Valorization of organic wastes using bioreactors for polyhydroxyalkanoate production: Recent advancement, sustainable approaches, challenges, and future perspectives

Microbial polyhydroxyalkanoates (PHA) are encouraging biodegradable polymers, which may ease the environmental problems caused by petroleum-derived plastics. However, there is a growing waste removal problem and the high price of pure feedstocks for PHA biosynthesis. This has directed to the forthcoming requirement to upgrade waste streams from various industries as feedstocks for PHA production. This review covers the state-ofthe-art progress in utilizing low-cost carbon substrates, effective upstream and downstream processes, and waste stream recycling to sustain entire process circularity. This review also enlightens the use of various batch, fedbatch, continuous, and semi-continuous bioreactor systems with flexible results to enhance the productivity and simultaneously cost reduction. The life-cycle and techno-economic analyses, advanced tools and strategies for microbial PHA biosynthesis, and numerous factors affecting PHA commercialization were also covered. The review includes the ongoing and upcoming strategies viz. metabolic engineering, synthetic biology, morphology engineering, and automation to expand PHA diversity, diminish production costs, and improve PHA production with an objective of zero-waste and circular bioeconomy for a sustainable future.

Automated summary

Microbial polyhydroxyalkanoates (PHA) are promising biodegradable polymers that can alleviate environmental problems caused by petroleum-based plastics. However, the increasing waste removal issue and the high cost of pure feedstocks for PHA biosynthesis have led to the need for utilizing waste streams from various industries as feedstocks for PHA production. This review summarizes the state-of-the-art progress in utilizing low-cost carbon substrates, effective upstream and downstream processes, and waste stream recycling to achieve process circularity. It also discusses the use of different bioreactor systems and advanced tools and strategies to enhance productivity and reduce costs in microbial PHA biosynthesis.