1、Designation: D1291 16D1291 17Standard Practice forEstimation of Chlorine Demand of Water1This standard is issued under the fixed designation D1291; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、 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 provides a means of estimating the quantity of chlorine required to be added to a unit volume of water toaccomplish a predeterm
3、ined treatment objective or to completely react with all chlorine reactable substances in the water, or both.1.2 Temperature, pH, and initial chlorine dosage are all variables in estimating the optimum chlorination practice. The effectsof these variables can be evaluated using this practice.1.3 Chlo
4、rine residual is determined using Test Method D1253.1.4 This practice is applicable to all types of water in which the stated treatment objective can be evaluated or residual chlorinecan be measured, or both.1.5 The values stated in SI units are to be regarded as standard. No other units of measurem
5、ent are included in this standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitati
6、ons prior to use. For a specific hazard statement, see 7.5.1.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD1253 Test Method for Residual Chlorine in WaterD1293 Test Methods for pH of WaterD3370 Practices for Sampling Water from Cl
7、osed Conduits3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard, see Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 chlorine demand, nthe amount of chlorine that must be added to a unit volume of water under specified conditions ofpH, tempe
8、rature, and contact time to completely react with all chlorine-reactable substances in the water.3.2.1.1 DiscussionIt is defined as the difference between the amount of chlorine applied and the amount of free chlorine remaining at the end of thecontact period.3.2.2 chlorine requirement, nthe amount
9、of chlorine that must be added to a unit volume of water under specified conditionsof pH, temperature, and contact time to achieve the objectives of chlorination.1 This practice is under the jurisdiction ofASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.03 on Samplin
10、g Water and Water-FormedDeposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water.Current edition approved Feb. 15, 2016Feb. 1, 2017. Published March 2016February 2017. Originally approved in 1953. Last previous edition approved in 20112016 a
11、sD1291 06 (2011).D1291 16. DOI: 10.1520/D1291-16.10.1520/D1291-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM web
12、site.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prio
13、r editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Practice4.1 Known amounts of
14、chlorine are added to a series of 500 mL aliquots of sample. The treated sample aliquots are permittedto stand for a specified contact time (or a variety of different specified contact times) under specified conditions of pH andtemperature. At the end of the contact time, the sample aliquots are eit
15、her analyzed for chlorine content by Test Method D1253or subjected to whatever evaluative technique is required to establish accomplishment of the treatment objective, or both.5. Significance and Use5.1 Chlorine is added to potable water, waste water, and industrial water for a variety of purposes.
16、Some of these purposes are:5.1.1 To eliminate or reduce the growth of microorganisms in water,5.1.2 To destroy or modify decomposable organic substances so as to reduce the biochemical oxygen demand of the water,5.1.3 To eliminate or reduce taste, odors, and color in the water,5.1.4 To separate grea
17、se in waste water by eliminating the protective colloidal effect of proteins present, and5.1.5 To destroy or modify substances in the waste water that react directly by oxidation, such as ammonia, cyanates, cyanides,ferrous iron, nitrites, phenol, phosphorus, sulfides, sulfites, thiocyanates, and ot
18、her oxidizable constituents.5.2 It is important to avoid over-chlorination in order to minimize chemical consumption, meet restrictions specified byregulatory agencies, and minimize equipment degradation.6. Apparatus6.1 All of the apparatus listed in Test Methods D1293 and D1253 may be required. Any
19、 other apparatus necessary to carry outthe final evaluation of the effects of chlorination will be required.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to the specificatio
