Waste Not, Want Not

Sewage plants and paper mills could soon be wringing clean-burning hydrogen fuel out of wood pulp and sewage sludge, says Ashok Bhattacharya, director of the Warwick Process Technology Group at the University of Warwick in England. He and his colleagues heat the waste under high pressure, inciting a reaction that releases hydrogen along with methane, water vapor, and traces of other gases. They run the mix through a chemical processor that pulls additional hydrogen from the methane and water; the processor incorporates a palladium-coated membrane that allows the hydrogen to escape while new waste is fed in, keeping the reaction going. This technique can capture 60 percent of the energy from the organic waste in the form of hydrogen— three times as much as previous methods. Bhattacharya is now trying to design reactors that are heated by their own hydrogen, making the recovery process simple and self-sustaining.