The biosand filter is an adaptation of the traditional slow sand filter which has been used for community water treatment for hundreds of years. The biosand filter is smaller and adapted for intermittent use which makes it suitable for households.
Water treatment is carried out by the sand inside the filter. The filter container can be made of concrete, plastic or any other water-proof, rust-proof and non-toxic material.
The concrete biosand filter typically uses a box about 0.9 m tall by 0.3 m square, or about 0.3 m in diameter. The filter box is cast from a steel mold or made with pre-fabricated pipe.
The container is filled with layers of sieved and washed sand and gravel (also referred to as filter media). There is a standing water height of 5 cm above the sand layer.
Similar to slow sand filters, a biological layer of microorganisms (also known as the biolayer or schmutzedecke) develops at the sand surface which contributes to the water treatment.
A perforated diffuser plate or basin is used to protect the biolayer from disturbance when water is poured into the filter.