Simultaneous partial nitrification, denitrification, and phosphorus removal in sequencing batch reactors via controlled reduced aeration and short-term sludge retention time decrease

Simultaneous bio-treatment processes of organic carbon (C)-, nitrogen (N)-, and phosphorus (P)-containing wastewater are challenged by insufficient carbon sources in the effluent. In the present study, two parallel anaerobic/aerobic sequencing batch reactors (R-1 and R-2) treating low C/N (< 4) wastewater were employed using different partial nitrification start-up strategies, controlled reduced aeration, and decreased sludge retention time. Advanced removal efficiencies for NH4+-N (>= 96%), total nitrogen (TN, >= 86%), PO43- -P (>= 95%), and CODintra (>= 91%) were realized, with TN and PO43- -P effluent concentrations of 10.0 +/- 3.5 and 0.11 +/- 0.3 mg/L in R-1 and 9.28 +/- 4.0 and 0.11 +/- 0.1 mg/L in R-2, respectively. Higher nitrite accumulation rate (nearly 100%) and TN (121.1 +/- 0.7 mg TN/g VSS.d) and P (12.5 +/- 0.6 mg PO43- -P/g VSS.d) removal loadings were obtained in R-2 by a thorough elimination of nitrite-oxidizing bacteria. Moreover, different microbial structures and nutrient removal pathways were identified. Denitrifying glycogen-accumulating organisms (Candidatus Competibacter) and phosphorus-accumulating organisms (PAOs) (Tetrasphaera) removed N and P with partial nitrification-endogenous denitrification pathways and aerobic P removal in R-1. In R-2, aerobic denitrifying bacteria (Psychrobacter) and PAOs ensured N and P removal through the partial nitrification-aerobic denitrification and aerobic P removal pathways. Compared to R-1, R-2 offers greater efficiency, convenience, and scope to further reduce carbon-source demand.

Automated summary

In this study, two parallel anaerobic/aerobic sequencing batch reactors (R-1 and R-2) were used to treat low C/N wastewater, achieving advanced removal efficiencies of NH4+-N, TN, PO43--P, and CODintra. R-2 showed higher efficiency and achieved greater nitrite accumulation rate and removal loadings for TN and P. Different microbial structures and nutrient removal pathways were identified in each reactor.