To make our research closer to reality, we made a PET film with low crystallinity, which was used to quickly detect the degradation effect of PET enzyme.
Methods:
Cut the Coca-Cola bottle into PET flakes (ϕ 6 mm, 10 mg) and then dissolve them in 0.5 mL 1,1,1,3,3,3-hexafluoro-2-propanol solution. Amorphous PET can be generated by the volatilization of the solution.
Results:
Figure 1 Process of self-made PET film. (a). 10 mg PET plastic bottle with high crystallinity. (b). PET treated with 1,1,1,3,3,3-hexafluoro-2-propanol solution. (c). PET film with low crystallinity.
Part 2 The prospect of biodegradation of plastics
Through an interview with Director Lu of Wuxi Environmental Protection Bureau, we learned that China's PET consumption and output are extremely high, and due to its good stability, it cannot be replaced by biodegradable plastics in a short time. Therefore, PET recycling is a very important part of China's sustainable development strategy.
We launched a survey of different ages and educational backgrounds, and finally obtained 2,309 feedbacks. According to the questionnaire, 85.86% of the people supported the recycling of plastics. Among the recycling methods, the proportion of chemical methods and biodegradation methods was equivalent, indicating that the chemical method still had its advantages with a mature and complete system. However, the biological method had just emerged, and it had also received support from most of the people, indicating its promising future.
We also analyzed the prospects for recycling of biodegradable plastics. 83.83% of the people said they support biodegradable recycled plastics. However, as to whether they will buy degraded and remade plastic products, 81.6% said they would buy and 41.62% of them said they would buy them according to different purposes. There are still some concerns about the safety and purity of plastics. That is exactly the shortcomings of the current physical and chemical recycling methods. Instead, the biodegradation method may contribute to releasing the concerns.
Part 3 Using envision
3.1 Proposed end users
We focus on three types of potential users that is waste treatment and plastic recycling plants, manufacturers and consumers.
1. Waste treatment or plastic recycling plant: degrade PET plastic into raw material powder and sell it to the manufacturer.
2. Manufacturer: purchase biodegradable raw material powder for secondary manufacturing (the performance of the material has not changed, and the safety is higher).
3. Consumers: consume products made by recycling biodegradable powders (such as water bottles).
3.2 How to use our project (Image)
Our project can be applied to degrade microplastics, and it is bound to be put into the natural environment in the end. Regardless of whether it is recombinant E. coli or yeast, safety should be a problem. Our initial idea is to build a device in a specific location, such as a garbage treatment plant or a plastic recycling plant. Then yeast can be cultivated and applied in special equipment. After the treatment, the bacteria shall be inactivated to prevent the outflow of the strains. Followed by our imaginary sketch of the Fermentation and PET Treatment and Recovery Device used at Waste Recycling Station.
Figure 2 imaginary sketch of the Fermentation and PET Treatment and Recovery Device used at Waste Recycling Station
3.3 How to implement in the real world
Policies:
In order to make our project closer to practical application, we first learned about relevant policies from Director Lu of the Environmental Protection Bureau. Director Lu indicated that if we could achieve efficient degradation and recycling of PET plastic, it would be promising. What is more, relevant policies are supportive of such a project.
Industrial application:
As for how to put it into applications, we interviewed with Golden Land Company and DuPont. We learn that currently PET is mainly degraded by chemical methods, and a large part of PET plastics are simply crushed and remolded, and then made of plastics with low performance requirements. The performance of this remolded plastic is not as good as that of new PET plastics. What is more, with repetitions increasing, it becomes worse and worse. Finally, incineration or landfill methods are used to disposal the plastics, which causes the waste of resources and pollution of the environment. Therefore, if our project (biological method) can efficiently degrade plastics and be scaled up, it will be beneficial to the world.
Besides, there are several suggestions from companies. Firstly, develop enzymes with higher enzyme activity and higher affinity for substrates. Secondly, improve the properties of the enzymes. Thirdly, explore new ways to improve its productivity. We should ensure that solid foundations are built in the early stages, and then subsequent work will be smoother. In addition, the application scenario may be more targeted. Therefore, it is necessary to develop some new enzymes for different environments. It is difficult to control enzyme activity in the actual environment. At present, we set various parameters in the laboratory. However, in view of the environmental changes in the actual application process, or the proportion of ingredients in the material and morphological changes, we need to use different enzymes. Additionally, AI machines can be involved in the process. Microsoft has just announced the release of an AI machine that allows users to design their own protein models. With further experimentation, the machine model has the potential of helping the production of more efficient enzymes.
In conclusion, although the current experiments are still in the preliminary stage, the prospects are very good. If the degradation efficiency can be further improved, there is still great commercial value.
Part 4 Safety aspects
4.1 The safety of the host and the design of its killing mechanism
We used Candida tropicalis with biosafety level 1 as the host for surface display.
In order to prevent the strain from leaking, we knocked out the URA3 gene in the wild strain through the CRISPR-Cas9 gene editing system. Therefore, Candida tropicalis loses the ability to synthesize uracil and becomes the uracil-deficient strain. Uracil-deficient Candida tropicalis cannot survive in an environment without uracil. Thus, it prevents the strain from leaking to the nature to a certain extent.
Part 5 Other challenges
5.1 PETase has strong specificity and cannot degrade materials and components other than PET. Therefore, we need to know the purity of the substrate.
To confirm the feasibility of the project, we have to know something in advance——1. How PET plastic bottles are sorted. 2. Whether the PET plastics sorted are 100% pure PET.
Plastic sorting
Through interviews, we learned that the current plastic sorting work is mainly done manually. Plastic sorting includes the classification of plastics and the peeling of different materials. Because the material is manually peeled off, the final substrate that enters the degradation device is generally high-purity PET.
Purity of PET
We learned in the interview with Golden Land Company that most of the PET plastics on the market are pure PET polymers. Therefore, for a small part of PET plastic waste that needs to combine with other components to achieve special properties, we can separate components after degradation. Besides, most of the drinking water bottles are 100% pure PET materials. Therefore, it proves that our solution has application value. For ordinary drinking-grade water bottles, we can use our solution to degrade them. They can be degraded into pure PET raw materials without by-products and processed for secondary processing without any loss of safety and functionality.
5.2 Factors that PET degradation companies need to consider
1. Free-to-operation, FTO: Analysis and investigation of whether there is a risk of infringement of third-party patent rights when using, producing or selling products containing the licensor’s patent in the licensed area.
2. Environmental impact assessment: engineering analysis, environmental risk assessment, pollution control measures and economic profit and loss analysis, etc.
Factories also need to comply with various relevant laws, local policies and regulations, such as the "Environmental Protection Law of the People's Republic of China" and "Environmental Protection Law of the People's Republic of China". Besides, implementation process must follow relevant technical specifications, such as "Recycling of Waste Plastics" (GB/T 37821-2019).
