Influence of liquid- and solid-state coupling anaerobic digestion process on methane production of cow manure and rice straw

Based on the different characteristics of cow manure and rice straw, liquid- and solid-state coupling anaerobic digestion (L-SS-AD) is designed in this study. In detail, cow dung was fermented in liquid anaerobic digestion (L-AD) process, while rice straw was treated in SS-AD process with L-AD digestate as inoculums to get the benefit of both the process. Optimization experiments were systematically performed in both two processes. The results showed that organic loading rate (OLR) of 10.0 kg VS/(m 3 d) was possible during the L-AD process, and the average specific methane production (SMP) was 225.2 mL CH 4 /g VS at a steady state. In addition, in batch test of SS-AD, the lower substrate-to-inoculum ratios (S 0 /I 0 ) favored the reaction rate and the optimal S 0 /I 0 of 0.9 was selected for further leach-bed experiment. Furthermore, a leach-bed reactor for SS-AD process was operated stably at the average OLR S of 2.17 kg VS/m 3 d with the feed interval of 2 weeks. The maximum SMP was 216.13 mL CH 4 /g VS. Finally, the total energy yield values of 15.45 kJ/g VS can be obtained from the integrated process. L-SS-AD process can improve the efficiency of methane production and provide data preference for full-scale industrial biogas project.