1、Designation: D7725 12Standard Test Method for theContinuous Measurement of Turbidity Above 1 TurbidityUnit (TU)1This standard is issued under the fixed designation D7725; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、last revision. A number 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 online and inline determi-nation of high-level turbidity in water that is greater than 1.0
3、turbidity units (TU) in municipal, industrial and environmentalusage.1.2 In principle there are three basic applications for on-linemeasurement set ups. This first is the slipstream (bypass)sample technique. For the slipstream sample technique aportion of sample is transported out of the process and
4、 throughthe measurement apparatus. It is then either transported back tothe process or to waste. The second is the in-line measurementwhere the sensor is brought directly into the process (seeFigure 8). The third basic method is for in-situ monitoring ofsample waters. This principle is based on the
5、insertion of asensor into the sample itself as the sample is being processed.The in-situ use in this method is intended for the monitoring ofwater during any step within a processing train, includingimmediately before or after the process itself.1.3 This test method is applicable to the measurement
6、ofturbidities greater than 1.0 turbidity unit (TU). The absoluterange is dictated by the technology that is employed.1.4 The upper end of the measurement range is left unde-fined because different technologies described in this methodcan cover very different ranges of turbidity.1.5 Many of the turbi
7、dity units and instrument designscovered in this method are numerically equivalent in calibra-tion when a common calibration standard is applied acrossthose designs listed in Table 1. Measurement of a commoncalibration standard of a defined value will also produceequivalent results across these tech
8、nologies. This methodprescribes the assignment of a determined turbidity values tothe technology used to determine those values. Numericalequivalence to turbidity standards is observed between differ-ent technologies but is not expected across a common sample.Improved traceability beyond the scope o
9、f this method may bepracticed and would include the listing of the make and modelnumber of the instrument used to determine the turbidityvalues.1.5.1 In this method, calibration standards are often definedin NTU values, but the other assigned turbidity units, such asthose in Table 1 are equivalent.
10、For example,a1NTUformazin standard is alsoa1FNU,a1FAU,a1BU,andsoforth.1.6 This standard does not purport to cover all availabletechnologies for high-level turbidity measurement.1.7 This test method was tested on different waters, and withstandards that will serve as surrogates to samples. It is theu
11、sers responsibility to ensure the validity of this test methodfor waters of untested matrices.1.8 Those samples with the highest particle densities typi-cally prove to be the most difficult to measure. In these cases,the process monitoring method can be considered with ad-equate measurement protocol
12、s installed.1.9 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 appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Re
13、fer to the MSDSsfor all chemicals used in this procedure.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD386
14、4 Guide for Continual On-Line Monitoring Systemsfor Water AnalysisD6698 Test Method for On-Line Measurement of TurbidityBelow 5 NTU in WaterD7315 Test Method for Determination of TurbidityAbove 11This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibilit
15、y 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 Jan. 1, 2012. Published June 2012. DOI: 10.1520/D772512.2For referenced ASTM standards, visit the AST
16、M 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 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Unite
17、d States.Turbidity Unit (TU) in Static Mode3. Terminology3.1 DefinitionsFor definitions of terms used in thismethod refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 Calibration turbidity standard, nA turbidity stan-dard that is traceable and equivalent to the refer
18、ence turbiditystandard to within statistical errors; calibration turbidity stan-dards include commercially prepared 4000 NTU Formazin,stabilized formazin, and styrenedivinylbenzene (SDVB). Dis-cussion - these standards may be used to calibrate the instru-ment. Calibration turbidity standards may be
19、instrument spe-cific.3.2.2 calibration-verification standards, nDefined stan-dards used to verify the accuracy of a calibration in theTABLE 1 Technologies for Measuring Turbidity Greater Than 1 TU that can be used for In-Line or On-Line ApplicationsDesign and Reporting Unit Prominent Application Key
