1、Designation: D7726 11Standard Guide forThe Use of Various Turbidimeter Technologies forMeasurement of Turbidity in Water1This standard is issued under the fixed designation D7726; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 year of 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 guide covers the best practices for use of variousturbidimeter designs for measurement of turbidity in w
3、atersincluding: drinking water, wastewater, industrial waters and forregulatory and environmental monitoring. This guide coversboth continuous and static measurements.1.1.1 In principle there are three basic applications foron-line measurement set ups. The first is the bypass orslipstream technique
4、a portion of sample is transported fromthe process or sample stream and to the turbidimeter foranalysis. It is then either transported back to the sample streamor to waste. The second is the in-line measurement the sensoris submerged directly into the sample or process stream, whichis typically cont
5、ained in a pipe. The third is in-situ where thesensor is directly inserted into the sample stream. The in-situprinciple is intended for the monitoring of water during anystep within a processing train, including immediately before orafter the process itself.1.1.2 Static covers both benchtop and port
6、able designs forthe measurement of water samples that are captured into a celland then measured.1.2 Depending on the monitoring goals and desired datarequirements, certain technologies will deliver more desirableresults for a given application. This guide will help the useralign a technology to a gi
7、ven application with respect to bestpractices for data collection.1.3 Some designs are applicable for either a lower or uppermeasurement range. This guide will help provide guidance tothe best-suited technologies based given range of turbidity.1.4 Modern electronic turbidimeters are comprised of man
8、yparts that can cause them to produce different results onsamples. The wavelength of incident light used, detector type,detector angle, number of detectors (and angles), and opticalpathlength are all design criteria that may be different amonginstruments. When these sensors are all calibrated with t
9、hesample turbidity standards, they will all read the standards thesame. However, samples comprise of completely differentmatrices and may measure quite differently among thesedifferent technologies.1.4.1 This guide does not provide calibration informationbut rather will defer the user to the appropr
10、iateASTM turbiditymethod and its calibration protocols. When calibrated ontraceable primary turbidity standards, the assigned turbidityunits such as those used in Table 1. are equivalent. Forexample, a 1 NTU formazin standard is also equivalent inmeasurement magnitude toa1FNU,a1FAU,anda1BUstandard a
11、nd so forth.1.4.2 Improved traceability beyond the scope of this guidemay be practiced and would include the listing of the make andmodel number of the instrument used to determine the turbidityvalues.1.5 This guide does not purport to cover all availabletechnologies for high-level turbidity measure
12、ment.1.6 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.7 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 establis
13、h appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.8 This guide does not purport to address all of the safetyconcerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safe
14、ty andhealth practices and determine the applicability of regulatorylimitations prior to use. Refer to the MSDSs for all chemicalsused in this procedure.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD3977 Test Methods for Determining Sediment Concentra-tion in Water S
15、amplesD6698 Test Method for On-Line Measurement of TurbidityBelow 5 NTU in Water1This guide is under the jurisdiction of ASTM Committee D19 on Water and isthe direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,and Open-Channel Flow.Current edition approved May 1, 2011. Publishe
16、d May 2011. DOI: 10.1520/D772611.2For 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 ASTM Internationa
17、l, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.D6855 Test Method for Determination of Turbidity Below 5NTU in Static ModeD7315 Test Method for Determination of TurbidityAbove 1Turbidity Unit (TU) in Static Mode2.2 Other References:United States Geological Surv
18、ey (USGS), National FieldManual for the Collection of Water Quality Datai. Web-site: http/www.usgs.gov/FieldManual/Chapters6/6.7.htm.Wagner, R.J. et al. Guidelines and Standard Procedures forContinuous Water-Quality Monitors: Station Operation,Record Computation, and Data Reporting, USGS Enter-prise
