Sofia Martinez
Plastic pollution is a pressing environmental issue. The durability of plastic means that it can take hundreds or even thousands of years to decompose, and during that time, it can break down into microplastics and release toxins that harm marine life and potentially human health. While recycling can help slow the accumulation of plastic waste, it is not a long-term solution as recycled plastic is more likely to end up in landfills or the ocean than back at a recycling facility. To address this challenge, scientists have been exploring innovative ways to speed up the decomposition of plastic. This introduction will discuss various methods proposed to accelerate plastic degradation, including the use of enzymes, microorganisms, and oxo-biodegradable technology, and evaluate their potential impact on waste management and the environment.
| Characteristics | Values |
|---|---|
| Ultraviolet light | Ultraviolet light can cause plastic to disintegrate through a process called photodegradation |
| Photodegradation | The breakdown of complex materials into simpler ones due to light exposure |
| Oxo-biodegradable technology | A catalyst is added to promote oxidation, reducing the molecular weight of the polymer by dismantling its molecular structure |
| Enzymes | RHP-shrouded enzymes can break down plastic into monomers when exposed to water and heat |
| Fungi | Trichoderma, a genus of saprophytic fungi, can produce hydrolytic enzymes which decompose polymers |
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What You'll Learn
Using enzymes to break down plastic
Plastic is a synthetic, petroleum-based polymer that is too large for microbes to break down. However, enzymes, which are a type of protein, can break down plastics.
Enzymes are produced by a type of bacteria that feeds on plastic bottles. In 2016, Japanese scientists discovered a plastic-eating bacterium that could break down plastics into their constituent parts. However, the process was too slow to be useful. Since then, researchers have been working to enhance the efficiency of the enzymes produced by the bacteria.
In 2018, an engineered version of the first enzyme, PETase, was found to break down plastic in a few days. By connecting PETase with a second enzyme, MHETase, scientists doubled the speed of the breakdown process. The linked super-enzyme is impossible for a bacterium to create, so scientists connected the two enzymes in a laboratory. This new combination of enzymes can break down plastics in a matter of days.
The super-enzyme can break down plastics such as PET (polyethylene terephthalate) and PEF (polyethylene furanoate), but it is unable to break down other types of plastic such as PVC (polyvinyl chloride). The use of enzymes to break down plastics could allow for infinite recycling, reducing our reliance on fossil resources.
In addition to the super-enzyme, researchers have also identified a bug that eats polyurethane, a type of plastic that is widely used but rarely recycled. When polyurethane breaks down, it releases toxic chemicals that would kill most bacteria. However, the identified bug uses the material as food to power the breakdown process.
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Increasing exposure to UV light
UV light can cause a chemical reaction in plastic, resulting in the severing of polymer molecules. This is known as photodegradation, the breakdown of complex materials into simpler ones due to light exposure. The process of photodegradation can be sped up by increasing the exposure of plastic to UV light. This can be done by ensuring the plastic is in a location with high UV exposure, such as an area without shade or cloud cover.
Additionally, the plastic itself can be manipulated to become more light-sensitive. This can be achieved by adding certain chemicals, such as carbonyls and metal blends, during the production process. Carbonyls, including carbon monoxide carbonyl and ketone carbonyl, are organic compounds that are interlaced with plastic molecules. Metal blends, such as cobalt, iron, and nickel, initiate a two-stage degradation process. In the first stage, these additives absorb UV light and cause weak links in the polymers. In the second stage, environmental factors like wind and rain work on the weakened plastic structure, eventually leading to its disintegration.
Furthermore, scientists have recently discovered that incorporating sugar molecules into polymers can make plastics more degradable when exposed to UV light. This technology adds sugars to the polymer chains, creating bonds that can be broken down by UV light. This process weakens the plastic, breaking it down into smaller polymer chains that are more sensitive to hydrolysis, making the plastic more biodegradable in natural environments.
While increasing UV exposure can speed up plastic decomposition, it is important to consider that UV stabilizers and antioxidants can be used to inhibit degradation. These substances absorb and disperse UV radiation, preventing the breakdown of plastic. Therefore, when attempting to speed up decomposition through UV exposure, it is crucial to avoid using plastics with UV stabilizers or similar additives.
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Using fungi to speed up decomposition
Plastic is a synthetic, petroleum-based polymer that is extremely durable. This durability makes plastic a long-term pollutant, as it does not readily decompose. However, some methods can be employed to speed up the decomposition of plastic, including the use of fungi.
Fungi are microorganisms that can break down complex materials, such as plastics, into simpler molecules through the production of powerful enzymes. This process is known as biodegradation and is considered the most effective and environmentally friendly way to degrade plastic. Fungi, such as Aspergillus terreus and Engyodontium album, have been shown to break down plastics in laboratory experiments. In one study, these fungi completely degraded plastic samples in just 140 days.
