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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.

Land application of biosolids from activated sludge wastewater treatment plant (WWTP) is an attractive disposal solution. However, to be land applied in the US and Canada, biosolids need to meet specific pathogen loads regulations at the time of land application (i.e., not immediately after treatment). This study examined bacterial regrowth potential after electro-dewatering of biosolids. During a 8-min typical electro-dewatering treatment performed in the laboratory or a control heat treatment, Escherichia coli and fecal coliform (FC) counts were reduced to below the detection limit. After treatment, the extent of E. coli and FC regrowth was assessed by incubating the biosolids in aerobic or anaerobic conditions. After aerobic incubation, FC and E. coli counts stabilized between 107-109 MPN/g-dry solids in all biosolids samples irrespective of treatments (electro-dewatering, heat-treatment and no treatment) despite different levels of pH and dryness. Total aerobic counts also stabilized between 107-109 CFU/g-dry solids after four days of incubation. Finally, stable FC and E. coli counts at the end of incubation of samples prepared by belt filter press during winter were 1 log lower than in samples prepared by centrifuge press during the summer. Although similar trends about the effects of dewatering processes were reported in the literature, it is not be possible to conclude because seasonal factors are confounded with process factors. After anaerobic incubation, E. coli and FC counts in electro-dewatered biosolids stabilized 1 log lower than their respective counts in heat-treated or not treated biosolids (107-108 vs 108-109 MPN/g-dry solids, respectively). This difference was not changed when electro-dewatering filtrate was added back into the electro-dewatered biosolids. At WWTP, biosolids are typically stored as large piles. It is therefore likely that a major portion of piles is anaerobic, and that storage (hence regrowth) takes place under anaerobic condition. This study suggests that the electro-dewatered biosolids would exhibit a lower level of regrowth than other biosolids. Microbial counts observed in this study would not allow land application of these biosolids after 7-day storage because the lowest counts observed for electro-dewatered biosolids under anaerobic conditions were just above the requirements for the US-EPA Class B (FC counts above 106 MPN/g-dry solids). However, these results suggest that this technology could be improved such that biosolids could meet land application regulations even after extended storage periods.