20、 Design Features Typical Instrument Range Suggested ApplicationNephelometric non- ratio(NTU)White light turbidimetersComply with EPA 180.1 for lowlevel turbidity monitoring.Detector centered at 90 degreesrelative to the incident lightbeam. Uses a white light spectralsource.0.012 to 40 NTU Regulatory
21、 reporting of cleanwaterRatio White Light tur bidimeters(NTRU)Complies with ISWTRregulations and Standard Method2130B. Can be used for bothlow and high level measurement.Used a white light spectralsource. Primary detectorcentered at 90. Other detectorslocated at other angles. Aninstrument algorithm
22、uses acombination of detector readingsto generate the turbidity reading.0.012 - 10,000 NTRU Regulatory Reporting of cleanwaterFormazin Nephelometric, near-IR turbidimeters, non-ratiometric (FNU)Complies with ISO 7027. Thewavelengthis less susceptible tocolor interferences. Applicablefor samples with
23、 color and goodfor low level monitoring.Detector centered at 90 degreesrelative to the incident lightbeam. Uses a near-IR (780-900nm) monochromatic light source.0.012 - 1,000 FNU 0 - 40 FNU ISO 7027Regulatory reportingFormazin Nephelometric near-IRturbidimeters, ratiometric(FNRU)Complies with ISO 70
24、27.Applicable for samples with highlevels of color and for monitoringto high turbidity levels.Uses a near-IR monochromaticlight source (780-900 nm).Primary detector centered at 90.Other detectors located at otherangles. An instrument algorithmuses a combination of detectorreadings to generate the tu
25、rbidityreading.0.012 - 1,000 FNU 0- 40 FNRU ISO 7027Regulatory reportingSurface Scatter Turbi dimeters(SSU)Turbidity is determined throughlight scatter from a definedvolume beneath the surface of asample. Applicable for reportingfor USEPA compliancemonitoring.Detector centered at 90 degreesrelative
26、to the incident lightbeam. Uses a “white light”spectral source.0.012-10,000 FNRU 10 - 10,000 SSUFormazin NephelometricTurbidity Multibeam Unit(FNMU)Is applicable to EPA regulatorymethod GLI Method 2.Applicable to drinking water andwastewater monitoringapplications.Detectors are geometricallycentered
27、 at 0 and 90. Aninstrument algorithm uses acombination of detector readings,which may differ for turbiditiesvarying magnitude.0.012 to 4000 NTMU 0 to 40 NTMU Reporting forEPA and ISO complianeFormazin Attenuation Unit(FAU)Compliance Reporting for ISO7027 for samples that exceed 40unitsUses a near-IR
28、 light source at860630 nm and the detector is 0degrees relative to the centerlineof the incident light beam. Themeasurement is an attenuationmeasurement.10 - 10,000+ FAU 100 - 10,000+ FAU Reporting for ISO7027 for levels in excess of 40unitsAttenuation Unit (AU) Not applicable for regulatorypurposes
29、. Best applied forsamples with high levelturbidity.Uses a white light spectralsource (400-680 nm range).Detector geometry is 0 relativeto the incident light beam.10 - 10,000+ AU 100 - 10,000+ AUFormazin Back Scatter (FBU) Not applicable for regulatorypurposes. Best applied to highturbidity samples.
30、Backscatter iscommon probe technology and isbest applied in higher turbiditysamples.Uses a near-IR monochromaticlight source in the 780-900 nmrange. Detector geometry isbetween 90 and 180 relative tothe incident light beam.10,000+ FBU 10,000 FBUForward Scatter Ratio Unit(FSRU)The technology encompas
31、ses asingle, light source and twodetectors. Light sources can varyfrom single wavelength topolychromatic sources. Thedetection angle for the forwardscatter detector is between 0 and90- degrees relative to thecenterline of the incident lightbeam.The technology is sensitive toturbidities as low as 1 T
32、U. Theratio technology helps tocompensate for color interferenceand fouling.The measurement of ambientwaters such as streams, lakes,and rivers. The range is typicallyfrom about 1 800 FSRU,depending on the manufacturer.Forward Scatter Ratio Unit(FSRU)D7725 122measurement range of interest. Discussion
33、 - these standardsmay not be used to perform calibrations, only calibrationverifications. Included verification standards are opto-mechanical lightscatter devices, gel-like standards, or any othertype of stable-liquid standard. Calibration verification stan-dards may be instrument specific.3.2.3 Det
34、ection Angle, nThe angle formed with its apex atthe center of the analysis volume of the sample, and such thatone vector coincides with the centerline of the incident lightsources emitted radiation and the second vector projects to thecenter of the primary detectors view. Discussion this angleis use
