, and if you ran a few pipes through them that temperature differential could drive a Stirling engine or heat a home. With interchangeable connections you could even heat the piles in the winter, if necessary. Not terribly efficient compared with a diesel generator, but since even a small home and garden can build up a fair pile of compost, it could still put out a useful amount of power. And if you’re getting methane, fertilizer and/or clean water out of it, then it pays itself off all over again.
There’s a whole new form of green energy brewing. Using microbes taken from soil or sediment, it’s now possible to build fuel cells which generate energy and run off biological wastes. The most popular models run off wastewater from homes or industries and can deliver electricity, hydrogen and methane. Very similar living machines can be used to desalinize salt-water, while producing energy.
The energy potential from this is impressive. A kilowatt from a cubic metre of slime (plus gas fuels), this makes household-level energy production start to look very possible. These cultures are not complicated, or genetically engineers – they can be cultured naturally all over the place. And like all bacterial cultures (such as those that make beer or saurkraut), they evolve to do the task better. Everything up to and including microbes building networks of nano-wires has been seen.
And best of all, it’s possible to do this without fancy platinum parts or complex proton exchange membranes. Kids are doing this as science fair products. With basic materials like metal screens, large plastic containers and activated charcoal. And that means that workable, open-source designs are just over the horizon.
Humanity has been culturing microorganisms as long as we can remember, but only now are we realizing the true potential. Recently, a kid in Kitchener-Waterloo learned taught the world how to compost plastic with microbes he cultured from the dump. Imagine a world where household and neighbourhood-scale Bio-Reactors handle our sewage, compost and wastewater, and give us heat, natural gas and electricity in return. None of this would have to be any more complicated than our furnaces already are, or any more expensive to install. And when combined with other green technologies like passive solar, gardening and rainwater harvesting, it could be the crucial step toward taking all of our homes off the grid.

Lecture – Bruce Logan on MIT Tech TV (23 min)