Enhanced Biological Treatment of Polluted Surface Water Using an Advanced Continuous Upflow Sequencing Batch Reactor: Combined Nutrient and Organic Matter Removal

Biological treatment systems capable of simultaneous organic and nutrient removal are essential for restoring polluted surface waters, particularly in regions lacking centralized infrastructure. This study evaluated a 4-L laboratory-scale Anaerobic–Anoxic–Aerobic Continuous Upflow Sequencing Batch Reactor, a modified ICEAS system, operated under varying conditions: influent COD concentrations of 100, 150, and 200 mg/L; hydraulic retention times (HRT) of 4, 6, and 8 h; and anoxic mixing durations of 30, 60, and 90 min. The reactor consistently achieved high removal efficiencies of 82.4 ± 4.2% for COD, 86.5 ± 4.4% for BOD₅, 87.7 ± 10.9% for TKN, and 63.3 ± 11.7% for TN, while phosphorus was completely removed under all conditions. Maximum removal efficiencies reached 89% for COD, 91% for BOD₅, 100% for TKN, and 67% for TN at a COD of 200 mg/L, 8 h HRT, and 90 min mixing. Nitrate concentrations increased with COD and HRT but decreased with longer mixing, confirming effective denitrification. Phosphorus remained undetectable in all effluents, while turbidity decreased to 1–2 NTU and electrical conductivity declined slightly. pH and alkalinity remained stable without chemical supplementation, indicating favorable internal buffering capacity. These findings demonstrate that the A3CUSBR provides a resilient and technically efficient solution for treating polluted surface waters with fluctuating influent quality. Its compact design and decentralized configuration highlight its potential as a sustainable treatment option for rural and resource-constrained communities.