The sand filter is a device that removes suspended particles such as soil, colors, plankton, bacteria and particles from corrosion with a sand filter (filtration).
The sand filters are designed as pressure cylinders. The inside of the columns is filled with silica sand or anthracite, usually a coarse particle layer on the sand filter nozzle to prevent clogging and then the particle layer is poured onto them. Due to the passing of water from the pores between the gravel particles, the suspended material trap and water is almost free of suspended particles . Of course, the accumulation of suspended particles in the sandblasting pile causes an increase in the pressure drop which, if this pressure drop exceeds a certain limit, should be washed off. The pressurized sandblasting filter is considered to be the most commonly used water purifier.
Sandblasting filters use for surface water treatment (rivers or wells), pool water, removing colors, cooling water towers, final filtration of industrial and human wastewater, filtration of drinking and industrial applications (city and industrial waste water treatment plants)
Sand filter structure:
A sand filter has a simple building. The main components of the sand filter include:
1. Main reservoir and main body of the sand filter: The sandblasting body can be made of carbon steel or stainless steel. In the last few decades, FRP tanks have grown in the water and wastewater industry. Two or three epoxy paint layers are used to protect corrosion. The thickness of the staining is directly related to the quality of the water entering. If the corrosion of the water entering the sand filter is high, then three layers of epoxy and coltara should be used, and the minimum thickness of the product is 180 microns in this case.
2. Fitting and sand filters: Two types of fitting can be used to control the water inside the sand filter; in the first case, four butterfly valve is used. Thus, when the water entering the sandwich filter is refined, 2 of these valves are open and the other 2 are closed, and during the operation of the backwash the process is the opposite of the case.
Automatic fitting filter is available in various sizes and can be installed on metal tanks. These fitting only need initial adjustment, and since then all filtration steps are performed automatically. A sand filter is fitted with an automatic electric valve for the appropriate conditions. First, the filtration period of the filter is too early (for example, every 6 hours it needs to be cooked) or when the operator is not available.
All of these duties is done by the operator and it is better to use these manual operated filters in places where there is a 24-hour operator. Otherwise, full automatic filter for sand filtering should be used, which will be described below.
Problems due to the lack of use of a sandy water filter
in pools, due to the pool's openness, if the pool water is not alternately replaced or not filtered by a sandy filter, stagnant and contaminated water due to the presence of foreign materials such as leaves, dirt, dust and growth and propagation germs, all types of microbial fungi and eggs of parasites cause diseases such as jaundice, intestinal fever, bloody diarrhea, skin diseases, etc. In particular, in public pools, this issue should be strongly considered and in no way should the use of a sand filter should not be postponed.
Sand filter under pressure:
Due to limitation in space and investment in small-scale refineries and industrial centers, usage of sandblast filtering was developed. The high filtration rate (100-300 m3 / m2.day), suitable size (cylindrical diameter of 1 to 3 meters), high water output, easy washing and, finally, low cost of construction and maintenance, this type of sand filter option for use in industries, factories, swimming pools, gardens and other similar centers.The pressure-filtered sandwich is designed to be pressurized cylinders filled with sand in the cylinder. The water flows from above and then loses its turbidity by passing through the sand bed, suspended particles, mud, organic matter, color, algae, bacteria and generally TSS clear water and refined from the bottom of the bed are collected and removed from the system by sand filter nozzles. Usually, to protect the nozzles and to maintain a sand bed, a coarse particles layer is placed on the nozzles.
Sand types used in sand filter
There are a variety of sand for use in sandy bedding, the most famous of which are:
1. Silica sand is the most common type of sand
2. Anthracite sand which is a kind of black sand
3. Silicate sand which is containing titanium compounds