IMPLEMENTATION

For implementation of the gene product, we propose a membrane based bioreactor system with a PVDF (polyvinylidene difluoride) membrane [1] impregnated with Fe3O4 Nanoparticles that have b FastPETase and Modified MHETase immobilised on them [2], [3]. As a preliminary step to reduce particle size we place plastic bottles in a plastic shredder.
Once passed through the plastic shredder, it is subjected to UV treatment to further weaken polymer bonds [4].
Following this, we feed a suspension of microplastics into the bioreactor.
We propose a pilot scale Membrane based Bioreactor(MBR), flow rate may be ranging from 40-90 l/h, HRT(Hydraulic retention time) from 20 -100 h [5],[6].
The Fe3O4 nanoparticles are immobilized with the enzymes FAST-PETase and our Mutated MHETase via solvothermal method [3]. Nanoparticles efficiently immobilise enzymes due to their large surface area and increased binding capacity. They also allow reusability [8] and additional stability compared to the free state of the enzyme [3].
The bioreactor system can potentially be solar driven, in line with other studies using solar driven membrane systems by incorporating a solar photoreactor [7]. This would serve the dual purpose of ensuring a renewable source of energy and raising the temperature of the bioreactor system. This can be a cost-effective method to improve the overall efficiency of PET hydrolases, since they show low activity at ambient temperature [3].

We have also looked at strategies to prevent blockage and antifouling of the membrane, on the recommendation of Dr Sangeetha Subramanian. She suggested adding microplastic feed as a suspension, or regular changing of membrane. We can also consider alternatives such as sparging air, mechanical cleaning and rotation or vibration of membrane [9].
Our enzyme based system generates terephthalic acid and ethylene glycol as by-products of PET degradation. These molecules are greatly viable in the industry, and lend themselves to several applications.

Applications of Terephthalic acid:

In polyester fibers based on purified TPA and in blends with other synthetic and natural fibers.
In paint as a carrier. [18]
Hot melt adhesives using polyesters and polyamides based on terephthalic acid.
In saturated low molecular weight polyesters used in powder and water-soluble coatings. [19] [20]
As a component for metal-organic framework synthesis. [21]
In the analgesic drug oxycodone, which can occasionally come as a terephthalate salt. [22]

Applications of Ethylene Glycol:

In hydraulic brake fluids, some stamp pad inks, ballpoint pens, solvents, paints. [26]
As an automotive antifreeze. Its high effectiveness as desiccant can be attributed to its high boiling point and water affinity. [23]
As a chemical intermediate in the production of 1,4-dioxane, which is used in capacitors [24]
As an anti corrosion additive in liquid cooling systems for personal computers [25]
In lengthy multiphase pipelines that transport natural gas from distant gas fields to a gas processing facility, it is frequently used to prevent the formation of natural gas clathrates, or hydrates. [26]

FUTURE PROSPECTS

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1. Plastic Segregation and Waste Disposal Systems

Our system can be installed in waste segregation and recycling units. It would ease and accelerate the process of PET degradation significantly. On our visits to municipal waste segregation units, we noted the labor involved in segregation of biodegradable and non-biodegradable waste. Our solution can potentially eliminate this step. With future infrastructural development in Indian railways, there is a possibility of integrating our system into the shredders installed for PET bottle disposal.

2. A Better Alternative for Plastic Degradation

Current plastic degradation strategies can be categorised into chemical, mechanical and biological. In India, the average plastic recycling rate is about 13% [12] and the rest, i.e. the unrecyclable plastic is often incinerated. Incineration causes leaching of toxic chemicals into the environment, such as carbon and oxygen free radicals, PAHs, PCBs and BPAs [13][14]. Chemical plastic degradation methods can produce several contaminants,and are more expensive and tedious, as they include an additional washing step [14].
Instead, degradation of plastic by our mutated enzymes results in the production of useful molecules such as, terephthalic acid and ethylene glycol. So, our solution eliminates the toxic by-products seen in conventional plastic degradation and recycling.

3. Circular Economy and Sustainability

According to a report, over 350 million metric tonnes of plastic wastes are produced globally [15]. Our project can help convert this enormous amount of waste into industrially important by-products, terephthalic acid and ethylene glycol, which can be consumed by paint, automobiles and pharmaceutical industries [16, 17]. This promotes circular economy and sustainability.
Our project helps alleviate hazardous impacts of plastic accumulation in land and water. It also enhances the quality of portable water by removal of microplastics. Improved water supply is an important economic resource that can improve living standards and aid poverty eradication [27]. Going forward, our project can contribute greatly to sustainable development.

4. Other Economic Aspects

Our project is a cost effective solution and easily scalable solution to the ever growing plastic waste problem. The PET crusher installation is the only 1-time investment to be made. It opens up avenues for new products to be created using transformed E.coli strains expressing FAST-PETase and mutated MHETase. An example could be a spray which can be used to break down PET into safer degradation products. So, it also provides additional employment opportunities.

References

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[2] Dhiman, S., Sharma, C., Kumar, A., Pathak, P., & Purohit, S. D. (2023). Microplastics in Aquatic and Food Ecosystems: Remediation Coupled with Circular Economy Solutions to Create Resource from Waste. Sustainability, 15(19), 14184.
[3] Li, Z., Chen, K., Yu, L., Shi, Q., & Sun, Y. (2022). Fe3O4 nanoparticles-mediated solar-driven enzymatic PET degradation with PET hydrolase. Biochemical Engineering Journal, 180, 108344.
[4] Taghavi, N., Zhuang, W. Q., & Baroutian, S. (2021). Enhanced biodegradation of non-biodegradable plastics by UV radiation: Part 1. Journal of Environmental Chemical Engineering, 9(6), 106464.
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[8] Thakur, K., Attri, C., & Seth, A. (2021). Nanocarriers-based immobilization of enzymes for industrial application. 3 Biotech, 11, 1-12.
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[11] Plastic pollution is growing relentlessly as waste management and recycling fall short, says OECD.
[12] India surpasses global averages of plastic recycling rate: Piyush Goyal | Mint
[13] Environmental and health impacts of open burning | | Wisconsin DNR.
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[17] Ethylene Glycol: Systemic Agent | NIOSH | CDC.
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[27] Making Water a Part of Economic Development: The Economic Benefits of Improved Water Management and Services | SIWI - Leading expert in water governance