1、Designation: D6855 10Standard 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 methodfor waters of untested matrices.1.4 This test method uses ca
4、libration 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 calibra
5、tion 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 appr
6、o-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Refer to theMSDSs for all chemicals used in this procedure.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1192 Guide for Equipment for Sampling Water and Stea
7、min Closed Conduits3D1193 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 Writing Quality Control Specificationsfor Standard Test Methods
8、 for Water AnalysisE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 Other Referenced Standards:USEPA Method 180.1 Methods for Chemical Analysis ofWater and Wastes, Turbidity4ISO 7027 (The International Organization for Standardiza-tion) Water Qualit
9、yfor the Determination of Turbidity53. Terminology3.1 DefinitionsFor definitions of terms used in thismethod refer to Terminology D1129.3.2 Definitions:3.2.1 calibration turbidity standarda turbidity standardthat is traceable and equivalent to the reference turbiditystandard to within statistical er
10、rors, including commerciallyprepared 4000 NTU Formazin, stabilized formazin (see 9.2.3),and styrenedivinylbenzene (SDVB) (see 9.2.4). These stan-dards may be used to calibrate the instrument.NOTE 1Calibration standards may be instrument specific.3.2.2 calibration verification standardsdefined standa
11、rdsused to verify the accuracy of a calibration in the measurementrange of interest. These standards may not be used to performcalibrations, only calibration verifications. Included standardsare opto-mechanical light scatter devices, gel-like standards, orany other type of stable liquid standard.NOT
12、E 2Calibration verification standards may be instrument specific.3.2.3 nephelometric turbidity measurementthe measure-ment of light scatter from a sample in a direction that is at 90with respect to the centerline of the incident light path. Unitsare NTU (Nephelometric Turbidity Units); when ISO 7027
13、technology is employed units are in FNU (Formazin Nephelo-metric Units).3.2.4 ratio turbidity measurementthe measurement de-rived through the use of a nephelometric detector that serves asthe primary detector and one or more other detectors used to1This test method is under the jurisdiction of ASTM
14、Committee D19 on Waterand is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-phology, and Open-Channel Flow.Current edition approved June 15, 2010. Published August 2010. Originallyapproved in 2003. Last previous edition approved in 2003 as D6855 03. DOI:10.1520/D6855-10.2For r
15、eferenced 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.3Withdrawn. The last approved version of this historical standard i
16、s referencedon www.astm.org.4Available from United States Environmental Protection Association (EPA),Ariel Rios Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460.5Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1*A Summary of Changes se
17、ction appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United Spensate for variation in incident light fluctuation, straylight, instrument noise, or sample color.3.2.5 reference turbidity standarda standard that i
18、s syn-thesized reproducibly from traceable raw materials by a skilledanalyst. All other standards are traced back to this standard.The reference standard for turbidity is formazin (see 9.2.2).3.2.6 seasoningthe process of conditioning laboratoryglassware with the standard to be diluted to a lower va
19、lue. Theprocess reduces contamination and dilution errors. See Appen-dix X2 for the suggested procedure.3.2.7 stray lightall light reaching the detector other thanthat contributed by the sample. For example: ambient lightleakage, internal reflections and divergent light in opticalsystems.3.2.8 turbi
20、dimeteran instrument that measures light scat-ter using a nephelometric detector. Examples include photo-electric nephelometers and ratio photoelectric nephelometers.3.2.9 turbidityan expression of the optical properties of asample that causes light rays to be scattered and absorbedrather than trans
21、mitted in straight lines through the sample.Turbidity of water is caused by the presence of suspended anddissolved matter such as clay, silt, finely divided organicmatter, plankton, other microscopic organisms, organic acids,and dyes.4. Summary of Test Method4.1 The optical property expressed as tur
22、bidity is measuredby the scattering effect that suspended particulate material haveon light; the 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 an
23、d composition of the particles in thewater, and also to the wavelength of the incident light.4.2 The method is based upon a comparison of the intensityof light scattered by the sample with the intensity of lightscattered by a reference suspension. Turbidity values aredetermined by a nephelometer, wh
24、ich measures light scatterfrom a sample in a direction that is at 90 with respect to thecenterline 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-depe
25、ndent manufacturing processes.Removal is often accomplished by coagulation, settling, andfiltration. 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
26、as thatfound in drinking water, process water, and high purityindustrial water.5.3 When reporting 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
