Conceptual artist Matthew Mazzotta installed a "methane digester" in a park in Cambridge, Mass. that powers the park's lamp:

Dog owners collect their dog waste in a special biodegradable bag and throw it into the digester –- an air-tight cylindrical container, where the dog feces are broken down by anaerobic bacteria.

A byproduct from that process is methane, which can then be released through a valve and burnt as fuel. In this case it is being used to power an old-fashioned gas-burning lamppost in a park.

The artist is keen to make sure that the energy is used as the community wishes, and so in the next couple of weeks the Park Spark project will be a holding a number of design meetings to gather ideas from the community for how to best use the flame. Suggestions already include a shadow-projection box, a popcorn stand and a teahouse.

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