Sidestream sand filters

The use of sidestream sand filters or self-cleaning filters may be advantageous in reducing the level of suspended solids to help maintain clean waterside surfaces. If the size of the cooling system and the extent of the problem justifies it, blending with better quality water supplies or treatment of part of the makeup water volume by reverse osmosis (RO) may prove economically viable. 

Cooling water makeup should contain less than 5 ppm SS. If the level of suspended solids is considerably higher, say over 20 ppm SS, pretreatment by the use of polyelectrolytes or filtration is recommended. If the SS level is perhaps 5 to 10 ppm or if there is air-blown dust entering a cooling system, a sidestream sand filter or self-cleaning filter will be of benefit. In cases of high SS, chemical polymeric dispersants may be suitable as a total replacement for the sidestream filter but preferably will be used in tandem with a filter. 

Exercise A recommendation has been made to install a single sidestream, pressure sand filter in the recirculating cooling waterline of an industrial... 

Where sidestream filters are employed, the oil will foul the sand, so these units will need cleaning (not usually successful) or recharging. 

---