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Recycling water is an important aspect of water resource and environment management policies, ensuring reliable alternative water resources, reducing environmental pollution and achieving a more sustainable form of development. This paper focuses on wastewater reuse as a strategy for integrated water management. Key economic, financial, regulatory, social and technical factors that help to make water reuse projects successful are reviewed. Selected examples from Northern and Western Europe and arid and semi-arid Mediterranean regions illustrate the contribution of wastewater reuse to integrated management of water resources.

This paper summarises the current non-potable, urban use of reclaimed water with particular reference to toilet flushing. It compares water quality standards for reclaimed water, the volumes of water required for toilet flushing and the qualities of greywater and domestic sewage that have previously been used for reuse. Worldwide examples of reuse schemes are presented with particular detail to two key European sites where greywater has been used for toilet flushing, the Millennium Dome in the UK and a residential block of flats in Annecy, France. It was demonstrated that the interest in water reuse is growing steadily, not only in acknowledged water deficient areas, but also in countries which have not historically appeared to have a water supply problem. The latter include Northern European States such as Belgium, France, the UK and Germany, as well as in tourist coastal areas and islands. This situation affords great opportunities for the creation of urban water recycling schemes.

[1] Intermittent filtration through porous media used for water and wastewater treatment can achieve high pathogen and colloid removal efficiencies. To predict the removal of bacteria, the effects of cyclic infiltration and draining events (transient unsaturated flow) were investigated. Using physical micromodels, we visualized the intermittent transport of bacteria and other colloids in unsaturated porous media. Column experiments provided quantitative measurements of the phenomena observed at the pore scale. Tagged Escherichia coli and a conservative tracer (NaI) were introduced in an initial pulse into a 1.5 m sand column. Subsequent hydraulic flushes without tagged bacteria or tracer were repeated every 4 hours for the next 4 days, during which outflow concentrations were monitored. Breakthrough behavior between colloids and dissolved tracer differed significantly, reflecting the differences in transport processes. Advancement of the wetting front remobilized bacteria which were held in thin water films, attached to the airwater interface (AWI), or entrapped in stagnant pore water between gas bubbles. In contrast, the tracer was only remobilized by diffusion from immobile to mobile water. Remobilization led to successive concentration peaks of bacteria and tracer in the effluent but with significant temporal differences. Observations at the pore-scale indicated that the colloids were essentially irreversibly attached to the solid-water interface, which explained to some extent the high removal efficiency of microbes in the porous media. Straining, cluster filtration, cell lysis, protozoa grazing, and bacteriophage parasitism could also contribute to the removal efficiency of bacteria.Citation: Auset, M., A. A. Keller, F. Brissaud, and V. Lazarova (2005), Intermittent filtration of bacteria and colloids in porous media, Water Resour. Res., 41, W09408,