Control of Sewer Flow using a Buffer Tank

Flow variations of the inlet to a wastewater treatment plant (WWTP) are problematic due to the biological purification process. A way to reduce variations from industrial areas is to insert a buffer tank. Traditionally the only on-line measurement is the inlet flow to the wastewater treatment plant and reliable measurements in the system are difficult to establish. A control scheme using only one on-line measured variable is shown to be able to give considerable reduction in the flow variations. To implement the control scheme two models are introduced. A linear model (delay model) from the buffer tank to the wastewater treatment plant and an autonomous model describing the daily variations in the household sewer flow. A Model Predictive Controller has been designed and tested in a laboratory set-up with good results.