Turning sewage waste into power

RESEARCHERS AT the University of Warwick's Warwick Process Technology Group have devised a process that turns wet waste from sewage farms and paper mills into a source of power.

University of Warwick researcher Dr. Ashok Bhattacharya and his team have cracked the problem of how to extract very pure levels of hydrogen from wet bio-matter, such as sewage or paper mill waste.

This very pure hydrogen can then be used in `fuel cells' to power homes, factories and cars. Eventually the research team's `plated membrane reactors' could be built as small industrial units, no bigger than a large room in some cases, and added directly to the sites of sewage plants or paper mills.

Several previous attempts to extract pure hydrogen from bio-matter to power fuel cells have only met with limited success, even with dry material. The new process extracts very pure hydrogen from the more difficult but exceedingly abundant wet bio-matter and even makes a virtue of the water content of the material to generate even more pure hydrogen, says the university's press release.

First the waste biomass is gasified breaking it down into its Methane (CH{-4}), water (H{-2}O), Carbon monoxide (CO), and carbon dioxide (CO{-2}), and some hydrogen. All these gases are then fed into a reactor, which uses them in a chemical reaction, which extracts the hydrogen from both the methane and the water.

In normal circumstances this reaction would reach equilibrium and simply stop once a certain amount of hydrogen had been generated. However the research team uses a palladium coated ceramic semi permeable membrane as part of the reactor, which only lets hydrogen pass through.

This allows the researchers to both harvest very pure hydrogen from the system (it can be over 95 per cent pure) and to keep the reaction going as long as it is fed with the waste biomass as the hydrogen never builds up to the point where a chemical equilibrium would be reached thus stopping the reaction.

The hydrogen produced by this new very energy efficient method can then be used to power hydrogen fuel cells.

This process is also much cleaner than traditional production of hydrogen as it does not use up fossil fuels, thus producing no more carbon-dioxide than would be produced naturally from the material biodegrading and it produces no other emissions such as nitrous oxides.

Other novel engineering in the process includes the use of a coated nanocrystalline catalyst to accelerate the reaction, and particular methods to manage heat transfer and pressure.

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