19、 Publishing Network, 2005. (http:/pubs.usgs.gov/tm/2006/tm1D3/)3. Terminology3.1 Definitions: For definitions of terms used in this methodrefer to Terminology D11293.23.2.1 Calibration turbidity standard, na turbidity stan-dard that is traceable and equivalent to the reference turbiditystandard to w
20、ithin statistical errors; calibration turbidity stan-dards include commercially prepared 4000 NTU Formazin,stabilized formazin, and styrenedivinylbenzene (SDVB).3.2.1.1 Discussionthese standards may be used to cali-brate the instrument.3.2.2 Calibration-verification standards, nDefinedstandards used
21、 to verify the accuracy of a calibration in themeasurement range of interest.3.2.2.1 Discussionthese standards may not be used toperform calibrations, only calibration verifications. Includedverification standards are opto-mechanical light-scatter de-vices, gel-like standards, or any other type of s
22、table-liquidstandard.3.2.3 Detection 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 vie
23、w.3.2.3.1 Discussionthis angle is used for the differentiationof turbidity-measurement technologies that are used in thismethod.3.2.4 Nephelometric-Detection Anglethe angle that isformed between the incident light source and the detector, andthat is at 90 degrees.3.2.5 Backscatter-detection Angle, n
24、The angle that isformed between the incident light source and the primarydetector, and that is greater than 90 degrees and up to 180degrees.3.2.6 Attenuation-detection Angle, nThe angle that isformed between the incident light source and the primarydetector, and that is at exactly 0 degrees.3.2.6.1
25、Discussionthis is typically a transmission mea-surement.3.2.7 Forward-scatter-detection angle, nThe angle that isformed between the incident light source and the primarydetector, and that is greater than 0 degrees but less than 90degrees.3.2.7.1 Discussionmost designs will have an angle be-tween 135
26、 degrees and 180 degrees.3.2.8 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.3.2.8.1 Discussionboth the light source and detector arepositioned above the surface
27、 of the sample. The angle formedbetween the centerline of the light source and detector istypically at 90 degrees. Particles at the surface and in a volumebelow the surface of the sample contribute to the turbidityreading.3.2.9 In-situ nephelometer, na turbidimeter that deter-mines the turbidity of
28、a sample using a sensor that is placeddirectly in the sample.3.2.9.1 Discussionthis turbidimeter does not requiretransport of the sample to or from the sensor.3.2.10 Nephelometric-turbidity measurement, nthe mea-surement of light scatter from a sample in a direction that is at90 with respect to the
29、centerline of the incident-light path. D3.2.10.1 Discussionunits are NTU (Nephelometric Tur-bidity Units). When ISO 7027 technology is employed unitsare FNU (Formazin Nephelometric Units).3.2.11 Pathlength, nThe greatest distance that the sum ofthe incident light and scattered light can travel withi
30、n a samplevolume (cell or view volume).3.2.11.1 Discussionthe pathlength is typically measuredalong the centerline of the incident-light beam plus thescattered light. The pathlength includes only the distance thelight and scattered light travel within the sample itself.3.2.12 Ratio-turbidity measure
31、ment, nthe measurementderived through the use of a nephelometric detector that servesas the primary detector, and one or more other detectors usedto compensate for variation in incidentlight fluctuation, straylight, instrument noise, or sample color.3.2.13 Reference-turbidity standard, na standard t
32、hat issynthesized reproducibly from traceable raw materials by theuser.3.2.13.1 Discussionall other standards are traced back tothis standard. The reference standard for turbidity is formazin.3.2.14 Seasoning, vthe process of conditioning labwarewith the standard that will be diluted to a lower valu
33、e to reducecontamination and dilution errors.3.2.15 Slipstream, nan on-line technique for analysis of asample as it flows through a measurement chamber of aninstrument.3.2.15.1 Discussionthe sample is transported from thesource into the instrument (for example, a turbidimeter),analyzed, and then tra
34、nsported to drain or back to the processstream. The term is synonymous with the terms “on-lineinstrument” or “continuous monitoring instrument.”3.2.16 Stray light, nall light reaching the detector otherthan that contributed by the sample.3.2.17 Turbidimeter, nan instrument that measures lightscatter
