Dow Water & Process Solutions,
Keywords: scale formation, reverse osmosis
Summary:In reverse osmosis, the ratio of treated water to the raw water supplied to the system is referred to as “recovery”. In recent years, there have been regulatory and economic pressures to increase recovery in several applications (e.g residential, industrial, and municipal). Formation of scale within reverse osmosis elements is one of the primary factors that can limit the maximum recovery obtainable. As species in the raw water are rejected by the membrane, their concentration is increased in elements, being a maximum at the reject-end of the system. Calculations based on different indices and equilibrium conditions are typically used to estimate the maximum recovery at which scale is avoided (without antiscalants), but any single constituent of moving feed water will exist within the RO system for less than a few minutes and the propensity for scale is also affected by local and dynamic conditions within an RO element. This talk describes various approaches to optimizing membrane, element, and system design that can be used to avoid scaling in RO systems. A testing method based on ICP measurements has been shown to be effective in evaluating incipient scale formation and in demonstrating differences in operating conditions and between aspects of different RO element designs.