Co-digestion of sugarcane bagasse, microalgal biomass and cow dung for biohydrogen and methane production

Abstract

This study investigated the use of untreated sugarcane bagasse (SCB), the biomass of a Chlorella sp., and cow dung (CD), as feedstocks for biohydrogen and methane production employing vermihumus as an inoculum. D‑optimal mixture design was used to optimize the proportion of each feedstock for a single-stage anaerobic digestion (AD), and two-stage dark fermentation (DF) followed by AD to produce methane as well as biohydrogen and methane, respectively. Using a single-stage AD, a methane yield of 230 mL-CH₄/g-volatile-solids (VS), equivalent to an energy yield of 8.2 kJ/g-VS, was attained under the optimal conditions of 29.5 g VS/L of SCB, 23.9 g-VS/L of Chlorella sp. biomass, and 6.6 g-VS/L of CD. DF conducted as the first stage of the two-stage process yielded 24.41 mL-H₂/g-VS, under the optimal conditions of 16.3 g-VS/L of SCB, 41.7 g‑VS/L of Chlorella sp. biomass, and 2.0 g-VS/L of CD. Further use of the hydrogenic effluent in AD yielded 140.17 mL CH₄/g-VS, leading to a total energy yield of 5.3 kJ/g-VS. Study results revealed that the single-stage AD process was effective in recovering energy (in the form of methane) from the feedstocks despite using no biomass pretreatment. They also showed that vermihumus could be used as an inoculum. The results also revealed the potential of the two-stage process for the production biohythane (a blend of biohydrogen and methane), a gas mixture that has better fuel properties than methane.