ASTM D7726-11(2016)e1
(Guide)Standard Guide for The Use of Various Turbidimeter Technologies for Measurement of Turbidity in Water
Standard Guide for The Use of Various Turbidimeter Technologies for Measurement of Turbidity in Water
SIGNIFICANCE AND USE
5.1 Turbidity is a measure of scattered light that results from the interaction between a beam of light and particulate material in a liquid sample. Particulate material is typically undesirable in water from a health perspective and its removal is often required when the water is intended for consumption. Thus, turbidity has been used as a key indicator for water quality to assess the health and quality of environmental water sources. Higher turbidity values are typically associated with poorer water quality.
5.1.1 Turbidity is also used in environmental monitoring to assess the health and stability of water-based ecosystems such as in lakes, rivers and streams. In general, the lower the turbidity, the healthier the ecosystem.
5.2 Turbidity measurement is a qualitative parameter for water but its traceability to a primary light scatter standard allows the measurement to be applied as a quantitative measurement. When used as a quantative measurement, turbidity is typically reported generically in turbidity units (TUs).
5.2.1 Turbidity measurements are based on the instruments’ calibration with primary standard reference materials. These reference standards are traceable to formazin concentrate (normally at a value of 4000 TU). The reference concentrate is linearly diluted to provide calibration standard values. Alternative standard reference materials, such as SDVB co-polymer or stabilized formazin, are manufactured to match the formazin polymer dilutions and provide highly consistent and stable values for which to calibrate turbidity sensors.
5.2.1.1 When used for regulatory compliance reporting, specific turbidity calibration standards may be required. The user of this guide should check with regulatory entities regarding specifics of allowable calibration standard materials.
5.2.2 The traceability to calibrations from different technologies (and other calibration standards) to primary formazin standards provides for a basis for defined turbidity uni...
SCOPE
1.1 This guide covers the best practices for use of various turbidimeter designs for measurement of turbidity in waters including: drinking water, wastewater, industrial waters, and for regulatory and environmental monitoring. This guide covers both continuous and static measurements.
1.1.1 In principle there are three basic applications for on-line measurement set ups. The first is the bypass or slipstream technique; a portion of sample is transported from the process or sample stream and to the turbidimeter for analysis. It is then either transported back to the sample stream or to waste. The second is the in-line measurement; the sensor is submerged directly into the sample or process stream, which is typically contained in a pipe. The third is in-situ where the sensor is directly inserted into the sample stream. The in-situ principle is intended for the monitoring of water during any step within a processing train, including immediately before or after the process itself.
1.1.2 Static covers both benchtop and portable designs for the measurement of water samples that are captured into a cell and then measured.
1.2 Depending on the monitoring goals and desired data requirements, certain technologies will deliver more desirable results for a given application. This guide will help the user align a technology to a given application with respect to best practices for data collection.
1.3 Some designs are applicable for either a lower or upper measurement range. This guide will help provide guidance to the best-suited technologies based given range of turbidity.
1.4 Modern electronic turbidimeters are comprised of many parts that can cause them to produce different results on samples. The wavelength of incident light used, detector type, detector angle, number of detectors (and angles), and optical pathlength are all design criteria that may be different among instruments. When these sensors are all calibra...
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This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
´1
Designation: D7726 − 11 (Reapproved 2016)
Standard Guide for
The Use of Various Turbidimeter Technologies for
Measurement of Turbidity in Water
This standard is issued under the fixed designation D7726; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial corrections were made throughout in November 2016.
1. Scope 1.4 Modern electronic turbidimeters are comprised of many
parts that can cause them to produce different results on
1.1 This guide covers the best practices for use of various
samples. The wavelength of incident light used, detector type,
turbidimeter designs for measurement of turbidity in waters
detector angle, number of detectors (and angles), and optical
including: drinking water, wastewater, industrial waters, and
pathlength are all design criteria that may be different among
for regulatory and environmental monitoring. This guide cov-
instruments. When these sensors are all calibrated with the
ers both continuous and static measurements.
sample turbidity standards, they will all read the standards the
1.1.1 In principle there are three basic applications for
same. However, samples comprise of completely different
on-line measurement set ups. The first is the bypass or
matrices and may measure quite differently among these
slipstream technique; a portion of sample is transported from
different technologies.
the process or sample stream and to the turbidimeter for
1.4.1 This guide does not provide calibration information
analysis. It is then either transported back to the sample stream
but rather will defer the user to the appropriateASTM turbidity
or to waste. The second is the in-line measurement; the sensor
method and its calibration protocols. When calibrated on
is submerged directly into the sample or process stream, which
traceable primary turbidity standards, the assigned turbidity
is typically contained in a pipe. The third is in-situ where the
unitssuchasthoseusedinTable1areequivalent.Forexample,
sensor is directly inserted into the sample stream. The in-situ
a 1 NTU formazin standard is also equivalent in measurement
principle is intended for the monitoring of water during any
magnitude toa1FNU,a1FAU,anda1BU standard and so
step within a processing train, including immediately before or
forth.
after the process itself.
