1、Designation: D6855 17Standard Test Method forDetermination of Turbidity Below 5 NTU in Static Mode1This standard is issued under the fixed designation D6855; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the static determination ofturbidity in water (see 4.1).1.2 This test method is applicable to the measurem
3、ent ofturbidities under 5.0 nephelometric turbidity units (NTU).1.3 This test method was tested on municipal drinkingwater, ultra-pure water, and low turbidity samples. It is theusers responsibility to ensure the validity of this test method forwaters of untested matrices.1.4 This test method uses c
4、alibration standards are definedin NTU values, but other assigned turbidity units are assumedto be equivalent.1.5 This test method assigns traceable reporting units to thetype of respective technology that was used to perform themeasurement. Units are numerically equivalent with respect tothe calibr
5、ation standard. For example, a 1.0 NTU formazinstandard is also equal to a 1.0 FNU standard, a 1.0 FNRUstandard, and so forth.1.6 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 ap
6、pro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.Refer to the MSDSs for all chemicals used in this test method.1.7 This international standard was developed in accor-dance with internationally recognized principles on stan
7、dard-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. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1192 Guid
8、e for Equipment for Sampling Water and Steamin Closed Conduits (Withdrawn 2003)3D1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD5847 Practice for Wri
9、ting Quality Control Specificationsfor Standard Test Methods for Water AnalysisD7315 Test Method for Determination of Turbidity Above 1Turbidity Unit (TU) in Static ModeE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 Other Referenced Standards:U.S.
10、 EPA Method 180.1 Methods for Chemical Analysis ofWater and Wastes, Turbidity4ISO 7027 Water Qualityfor the Determination of Turbid-ity53. 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
11、.1 calibration turbidity standard, na turbidity standardthat is traceable and equivalent to the reference turbiditystandard to within statistical errors.3.2.1.1 DiscussionCalibration turbidity standards includecommercially prepared 4000 NTU formazin, stabilized for-mazin (see 9.2.3), and styrenedivi
12、nylbenzene (SDVB) (see1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.07 on Sediments,Geomorphology, and Open-Channel Flow.Current edition approved Nov. 1, 2017. Published November 2017. Originallyapproved in 2003. Last p
13、revious edition approved in 2012 as D6855 12. DOI:10.1520/D6855-17.2For 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 we
14、bsite.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from United States Environmental ProtectionAgency (EPA), WilliamJefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460,http:/www.epa.gov.5Available from International Organization
15、for Standardization (ISO), ISOCentral Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,Geneva, Switzerland, http:/www.iso.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194
16、28-2959. 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 Recommendations issued by the World Trade Organization Techn
17、ical Barriers to Trade (TBT) Committee.19.2.4). These standards may be used to calibrate the instrument.Calibration standards may be instrument specific.3.2.2 calibration verification standards, ndefined stan-dards used to verify the accuracy of a calibration in themeasurement range of interest.3.2.
