Facilitated methanogenesis involved in anaerobic digestion of dairy manure by soil

Abstract Shaping the microbial community involved in anaerobic digestion (AD) systems to achieve highly efficient methane production is a major challenge. In order to improve the methane recovery from dairy manure, soil, which has the potential of enhancing methane production from biomass, was used in an AD system as an additive. The results showed that the AD process performance and methane production efficiency were significantly improved by soil; an improvement in daily methane production, reduced time to steady state, enhancement of the methane content, and reduction in carbon dioxide content were obtained. The maximum methane production was obtained at a feedstock: soil ratio of 2.5:1 with yellow soil addition, which was 147.7 L/kg volatile solids (VS) and 25.4% higher than that of the control. High-throughput sequencing of the 16S ribosomal RNA gene and synthetic solution with cations equivalent to those of yellow and black soil revealed that soil addition mainly stimulated the growth of bacterial genera Ochrobactrum and Clostridium and archaeal genera Methanosaeta and Methanosarcina . The method of ion extraction was used to extract ions from the soil, and the ions were verified to be a main contributor to methane production improvement. By mimicking the cation components of soil, a synthetic solution was prepared and used in the AD system. The results showed that the cations contained in the ion liquid played a key role in improving methane production. The contribution of VS in the soil to the AD system was studied and found to have no significant effect on the improvement in methane production. It was found that the cations in soil played a key role in enhancing AD efficiency. Therefore, the simplified, low cost, and efficient approach used in this study had good practicability and could be used for treating other various biowastes with high energy recovery, which has the potential of promoting the development of AD technology.