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Sand
filters are designed as single-pass or multi-pass filters
and use sand as the media for filtration. The sand is usually
two to three feet deep and contained in a liner made of concrete,
plastic, or other impermeable material. Depending on the design,
the filter may be situated above ground, partially above ground,
or below ground. The filter surface may be open or covered.
Partially treated wastewater is applied to the filter surface
in intermittent doses and receives treatment as it slowly
trickles through the media. In most sand filters, the wastewater
then collects in an underdrain and flows to further treatment
and/or dispersal.
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