Facilitating sludge granulation and favoring glycogen accumulating organisms by increased salinity in an anaerobic/micro-aerobic simultaneous partial nitrification, denitrification and phosphorus removal (SPNDPR) process.

• Salinity accelerated the formation of granule in a low dissolved oxygen process. • The extracellular polymeric substances played an essential role in the granulation. • Observed nitrite accumulation ratio (NAR) increased to 98.9% under salinity stress. • Salinity favored glycogen-accumulating organisms, promoting N-removal potential. This study used salinity (0.5 wt%, 0.75 wt%) to accelerate the formation of ammonia oxidizing bacteria (AOB)-enriched aerobic granular sludge in a lab-scale anaerobic/micro-aerobic simultaneous partial nitrification, denitrification and phosphorus removal (SPNDPR) reactor. Results confirmed that the average granule diameter increased from 298.7 to 425.4 µm after 45 days of salinity stress even with low dissolved oxygen. Extracellular polymeric substances increased from 149.5 to 387.7 mg/g VSS after salinity (0.75 wt%) treatment, in turn accelerating granulation. Partial nitrification was maintained under the salinity condition due to the relative high activity and abundance of AOB, and the observed nitrite accumulation ratio averaged 98.9%. Salinity favored glycogen-accumulating organisms over polyphosphate-accumulating organisms (PAOs)/denitrifying-PAOs, with the abundance of Candidatus_ Competibacter increasing from 4.86% to 15.34% and the simultaneous partial nitrification–denitrification efficiency increasing from 74.4% to 91.1%, promoting N-removal potential. The P-removal performance was good under 0.5 wt% salinity but was inhibited under 0.75 wt% salinity. [ABSTRACT FROM AUTHOR]