ASTM D4582-23

Standard Practice for Calculation and Adjustment of the Stiff and Davis Stability Index for Reverse Osmosis

SIGNIFICANCE AND USE
5.1 In the design and operation of reverse osmosis installations, it is important to predict the calcium carbonate scaling properties of the concentrate stream. Because of the increase in total dissolved solids in the concentrate stream and the differences in salt passages for calcium ion, bicarbonate ion, and free CO2, the calcium carbonate scaling properties of the concentrate stream will generally be quite different from those of the feed solution. This practice permits the calculation of the S & DSI for the concentrate stream from the feed water analyses and the reverse osmosis operating parameters.  
5.2 A positive S & DSI indicates the tendency to form a calcium carbonate scale, which can be damaging to reverse osmosis performance. This practice gives procedures for the adjustment of the S & DSI.
SCOPE
1.1 This practice covers the calculation and adjustment of the Stiff and Davis Stability Index (S & DSI) for the concentrate stream of a reverse osmosis device. This index is used to determine the need for calcium carbonate scale control in the operation and design of reverse osmosis installations. This practice is applicable for concentrate streams containing more than 10 000 mg/L of total dissolved solids. For concentrate streams containing less than 10 000 mg/L of total dissolved solids, refer to Practice D3739.  
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Jun-2023
• ICS: 71.120.99 - Other equipment for the chemical industry
• Technical Committee: D19 - Water
• Drafting Committee: D19.08 - Membranes and Ion Exchange Materials

Relations

• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D6161-19 - Standard Terminology Used for Microfiltration, Ultrafiltration, Nanofiltration, and Reverse Osmosis Membrane Processes
• Effective Date: 01-Jul-2019
• Refers: ASTM D3739-19 - Standard Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis
• Effective Date: 01-Jul-2019
• Refers: ASTM D1293-12 - Standard Test Methods for pH of Water
• Effective Date: 01-Jan-2012
• Refers: ASTM D3739-06(2010) - Standard Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis (Withdrawn 2019)
• Effective Date: 01-May-2010
• Refers: ASTM D1129-10 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2010
• Refers: ASTM D6161-10 - Standard Terminology Used for Microfiltration, Ultrafiltration, Nanofiltration and Reverse Osmosis Membrane Processes (Withdrawn 2019)
• Effective Date: 01-Feb-2010
• Refers: ASTM D511-09 - Standard Test Methods for Calcium and Magnesium In Water
• Effective Date: 01-May-2009
• Refers: ASTM D511-08 - Standard Test Methods for Calcium and Magnesium In Water
• Effective Date: 01-Oct-2008
• Refers: ASTM D4195-08 - Standard Guide for Water Analysis for Reverse Osmosis and Nanofiltration Application
• Effective Date: 01-May-2008
• Refers: ASTM D4194-03(2008) - Standard Test Methods for Operating Characteristics of Reverse Osmosis and Nanofiltration Devices
• Effective Date: 01-May-2008
• Refers: ASTM D1067-06 - Standard Test Methods for Acidity or Alkalinity of Water
• Effective Date: 15-Dec-2006
• Refers: ASTM D3739-06 - Standard Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis
• Effective Date: 15-Dec-2006
• Refers: ASTM D1129-06a - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D1129-06ae1 - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006

Overview

ASTM D4582-23 is the Standard Practice for Calculation and Adjustment of the Stiff and Davis Stability Index (S & DSI) for Reverse Osmosis. Developed by ASTM International, this standard provides guidance for assessing and controlling calcium carbonate scaling in the concentrate streams of reverse osmosis (RO) installations, particularly those handling high total dissolved solids (TDS) concentrations. By enabling the calculation and adjustment of the S & DSI, the standard assists designers and operators to optimize system performance, minimize scaling-related damage, and ensure the longevity and efficiency of RO membranes.

Key Topics

• Calcium Carbonate Scaling Prediction
  The standard outlines methods to calculate the tendency of a RO concentrate stream to form calcium carbonate scale, a critical consideration for system operation.

• Stiff and Davis Stability Index Calculation
  Procedures are given for computing the S & DSI using feed water analysis and RO operating parameters. The index is specifically tailored for concentrate streams with TDS greater than 10,000 mg/L, which are typical in seawater desalination and certain industrial applications.

• Adjustment Procedures
  ASTM D4582-23 presents actionable steps for adjusting the S & DSI. These include lowering system recovery, modifying calcium and alkalinity concentrations, or adjusting the alkalinity-to-CO₂ ratio, thereby reducing scaling risk.

• Applicability
  This practice is intended for RO systems treating water with high dissolved solids. For systems with lower TDS levels, users are directed to ASTM Practice D3739.

• Terminology and Units
  The standard uses SI units as its default and provides clear definitions for all relevant chemical and operational terms, ensuring consistency and clarity.