1.4.2 Improved traceability beyond the scope of this guide
1.1.2 Static covers both benchtop and portable designs for
maybepracticedandwouldincludethelistingofthemakeand
the measurement of water samples that are captured into a cell
modelnumberoftheinstrumentusedtodeterminetheturbidity
and then measured.
values.
1.2 Depending on the monitoring goals and desired data
1.5 This guide does not purport to cover all available
requirements, certain technologies will deliver more desirable
technologies for high-level turbidity measurement.
results for a given application. This guide will help the user
1.6 The values stated in SI units are to be regarded as
align a technology to a given application with respect to best
standard. No other units of measurement are included in this
practices for data collection.
standard.
1.3 Some designs are applicable for either a lower or upper
1.7 This standard does not purport to address all of the
measurement range. This guide will help provide guidance to
safety concerns, if any, associated with its use. It is the
the best-suited technologies based given range of turbidity.
responsibility 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.
This guide is under the jurisdiction of ASTM Committee D19 on Water and is
the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,
1.8 This guide does not purport to address all of the safety
and Open-Channel Flow.
concerns, if any, associated with its use. It is the responsibility
Current edition approved Nov. 1, 2016. Published November 2016. Originally
of the user of this standard to establish appropriate safety and
approved in 2011. Last previous edition approved in 2011 as D7726 – 11. DOI:
10.1520/D7726-11R16E01. health practices and determine the applicability of regulatory
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D7726 − 11 (2016)
limitations prior to use. Refer to the MSDSs for all chemicals 3.2.4 continuous, adj—the type of automated measurement
used in this procedure. at a defined-time interval, where no human interaction is
required to collect and log measurements.
2. Referenced Documents
3.2.4.1 Discussion—Measurement intervals range from sec-
onds to months, depending on monitoring goals of a given site.
2.1 ASTM Standards:
D1129 Terminology Relating to Water
3.2.5 design, n—a more detailed technology description that
D3977 Test Methods for Determining Sediment Concentra-
will encompass all of the elements making up a technology,
tion in Water Samples
plus any inherent criteria used to generate a specific turbidity
D6698 Test Method for On-Line Measurement of Turbidity
value.
Below 5 NTU in Water
3.2.5.1 Discussion—The design will typically translate into
D6855 Test Method for Determination of Turbidity Below 5
a specific make or model of an instrument.
NTU in Static Mode
D7315 Test Method for Determination of TurbidityAbove 1 3.2.6 detection angle, n—the angle formed with its apex at
Turbidity Unit (TU) in Static Mode the center of the analysis volume of the sample, and such that
one vector coincides with the centerline of the incident light
2.2 Other References:
source’s emitted radiation and the second vector projects to the
USGS National Field Manual for the Collection of Water
center of the primary detector’s view.
Quality Data
3.2.6.1 Discussion—This angle is used for the differentia-
Wagner’s Field Manual Guidelines and Standard Procedures
tionofturbidity-measurementtechnologiesthatareusedinthis
for Continuous Water-Quality Monitors: Station
Operation, Record Computation, and Data Reporting guide.
3.2.6.2 attenuation-detection angle, n—the angle that is
3. Terminology formed between the incident light source and the primary
detector, and that is at exactly 0 degrees.
3.1 Definitions:
(1) Discussion—This is typically a transmission measure-
3.1.1 For definitions of terms used in this standard, refer to
ment.
Terminology D1129.
3.2.6.3 backscatter-detection angle, n—the angle that is
3.2 Definitions of Terms Specific to This Standard:
formed between the incident light source and the primary
3.2.1 calibration drift, n—the error that is the result of drift
detector, and that is greater than 90 degrees and up to 180
in the sensor reading from the last time the sensor was
degrees.
calibrated and is determined by the difference between
3.2.6.4 nephelometric-detection angle, n—the angle that is
cleaned-sensor readings in calibration standards and the true,
formed between the incident light source and the detector, and
temperature-compensated value of the calibration standards.
that is at 90 degrees.
3.2.2 calibration turbidity standard, n—a turbidity standard
3.2.6.5 forward-scatter-detection angle, n—the angle that is
that is traceable and equivalent to the reference turbidity
formed between the incident light source and the primary
standard to within statistical errors; calibration turbidity stan-
detector, and that is greater than 0 degrees but less than 90
dards include commercially prepared 4000 NTU Formazin,
degrees.
stabilized formazin, and styrenedivinylbenzene (SDVB).
(1) Discussion—Most designs will have an angle between
3.2.2.1 Discussion—These standards may be used to cali-
135 degrees and 180 degrees.
brate the instrument.
