Deciphering acidogenic process towards biohydrogen, biohythane, and short chain fatty acids production: multi-output optimization strategy

Abstract

Optimization of process parameters is crucial to understand the acidogenic fermentation process and its regulation towards the production of specific metabolites, viz., biohydrogen (H2), methane (CH4), biohythane (H2+CH4), and volatile fatty acids (VFA). Design of experiments (DOE) based on orthogonal array (OA) was employed to optimize and evaluate the influence of eight critical factors on multiple metabolic output parameters. Analysis of the experimental data revealed a specific influential regime of selected factors in terms of biogas generation and/or VFA synthesis. Application of pretreated inoculum as biocatalyst and high substrate concentration showed substantial enhancement of both H2 and VFA production. High COD of 10 g/L in combination with pretreated inoculum resulted in higher cumulative hydrogen production (CHP), while the higher fraction of acetic acid in the fermentation broth resulted in a higher degree of acidification (DOA). H2/H2+CH4 ratio varied from 0.1 to 0.97 and the application of untreated inoculum was shown to favor biohythane (H2+CH4) production. Overall, this communication holistically documented the feasibility of regulating acidogenic fermentation process towards a spectrum of metabolic end products of high value, while waste treatment was also achieved.