Prefiltration is an important step in municipal water supply treatment systems.rnThe keystone in many of these systems is either granular media filters or membranes.rnThe Romans were using gravity media (sand) filters over two-thousand years ago torn"purify" drinking water. People were undoubtedly doing this well before written history.rnInterestingly, millennia later, granular media filters are still the most prominent treatmentrnfor drinking water. However, while early Romans needed to treat only a few thousandrngallons per day, today's a treatment facility often treats hundreds of millions of gallonsrndaily.rnReal estate can become a big issue with media filters as the price of land skyrocketsrnand needed water quantities rise. Little, other than brief sedimentation, is often used tornpretreat before media filters. As facilities cry for more volume through smallerrnfootprints, an unmet need is to remove much of the solids load before the media filters.rnIn recent years, membrane systems have become a popular means of treating water forrnpotable uses. Microfiltration, ultrafiltration, nanofiltration and reverse osmosis are allrnmembrane technologies that have found a place in water treatment. None of thesernmembrane systems can tolerate high suspended solids concentrations or large particlernsizes. Pretreatment is required to remove most non-dissolved solids. Cartridges arernappropriate technologies for this in some cases but their "commodity" status limits theirrneconomic optimization in many applications. Other pretreatment technologies arernnecessary to meet these needs.rnAsk the people in Tampa Bay, Florida how important pretreatment is to a reversernosmosis membrane system. Expensive re-designs, additional equipment costs andrndelays were incurred when pretreatment was improperly addressed.rnMore emphasis needs to be, and will be, placed upon pretreatment for potable waterrntreatment systems worldwide. Additional reasons for this emphasis will be addressed inrnthe paper along with some technologies to meet this unmet need.
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