Plastic pollution is a huge problem worldwide. According to the data of UN Environment Programmes, since the early 2000s, humans have been creating more plastic waste than ever before, with around 400 million tonnes generated annually. Much of this waste circulates through our waterways and oceans, where garbage patches the size of Texas exist.
Although cleanup is possible and is being undertaken by various organizations, it is not without challenges, both in terms of scale and recyclability. Only 9% of plastic waste is recycled. To a large extent, this is due to the fact that this process is time-consuming and expensive. The value of plastic degrades with each reuse, and new plastic is cheap to make.
Scientists are working on the biological decomposition and recycling of plastic. In the lab of biologist Steven Techtmann at Michigan Tech, bacteria with hardy “stomaches” are seen as microbial guinea pigs that chew through recycled plastic to produce an edible, protein-rich byproduct. The idea is that people might start eating plastic too, reports Vice.
Using different organisms to do the dirty work of recycling isn’t a new idea. Scientists know that mealworms, the larvae of the mealybugs (Tenebrio molitor), can decompose polystyrene into the organic matter at a rate of approximately 34-39 mg per day.
Recently, researchers from Spain discovered an enzyme in the saliva of wax worms capable of breaking down polyethylene (or PE), which accounts for up to 30% of plastic used daily.
Since there are quite a few bacteria in nature, such as Alcanivorax borkumensis, which have been used in the past to clean up oil spills, Techtmann wondered if these tiny microorganisms could turn their voracious appetites to plastic. And if we go even further: can they turn plastic into food? In this vision of the future, people will not eat plastic itself, but the cells that are formed when bacteria feed on plastic.
“If you think about it from a molecular level, the components of bacteria are very similar to food we already eat,” Techtmann said. “There’s a lot of protein in them; they’ve got lipids, fats, and vitamins. The product we’re producing at the end is very much like a protein powder that’s already been processed. So what’s leftover are microbial cells, but none of them are alive. You’re really just using them for the protein and lipids they provide.”
The official name of the project is Biological Plastic Reuse by Olefin and Ester Transforming Engineered Isolates and Natural Consortia, or BioPROTEIN. It’s an interdisciplinary effort, funded in part by DARPA, that brings together biologists, engineers, and chemists at the Michigan Institute of Technology to realize a concept that’s firmly in the realm of science fiction.
Plastics — mostly conventional ones such as polyethylene, polypropylene, and polyethylene terephthalate used in bottles — are chemically treated for several hours in a reactor. This process turns the plastic into an oily sludge that allows bacteria to metabolize the material more quickly, in days rather than years.
These more recycled pieces of plastic are then fed to a diverse community of bacteria such as Pseudomonas and Rhodococcus. Bacteria eat, multiplying their numbers and creating more bacterial cells, which are 55% protein. After all the plastic sludge has been consumed, the bacteria are sent to a microbial “slaughter house”, so to speak.
“None of these bacteria are related to any of the bacteria that could make humans sick. And the process we’re developing kills of all the bacteria prior to using [them] as food,” Techtmann said, referring to the heat treatment used to make raw milk safe for human consumption.
Currently, chemical pretreatment is energy-intensive, so scientists are looking for ways to provide enough energy — perhaps with solar panels attached to the sidewalls of the versatile device. Another hurdle is ensuring the product is safe for human consumption and demonstrating this to food regulatory authorities, which Techtmann and his team are currently working on.
If all goes according to plan, Techtmann and his colleagues see their technology for converting plastic waste into protein as another potential sustainable food source. While it’s still a work in progress, the team has managed to create a small amount of this protein powder, but no one has yet tasted it.