3.2.6.6 surface-scatter detection, n—a turbidity measure-
ment that is determined through the detection of light scatter
3.2.3 calibration-verification standards, n—defined stan-
caused by particles within a defined volume beneath the
dards used to verify the accuracy of a calibration in the
surface of a sample.
measurement range of interest.
(1) Discussion—Both the light source and detector are
3.2.3.1 Discussion—These standards may not be used to
positioned above the surface of the sample. The angle formed
perform calibrations, only calibration verifications. Included
between the centerline of the light source and detector is
verification standards are opto-mechanical light-scatter
typically at 90 degrees. Particles at the surface and in a volume
devices, gel-like standards, or any other type of stable-liquid
standard. below the surface of the sample contribute to the turbidity
reading.
3.2.7 fouling, v—the measurement error that can result from
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
a variety of sources and is determined by the difference
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
between sensor measurements in the environment before and
Standards volume information, refer to the standard’s Document Summary page on
after the sensors are cleaned.
the ASTM website.
Available from United States Geological Survey (USGS), USGS Headquarters,
3.2.8 in-situ nephelometer, n—a turbidimeter that deter-
12201 Sunrise Valley Drive, Reston, VA 20192, http://www.usgs.gov/FieldManual/
Chapters6/6.7.htm. mines the turbidity of a sample using a sensor that is placed
Wagner, R. J., et al, Guidelines and Standard Procedures for Continuous
directly in the sample.
Water-Quality Monitors: Station Operation, Record Computation, and Data
3.2.8.1 Discussion—This turbidimeter does not require
Reporting, USGS Enterprise Publishing Network, 2005, available from: http://
pubs.usgs.gov/tm/2006/tm1D3. transport of the sample to or from the sensor.
´1
D7726 − 11 (2016)
3.2.9 metadata, n—the ancillary descriptive information 3.2.18.1 Discussion—In ASTM turbidity test methods, the
that describes instrument, sample, and ambient conditions technology is based on type and number of light sources, and
under which data were collected. their respective wavelength, detector angle(s), and number of
3.2.9.1 Discussion—Metadata provide information about detectorsusedinthetechnologytogeneratetheturbidityvalue.
data sets. An example is the useful background information
3.2.19 turbidimeter, n—an instrument that measures light
regarding the sampling site, instrument setup, and calibration
scatter caused by particulates within a sample and converts the
and verification results for a given set of turbidity data
measurement to a turbidity value.
(especially when data are critically reviewed or compared
3.2.19.1 Discussion—The detected light is quantitatively
against another data set).
converted to a numeric value that is traced to a light-scatter
3.2.10 nephelometric-turbidity measurement, n—the mea- standard. See Test Method D7315.
surement of light scatter from a sample in a direction that is at
3.2.20 turbidity, n—an expression of the optical properties
90° with respect to the centerline of the incident-light path.
of a sample that causes light rays to be scattered and absorbed
3.2.10.1 Discussion—Units are NTU (Nephelometric Tur-
rather than transmitted in straight lines through the sample.
bidity Units). When ISO 7027 technology is employed units
3.2.20.1 Discussion—Turbidity of water is caused by the
are FNU (Formazin Nephelometric Units).
presence of matter such as clay, silt, finely divided organic
3.2.11 pathlength, n—The greatest distance that the sum of matter, plankton, other microscopic organisms, organic acids,
the incident light and scattered light can travel within a sample
and dyes.
volume (cell or view volume).
3.2.11.1 Discussion—The pathlength is typically measured 4. Summary of Practice
along the centerline of the incident-light beam plus the
4.1 This guide is to assist the user in meeting and under-
scattered light. The pathlength includes only the distance the
standing the following criteria with respect to turbidity mea-
light and scattered light travel within the sample itself.
surements:
3.2.12 ratio-turbidity measurement, n—the measurement
4.1.1 The selection of the appropriate technology for mea-
derived through the use of a nephelometric detector that serves
surement of a given sample with implied characteristics.
as the primary detector, and one or more other detectors used
4.1.2 Help in the selection of a measurement technology
to compensate for variation in incidentlight fluctuation, stray
that will help meet the scope of requirements (goals) for use of
light, instrument noise, or sample color.
the data.
4.1.3 Assist in the selection of a technology that is best
3.2.13 reference-turbidity standard, n—a standard that is
suited to withstand the expected environmental and sample
synthesized reproducibly from traceable raw materials by the
deviations over the course of data collection. Examples of
user.
deviations would be expected measurement range and interfer-
3.2.13.1 Discussion—All other standards are traced back to
ences.
this standard. The reference standard for turbidity is formazin.
4.1.4 Understand both the general strengths and limitations
3.2.14 seasoning, v—the process of conditioning labware
for a given type (design) of technology in relation to overcom-
with the standard that will be diluted to a lower value to reduce
ing known interferences in turbidity measurement.
contamination and dilution errors.
