Dilution of wastewater in sewerage networks is a major concern for wastewater operators. To tackle this problem on a regional scale, the Flemish wastewater operator Aquafin developed software enabling the prioritisation of intervention, highlighting the so-called dilution wet spots in the region in a transparent and straightforward way. Quantitative assessment reveals that in 108 of the 194 investigated catchments more than 50% of the dry weather flow is due to dilution. In the search for a hands-on, accurate method that could reveal the major inputs of infiltration and inflow within a sewer system, a promising tracing method based on isotopes was tested on two different case studies. To verify the application potential of such a method on a regional scale (Flanders), the isotope contents of drinking water and groundwater were compared for 65 catchments, with contrasting results.

Combined sewer overflows (CSO) are the “ugly ducklings” of urban wastewater infrastructure, rather unknown, rarely loved. Contrary to wastewater treatment plants (WWTP) where, commonly, process parameters are carefully registered, still relatively little is known about the spill behaviour of CSOs. In spite of the considerable bandwidth of pollution magnitude reported in literature, it can be generally accepted that CSO impact certainly is not negligible. As the sole wastewater utility in Flanders (6,100,000 inhabitants), Aquafin operates, next to 230 WWTP’s and almost 1,000 pumping stations, some 3,100 CSOs. In search for an optimum CSO management strategy, Aquafin prospected several modelling and monitoring possibilities. As a result, a CSO action plan could be drawn up tailored to the estimated relevance of the CSO under consideration. In a further step a cost-benefit analysis of several static and dynamic remediation measures was undertaken. Real Time Control (RTC) strategies turned out to be the most cost efficient solution for CSO impact mitigation.

Characterizing the emissions and impact of combined sewer overflows (CSOs) remains one of the key challenges in the field of urban wastewater. Considering the large number of existing CSOs, decision-makers need a pragmatic approach that allows fairly easy, hands-on determination of emissions (particularly loads) without compromising accuracy. This philosophy is incorporated in the Cockle tool presented here, which uses stochastically processed input from a vast amount of pre-registered water quality data (pollutant concentrations) in combination with spill flow time series either generated from hydrodynamic models or converted from monitored overflow water levels. Uncertainty is intrinsically covered by the statistical output range of the reported results. As a fully automated tool, Cockle allows to readily assess emissions within a chosen time frame, facilitating more accurate guidance for further remediation actions and/or mapping of the current state for operational follow-up.

This study presents the development of an Early Warning System (EWS) called EPIGONE focusing on the detection of dry weather overflows in the vicinity of throttle structures in sewer systems. Throttle structures are considered as vital parts of a sewer system as they are control sections limiting flow rates to a designed operational value. Because these structures are by definition prone to potential clogging or blockages, a close follow-up of the daily operation by an EWS facilitates increased vigilance or even alarm. Primary goal of EPIGONE is to alert operators and thus allow fast intervention in case of suspected failures of these structures within a settled timeframe. EPIGONE combines overflow water level measurements with rainfall radar information to determine Combined Sewer Overflow (CSO) activity during dry weather as this dual condition will indicate malfunctioning. This combination of measurements was found to be the most cost effective set-up to deploy on a large scale. Water level data are recorded and logged on-site and sent to a central controller via GSM/GPRS, where an algorithm determines dry weather overflow conditions. Rainfall radar data are used as criterion to decide on dry weather conditions. From there on alarms are sent out to multiple recipients via e-mail and/or text messages (SMS). Next to this, it is obvious that this system can also be used for ‘regular’ wet weather CSO monitoring.