Cooking poo. Think of it as a green solution to a brown problem.
In London, the Thames water utility generates 14% of its power requirements by burning effluent; in Sheffield, the light from street lamps is provided by a high-temperature process called "gasification", whereby methane is extracted from sludge; in the United States and elsewhere, anaerobic digestion (whereby bacteria breakdown the organic matter) also provides methane, which can be used as a heat or power source.
Sludge, the solids that remain after sewage has been processed, is high in BTUs (a measurement of fuel energy), meaning it burns efficiently.
Given its supply is unlikely to dry up as long as humans continue to roam the earth - or at least populate cities, the infrastructures of which can collect excrement in sufficient volumes - it makes sense, both economically and environmentally, to ponder the potential of poo.
In Dunedin, there are plans afoot to better capitalise on our waste.
Neville Auton, the Dunedin City Council's energy manager, says stage two of the Tahuna Plant upgrade includes feasibility studies into sludge gas generation.
"Under the upgrade there is a proposal for an anaerobic digester and generation unit. That is under review, with the option of taking biosolids from Tahuna to the Green Island wastewater treatment site to make an energy centre there.
"We have an existing chain of digesters at Green Island that produce methane. Some of it feeds a boiler down there which keeps the digesters warm, so it is self-fulfilling. The remainder of the methane is flared off at the moment. About 500m away, we have the landfill. We are just starting that capture process," Mr Auton explains.
"By July, we want to have requests for proposals for the Green Island site ... it's about making the correct choice for the future rather than the best economic choice now."
