| 摘要 |
Raw water to which flocculant may have been added continuously or intermittently is introduced through nozzles or openings arranged at intervals along a pipe in a closed chamber maintained full of water under pressure. Flocculation occurs in the circulatory flow produced, and in the interstices of a shallow coarse-grained filter bed through which the water flows downwards. The filtered water is passed upwards to the inlet of a further filter operating under gravity at atmospheric pressure and having a deeper bed of finer-grain material through which the water again flows downwards. Each bed is washed by combined upward flow of water and air. Four secondary (fine-grain) filters may be disposed above two primary (coarse-grain) filters. One primary filter may be washed by water treated by both the other primary filter (temporarily operated at increased speed) and the four secondary filters. One secondary filter may be washed by water treated by the other three secondary filters. |
