Effect of aeration and filling patterns on nutrient removal performance in a sequencing batch reactor

A sequencing batch reactor (SBR) was used to carry out an experimental study under well defined conditions to investigate the effect of filling and aeration pattern on nutrient removal efficiency and settling characteristics. The SBR was operated with a cycle time of 8 hours under 4 different operational conditions. The filling time was increased while aeration time was gradually reduced during these four runs. When mixing time to process time ratio (T_M/T_P) exceeded 0.65, sludge settleability began to deteriorate. It seemed that deterioration in sludge settleability was not due to long fill time but to prolonged anaerobisis. The change in sludge characteristics did not have a major effect on nutrient removal. From the experimental results, it can be concluded that aerated time fraction is the most important operational parameter that influences nutrient removal efficiency. In nutrient removal SBR, filling pattern plays a significant part in the efficient utilization of external carbon source rather than in creating concentration gradient needed for kinetic selection. A predetermined MLSS concentration can be maintained in the reactor even at high SVI values by adjusting the duration of settling and V₀/V_T ratio.