ASTM D4993-89(2003)
(Practice)Standard Practice for Calculation and Adjustment of Silica (SiO2) Scaling for Reverse Osmosis
Standard Practice for Calculation and Adjustment of Silica (SiO<sub>2</sub>) Scaling for Reverse Osmosis
SIGNIFICANCE AND USE
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.
Scaling by SiO2 will adversely affect the reverse osmosis performance. This practice gives various procedures for the prevention of scaling.
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.
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 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.
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Designation:D4993–89(Reapproved2003)
Standard Practice for
Calculation and Adjustment of Silica (SiO ) Scaling for
Reverse Osmosis
This standard is issued under the fixed designation D 4993; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope the concentration of SiO in the feed solution and the recovery
of the reverse osmosis system.
1.1 This practice covers the calculation and adjustment of
4.2 This practice also presents techniques to eliminate
silica (SiO ) for the concentrate stream of a reverse osmosis
scaling by decreasing the recovery, decreasing the SiO con-
system. The calculations are used to determine the need for 2
centration in the feedwater, adjusting the pH of the feedwater,
scale control in the operation and design of reverse osmosis
and increasing the temperature of the feedwater.
installations. This practice is applicable for all types of reverse
osmosis devices (tubular, spiral wound, and hollow fiber).
5. Significance and Use
1.2 This practice is applicable to both brackish waters and
5.1 In the design and operation of reverse osmosis installa-
seawaters.
tions, it is important to predict the SiO scaling properties of
1.3 This standard does not purport to address all of the
the concentrate stream. Because of the increase in the concen-
safety concerns, if any, associated with its use. It is the
tration of SiO and the change in pH, the scaling property of
responsibility of the user of this standard to establish appro-
the concentrate stream will be quite different from that of the
priate safety and health practices and determine the applica-
feed solution. This practice permits the calculation of the
bility of regulatory limitations prior to use.
scaling potential for the concentrate stream from the feedwater
2. Referenced Documents analysis and the reverse osmosis operating parameters.
5.2 Scaling by SiO will adversely affect the reverse osmo-
2.1 ASTM Standards:
sis performance. This practice gives various procedures for the
D 859 Test Method for Silica in Water
prevention of scaling.
D 1067 Test Methods for Acidity or Alkalinity of Water
+3
5.3 The presence of certain metals, for example, Al , may
D 1129 Terminology Relating to Water
significantly alter the solubility of SiO via formation of
D 1293 Test Methods for pH of Water
insoluble metal silicates. This practice does not address this
D 3739 Practice for Calculation and Adjustment of Lange-
phenomena.
lier Saturation Index for Reverse Osmosis
D 4194 Test Methods for Operating Characteristics of Re-
6. Procedure
verse Osmosis and Nanofiltration Devices
6.1 Determine the concentration of SiO in the feed stream
3. Terminology in accordance with Test Method D 859.
6.2 Measure the temperature of the feed solution.
3.1 For definitions of terms relating to water used in this
6.3 Measure the pH of the feed solution using Test Methods
practice, refer to Terminology D 1129. For terms relating to
D 1293.
reverse osmosis, refer to Test Methods D 4194.
NOTE 1—If acid is used for control of CaCO scale, measure the pH
4. Summary of Practice
after acid addition.
4.1 This practice consists of calculating the potential for
6.4 Determine the total alkalinity of the feed solution using
scaling by SiO in a reverse osmosis concentrate stream from
Test Methods D 1067 and express as CaCO .
NOTE 2—If acid is used for control of calcium carbonate (CaCO )
This practice is under the jurisdiction of ASTM Committee D19 on Water and scale, determine the total alkalinity after acid addition.
is the direct responsibility of Subcommittee D19.08 on Membranes and Ion
Exchange Materials.
Current edition approved June 10, 2003. Published August 2003. Originally
e1
approved in 1989. Last previous edition approved in 1998 as D 4993 – 89 (1998) .
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 11.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4993–89 (2003)
FIG. 1 Solubility of SiO vs. Temperature
7. Calculation
7.1 Calculate the SiO concentration in the concentrate
stream from the SiO concentration in the feed solution, the
recovery of the reverse osmosis system, and the SiO passage
as follows: FIG. 2 SiO pH Correction Factor
1 2 Y SP !
~
SiO2
SiO 5 SiO 3
2c 2f
1 2 Y
7.5 Calculate the solubility of SiO corrected for pH
(SiO ) by multiplying the solubility of SiO obtained in 7.3
2corr. 2
by the pH correction factor obtained in 7.4.
where:
7.6 Compare the silica concentration in the concentrate
SiO = silica concentration in concentrate as SiO ,
2c 2
(SiO ) obtained in 7.1 with the silica solubility (SiO )
2c 2corr.
mg/L,
obtained in 7.5.IfSiO is greater than SiO , silica scaling
SiO = silica concentratio
...
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