35、 caused by particulates within a sample and converts themeasurement to a turbidity value.3.2.17.1 Discussionthe detected light is quantitativelyconverted to a numeric value that is traced to a light-scatterstandard. See Test Method D7315.D7726 1123.2.18 Turbidity, nan expression of the optical prope
36、rtiesof a sample that causes light rays to be scattered and absorbedrather than transmitted in straight lines through the sample.3.2.18.1 Discussionturbidity of water is caused by thepresence of matter such as clay, silt, finely divided organicmatter, plankton, other microscopic organisms, organic a
37、cids,and dyes.3.2.19 Calibration drift, nthe error that is the result ofdrift in the sensor reading from the last time the sensor wascalibrated and is determined by the difference betweencleaned-sensor readings in calibration standards and the true,temperature-compensated value of the calibration st
38、andards.3.2.20 Fouling, vthe measurement error that can resultfrom a variety of sources and is determined by the differencebetween sensor measurements in the environment before andafter the sensors are cleaned.3.2.21 Continuous, adjthe type of automated measure-ment at a defined-time interval, where
39、 no human interaction isrequired to collect and log measurements. Discussion - mea-surement intervals range from seconds to months, dependingon monitoring goals of a given site.3.2.22 Sonde, na monitoring instrument that contains twoor more measurement sensors that share common power,transmitting, a
40、nd data logging.3.2.22.1 Discussion a sonde usually has one end thatcontains the measurement sensors, which are in close proxim-ity to each other and together are submerged in a sample.3.2.23 Metadata, nthe ancillary descriptive informationthat describes instrument, sample, and ambient conditionsund
41、er which data were collected.3.2.23.1 DiscussionMetadata provide information aboutdata sets. An example is the useful background informationregarding the sampling site, instrument setup, and calibrationand verification results for a given set of turbidity data,(especially when data are critically re
42、viewed or comparedagainst another data set).3.2.24 Technology, na general classification of a turbidi-meter design that incorporates the type and wavelength of theincident-light source, detection angles, and the number ofdetectors used to generate a turbidity measurement and itsdefined reporting uni
43、t.3.2.24.1 Discussion in ASTM turbidity methods, thetechnology is based on type and number of light sources, andtheir respective wavelength, detector angle(s), and number ofdetectors used in the technology to generate the turbidity value.3.2.25 Design, na more detailed technology descriptionthat wil
44、l encompass all of the elements making up a technol-ogy, plus any inherent criteria used to generate a specificturbidity value.3.2.25.1 Discussionthe design will typically translate intoa specific make or model of an instrument.4. Summary of Practice4.1 This guide is to assist the user in meeting an
45、d under-standing the following criteria with respect to turbidity mea-surements:4.1.1 The selection of the appropriate technology for mea-surement of a given sample with implied characteristics4.1.2 Help in the selection of a measurement technologythat will help meet the scope of requirements (goals
46、) for use ofthe data.4.1.3 Assist in the selection of a technology that is bestsuited to withstand the expected environmental and sampledeviations over the course of data collection. Examples ofdeviations would be expected measurement range and interfer-ences.4.1.4 Understand both the general streng
47、ths and limitationsfor a given type (design) of technology in relation to overcom-ing known interferences in turbidity measurement.4.1.5 Provide general procedures that can be used to deter-mine whether a given technology is suitable for use in a givensample or a given application.4.1.6 Understand t
48、he need for the user to include criticalmetadata related to turbidity measurement.4.1.7 This guide will help the user select the appropriatetechnology for regulatory purposes.5. Significance and Use5.1 Turbidity is a measure of scattered light that results fromthe interaction between a beam of light
49、 and particulate materialin a liquid sample. Particulate material is typically undesirablein water from a health perspective and its removal is oftenrequired when the water is intended for consumption. Thus,turbidity has been used as a key indicator for water quality toassess the health and quality of environmental water sources.Higher turbidity values are typically associated with poorerwater quality.5.1.1 Turbidity is also used in environmental monitoring toassess the health and stability of water-based ecosystems suchas in lakes, r
