Caproic acid production from anaerobic fermentation of organic waste - Pathways and microbial perspective

This review aims to provide a holistic synopsis of the current state of the art knowledge on caproic acid production via anaerobic fermentation from the perspectives of microbes and metabolic pathway. The pure bacterial isolations with ability of caproic acid synthesis were summarized for metabolic identification and syntrophic potentials. Compared with single bacterium, mixed microflora with caproic acid production capacity is more conducive to caproic acid recovery and stability of the fermentation system. The anaerobic fermentation influencing factors, such as pH, temperature, electron donor and acceptor, hydrogen partial pressure, and competition between microbes were discussed. It is found that these factors essentially affect the performance of microbes causing system fluctuation thus decreased caproic acid production. Facing with the immature caproic acid separation technology, were compared from the prospect of application and electrodialysis was proposed as the mainstream technology in future. Simultaneously, it is believed that in-situ separation strategy can improve the yield and purity of caproic acid. Targeting on a large scale caproic acid production through anaerobic fermentation, it is also necessary to strengthen the research on the synergy and competition between microbes in the process of anaerobic fermentation, and to establish a readiness caproic acid separation technology. This work is expected to contribute to the goal of carbon summit and carbon neutrality.