Characteristics and dominant microbial community structure of granular sludge under the simultaneous denitrification and methanogenesis process

• Characteristics of the SDMGS were investigated.
• Methanosaeta and Methanobacterium were the dominant archaeal communities.
• Proteobacteria, Bacteroidetes and Firmicutes were the three dominant bacteria.
• Enterobacteriaceae could be the core bacterium accounted for the SDM.

Batch experiments under different COD/NO3−-N ratios were carried out to investigate physicochemical characteristics and microbial community structure of granular sludge under the simultaneous denitrification and methanogenesis (SDM) process. COD/NO3−-N ratio of 8.0 was proved to be a critical point of the SDM process and sludge at this ratio was selected for analysis. BET, SEM, FTIR and zeta potential measurement were used to characterize the micro-structure, functional groups and surface charge of the granular sludge related to nitrate addition. SEM observation showed that rod-shaped bacteria were predominant at the surface of granules and FTIR spectrum (1745 cm−1) presented an evidence for the carboxyl group protonation upon reduction of the cytochrome c oxidase. Furthermore, high-throughput sequencing technology was used to analyze the microbial structure and diversity. Archaea was found to be accounted for 3.33% of the total microbial communities and Methanosaeta and Methanobacterium were the dominant archaeas. Otherwise, Proteobacteria (63.00%), Bacteroidetes (21.79%) and Firmicutes (9.73%) phyla were identified to be the three dominant bacterial communities. Enterobacteriaceae was detected with a content of 50.24% of the total bacterial sequences and might be the core bacterium contributed to the SDM process. The results would provide vital guidances for the design and stable operation of nitrate-containing wastewater treatment.