A Planning Tool for COD Flow Optimisation to a Waste Water Treatment Plant

The waste water flows to a typical wastewater treatment plant (WWTP) is comprised from periodic domestic flows and more stochastic industrial flows. Especially variations in the flow of Chemical Oxygen Demand (COD) at the inlet to the WWTP are problematic due to the biological purification process and bio gas production. Traditionally the inlet is un-controlled. A way to reduce variations is to insert a buffer tank near the industrial areas and control the tank outlet according to a prediction of household COD flow. As a first step a planning tool for operator control of the buffer tank outlet 24 hours ahead is designed. The WWTP in the Danish town Fredericia is used as a case. At the moment the only on-line measurement is the inlet flow to the wastewater treatment plant and reliable measurements in the network are difficult to establish. A Model Predictive Control scheme is shown to be able to give considerable reduction in the COD flow variations. To do this two models are introduc ed; one describing the buffer tank and sewer network from the tank to the WWTP and one describing the daily variations in the household flow. Additionally prediction of the industrial outlet is included. The control scheme has been tested showing good results in a SWMM simulation environment (ProtectionAgency, 2016) based on network architecture and measurements in Fredericia.