Method and apparatus for high efficiency reverse osmosis operation

Abstract

A process for treatment of water via membrane separation equipment. Hardness and non-hydroxide alkalinity are removed from feedwaters to very low levels, preferably by simultaneous removal in a weak acid cation ion exchange resin. Then, ionization of sparingly ionizable components in the feedwater is substantially accomplished by increasing the pH of the feedwater preferably up to about pH 10.5, or higher. In this manner, species such as silica become highly ionized, and (a) their rejection by the membrane separation process is significantly increased, and (b) their solubility in the reject stream from the membrane process is significantly increased. Passage of weakly ionized species such as boron, silica, and TOC is reduced by a factor of ten or more. Recovery ratio of ninety percent (90%) or higher is achievable with most brackish feedwaters, while simultaneously achieving a substantial reduction in cleaning frequency. The method is particularly useful for the preparation of high purity water. Although the silica level in the reject water in this process is increased from the conventional range of approximately 150 ppm to a level of 450 ppm or better (thus increasing recovery rates), significantly improved levels of silica contamination in the ion-exchanged polished permeate are achieved. New Ultra Pure Water (UPW) systems utilizing this process will have thirty to fifty percent lower capital costs and at least twenty five percent lower operating costs compared to conventional UPW systems.