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Over the course of the last 35 years, with the commercialization of reverse osmosis (RO),there has been a major shift in desalting technology away from evaporation and ionexchange as the sole processes to provide water suitable for drinking and industrial uses.However, for all its successes over the years, there are areas where RO is having difficulty, economically,meeting customer requirements. The problems can succinctly be narrowed to themembranes having inadequate rejection of weak inorganic and organic acids and silica.Weak inorganic acids such as boric acid are becoming increasingly a problem in drinkingwater. The drinking water boron specification has a provisional guideline by the World Health Organizationof 0.5 mg/L. In seawater RO, meeting this requirement is expensive and, in somecountries, such as Japan (1.0 mg/L specification) specialized unit operations arenecessary to meet the standard. Organic acids, such as total organic carbon (TOC) and haloacetic acid (HAA) compounds, can be present at hazardous levels in potable and wastewaters; they are known to beinadequately rejected by membranes, particularly if their molecular weights are low. Thesilica content of water used in super critical boilers and ultra pure water applications mustbe extremely low, in the parts per billion/trillion. Feed waters with high silica levels,existing in the southwest US, Latin America, China and elsewhere, are economicallydifficult to desalinate due to high energy consumption and inefficient utilization of sourcewater (poor conversions).In all these situations, technologies are available to reduce the levels of these compoundsto acceptable values; but there is a significant cost to the added processing steps. A newproprietary process has been developed, using well-established water chemistry, whichpermits very high rejections of these acids, including silica. The innovation involvesoperating a conditioned membrane system at high pH. This paper discusses the theoryand pretreatment of the water before it enters standard RO modules to achieve these lowcontaminant concentrations. The paper focuses on the excellent quality of the derivedpermeate by presenting case histories of the successful employment of the innovation.Future applications of the technology are also discussed. Includes 5 references, figures.

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Edition: Vol. - No. Published: 05/01/2001 Number of Pages: 13File Size: 1 file , 1.9 MB