1、Designation: D3739 06 (Reapproved 2010)Standard Practice forCalculation and Adjustment of the Langelier SaturationIndex for Reverse Osmosis1This standard is issued under the fixed designation D3739; the number immediately following the designation indicates the year oforiginal adoption or, in the ca
2、se of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the calculation and adjustment ofthe Langelier saturation index for t
3、he concentrate stream of areverse osmosis device. This index is used to determine theneed for calcium carbonate scale control in the operation anddesign of reverse osmosis installations. This practice is appli-cable for concentrate streams containing xx 10 to 10 000 mg/Lof total dissolved solids. Fo
4、r concentrate containing over10 000 mg/L see Practice D4582.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is ther
5、esponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D511 Test Methods for Calcium and Magnesium In WaterD1067 Test Methods for Acidity or Al
6、kalinity of WaterD1129 Terminology Relating to WaterD1293 Test Methods for pH of WaterD1888 Methods of Test for Particulate and Dissolved Mat-ter in Water3D4194 Test Methods for Operating Characteristics of Re-verse Osmosis and Nanofiltration DevicesD4195 Guide for Water Analysis for Reverse Osmosis
7、 andNanofiltration ApplicationD4582 Practice for Calculation and Adjustment of the Stiffand Davis Stability Index for Reverse OsmosisD6161 Terminology Used for Microfiltration, Ultrafiltra-tion, Nanofiltration and Reverse Osmosis Membrane Pro-cesses3. Terminology3.1 For definitions of terms used in
8、this practice, refer toTerminology D1129 and Terminology D6161.3.2 Definitions of Terms Specific to This Standard:3.2.1 For descriptions of terms relating to reverse osmosis,refer to Test Methods D4194.3.2.2 Langelier Saturation Indexan index calculated fromtotal dissolved solids, calcium concentrat
9、ion, total alkalinity,pH, and solution temperature that shows the tendency of awater solution to precipitate or dissolve calcium carbonate.4. Summary of Practice4.1 This practice consists of calculating the Langelier Satu-ration Index for a reverse osmosis concentrate stream from thetotal dissolved
10、solids, calcium ion content, total alkalinity, pH,and temperature of the feed solution, and the recovery of thereverse osmosis system.4.2 This practice also presents techniques to lower theLangelier Saturation Index by decreasing the recovery, bydecreasing the calcium content of the feedwater, or by
11、 chang-ing the ratio of total alkalinity to free carbon dioxide in thefeedwater.5. Significance and Use5.1 In the design and operation of reverse osmosis installa-tions, it is important to predict the calcium carbonate scalingproperties of the concentrate stream. Because of the increase intotal diss
12、olved solids in the concentrate stream and the differ-ence in passages for calcium ion, bicarbonate ion, and freeCO2, the calcium carbonate scaling properties of the concen-trate stream will generally be quite different from those of thefeed solution. This practice permits the calculation of the1Thi
13、s practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.08 on Membranes and IonExchange Materials.Current edition approved May 1, 2010. Published May 2010. Originallyapproved in 1978. Last previous edition approved in 2006 as D3739 06.