27、 sets.5.3.1 Table 1 describes technologies and reporting results(see also Refs (1),(2),(3).6Those technologies listed areappropriate for the range of measurement prescribed in thismethod. Others may come available in the future. Fig. X5.1provides a flow chart to aid in selection of the appropriatete
28、chnology for low-level static turbidity applications.5.3.2 If a design that falls outside 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 a
29、pplication, bubbles, color and large particles,although they cause turbidity, may result in interferences inmeasured turbidity as determined by this method. Bubblescause a positive interference and color typically causes anegative interference. Dissolved material that imparts a colorto the water may
30、 cause errors in pure nephelometric reading-s,unless the instrument has special compensating 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 wav
31、elengths of incident light aresignificantly absorbed, a negative interference will result 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 insid
32、e and outside and dis-carded when they become etched or scratched. The samplecells 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 Ideally, the same inde
33、xed 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 3Indexing of the sample cell to the instrument well is accom-pl
34、ished by placing a mark on the top of the sample cell and a similar markon the upper surface of the well so that the sample cell can be placed inthe well in an exact position each time.NOTE 4Sample cells can be matched by first filling with dilutionwater (see 8.2). Allow the sample cell to stand for
35、 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 severe errors in measur
36、ement.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 having6The boldface numbers in parenthese
37、s refer to the list of references at the end ofthis standard.D6855 102turbidities of less 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, d
38、efined verifica-tion standards (see 12.2).NOTE 5Consult manufacturers instructions for 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 method.7.3 Photoelectric Nephelomete
39、r:7.3.1 This instrument uses a light source for illuminating thesample and a single photodetector with a readout device toTABLE 1 Applicable Technologies Available for Performing Static Turbidity Measurements Below 5 NTUDesign andReporting UnitProminent Application Key Design Features Typical Instru
40、ment Range Suggested ApplicationNephelometricnon-ratio (NTU)White light turbidimeters. Complywith USEPA Method 180.1 (1)for low level turbidity monitoring.Detector centered at 90 relativeto the incident light beam. Usesa white light spectral source.0.020 to 40 Regulatory reportingof clean waterRatio
41、 White Lightturbidimeters (NTRU)Complies with ISWTR regulations andStandard Method 2130B. (2)Can be used for bothlow and high levelmeasurement.Used a white light spectral source.Primary detector centered at 90.Other detectors located at other angles.An instrument algorithm uses acombination of detec
42、tor readings togenerate the turbidity reading.0.020 to10 000 Regulatory Reporting ofclean waterNephelometric, near-IRturbidimeters,non-ratiometric (FNU)Complies with ISO 7027.The wavelength is less susceptibleto color interferences.Applicable for samples with colorand good for low level monitoring.D
43、etector centered at 90 relative tothe incident light beam. Uses a near-IR(780-900 nm) monochromatic light source.0.012 to 1000 0 - 40 ISO 7027Regulatory reportingNephelometric near-IRturbidimeters,ratio metric (FNRU)Complies with ISO 7027. Applicablefor samples with high levelsof color and for monit
44、oringto high turbidity levels.Uses a near-IR monochromatic lightsource (780-900 nm). Primary detectorcentered at 90. Other detectors locatedat other angles. An instrument algorithmuses a combination of detector readingsto generate the turbidity reading.0.012 to 10 000 0 - 40 ISO 7027Regulatory repor
45、tingNephelometric TurbidityMultibeam Unit (NTMU)Is applicable to EPA regulatorymethod GLI Method 2. (2)Applicable to drinking waterand wastewater monitoring applications.Detectors are geometrically centered at90 and 180. An instrument algorithm usesa combination of detector readings,which may differ
46、 for turbiditiesvarying magnitude.0.012 to 4000 0 to 40 Reporting forEPA and ISO compliancemNTU Is applicable to reporting of cleanwaters and filter performancemonitoring. Very sensitive toturbidity changes in lowturbidity samples. (3)Nephelometric method involving alaser-based light source at 660-n
47、m anda high sensitivity photo-multplier tube(PMT) detector for light scattered at 90.1000 mNTU=1NTU5 to 5000 mNTU or0.005 to 5.000 NTU0-5000 mNTU, for EPAcompliance reporting ondrinking water systemsFIG. 1 Photoelectric NephelometerD6855 103indicate the intensity of light scattered at right angle(s)
48、 (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 free from significant drift after a short warm-up period. Thelight source shall be a Tungsten lamp ope
49、rated at a colortemperature between 2200 and 3000 K (USEPA Method180.1). Light Emitting Diodes (LEDs) or laser diodes indefined wavelengths ranging from 400 to 900 nm may also beused if accurately characterized 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 by a wavelength of between 400 and 900 nmwith a ban
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