Pressure Sand filter

In recent year a mistaken idea has grown that biological or slow sand filtration is an old fashioned outdated method of water treatment which has been completely superseded by rapid sand filtration this is defiantly not the case slow sand filtration is still the chosen method of water purification in a number of high industrialized cities as well as urban areas in a number of cities in U.S and Europe slow sand filters have recently been constructed

The advantages of a slow sand filter are 1) simple to construction and operation 2) the cost of construction cheaper than that of rapid sand filters 3) the physical chemical and bacteriological quality of filter water is very high when working ideally, slow sand filter have been shown to reduce total bacterial counts by 99.9 to 99.9 per cent and E.coil by 99to 99.9 per cent

Normally the filter may run weeks or even month without cleaning when the bed resistant increase to such an extant that the regulation valves has to be kept fully open it is time to clean the filter bed since any further increase is drained off and the sand bed is clean by scraping of the top portion of the sand layer to a depth of 1 or 2 cm this operation may be carried out by unskilled laborers using hand tool or by mechanical equipment after several year of operation and say 20 or 30 scraping the thickness of the sand bed will have reduced to about 0.5 to 0.8 meter then the plant is closed down and a new bed is constructed.

Process :
The filter is equipped with certain valves and device which are incorporated in the outlet pipe system the propose of the device is to maintain a constant rate of filtration an important components of the regulation system is the venture mater which meager the bad resistant or loss of head when the resistant built up the operator open the regulation valves so as to maintain a steady rate of filtration when the loss of head exceed 1.3 meter it is uneconomical to run the filter.