Sand filters are used to remove suspended solids in the water. Generally, this filtration method is used upstream to a physiquo-chemical treatment process. Having one or more layers of filtering materials, sand filters only remove large solids in suspension (usually in the range of 40 microns or more). The effective size of each sand granule is typically from 0.35 mm - 1.2 mm. The larger the sand particle size the finer the filtration is.
The removal of suspended solids less than 40 microns requires filters with two or three layers of filtering media. These filters are called dual or multimedia sand filters. When the configuration of the layers is appropriately developed, these filters can remove solids in suspension whose size does not exceed 5μ.
The higher the concentration of suspended solids, the bigger the diameter of the filter should be. All filters have a maximum concentration of suspended solids that can be handled without compromising the filter's performance.
The backwash water is used to clean and rinse the filters to remove suspended solids remain trapped in the different layers. The washing water may come from either of the filters themselves or from an external source of clean water (such as a storage tank).
An electronic system base of PLC and measurement instruments allows the automation of the filter backwash cycle to ensure the desired quality of output water