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Closing the loop on plastics: Biological and hybrid routes for converting plastic waste to polyhydroxyalkanoates.
Summary
Scientists are exploring how to turn plastic waste into biodegradable plastic using bacteria, essentially recycling trash into a safer material that breaks down naturally instead of piling up in landfills or oceans. This review pulls together existing research on the process, highlighting that while promising, the technology still faces hurdles like breaking down plastic efficiently and scaling it up affordably. If perfected, this approach could reduce the amount of plastic waste that degrades into microplastics, which have been found in human blood, organs, and even breast milk, raising ongoing health concerns.
Polyhydroxyalkanoate (PHA) production from plastic-derived substrates offers a promising route to mitigate plastic pollution while reducing dependence on conventional PHA feedstocks. Plastic waste represents an abundant carbon source for microbial fermentation, but efficient conversion remains limited by incomplete deconstruction, inhibitory intermediates, low carbon recovery, and challenges in process integration. Plastic-derived streams contain diverse compounds, including fatty acids, hydrocarbons, fatty alcohols, aldehydes, esters, and aromatic compounds generated during depolymerization. These intermediates can be metabolized by selected microorganisms, particularly Pseudomonas species with versatile fatty-acid and hydrocarbon pathways, as well as Cupriavidus necator and mixed microbial cultures. Unlike reviews that address plastic upcycling or PHA biosynthesis separately, this review focuses on the deconstruction-fermentation interface that governs plastic-to-PHA conversion. It consolidates current progress in plastic deconstruction, substrate conditioning, microbial metabolism, fermentation control, polymer recovery, and techno-economic and life-cycle considerations. By emphasizing substrate composition, biological compatibility, plastic‑carbon recovery, and final polymer quality, the review identifies priorities for scalable and environmentally sustainable PHA production from plastic-derived substrates.