全球大约 11 亿人口无法获得干净的饮用水 ，甚至大约 26 亿人口生活在卫生条件很差的环境。因为饮用水受到污染，每天死亡 5.000 人口, 其中多数是孩子。
我们用水的同时，自然产生污水; 我们饮食的同时, 自然会排泄产生营养物质和有机碳化合物。正如对固体垃圾进行分类, 处理和重新回收利用一样，我们必须以同样方式对液体垃圾和污水进行处理。
Lack of clean water and sanitation is the number one cause for epidemic diseases and deaths in developing countries. Over 5,000 people, most of them children, are killed every day by water pollution.
As the world population is growing and climatic conditions are worsening, water scarcity is rising. Over 70 % of human water consumption serves for irrigation. This percentage is bound to rise further to permit feeding growing populations in arid and semi-arid regions.
Competition for water is becoming fiercer. Lack of this precious resource is already becoming a fundamental reason for violence, population displacement and war.
Not only our fossil energy resources, but also our resources of fresh water and phosphorus are gradually depleting. Energy, water and nutrients will certainly become more expensive and less affordable for the poor.
In many regions soil fertility is gradually decreased by erosion. Soil layers become thinner. Soils loose organic carbon, and thus their water and nutrient absorbing capacity. They become less fertile and need even more irrigation and fertilizer.
Only sustainable solutions can mitigate these global challenges.
The only really sustainable solution is to close the loops by reuse of water, nutrients and organic carbon, and by recovery of energy. In addition, we must reduce consumption.
We have to understand that wastewater is our most dependable water resource; as we use water, we produce wastewater. As we eat, we discharge nutrients and energy-rich organic carbon. As we separate and recycle solid waste, we now must begin to separate and recycle wastewater and its ingredients.
Sustainable solutions create value from waste.
Only adapted solutions can be successful. They must be adapted to regional and local conditions: climatic, environmental, social, cultural, technical, as well as economical conditions.
Solutions must be efficient and affordable. Sanitation technology developed long ago in water-rich, industrialized and wealthy countries is not suitable for arid and poor developing countries and for emerging countries. It is a terrible mistake that "conventional" sanitation technology, which is wasting a lot of fresh water as transport medium, is still employed where it should have no place.
Different solutions are required for cities with sewers, cities without sewers, small towns, suburbs, rural villages, isolated hotels, resorts, and single dwellings. Each solution must be adapted to its application.
Reduce, Treat and Reuse
The ideal solution would be to treat all wastewater and reuse the effluents for irrigation. In this way, the world's fresh water consumption would be reduced by the entire wastewater flow.
Decentralized treatment is required to produce irrigation water where it is needed. Treated effluent is used for the irrigation of yards, gardens, parks, golf courses and fields in the vicinity of dwellings, office buildings, hotels or resorts.
Where not all of the wastewater is needed for irrigation, treated effluents are alternatively used as service water for flushing and washing purposes, therewith also reducing fresh water consumption.
Where more wastewater is produced than can be reused for irrigation or as service water, rain water and well treated effluents should be used for ground infiltration and groundwater replenishing wherever possible. After additional soil filtration the water can be recovered as fresh water.
Decentralized treatment and reuse make expensive and long sewer networks redundant. In addition it reduces size and costs of water lines.
Where wastewater is treated in central plants, the effluent quality should be sufficient to permit downstream reuse for irrigation or as a fresh water resource.