ASTM D6238-98(2017) Standard Test Method for Total Oxygen Demand in Water.pdf

1、Designation: D6238 98 (Reapproved 2017)Standard Test Method forTotal Oxygen Demand in Water1This standard is issued under the fixed designation D6238; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A num

2、ber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of totaloxygen demand in the range from 100 to 100 000 mg/L, inwater and wastewater including br

3、ackish waters and brines (see6.5). Larger concentrations, or samples with high suspendedsolids, or both, may be determined by suitable dilution of thesample.1.1.1 Since the analysis is based on the change in oxygenreading of the carrier gas compared to that when a sample isintroduced (see 4.1), the

4、measurement range is a function of theamount of oxygen in the carrier gas. The higher the desiredconcentration range, the more oxygen required in the carriergas. Under recommended conditions, the carrier gas concen-tration should be between two to four times the maximumdesired oxygen demand.1.1.2 Th

5、e lower measurement range is limited by thestability of the baseline oxygen detector output. This signal isa function of the permeation system temperature, carrier gasflow rate, oxygen detector temperature, and reference sensorvoltage. Combined, these variables limit the minimum recom-mended range t

6、o 2 to 100 mg/L.1.1.3 The upper measurement range is limited by themaximum oxygen concentration in the carrier gas (100 %).With the recommended conditions of carrier gas concentrationbeing two to four times the maximum oxygen demand, thislimits the maximum possible oxygen demand to between250 000 to

7、 500 000 mg L. However, as a practical applicationto water analysis, this test method will consider a maximumrange of 100 000 mg/L.1.2 This test method is applicable to all oxygen-demandingsubstances under the conditions of the test contained in thesample that can be injected into the reaction zone.

8、 The injectoropening limits the maximum size of particles that can beinjected. If oxygen-demanding substances that are water-insoluble liquids or solids are present, a preliminary treatmentmay be desired. These pretreatment methods are described inAnnex A2.1.3 This test method is particularly useful

9、 for measuringoxygen demand in certain industrial effluents and processstreams. Its application for monitoring secondary sewageeffluents is not established. Its use for the monitoring of naturalwaters is greatly limited by the interferences defined in Section6.1.4 In addition to laboratory analysis,

10、 this test method isapplicable to on-stream monitoring. Sample conditioning tech-niques for solids pretreatment applications are noted in AnnexA2.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not pur

11、port 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, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.7 This international standa

12、rd was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Ref

13、erenced Documents2.1 ASTM Standards:2D888 Test Methods for Dissolved Oxygen in WaterD1129 Terminology Relating to WaterD1192 Guide for Equipment for Sampling Water and Steamin Closed Conduits (Withdrawn 2003)3D1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias

14、 ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3856 Guide for Management Systems in LaboratoriesEngaged in Analysis of Water1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subco

15、mmittee D19.06 on Methods forAnalysis forOrganic Substances in Water.Current edition approved Dec. 15, 2017. Published January 2018. Originallyapproved in 1998. Last previous edition approved in 2011 as D6238 98 (2011).DOI: 10.1520/D6238-98R17.2For referenced ASTM standards, visit the ASTM website,

16、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.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100

17、 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Re

18、commendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1D5789 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Organic Constituents(Withdrawn 2002)3D5847 Practice for Writing Quality Control Specificationsfor Standard Test Met

19、hods for Water Analysis3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard, refer toTerminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 total oxygen demand (TOD), nthe amount of oxygenrequired to convert the elements in compounds to their moststa

20、ble oxidized forms.4. Summary of Test Method4.1 The total oxygen demand (TOD) measurement isachieved by continuous analysis of the concentration of oxygenin a combustion process gas effluent. The decrease in oxygenresulting from introduction of the sample into the combustionzone is a measure of oxyg

21、en demand.4.2 The oxidizable components in a liquid sample intro-duced into a carrier gas stream containing a fixed amount ofoxygen flowing through a 900C combustion tube are con-verted to their stable oxides. The momentary reduction in theoxygen concentration in the carrier gas is detected by anoxy

