Microorganisms – plastic eaters from the compost

How effective bacteria and mushrooms work can be seen at the compost heap: within weeks they break down potato bowls, obstacles, tea bags and leaves, so that valuable composters are created at the end. Wouldn’t it be nice if microorganisms in the same manner remove the plastic mountains of the world? Of the over 400 million tons of plastic waste that are produced every year worldwide, only around ten percent are recycled. In fact, researching small life have discovered that have appetite for plastic. You can help in some areas to improve recycling. The problem: it depends on the type of material.

“Only a few selected plastics are rebuilt or dismantled by microorganisms and enzymes,” says Wolfgang Streit, professor of microbiology at the University of Hamburg. This includes one of the most important plastics, namely polyethylene terephthalate (PET), from which bottles and foils are made. Bacteria also offers attack surfaces on an ester-based polyurethane (PU) based on Ester-based. »All other polymers, such as PE films, PVC and polypropylene, cannot be broken down. There are no enzymes for this, no microorganisms. «Due to their high chemical stability, these substances are inviolable, so to speak. Specifically, this means: “A fishing network or a cell phone cover that someone throws into the sea will probably be found again after a thousand years,” says Streit. It looks different with a PET bottle. “I would be optimistic that after a hundred to 400 years she would disappear completely from nature.” Even the smallest particles would eventually be destroyed by bacteria.

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Therefore, the biochemist Christian Sonnensdecker from the University of Leipzig focuses on the development of biological recycling processes on PET. »Seen Molecular, it is a polyester, i.e. an ester bond. This is, unlike other plastics, to a certain extent unstable, «he explains. Such bonds also occur in nature: plants are covered with a protective layer that mostly consists of cutin, a natural polyester. This waxy shell preserves you from UV radiation, water loss and pests. In order to attack the plant, microorganisms produce enzymes that recognize and split the ester bonds. Science takes advantage of the same enzymes. Sonnendecker’s team examined compost heaps in the Leipzig southern cemetery. The unusual undertaking was worthwhile: the scientists discovered an enzyme in the waste that reduces PET above average. The researchers had selected the plant compost as a field of research. “In the bunch that is naturally to 70 degrees, organisms and enzymes live that endure high temperatures.” The Leipzig team was targeting such thermostable enzymes. PET only becomes easy to attack at temperatures from 60 degrees. This means that the dismantling process is severely accelerated by moderate heat.

The idea of using enzymes is not new. The French company Carbios has already developed a technology for the enzymatic recycle from PET and has started to build a commercial system. The enzymes disassemble the material into its basic building blocks, from which high -quality new plastic can be produced. One of the biggest advantages is that there is no “downcycling”: in conventional processes, the loss of quality is so large that plastics can often only be recycled a few times.

Similarly, the Leipzig Super-Ezym should disassemble plastic. “Unlike Carbios, the PET is not pretreated with us,” says Sonnensdecker. Instead, the waste-for example PET shells, as you know them from strawberry packaging-is put into the reactor chopped into the reactor. Then water and enzyme are added and heated, as the biochemist explains. “In the end we have the breakdown pet, very simple.”

“We are currently developing our enzymes to make them even more efficient,” reports the researcher. They are already being used for research purposes. In the future, Sonnendecker’s team also wants to support companies to develop plastics that are easily degradable. “If the plastic was properly designed, namely based on the model of nature, there are also chemically many options, which then split again so that you get the basic building blocks.”

Wolfgang Streit and his team are not only interested in PET, but also in Nylon – a stable plastic made of oil that can be used in many ways. Nylon stockings that came onto the market in the 1940s are primarily known. In addition, due to its stability and tear resistance, the polyamide is also used for climbing ropes, seat belts, hot air balloons or planning. The fabric is widespread, but has so far been poorly recycled. In search of organisms degrading nylon, disputes examined team plastic waste made from Hamburg waters. “You often get past garbage on the Alster. We sometimes get it into the laboratory and see if any bacteria have already worked on it. «Very optimistic to find a kind of” super bug “is not a dispute. “It is a tedious work. But we also want to know how microorganisms deal with the fabrics. Do you settle on it? Or do you have enzymes to reduce them? “

The microbiologist assumes that nature still has a lot to offer. Probably, he says, there are a number of bacteria that can at least decompose PET – albeit slowly. Mushrooms would also be a worthwhile field of research. The fact that mushrooms and bacteria rememble a plastic mountain like a pile of leaves probably remains a dream despite everything. “But it is too early to put your head in the sand,” says Streit. »We also just need more research in this area. You can also find cool enzymes. “