Nitrogen removal from high-saline municipal wastewater via anammox-based process driven by both nitritation and denitratation

Abstract

Nitrogen removal from saline municipal wastewater has recently attracted attention; thus, developing energy-efficient technology such as anaerobic ammonium oxidation (anammox) for advanced nitrogen removal of hypersaline wastewater is significant. In this study, the long-term salt adaptation and evolution mechanisms of an anammox-based process driven by both nitritation (NH4+→NO2—, PN) and denitratation (NO3—→NO2—, PD) were investigated under salinities ranging from 1.0% to 3.0% (10–30 g NaCl/L). At 1.0% salinity, PN evolved into the major nitrite production pathway with thorough suppression of nitrite oxidation. At 1.5% salinity, nitrite reduction was inhibited along with suspended sludge loss due to poor sludge settleability. Under 2.0% salinity with only-biofilm, the highest nitrogen removal efficiency (81.2%) was observed with influent and effluent total inorganic nitrogen concentrations of 44.5 and 8.2 mg N/L, respectively. Notably, results showed that anammox bacteria occupied up to 1.07% of the microbial community (qPCR: 1.14×1011 copies/(g dry sludge)) and has strong adaptability to salinity. With salinity increases, anammox contribution kept over 85% and Ca. Kuenenia (0.57%→0.22%) was more tolerant than Ca. Brocadia (0.46%→0.02%). Metagenomic sequencing revealed that the multiple nitrite substrates production by Nitrosomonas (amoA-enriched), Denitratisoma and Denitromonas (narG-enriched) guaranteed the high anammox contribution. This study provides a multifaceted understanding of the anammox-based process, which can enable improved application in real saline wastewater treatment.