Long-term adaptation of two anammox granules with different ratios of Candidatus Brocadia and Candidatus Jettenia under increasing salinity and their application to treat saline wastewater.

Nitrogen removal in saline wastewater is a challenge of the anaerobic ammonium oxidation (anammox) process, which is dominated by freshwater anammox bacteria (FAB). Candidatus Brocadia and Candidatus Jettenia, the most widely used FABs, have been separately applied and evaluated for their ability to treat saline wastewater. To understand the effect of salinity on nitrogen removal capability when they present together in an anammox granule, we compared two anammox granules: GRN1 was evenly dominated by Ca. Brocadia (42 %) and Ca. Jettenia (43 %), while GRN2 was dominated with mostly Ca. Brocadia (90 %) and a small amount of Ca. Jettenia (1 %). Each granule was inoculated into a continuous column reactor to treat artificial wastewater containing 150 mg NH4+-N/L and 150 mg NO2--N/L under increasing saline conditions for 250 days. GRN1 showed superior and more stable nitrogen removal than GRN2 under saline conditions of up to 15 g NaCl/L. Under high-saline conditions, both the granules' sizes decreased (larger GRN1 than GRN2 in initial). The mass percent of Na salt increased (more in GRN2) and mineral contents decreased more in GRN1. High-throughput sequencing for microbial community analysis showed that Planctomycetes in GRN1 (85 %) and GRN2 (92 %) decreased to 14 % and 12 %, respectively. The ratio of Ca. Brocadia and Ca. Jettenia in GRN1 changed to 37 % and 63 %, respectively, whereas the ratio in GRN2 (99 % and 1 %, respectively) did not change. Both salt-adapted granules were applied to the two-stage partial nitritation and anammox (PN/A) process to treat high strength ammonium (400 mg/L) wastewater under high saline condition (15 g NaCl/L). The PN/A process containing GRN1 showed more stable nitrogen removal performance during approximately 100 days of operation. These results suggest that the anammox granules evenly dominated by two FABs, Ca. Brocadia and Ca. Jettenia, would be advantageous to treat high-strength NH4+ wastewater under high-saline conditions.