Acidogenic Biohydrogen Production Integrated With Biorefinery Approach

Abstract Short-chain (volatile) fatty acids (C2–C4; SCFA) generated during biohydrogen process via anaerobic fermentation is an unrecognized treasure with multifaceted applications in the synthesis of biofuels and bioproducts. These carboxylic fatty acids are often abundantly available in dark fermentation effluents as raw materials. They are undervalued due to their disposal in wastewaters and side streams of biological hydrogen production by dark fermentation. Research community is now realizing the enormous potential of these short-chain carboxylic acids as low-cost alternatives to chemical fertilizers and carbon substrates. SCFAs exist as amenable feedstock for a wide range of bioprocesses, viz., biohydrogen, bioelectricity, bioplastics, and algal cultivation. Prevalence of microbial community structure during dark fermentation plays an important role in efficient utilization of SCFAs or conversion into different products based on the fatty acid composition. Biological and electrogenic interventions can help in chain elongation of SCFA to medium-chain fatty acids enabling huge innovation potential for SCFA utilization. In the present chapter, current state of the art in applications of SCFAs as economical feedstock for various bioprocesses was evaluated. From a bioeconomy perspective, it is crucial to integrate bioprocesses where side-streams generated from one process act as feedstock for other process resulting in an intricate network of multilevel processes in a biorefinery approach.