14、DOI:10.1520/D3739-06R10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version
15、 of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Langelier Saturation Index for the concentrate stream from thefeed water analyses and the reverse osmosis operating param-eters
16、.5.2 A positive Langelier Saturation Index indicates thetendency to form a calcium carbonate scale, which can bedamaging to reverse osmosis performance. This practice givesvarious procedures for the adjustment of the Langelier satura-tion index.5.3 The tendency to form CaCo3scale can be suppressed b
17、ythe addition of antiscalents or crystal modifiers. Suppliers ofantisealents and crystal modifiers can provide information onthe scale inhibition peformance of these types of chemical.Their use may be appropriate for reducing scale formation inRO systems. The RO system supplier should be consulted p
18、riorto the use of antisealents and crystal modifiers to ensure theywill not have a negative impact on the RO system.6. Procedure6.1 Determine the calcium concentration in the feed solu-tion in accordance with Test Methods D511 and express asCaCO3as demonstrated in 6.6.6.2 Determine the total dissolv
19、ed solids of the feed solutionusing Methods of Test D1888.6.3 Determine the total alkalinity of the feed solution usingTest Methods D1067, and express as CaCO3.6.4 Measure the pH of the feed solution using Test MethodsD1293.6.5 Measure the temperature of the feed solution.6.6 Convert feed water alka
20、linity and calcium as mg/LCaCO3:Caf5 Ca12# 3100gCaCo3mol31000mgg31eqCaCO31eqCa12(1)Alkf5 HCO3# 3100gCaCO3mol31000mgg31eqCaCO32eqHCO3(2)where:Cac= calcium concentration in concentrate as CaCO3,mg/L,Caf= calcium concentration in feed as CaCO3, mg/L,Alkc= alkalinity in concentrate as CaCO3, mg/L, andAl
21、kf= alkalinity in feed as CaCO3, mg/L.6.7 Measure the concentration of all major ions using themethods cited in Guide D4195. At a minimum, measure theconcentration of Mg+,Na+,K+,SO4=, and Cl.7. Calculation7.1 Calculate the calcium concentration in the concentratestream from the calcium concentration
22、 in the feed solution, therecovery of the reverse osmosis system, and the calcium ionpassage as follows:Cac5 Caf31 2 YSPCa!1 2 Y(3)where:Cac= calcium concentration in concentrate, as CaCO3,mg/L,Caf= calcium concentration in feed, as CaCO3, mg/L,Y = recovery of the reverse osmosis system, ex-pressed
23、as a decimal, andSPCa= calcium ion passage, expressed as a decimal.NOTE 1SPcacan be obtained from the supplier of the specific reverseosmosis system. For most reverse osmosis devices SPcacan be consideredto be zero, in which case the equation simplifies to:Cac5 Caf31/1 2 Y! (4)This assumption will i
24、ntroduce only a small error.7.2 Calculate the total dissolved solids (TDS) in the con-centrate stream from the total dissolved solids in the feedsolution, the recovery of the reverse osmosis system, and thepassage of total dissolved solids as follows:TDSc5 TDSf31 2 YSPTDS!1 2 Y(5)where:TDSc= concent
25、ration of total dissolved solids in con-centrate, mg/L,TDSf= concentration of total dissolved solids in thefeed, mg/L,Y = recovery of the reverse osmosis system, ex-pressed as a decimal, andSPTDS= passage of total dissolved solids, expressed as adecimal.NOTE 2SPTDS can be obtained from the supplier
26、of the specificreverse osmosis system. For most reverse osmosis devices SPTDS can beassumed to be zero, in which case the equation simplifies to:TDSc5 TDSf31/1 2 Y! (6)The error introduced will usually be negligible.7.3 Calculate the alkalinity in the concentrate stream fromthe alkalinity in the fee
27、d solution, the recovery of the reverseosmosis system, and the passage of alkalinity, by:Alkc5 Alkf31 2 YSPalk!1 2 Y(7)where:Alkc= alkalinity in concentrate, as CaCO3, mg/L,Alkf= alkalinity in feed, as CaCO3, mg/L,Y = recovery of the reverse osmosis system, expressedas a decimal, andSPalk= alkalinit
