Effect of the EC Urban Wastewater Treatment Directive on Marine Treatment Practice

The EC Directive on urban wastewater treatment will have a considerable impact on the methods used for the treatment and disposal of sewage at coastal locations. The Directive requires the natural processes involved in marine treatment to be enhanced by the use of land-based treatment to meet the same standards. This paper discusses the implications of this change, in particular the problems involved in constructing and operating conventional treatment plants at coastal locations. Planning problems, both locally and on a catchment basis, are considered. It is concluded that these difficulties point to a need for new thinking in catchment planning and in the design and construction methods used for treating wastewaters in coastal communities. This is illustrated with UK and continental examples. In addition, the implications in terms of outfall design are discussed. It is shown that the change of emphasis towards land-based treatment does not necessarily reduce the need for a high degree of dilution and dispersion in the sea in order to meet environmental standards. As a result, sound planning, design and operation of long sea outfalls remain as important as ever.