Effect of H2 addition on the microbial community structure of a mesophilic anaerobic digestion system

Abstract

In situ biogas upgrading by H2 addition is a promising technology to increase the calorific value of biogas；however, its effects on microbial community structure remain unclear. Therefore, mesophilic digestion of swine manure was carried out in a reactor with an H2 addition rate of 7.2 mL/min (at a 4:1H2: CO2 ratio) and an organic loading rate of 2.0 g of volatile solids (VS)/(L∙d). After H2 was injected into the reactor, the maximum average methane yield increased from 189 to 245 L/kg VS under intermittent mixing conditions. The acetate concentration increased to a maximum of 1600 mg/L but the methane yield was reduced to 210 L/kg VS, which was attributed to a reduction in acetoclastic methanogen abundance in the system due to continuous mixing. The combination of homoacetogenic Clostridium and the Methanosaeta acetoclastic methanogens instead of hydrogenotrophic methanogens appears to have played a vital role in converting the added H2 into CH4 in the mesophilic reactor. However, hydrogenotrophic methanogens accounted for approximately 10% of the total metabolic activity while having a relative abundance of less than 0.5% among the methanogens, after the acetoclastic were inhibited.