How cow stomachs could “eat” plastic

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Enzymes and microorganisms have been found in the rumen of dairy cows that can break down plastics that are difficult to recycle.

The recycling of plastic waste remains a major problem. For example, the end product often cannot be reused for sensitive applications such as food packaging. If one does not want to incinerate the waste, the only option then is landfill – and from there the petrochemically produced material often migrates into the environment in the form of microplastics.

High-performance cow

Accordingly, researchers have been searching for a long time for a way to use microorganisms to break down plastic as residue-free as possible. In the stomach of cows – or more precisely, in the largest of the three forestomachs, the rumen – living organisms have now been discovered that are supposed to be able to digest certain plastics. This was reported by a team from the University of Natural Resources and Life Sciences, Vienna (BOKU).

It was already known in research that kutin, a polyester-like substance found in plant cells, can be degraded by naturally occurring microorganisms. Since cows are high-performance consumers of plant food, the BOKU team led by chemist Doris Ribitsch thought that this must also happen in the rumen. In fact, the microbes were also identified in the rumen’s gastric fluid. They produce enzymes that can break down the kutin.

PET, PEF and PBAT broken down

Subsequently, various types of plastic, ranging from more problematic ones such as PET to plastic variants that are considered biodegradable or at least easily recyclable (PEF, PBAT), were brought into contact with the rumen fluid – the same is widely available at low cost because it has so far been considered slaughterhouse waste. It was found that all three polymers tested could be broken down into their individual components.

Compared to the existing literature for pure enzymes or supernatants from individual microorganisms, the activity, i.e. polyester hydrolysis, in the rumen fluid was “relatively high.” Apparently, more than one enzyme was at work here. The process is synergistic. The next step is to investigate which microorganisms and their enzymes are the most active in polyester degradation. In principle, however, adventurous waste disposers could already reach for the inexpensive rumen fluid to venture experiments.

 

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