Molds as biogas "boosters"

Mushroom enzymes help with methane production in biogas plants

Mold fungus cultures as enzyme producers University of Bonn
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Scientists at the University of Bonn have developed a method that can be used to produce highly effective enzyme mixtures at a fraction of the world market price. For example, your method could help make biogas plants significantly more effective.

Many only know it from the forest walk or as unappetizing fouling on old bread. However, Udo Hölker does not let anything get in the way of his experimental objects: "Forget bacteria - mushrooms can do much more!" The university scientist and managing director of the company "Bioreact" wants to put the amazing abilities of fungal microorganisms at the service of the environment. His plan: Enzyme blends, which are produced by different molds, are supposed to boost methane production in biogas plants - "and that without competition."

The easily combustible gas can be used on the one hand to generate electricity in block heating power plants, but is also suitable for fuel cells. Naturally, it arises, for example, in the rumen of cows. In abomasal surgery, veterinarians are happy to make sure by flame testing that they have not forcibly perforated the rumen wall with their scalpel. The authors of bovine flatulence are so-called "methanogenic" bacteria. And they are not fussy: under suitable conditions, they can produce methane from almost all organic waste. Renewable raw materials, feed waste, dairy residues or leftovers from restaurants accept them as much as they like manure or liquid manure.

Mushrooms help bacteria

"A large part of renewable raw materials such as grass or corn, but also of bio-waste consists of difficult to degrade long sugar chains - examples are cellulose or hemicelluloses - and it bites the teeth from the methanogenic bacteria, " explains. Hölker. Therefore, the idea has long circulated to help the bacteria in their work: Certain enzymes can crack the sugar chains and dissect into digestible for the methane producers appetizers. The only problem is that the enzymes are expensive and they have their preferences. "With one or two enzymes, the organic material can not be prudently rationalized, and the substances that break it up are simply too different, " says the microbiologist. Conclusion: Mixtures of many enzymes have to go, and they should also be cheap.

This is where Hölkers mushrooms come in: "Mushrooms adapt their extracellular enzymes to the available substrate. In other words, if you put them on a high-cellulite diet, they will produce just the enzymes they need to break down those long sugar chains. "Together with his staff, the microbiologist has isolated several fungi that are particularly good at it. In a pilot plant, they should now demonstrate their skills. "For this purpose, we give several fungi that have to 'tolerate each other well', to a source nutrient, such as beet pellets, and let them grow for a while, " explains Hölker. display

"After a certain time, we then add a little bit of the residue from which we want to produce biogas. We allow the mushroom mix 24 hours to adjust to the new substrate and produce the desired enzymes, then transfer it to the biogas fermenters with the methane bacteria. There, the enzymes split the biomass, so that the bacteria can produce methane from it. "The whole thing goes on continuously: A conveyor screw is initially inoculated with fungal spores and roach pellets and transports the thriving culture along with the enzymes in the following days gradually into the fermenter.

More effective and cheaper

The idea has at least worked excellently in the laboratory so far: "The biogas yield is 30 to 50 percent higher than without our enzyme additive - with mixtures of four or five pure, conventionally produced enzymes you can not achieve a comparable increase." These are Moreover, they are considerably more expensive to produce, especially because they usually have to be costly concentrated and cleaned before they can be sold. For the biogas production is the unnecessary effort: Whether the reactor in addition to the desired enzymes also land a few kilograms of mushroom mycelium, ultimately does not matter. "Our enzymes cost only a fraction of the world market price that would be paid for pure enzymes, " says the managing director of "Bioreact" and head of eleven employees, not without pride. "When it comes to inexpensive fungal enzyme blends, we're unbeatable!"

(Rheinische Friedrich-Wilhelms-University Bonn, 14.04.2004 - NPO)