What are slow sand filters?

Slow sand filters (SSF) are a water treatment method that use sand on which microorganisms grow. These microorganisms are capable of degrading biological and chemical pollutants in runoff water, including Phytophthora and tobacco mosaic virus (TMV).

The disadvantage of SSFs is that slow flow rate of water through the sand is needed to attain treatment. A rule of thumb is one square foot of sand bed can treat about 0.06 gallons (0.2 liters) per minute. A large sand filter is needed to treat large volumes of water.

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