Control of COD Flow to a Waste Water Treatment Plant

Abstract.Flow variations of the inlet to a wastewater treatment plant (WWTP)are problematic due to the biological purification process. A way to reduce vari-ations from industrial areas is to insert a buffer tank and control the outlet fromthis. Traditionally the only on-line measurement is the inlet flow to the wastewatertreatment plant and reliable measurements in the system are difficult to establish.This lack of on-line measurements makes online control impossible, instead theaim of the project is to make a day-ahead plan for the buffer tank outlet. In thiswork two approaches are tested. First a model predictive controller (MPC) is de-signed to make a plan for keeping the Chemical Oxygen Demand (COD) flowto the WWTP constant assuming that the flows and concentrations can be pre-dicted. Secondly the total mass flow to the WWTP is kept constant only usingflow predictions in the optimisation. This leads to variations in the COD flow.The severeness of these variations is simulated and compared to the uncontrolledsituation. It turns out that control of the total flow gives improvements in the CODflow variations compared to the existing sewer network without control.