Simultaneous nitrification and denitrification pattern in aerated moving-bed sequencing batch reactor: Choosing appropriate SRT for different COD/N ratios

Abstract

ABSTRACT The effect of chemical oxygen demand (COD)/N ratio and sludge retention time (SRT) on the simultaneous nitrification and denitrification (SND) process in aerated moving-bed sequencing batch reactor (A-MBSBR), for treating synthetic municipal wastewater, was studied. Three lab-scale reactors with SRTs of 5, 10, and 15 days were operated under COD/N ratios of 10 (phase1) and 20 (phase2). The high correlation coefficients between nitrification and denitrification efficiencies in both phases demonstrated that the denitrification efficiency in A-MBSBRs was strongly affected by nitrification efficiency (nitrate concentration). The high COD/N ratio of 20 in phase2 led to weaker nitrification (29.6–39.1%) and consequently weaker denitrification (15.8–27.9%) under all SRTs, compared with nitrification and denitrification efficiencies (44.4–62.7% and 26.3–42.8%) in phase1 with COD/N ratio of 10. This was most probably due to a better balance between the population of heterotrophs and autotrophs in phase1. In phase2, increasing SRT from 5 to 15 days was beneficial for both nitrification and denitrification reactions. Therefore, the optimal SND efficiency in phase2 was expected to be achieved under SRTs higher than 15 days. In phase1, the highest and the lowest nitrification and denitrification efficiencies were obtained at SRTs of 10 and 5 days, respectively.