Aerobic granular sludge systems for treating hypersaline pharmaceutical wastewater: Start-up, long-term performances and metabolic function

The complex organics, residue pharmaceuticals and high salinity in pharmaceutical wastewater pose great challenges to biological wastewater treatment. In this study, granular sludge process was used for treating pharmaceutical wastewater because of its high pollutant removal efficiency. The results suggested that granules could not form within 90-d cultivation when directly fed with target hypersaline pharmaceutical wastewater (R P ) due to suppression of EPS secretion by high concentration of inhibitory organics, while granules were successfully developed with hypersaline synthetic wastewater (R S ) and diluted pharmaceutical wastewater (R D ), respectively. Further comparison of pollutant removal performance from target pharmaceutical wastewater showed that simultaneous removal of organics (effluent bCOD < 1 mg L -1 ) and nitrogen (average TN removal efficiency of 70.3%) could be achieved in R D . Nevertheless, long acclimation period (i.e., 20 d) was needed for granules when carbon source was shifted from simple sodium acetate to complex organic pollutants in pharmaceutical wastewater, with nitrite significantly accumulated in R S . Analysis of microbial community and nitrogen metabolism pathway indicated the higher abundance of nitrite oxidoreductase than that in the R S to alleviate nitrite accumulation in the R D , and functional strains such as Paracoccus and Mycobacterium played critical roles for high efficiency of organic degradation, nitrification and denitrification. • Granules could not form when directly fed with target pharmaceutical wastewater. • Granules cultivated by diluted pharmaceutical wastewater showed long-term stability. • High removal efficiency of COD and N was found treating pharmaceutical wastewater. • Paracoccus and Mycobacterium played key roles in organic removal and SND. • High abundance of enzymes involved in nitrogen metabolic pathway could be detected.