4.1.5 Provide general procedures that can be used to deter-
3.2.15 slipstream, n—an on-line technique for analysis of a
mine whether a given technology is suitable for use in a given
sample as it flows through a measurement chamber of an
sample or a given application.
instrument.
4.1.6 Understand the need for the user to include critical
3.2.15.1 Discussion—The sample is transported from the
metadata related to turbidity measurement.
source into the instrument (for example, a turbidimeter),
4.1.7 This guide will help the user select the appropriate
analyzed, and then transported to drain or back to the process
technology for regulatory purposes.
stream. The term is synonymous with the terms “on-line
instrument” or “continuous monitoring instrument.”
5. Significance and Use
3.2.16 sonde, n—a monitoring instrument that contains two
5.1 Turbidityisameasureofscatteredlightthatresultsfrom
or more measurement sensors th
...
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
Designation: D7726 − 11 (Reapproved 2016)
Standard Guide for
The Use of Various Turbidimeter Technologies for
Measurement of Turbidity in Water
This standard is issued under the fixed designation D7726; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial corrections were made throughout in November 2016.
1. Scope 1.4 Modern electronic turbidimeters are comprised of many
parts that can cause them to produce different results on
1.1 This guide covers the best practices for use of various
samples. The wavelength of incident light used, detector type,
turbidimeter designs for measurement of turbidity in waters
detector angle, number of detectors (and angles), and optical
including: drinking water, wastewater, industrial waters, and
pathlength are all design criteria that may be different among
for regulatory and environmental monitoring. This guide cov-
instruments. When these sensors are all calibrated with the
ers both continuous and static measurements.
sample turbidity standards, they will all read the standards the
1.1.1 In principle there are three basic applications for
same. However, samples comprise of completely different
on-line measurement set ups. The first is the bypass or
matrices and may measure quite differently among these
slipstream technique; a portion of sample is transported from
different technologies.
the process or sample stream and to the turbidimeter for
1.4.1 This guide does not provide calibration information
analysis. It is then either transported back to the sample stream
but rather will defer the user to the appropriate ASTM turbidity
or to waste. The second is the in-line measurement; the sensor
method and its calibration protocols. When calibrated on
is submerged directly into the sample or process stream, which
traceable primary turbidity standards, the assigned turbidity
is typically contained in a pipe. The third is in-situ where the
units such as those used in Table 1 are equivalent. For example,
sensor is directly inserted into the sample stream. The in-situ
a 1 NTU formazin standard is also equivalent in measurement
principle is intended for the monitoring of water during any
magnitude to a 1 FNU, a 1 FAU, and a 1 BU standard and so
step within a processing train, including immediately before or
forth.
after the process itself.
1.4.2 Improved traceability beyond the scope of this guide
1.1.2 Static covers both benchtop and portable designs for
may be practiced and would include the listing of the make and
the measurement of water samples that are captured into a cell
model number of the instrument used to determine the turbidity
and then measured.
values.
1.2 Depending on the monitoring goals and desired data
1.5 This guide does not purport to cover all available
requirements, certain technologies will deliver more desirable
technologies for high-level turbidity measurement.
results for a given application. This guide will help the user
1.6 The values stated in SI units are to be regarded as
align a technology to a given application with respect to best
standard. No other units of measurement are included in this
practices for data collection.
standard.
1.3 Some designs are applicable for either a lower or upper
1.7 This standard does not purport to address all of the
measurement range. This guide will help provide guidance to
safety concerns, if any, associated with its use. It is the
the best-suited technologies based given range of turbidity.
responsibility 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.
This guide is under the jurisdiction of ASTM Committee D19 on Water and is
the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,
1.8 This guide does not purport to address all of the safety
and Open-Channel Flow.
concerns, if any, associated with its use. It is the responsibility
Current edition approved Nov. 1, 2016. Published November 2016. Originally
of the user of this standard to establish appropriate safety and
approved in 2011. Last previous edition approved in 2011 as D7726 – 11. DOI:
10.1520/D7726-11R16E01. health practices and determine the applicability of regulatory
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D7726 − 11 (2016)
limitations prior to use. Refer to the MSDSs for all chemicals 3.2.4 continuous, adj—the type of automated measurement
used in this procedure. at a defined-time interval, where no human interaction is
required to collect and log measurements.
2. Referenced Documents
3.2.4.1 Discussion—Measurement intervals range from sec-
onds to months, depending on monitoring goals of a given site.
2.1 ASTM Standards:
D1129 Terminology Relating to Water
3.2.5 design, n—a more detailed technology description that
D3977 Test Methods for Determining Sediment Concentra-
will encompass all of the elements making up a technology,
tion in Water Samples
plus any inherent criteria used to generate a specific turbidity
D6698 Test Method for On-Line Measurement of Turbidity
value.
