Omar Khalid
Plastic pollution is a pressing global issue, with microplastics and nanoplastics found in fruits, vegetables, and almost every human organ. While recycling is one solution, current methods often result in lower-quality plastic. However, recent scientific advancements offer new ways to safely break down plastic more effectively. These include the discovery of plastic-eating bacteria and enzymes that can break down plastic into its basic elements, enabling high-quality recycling. Additionally, new techniques for chemical recycling, such as using lower temperatures and specific catalysts, show promise in reducing the environmental impact of plastic breakdown. These innovations provide hope in the fight against plastic pollution, aiming to give plastics a new life as valuable raw materials.
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What You'll Learn
Plastic-eating bacteria
Plastic pollution is a pressing issue, with only 9% of all plastic ever made having been recycled. The rest ends up in landfills and waterways, with over 12 million metric tonnes of plastic entering the ocean every year. This has become a serious problem for marine life.
Since then, other plastic-eating bacteria have been discovered, including a species found in the guts of lesser waxworms that can digest low-density polyethylene (PE). Researchers have also engineered a strain of E. coli that can transform PET waste into adipic acid, which is used to make nylon materials, drugs, and fragrances.
The use of bacteria to break down plastic has advanced beyond the laboratory, with a French company, Carbios, running an operation that processes PET plastic waste into precursor molecules for new plastic. This brings us closer to achieving infinitely recyclable plastic.
There are some challenges with plastic-eating bacteria, such as the slow digestion rate and the fact that certain bacteria can only break down specific types of plastic. However, the potential of these microbes in tackling plastic pollution is significant, and the field of plastic biorecycling continues to evolve.
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Enzymes to break down plastic
The escalating issue of plastic waste has reached a magnitude where traditional methods of plastic waste management, including incineration and landfilling, can no longer effectively address the problem. Enzymes might be a solution. Synthetic polymers don't exist in the wild, but similar molecules, such as waxes, do. Nature has provided enzymes to break those down.
Recent evidence shows that some microbes are learning how to work on petroleum-derived polymers. In 2016, Japanese scientists reported a bacterium that eats polyethylene terephthalate (PET) in samples taken from a recycling plant. This bacterium, Ideonella sakaiensis, secretes two enzymes capable of degrading PET. The first enzyme, called PETase, breaks down PET into mono (2-hydroxyethyl) terephthalic acid (MHET). A second enzyme called MHETase then produces ethylene glycol and terephthalic acid.
Other enzymes called cutinases, obtained from bacteria such as Thermobifida cellulosilytica, can also break down PET. However, these enzymes face challenges in terms of efficiency due to the presence of repeating aromatic terephthalate units that elevate the crystallinity of PET. As a result, the degradation process by these enzymes is slow and often incomplete.
Researchers are now isolating relevant enzymes from microbes and engineering them to increase their activity. The goal is to use these enzymes to break down polymers into their original raw materials so they can be recycled or to help manage waste by breaking down small polymer particles in compost heaps and wastewater treatment plants.
One company, Carbios, is at the forefront of commercially breaking down polymers with enzymes. They are building a recycling plant in France that will use enzymes to convert 50,000 metric tons per year of PET into its raw materials: terephthalic acid and ethylene glycol. Carbios has also developed an enzyme to break down polylactic acid (PLA), a biobased polymer.
Another example of an enzyme that breaks down plastic is a mutant bacterial enzyme first discovered in a compost heap of leaves. This enzyme can break down plastic bottles in hours, and the leftover material can be recycled into high-quality new bottles.
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Chemical recycling
There are different chemical recycling technologies, including pyrolysis, gasification, hydro-cracking, and depolymerisation. Pyrolysis, or thermal cracking, involves heating plastic waste to temperatures over 400 °C under low-oxygen conditions. This breaks down long polymer chains into a range of basic hydrocarbon products like gas, wax, diesel, and naphtha, which can be used as fuel or fed into petrochemical plants to become polyethylene and polypropylene again. However, pyrolysis has been criticised as it mostly produces fuels, and the burning and use of these fuels do not constitute "recycling". The fuels produced by pyrolysis can also be highly toxic, and the process generates large amounts of hazardous waste.
Gasification is another method, where waste materials are heated to very high temperatures (1000-1500 °C) in low-oxygen environments. The oxygen breaks the molecules down into their simplest components, creating syngas, a mix of hydrogen, carbon monoxide, and carbon dioxide, which can be used to produce chemicals for plastic production, fuel, and fertiliser.
Depolymerisation uses chemistry, solvents, and heat to turn polymers back into smaller molecules (monomers), which can then be fed back into the plastic production process as secondary raw materials. This process can only be applied to 'condensation' polymers such as PET and polyamides.
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Recycling plastic into valuable raw materials
Plastic pollution is a pressing issue, with an estimated 4.9 billion tons of plastic improperly disposed of, ending up in landfills, the ocean, and other parts of the environment. To address this problem, researchers have been working on innovative ways to break down plastic and recycle it into valuable raw materials.
