A common requirement for the influent of RO surface water filtration is to have a 15-minute silt density index value (SDI 15 from ASTM D4189-07) of less than 3.0.  With a conventional cartridge filter, this requirement is not likely to be met. This is especially true when processing highly challenging water. The figure on the right shows the SDI of typical filtrate from a 1-micron cartridge filter processing feed water with an SDI of 6.7.

The Coiled Membrane Filter (CMF) from FSI is ideal for the RO pretreatment application. It can remove submicron solids in many water and wastewater treatment processes to provide a sustainable high-quality feed to improve RO system Reliability, Availability and Maintainability (RAM). CMF is the most cost-effective filtration system for removing high concentrations of submicron solids from water (up to 5% by weight) for industrial and municipal applications. For service with highly challenging surface water (SDI 15 = 6.7), the system can provide an effluent with 

SDI 15 < 2 and Turbidity <1.0 with no additives (i.e. coagulants).