20、ns of the Committee on Analytical Reagents of the American Chemical Society, wheresuch specifications are available. 3 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently highpurity to permit its use without lessening the accuracy of the determination.7.2 P
21、urity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water conforming toSpecification D1193, Type III, which has been rendered chlorine demand-free. Chlorine demand can be removed by treating withexcess chlorine and allowing this treated solution to stand
22、 in sunlight for several hours to destroy the chlorine residuals. TestMethod D1253 may be used to assure complete destruction of these residuals.7.3 Acetic Acid Solution (1 + 1)Mix equal volumes of glacial acetic acid and water.7.4 Calcium Hydroxide Solution (10.7 g/L)Weigh 10.7 g of 100 % hydrated
23、lime, Ca(OH)2, and suspend in water. Dilute thesuspension to 1 L. Shake well each time before using.7.5 Chlorine Solution, StandardPrepare one of the standard solutions described in 7.5.1 and 7.5.2; standardize as describedin 7.5.3.7.5.1 Chlorine WaterPass chlorine gas through reagent water until th
24、e solution contains from 0.5 to 10.0 mg/L Cl2.(WarningUse a slow rate of addition and carry out the operation under a hood. Store in a glass stoppered amber bottle andstandardize daily before use.)7.5.2 Sodium Hypochlorite Solution, StandardDilute a commercial sodium hypochlorite or bleach solution
25、containing 10 to100 g of available chlorine per litre with water to provide a solution containing from 0.5 to 10 mg available chlorine per litre,depending upon the maximum expected chlorine requirement for the sample. This solution must be standardized before use.7.5.3 Standardize the chlorine water
26、 or sodium hypochlorite solution, standard, as follows:7.5.3.1 Transfer 10 mL of the solution to be standardized to a porcelain dish.7.5.3.2 Add 10 mL of acetic acid (1 + 1) (see 7.3) and 10 mL of potassium iodide solution (see 7.8).7.5.3.3 Titrate with sodium thiosulfate solution (0.10 N) (see 7.11
27、) until the yellow color of the liberated iodine is almostdischarged.7.5.3.4 Add 1 mL of starch indicator solution (see 7.12) and continue the titration to a colorless endpoint.7.5.3.5 Calculate the concentration of available chlorine as follows:Available chlorine,mg/mL5A3B335.45C3 Reagent Chemicals
28、, American Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalF
29、ormulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville, MD.D1291 172where:A = sodium thiosulfate solution, standard, mL,B = normality of sodium thiosulfate solution, standard, andC = chlorine solution titrated, mL.7.6 Hydrochloric Acid (1 + 1)Mix equal volumes of concentrated HCl (sp gr 1.
30、19) and water.7.7 Potassium Dichromate Solution (0.100 N)Dissolve 4.904 g of anhydrous potassium dichromate (K2Cr2O7) of primarystandard quality in water and dilute to 1000 mL in a volumetric flask.7.8 Potassium Iodide Solution (50 g/L)Dissolve 50 g of potassium iodide (KI) in 1 L of freshly boiled
31、and cooled water.Add1 g of sodium bicarbonate (NaHCO3) to stabilize the solution. Store in an amber bottle and avoid direct exposure to sunlight.7.9 Sodium Hydroxide Solution (10 g/L)Dissolve 10 g of sodium hydroxide (NaOH) in water and dilute to 1 L.(WarningHeat is generated when dissolving sodium
32、hydroxide in water.)7.10 Sodium Thiosulfate Solution, Standard (0.10 N)Transfer 25 g of sodium thiosulfate pentahydrate (Na2S2O35H2O) to a 1-L volumetric flask containing about 800 mL water. Dissolve the compound in the water by shaking and periodicinversion. Add 1 g of sodium carbonate (Na2CO3) and
33、 dissolve. Dilute the solution to 1 L with water.7.10.1 Standardize the sodium thiosulfate solution: Add 70 mL of water to a porcelain dish, and add, with constant stirring, 1mL of concentrated sulfuric acid (H2SO4), 10.0 mL of 0.100 N K2Cr2O7, and 20 mL of potassium iodide solution (see 7.8). Permi
34、tthe reaction mixture to stand in the dark for about six minutes. Then titrate with the sodium thiosulfate solution until the yellowcolor of the liberated iodine is almost discharged. Add 1 mL of starch indicator solution (see 7.12) and continue the titration toa colorless endpoint.7.10.1.1 The norm
35、ality can be calculated as:Normality,Na2S2O35 1Na2S2O3 required in titration,mL7.10.1.2 Perform this standardization in triplicate and average the results.7.11 Starch Indicator SolutionMake a paste of 1 g of soluble starch and mix into 1 L of boiling water. Then, add 20 g ofpotassium hydroxide (KOH)
