ACHEMA: Biofuels Research

Researchers Show How Market Waste Can be Turned Into Fuel

06/20/2012 | Editor: Dominik Stephan

Market waste is rubbish? Not really: New researches show how residues can be turned into valueable biofuels.
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Market waste is rubbish? Not really: New researches show how residues can be turned into valueable biofuels. (Picture: Fraunhofer)

Mushy tomatoes, brown bananas and overripe cherries – to date, waste from wholesale markets has ended up on the compost heap at best. In future it will be put to better use: Researchers have developed a new facility that ferments this waste to make methane, which can be used to power vehicles...

Drivers who fill up with natural gas instead of gasoline or diesel spend less on fuel and are more environmentally friendly. Natural gas is kinder on the wallet, and the exhaust emissions it produces contain less carbon dioxide and almost no soot particles. As a result, more and more motorists are converting their gasoline engines to run on natural gas. But just like oil, natural gas is also a fossil fuel, and reserves are limited.

Researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart have now developed an alternative: They have found a way to obtain this fuel not from the Earth’s precious reserves of raw materials, but from fruit and vegetable waste generated by wholesale markets, university cafeterias and canteens. Fermenting this food waste produces methane, also known as biogas, which can be compressed into high-pressure cylinders and used as fuel.

Pilot Plant is Underway

In early 2012, the researchers will begin operating a pilot plant adjacent to Stuttgart’s wholesale market. The facility uses various microorganisms to generate sought-after methane from the food waste in a two-stage digestion process that lasts just a few days. “The waste contains a lot of water and has a very low lignocellulose content, so it’s highly suitable for rapid fermentation,” says Dr.-Ing. Ursula Schließmann, head of department at the IGB.

Raw Materials Composition Poses Challenge

But it still presents a challenge, because its precise composition varies every day. Sometimes it has a high proportion of citrus fruits, while other times there are more cherries, plums and lettuce. On days with a higher citrus fruit content, the researchers have to adjust the pH value through substrate management, because these fruits are very acidic. “We hold the waste in several storage tanks, where a number of parameters are automatically calculated – including the pH value. The specially designed management system determines exactly how many liters of waste from which containers should be mixed together and fed to the microorganisms,” explains Schließmann. It is vital that a correct balance be maintained in the plant at all times, because the various microorganisms require constant environmental conditions to do their job.

But there are still challenges to overcome...

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