Semi-continuous anaerobic digestion for biogas production: influence of ammonium acetate supplement and structure of the microbial community

Background: As an efficient disposal method of food waste, anaerobic digestion (AD) for biogas production is widely used. In order to understand the enhanced efficiency and stability of AD by appropriate amounts of ammonia and volatile fatty acids (NH4+/VFAs), the characteristics of the corresponding microbial community with ammonium acetate supplement were investigated by denatured gradient gel electrophoresis (DGGE) and pyrosequencing analyses of samples, with or without supplement of NH4+/VFAs. Results: In this study, four different supplement strategies of adding ammonium acetate were investigated, including a blank group (without supplement of ammonium acetate), a low group (L group, 0.7 g/L/d), a moderate group (M group, 1.0 g/L/d) and a high group (H group, 1.3 g/L/d), respectively. The average daily gas production was 1,839 mL/d, 1,655 mL/d, 1,448 mL/d and 1,488 mL/d for L, M, H and blank groups, respectively. The results reveal that the absence or overload of NH4+/VFAs leads to the inhibition or failure of the AD operation. The blank and H groups were selected for further investigation of the microbial community by DGGE and pyrosequencing analyses. A significant difference of the microbial communities at different AD stages was observed between the blank and H groups. Conclusions: Ammonium acetate, as an efficient supplement, significantly influences the characteristics of a semi-continuous AD operation. The DGGE and pyrosequencing analyses indicated that the different bacterial and archaeal communities occurred in the blank and H groups at different AD stages. Thus, an appropriate ammonium acetate supplement may maintain the balance of the microbial community and could be applied to adjust the AD operation and microbial composition towards optimal biogas production.