Hydrogen and Methane Production, Energy Recovery, and Organic Matter Removal from Effluents in a Two-Stage Fermentative Process

This study evaluates the potential for using different effluents for simultaneous H2 and CH4 production in a two-stage batch fermentation process with mixed microflora. An appreciable amount of H2 was produced from parboiled rice wastewater (23.9 mL g−1 chemical oxygen demand [COD]) and vinasse (20.8 mL g−1 COD), while other effluents supported CH4 generation. The amount of CH4 produced was minimum for sewage (46.3 mL g−1 COD), followed by parboiled rice wastewater (115.5 mL g−1 COD) and glycerol (180.1 mL g−1 COD). The maximum amount of CH4 was observed for vinasse (255.4 mL g−1 COD). The total energy recovery from vinasse (10.4 kJ g−1 COD) corresponded to the maximum COD reduction (74.7 %), followed by glycerol (70.38 %, 7.20 kJ g−1 COD), parboiled rice wastewater (63.91 %, 4.92 kJ g−1 COD), and sewage (51.11 %, 1.85 kJ g−1 COD). The relatively high performance of vinasse in such comparisons could be attributed to the elevated concentrations of macronutrients contained in raw vinasse. The observations are based on kinetic parameters of H2 and CH4 production and global energy recovery of the process. These observations collectively suggest that organic-rich effluents can be deployed for energy recovery with sequential generation of H2 and CH4.