Applications

• Reverse Osmosis Design and Operation
  Engineering teams use this standard when designing new RO installations or optimizing existing systems, ensuring that scaling tendencies are adequately controlled to protect membrane integrity and system performance.

• Water Treatment Facilities
  Facilities engaged in seawater desalination, brackish water treatment, or industrial process water purification benefit from standardized procedures to prevent scale buildup and associated maintenance issues.

• Operational Troubleshooting
  Operators can use the S & DSI calculations prescribed in ASTM D4582-23 as part of troubleshooting protocols to quickly identify and remedy scaling risks.

• Regulatory Compliance and Reporting
  The standard supports environmental and quality compliance efforts by providing a recognized method for documenting water chemistry and operational parameters in high-TDS applications.

Related Standards

• ASTM D3739: Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis - for applications with less than 10,000 mg/L TDS.
• ASTM D511: Test Methods for Calcium and Magnesium in Water - referenced for analytical procedures.
• ASTM D1067: Test Methods for Acidity or Alkalinity of Water.
• ASTM D1129: Terminology Relating to Water.
• ASTM D1293: Test Methods for pH of Water.
• ASTM D1888: Methods of Test for Particulate and Dissolved Matter in Water.
• ASTM D4194 & D4195: Related to the operational characteristics of RO and analytical methodologies.

