Improved nitrogen removal performance by enhanced denitratation/anammox as decreasing temperature for municipal wastewater treatment

Low temperature is one of the obstacles in mainstream anammox. This study aimed to evaluate the stability of a step-feed bioreactor dominated by denitratation/anammox (PD/A) for treating municipal wastewater with decrease in temperature (21.5 °C→12.6 °C). During long-term operation, nitrogen removal efficiency (NRE) was improved from 72.2% (21.5 °C→14.9 °C) to 77.2% (stable at 13.9 °C) with influent and effluent total inorganic nitrogen of 44.6 and 10.1 mg N/L. Better low temperature tolerance of nitrate reduction than nitrite reduction enhanced denitratation and increased nitrite substrates for anammox. Microbial structure analysis revealed that Ca. Brocadia increased by 167% and reached 0.27% on biofilm at low temperature. Finally, anammox contribution improved from 41.8% to 60.2%, saving organic carbon for denitrification, which was responsible for better NRE. Moreover, Ferribacterium, Dechloromonas, and Thauera were the major denitrifiers distributed in suspended sludge. Overall, this study provides an optimistic prospect for promoting anammox in mainstream applications at low temperature.