22、gen sensor and indicated on a digital display or recorded.4.3 The TOD for the sample is obtained by comparing thepeak height to a calibration curve of peak heights for TODstandard solutions. The TOD for the standard solution is basedon experimentally observed reactions in which carbon isconverted to

23、 carbon dioxide, hydrogen to water, combinednitrogen including ammonia to nitric oxide, and elemental ororganic sulfur to sulfur dioxide. Sample injection is achievedby means of an automatic valve, that provides unattendedmultiple sampling in the laboratory or on-stream monitoring.4.4 For monitoring

24、 applications, pretreatment of the samplemay be required. However, no single instruction can be writtensince pretreatment steps will be a function of the specificcharacteristics of the sample stream.5. Significance and Use5.1 The measurement of oxygen demand parameters iscritical to the control of p

25、rocess wastewaters. Biochemicaloxygen demand (BOD) and chemical oxygen demand (COD)analyzers have long time cycles and in the case of CODanalyzers use corrosive reagents with the inherent problem ofdisposal. Total oxygen demand analysis is faster, approxi-mately 3 min, and uses no liquid reagents in

26、 its analysis.5.2 TOD can be correlated to both COD and BOD, provid-ing effective on-line control.5.3 TOD offers several features which make it a moreattractive measurement than carbon monitoring using totalcarbon (TC) or total organic carbon (TOC) analyzers. TOD isunaffected by the presence of inor

27、ganic carbon. TOD analysiswill also indicate noncarbonaceous materials that consume orcontribute oxygen. For example, the oxygen demand ofammonia, sulfite and sulfides will be reflected in the TODmeasurement. Also, since the actual measurement is oxygenconsumption, TOD reflects the oxidation state o

28、f the chemicalcompound (that is, urea and formic acid have the same numberof carbon atoms, yet urea has five times the oxygen demand offormic acid).6. Interferences6.1 The dissolved oxygen concentrations will contribute amaximum error of 8 ppm. This error is only significant onranges below 0 to 100

29、ppm when samples have no dissolvedoxygen (DO) content. When operating in this range andsamples contain low DO concentrations then compensationmay be necessary. Measure the DO in both solutions inaccordance with Test Methods D888. Adjust the TOD result asfollows: If DO of the sample is less than in t

30、he standard,subtract DO variation. If DO of the sample is greater than inthe standard, add DO variation to the TOD result.6.2 Sulfuric acid will normally decompose under samplecombustion conditions as follows:H2SO4900CCatalystH2O1SO2112O2(1)The oxygen release will result in a reduction in the TODrea

31、ding. However, alkali metal sulfates (that is, sodium andpotassium salts) do not decompose under the combustionconditions. If sulfates are present in the samples, adjust to pH11 with NaOH prior to analysis.6.3 Nitrate salts decompose under sample combustion con-ditions as follows:2 NaNO3900CCatalyst

32、Na2O12NO1112O2(2)The resulting generation of oxygen reduces the oxygendemand.6.4 Heavy metal ions have been reported to accumulate inthe system resulting in a significant loss of sensitivity. Thehistory of the combustion column appears to be a major factorcontributing to interferences of this nature

33、. Similarly, highconcentrations of dissolved inorganic salts will tend to build upand coat the catalyst as indicated by a loss of sensitivity. Tocorrect the problem, replace the combustion tube and refrac-tory packing material and clean the catalyst in accordance withthe manufacturers recommendation

34、s. The effects of theseproblems can be minimized by dilution of the sample.D6238 98 (2017)26.5 Some brackish waters and natural brines may exhibitbase line drift. In such cases, continue to inject samples until astable response is observed.7. Apparatus7.1 Total Oxygen Demand Instrument(See Fig. 1),