The use of fungi to degrade plastics is a biological process that can be optimized to increase efficiency. For example, researchers have identified environmental conditions that enable fungi to more effectively latch onto and break down plastics. Additionally, the addition of pro-oxidant ions can enhance the degradation process. These ions facilitate the cleavage of plastic molecules into smaller fragments that can be more easily degraded by fungi.
Furthermore, specific fungal species are known to produce enzymes that are particularly effective at degrading plastics. For instance, Rhizopus delemer and Candida antarctica are fungal species that produce lipases, a type of enzyme that catalyzes the hydrolysis of lipids. Other enzymes, such as cutinases and proteases, are also involved in plastic degradation and are produced by various fungal species.
The application of fungi to degrade plastics can be done by scattering granules containing the biological substance over a given surface. This method has been developed by researchers at Nicolaus Copernicus University and is currently manufactured in a laboratory in Toruń. While this process is not yet used on a large scale, it offers a promising solution for treating plastic waste in recycling, landfill, and illegal dumping sites.
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Employing oxo-biodegradable technology
Oxo-biodegradable plastic is a type of plastic that biodegrades faster in the presence of oxygen, breaking down into harmless, biodegradable matter within a few months to a few years. Unlike traditional plastics, which can take hundreds or even thousands of years to decompose, oxo-biodegradable plastic can significantly shorten the degradation process.
This type of plastic is made from petroleum-based raw materials and a small number of metal salts. The metal in its composition allows the molecular structure of the plastic to break down when exposed to heat and oxygen. The plastic then reaches a state where microorganisms can process it, transforming it into carbon dioxide, water, and biomass.
One of the key advantages of oxo-biodegradable plastic is that it does not require a biological process to initiate degradation. Instead, it relies on abiotic factors like oxygen and heat to begin breaking down. Additionally, microorganisms can accelerate the degradation process once the plastic has reached a manageable state for them to consume.
However, it is important to note that oxo-biodegradable plastic has faced scrutiny for its environmental impact. Some studies suggest that instead of fully biodegrading, oxo-biodegradable plastics tend to fragment into smaller pieces, including microplastics, which can persist in the environment. These microplastics may take longer to degrade than initially anticipated, depending on environmental conditions.
Despite the potential benefits of accelerated degradation, oxo-biodegradable plastic has been banned in several places, including Switzerland and the EU. In the US, the Federal Trade Commission (FTC) has taken a stance against the use of the terms '"degradable" or "biodegradable" for oxo-biodegradable products without strong scientific evidence to support these claims.
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Adding water and heat to compostable plastics
Plastic is a synthetic, petroleum-based polymer that is extremely durable. This durability makes plastic a potential long-term pollutant, as it does not readily decompose. Compostable plastics have been touted as a solution to this problem, but they can take years to break down, sometimes lasting as long as traditional plastics.
Scientists at the University of California, Berkeley, and the University of Massachusetts Amherst have developed a new process to speed up the decomposition of compostable plastics using water and heat. This process involves embedding polyester-eating enzymes in the plastic during its manufacturing. These enzymes are protected by a polymer wrapping, which prevents them from becoming inactive. When exposed to heat and water, the enzyme sheds its polymer coating and starts breaking down the plastic polymer into its building blocks. In the case of polylactic acid (PLA), a common compostable plastic, the enzyme breaks it down into lactic acid, which can feed soil microbes in compost.
The RHP-shrouded enzymes do not change the characteristics of the plastic, which can be melted and extruded into fibres like normal polyester plastic at temperatures of around 170°C (338°F). Degradation occurs faster at higher temperatures. At room temperature, 80% of the modified PLA fibres degraded entirely within about one week. Under industrial composting conditions, the modified PLA degraded within six days at 50°C (122°F), while another polyester plastic, PCL (polycaprolactone), degraded in two days under the same conditions at 40°C (104°F).
The new technology should theoretically be applicable to other types of polyester plastics, allowing the creation of compostable plastic containers. However, there is still work to be done, as Xu, the lead researcher, is currently developing RHP-wrapped enzymes that can degrade other types of polyester plastics. Xu is also modifying the RHPs so that the degradation can be controlled and stopped at a specified point to prevent the complete destruction of the material. This could be useful for recycling, as the plastic could be remelted and turned into new plastic products.
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Frequently asked questions
Plastic is made of synthetic, petroleum-based polymers, which are too large for microbes to break down.
One way to speed up the decomposition of plastic is to expose it to ultraviolet (UV) light, which causes plastic to disintegrate through a process called photodegradation.
Yes, researchers have found that certain enzymes can break down plastic within days or weeks. Additionally, specific microorganisms like fungi can be used to accelerate plastic decomposition.
Many grocery stores accept plastic bags for recycling, which is preferable to sending them to landfills. When recycled, plastic can be turned into products like benches that are less likely to be thrown away.
