Plastic as a carbon resource: Bioconversion of polyethylene after thermal oxo-degradation
Date
2024-08
Authors
Rodriguez Ocasio, Efrain
Major Professor
Advisor
Jarboe, Laura R
Brown, Robert C
Shao, Zengyi
Mansell, Thomas J
Yandeau-Nelson, Marna
Committee Member
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Abstract
Over 8 billion tons of plastics have been produced, and the available strategies for its disposal have proven insufficient due to economic and environmental sustainability limitations. As a result, most of the plastic that has ever been ever made has ended or will end in landfills and our ecosystems. Plastics are not biodegradable because the breakdown of the polymers into molecules that microorganisms can utilize is estimated to take thousands of years. However, combining thermal oxo-degradation (TOD) with biocatalytic conversion can drastically reduce the rate-limiting step of plastic degradation and open an avenue for plastic waste upgrading. TOD rapidly deconstructs polymer backbones while adding oxygen functionalities to the fragmented products. The products of this process with plastic feedstocks are mixtures of fatty substrates - including fatty acids and fatty alcohols – and hydrocarbons. These molecules can be upgraded by microorganisms. A screening process identified a nonconventional yeast suitable for the bioconversion of thermally oxo-degraded high-density polyethylene (HDPE), the world's most common plastic. The selected yeast can utilize TOD products as sole carbon source and at rates comparable to growth in dextrose, without the need for emulsification. In this dissertation, the biological uptake and conversion mechanisms of TOD-processed plastics and the results of an adaptive evolution process that increased the growth rate in TOD product by >200% will be discussed. The selected yeast could be further developed into plastic conversion cell factory, enabled by the rapid deconstruction of plastics by TOD. This work presents a viable plastic upcycling avenue.
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dissertation