| Filtration and Backwashing | | | | | Filtration and Disinfection: All pools, spas, and fountains should have properly sized equipment to filter and disinfect the water. The three main types of filters are sorptive media, sand, and cartridge. Each has advantages and disadvantages. For two of these, a backwashing system is required to clean the filtration system. Depending upon the type of filtration used, a substantial amount of water may be discharged during this operation. The frequency of backwashing depends on the level of usage for the pool. Heavily used pools need more frequent backwashing. A large community pool contains around 325,000 gallons of water. Filters and pumps are designed so that the entire volume of the pool should be filtered every six-eight hours that the pool is in use (every 30 – 60 minutes for spas). This means that the recirculation / backwashing rate for large community pools is as high as 650 gallons per minute.
Minimize Backwashing: One way to reduce the frequency of backwashing is to change the method for the daily cleaning of the pool. Use a vacuum system that does not send any of the water or dirt through the central filter system. The vacuum system filters out dirt and sediment into cartridge filter that is washed at the end of each day
Backwash Automation: Filter backwash controllers are available that can initiate backwashes based on pressure differential, gallons filtered since last backwashed, and time since last backwash. If the first backwash is not successful at meeting the pressure goal, it can be programmed to perform additional backwashes as needed. Operators may specify what weekdays and times are acceptable to backwash. The system can backwash only if it is necessary - keeping your filter running at optimal performance, reducing filtration downtime and saving water.
Reuse of Backwash Water: Where backwash water is produced, it can be used for landscape irrigation if the chlorine content is less than 2.0 milligrams per liter and the dissolved solids are not greater than the plants can tolerate. Lists of plants and their salt tolerance can be found at most land-grant universities. Allowing the water to settle until the chlorine concentration of the water is below 2.0 milligrams per liter will place the water within municipal potable-water parameters, at which time it is safe to use for landscape irrigation.
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