Who will eat all the plastic and can we find this hero
In March, scientists at the University of Texas announced they had created an enzyme that could crack down on millions of tons of plastic in landfills around the world! The new enzyme received the bright name FAST-PETase: it is functional (functional), active (active), stable (stable), and tolerant (permissible). And it processes PET (PET) plastic in a day, a maximum of a week, when in nature it takes hundreds of years!
Have you seen this kind of news before? Another discovery does not excite the imagination? In this post, we will explain why.
Discovering a new plastic-recycling enzyme has been a popular pastime since at least 2008, when 17-year-old Daniel Bard rocked another science fair with bacteria that could kill 43% of plastic. Since then, new enzymes have eaten plastic at two, three, or six times faster. So why are we, at best, sorting plastic for recycling while new reports of “landfills” flash across the news feeds?
Plastic is diverse
Enzymes that process plastic can only work with one kind of plastic; rarely with several. Usually it is PET (polyethylene glycol terephthalate), which makes up only 20% of all plastic waste. From a chemical point of view, it is much easier to destroy than polyethylene or polypropylene, which are used for packaging.
To date, the most well-known microorganism that recycles plastic is Ideonella sakaiensis, a bacterium discovered in 2016 in soil samples taken near a plastic recycling factory in Japan. Under certain conditions, she cracks down on plastic in six weeks – but only with PET. There are thousands of types of plastic used in the world, and PET is only a small part of it. In terms of global production in 2015, it ranked only sixth among all types of plastic. Ideonella will not handle plastic caps or straws – they are made of polypropylene. Shampoo bottles, bags, wrapping film – it’s all made of polyethylene of different densities. The packing filler disappears – it is based on polystyrene. Just like sponges and polyurethane foam – they are made of polyurethane.
Of course, the processing organisms do not end with Ideonella. Some types of flour worms can eat and recycle styrofoam. And certain types of fungi decompose polypropylene by 90%. But for the vast majority of plastics in the world, their superhero has not yet been found and it is not certain that it will be found. Bacteria have had millions of years to learn how to decompose wood, fruit and other organic matter. They first encountered plastic only in the middle of the last century.
World production of polymer resins and fibers in millions of tons. Source
Choosing your body for each type of plastic is a completely thankless task, so you should think about something universal. However, this can end badly, and below we will give an example of such a scenario.
Need certain conditions
Many microorganisms are very capricious and process plastic only in a limited range of temperatures, in a special environment or for a long time. The more stringent the conditions, the more difficult it is to scale the solution. Recycling plastic in the natural environment is then out of the question.
In order to really change something, an incredible number of such organisms will have to be released into nature. But bacteria are not bees; they themselves will not fly to the “flower”. Without external factors – winds, ocean currents, or even bulldozers – bacteria cannot travel any significant distance. Competition at this biological level is very high, the strongest survive – that is, the one who has mastered the necessary habitat, and not the microorganism planted by us. Do not take and spray enzymes / bacteria over Great Pacific Garbage Patch; many simply do not get to a tasty morsel.
More justified here seems to be the approach used in water treatment plants: we populate bacteria in special tanks and feed them what we want to get rid of. This is already the case with other types of waste. But here we are faced with additional costs for transporting waste to recycling sites. Considering the scale of the problem, the costs will be rather big.
It’s expensive, but the plastic is not getting smaller
Most enzymes break down plastic polymers into monomers that are only suitable for re-creating plastic.
This brings us to two problems. The volume of plastic in the world is not decreasing, whatever one may say. At the same time, the production of plastic from scratch is quite cheap. Building processing plants, shipping tons of raw materials, and providing conditions for bacteria will eventually provide us with raw materials that cost nothing. The business model is very questionable.
Even if in the future there are enzymes or bacteria that can naturally process plastic, it could be very dangerous. Such bacteria can release toxic waste and destroy plastic that is still in use – for example, in the device from which you are reading this post.
Today, enzymes and bacteria can only be used within some existing processing systems. They do not offer anything fundamentally new: we still need to sort, collect and send plastic to recycling plants.
Is everything really hopeless?
No, there is good news. As mentioned at the beginning of the post, the University of Texas at Austin discovered an enzyme that can process plastic in a matter of hours at a relatively affordable temperature of 50 ° C. Artificial intelligence is used to develop this enzyme.
Recently, the French company Carbios launched a production line based on enzyme-degraded plastic. It already successfully produces PET bottles. And, although we said above that the total amount of plastic does not decrease from this, reuse is still good. By 2024, the company expects to reach the commercial scale of work. In this way, it will be possible to more successfully recycle plastic from mixed waste.
In parallel, scientists are developing biodegradable materials that can replace plastic. At MIT, for example, they do it with cellulose. The English company Notpla uses algae and other plants to create films and various coatings to replace plastic ones. In Europe, legislators are seeking to limit the use of plastic that is difficult to recycle.
Microorganisms for plastic recycling are usually found in nature and then improved. But some scientists offer completely their own design options. In 2019, a group of Australian scientists presented studydedicated to the processing of microplastics through oxidation accelerated by carbon materials and subsequent decomposition as a result of interaction with water at certain temperatures. It sounds simple, but to make it work, you need the most complex structure of carbon nanotubes. And the research itself is only the first step in a long chain to production, which can break at any moment.
red herring
There is a popular opinion among eco-activists: plastic recycling within the framework of the general ecological situation is what the British call red herring (“red herring”); something that distracts us from a more important issue. While everyone is discussing the bill to ban plastic straws, they are ignoring issues related to the carbon footprint and global warming. Bacteria can recycle even all the plastic, but this will not save us from melting glaciers, rising general water levels, constant forest fires and man-made natural disasters.