One notable development is the creation of a mutant bacterial enzyme that can break down plastic bottles in just a few hours. This enzyme, discovered in a compost heap of leaves, optimizes the breakdown process by reducing plastic bottles to simple chemical elements. These elements can then be efficiently reprocessed into food-grade plastic, enabling high-quality recycling. This technology has the potential to revolutionize the recycling industry and reduce plastic waste.
Another approach to recycling plastic involves chemical processes such as 'depolymerization' and 'conversion.' Depolymerization, also known as 'chemolysis' or 'solvolysis', utilizes chemistry, solvents, and heat to break down polymers into monomers, the building blocks for creating new chemicals and plastics. Conversion, on the other hand, transforms mixed plastic into liquid or gaseous feedstocks for reuse in chemical production. These chemical recycling methods have a lower carbon footprint than traditional end-of-life practices like incineration and landfilling.
In addition to chemical recycling, physical recycling methods, such as dissolution, have emerged as complementary solutions. Dissolution dissolves plastic waste using solvents to extract polymers and create new recycled plastic products. These processes contribute to a circular economy by reducing the need for virgin resources and promoting sustainability.
The development of new technologies, such as the supercritical water technique used by Mura, offers promising avenues for tackling plastic waste. By recycling plastic into valuable raw materials, we can not only reduce environmental pollution but also create new opportunities for industrial applications and a more sustainable future.
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Reducing plastic usage
Plastic pollution is a pressing issue that poses a serious danger to marine life and human health. While innovators are working to improve recycling methods, it is important to focus on reducing plastic usage to combat this issue. Here are some ways to reduce plastic usage and minimize its harmful impact:
Reduce, Reuse, and Recycle:
The three Rs – Reduce, Reuse, and Recycle – are essential principles in minimizing plastic waste. Reducing plastic usage starts with conscious choices to refuse single-use plastics and opt for reusable alternatives. Instead of disposable bags, adopt reusable bags for shopping. Bring your own containers for leftovers when dining out, and use reusable water bottles instead of buying bottled water. Reusable dishes, glasses, and silverware are also preferable to disposable options.
Buy Used and Buy Smart:
Consider buying used plastic items instead of always purchasing new ones. Thrift stores, garage sales, and online platforms often offer a wide range of plastic items in good condition, from toys to kitchenware. When buying new, choose products with minimal packaging and opt for larger containers to reduce the overall amount of packaging material. Support brands that utilize recycled plastic materials, and look for opportunities to buy staples like rice and pasta in bulk, storing them in reusable jars at home.
Avoid Microplastics:
Microplastics are tiny plastic particles that can be released into the environment, especially during the washing of synthetic clothing. To reduce microplastic pollution, opt for natural fiber clothing whenever possible. When it comes to laundry, air-drying polyester, acrylic, or nylon clothing can help reduce the release of microplastics into wastewater.
Properly Dispose of Plastic Waste:
Familiarize yourself with your local recycling guidelines to ensure you're properly disposing of plastic waste. Plastic bags, wrap, and film, for example, may need to be recycled separately from your household recycling bin. Some communities have specific drop-off locations for compostable plastics. Additionally, consider organizing or participating in recycling drives to collect and properly recycle plastic bottles and containers.
Support Anti-Plastic-Pollution Initiatives:
Stay informed about anti-plastic-pollution initiatives and legislation in your area. Support and advocate for policies that discourage the use of single-use plastics, such as plastic bags. Participate in community efforts, like beach cleanups, to help remove plastic waste from the environment and raise awareness about the issue.
By adopting these habits and advocating for systemic change, we can significantly reduce plastic usage and minimize the harmful impact of plastic pollution on our planet and our health.
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Frequently asked questions
Scientists have discovered a few methods to break down plastic:
- Using enzymes derived from bacteria that can break down plastics such as PET, one of the most common plastics found in clothing and packaging.
- Using a catalyst of platinum with aluminum oxide to break down polyethylene, a common plastic used in bags and food packaging, without the need for high temperatures or solvents.
- Using a modified enzyme that can break down plastics through depolymerization, separating the building blocks of plastics into monomers that can be built back into virgin plastic.
Larger pieces of plastic gradually break down due to sunlight, oxidation, friction, or animals nibbling on them. This process continues indefinitely, with the plastic eventually becoming microplastics and nanoplastics that are barely visible. These microplastics can end up in the natural environment, including in fruits and vegetables, and can be ingested by humans and animals.
Plastic pollution is a significant issue, with a patch of plastic rubbish in the Pacific Ocean seven times the size of Great Britain and plastic waste choking beaches and landfills worldwide. Current methods of recycling plastic often result in lower-quality material, and the smooth plastic of water bottles degrades with each recycling. By finding ways to safely break down plastic, we can reduce plastic pollution and create valuable raw materials instead of polluting waste.
