FS Sand Filters

Continuous Sand Filters: description and operation

Continuous sand filters are devices used to remove impurities from water through a filtration process.Considering the successive stages in which a civil wastewater plant is composed, this solution operates at the tertiary treatment level, with an output of a few mg/l of total suspended solids. In industrial plants, this technology is often installed downstream of other solutions, to accomplish a final finishing before reintroducing the “blue resource” back into rivers, lakes or seas.

This is the process, in brief.

1. The filter is equipped with a system that evenly distributes raw feed water to the base of the sand bed: this by means of an annular distributor.
2. The water passes through the sand bed from bottom to top and comes out filtered by a surface weir.
3. At the same time, dirty sand is removed from the filter bed by an air pump (airlift), which picks it up from the bottom and lifts it to the top of the filter.
4. Here it is fed into a washing chamber (washer), thus preventing the filter bed from becoming packed. Here the removal of impurities from the sand takes place. In the washer, the sand is cleaned by a flow of raw water countercurrent to the gravitational motion of the sand itself.
5. The washed sand falls back to the top of the filter bed.
6. The dirty wash water leaves the filter with continuous flow through a separate drain.

Sand filters of this type allow continuous and efficient operation. In fact, dirty sand is continuously removed from the filter bed, which is active by the action of an air pump that draws it from the bottom of the filter by lifting it up to the washing chamber.