Bacteria found in any of the compartments of a cow’s stomach can break down plastic, according to the research.
Since the 1950s, more than 8 billion tons of plastic – equivalent to the weight of 1 billion elephants – have been produced, mainly driven by packaging, disposable packaging, packaging and bottles. As a result, plastic pollution is ubiquitous in the water and air, with people unknowingly consuming and breathing in microplastic particles. In recent years, researchers have worked to harness the ability of tiny microscopic beetles to break down the stubborn material.
There are microbes that can break down natural polyester, for example in the peel of tomatoes or apples. Given that cow feed contains these natural polyesters, scientists suspected that the bovine stomach would contain an abundance of microbes that break down all plant material.
To test this theory, Dr. Doris Ribitsch from the University of Natural Resources and Life Sciences, Vienna and her colleagues Liquid from the rumen, a compartment of a cow’s stomach, from a slaughterhouse in Austria. A cow typically produces a rumen volume of around 100 liters, noted Ribitsch. “You can imagine how much rumen fluid accumulates in slaughterhouses every day – and that’s just rubbish.”
This liquid was incubated with the three types of polyesters – PET (a synthetic polymer widely used in textiles and packaging); PBAT (biodegradable plastic often used in compostable plastic bags); and PEF (a bio-based material made from renewable raw materials). Each plastic was tested in both film and powder form.
The results showed that all three plastics could be broken down by the microorganisms from cow stomachs in the laboratory, whereby the plastic powders are broken down more quickly than plastic films. The next steps, she said, were to identify the microbes that are critical to plastic breakdown from the thousands in the rumen, and then identify the enzymes they produce. Once the enzymes have been identified, they can be produced and used in recycling plants.
Currently, plastic waste is mainly incinerated. To a lesser extent, it is melted for use in other products, but at some point it becomes damaged and can no longer be used. Another method is chemical recycling – turning plastic waste into basic chemicals – but it’s not an environmentally friendly process. The use of enzymes is billed as green chemical recycling.
Other researchers are more advanced in developing and scaling such enzymes. In September, a superenzyme was made by combining two separate enzymes, both found in the plastic-eating beetle that was discovered in a Japanese landfill in 2016.
In 2018, the researchers revealed an engineered version of the first enzyme that began to degrade the plastic within a few days. But the superenzyme works six times faster. In early April, French company Carbios revealed another enzyme, originally discovered in a compost heap made from leaves, that breaks 90% of plastic bottles down within 10 hours.
In the rumen fluid, there appears to be not just one type of enzyme, but rather different enzymes that work together to achieve degradation, the authors suggested in the journal Frontiers in Bioengineering and Biotechnology.
Carbios is working on scaling its technology, noted Ribitsch. “But of course it’s always good to have even better enzymes that might recycle other polymers, not just PET for example … so it can be seen as a general recycling material.”