The main aim of sand filtration is to remove suspended solids, oils and surface agents from the water coming from the air/water separators. During the filtering stage the filtered substances cause an increase in head loss. When the pre-set value is reached backwashing occurs automatically using filtered water. However, due to the weight of filtered substances, using only water doesn't adequately clean the filter. Our backwashing system uses both water and air.
Traditionally, the filter medium is made from fine granulometries which allow for an effective filtration process but this has the disadvantage of requiring frequent backwashing operations (and consequent filtering interruptions). On the other hand, using a coarse filter medium, backwashings are reduced but the filtration results are not as good. Therefore, to benefit from the advantages of different granulometries, we use a multi-layered filter (with a granulometry range from 0.3 mm to 8 mm).
- Special anti-clogging water distribution system
- Multi-layered granulometry to maximize efficiency
- No loss of sand during process
- More efficient backwashing
- Pilot unit available for on-site trial
The quality of filtration depends mostly on a good distribution of inlet water, water and air backwashing and homogeneous drainage in each point of filtering volume. The best drainage and distribution of backwashing water are obtained by means of a “double bottom” plate: the top of it is equipped with at least 40 to 50 nozzles each m² which allows the inlet water to pass through the sand layers and allows retention of filtered substances. The nozzles for the water and air backwashing system are made of polypropylene and have elongated ends with holes or slots through which the air can pass. These holes normally have a diameter of 0.25 mm, i.e. smaller than that of the smallest grain of sand. In this way an homogeneous air cushion forms between the plate (which supports the nozzles) and the filter bottom, thereby a uniform distribution of air is obtained. The efficiency of this type of filter can achieve less than 5 microns.