Molecular up-cycling: bio-transforming waste plastic into value-added products

It is estimated that 8 million tonnes of plastic waste end up in the oceans each year and that by 2050 there could be more plastic in the seas by weight than fish. This plastic is both incredibly dangerous to marine ecosystems and also sequesters materials prepared from non-renewable fossil fuels, with just ~14% currently being recycled globally each year. It has been estimated that recycling the remaining 86% of plastics could generate up to $120bn, but new methods and processes to transform waste plastic into value-added products must be developed in order to realise this potential. The proposed research will focus on polyethylene terephthalate (PET) as a feedstock for a bio-based 'molecular up-cycling' platform to produce value-added, industrially relevant small molecules. PET accounts for 15% of plastic waste in the UK, out of which ~60% is accounted for by synthetic fibres and 30% by plastic bottles, whilst other uses include plastic wrappers and films and thermoforming for manufacturing. Although chemical and thermal methods for PET recycling are well-established, there is a dramatic loss in value throughout the plastic life-cycle, with the value of the waste PET bottles being 86% lower than the virgin polymer.

This Fellowship proposal unites cutting edge research from both the chemical and biological sciences to transform waste PET into high-value small molecules. The research will address the global plastic waste disaster twofold by (i) decreasing the amount of plastic waste deposited in the environment in the future and (ii) transforming pre-existing, low-value waste products into industrially relevant, value-added products via a new 'molecular up-cycling' process. The research will be organised into two phases. Initially, a robust and efficient plastic degradation process will be developed. This will exploit PET degrading enzymes that have been isolated from microbes found in landfill sites, which have evolved to use PET as a carbon source for growth. In the second phase, the PET degradation technology will be integrated with 'microbial cell factories', which we will genetically programme to turn the degradation products of PET into industrially relevant small molecules. The initial target of the project will be the synthesis of vanillin - the primary extract from the vanilla bean and the primary molecule responsible for the characteristic smell and taste of vanilla. Vanillin is used extensively for flavours and fragrances and is also a valuable intermediate in the production of fine chemicals such as pharmaceuticals. As such, it has huge commercial value, with the global market for vanillin estimated to reach $724.5 million by 2025. Beyond this, the project also holds great potential for the production of a range of other high-value small molecules which are accessible through developing and integrating novel, bio-compatible chemical reactions with the PET degradation system. Such compounds include pharmaceuticals, fragrance/flavouring compounds, agrochemicals and polymers. As such, it is anticipated that this project will have significant academic and industrial value, as well having a positive impact on the environment by removing plastic waste from the natural environment.

The proposed research will focus on poly(ethylene terephthalate) (PET) as a feedstock for a bio-based 'molecular up-cycling' platform to produce value-added, industrially relevant small molecules from plastic waste. PET accounts for 15% of plastic waste in the UK, out of which ~60% is accounted for by synthetic fibres and 30% by plastic bottles, whilst other uses include wrappers, films and thermoforming for manufacturing. Although chemical and thermal methods for PET recycling are well-established, there is a dramatic loss in value throughout the plastic life-cycle, with the value of the waste PET bottles being 86% lower than the virgin polymer. The research will be organised into two phases: (1) The development of a robust and efficient plastic biodegradation process and (2) Integration of plastic degradation with in vivo engineered pathways and biocompatible chemistry for the production of value-added small molecules, with an initial focus on the production of vanillin. Our strategy for Phase 1 is to express a PET hydrolase (PETase) on the surface of an E. coli biofilm, which will be used as a biocatalyst presentation platform. In Phase II of the project, the PET degradation system will be integrated with engineered in vivo pathways for the production of high-value small molecules, with an initial focus on vanillin. This multi-disciplinary research will draw on advances in metabolic engineering, microbiology, synthetic organic chemistry and synthetic biology for the development of a versatile and tunable platform for the sustainable production of industrially relevant small molecules, with significant environmental and economic impact and provide vital proof-of-concept for further development of processes using plastic waste as a feedstock for microbial cell factories.

Environmental and Public Impact:
This project will address an urgent unmet need for new technologies to breakdown and remove plastics from the environment and responds to public calls for reduction of plastic waste. These recalcitrant polymeric materials are pervasive throughout marine and soil ecosystems and have even recently been detected in drinking water, raising serious concerns about potential risks to human health and that of marine organisms. Consequently, there is mounting pressure on local authorities, governments and retail industries to reduce the amount plastic waste released into the environment, with new regulations such as the banning of plastics straws being proposed. However, these measures do not address the millions of tonnes of plastic waste that has already bioaccumulated, which is the focus of the proposed research. Crucially, this research will break the cycle of relatively high-value virgin plastics, which are made from small molecules from petrochemical origin, being made into disposable items, recycled and transformed into low-value second generation products or ending up in landfill, rivers and oceans.

Academic Impact:
This research will provide vital proof-of-concept for the molecular up-cycling of plastic waste, prompting further research in the area, thereby contributing to a toolbox of technologies for the transformation of plastic - an environmental pollutant - into industrially relevant, value-added products. Importantly, the unique merging of synthetic organic chemistry and synthetic biology for the valorisation of plastic waste will also go some way to address the prevailing disciplinary gap between these two fields.

Industrial and Economic Impact:
Production of commercially valuable bulk chemicals such as vanillin, benzyaldehyde and benzyl alcohol from a waste product will drastically reduce process costs and environmental footprint for the production of these chemicals. There is also the potential for a start-up or spin out company from this project, focusing on the production of bulk chemicals from plastic waste. This would generate jobs and revenue, boost the local economy and have a positive social impact.