Our project aimed at creating a single-cell E. coli system for the upcycling of PET into PCA, which in turn can be the starting point for other high-value chemicals such as vanillic acid. We also tried to upscale the expression and purification of two enzymes that are partly responsible for the upcycling pathway. On a larger scale, we wanted to target the very critical problem of plastic accumulation in our environment due to lack of functional recycling systems by creating economic incentives for collecting PET plastics and turning this material into other chemicals that industries would be able to use.

If successful, our system could hypothetically be implemented in several areas. The first thought would be to create bioreactors containing our E. coli strain that would continuously be fed plastic slurry that had been collected in a system similar to the deposit system used in several countries around the world, and high-value chemicals could then be isolated from this bioreactor. However, we also think that our system, if successful, could be implemented to rid our environment of plastic that is already there, such as microplastics.

Industrial production of chemicals using new sources

Protocatechuic acid, PCA, was the target chemical we tried to produce this year. PCA has been investigated in several pharmacological studies, for example as an anticancer agent and an antioxidant. It is also a known precursor for several types of polymers, plastics and chemicals. Additionally, PCA is naturally occurring in several types of spices, vegetables and fruits. Taken together, there are several applications for PCA in different fields (Upadhyay & Lali 2021).

Several of these materials can be, and usually are, made from sources that put a strain on our environment. A common example is plastics and polymers being produced from oil, a limited fossil resource. At the same time, due to technical advancements, the demand for these types of materials is rising. This has led science to investigate other, more sustainable (and cheaper) sources. PCA production in Aspergillus niger is one such example (Lubbers & de Vries 2021).

Our project, PETerminator, investigates another source for PCA. Our modular design also aims to make it easy to switch out enzymes so that other end products could potentially be produced. If successful, our system PETerminator could potentially be used as a one-cell chemical factory that uses what others may call trash as the source material. This would not only be beneficial for companies within this sector since it would allow for cheaper raw materials, but it would also benefit our planet since it would create monetary incentives for collecting PET plastics and turning them into new products.

Water processing: Clean water for human society

In a modern society, we take clean freshwater for granted. Most communities have running water that has been treated to some degree, most likely in a water treatment facility or a wastewater treatment plant. Thanks to recent scientific achievements, many harmful or undesirable chemicals can be filtered out or otherwise removed chemically. However, one of many important exceptions are microplastics. These microplastics stem from many sources of plastics, each containing different additives that give them specific properties. There are unfortunately not many communities that are able to fully remove these particles from the water, whether it is drinking or sewage water.

There are usually several steps, or stages, involved with treating water, and these differ depending on the origin of the water and its future purpose. The first stages will clean out organic and inorganic material that can be captured via filters and membranes, whereas later stages are more chemical than mechanical in nature. There have been studies showing that microplastics tend to float, which potentially could be used in order to remove 99,9% of microplastics. However, this is not always true and a small fraction can escape. Another approach that has been discussed is using coagulants, but studies have had varied results. Different types of membranes and bio-polymers are other alternatives, with successful results. The downside of many of these techniques is that large portions of microplastics will accumulate in sludge, membranes and filters, and the plastic particles may end up in the environment again when these products are themselves disposed of (Kuok Ho & Hadibarata 2021).

Our system, PETerminator, could potentially be a factor in treating water used in our communities. It would not only remove the microplastics from the water, but chemically upcycle them so that the microplastics couldn’t be re-introduced into the water. If possible, the PCA could be purified from the water. The aim of our modular approach is to facilitate easy adaptation of our system, so perhaps the bacteria could be engineered to upcycle the plastics into a harmless chemical or another chemical better suited for removal from the water. Either way, we believe that adding a biological treatment step in addition to the mechanical and chemical processes already established may be one possible approach to removing microplastics from the water.