28、y passage, expressed as a decimal.NOTE 3SPalkis dependent on the pH of the feed solution and its valueshould be obtained from the supplier of the specific reverse osmosissystem.7.4 Calculate the free carbon dioxide content (C)intheconcentrate stream by assuming that the CO2concentration inthe concen
29、trate is equal to the CO2concentration in the feed:Cc=Cf. The concentration of free carbon dioxide in the feedsolution is obtained from Fig. 1 as a function of the alkalinity,temperature, and the pH of the feed solution.D3739 06 (2010)2Cc5 0.03742 3 LnTDSc! 0.0209 3 Temp 1 2.5 (8)7.4.1 Calculate the
30、 pH of the concentrate stream (pHc) usingthe ratio of alkalinity (from 7.3) to free CO2in the concentrate(from 7.4), Fig. 1, or use Eq 9.pHc 5 0.423 3 Ln Alkc/CO2c! (9)7.4.2 Calculate CO2fassuming CO2c=CO2f:Co2f5 Alkf3 expSpHf 6.3022!0.423D5 CO2c(10)7.5 From Fig. 2 obtain: pCa as a function of Cac,
31、pAlk as afunction of Alkc, or use Eq 8, Eq 11, and Eq 12.NOTE 4Temperature of concentrate is assumed equal to temperatureof feed solution.pCac5 0.4343 3 LnCac! 1 5(1)pAlkc5 0.45 3 LnAlkc! 1 4.8 (12)7.6 Calculate pH at which concentrate stream is saturatedwith CaCO3(pHs) as follows:pHs5 pCa 1 pAlk 1
32、“C” (13)7.7 Calculate the Langelier Saturation Index of the concen-trate (LSIc) as follows:LSIc5 pHc2 pHs(14)FIG. 1 pH Versus Methyl Orange Alkalinity/Free CO2FIG. 2 Langelier Saturation IndexD3739 06 (2010)38. Adjustments of LSIc8.1 If the LSIcis unacceptable based on the suppliersrecommendation, a
33、djustments can be made by one of thefollowing means. A new LSIccan then be calculated.8.1.1 The recovery (Y) can be lowered and the LSIccan becalculated as above by substituting a new value for therecovery.8.1.2 Decreasing the calcium concentration in the feedsolution by means of sodium cycle ion ex
34、change (softening)will increase the pCa and will therefore decrease the LSIc.Softening will not change the alkalinity or pH of the feedsolution and the slight change in TDSfmay be considerednegligible.After softening, the LSIccan be calculated as aboveusing the lower value for calcium concentration.
35、8.1.3 Adding acid (HCl, CO2,H2SO4, etc.) to the feedsolution changes the Alkf,Cf, pH, and SPalk. The slight changein TDSfcan usually be neglected. Acid addition will decreasethe LSIc; however, since many variables change with acidifi-cation, trial and error computations are required to determinethe
36、amount of acid needed to obtain the desired LSIc. Thenumber of trial and error computations required to determinethe amount of acid needed can be reduced greatly by using thepHscalculated in 7.6. Since pHcwill usually be 0.5 units higherthan the pHf, the first computation can be made with anacidifie
37、d feed solution which is 0.5 unit lower than the pHscalculated in 7.6.8.1.3.1 For an assumed pH (pHacid), obtained from additionof acid to the feed solution, obtain the ratio of Alkacid/Cacidfrom Fig. 1. From this ratio, Alkf, and Cfcalculate themilligrams per litre of acid used (x). For example, fo
38、r H2SO4addition (100 %):AlkacidCacid5Alkf2 1.02xCf1 0.90x(15)8.1.3.2 Calculate the total alkalinity of the acidified feed-water (Alkacid) and the CO2content in the acidified feedwater(Cacid) as follows:Alkacid5 Alkf2 1.02x (16)Cacid5 Cf1 0.90x (17)8.1.3.3 Using Alkacid,Cacid, and the suppliers value
39、 forSPalkfor the new pH, calculate the LSIcin accordance withSection 7.8.1.3.4 If HCl (100 %) is used for acidification, the Eq 15 is:AlkacidCacid5Alkf2 1.37yCf1 1.21y(18)where:y = HCI (100%), mg/L.9. Reverse Osmosis in Operation9.1 Once a reverse osmosis system is operating, the Lange-lier Saturati
40、on Index can be directly calculated from theanalysis of Alkc,Cac, TDSc, and pHcof the concentrate streamand compared with the projected LSIccalculated in Section 7.10. Keywords10.1 CaCO3scale; Langelier Saturationndex; LSI; reverseosmosis; scalingASTM International takes no position respecting the v
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44、dard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D3739 06 (2010)4
