Process Description:
The ‘Filtromatic’ filter consists of a sand filter bed, divided into a series of individual cells. Each cell contains media and a nozzle plate filter floor.
A feed channel along the full length of the filter tank distributes flow evenly into the filter bed. Filtered effluent is collected below the nozzle floor and discharged over a weir at the end of the filter tank. The void below the filter floor acts as clean water reservoir, from which the backwash pump draws filtered water for backwashing.
The backwash sequence is initiated by rising head in the filter or by elapsed time. A travelling bridge complete with backwash pump and optional air-scour equipment traverses the length of the filter, washing each cell in turn. Following completion of the cycle, the travelling bridge returns to its start position to await the next backwash signal. There are two standard widths of filter 5m and 3m, the length of the filter being varied to provide the required filter area. Filter tanks can be constructed in concrete or steel tank packaged form.

Filtromatic at Silchester WwTW, Thames Water

Filter Construction:
The filter is available either as a site constructed unit or, in the case of smaller applications, as a packaged unit. Site constructed units include the bridge and drive, cells, backwash hood and pump, controls and accessories necessary for operation. These site constructed units normally contain 10 to 50 cells, each of which may filter up to 50m³/h, depending on the chosen design and maximum filtering rates.
The packaged units, which include filter tank, cells, bridges, controls, backwash hood and pump are available with filtering areas from 12.5m² to 25m².

Cell Construction:
The Filtromatic filter can be designed with either pre-stressed concrete or fabricated steel filter cells. The cells may be shipped as complete units, ready for installation in the filter tank. Since the cells are self-supporting over their entire width, installation is reduced to simply setting the cells on supporting ledges built into the tank wall and grouting them in place.
Cell floors are smooth and uniform and are fitted with polypropylene nozzles. The nozzles are of a non-clog design and offer uniform distribution for filtering and backwashing.