Role of soil in improving process performance and methane yield of anaerobic digestion with corn straw as substrate

Solid-state anaerobic digestion is widely used in lieu of liquid-stage anaerobic digestion for treating biowastes due to the former's advantages. However, unsatisfactory process performance and low methane yields inhibit the development of solid-state anaerobic digestion for treating lignocellulosic material. Soil, with the potential of inter-species electron transfer, buffer capacity, and nutritional elements for microbial growth, was used to improve the anaerobic digestion efficiency. At the same time, simultaneous NaOH treatment was adopted to simplify the lignocellulose treatment process. Results include daily methane yield enhancement and improved methane content. The maximum methane yield (344 L/kg volatile solid) was obtained at 1% NaOH for the group with soil addition; pH was maintained in a suitable range (6.6-7.8). The difference in total methane yield between a solid-state digester with no NaOH but with soil addition and a digester with 1% NaOH without soil addition was not significant, which indicates that soil stimulated the potential methane yield and could be an alternative for simultaneous NaOH treatment. The cations contained in soil is verified to be the main reason to improve the anaerobic digestion efficiency. Therefore, the discovery found in this study can be the reference for various biowastes conversion via solid-state anaerobic digestion.