35、includ-ing a pure nitrogen source, an oxygen permeation system,sample injection valve, catalyst-combustion zone, gas flowcontrols, oxygen sensor and display or recorder, as detailed inAnnex A2.47.2 Homogenizing ApparatusA high speed blender, or amechanical or ultrasonic homogenizer is satisfactory f

36、or ho-mogenizing immiscible liquid samples and suspended solids(see Annex A1).8. Reagents and Materials8.1 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 Analyti

37、cal Reagents of the American Chemical Society,where such specifications are available.5Other 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.8.2 Purity of WaterUnless otherwise ind

38、icated, referencesto water shall be understood to mean reagent water conformingto Specification D1193, Type II except that distillation is notnecessary.4The sole source of supply of the apparatus known to the committee at this timeis Ionics, Inc., P.O. Box 9131, 65 Grove Street, Watertown, MA 02272.

39、 If you areaware of alternative suppliers, please provide this information to ASTM Headquar-ters. Your comments will receive careful consideration at a meeting of theresponsible technical committee that you may attend.5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Soc

40、iety, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,M

41、D.FIG. 1 Flow Diagram for TOD AnalyzerD6238 98 (2017)38.3 Carrier Gas SupplyPrepurified nitrogen containingoxidizable or reducible gases in concentrations of less than 10ppm is recommended. Other pure inert gases, such as helium orargon, are acceptable. The required oxygen is added to thecarrier gas

42、 by means of the permeation system in the apparatus.Alternatively, a bottled, fixed oxygen concentration carrier gasmay be used in place of a permeation system.8.4 Total Oxygen Demand Calibration Standard Solutions:8.4.1 Potassium Acid Phthalate (KHP) Solution Stock(10 000 mg/L TOD) Dissolve 8.509 g

43、 of potassium acidphthalate (KHP) in water in a volumetric flask and dilute 1 L.This solution is stable for several weeks at average roomtemperature but is eventually subject to bacteriological dete-rioration. Refrigeration extends the shelf-life.8.4.2 Acetic Acid Solution, Stock(111 900 mg/LTOD) Fo

44、rcalibration standards above 10 000 mg/L, the use of acetic acidis recommended. Pipet 100 mL of glacial acetic acid to a 1-Lvolumetric flask containing approximately 500 mL of water.Dilute to 1 L with water and mix thoroughly. This solution isstable for several weeks at average room temperature but

45、iseventually subject to bacteriological deterioration. Refrigera-tion extends the shelf-life.8.4.3 Water solutions of other pure organic compounds maybe used as standards based on the compounds theoreticaloxygen demand.8.4.4 Calibration StandardsPrepare by appropriate dilu-tion of the above stock so

46、lutions.9. Sampling9.1 Collect the sample in accordance with Guide D1192 andPractices D3370.9.2 Because of the possibility of oxidation or bacterialdecomposition of some components of aqueous samples, thetime lapse between collection of samples and analysis must bekept to a minimum. After collection

47、, keep the samples atapproximately 4C.9.3 Sample preservation may also be accomplished by theaddition of NaOH to a pH of 12 or higher, or HCl to a pH of2 or lower. Do not use sulfuric acid or nitric acid to preservethe sample (see Section 6).10. Preparation of Apparatus10.1 Provide required services

48、 and adjust variables (carriergas flow rate, permeation tube lengths etc.) according tomanufacturers specifications for the desired oxygen demandrange. Set the furnace temperature to the specified temperaturesetting. Allow approximately 1 h for the instrument to ap-proach equilibrium.10.2 Monitor ox

49、ygen sensor output stability as an indicationof degree of equilibrium. Detector output must be stable beforeproceeding.10.3 It is recommended that the furnace and instrumentcontrols along with the carrier gas flow remain on continuouslyonce the analyzer is activated (that is, do not shutdownovernight).10.4 Preliminary Operation:10.4.1 Place sample/standard inlet tubing into a full scalestandard solution container, and rinse water tubing into adeionized water container.10.4.2 Place instrument in calibrate, active operation mode.10.4.3 Operate instrum