Managing wastewater flows - A case study of six wastewater treatment plants

Abstract

Climate change, ageing infrastructure, significant underinvestment and urbanisation are all growing challenges, which makes sustainable infrastructure for wastewater systems increasingly important. These challenges might result in an increase in the level of wastewater entering the wastewater treatment plant (WWTP). This can result in higher pollutant discharges from the WWTP, as the treatment performance decreases during high flows. The aim of the thesis is to support the identification of appropriate measures or strategies to maintain high treatment efficiency despite periods of high flow. This thesis includes a case study at six WWTPs, which combines model development and scenario analyses with interview studies. It evaluates whether the developed sim plified model can be used and how different future scenarios can affect phosphorus mass discharges from the WWTPs through the simplified model. The model estimates effluent phosphorus concentrations based on daily flow data and shows good overall precision, with an average deviation of 7% from actual values. However, the perfor mance varies between WWTPs and years. Scenario analysis reveals that reducing ef fluent concentrations and decreasing infiltration and inflow (I/I) or sewage water could reduce phosphorus discharges. Further increasing the WWTPs capacity showed limited impact for the studied wastewater treatment plants. The thesis also collects valuable information considering managing flows and reduc ing discharges to the recipient from industry professionals from the WWTP and sewer network. The interviews highlight future challenges such as economic conditions, the renewal rate of the sewer network, and increased precipitation and seawater intrusion. The appropriateness of measures to manage flow and decrease discharges are also eval uated, where all suggested measures are considered appropriate. However, measures targeting the sewer network are viewed as even more appropriate than measures target ing the WWTP. The interviews also conclude that to ensure sustainable wastewater systems, a combina tion of technical solutions , policy tools, and stakeholder engagement is recommended. Continued investment, regulatory pressure, and increased awareness will be important in improving water quality and efficiently managing future wastewater flows.