Treated surface water from lakes, rivers and dams is often used to meet the demand for drinking and process water. Because the concentration of turbid and suspended matter can vary greatly throughout the year due to different weather events such as heavy rain or flooding, the quality of such water sources can change rapidly. A major disadvantage of surface water is often the seasonally fluctuating temperature, since warm water becomes contaminated more quickly and the treatment processes run more slowly at low temperatures. It is therefore very important to use only highly efficient treatment processes that are able to cope with this fluctuating water composition with high peak levels of pollution concentration. Possible applications for the treated surface water are for example cooling water, boiler feed water, process water or drinking water.
In contrast to the extraction of water from underground sources, treatment by filtration is always necessary with regard to hygienic safety. In the case of unfavorable raw water properties, chemical and/or biological treatment stages are also essential. The water taken from a river is pre-cleaned by rakes, separators or settling tanks. This is followed by filtration and chemical treatment. The efficiency of the filter stage should also handle extreme increases in suspended matter content of more than 1000 mg/L in flood situations. Plankton and bacteria must also be removed in the filter stage. Filters that can be automatically backwashed are particularly suitable for this, as they can easily cope with changing water quality. They also help reduce operating and maintenance costs compared to large sand and gravel filters.
Since the adaptability of the water treatment plants was often overwhelmed when it came to supplying drinking water, artificial infiltration of mechanically and physico-chemically pretreated river water with subsequent fine treatment was introduced at some river intake points as an additional treatment stage.