Below 5 NTU in Water
3.2.5.1 Discussion—The design will typically translate into
D6855 Test Method for Determination of Turbidity Below 5
a specific make or model of an instrument.
NTU in Static Mode
D7315 Test Method for Determination of Turbidity Above 1 3.2.6 detection angle, n—the angle formed with its apex at
Turbidity Unit (TU) in Static Mode the center of the analysis volume of the sample, and such that
one vector coincides with the centerline of the incident light
2.2 Other References:
source’s emitted radiation and the second vector projects to the
USGS National Field Manual for the Collection of Water
center of the primary detector’s view.
Quality Data
3.2.6.1 Discussion—This angle is used for the differentia-
Wagner’s Field Manual Guidelines and Standard Procedures
tion of turbidity-measurement technologies that are used in this
for Continuous Water-Quality Monitors: Station
guide.
Operation, Record Computation, and Data Reporting
3.2.6.2 attenuation-detection angle, n—the angle that is
formed between the incident light source and the primary
3. Terminology
detector, and that is at exactly 0 degrees.
3.1 Definitions:
(1) Discussion—This is typically a transmission measure-
3.1.1 For definitions of terms used in this standard, refer to
ment.
Terminology D1129.
3.2.6.3 backscatter-detection angle, n—the angle that is
3.2 Definitions of Terms Specific to This Standard:
formed between the incident light source and the primary
3.2.1 calibration drift, n—the error that is the result of drift
detector, and that is greater than 90 degrees and up to 180
in the sensor reading from the last time the sensor was
degrees.
calibrated and is determined by the difference between
3.2.6.4 nephelometric-detection angle, n—the angle that is
cleaned-sensor readings in calibration standards and the true,
formed between the incident light source and the detector, and
temperature-compensated value of the calibration standards.
that is at 90 degrees.
3.2.2 calibration turbidity standard, n—a turbidity standard
3.2.6.5 forward-scatter-detection angle, n—the angle that is
that is traceable and equivalent to the reference turbidity
formed between the incident light source and the primary
standard to within statistical errors; calibration turbidity stan-
detector, and that is greater than 0 degrees but less than 90
dards include commercially prepared 4000 NTU Formazin,
degrees.
stabilized formazin, and styrenedivinylbenzene (SDVB).
(1) Discussion—Most designs will have an angle between
3.2.2.1 Discussion—These standards may be used to cali-
135 degrees and 180 degrees.
brate the instrument.
3.2.6.6 surface-scatter detection, n—a turbidity measure-
ment that is determined through the detection of light scatter
3.2.3 calibration-verification standards, n—defined stan-
caused by particles within a defined volume beneath the
dards used to verify the accuracy of a calibration in the
surface of a sample.
measurement range of interest.
(1) Discussion—Both the light source and detector are
3.2.3.1 Discussion—These standards may not be used to
positioned above the surface of the sample. The angle formed
perform calibrations, only calibration verifications. Included
between the centerline of the light source and detector is
verification standards are opto-mechanical light-scatter
typically at 90 degrees. Particles at the surface and in a volume
devices, gel-like standards, or any other type of stable-liquid
standard. below the surface of the sample contribute to the turbidity
reading.
3.2.7 fouling, v—the measurement error that can result from
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
a variety of sources and is determined by the difference
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
between sensor measurements in the environment before and
Standards volume information, refer to the standard’s Document Summary page on
after the sensors are cleaned.
the ASTM website.
Available from United States Geological Survey (USGS), USGS Headquarters,
3.2.8 in-situ nephelometer, n—a turbidimeter that deter-
12201 Sunrise Valley Drive, Reston, VA 20192, http://www.usgs.gov/FieldManual/
mines the turbidity of a sample using a sensor that is placed
Chapters6/6.7.htm.
Wagner, R. J., et al, Guidelines and Standard Procedures for Continuous
directly in the sample.
Water-Quality Monitors: Station Operation, Record Computation, and Data
3.2.8.1 Discussion—This turbidimeter does not require
Reporting, USGS Enterprise Publishing Network, 2005, available from: http://
pubs.usgs.gov/tm/2006/tm1D3. transport of the sample to or from the sensor.
´1
D7726 − 11 (2016)
3.2.9 metadata, n—the ancillary descriptive information 3.2.18.1 Discussion—In ASTM turbidity test methods, the
that describes instrument, sample, and ambient conditions technology is based on type and number of light sources, and
under which data were collected. their respective wavelength, detector angle(s), and number of
detectors used in the technology to generate the turbidity value.
3.2.9.1 Discussion—Metadata provide information about
data sets. An example is the useful background information
3.2.19 turbidimeter, n—an instrument that measures light
regarding the sampling site, instrument setup, and calibration
scatter caused by particulates within a sample and converts the
and verification results for a given set of turbidity data
measurement to a turbidity value.
