Syntic fibre is used as filter media. The filter media is usually chemical and temperature resistant. The filter media is usually chemical and temperature resistant.

The tube settler removes suspended solids. It is classified as a secondary treatment. This is inclined at a position at 45-60 degree.

During cleaning, water above filter is drained until water lies a few centimetres above top of bed when air from a compressed air unit is blown in reverse to normal flow direction at a rate of about 1-1.5 m³ free air/m² of bed area.

Splashing, diffusion, etc. increases aerobic conditions and it is increased eir by forced-air flowing through bed or natural convection of air if filter medium is porous.

When head loss becomes excessive and beyond 1.5-2.5 m, filter should be cleaned. The maximum head loss experienced in rapid sand filters is usually 3 metres.

A typical trickling filter is circular and between 10 meters and 20 meters across and between 2 meters to 3 meters deep. A circular wall, often of brick, contains a bed of filter media which in turn rests on a base of under-drains.

The calculated diameter is 15.3 m. Area is first calculated by dividing flowrate with velocity. That is 2200/12 =184 m2. Then square root (184 x (4/3.14)) = 15.3 m.

Tube settlers decrease vertical distance of settling. Hence floc particles settle faster. A floc particle must settle before agglomerating to form larger particles.

The porosity of such syntic media is around 88-90%. These media are highly porous. Hence this is highly efficient in removal of colloidal and suspended solids.

The penetration of suspended solids is deep through filter bed. The length of run is two days. Before starting operation again, pre-treatment of rapid sand filter beds is done by coagulation.