1、Designation: D 3739 06Standard Practice forCalculation and Adjustment of the Langelier SaturationIndex for Reverse Osmosis1This standard is issued under the fixed designation D 3739; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 the concentrate
3、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. For concentrate c
4、ontaining over10 000 mg/L see Practice D 4582.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regul
5、atory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D511 Test Methods for Calcium and Magnesium In WaterD 1067 Test Methods for Acidity or Alkalinity of WaterD 1129 Terminology Relating to WaterD 1293 Test Methods for pH of WaterD 1888 Methods of Test for Particulate and Dissol
6、vedMatter in Water3D 4194 Test Methods for Operating Characteristics of Re-verse Osmosis and Nanofiltration DevicesD 4195 Guide for Water Analysis for Reverse OsmosisApplicationD 4582 Practice for Calculation and Adjustment of the Stiffand Davis Stability Index for Reverse OsmosisD 6161 Terminology
7、Used for Microfiltration, Ultrafiltra-tion, Nanofiltration and Reverse Osmosis Membrane Pro-cesses3. Terminology3.1 For definitions of terms used in this practice, refer toTerminology D 1129 and Terminology D 6161.3.2 Definitions of Terms Specific to This Standard:3.2.1 For descriptions of terms rel
8、ating to reverse osmosis,refer to Test Methods D 4194.3.2.2 Langelier Saturation Indexan index calculated fromtotal dissolved solids, calcium concentration, total alkalinity,pH, and solution temperature that shows the tendency of awater solution to precipitate or dissolve calcium carbonate.4. Summar
9、y of Practice4.1 This practice consists of calculating the Langelier Satu-ration Index for a reverse osmosis concentrate stream from thetotal dissolved solids, calcium ion content, total alkalinity, pH,and temperature of the feed solution, and the recovery of thereverse osmosis system.4.2 This pract
10、ice also presents techniques to lower theLangelier Saturation Index by decreasing the recovery, bydecreasing the calcium content of the feedwater, or by 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 os
11、mosis installa-tions, it is important to predict the calcium carbonate scalingproperties of the concentrate stream. Because of the increase intotal dissolved solids in the concentrate stream and the differ-ence in passages for calcium ion, bicarbonate ion, and freeCO2, the calcium carbonate scaling
12、properties of the concen-trate stream will generally be quite different from those of thefeed solution. This practice permits the calculation of the1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.08 on Membranes and IonExcha
13、nge Materials.Current edition approved Dec. 15, 2006. Published January 2007. Originallyapproved in 1978. Last previous edition approved in 2005 as D 3739 05.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of A
14、STMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.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 anal
15、yses and the reverse osmosis operating param-eters.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 T
16、he tendency to form CaCo3scale can be suppressed bythe 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 sys
17、tems. The RO system supplier should be consulted priorto 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 D511and express asCaCO3as de
18、monstrated in 6.6.6.2 Determine the total dissolved solids of the feed solutionusing Methods of Test D 1888.6.3 Determine the total alkalinity of the feed solution usingTest Methods D 1067, and express as CaCO3.6.4 Measure the pH of the feed solution using Test MethodsD 1293.6.5 Measure the temperat
19、ure of the feed solution.6.6 Convert feed water alkalinity 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,A
20、lkc= alkalinity in concentrate as CaCO3, mg/L, andAlkf= alkalinity in feed as CaCO3, mg/L.6.7 Measure the concentration of all major ions using themethods cited in Guide D 4195. At a minimum, measure theconcentration of Mg+,Na+,K+,SO4=, and Cl.7. Calculation7.1 Calculate the calcium concentration in
21、 the concentratestream from the calcium concentration 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
22、= recovery of the reverse osmosis system, ex-pressed 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 simp
23、lifies to:Cac5 Caf31/1 2 Y! (4)This assumption will introduce 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 foll
24、ows:TDSc5 TDSf31 2 YSPTDS!1 2 Y(5)where:TDSc= concentration 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 ad
25、ecimal.NOTE 2SPTDS can be obtained from the supplier 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
26、 the concentrate stream fromthe alkalinity in the feed 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 osmos
27、is system, expressedas a decimal, andSPalk= alkalinity 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 stre
28、am by assuming that the CO2concentration inthe concentrate 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.D 3739 062Cc5 0.03742 3 LnT
29、DSc! 0.0209 3 Temp 1 2.5 (8)7.4.1 Calculate the 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
30、 From Fig. 2 obtain: pCa as a function of Cac, 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 saturat
31、edwith CaCO3(pHs) as follows:pHs5 pCa 1 pAlk 1 “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 IndexD 3739 0638. Adjustments of LSIc8.1 If the LSIcis unacceptabl
32、e based on the suppliersrecommendation, adjustments 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 fee
33、dsolution by means of sodium cycle ion exchange (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 t
34、he lower value for calcium concentration.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 c
35、omputations are required to determinethe 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 firs
36、t computation can be made with anacidified 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 pe
37、r litre of acid used (x). For example, for 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 Usi
38、ng Alkacid,Cacid, and the suppliers value 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 sys
39、tem is operating, the Lange-lier Saturation 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 Interna
40、tional takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely th
41、eir own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should
42、 be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standa
43、rds, at the address shown below.This standard 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).D 3739 064
