Grey water: characterization, treatment and recycling

Although globally abundant, the world's water resources are very unevenly distributed. While the total volume of fresh water on earth is estimated at 41,600 billion cubic meters, less than 1% is available for human use . At present, arid and desert zones, as well as certain temperate but densely populated regions, are experiencing a progressive depletion of their reserves. We are also witnessing a sharp increase in water requirements, due to the massive use of irrigation, the combined growth of the world's population and the consumption of each individual. As a result, overall pressure on available resources is increasing. In 1970, this was 14,000 m ³ per person per year, compared with 8,000 m ³ in 2008 .

This context of recurring water accessibility problems has led, among other things, to the development of wastewater recycling solutions. These solutions make it possible to reduce the amount of water drawn from the resource to meet the needs of the population. In fact, recycled water can be substituted for drinking water in applications where lower quality is sufficient. Recycled water can be used in fields as varied as agricultural irrigation, groundwater recharge, garden watering and fire protection. Countries with extensive experience of grey water recycling on various scales are undoubtedly the USA and Australia, where recycled water is mainly used in agriculture, and Japan, where the reuse of treated wastewater is mandatory in certain regions, in buildings with a living area of over 30,000 m ² . To a lesser extent, Germany and the UK are currently developing projects on the scale of small residential districts.

This article attempts to take a global approach to the issue of grey water. This approach is not limited to the geographical perimeter of France, but extends to all regions of the world where there is a quantitative and qualitative shortage of water resources. The following topics will be addressed:

• flows and composition of raw grey water ;

• legislation in force in France, Europe and other countries;

• treatment for recycling ;

• the cost of such treatments.