1、Designation: D 1291 06Standard Practice forEstimation of Chlorine Demand of Water1This standard is issued under the fixed designation D 1291; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in pa
2、rentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides a means of estimating the quan-tity of chlorine required to be added to a unit volume of waterto accomplish a predetermined
3、 treatment objective or tocompletely react with all chlorine reactable substances in thewater, or both.1.2 Temperature, pH, and initial chlorine dosage are allvariables in estimating the optimum chlorination practice. Theeffects of these variables can be evaluated using this practice.1.3 Chlorine re
4、sidual is determined using Test MethodD 1253.1.4 This practice is applicable to all types of water in whichthe stated treatment objective can be evaluated or residualchlorine can be measured, or both.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its
5、 use. It is theresponsibility 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. For a specifichazard statement, see Note 1.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating
6、to WaterD 1193 Specification for Reagent WaterD 1253 Test Method for Residual Chlorine in WaterD 1293 Test Methods for pH of WaterD 3370 Practices for Sampling Water from Closed Conduits3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 chlorine demandthe amount of chlorine that
7、mustbe added to a unit volume of water under specified conditionsof pH, temperature, and contact time to completely react withall chlorine-reactable substances in the water. It is defined asthe difference between the amount of chlorine applied and theamount of free chlorine remaining at the end of t
8、he contactperiod.3.1.2 chlorine requirementthe amount of chlorine thatmust be added to a unit volume of water under specifiedconditions of pH, temperature, and contact time to achieve theobjectives of chlorination.3.2 DefinitionsFor definitions relating to this practice, seeTerminology D 1129.4. Sum
9、mary of Practice4.1 Known amounts of chlorine are added to a series of 500mL aliquots of sample. The treated sample aliquots arepermitted to stand for a specified contact time (or a variety ofdifferent specified contact times) under specified conditions ofpH and temperature. At the end of the contac
10、t time, the samplealiquots are either analyzed for chlorine content by TestMethod D 1253 or subjected to whatever evaluative techniqueis required to establish accomplishment of the treatmentobjective, or both.5. Significance and Use5.1 Chlorine is added to potable water, waste water, andindustrial w
11、ater for a variety of purposes. Some of thesepurposes are:5.1.1 To eliminate or reduce the growth of microorganismsin water,5.1.2 To destroy or modify decomposable organic sub-stances so as to reduce the biochemical oxygen demand of thewater,5.1.3 To eliminate or reduce taste, odors, and color in th
12、ewater,5.1.4 To separate grease in waste water by eliminating theprotective colloidal effect of proteins present, and5.1.5 To destroy or modify substances in the waste waterthat react directly by oxidation, such as ammonia, cyanates,cyanides, ferrous iron, nitrites, phenol, phosphorus, sulfides,sulf
13、ites, thiocyanates, and other oxidizable constituents.5.2 It is important to avoid over-chlorination in order tominimize chemical consumption, meet restrictions specified byregulatory agencies, and minimize equipment degradation.1This practice is under the jurisdiction of ASTM Committee D19 on Water
14、 andis the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits, Analysis of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of Water.Current edition approved Sept. 1, 2006. Published September 2006. Originallyapproved in 1953. L
15、ast previous edition approved in 2001 as D 1291 01.2For 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.1Copyright
16、 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Apparatus6.1 All of the apparatus listed in Test Methods D 1293 andD 1253 may be required. Any other apparatus necessary tocarry out the final evaluation of the effects of chlorination willbe
17、required.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specificatio
18、ns are available.3Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water
19、conformingto Specification D 1193, Type III, which has been renderedchlorine demand-free. Chlorine demand can be removed bytreating with excess chlorine and allowing this treated solutionto stand in sunlight for several hours to destroy the chlorineresiduals. Test Method D 1253 may be used to assure
