Evolution of a wastewater treatment plant challenges traditional design concepts

Traditional design and upgrade concepts for wastewater treatment plants (WWTPs) are based on the forecasting of load parameters over a period of 25-40 years. This approach is adequate as long as the environment of a WWTP is stable or predictable over this long time period. However, these conditions are usually not met, as the catchment area, discharge requirements, available technology and institutional conditions of a WWTP may change drastically over time. The complexity and consequences of these dynamics are shown exemplary in a case study analyzing the historical development of a plant from the initial planning steps to the current date. We conclude that the dynamics and complexity of the wastewater system makes reliable predictions impossible, and therefore question the current design and upgrade approach. Instead, we propose to improve the planning and design of wastewater infrastructures through methodologies that systematically account for future uncertainty, like, e.g. scenario planning.