Water processing: Cleaning up our environment

It should come as no surprise that plastic pollution in our oceans and lakes is a huge problem. Images of dead sea birds with guts full of plastics, dolphins and turtles trapped in fishing nets, and entire islands of Coca-cola PET bottles are sadly familiar images. In fact, 150 million metric tonnes of plastic is currently polluting our ocean, and 8 million metric tons of plastic waste is released into the ocean from coastal regions every year, which means that this is a growing problem (World Wildlife Fund 2019). However, this visible surface plastic only accounts for 1% of the total amount of plastics. The remaining 99% is believed to sink to the seafloor and get buried in sediment, where we are unable to collect it. Some of it is grinded by the forces of the ocean over time, or released when we wash our polyester clothing, producing microplastics. The scientific field is also learning more about nanoplastics every day, which pose an even bigger threat than microplastics. Due to their size, nanoplastics are able to accumulate within cells and bloodstreams of humans and animals, as well as affecting microorganisms that are important for the health of oceans (Buranyi 2019). There is no way around it, we need to rid our environment of plastics sooner than later, especially since we still do not know the full impact of high levels of plastic in our environment (Burns & Boxall 2018).

One very important aspect before discussing how PETerminator would be implemented in this manner, is to realise that GMOs should be contained within a controlled environment, or be designed in a way that allows for control so that the engineered bacteria do not threaten existing microfauna in nature. Simply releasing PETerminator into the ocean is not a viable option with this in mind. However, a possible implementation of our system could be to funnel ocean or lake water with high amounts of microplastics through a bioreactor with our bacteria, and similarly to the previously described method, PET would be upcycled to either a suitable harmless chemical or purified out as PCA. The major issue, however, is the sheer volume of plastic in our waters. There is also no existing infrastructure, unlike the previously discussed water plants and treatment facilities, that could facilitate implementation more easily. That being said, a successfully engineered PETerminator may be able to treat local spots with concentrated amounts of microplastics, or be used together with efforts such as the Ocean Cleanup foundation (The Ocean Cleanup 2022).

The major issue, however, is the sheer volume of plastic in our waters. There is also no existing infrastructure, unlike the previously discussed water plants and treatment facilities, that could facilitate implementation more easily. That being said, a successfully engineered PETerminator may be able to treat local spots with concentrated amounts of microplastics, or be used together with efforts such as the Ocean Cleanup foundation [4].

Producer’s responsibility and recycling incentives

Plastic is a cheap, versatile material. But, we as a society are incredibly bad at recycling. A lot of the blame is on consumers. They tend to buy new rather than repair or go for second hand options, or buy the latest model despite their current version working fine. Consumers choose price over repairability and environmentally conscious products. Many are simply not aware that their fleece sweater releases tiny PET particles every time it is washed. However, blame can also be directed at the producers of these products. A great example is the policy called “planned obsolescence”, where companies intentionally design a product so that it will become obsolete, forcing the customer to buy another one, generating sales (Kramer 2012). A countermeasure to this is the French repairability index, where certain electrical products are rated based on how easy it is to repair by law. The aim is to guide consumers in choosing products that can be repaired, but most importantly to force producers to be conscious about how their products can be repaired and improve this. The idea is that consumers will not buy products with a bad rating (mdepypere 2021).

In Sweden, we have a national recycling system for packages that is run by the non-profit Förpackningsinsamlingen, FTI. FTI was created by companies within the material industry as a response to the Producer’s responsibility that was put into law by the Swedish government in 1994. The law says that the company that sells a product with packaging is also responsible for gathering said packaging and responsibly recycling it. Not to mention, many of the packages, such as aluminium packaging, is actually cheaper to recycle than to produce new and will still give a high quality product. In other words, the Swedish government made producers responsible for (at least some) of the waste they generate (FTI 2022). Another Swedish example that is also present in other countries is using a deposit system for aluminium cans and PET bottles. Consumers pay a small fee when buying these items, which they get back once they return the cans and bottles. This has been very successful, with 85% of all packages being returned (Pantamera 2022).

The previously mentioned systems have been very successful, but not all plastic comes in the form of packaging and soda bottles. We can learn from these strategies though, and the main conclusion is: Money is great motivation. This is why we designed our PETerminator to upcycle rather than just degrade PET. If PETerminator would be successful, it would give companies monetary incentive to collect these other products containing PET plastics so that more valuable products could be created from it.