Biosynthesis of polyhydroxyalkanoate (PHA) by organic waste-derived volatile fatty acids (VFAs)

Abstract

Polyhydroxyalkanoates (PHA) are promising alternatives to non-degradable petroleum-derived plastics owing to their excellent biodegradability. Nevertheless, the industrialization and market promotion of PHA products still suffer from the stubbornly high production cost. In general, the consumption of organic substrate and maintenance of the fermentation process jointly led to the high price of PHA products. To this end, the exploration of low-cost substrates, isolation of functional strains, and optimization of the fermentation process have attracted much attention in recent decades. As typical substrates, volatile fatty acids (VFAs) could be readily utilized by functional microorganisms to synthesize PHA. More importantly, VFAs could be produced from diverse organic wastes through anaerobic digestion (AD). In this review, we first introduced the isolated microbes for the biosynthesis of PHA and the corresponding metabolic pathways, as well as the classifications and properties of PHA products and their applications. After that, we summarized the recent advances in the AD for improving production and orient modulation of VFAs. Then, the factors affecting the fermentation process from VFAs to PHA were comprehensively discussed in terms of carbon-nitrogen ratio (C/N), medium pH, incubation period, fermentation temperature, and dissolved oxygen (DO). Finally, the production of PHA from VFAs and the environmental sustainability and techno-economic analysis of this concept were summarized. Based on the above discussion, the research gaps and challenges were proposed.