Are microbes the future of recycling? It is complicated
Since the first factories started making polyester from petroleum in the 1950s, humans have produced an estimated 9.1 billion tons of plastic. Of the waste generated by this plastic, less than a tenth was recycled, according to researchers estimate. About 12% was incinerated, releasing dioxins and other carcinogens into the air. Most of the rest, a mass equivalent to about 35 million blue whales, has accumulated in landfills and the natural environment. Plastic inhabits the oceans and accumulates in the guts of seagulls and great white sharks. It’s raining, in small spots, on cities and National parks. According to some research, from production to disposal, it is responsible for more greenhouse gas emissions that the aeronautical industry.
This pollution problem is aggravated, according to experts, by the fact that even the small part of plastic that is recycled is destined, sooner or later, to end up in the trash. Conventional thermomechanical recycling – in which old containers are ground into flakes, washed, melted, and then reformed into new products – inevitably results in products that are more fragile and less durable than the starting material. At best, the material of a plastic bottle could be recycled in this way about three times before becoming unusable. More likely, it will be “downcycled” into less valuable materials like clothing and carpets, materials that will end up being disposed of in landfills.
“Thermomechanical recycling is not recycling,” said Alain Marty, scientific director of Carbios, a French company that develops alternatives to conventional recycling.
“At the end,” he added, “you have exactly the same amount of plastic waste.”
Carbios is one of a contingent of startups trying to commercialize a type of chemical recycling called depolymerization, which breaks down polymers – the chain-like molecules that make up a plastic – into their fundamental molecular building blocks, called monomers. These monomers can then be reassembled into polymers that are, in terms of physical properties, like new. In theory, proponents say, a single plastic bottle could be recycled this way forever.
But some experts warn that depolymerization and other forms of chemical recycling may face many of the same problems that already plague the recycling industry, including competition from cheap virgin plastics made from petroleum feedstocks. They say that to stem the tide of flooding plastic landfills and the oceans, what is needed most is not new recycling technologies, but tougher regulations on plastic producers and stronger incentives. to use the recycling technologies that already exist.
However, thanks to potentially lucrative corporate partnerships and the tightening of European restrictions on plastic producers, Carbios is pursuing its vision of a circular plastic economy, which does not require the extraction of oil to manufacture new plastics. The company’s approach is based on a technology that is still unconventional in the field of recycling: genetically modified enzymes.
Enzymes catalyze chemical reactions inside organisms. In the human body, for example, enzymes can convert starches into sugars and proteins into amino acids. In recent years, Carbios has refined a method that uses an enzyme present in a microorganism to convert polyethylene terephthalate (PET), a common ingredient in textiles and plastic bottles, into its constituent monomers, the acid terephthalic and mono ethylene glycol.
Although scientists have known to the existence of plastic-eating enzymes for years – and Marty says Carbios has been working on enzyme recycling technology since its inception in 2011 – a discovery made six years ago outside a plastic recycling plant bottles in Sakai, Japan, helped energize the estate. There, a group led by researchers from the Kyoto Institute of Technology and Keio University discovered a single bacterial species, Ideonella sakaiensis, which could both break down PET and use it for food. The microbe harbored a pair of enzymes that together could cleave the molecular bonds that hold PET together. In the wake of the discovery, other research groups have identified other enzymes capable of accomplishing the same feat.