Study of two-phase anaerobic digestion of corn stover: Focusing on the conversion of volatile fatty acids and microbial characteristics in UASB reactor

Methanogenic performance and microbial communities including both bacteria and archaea in UASB reactor treating acidogenic metabolites from acidification of ensiled corn stover (ECS) were investigated. Gradient organic loading rates (OLRs) were adopted to study the conversion of volatile fatty acids (VFAs) characterized by high concentration of acetic acid and propionic acid. The removal rate of chemical oxygen demand (COD) reached above 80.0 % at OLR of 8 g/L·d and volumetric methane production rate improved significantly as the OLR increased. When OLR was 10 g COD/L·d, acetic and propionic acids in effluent were accumulated and failure of methane production occurred. Compared with the control, the methanogenic inhibition was caused by the presence of high concentration of propionic acid. The profile of conversion of individual VFAs in UASB reactors was investigated at different OLRs. Furthermore, microbial communities in anaerobic sludge at OLR of 8 g COD/L·d were compared with those in inoculum and the shift of bacteria and archaea were analyzed. The abundances of some representative acetogenic bacteria such as Proteobacteria (14.18 %) and Bacteroidetes (11.16 %) increased obviously, which contributed to the oxidation and decomposition of organic acids. Acetotrophic methanogen (Methanosaeta) and hydrogenotrophic methanogen (Methanobacterium) played synergistic roles with acetogens to efficiently complete the VFAs conversion. This study will be of great importance to guide the application of two-phase AD of agricultural waste in full-scale plant.