Sequencing batch reactor (SBR) and anoxic and oxic process (A/O) display opposite performance for pollutant removal in treating digested effluent of swine wastewater with low and high COD/N ratios

Sequencing batch reactor (SBR) and anoxic/oxic process (A/O) are the predominant process for the treatment of digested effluent of swine wastewater. However, which is optimal process for their treatment? The question remains unclear. In this study, lab-scale SBR and A/O anoxic/oxic process were employed to treat digested effluent with addition of different proportion (v/v 10%-40%) of raw swine wastewater in order to make clear performance difference of the pollutant removal. The results showed that the NH4+-N and TN removal efficiencies of the A/O were more than 5.5 and 6.0 percentage points higher than that of the SBR respectively when the proportion of added raw wastewater was 20% (low COD/N ratios), due to the limitations caused by the low BOD5 concentration and the higher dissolved oxygen concentration during the anoxic phase. While, the NH4+-N and TN removal efficiencies of the SBR were more than 3.3 and 14.3 percentage points higher than that of the A/O respectively when the added raw wastewater proportion was 40% (high COD/N ratios), owing to limitation by the lower mixed liquor recycling ratio in the A/O. The sludge activity tests and microbial community analysis showed that the SBR displayed higher ammonia-oxidizing and anammox activity, whereas the A/O revealed higher denitrifying activity. These results uncovered that there are differences when A/O and SBR were employed to treat digested effluent and provide good insights for process selection when treating different C/N ratios wastewater.

Automated summary

This study compared the performance of sequencing batch reactor (SBR) and anoxic/oxic process (A/O) in treating digested effluent of swine wastewater. The results showed that A/O achieved higher removal efficiencies of NH4+-N and TN when the proportion of added raw wastewater was low, while SBR performed better when the proportion was high. Sludge activity tests and microbial community analysis confirmed the differences in the two processes.