Optimization of sequencing batch reactor for wastewater treatment using chemically enhanced primary treatment as a pre-treatment

The sequencing batch reactor (SBR) is a wastewater treatment option feasible for low flows. The objective of this research was to optimize SBR by varying its operational parameters, viz. (i) settling time and (ii) reaction time. The study was conducted in two phases. In Phase 1, raw wastewater was fed into the SBR after conventional settling, while in Phase 2 raw wastewater was fed into the SBR after coagulation-flocculation-sedimentation. A bench-scale model was set up and domestic wastewater was used for this study. Performance of the treatment system was evaluated through 5-day biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS). The results demonstrated that reaction time was reduced to 4 h in Phase 2 compared to 10 h in Phase 1. The BOD, COD and TSS removal efficiencies observed in Phase 1 were 80%, 80% and 73%, respectively, and for Phase 2 the removal efficiencies were 74%, 75% and 80% respectively. National Environmental Quality Standards (NEQS) were met in both cases and the treatment cost per cubic metre of wastewater for Phase 2 was 2.5 times lower compared to Phase 1.