(especially when data are critically reviewed or compared
3.2.19.1 Discussion—The detected light is quantitatively
against another data set).
converted to a numeric value that is traced to a light-scatter
3.2.10 nephelometric-turbidity measurement, n—the mea- standard. See Test Method D7315.
surement of light scatter from a sample in a direction that is at
3.2.20 turbidity, n—an expression of the optical properties
90° with respect to the centerline of the incident-light path.
of a sample that causes light rays to be scattered and absorbed
3.2.10.1 Discussion—Units are NTU (Nephelometric Tur-
rather than transmitted in straight lines through the sample.
bidity Units). When ISO 7027 technology is employed units
3.2.20.1 Discussion—Turbidity of water is caused by the
are FNU (Formazin Nephelometric Units).
presence of matter such as clay, silt, finely divided organic
3.2.11 pathlength, n—The greatest distance that the sum of
matter, plankton, other microscopic organisms, organic acids,
the incident light and scattered light can travel within a sample and dyes.
volume (cell or view volume).
3.2.11.1 Discussion—The pathlength is typically measured 4. Summary of Practice
along the centerline of the incident-light beam plus the
4.1 This guide is to assist the user in meeting and under-
scattered light. The pathlength includes only the distance the
standing the following criteria with respect to turbidity mea-
light and scattered light travel within the sample itself.
surements:
3.2.12 ratio-turbidity measurement, n—the measurement
4.1.1 The selection of the appropriate technology for mea-
derived through the use of a nephelometric detector that serves
surement of a given sample with implied characteristics.
as the primary detector, and one or more other detectors used
4.1.2 Help in the selection of a measurement technology
to compensate for variation in incidentlight fluctuation, stray
that will help meet the scope of requirements (goals) for use of
light, instrument noise, or sample color.
the data.
4.1.3 Assist in the selection of a technology that is best
3.2.13 reference-turbidity standard, n—a standard that is
suited to withstand the expected environmental and sample
synthesized reproducibly from traceable raw materials by the
deviations over the course of data collection. Examples of
user.
deviations would be expected measurement range and interfer-
3.2.13.1 Discussion—All other standards are traced back to
ences.
this standard. The reference standard for turbidity is formazin.
4.1.4 Understand both the general strengths and limitations
3.2.14 seasoning, v—the process of conditioning labware
for a given type (design) of technology in relation to overcom-
with the standard that will be diluted to a lower value to reduce
ing known interferences in turbidity measurement.
contamination and dilution errors.
4.1.5 Provide general procedures that can be used to deter-
3.2.15 slipstream, n—an on-line technique for analysis of a
mine whether a given technology is suitable for use in a given
sample as it flows through a measurement chamber of an
sample or a given application.
instrument.
4.1.6 Understand the need for the user to include critical
3.2.15.1 Discussion—The sample is transported from the
metadata related to turbidity measurement.
source into the instrument (for example, a turbidimeter),
4.1.7 This guide will help the user select the appropriate
analyzed, and then transported to drain or back to the process
technology for regulatory purposes.
stream. The term is synonymous with the terms “on-line
instrument” or “continuous monitoring instrument.”
5. Significance and Use
3.2.16 sonde, n—a monitoring instrument that contains two
5.1 Turbidity is a measure of scattered light that results from
or more measurement sensors that share common power,
the interaction between a beam of light and pa
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
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Designation: D7726 − 11 D7726 − 11 (Reapproved 2016)
Standard Guide for
The Use of Various Turbidimeter Technologies for
Measurement of Turbidity in Water
This standard is issued under the fixed designation D7726; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial corrections were made throughout in November 2016.
1. Scope
1.1 This guide covers the best practices for use of various turbidimeter designs for measurement of turbidity in waters including:
drinking water, wastewater, industrial waters, and for regulatory and environmental monitoring. This guide covers both continuous
and static measurements.
1.1.1 In principle there are three basic applications for on-line measurement set ups. The first is the bypass or slipstream
techniquetechnique; a portion of sample is transported from the process or sample stream and to the turbidimeter for analysis. It
is then either transported back to the sample stream or to waste. The second is the in-line measurementmeasurement; the sensor
is submerged directly into the sample or process stream, which is typically contained in a pipe. The third is in-situ where the sensor
is directly inserted into the sample stream. The in-situ principle is intended for the monitoring of water during any step within a
processing train, including immediately before or after the process itself.
1.1.2 Static covers both benchtop and portable designs for the measurement of water samples that are captured into a cell and
then measured.
1.2 Depending on the monitoring goals and desired data requirements, certain technologies will deliver more desirable results
for a given application. This guide will help the user align a technology to a given application with respect to best practices for
data collection.
1.3 Some designs are applicable for either a lower or upper measurement range. This guide will help provide guidance to the
best-suited technologies based given range of turbidity.
