Effect of low salinity on nitrogen removal from municipal wastewater via a double-anammox process coupled with nitritation and denitratation: Performance and microbial structure

Saline wastewater present in municipal pipe networks poses challenges to biological nitrogen removal due to its inhibition on microorganisms. This study focuses on the effects of low salinity (0.0%, 0.4%, 0.7% and 1.0%) on a system featuring a combination of nitritation/anammox in oxic stage and denitratation/anammox in anoxic stage (double-anammox) in a step-feed SBR for municipal wastewater over a period of 130 days. The results showed that a maximum nitrogen removal efficiency of 81.2% was achieved at a salinity of 1.0% with anammox contribution of 76.5%. Analysis of anammox contribution and sludge activities discovered that low salinity promoted both nitritation and denitratation, further enhancing the coupling with anammox. Further, microbial analysis confirmed that Ca. Brocadia was enriched on biofilms from 0.21% to 0.51% and Nitrosomonas was enriched in flocs from 0.50% to 1.04%. Overall, the double-anammox process appears to be a promising method for the treatment of saline wastewater.

Automated summary

This study investigates the impact of low salinity levels on a double-anammox system in treating municipal wastewater, finding that a salinity of 1.0% led to a nitrogen removal efficiency of 81.2%, with a significant contribution of 76.5% from anammox. Low salinity was also found to promote nitritation and denitratation, enhancing the overall nitrogen removal efficiency. The enrichment of specific microbial populations, such as Ca. Brocadia and Nitrosomonas, further supported the effectiveness of the double-anammox process in treating saline wastewater.