Effect of influent flowrate on the performance of biological wastewater treatment processes

Abstract

The organic and nutrient removal efficiency of municipal wastewater treatment plant (WWTP) can be affected by various environmental factors including sewage influent flowrate, pH, and water temperature. In this study, we investigated the effect of sewage influent flowrate on the organic and nutrient removal efficiency. Three biological wastewater treatment processes (membrane bioreactor [MBR], sequencing batch reactor [SBR], anoxic/anaerobic/oxic [A2O]) were operated with a designed sewage flow rate of 1.5 m3/d. The organic and nutrient removal efficiency were investigated when the sewage influent flowrate gradually decreased from 100% to 70%, 40%, and 10% of the design flowrate. The organic removal efficiencies deteriorated slightly as the sewage influent flowrate decreased from 100% to 10% for all the three processes. At 10% of flowrate condition, MBR process showed highest soluble chemical oxygen demand (SCOD) removal efficiency (89%), with slightly lower SCOD removal obtained with A2O (74%) and SBR (70%) processes. Total nitrogen (T-N) and total phosphorus (T-P) removal efficiency decreased significantly with decreasing influent flowrate. In particular, the T-N removal rate of the SBR process decreased to 31% at 10% of flowrate condition. It can be concluded that at least 10%–40% of design flowrate should be maintained for the efficient treatment in biological WWTPs.