18、2.1 DiscussionThese standards may not be used toperform calibrations, only calibration verifications. Includedstandards are opto-mechanical light scatter devices, gel-likestandards, or any other type of stable liquid standard. Calibra-tion verification standards may be instrument specific.3.2.3 neph
19、elometric turbidity measurement, nthe mea-surement of light scatter from a sample in a direction that is at90 with respect to the centerline of the incident light path.3.2.3.1 DiscussionUnits are NTU (nephelometric turbid-ity units); when ISO 7027 technology is employed units are inFNU (formazin nep
20、helometric units).3.2.4 ratio turbidity measurement, nthe measurement de-rived through the use of a nephelometric detector that serves asthe primary detector and one or more other detectors used tocompensate for variation in incident light fluctuation, straylight, instrument noise, or sample color.3
21、.2.5 reference turbidity standard, na standard that issynthesized reproducibly from traceable raw materials by theuser.3.2.5.1 DiscussionAll other standards are traced back tothis standard. The reference standard for turbidity is formazin(see 9.2.2).3.2.6 seasoning, nthe process of conditioning labw
22、arewith the standard to be diluted to a lower value.3.2.6.1 DiscussionThe process reduces contamination anddilution errors. See Appendix X2 for the suggested procedure.3.2.7 stray light, nall light reaching the detector other thanthat contributed by the sample.3.2.7.1 DiscussionExamples: ambient lig
23、ht leakage, inter-nal reflections and divergent light in optical systems.3.2.8 turbidimeter, nan instrument that measures lightscatter caused by particulates within a sample and converts themeasurement to a turbidity value.3.2.8.1 DiscussionThe detected light is quantitativelyconverted to a numeric
24、value that is traced to a light-scatterstandard.3.2.9 turbidity, nan expression of the optical properties ofa sample that causes light rays to be scattered and absorbedrather than transmitted in straight lines through the sample.3.2.9.1 DiscussionTurbidity of water is caused by thepresence of suspen
25、ded and dissolved matter such as clay, silt,finely divided organic matter, plankton, other microscopicorganisms, organic acids, and dyes.4. Summary of Test Method4.1 The optical property expressed as turbidity is measuredby the scattering effect that suspended particulate material haveon light; the
26、higher the intensity of scattered light, the higherthe turbidity. In samples containing particulate material, themanner in which sample interferes with light transmittance isrelated to the size, shape, and composition of the particles inthe water, and also to the wavelength of the incident light.4.2
27、 This test method is based upon a comparison of theintensity of light scattered by the sample with the intensity oflight scattered by a reference suspension. Turbidity values aredetermined by a nephelometer, which measures light scatterfrom a sample in a direction that is at 90 with respect to thece
28、nterline of the incident light path.5. Significance and Use5.1 Turbidity is undesirable in drinking water, plant effluentwaters, water for food and beverage processing, and for a largenumber of other water-dependent manufacturing processes.Removal is often accomplished by coagulation, settling, andf
29、iltration. Measurement of turbidity provides a rapid means ofprocess control for when, how, and to what extent the watermust be treated to meet specifications.5.2 This test method is suitable to turbidity such as thatfound in drinking water, process water, and high purityindustrial water.5.3 When re
30、porting the measured result, appropriate unitsshould also be reported. The units are reflective of thetechnology used to generate the result, and if necessary,provide more adequate comparison to historical data sets.5.3.1 Table 1 describes technologies and reporting results(see also Refs (1-3)6). Th
31、ose technologies listed are appropriatefor the range of measurement prescribed in this test method.Others may come available in the future. Fig. X5.1 provides aflow chart to aid in selection of the appropriate technology forlow-level static turbidity applications.5.3.2 If a design that falls outside
32、 of the criteria listed inTable 1 is used, the turbidity should be reported in turbidityunits (TU) with a subscripted wavelength value to characterizethe light source that was used.6. Interferences6.1 For this application, bubbles, color, and large particles,although they cause turbidity, may result
33、 in interferences inmeasured turbidity as determined by this test method. Bubblescause a positive interference and color typically causes anegative interference. Dissolved material that imparts a colorto the water may cause errors in pure nephelometric readings,unless the instrument has special comp
