The biogas fermentation was carried out in 30 L anaerobic stirred-tanks at 55℃ by using straw as substrate

in which the effect of exogenous H2 was particularly investigated. The results showed that the in-situ upgrading of biogas by means of introducing exogenous H2 was realized. At the stirring rate 100 r·min-1

the relative average volume of CH4 fraction increased from 69.6% to 94.4% while the relative average volume of CO2 fraction decreased from 30.4% to 5.6%. Compared with the bench-scale experiment without stirring

the utilization and conversion of the exogenous H2 increased from 91.0% to 93.1% and from 85.0% to 96.8%

respectively

at the stirring rate of 50 r·min-1. The introduction of exogenous H2 significantly promoted the degradation of propionic acid

butyric acid and isobutyric acid

which could effectively avoid the accumulation of volatile fatty acids in the fermentation process. At the same time

the strong agitation had an important influence on the decomposition of acetic acid and the consumption of CO2 in the biogas slurry. In addition

the introduction of exogenous H2 could change the proportion of the methanogenic microorganism in the fermentation system without obviously affecting the methanogenic microbial community.