An investigation into the effect of MLSS on the effluent quality and sludge settleability in an aerobic-anoxic sequencing batch reactor (AASBR)

摘要

The aim of this study is to enhance the effluent quality and improve the sludge settleability by determining the effects of the mixed liquor suspended solids (MLSS) on the solid’s settling behaviour and the treatment efficiency in an aerobic-anoxic sequencing batch reactor (AASBR). The results obtained from this study revealed that raising the MLSS concentration from 2 to 3 g/l improved the chemical oxygen demand (COD), ammonia-nitrogen (NH3-N) and nitrate-nitrogen NO3-N removal efficiency, and led to an increase in the sludge volume index (SVI) value. Moreover, increasing the MLSS concentration from 3 to 4 g/l did not significantly affect the COD, NH3-N and NO3-N removal rates or the solid’s settling behaviour. However, increasing the MLSS concentration from 4 to 6 g/l significantly reduced the COD and nitrate removal efficiency and the sludge settling rate slowed down. The results proved that the optimal MLSS concentration for COD, NH3-N and NO3-N removal is between 3 and 4 g/l. In this range the removal rates for COD, NH3-N and NO3-N were 93%, 95% and 96% respectively, and the effluent quality was 35 mg/l, 0.43 mg/l and 0.75 mg/l for COD, NH3-N and NO3-N respectively. In addition, a good solid separation occurred during that range with SVI value of 81 ml/g; this finding was supported by a morphological study along with scanning electron microscopy (SEM).