Effects of salinity on the simultaneous anammox and denitrification process: performance, sludge morphology, and shifts in microbial communities

In this study, the long-term effects of different salinities on the
performance, sludge morphology, and shifts in microbial communities were
studied in a simultaneous anammox and denitrification (SAD) process at a
C/N ratio of 0.5. Stable nitrogen removal efficiencies of 86.96% and
84.58% and nitrogen removal rates of 0.95 kg/(m3·d) and 0.93 kg/(m3·d)
could be achieved under low (25 mmol/L) and moderate (50 mmol/L) salinity,
respectively. However, the performance collapsed when the system was
exposed to high salinity (100 mmol/L). The content of extracellular
polymeric substances increased as salinity increased, which resulted in
larger sizes of granular sludge under low and moderate salinities.
Nevertheless, high salinity shock disintegrated granular sludge, thereby
decreasing the average granule size. The Illumina-Miseq sequencing results
revealed that Candidatus Jettenia was the sole salinity-tolerant AnAOB
genus during the entire operation, whereas the main denitrification
bacterial genera shifted from Denitrisoma under low salinity to
Denitrisoma, Thauera, and Ignavibacterium under high salinity. The results
of this study provide a comprehensive and practical evaluation of the SAD
process for organic nitrogen-rich saline wastewater treatment.