Bacterial community dynamics in a swine wastewater anaerobic reactor revealed by 16S rDNA sequence analysis

Anaerobic digestion is a microbiological process of converting organic wastes into digestate and biogas in the absence of oxygen. In practice, disturbance to the system (e.g., organic shock loading) may cause imbalance of the microbial community and lead to digester failure. To examine the bacterial community dynamics after a disturbance, this study simulated an organic shock loading that doubled the chemical oxygen demand (COD) loading using a 4.5 L swine wastewater anaerobic completely stirred tank reactor (CSTR). Before the shock (loading rate = 0.65 g COD/L/day), biogas production rate was about 1-2 L/L/day. After the shock, three periods representing increased biogas production rates were observed during days 1-7 (∼4.0 L/L/day), 13 (3.3 L/L/day), and 21-23 (∼6.1 L/L/day). For culture-independent assessments of the bacterial community composition, the 454 pyrosequencing results indicated that the community contained >2500 operational taxonomic units (OTUs) and was dominated by three phyla: Bacteroidetes, Firmicutes, and Proteobacteria. The shock induced dynamic changes in the community composition, which was re-stabilized after approximately threefold hydraulic retention time (HRT). Intriguingly, upon restabilization, the community composition became similar to that observed before the shock, rather than reaching a new equilibrium.