36、, mix thoroughly, and allow to stand for 2 h.Add 6 mLof glacial acetic acid (99.5 %). Mix thoroughlyand then add sufficient HCl (sp gr 1.19) to adjust the pH value of the solution to 4.0. Store in a glass-stoppered bottle. Starchsolution prepared in this manner will remain chemically stable for 1 ye
37、ar.7.12 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid (H2SO4).8. Sampling8.1 Collect the sample in accordance with Practices D3370.8.2 Conduct the test immediately following collection of the samples.9. ProcedureNOTE 1The area used for the test must not be in direct sunlight; tests should be
38、run at the same temperature at which chlorination will be carriedout. The temperature of the water just prior to, or immediately after, chlorination must not exceed 50C.9.1 Transfer 500 mL portions of sample to separate 1000 mL beakers.NOTE 2The number of aliquots required to determine chlorine requ
39、irement or demand is left to the judgment of the analyst. It will depend upon thedegree of familiarity that the analyst has with the water being tested as well as other variables.NOTE 3One of two different sources of chlorine can be used in the chlorine addition, either chlorine water or sodium hypo
40、chlorite solution. In general,the type of chlorine that is used in the process should be used in the test. Chlorine water will tend to lower the pH of the water while sodium hypochloritesolution will tend to raise the pH.9.2 If chlorine water is used for chlorination, add the estimated maximum amoun
41、t of chlorine (as chlorine water) to one of thesample aliquots. If sodium hypochlorite solution is used for chlorination, add the estimated minimum amount of chlorine (assodium hypochlorite solution). Immediately measure the pH of the sample aliquot by Test Methods D1293. If the pH is not belowthe l
42、ower limit of the desired pH range, continue with 9.3. If the pH does fall below the lower limit of the desired range, add sodiumhydroxide solution dropwise with continual stirring to bring the pH up to approximately the midpoint of the pH range, noting theamount of sodium hydroxide solution require
43、d. Then, discard this solution and transfer another 500 mL aliquot of sample to a 1-Lbeaker to replace it. Add the same amount of sodium hydroxide solution as was required for pH adjustment of the first samplealiquot to all of the sample aliquots. Proceed to 9.3.9.3 If the estimated maximum amount o
44、f chlorine was added to the first sample aliquot, add incrementally smaller amounts ofchlorine to each of the other sample aliquots, with the estimated minimum amount of chlorine being added to the last samplealiquot. If the estimated minimum amount of chlorine was added to the first sample aliquot,
45、 add incrementally greater amountsof chlorine to each of the other sample aliquots with the estimated maximum amount of chlorine being added to the last samplealiquot. Stir each sample aliquot gently after addition of chlorine. Proceed to 9.4.D1291 1739.4 Measure the pH of each sample aliquot by fol
46、lowing Test Methods D1293.9.5 If the pH is higher than the desired pH range, carefully adjust the pH downward by adding, with constant gentle stirring,hydrochloric acid (1 + 1) dropwise until the pH reaches the upper limit of the desired range.NOTE 4Care must be taken during the addition of HCl (1 +
47、 1) to make sure that the pH is not lowered too rapidly and that the lower limit of thedesired pH range is not exceeded. A rapid reaction (which itself lowers the pH) may ensue if the pH is taken too low.9.6 Permit each portion of sample to stand for the desired contact time.NOTE 5Depending upon the
48、 application, a single contact time or a series of different contact times may be used for each sample aliquot. This is leftto the judgment of the analyst.9.7 To estimate chlorine demand, determine residual-free chlorine on all of the sample aliquots at the end of the desired contacttime by Test Met
49、hod D1253.9.8 To estimate chlorine requirement, perform whatever test is necessary on all of the sample aliquots at the end of the desiredcontact time to determine whether the objectives of chlorination have been met. If it is desired to maintain a certain concentrationof residual available chlorine, perform the chlorine determination by Test Method D1253.10. Calculation10.1 Calculate the chlorine dosage in milligrams per litre for each treated sample solution using Eq 1:Chlorine dosage,mg/L52AB (1)where:A = chlorinating solution added to each sample
