Biochemical methane potential of Jatropha press cake: Effect of steam explosion pretreatment and co-digestion with crude glycerol

Abstract

Biodiesel production from Jatropha curcas generates a considerable amount of Jatropha press cake (JPC) and crude-glycerol (CG) biowastes with intense biogas production potential. However, JPC contains a larger amount of lignocellulosic materials that potentially affect the hydrolysis stage of the anaerobic digestion process, while CG significantly lacks nitrogen needed for microbial biomass growth. Therefore, the present study sought to explore the optimal steam explosion (SE) pretreatment and co-digestion conditions that can improve the methane yields of JPC with inhibitor formation reduction. The effects of different temperature-time combinations during SE on soluble chemical oxygen demand (sCOD) and methane yield of JPC were evaluated using response surface methodology coupled with central composite design (RSM-CCD). JPC was also co-digested with CG, and the methane yield of the mixture was investigated by varying the total organic loading (TOL) and CG levels. The RSM-CCD model predicated that the maximum methane yield (330.14 ml g−1 VS) could be achieved after exploding the JPC at 202 °C for 9.39 min, while relatively high temperature (209 °C) and retention time (13.68 min) were needed to obtain a higher predicted sCOD yield (94.48 g L−1). During the co-digestion processes, the methane yields of the mixture were significantly varied, and co-digesting 2% CG with JPC at 2 g VS L−1 TOL was the optimum condition to obtain a maximum methane yield of 325.25 ml g−1 VS. Thus, considering the environmental and economic advantage of biowaste utilization, co-digesting JPC with CG was the best option for improving the methane yield of the mixture compared to SE pretreatment.