Mechanism of stable sewage nitrogen removal in a partial nitrification-anammox biofilm system at low temperatures: Microbial community and EPS analysis.

Stable sewage nitrogen removal with nitrogen removal efficiency of 87.5 ± 2.2% was achieved in a partial nitrification-anammox (PNA) biofilm system at low temperatures (12.8-16.3 °C). High-throughput sequencing analysis indicated that the microbial community structure in the sequencing batch biofilm reactor (SBBR) remained reasonably stable. Candidatus Brocadia was the only detected anammox genus and remained stable at 0.3-0.5%. Some psychrotolerant microorganisms that could secrete cryoprotective extracellular polymeric substances (EPS), including Flavobacterium and Thermomonas, were enriched at low temperatures. This could be conducive to the stable operation of the PNA-SBBR. Moreover, according to the EPS composition and characteristics analysis, the secretion of tightly-bound EPS that bound to the cell surface containing plentiful protein was stimulated at low temperatures, further improving the system stability. Overall, the reasonably stable microbial community structure, enrichment of psychrotolerant microorganisms, and increased secretion of EPS could play important roles for stable sewage nitrogen removal at low temperatures.