The Future of Plastic Recycling is in our Hands—and Cows’ Guts

Biologic compounds are opening up promising new pathways for the commercial recycling of plastics.

On July 2, 2021, several news agencies^[i] published the discovery of a new source of enzymes that can degrade plastic. A paper originally published in Frontiers of Bioengineering and Biotechnology^[ii] by an Austrian research team led by Dr. Doris Ribitsch of the University of Natural Resources and Life Sciences in Vienna outlined that bacteria from a cow’s rumen—one of the four sections of its stomach—can digest certain types of plastics, representing a sustainable way to reduce such kind of litter^[iii]. Given that cows’ diets contain naturally occurring polyesters, scientists suspected that the bovine stomach contains microbes that can degrade such compounds.

The team gathered bovine rumen liquid and incubated it with three types of polyesters – PET (polyethylene terephthalate, a synthetic polymer commonly used in textiles and packaging); PBAT (polybutylene adipate terephthalate, a biodegradable plastic often used in compostable plastic bags); and PEF (polyethylene furanoate, a biobased material made from renewable resources). 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 cows’ stomachs in a laboratory setting, with the plastic powders breaking down quicker than plastic film. The next steps, Dr. Ribitsch said, were to identify those microbe strains crucial to plastic degradation from the thousands of strains present in the rumen, and then identify the enzymes produced by them. Once the enzymes have been identified, they can be reproduced and applied in recycling plants.

This team is not the first to study the use of enzymes as a form of green chemical recycling. Earlier research had shown that some fungi could break down PET plastic, which makes up about 20% of global plastic production. Maria Dimarogona et al. published^[iv] a 2015 study about a chemical called Fusarium oxysporum cutinase, abbreviated as FoCut5a, with the potential to modify PET. Cutinases are enzymes^[v] that degrade cutin, a polyester of fatty acids that form the main component of a plant’s cuticle, the protective covering of plant leaves and shoots. The activity of the recombinant enzyme was tested on a variety of synthetic esters and polyester analogs.

But bacteria are far easier to harness for industrial uses. On March 11, 2016, a Japanese team, Shosuke Yoshida et al., published in Science^[vi] a study of the first known bacterium that degrades and assimilates PET. This species, Ideonella sakaiensis 201-F6, breaks down plastic by using two enzymes to hydrolyze (that is, break down in the presence of water) PET, converting it efficiently into its two environmentally benign components—terephthalic acid and ethylene glycol. The Japanese research team sifted through hundreds of samples of PET waste before finding a colony of organisms using plastic as a food source. Further tests found the bacteria almost completely degraded low-quality plastic within six weeks. Moreover, this strain was voracious compared to other biological agents, including a related bacteria, leaf compost, and a fungus enzyme that had recently been found to have an appetite for PET.

According to an article in The Guardian^[vii], on April 16, 2018, an international team led by Professor John McGeehan at the University of Portsmouth, UK experimented with modifying the enzyme to see how it evolves. However, tests showed they had inadvertently made the molecule even more effective at breaking down the PET plastic used for soft drink bottles. “It is a modest improvement – 20% better,” said McGeehan in the National Academy of Sciences Journal Proceedings. “It’s incredible because it tells us that the enzyme is not yet optimized. It gives us scope to use all the technology used in other enzyme development for years and years and make a super-fast enzyme.”

Professor Mc Geehan declared at that time, “What we are hoping to do is use this enzyme to turn this plastic back into its original components, so we can literally recycle it back to plastic. It means we won’t need to dig up any more oil and, fundamentally, it should reduce the amount of plastic in the environment.”

Despite these advances in enzymes, the characteristics of research organizations and government systems keep them in the R&D stage, considering the nature of the patents that research agencies have secured on them. International organizations have a long way to go in order to press governments to make this technology publicly accessible. Today, many government waste disposal agencies still gather and dispose of plastic in giant landfills or the ocean. With the admonition of environmentally-focused politicians about the consequences of microplastics on the environment, many such governments have initiated campaigns to reduce the use of plastic and promote multiple alternative ways of recycling.

Many agencies and private entrepreneurs have set up recycling centers where they collect plastic waste, sort it, and chop it into small pieces to re-use by melting them under thermo-compression or subjecting them to chemical depolymerization. Some of these engineering processes are expensive and unlikely to become economically viable. Not many plastics can be re-used in thermo-compression, especially for an indefinite number of times; therefore, many governments have banned the import of plastic waste for subsequent chip making. This was a lucrative business as, in many cases, governments would pay to process their way out of their plastic waste. Recycling companies would export material to manufacturing countries to reconvert it and send it back to the original material exporting countries as components of manufactured items. China used to be in this remanufacturing or “upcycling” business, but in 2017 started to ban some types of solid waste, including plastic and unsorted paper, that produced more pollution than benefits.

With the growing public awareness of environmental issues and the success of China’s green development drive, the country’s solid waste imports have decreased significantly. On November 27, 2020, Beijing announced that China would ban all solid waste imports starting January 1, 2021.^[viii] As a result, many companies that had been operating in China as of 2017, importing solid waste from the USA, shifted their facilities to more permissive geographies like Indonesia and Malaysia. They converted solid waste into reusable plastic chips to export to China. Others moved to consumer countries such as Poland or planned to set up conversion facilities in the US.

To ensure that such businesses are viable, site selection methodology must be used conscientiously so that recycling plants, whether using old technologies or new promising enzymes, are economically feasible. Regulatory considerations and government support are necessary decision criteria, but the risks associated with proposed solutions need to be accounted for and assessed. Other factors impacting cost also need to be considered, such as land, construction cost, and the cost of other fixed assets, as well as variables such as energy, transportation, and talent—the most critical factor of all.

Tractus is a strategy consulting firm specializing in site selection, and we can help your business make appropriate decisions in the continuously changing modern world. If you have any questions related to this article, or the site selection process across Asia or the rest of the world, contact Tractus China Country Manager Herminio Andres at herminio.andres@tractus-asia.com.

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[i] https://www.theguardian.com/environment/2016/mar/10/could-a-new-plastic-eating-bacteria-help-combat-this-pollution-scourge

[ii] Front. Bioeng. Biotechnol., 02 July 2021 | https://doi.org/10.3389/fbioe.2021.684459

[iii] https://phys.org/news/2021-07-microbes-cow-stomachs-plastic.html

[iv] Biochim Biophys Acta. 2015 Nov;1850(11):2308-17. Epub 2015 Aug 17.  PMID: 26291558 DOI: 10.1016/j.bbagen.2015.08.009. https://pubmed.ncbi.nlm.nih.gov/26291558/

[v] Serine hydrolases

[vi] Science (Vol. 351, Issue 6278, pp. 1196-1199. DOI: 10.1126/science.aad6359) https://science.sciencemag.org/content/351/6278/1196

[vii] The Guardian , Mon Apr 16, 2018, 15.00 EDT16   https://www.theguardian.com/environment/2018/apr/16/scientists-accidentally-create-mutant-enzyme-that-eats-plastic-bottles?CMP=share_btn_tw

[viii] http://www.xinhuanet.com/english/2020-11/27/c_139547665.htm