Development of aerobic micro granular sludge in a sequencing batch airlift reactor for simultaneous removal of COD, NH4+, PO43-, and SO42-

This study investigates the long-term effectiveness of an automated Sequencing Batch Airlift Reactor (SBAR) in simultaneous removal of COD, NH4+, PO43, and SO42− by developing aerobic micro granular sludge. For this an automated SBAR (3 L capacity) with pH and DO controls, operated for 8 h (short) followed by 16 h (long) cycles; was employed using synthetic wastewater over a year. This study operated in six different phases with durations of 23, 27, 73, 125, 67, and 52 days, respectively within a temperature range of 31.5 ± 3.5 °C. During the entire phases, influent concentrations were maintained approximately at NH4+-N = 50 mg/L, COD = 480 mg/L, and SO42−-S = 35 mg/L, while PO43−-P was maintained at 10 mg/L for Phases I–IV and then decreased to 5 mg/L for Phases V–VI. Sludge was not wasted during the entire operation from SBAR and thus maintained a very high solids retention time (SRT) to promote the growth of slow growing bacteria like anammox and achieved zero sludge discharge. In the stabilized conditions in the final phase, the SBAR performed well for an average simultaneous removal of COD (96.67 ± 1.17%), NH4+-N (91.70 ± 3.66%), TN (83.21 ± 3.61%), PO43−-P (91.37 ± 1.55%) and SO42−-S (70.73 ± 4.13%). Batch studies and microbial identification studies carried out using biomass drawn from SBAR showed that mixed culture involving anammox, autotrophic nitrification, heterotrophic denitrification, thiobacillus denitrification, and heterotrophic nitrification and aerobic denitrification (HN-AD) played significant roles in nitrogen removal. Enhanced phosphate removal was achieved by P binding to loosely bound extracellular polymeric substances in addition to the enhanced biological phosphorus removal. Overall, these findings highlight the effectiveness in cultivating majorly aerobic micro granular sludge and sustainability of the SBAR in simultaneous removal of COD, NH4+, PO43−, and SO42−. The developed process could be a good choice for decentralized wastewater treatment systems, particularly in resource-constrained regions and contributes to achieving United Nations Sustainable Development Goal #6.