CEE April-June 2012

The main functions of UF membranes that underpin its advantages in RO pretreatment are described below: • Effectively removes all the suspended solids (TSS) from the RO feed-water due to sufficiently small pore size of membranes. • Effectively removes bacteria, silicates, colloids, organics, pathogens and viruses, all of which often cannot be effectively removed by conventional pre-treatment or even with microfiltration. • Results in an SOl value of the RO feed water always being less than 3 and turbidity being always less than 1, which is also the standard requirement of the RO feed. • Lower SOl and turbidity translates into lower RO feed pressure, thus saving on electricity costs. • Lower SOl also results in less frequent RO Cleani ng, which translates into chemical cost savings and a lengthened lifespan of the RO membrane. Special features In addition to the regular advantages that the UF membrane brings to the pre-treatment process, Hyflux Kristal® membranes have several additional features that provide it with an edge. Kristal is a polymeric hollow fiber membrane made of specially formulated modified and hydrophilic polyethersulfone (PES). This feature delivers reduced fouline when handli ng streams of very high suspended solid organic content, and an ultra-thin skin built above Kristal's porous substrate allows it to achieve both high water flux and mechanical strength. It also has a simple, modular and compact design that enables it to provide a larger membrane area per unit volume at a smaller foot print size for lower capital and installation costs. Knstal Hollow F 1bre Membrane C ross-section Figure I: Kristaf'Y Hollow Fiber Membrane Cross-Section Furthermore, its out-to-in and cross-flow configuration reduces the challenges posed by fouling on the UF membrane itself, which improves the performance and lengthens the life of the UF membranes. The out– to-in configuration means that the feed stream flows on the outside of the membrane with the filtrate flowing through to the inside of the fibers. This means that unlike an in-to-out filtration , where feed-water is introduced into the fibers, each of which sometimes being as fine as single strand of hai r, there is no possibility of entire fibers being irrecoverable choked due to foul ants present in the feed-water. IN-TO-OUT Figure 1: Out- To-In & In- To Out Cross-Flow Configuration 31