Effects of mixing and sodium formate on thermophilic in-situ biogas upgrading by H2 addition

The effects of hydrogen (H-2) injection amount, mixing, and sodium formate on in-situ biogas upgrading performance and microbial community structure were investigated during thermophilic digestion of pig manure in a continuous stirred tank reactor with a working volume of 11.2 L and an organic loading rate of 2.0g volatile solid (VS)/(Ld). Continuous mixing was favorable for in-situ biogas upgrading. The relative methane content and methane yield were maintained at approximately 80% and 269 L/kg VS, respectively, under continuous mixing conditions with an H-2 injection rate of 0.66 ml/(minVileactor) and an 1-12:CO2 ratio of 4:1. The added H-2 inhibited acetate production, but not propionate production, during acidogenesis. Sodium formate was more beneficial for the acetogenesis of propionate degradation and restored system stability. Strictly hydrogenotrophic methanogens (Methanoculleus, Methanobrevibacter, and Methanobacterium) were dominant in the thermophilic in-situ biogas upgrading system. The syntrophic relationship between syntrophic acetate-oxidizing bacteria (Gelria) and hydrogenotrophic methanogens was weakened after the addition of H-2. (C) 2019 Elsevier Ltd. All rights reserved.