1.4 Modern electronic turbidimeters are comprised of many parts that can cause them to produce different results on samples.
The wavelength of incident light used, detector type, detector angle, number of detectors (and angles), and optical pathlength are
all design criteria that may be different among instruments. When these sensors are all calibrated with the sample turbidity
standards, they will all read the standards the same. However, samples comprise of completely different matrices and may measure
quite differently among these different technologies.
1.4.1 This guide does not provide calibration information but rather will defer the user to the appropriate ASTM turbidity
method and its calibration protocols. When calibrated on traceable primary turbidity standards, the assigned turbidity units such
as those used in Table 1. are equivalent. For example, a 1 NTU formazin standard is also equivalent in measurement magnitude
to a 1 FNU, a 1 FAU, and a 1 BU standard and so forth.
1.4.2 Improved traceability beyond the scope of this guide may be practiced and would include the listing of the make and
model number of the instrument used to determine the turbidity values.
1.5 This guide does not purport to cover all available technologies for high-level turbidity measurement.
1.6 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information
only.standard. No other units of measurement are included in this standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
This guide is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology, and
Open-Channel Flow.
Current edition approved May 1, 2011Nov. 1, 2016. Published May 2011November 2016. DOI: 10.1520/D7726–11.Originally approved in 2011. Last previous edition
approved in 2011 as D7726 – 11. DOI: 10.1520/D7726-11R16E01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D7726 − 11 (2016)
1.8 This guide does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of
the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. Refer to the MSDSs for all chemicals used in this procedure.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D3977 Test Methods for Determining Sediment Concentration in Water Samples
D6698 Test Method for On-Line Measurement of Turbidity Below 5 NTU in Water
D6855 Test Method for Determination of Turbidity Below 5 NTU in Static Mode
D7315 Test Method for Determination of Turbidity Above 1 Turbidity Unit (TU) in Static Mode
2.2 Other References:
United States Geological Survey (USGS), —National Field Manual for the Collection of Water Quality Dataǁ.USGS National
Field Manual Website: http//www.usgs.gov/FieldManual/Chapters6/6.7.htm. for the Collection of Water Quality Data
Wagner, R.J. et al. Wagner’s Field Manual Guidelines and Standard Procedures for Continuous Water-Quality Monitors: Station
Operation, Record Computation, and Data Reporting, ReportingUSGS Enterprise Publishing Network, 2005. (http://
pubs.usgs.gov/tm/2006/tm1D3/)
3. Terminology
3.1 Definitions—Definitions: For definitions of terms used in this method refer to Terminology D1129.
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 calibration drift, n—the error that is the result of drift in the sensor reading from the last time the sensor was calibrated
and is determined by the difference between cleaned-sensor readings in calibration standards and the true, temperature-
compensated value of the calibration standards.
3.2.2 Calibrationcalibration turbidity standard, n——aa turbidity standard that is traceable and equivalent to the reference
turbidity standard to within statistical errors; calibration turbidity standards include commercially prepared 4000 NTU Formazin,
stabilized formazin, and styrenedivinylbenzene (SDVB).
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from United States Geological Survey (USGS), USGS Headquarters, 12201 Sunrise Valley Drive, Reston, VA 20192, http://www.usgs.gov/FieldManual/
Chapters6/6.7.htm.
Wagner, R. J., et al, Guidelines and Standard Procedures for Continuous Water-Quality Monitors: Station Operation, Record Computation, and Data Reporting, USGS
Enterprise Publishing Network, 2005, available from: http://pubs.usgs.gov/tm/2006/tm1D3.
3.2.2.1 Discussion—
theseThese standards may be used to calibrate the instrument.
3.2.3 Calibration-verificationcalibration-verification standards, n——Defineddefined standards used to verify the accuracy of
a calibration in the measurement range of interest.
3.2.3.1 Discussion—
theseThese standards may not be used to perform calibrations, only calibration verifications. Included verification standards are
opto-mechanical light-scatter devices, gel-like standards, or any other type of stable-liquid standard.
3.2.4 continuous, adj—the type of automated measurement at a defined-time interval, where no human interaction is required
to collect and log measurements.
3.2.4.1 Discussion—
Measurement intervals range from seconds to months, depending on monitoring goals of a given site.
3.2.5 Detection Angle, design, n—The angle formed with its apex at the center of the analysis volume of the sample, and such
that one vector coincides with the centerline of the incident light source’s emitted radiation and the second vector projects to the
center of the primary detector’s view. a more detailed technology description that will encompass all of the elements making up
a technology, plus any inherent criteria used to generate a specific turbidity value.
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D7726 − 11 (2016)
3.2.5.1 Discussion—
this angle is used for the differentiation of turbidity-measurement technologies that are used in this method.The design will
typically translate into a specific make or model of an instrument.
