| 摘要 |
An intermittently operating slow sand filter uses the damming of water in a raised pipe to provide a constant level of water in a slow sand filter container. The container includes a water inlet and outlet, and is partially filled with sand or other filter material. A pipe from the water outlet in the slow sand filter is raised upward to the desired level of water over the sand before descending to a water reservoir. Water backs up in the pipe and the container to the desired level above the top of the sand, even when the flow of water is intermittent. The schmutzdeuke forms at the top of the filter medium. The water level in such a manually operated slow sand filter, using fine quartz sand as the filter medium, and at ambient temperatures (about 21.degree.C) is maintained above about 1 cm above the top of the filter medium and below about 8 cm above the top of the slow sand filter. In another intermittently operating slow sand filter, the water level is controlled automatically when not being used at a desired maintenance level, and otherwise is kept in a desired range of levels above the top of the sand (or other filter material) in a partially filled container. Automatic control is provided by a control system that senses the water level in the slow sand filter. The supply of water may be froma pump or from a gravity flow controlled by a valve. The water from the automatic intermittently operating slow sand filter is supplied to a reservoir. Water level in the reservoir may also be controlled within a desired range using upper and lower level limit detectors and a valve on an outlet line from the container to the reservoir.
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