A holistic analysis of ANAMMOX process in response to salinity: From adaptation to collapse

The application of anaerobic ammonium oxidation (ANAMMOX) process to industrial wastewater treatment usually faces the challenge of high salinity. However, most of the current ANAMMOX sludge was enriched from low-salinity water, resulting in the critical gap between the inoculum and saline waste-water. In this work, an ANAMMOX reactor fed with inoculum enriched from low-salinity water successfully adapted to saline wastewater (500 mmol/L NaCl, 2.92%) after a long-term stepwise acclimatization. The nitrogen removal rate and total nitrogen removal efficiency reached 9.72 kg.m(-3)d(-1) and 80.90%, respectively. However, further salinity increase to 600 mmol/L caused a collapse of reactor performance. The proportion of inorganic matters improved along with the increase of salinity, which might be attributed to the compact particles observed in the microstructure of ANAMMOX sludge. A microbial community succession occurred in response to the increase of salinity. When the salinity increased to 160 mmol/L, the dominant functional bacteria shifted from Candidatus Kuenenia to unclassified Brocadiaceae, which was supposed to be salt-tolerant. The up and down regulations of polysaccharides and 5 potential in EPS were positive strategies for salinity adaptation of ANAMMOX bacteria. However, the barrier of seawater salinity (3-5%) could not be overcome. The present work would provide a holistic view for the enrichment of salt-tolerant ANAMMOX bacteria and help in the selection of seeding sludge for the treatment of saline wastewater by ANAMMOX process.