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1.1 This practice covers the calculation and adjustment of silica (SiO₂) for the concentrate stream of a reverse osmosis system. The calculations are used to determine the need for scale control in the operation and design of reverse osmosis installations. This practice is applicable for all types of reverse osmosis devices (tubular, spiral wound, and hollow fiber).

1.2 This practice is applicable to both brackish waters and seawaters.

1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

5.1 In the design and operation of reverse osmosis installations, it is important to predict the SiO₂ scaling properties of the concentrate stream. Because of the increase in the concentration of SiO₂ and the change in pH, the scaling property of the concentrate stream will be quite different from that of the feed solution. This practice permits the calculation of the scaling potential for the concentrate stream from the feedwater analysis and the reverse osmosis operating parameters.

5.2 Scaling by SiO₂ will adversely affect the reverse osmosis performance. This practice gives various procedures for the prevention of scaling.

5.3 The presence of certain metals, for example, Al⁺³, may significantly alter the solubility of SiO₂ via formation of insoluble metal silicates. This practice does not address this phenomena.