35、d for the differentiation of turbidity-measurement tech-nologies that are used in this method.3.2.3.1 Nephelometric-Detection Angle, nThe angle thatis formed between the incident light source and the detector,and that is at 90-degrees3.2.3.2 Backscatter- detection Angle, nThe angle that isformed bet
36、ween the incident light source and the primarydetector, and that is greater than 90- degrees and up to180-degrees.3.2.3.3 Attenuation-detection Angle, nThe angle that isformed between the incident light source and the primarydetector, and that is at exactly 0- degrees.3.2.3.4 Discussionthis is typic
37、ally a transmission mea-surement.3.2.3.5 Forward-scatter-detection angle, nThe angle thatis formed between the incident light source and the primarydetector, and that is between 0 and 90-degrees.3.2.3.6 Discussionmost designs will have an angle be-tween 10 and 45 degrees.3.2.4 In-situ Turbidimeter,
38、nA turbidimeter that deter-mines the turbidity of a sample using a sensor that is placeddirectly in the sample. Discussion - this turbidimeter does notrequire transport of the sample to or from the sensor.3.2.5 nephelometric-turbidity measurement, nThe mea-surement of light scatter from a sample in
39、a direction that is at90 with respect to the centerline of the incident-light path.Discussion - units are NTU (Nephelometric Turbidity Units).When ISO 7027 technology is employed units are FNU(Formazin Nephelometric Units).3.2.6 ratio- turbidity measurement, nThe measurementderived through the use o
40、f a nephelometric detector that servesas the primary detector, and one or more other detectors usedto compensate for variation in incident-light fluctuation, straylight, instrument noise, or sample color.3.2.7 reference-turbidity standard, nA standard that issynthesized reproducibly from traceable r
41、aw materials by theuser. Discussion - all other standards are traced back to thisstandard. The reference standard for turbidity is formazin.3.2.8 seasoning, vThe process of conditioning labwarewith the standard that will be diluted to a lower value.Discussion - the process reduces contamination and
42、dilutionerrors. See Appendix X2 for suggested procedure.3.2.9 slipstream, nAn on-line technique for analysis of asample as it flows through a measurement chamber of aninstrument. Discussion - the sample is transported from thesource into the instrument (for example a turbidimeter), ana-lyzed, and th
43、en transported to drain or back to the processstream. The term is synonymous with the terms “on-lineinstrument” or “continuous-monitoring instrument.”3.2.10 stray light, nall light reaching the detector otherthan that contributed by the sample.3.2.11 turbidimeter, nAn instrument that measures lights
44、catter caused by particulates within a sample and converts themeasurement to a turbidity value. Discussion - the detectedlight is quantitatively converted to a numeric value that istraced to a light-scatter standard. See Test Method D7315-06.3.2.12 turbidity, nAn expression of the optical properties
45、of a sample that cause light rays to be scattered and absorbedrather than transmitted in straight lines through the sample.Discussion - Turbidity of water is caused by the presence ofmatter such as clay, silt, finely divided organic matter, plank-ton, other microscopic organisms, organic acids, and
46、dyes3.2.13 Surface-Scatter Detection, nA turbidity measure-ment that is determined through the detection of light scattercaused by particles within a defined volume beneath thesurface of a sample. Discussion - both the light source anddetector are positioned above the surface of the sample. Theangle
47、 formed between the centerline of the light source anddetector is typically at 90-degrees. Particles at the surface andin a volume below the surface of the sample contribute to theturbidity reading.4. Significance and Use4.1 Turbidity is undesirable in drinking water, plant effluentwaters, water for
48、 food and beverage processing, and for a largenumber of other water dependent manufacturing processes.Removal of suspended matter is accomplished by coagulation,settling, and filtration. Measurement of turbidity provides arapid means of process control to determine when, how, and towhat extent the w
49、ater must be treated to meet specifications.4.2 This test method is suitable for the on-line monitoring ofturbidity such as that found in drinking water, process water,and high purity industrial waters.4.3 The instrumentation used must allow for the continuouson-line monitoring of a sample stream.4.4 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 sets.4.4.1 Table 1 describing techno