20、 completedestruction of these residuals.7.3 Acetic Acid Solution (1 + 1)Mix equal volumes ofglacial acetic acid and water.7.4 Calcium Hydroxide Solution (10.7 g/L)Weigh 10.7 gof 100 % hydrated lime, Ca(OH)2, and suspend in water. Dilutethe suspension to 1 L. Shake well each time before using.7.5 Chl
21、orine Solution, StandardPrepare one of the stan-dard solutions described in 7.5.1 and 7.5.2; standardize asdescribed in 7.5.3.7.5.1 Chlorine WaterPass chlorine gas through reagentwater until the solution contains from 0.5 to 10.0 mg/L Cl2.NOTE 1Warning: Use a slow rate of addition and carry out theo
22、peration under a hood. Store in a glass stoppered amber bottle andstandardize daily before use.7.5.2 Sodium Hypochlorite Solution, StandardDilute acommercial sodium hypochlorite or bleach solution containing10 to 100 g of available chlorine per litre with water to providea solution containing from 0
23、.5 to 10 mg available chlorine perlitre, depending upon the maximum expected chlorine require-ment for the sample. This solution must be standardized beforeuse.7.5.3 Standardize the chlorine water or sodium hypochloritesolution, standard, as follows:7.5.3.1 Transfer 10 mL of the solution to be stand
24、ardized toa porcelain dish.7.5.3.2 Add 10 mL of acetic acid (1 + 1) (see 7.3) and 10mL of potassium iodide solution (see 7.8).7.5.3.3 Titrate with sodium thiosulfate solution (0.10 N)(see 7.11) until the yellow color of the liberated iodine isalmost discharged.7.5.3.4 Add 1 mL of starch indicator so
25、lution (see 7.12) andcontinue the titration to a colorless endpoint.7.5.3.5 Calculate the concentration of available chlorine asfollows:Available chlorine, mg/mL 5A 3 B3 35.45Cwhere:A = sodium thiosulfate solution, standard, mL,B = normality of sodium thiosulfate solution, standard,andC = chlorine s
26、olution titrated, mL.7.6 Hydrochloric Acid (1 + 1)Mix equal volumes of con-centrated HCl (sp gr 1.19) and water.7.7 Potassium Dichromate Solution (0.100 N)Dissolve4.904 g of anhydrous potassium dichromate (K2Cr2O7)ofprimary standard quality in water and dilute to 1000 mL in avolumetric flask.7.8 Pot
27、assium Iodide Solution (50 g/L)Dissolve 50 g ofpotassium iodide (KI) in 1 Lof freshly boiled and cooled water.Add1gofsodium bicarbonate (NaHCO3) to stabilize thesolution. Store in an amber bottle and avoid direct exposure tosunlight.7.9 Sodium Hydroxide Solution (10 g/L)Dissolve 10 g ofsodium hydrox
28、ide (NaOH) in water and dilute to 1 L.NOTE 2Caution: Heat is generated when dissolving sodium hydrox-ide 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 mLwater. Dissolve the com
29、pound in the water by shaking andperiodic inversion.Add1gofsodium carbonate (Na2CO3) anddissolve. Dilute the solution to 1 L with water.7.10.1 Standardize the sodium thiosulfate solution: Add 70mL of water to a porcelain dish, and add, with constant stirring,1 mL of concentrated sulfuric acid (H2SO4
30、), 10.0 mL of 0.100N K2Cr2O7, and 20 mL of potassium iodide solution (see 7.8).Permit the reaction mixture to stand in the dark for about sixminutes. Then titrate with the sodium thiosulfate solution untilthe yellow color of the liberated iodine is almost discharged.Add 1 mL of starch indicator solu
31、tion (see 7.12) and continuethe titration to a colorless endpoint.7.10.1.1 The normality can be calculated as:Normality, Na2S2O351Na2S2O3required in titration, mL7.10.1.2 Perform this standardization in triplicate and aver-age the results.7.11 Starch Indicator SolutionMake a paste of1gofsoluble star
32、ch and mix into 1 L of boiling water. Then, add 20g of potassium hydroxide (KOH), mix thoroughly, and allow tostand for 2 h. Add 6 mL of glacial acetic acid (99.5 %). Mixthoroughly and then add sufficient HCl (sp gr 1.19) to adjustthe pH value of the solution to 4.0. Store in a glass-stopperedbottle
33、. Starch solution prepared in this manner will remainchemically stable for 1 year.3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for La
34、boratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.D 1291 0627.12 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid(H2SO4).8. Sampling8.1 Collect the sample in accordance with Practi
35、ces D 3370.8.2 Conduct the test immediately following collection of thesamples.9. ProcedureNOTE 3The area used for the test must not be in direct sunlight; testsshould be run at the same temperature at which chlorination will be carriedout. The temperature of the water just prior to, or immediately
