CSO generator

Quantifying CSO loads for optimization

One issue identified with using an influent generator model is that it only used data available at the wastewater treatment plant (WWTP). Because these data are not available in the sewer system, the need was felt for a new generator. The Combined Sewer Overflow (CSO) generator is a tool designed by Aquafin for the quantification of CSO emissions (loads) from sewerage systems, a task that is indispensable for the planning, performance evaluation and optimization of urban drainage systems.

As this requires the determination of both water quantity and quality with adequate accuracy and reliability, Aquafin strives at closing the gap between state-of-the-art detailed hydrodynamic modelling and phenomenological simulation of wastewater quality. Based on available detailed input (rain) and output (water level, flow) from a hydrodynamic model, the wastewater quality (here: NH4, TSS) is emulated at arbitrary locations in a sewer system using a parsimonious model. Long-term water quality monitoring data is used for calibration.

Conceptually, this approach resembles the use of influent generators which can be found throughout WWTP modelling. The output of concentration time series is produced based on the following calibration parameters:

  • mean and peak dry weather load
  • time shift between the daily dry weather peak load and peak flow
  • the maximum dry weather water level
  • rain intensity dependent delay of the pollutant concentration with respect to the flow at the beginning of a rain event
  • rain intensity dependent retention time of the water in the sewer system