Combined Urban Drainage Networks (UDNs) collect and convey both wastewater and storm water. This mixed water is sent to wastewater treatment plants (WWTPs) before being released to the environment. During heavy-rain events, UDN and WWTP capacities can be easily exceeded, causing untreated water discharges, known as combined sewer overflows (CSOs). To avoid this, modern UDNs include infrastructure such as tanks, gates and pumps, which can provide storage during heavy rain and release water gradually to the WWTP.
Real-time control (RTC) based on model predictive control (MPC) has been shown to be efficient for the management of UDNs. However, RTC techniques are mainly based on managing flows and does not take into account the polluting load (quality) of the water, which varies considerably depending on the rain events and storage periods. Similarly, the efficiency of WWTP processes depends on both the quantity and quality of the treated water. Untreated water may be refused at different by-pass points, leading to CSOs. Until now, UDNs and WWTPs have been managed separately. It is clear that integrated and coordinated management of quantity and quality in both systems is required in order to optimise overall efficiency and maintain the quality of waters into which treated water is discharged, as required by the EU Water Framework Directive (2000/60/EC).
The LIFE EFFIDRAIN project would demonstrate an integrated real-time control (RTC) strategy for UDNs and WWTPs to minimise the discharge of pollutants into receiving waters. The strategy would be tested in Bordeaux (France) and Badalona (Spain) and would:
- Demonstrate integrated RTC management of the waste water systems at the pilot sites during a range of rain events;
- Assess and quantify the benefits of the proposed solution compared to the control strategies currently in use; and
- Validate the applicability of the proposed solution in a variety of urban areas.
LIFE EFFIDRAIN would install sensors at the pilot sites to generate data that will be used to create a database of environmental scenarios taking into account weather conditions, real control actions and their effects on the different subsystems. It would also provide operational quality forecasts for both pilot sites, covering total suspended solids in sewer systems. Once the capability to monitor and forecast quality parameters in the sewer system and the WWTP is in place, procedures to compute optimal control strategies for water quantity and quality would be developed and tested using a virtual reality based on the UDN and WWTP detailed models.
The LIFE-EFFIDRAIN demonstrated the feasibility of minimising the occurrence of combined sewer overflows (CSO) by managing urban drainage networks in coordination with WWTPs. Furthermore, by complementing the real-time control (RTC) system with a series of online quality sensors and by implementing the proposed integrated management approaches, the project showed that the polluting load of any unavoidable CSO could also be managed.
Additionally, the project showed that adopting any of the RTC approaches for urban drainage systems allows operators to make efficient use of the existing detention infrastructure in UDNs, thereby significantly reducing CSO. The cost was demonstrated to be much lower than investing in additional infrastructure. With an installed RTC system, the project also showed that significant reductions to CSO volume could be achieved by using optimisation-based or rule-based techniques to calculate the best operational strategies for filling and emptying tanks. Again, costs can be considerably reduced.
The project developed customised software for its pilot schemes in Badalona and Bordeaux. The software simulates integrated urban drainage system according to RTC orders based on measurements obtained from the UDN and WWTP simulators. The project calculated that the Badalona pilot scheme could achieve a 6% reduction in the mass of pollutants released to the sea, while the Bordeaux pilot scheme could achieve an improvement of 30%. A cost-benefit analysis carried out at both pilot sites found that both volume-based and pollution-based strategies achieve benefits that exceed expected costs.
Finally, by developing methods to optimise the CSO management, the project serves as a valuable tool for determining the limitations of current infrastructure for achieving environmental objectives and complying with regulations. It is beneficial for all urban drainage and sanitation systems containing detention or storage infrastructure to make the most efficient and environmentally friendly use of any existing infrastructure. But it is especially true for cities that contain waters used for swimming or biodiversity-rich habitats that could be damaged by the pollutant loads in CSO.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).