| 摘要 |
A chemical composition is added (1) below the level of the filter inlet, in order to alter pH and dissolve any precipitate stuck to the filter bed material or suspended in the water. A process for reducing the salt content of water comprises precipitating the salt by altering the pH of the water, brought about by adding a first chemical composition (1). The process is carried out at least partly while the water is flowing through a continuously operating sand filter (4) with a moving filter bed. The filter has an inlet for untreated water in the filter bed, an outlet (6) for the filtrate and a cleaning device for the filter bed material, this device having an outlet (7) for the water used for cleaning. Filtration occurs in a region of the filter bed above the level of the inlet for the untreated water. Spent filter bed material shifts downwards to below the level of this inlet and is transported from a lower part of the filter to a cleaning device. The cleaned filter bed material is then returned to the upper part of the filtration region. At least some of the precipitation occurs in the filtration region and a second addition of a chemical composition occurs below the level of the filter inlet, altering pH so that any precipitate stuck to the filter bed material or suspended in the water in the filter bed material is dissolved in this region or during transport to the cleaning device. An Independent claim is included for the process apparatus. |
