Evaluating the Influence of Temperature and Flow Rate on Biogas Production from Wood Waste via a Packed-Bed Bioreactor

Abstract

Operating a bioreactor with a low contact area greatly reduces the efficiency of methanogenic bacteria to produce biogas using an anaerobic digestion process. In this work, a packed-bed bioreactor under a flow-mixing technique was used to enhance the contact area to produce biogas from sawdust. The bioreactor was designed with a diameter of 10 cm and a height of 60 cm and was packed with 1.5-cm spherical glass beads. The effect of the digestion temperature on the cumulative biogas production was investigated at different temperatures (i.e., 30, 35, 40, 45, and 50 °C). Also, the influence of the flow-mixing technique on the biogas yield was evaluated at different substrate flow rates of 0.5. 1, 1.5, 2, and 2.5 m3/h. It was observed that the best operating conditions for the methanogenic bioconversion to achieve high biomethane production (> 71.2%) were 40 °C and 1.5 m3/h for the temperature and substrate flow rate, respectively. At these conditions, the biogas and biomethane yields were 850 mL/g VS and 605.2 mL CH4/g VS, respectively. The results show that at a mild flow rate, a biothin film of a high surface area formed over the packing, with a low resistance to transport processes. Moreover, at a high flow rate, the thin film was destroyed, achieving a low biogas yield. Finally, this technique produced a high efficiency, high homogeneity mixture, simple operation, and low mixing time in the packed-bed bioreactor.