3.2.4 Nephelometric-Detection Angle—the angle that is formed between the incident light source and the detector, and that is
at 90 degrees.
3.2.5 Backscatter-detection Angle, n—The angle that is formed between the incident light source and the primary detector, and
that is greater than 90 degrees and up to 180 degrees.
3.2.6 Attenuation-detection Angle, n—The angle that is formed between the incident light source and the primary detector, and
that is at exactly 0 degrees.
3.2.6.1 Discussion—
this is typically a transmission measurement.
3.2.7 Forward-scatter-detection angle, n—The angle that is formed between the incident light source and the primary detector,
and that is greater than 0 degrees but less than 90 degrees.
3.2.7.1 Discussion—
most designs will have an angle between 135 degrees and 180 degrees.
3.2.6 Surface-Scatter Detection,detection angle, n—the angle formed with its apex at the center of the analysis volume of the
sample, and such that one vector coincides with the centerline of the incident light source’s emitted radiation and the second vector
projects to the center of the primary detector’s view.
3.2.6.1 Discussion—
This angle is used for the differentiation of turbidity-measurement technologies that are used in this guide.
3.2.6.2 attenuation-detection angle, n—the angle that is formed between the incident light source and the primary detector, and
that is at exactly 0 degrees.
(1) Discussion—This is typically a transmission measurement.
3.2.6.3 backscatter-detection angle, n—the angle that is formed between the incident light source and the primary detector, and
that is greater than 90 degrees and up to 180 degrees.
3.2.6.4 nephelometric-detection angle, n—the angle that is formed between the incident light source and the detector, and that
is at 90 degrees.
3.2.6.5 forward-scatter-detection angle, n—the angle that is formed between the incident light source and the primary detector,
and that is greater than 0 degrees but less than 90 degrees.
(1) Discussion—Most designs will have an angle between 135 degrees and 180 degrees.
A3.2.6.6 surface-scatter detection, n—a turbidity measurement that is determined through the detection of light scatter caused
by particles within a defined volume beneath the surface of a sample.
3.2.8.1 Discussion—
both the light source and detector are positioned above the surface of the sample. The angle formed between the centerline of the
light source and detector is typically at 90 degrees. Particles at the surface and in a volume below the surface of the sample
contribute to the turbidity reading.
(1) Discussion—Both the light source and detector are positioned above the surface of the sample. The angle formed between
the centerline of the light source and detector is typically at 90 degrees. Particles at the surface and in a volume below the surface
of the sample contribute to the turbidity reading.
3.2.7 fouling, v—the measurement error that can result from a variety of sources and is determined by the difference between
sensor measurements in the environment before and after the sensors are cleaned.
3.2.8 In-situin-situ nephelometer, n—a turbidimeter that determines the turbidity of a sample using a sensor that is placed
directly in the sample.
3.2.8.1 Discussion—
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D7726 − 11 (2016)
thisThis turbidimeter does not require transport of the sample to or from the sensor.
3.2.9 metadata, n—the ancillary descriptive information that describes instrument, sample, and ambient conditions under which
data were collected.
3.2.9.1 Discussion—
Metadata provide information about data sets. An example is the useful background information regarding the sampling site,
instrument setup, and calibration and verification results for a given set of turbidity data (especially when data are critically
reviewed or compared against another data set).
3.2.10 Nephelometric-turbiditynephelometric-turbidity measurement, n—the measurement of light scatter from a sample in a
direction that is at 90° with respect to the centerline of the incident-light path. D
3.2.10.1 Discussion—
unitsUnits are NTU (Nephelometric Turbidity Units). When ISO 7027 technology is employed units are FNU (Formazin
Nephelometric Units).
3.2.11 Pathlength,pathlength, n—The greatest distance that the sum of the incident light and scattered light can travel within
a sample volume (cell or view volume).
3.2.11.1 Discussion—
theThe pathlength is typically measured along the centerline of the incident-light beam plus the scattered light. The pathlength
includes only the distance the light and scattered light travel within the sample itself.
3.2.12 Ratio-turbidityratio-turbidity measurement, n—the measurement derived through the use of a nephelometric detector that
serves as the primary detector, and one or more other detectors used to compensate for variation in incidentlight fluctuation, stray
light, instrument noise, or sample color.
3.2.13 Reference-turbidityreference-turbidity standard, n—a standard that is synthesized reproducibly from traceable raw
materials by the user.
3.2.13.1 Discussion—
allAll other standards are traced back to this standard. The reference standard for turbidity is formazin.
3.2.14 Seasoning,seasoning, v—the process of conditioning labware with the standard that will be diluted to a lower value to
reduce contamination and dilution errors.
3.2.15 Slipstream,slipstream, n—an on-line technique for analysis of a sample as it flows through a measurement chamber of
an instrument.
3.2.15.1 Discussion—
theThe sample is transported from the source into the instrumen
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