Practical Value

Implementing ASTM D4582-23 ensures reliable calculation and adjustment of scaling indices in high-TDS reverse osmosis systems, directly supporting asset protection and process efficiency. By adhering to standardized calculations for the Stiff and Davis Stability Index, water treatment professionals can better predict, monitor, and control calcium carbonate scale formation, thereby minimizing downtime, reducing costs, and extending the life of critical equipment.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D4582 − 23
Standard Practice for
Calculation and Adjustment of the Stiff and Davis Stability
Index for Reverse Osmosis
This standard is issued under the fixed designation D4582; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope in Water (Withdrawn 1989)
D3739 Practice for Calculation and Adjustment of the Lan-
1.1 This practice covers the calculation and adjustment of
gelier Saturation Index for Reverse Osmosis
the Stiff and Davis Stability Index (S & DSI) for the concen-
D4194 Test Methods for Operating Characteristics of Re-
trate stream of a reverse osmosis device. This index is used to
verse Osmosis and Nanofiltration Devices
determine the need for calcium carbonate scale control in the
D4195 Guide for Water Analysis for Reverse Osmosis and
operation and design of reverse osmosis installations. This
Nanofiltration Application
practice is applicable for concentrate streams containing more
D6161 Terminology Used for Microfiltration, Ultrafiltration,
than 10 000 mg ⁄L of total dissolved solids. For concentrate
Nanofiltration, and Reverse Osmosis Membrane Processes
streams containing less than 10 000 mg ⁄L of total dissolved
solids, refer to Practice D3739.
3. Terminology
1.2 The values stated in SI units are to be regarded as
3.1 Definitions—For definitions of terms used in the
standard. The values given in parentheses after SI units are
practice, refer to Terminologies D1129 and D6161.
provided for information only and are not considered standard.
3.2 Definitions of Terms Specific to This Standard:
1.3 This standard does not purport to address all of the
3.2.1 alkalinity, n—the quantitative capacity of aqueous
safety concerns, if any, associated with its use. It is the
media to react with hydrogen ions; “M” alkalinity is that which
responsibility of the user of this standard to establish appro-
will react with acid as the pH of the sample is reduced to the
priate safety, health, and environmental practices and deter-
methylorange endpoint of about 4.5; “P” alkalinity is that
mine the applicability of regulatory limitations prior to use.
which reacts with acid as the pH of the sample is reduced to the
1.4 This international standard was developed in accor-
phenolphthalein end point of 8.3; “M” is the total alkalinity
dance with internationally recognized principles on standard-
which is the sum of hydroxide, carbonate, and bicarbonate
ization established in the Decision on Principles for the
contents and “P” includes all the hydroxyl and half the
Development of International Standards, Guides and Recom-
carbonate content.
mendations issued by the World Trade Organization Technical
3.2.2 calcium carbonate equivalents (mg/L as CaCO ), n—a
Barriers to Trade (TBT) Committee.
method for expressing mg/L as ion in terms of calcium
carbonate; concentration in calcium carbonate equivalents is
2. Referenced Documents
calculated by multiplying concentration in mg/L of the ion by
2.1 ASTM Standards:
the equivalent weight of calcium carbonate (50) and dividing
D511 Test Methods for Calcium and Magnesium In Water
by the equivalent weight of the ion.
D1067 Test Methods for Acidity or Alkalinity of Water
3.2.3 concentrate, n—the stream exiting a crossflow mem-
D1129 Terminology Relating to Water
brane device which has increased concentration of solutes and
D1293 Test Methods for pH of Water
particles over the feed stream; portion of the feed stream which
D1888 Methods Of Test for Particulate and Dissolved Matter
does not pass through the membrane; the stream in which
dissolved solids or particulates, or both, are concentrated in a
1 membrane separation process.
This practice is under the jurisdiction of ASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.08 on Membranes and Ion
3.2.4 feed water, n—that water entering a device or process.
Exchange Materials.
3.2.5 ionic strength, n—measure of the overall electrolytic
Current edition approved June 15, 2023. Published July 2023. Originally
approved in 1986. Last previous edition approved in 2010 as D4582 – 10 which was
potential of a solution, the strength of a solution based on both
withdrawn January 2019 and reinstated in June 2023. DOI: 10.1520/D4582-23.
the concentrations and valencies of the ions present.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4582 − 23
3.2.6 molality (− m1), n—moles (gram molecular weight) of 6. Procedure
solute per 1000 g of solvent.
6.1 Determine the calcium concentration in the feed solu-
3.2.7 pH, n—negative logarithm of the effective hydrogen-
tion in accordance with Test Methods D511 and express as
ion activity, approximately –log10 [H+] where [H+] is equiva-
CaCO as demonstrated in 6.6.
lents per litre concentration.
6.2 Determine the total dissolved solids of the feed solution
3.2.8 recovery—Y (conversion), n—the ratio of product
using Test Methods D1888.
quantity (permeate stream flow rate) over the feed quantity
6.3 Determine the total alkalinity of the feed solution using
(feed stream flow rate), given as fraction or in percent.
Test Methods D1067 and express as CaCO .
3.2.9 reverse osmosis (RO), n—the separation process
6.4 Measure the pH of the feed solution using Test Methods
where one component of a solution is removed from another
D1293.
component by flowing the feed stream under pressure across a
semipermeable membrane that causes selective movement of
6.5 Measure the temperature of the feed solution.
solvent against its osmotic pressure difference; RO removes
6.6 Convert feed water alkalinity and calcium as mg/L
ions based on electro chemical forces, colloids, and organics
CaCO .
down to 150 molecular weight.
100gCaCO 1000 mg 1eqCaCO
3.2.9.1 Discussion—May also be called hyperfiltration.
3 3
Ca 5 @Ca # × × × (1)
f 12
mol g 1eqCa
3.2.10 saturation, n—the point at which a solution contains
100gCaCO 1000mg 1eqCaCO
enough of a dissolved solid, liquid, or gas so that no more will
3 3
Alk 5 HCO × × × (2)
@ #
f 3 2
mol g 2eqHCO
dissolve into the solution at a given temperature and pressure.
3.2.11 Stiff & Davis stability index, S & DSI , n—an index
where:
calculated from total dissolved solids, calcium concentration,
Ca = calcium concentration in feed as CaCO , mg/L, and
f 3
total alkalinity, pH, and solution temperature that shows the
Alk = alkalinity in feed as CaCO , mg/L.
f 3
tendency of a water solution to precipitate or dissolve calcium
6.7 Measure the concentration of all major ions using the
carbonate.
methods cited in Guide D4195. At a minimum, measure the
3.2.11.1 Discussion—S & DSI is used primarily for seawa-
+ + + + −
concentration of Mg , Na , K , SO , and Cl .
ter RO applications. See Practice D4582 and D3739.
4. Summary of Practice
7. Calculation
4.1 This practice consists of calculating the S & DSI for a
7.1 Calculate the calcium concentration in the concentrate
reverse osmosis concentrate stream from the total dissolved
stream from the calcium concentration in the feed solution, the
solids, calcium ion content, total alkalinity, pH, and tempera-
recovery of the reverse osmosis system, and the calcium ion
ture of the feed solution and the recovery of the reverse
passage as follows:
osmosis system.
1 2 Y SP
~ !
Ca
Ca 5 Ca × (3)
S D
c f
4.2 This practice also presents techniques to lower the S &
1 2 Y
DSI by decreasing the recovery; decreasing the calcium and
where:
alkalinity concentrations; or by changing the ratio of total
Ca = calcium concentration in concentrate as CaCO ,
alkalinity to free carbon dioxide in the feedwater. c 3
mg/L,
5. Significance and Use Ca = calcium concentration in feed as CaCO , mg/L,
f 3
Y = recovery of the reverse osmosis system, expressed as
5.1 In the design and operation of reverse osmosis
a decimal between 0 and 1, and
installations, it is important to predict the calcium carbonate
SP = calcium ion passage, expressed as a decimal.
Ca
scaling properties of the concentrate stream. Because of the
NOTE 1—SP can be obtained from the supp
...