36、after,chlorination must not exceed 50C.9.1 Transfer 500 mL portions of sample to separate 1000mL beakers.NOTE 4The number of aliquots required to determine chlorine re-quirement or demand is left to the judgment of the analyst. It will dependupon the degree of familiarity that the analyst has with t
37、he water beingtested as well as other variables.NOTE 5One of two different sources of chlorine can be used in thechlorine addition, either chlorine water or sodium hypochlorite solution.In general, the type of chlorine that is used in the process should be usedin the test. Chlorine water will tend t
38、o lower the pH of the water whilesodium hypochlorite solution will tend to raise the pH.9.2 If chlorine water is used for chlorination, add theestimated maximum amount of chlorine (as chlorine water) toone of the sample aliquots. If sodium hypochlorite solution isused for chlorination, add the estim
39、ated minimum amount ofchlorine (as sodium hypochlorite solution). Immediately mea-sure the pH of the sample aliquot by Test Method D 1293.Ifthe pH is not below the lower limit of the desired pH range,continue with 9.3. If the pH does fall below the lower limit ofthe desired range, add sodium hydroxi
40、de solution dropwisewith continual stirring to bring the pH up to approximately themidpoint of the pH range, noting the amount of sodiumhydroxide solution required. Then, discard this solution andtransfer another 500 mL aliquot of sample to a 1-L beaker toreplace it. Add the same amount of sodium hy
41、droxide solutionas was required for pH adjustment of the first sample aliquot toall of the sample aliquots. Proceed to 9.3.9.3 If the estimated maximum amount of chlorine wasadded to the first sample aliquot, add incrementally smalleramounts of chlorine to each of the other sample aliquots, withthe
42、estimated minimum amount of chlorine being added to thelast sample aliquot. If the estimated minimum amount ofchlorine was added to the first sample aliquot, add incremen-tally greater amounts of chlorine to each of the other samplealiquots with the estimated maximum amount of chlorine beingadded to
43、 the last sample aliquot. Stir each sample aliquotgently after addition of chlorine. Proceed to 9.4.9.4 Measure the pH of each sample aliquot by followingTest Method D 1293.9.5 If the pH is higher than the desired pH range, carefullyadjust the pH downward by adding, with constant gentlestirring, hyd
44、rochloric acid (1 + 1) dropwise until the pHreaches the upper limit of the desired range.NOTE 6Care must be taken during the addition of HCl (1 + 1) to makesure that the pH is not lowered too rapidly and that the lower limit of thedesired pH range is not exceeded.Arapid reaction (which itself lowers
45、 thepH) may ensue if the pH is taken too low.9.6 Permit each portion of sample to stand for the desiredcontact time.NOTE 7Depending upon the application, a single contact time or aseries of different contact times may be used for each sample aliquot. Thisis left to the judgment of the analyst.9.7 To
46、 estimate chlorine demand, determine residual-freechlorine on all of the sample aliquots at the end of the desiredcontact time by Test Method D 1253.9.8 To estimate chlorine requirement, perform whatever testis necessary on all of the sample aliquots at the end of thedesired contact time to determin
47、e whether the objectives ofchlorination have been met. If it is desired to maintain a certainconcentration of residual available chlorine, perform the chlo-rine determination by Test Method D 1253.10. Calculation10.1 Calculate the chlorine dosage in milligrams per litre foreach treated sample soluti
48、on using Eq 1:Chlorine dosage, mg/L 5 2AB(1)where:A = chlorinating solution added to each sample aliquot,mL, andB = available chlorine per millilitre of chlorinating solu-tion, mg (see 7.5.3).10.2 Chlorine demand is estimated using Eq 2:Chlorine demand, mg/L 5 C 2 D(2)where:C = chlorine dosage, mg/L
49、, andD = free chlorine remaining at the end of contact time,mg/L.NOTE 8To calculate chlorine consumed, see Appendix X1.11. Precision and Bias11.1 PrecisionThe estimation of chlorine requirement ordemand, or both, is a practice. For measuring chlorine values,this practice refers the user to Test Method D 1253.Astatementfor the precision and bias of chlorine measurement is located inTest Method D 1253.12. Keywords12.1 chlorine; disinfection; drinking water; residual chlo-rine; water treatmentD 1291 063APPENDIX(Nonmandatory Information)X1. CALCULATION OF CH
