Biosynthesis of polyhydroxyalkanoates (PHAs) from organic waste-derived volatile fatty acids (VFAs)

Abstract

Polyhydroxyalkanoates (PHAs) 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 costs. In general, the consumption of organic substrates and the maintenance of the fermentation process together contribute to the high cost 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) can be readily utilized by functional microorganisms to synthesize PHAs. More importantly, VFAs can be produced from diverse organic wastes via anaerobic digestion (AD). In this review, we first provided an introduction to the isolated microbes for the biosynthesis of PHAs 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 AD for improving the production and orient modulation of VFAs. Then, the factors affecting the fermentation process from VFAs to PHAs 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 PHAs 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.