11. Maintenance means backwashing where the flow of clean water is reversed back into the filter. 12. :: : Recent studies have assessed to combine relaxation and backwashing for optimum results,. 13. Slow sand filters and self-cleaning screen filters employ mechanisms other than backwashing to remove trapped particles. 14. Relaxation and backwashing effectiveness will decrease with operation time as more irreversible fouling accumulates on the membrane surface. 15. A typical backwashing session can waste a few hundred gallons of water water that must be replaced. 16. Alternatively, in engineering applications, such as swimming pool water treatment plants, they may be cleaned by backwashing . 17. Self-cleaning screen filters utilize point-of-suction backwashing to clean the screen without interrupting system flow. 18. Finally, iron filter media requires high flow rates for proper backwashing and such water flows are not always available. 19. Small amounts of sand can be lost in the backwashing process and the bed may need to be topped up periodically. 20. Backwashing is an important operation employed to remove filtered solids as this build up causes resistance to filtration to increase with time.
