ASTM D4993 - 08(2014)

    Standard Practice for Calculation and Adjustment of Silica (SiO2) Scaling for Reverse Osmosis

    Active Standard ASTM D4993 | Developed by Subcommittee: D19.08

    Book of Standards Volume: 11.02


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    Significance and 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.

    1. Scope

    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.


    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    D859 Test Method for Silica in Water

    D1067 Test Methods for Acidity or Alkalinity of Water

    D1129 Terminology Relating to Water

    D1293 Test Methods for pH of Water

    D3739 Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis

    D4194 Test Methods for Operating Characteristics of Reverse Osmosis and Nanofiltration Devices

    D6161 Terminology Used for Microfiltration, Ultrafiltration, Nanofiltration and Reverse Osmosis Membrane Processes


    ICS Code

    ICS Number Code 71.060.20 (Oxides)

    UNSPSC Code

    UNSPSC Code 12352309(Silica)


    DOI: 10.1520/D4993

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