Enhancing RO system performance utilizing antiscalants

Abstract

When using reverse osmosis (RO), spraying soluble salts, such as calcium carbonate or barium sulfate, having a very low solubility limit, constitute a very specific potential of scaling the membrane surface. Due to the removal of permeate, the salt concentration of the retentate stream increases along the RO module's length. RO systems operating at high recoveries may experience high levels of sparingly soluble salts in the concentrating retentate. If the solubility limits of these salts are exceeded, salts precipitation starts. Evidently scale formation on the membrane surface has a detrimental effect on both permeate flux and quality. In practice, the deposition of scales at the RO membrane surface is prohibited by adding antiscalants to the feed. In the present work it has been attempted to introduce a simple model for arriving at the maximum feasible recovery as constrained by the chemical analysis of the saline feed water under consideration, its temperature, the level of the concentration polarization experienced within the RO system, and the ever improving performance achievable through the continuous development of RO antiscalants. However, for the optimal operation of the RO system the proper dosage of the respective antiscalants as a function of the system recovery will continue to add to the subject complexity and is subject to some discussions with the antiscalants suppliers. During RO, adequate antiscalant dosing at proper pH and pretreatment conditions will contribute considerably to the optimal utilization of the performance capabilities of RO membranes in terms of permeate flux and quality. The recommended model as presented in this work is aimed to be an important and convenient step towards the realization of the abovementioned objectives and hence the cost effective production of desalted water.