The wash water required for a rapid filter may vary from 3-6% of total amount of water filtered. Upward wash water rates are usually of order of 0.3-1.0 m/min.

The bed depth is considered as 600-760 mm. The depth for gravels is considered as 400-600 mm. These are assumptions made while designing a rapid sand filtration.

While designing a pressure sand filter bulk density of sand is considered as 1750 kg/ m³. The sand is generally measured in bags. Each bag weighs around 140 Kg.

The specified minimum backwash time for a rapid filter is 5 minutes. The amount of water required to wash a rapid filter may vary from 3-6% of total amount of water filtered. The surface wash rate is usually 10-12 m³/m² h.

Primary clarification is necessary prior to trickling filters. Screening of materials prior to letting it into trickling filter is necessary. This is done to prevent clogging.

The rise velocity assumed is 18-20 m/hr. Based on this sizing of filter is carried out. Based on this diameter of vessel is derived.

Tube settlers use multiple tubular channels sloped at an angle of 60° and adjacent to each or, which combine to form an increased effective settling area. This provides for a particle settling depth that is significantly less than settling depth of a conventional clarifier, reducing settling times.

Polyvaniladene has been used as a medium in case of high rate filtration. This is a syntic medium. This is highly porous.

The surface loading rate of tube settlers is 11-15 m²/mm². Based on this area required is calculated. Also number of tube settlers is n calculated.

Filtration cycle is interrupted for air washing when filter resistance through filter media reaches terminal filtration.