A high-performance electropositive filter
Reverse osmosis (RO) membranes have become the industry standard for purification of any feed water source. They are used extensively for producing high-purity, low-conductivity process water. They are also used for producing ultrapure water from fresh water because RO is presumed to be the ultimate purifier.
Because RO filters are readily fouled by colloidal particles and biofilms, some method of prefiltration is used to protect them. Backwashable ultraporous membranes (UP) are used as prefilters in medium- and large-volume systems, and disposable nonwoven depth filters are used for smaller RO systems. Ionexchange resin and granular carbon beds are also used upstream of RO, but such prefilters are themselves often fouled by particulate contaminants such as humic and fulvic acids.
A multibarrier RO system has been developed by Kinetico–Pall for point-ofuse (POU) drinking water applications (1). That device passed the National Sanitary Foundation’s (NSF) certification to the Environmental Protection Agency’s (EPA) standards (2). A recent article showing data on POU systems suggests that RO is unreliable for removing bacteria to the EPA standard (3). The authors believe that leakage is due to minor flaws in the membrane. For POU applications, they propose using a small “high-flow” hollowfiber membrane postfilter.