How to combine SBR and A/O process for pollutant removal in treating digested effluent of swine wastewater

To solve the problem of low chemical oxygen demand (COD)/N and poor efficiency of single-stage sequencing batch reactor (SBR) or anoxic/oxic process (A/O) in treatment of digested effluent of swine wastewater, combined SBR-A/O and A/O-SBR processes were employed in the addition ratios of 0, 10%, 30%, and 40% (V/V)) of raw swine wastewater (RS). Analysis of pollutants removal performance of SBR-A/O and A/O-SBR systems showed no significant difference between the two systems without RS addition. However, after adding RS, the pollutants removal efficiency of the two systems increased with the increase in the ratio of RS, with SBR-A/O system presenting better pollutants removal performance than A/O-SBR system. The SBR-A/O system exhibited the best pollutant removal performance in the 40% RS addition, with the effluent concentrations of COD, ammonium nitrogen (NH₄⁺-N), and total inorganic nitrogen (TIN) reaching 428, 8.82, and 134 mg/L, respectively. The first-stage reactor (SBR) of SBR-A/O system ensured high NH₄⁺-N and TIN removal owing to its high COD/NO_x-N and dissolved oxygen levels, while the second-stage reactor (A/O) of the SBR-A/O system ensured low effluent COD. The COD, NH₄⁺-N, and TIN removal efficiencies of the SBR-A/O system were 3.3, 0.2, and 0.6 percentage points higher than those of the A/O-SBR system in the 40% RS addition, respectively. The better pollutants removal efficiency of SBR-A/O system could be attributed to the higher sludge concentration, sludge specific activity, and functional bacterial abundance, when compared with those in the A/O-SBR system.