Effect of the dilution rate and hydraulic retention time on the efficiency of the sequencing batch reactor (SBR) system with electroplating wastewater

Effects of dilution rates, glucose supplementation and hydraulic retention times (HRTs) on the efficiency and performance of the SBR system with electroplating wastewater (EPWW) solutions containing CN− and Zn2+ were conducted in laboratory conditions. The results showed that the system efficiency was increased with the increasing dilution rate of EPWW. The system showed that the highest COD, BOD5, TN, TKN, CN− and Zn2+ removal efficiencies were 91 ± 2, 71 ± 6, 48.6 ± 1.0, 56.9 ± 5.3, 62.4 ± 3.0 and 88.0 ± 0.6%, respectively, at the 1:5 diluted-EPWW solution containing 100 mg/L glucose (BOD5:TN ratio of 100:10) and HRT of 10 days (organic loading of 0.008 kg BOD5/m3-d, CN− loading of 0.86 g/m3-d and Zn2+ loading of 1.2 g/m3-d). The system efficiency was increased with the increase of HRT or organic loading. The highest COD, BOD5, TN, TKN, CN− and Zn2+ removal efficiencies of 98 ± 0, 93 ± 2, 61.6 ± 1.6, 67.5 ± 2.4, 74.3 ± 1.0 and 98.5 ± 0.1%, respectively, were detected with 1:5 diluted EPWW containing 200 mg/L of glucose at the mixed liquor suspended solids (MLSS) of 2500 mg/L and an HRT of 10 days (organic loading of 0.020 kg BOD5/m3-d, CN− loading of 0.9 g/m3-d and Zn2+ loading of 1.1 g/m3-d). Moreover, CN− and Zn2+ showed a strong repression effect on nitrifying bacteria, especially Nitrobacter sp., but they did not show any repression effect on the heterotrophic and denitrifying bacteria.