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Pilot plant converts fruit and veggie waste into natural gas for cars

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February 9, 2012

The pilot plant in Stuttgart that makes biogas out of waste from wholesale markets (Photo:...

The pilot plant in Stuttgart that makes biogas out of waste from wholesale markets (Photo: Fraunhofer IGB)

Some readers might remember the Mr. Fusion unit in Back to the Future that Doc Brown fills with household garbage, including a banana peel and some beer, to power the iconic time-traveling DeLorean. While we're still some way from such direct means of running our cars on table scraps, researchers at Fraunhofer have developed a pilot plant that ferments the waste from wholesale fruit and veg markets, cafeterias and canteens to make methane, which can be used to power vehicles.

Given the rising oil prices in recent years, many drivers have been converting their cars to run on natural gas. But like oil, natural gas is a fossil fuel with limited reserves whose price has also risen in recent years and is likely to continue to do so. Fraunhofer's development provides an alternative way to obtain natural gas, not from Earth's reserves, but from fruit and vegetable waste.

The pilot plant is part of the ETAMAX project and has been constructed adjacent to Stuttgart's wholesale market. Due to begin operation in the next few months, the plant generates methane by using various microorganisms that act on 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 Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB).

Because the microorganisms require constant environmental conditions to function and the waste can vary in composition every day - some days it will contain a high proportion of acidic citrus fruits, on others it might have more cherries, plums or lettuce - the researchers must adjust the pH value through substrate management.

"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.

Enhancing the environmental benefits of the plant, everything the plant generates can be utilized, including the liquid filtrate and the sludgy residue that can't be broken down any further by the microorganisms. The filtrate water, which contains nitrogen and phosphorous, is used as a culture medium for the cultivation of algae at a second sub-project in Reutlingen. And while two thirds of the biogas produced at the Stuttgart plant is methane, around 30 percent is carbon dioxide, which is also used to cultivate the algae. Meanwhile, the remaining sludgy fermentation residue is delivered to the Paul Scherrer Institute in Switzerland and the Karlsruhe Institute of Technology, where it is also converted into methane.

In addition to Fraunhofer, the ETAMAX project also involves the participation of energy company Energie Baden-Württemberg (EnBW), which uses membranes to process the generated biogas, and Daimler, which supplies a number of experimental vehicles designed to run on natural gas. The German Federal Ministry of Education and Research (BMBF) has funded the five-year project to the tune of six million euros (approx. US$7.97 million). If the various components mesh together as hoped, similar plants could be built where large quantities of organic waste can be found.

Source: Fraunhofer

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
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11 Comments

Just like liquid phase injection of LPG cars in australia should be running off liqufied natural gas, we have three plants in WA about to get another 3 plants in QLD. We have the potential to show the rest of the world how becoming green should be done! Nat gas can come from treating sewerage so that nat gas and fertiliser is the only waste product as well as old garbage dumps designed to do so. Nat gas is the natural way to carry our beloved hydrogen energy

Mark Scope
9th February, 2012 @ 05:20 pm PST

if this became the mainstream method of waste-food management, the energy potential could be massive, that and we wouldn't be throwing so much waste into landfill with no benefits. This is an affordable, realistic way of generating energy from a hugely available and otherwise useless resource, not to mention being a part of the carbon cycle as it excludes reservoir carbon cources. love it

Rhaski
9th February, 2012 @ 06:50 pm PST

Great idea, I'd love to have one on a scale I could use for my vehicle....

Richie Suraci
10th February, 2012 @ 10:32 am PST

The best answer to this already exists in AlphaGen Inc. E-85 Ethanol that converts ANY biowaste to E-85 flex fuel

Mikal Sabir
10th February, 2012 @ 11:56 am PST

Isn't this what we have always known as a methane digester - an up scaled model of the type New Zealand aid has been helping set up in some African countries. What I don't understand is why this ancient technology has not been developed for more general use in the 1st world [so called] countries before this ! Is it not sophisticated enough ?

There are many small methane plants in operation round the world - just the tapping into old landfill deposits is a very basic example and used in many places.

However, it is wonderful to see action in this area and good to hear of the WA and QLD developments Mark.

icykel
10th February, 2012 @ 12:44 pm PST

I'd like to see our companies build those plants here all over the U.S.A instead of depending on foreign oil.

Gargamoth
10th February, 2012 @ 01:39 pm PST

some waste companies generate methane through household food waste,surely that could be scaled up and made more use of in the domestic fuel market for hard pressed consumers.

floccipaucinihilipilification
10th February, 2012 @ 02:17 pm PST

If they can make a profit at it I'm all for it.

Even with the best digesters the sewage to methane ratio is fairly low but if you throw in fresh biomass (uneaten) it gets much better. How much grass clippings and other yard waste do lawn care companies have to get rid of every day?

Slowburn
10th February, 2012 @ 10:58 pm PST

I thank the individual has access to such a fuel making ability, Its called a 'still'for fuel purposes one can obtain a lic. to do so..Evidently we are not totally dependent on foriegn Oil if our number 1 export is oil...

jtd405
11th February, 2012 @ 04:34 am PST

I always reckoned that if you owned a garbage tip, you stood to make a fortune.

pointyup
14th February, 2012 @ 02:52 pm PST

I wonder how the "natural gas" produced by these processes compares to E-85, and other sources?

The comparisons should be in terms of costs to produce, efficiency of product, and resulting effects on the environment.

Observer101
22nd February, 2012 @ 08:38 am PST
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