A DeepBed filter may be defined as a granular filter for removal of TSS from secondary treatment effluent using a media depth of at least four feet at a filtration rate of more than 2 gpm/ft2. Coarse media is normally used to encourage deep penetration of solids into the media bed. This allows for longer filtration runtimes. Simultaneous air and water backwashes are used to ensure cleaning of the filters as required. Severn Trent Services offers gravity, pressure and modular filters and pre-assembled gravity deep bed filters.