Compliance with the urban wastewater treatment directive in relation to CSOs in major cities across Europe

Compliance with the European Union Urban Waste Water Treatment Directive (‘the Directive’) is a pre-requisite for achieving the primary objective of the Water Framework Directive. 11 EU-27 Member States had to comply with certain requirements of the Directive by 2005. Figures released in 2009 revealed a lack of compliance for wastewater treatment, but 100% compliance for wastewater collection in 8 out of the 11 Member States. This high level of compliance has been facilitated by significant investment in collection and combined sewer overflow (CSO) discharge prevention approaches and technologies. For cities with population equivalent in excess of 1 million, the most common approach to resolving CSO issues was identified to be the addition of extra capacity. Within some cities the use of these approaches was complemented by the use of real-time control (RTC) and several cities combined both of these approaches with waste water treatment plant (WWTP) expansion and/or sewer separation. Two cities were identified as utilising source control techniques, alongside conventional approaches. Four projects utilised tunnels, in combination with WWTP expansion and RTC. It is apparent that there is not a ‘one size fits all’ intervention in dealing with problematic CSOs, when trying to comply with the Directive