In this article, the interaction between acetic acid and methanogenic bacteria activity was investigated. The dry anaerobic digestion was conducted with four lab-scale reactors (R1–R4) and acetic acid at different concentrations were fed as additional substrate to R1–R4. The results showed that the population of acetocastic-utilizing methanogens decreased along with the increasing of acetic acid, in which the concentration was above 120,000 mg·L^–1 during the stable stage with coefficient of 0.8984. The activity of methanogenic microorganisms in R2 was the best of all reactors. The maximal biogas production rate in R2 was 1.73 m³ m^–3 day^–1 with the methane content of 55%.

The dry anaerobic digestion performances were investigated at the temperature of 35±1°Cwith addition of propionic acid at different concentrations in five lab-scale reactors (R1-R5) to investigate the effect of propionic acid accumulation on methane production in dry mesophilic anaerobic digestion. And the volatile fatty acids, biogas and microbial community were detected. The active of microbial community and the methane generation would be inhibited when the propionic acid exceeded 30 gL¹, which affected not only syntrophic propionate-oxidizing bacteria but also acetate-utilizing methanogens. Eubacteria decreased sharply accompany with the higher concentration of propionic in R4 and R5. The relative abundance of acetoclastic methanogens was directly correlated with volatile solids removals and methane generation in dry anaerobic reactors. Otherwise, the quantity of syntrophic propionate-oxidizing bacteria was positively linear correlated with propionic acid when the concentration was below 30 gL¹. The methanogenic bacteria activity in R3 was the best with the methane yield of 27.01 mLCH₄ g^-1 VS d^-1. The results suggested that appropriate propionate could enhance methane production in the dry anaerobic fermentation.