34、ensating features toreduce these interferences. Certain turbulent motions alsocreate unstable reading conditions of nephelometers.6.2 Color is characterized by absorption of specific wave-lengths of light. If the wavelengths of incident light aresignificantly absorbed, a negative interference will r
35、esult un-less the instrument has special compensating features.6.3 Scratches, finger marks, or dirt on the walls of thesample cell may give erroneous readings. Sample cells shouldbe kept scrupulously clean both inside and outside and dis-carded when they become etched or scratched. The sample6The bo
36、ldface numbers in parentheses refer to the list of references at the end ofthis standard.D6855 172cells must not be handled where the light strikes them whenpositioned in the instrument well.6.3.1 Sample cell caps and liners must also be scrupulouslyclean to prevent contamination of the sample.6.4 I
37、deally, the same indexed sample cell should be usedfirst for standardization followed by unknown (sample) deter-mination. If this is not possible, then sample cells must bematched. Refer to the instrument manual for instructions onmatching sample cells.NOTE 1Indexing of the sample cell to the instru
38、ment well isaccomplished by placing a mark on the top of the sample cell and a similarmark on the upper surface of the well so that the sample cell can be placedin the well in an exact position each time.NOTE 2Sample cells can be matched by first filling with dilutionwater (see 8.2). Allow the sampl
39、e cell to stand for 5 to 10 min to allow forbubbles to vacate the sample. This is followed by cleaning and polishingthe outside of the cell. Cells are then measured on the same turbidimeterand should read no different than 0.01 NTU.6.5 Condensation of optical elements or sample cells canlead to seve
40、re errors in measurement.7. Apparatus7.1 Two types of instruments are available for the nephelo-metric method, the nephelometer and ratio nephelometer (seeFigs. 1 and 2).7.2 The resolution of the instruments should permit detec-tion of differences of 0.01 NTU or less in waters havingturbidities of l
41、ess than 5.0 NTU. The instrument must measurethe range from 0.02 to 5.0 NTU. See 12.1 for calibration ofinstruments. Calibration verification in the immediate range ofinterest must be performed using acceptable, defined verifica-tion standards (see 12.2).NOTE 3Consult manufacturers instructions for
42、guidance associatedwith verification methods and verification devices.7.2.1 Consult the manufacturer to ensure that your instru-ment meets or exceeds the specifications of this test method.7.3 Photoelectric Nephelometer:7.3.1 This instrument uses a light source for illuminating thesample and a singl
43、e photodetector with a readout device toindicate the intensity of light scattered at right angle(s) (90) tothe centerline of the path of the incident light. The photoelec-tric nephelometer should be designed so that minimal straylight reaches the detector in the absence of turbidity and shouldbe fre
44、e from significant drift after a short warm-up period. Thelight source shall be a Tungsten lamp operated at a colortemperature between 2200 and 3000 K (U.S. EPA Method180.1). Light Emitting Diodes (LEDs) or laser diodes indefined wavelengths ranging from 400 to 900 nm may also beused if accurately c
45、haracterized to be equivalent in perfor-mance to tungsten using calibration and calibration verificationstandards. If LEDs or laser diodes are used, then the LED orlaser diode should be coupled with a monitor detection deviceto achieve a constant output. LEDs and laser diodes should becharacterized
46、by a wavelength of between 400 and 900 nmwith a bandwidth of less than 60 nm. The total distancetraversed by incident light and scattered light within the sampleis not to exceed 10 cm. The angle of light acceptance to thedetector shall be centered at 90 to the centerline of the incidentlight path an
47、d shall not exceed 610 from the 90 scatter pathTABLE 1 Applicable Technologies Available for Performing Static Turbidity Measurements Below 5 NTUDesign and ReportingUnitProminent Application Key Design FeaturesTypical InstrumentRangeSuggested ApplicationNephelometric non-ratio (NTU)White light turbi
48、dimeters. Comply withU.S. EPA Method 180.1 (1) for low-level turbidity monitoring.Detector centered at 90 relative to the in-cident light beam. Uses a white light spec-tral source.0.020 to 40 Regulatory reporting ofclean waterRatio white light turbidi-meters (NTRU)Complies with ISWTR regulations and
49、Standard Method 2130B. (2) Can beused for both low- and high-level mea-surement.Used a white light spectral source. Primarydetector centered at 90. Other detectorslocated at other angles. An instrument algo-rithm uses a combination of detector read-ings to generate the turbidity reading.0.020 to10 000 Regulatory Reporting ofclean waterNephelometric, near-IRturbidimeters, non-ratiometric (FNU)Complies with ISO 7027. The wave-length is less susceptible to color inter-ferences. Applicable for samples withcolor and good for low-level monitoring.Detector
