ASTM D6855-17(2023)
(Test Method)Standard Test Method for Determination of Turbidity Below 5 NTU in Static Mode
Standard Test Method for Determination of Turbidity Below 5 NTU in Static Mode
SIGNIFICANCE AND USE
5.1 Turbidity is undesirable in drinking water, plant effluent waters, water for food and beverage processing, and for a large number of other water-dependent manufacturing processes. Removal is often accomplished by coagulation, settling, and filtration. Measurement of turbidity provides a rapid means of process control for when, how, and to what extent the water must be treated to meet specifications.
5.2 This test method is suitable to turbidity such as that found in drinking water, process water, and high purity industrial water.
5.3 When reporting the measured result, appropriate units should also be reported. The units are reflective of the technology used to generate the result, and if necessary, provide more adequate comparison to historical data sets.
5.3.1 Table 1 describes technologies and reporting results (see also Refs (1-3)).6 Those technologies listed are appropriate for the range of measurement prescribed in this test method. Others may come available in the future. Fig. X5.1 provides a flow chart to aid in selection of the appropriate technology for low-level static turbidity applications.
5.3.2 If a design that falls outside of the criteria listed in Table 1 is used, the turbidity should be reported in turbidity units (TU) with a subscripted wavelength value to characterize the light source that was used.
SCOPE
1.1 This test method covers the static determination of turbidity in water (see 4.1).
1.2 This test method is applicable to the measurement of turbidities under 5.0 nephelometric turbidity units (NTU).
1.3 This test method was tested on municipal drinking water, ultra-pure water, and low turbidity samples. It is the users responsibility to ensure the validity of this test method for waters of untested matrices.
1.4 This test method uses calibration standards are defined in NTU values, but other assigned turbidity units are assumed to be equivalent.
1.5 This test method assigns traceable reporting units to the type of respective technology that was used to perform the measurement. Units are numerically equivalent with respect to the calibration standard. For example, a 1.0 NTU formazin standard is also equal to a 1.0 FNU standard, a 1.0 FNRU standard, and so forth.
1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Refer to the MSDSs for all chemicals used in this test method.
1.7 This international standard was developed in 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.
General Information
Relations
Standards Content (Sample)
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.
Designation: D6855 − 17 (Reapproved 2023)
Standard Test Method for
Determination of Turbidity Below 5 NTU in Static Mode
This standard is issued under the fixed designation D6855; 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.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the static determination of
D1129 Terminology Relating to Water
turbidity in water (see 4.1).
D1192 Guide for Equipment for Sampling Water and Steam
1.2 This test method is applicable to the measurement of
in Closed Conduits (Withdrawn 2003)
turbidities under 5.0 nephelometric turbidity units (NTU).
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of
1.3 This test method was tested on municipal drinking
Applicable Test Methods of Committee D19 on Water
water, ultra-pure water, and low turbidity samples. It is the
D3370 Practices for Sampling Water from Flowing Process
users responsibility to ensure the validity of this test method for
Streams
waters of untested matrices.
D5847 Practice for Writing Quality Control Specifications
1.4 This test method uses calibration standards are defined for Standard Test Methods for Water Analysis
in NTU values, but other assigned turbidity units are assumed D7315 Test Method for Determination of Turbidity Above 1
to be equivalent. Turbidity Unit (TU) in Static Mode
E691 Practice for Conducting an Interlaboratory Study to
1.5 This test method assigns traceable reporting units to the
Determine the Precision of a Test Method
type of respective technology that was used to perform the
2.2 Other Referenced Standards:
measurement. Units are numerically equivalent with respect to
U.S. EPA Method 180.1 Methods for Chemical Analysis of
the calibration standard. For example, a 1.0 NTU formazin
Water and Wastes, Turbidity
standard is also equal to a 1.0 FNU standard, a 1.0 FNRU
ISO 7027 Water Quality—for the Determination of Turbid-
standard, and so forth.
ity
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions:
priate safety, health, and environmental practices and deter-
3.1.1 For definitions of terms used in this standard, refer to
mine the applicability of regulatory limitations prior to use.
Terminology D1129.
Refer to the MSDSs for all chemicals used in this test method.
3.2 Definitions of Terms Specific to This Standard:
1.7 This international standard was developed in accor-
3.2.1 calibration turbidity standard, n—a turbidity standard
dance with internationally recognized principles on standard-
that is traceable and equivalent to the reference turbidity
ization established in the Decision on Principles for the
standard to within statistical errors.
Development of International Standards, Guides and Recom-
3.2.1.1 Discussion—Calibration turbidity standards include
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
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.
The last approved version of this historical standard is referenced on
www.astm.org.
1 4
This test method is under the jurisdiction of ASTM Committee D19 on Water Available from United States Environmental Protection Agency (EPA), William
and is the direct responsibility of Subcommittee D19.07 on Sediments, Jefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460,
Geomorphology, and Open-Channel Flow. http://www.epa.gov.
Current edition approved Nov. 1, 2023. Published December 2023. Originally Available from International Organization for Standardization (ISO), ISO
approved in 2003. Last previous edition approved in 2017 as D6855 – 17. DOI: Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
10.1520/D6855-17R23. Geneva, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6855 − 17 (2023)
commercially prepared 4000 NTU formazin, stabilized for- manner in which sample interferes with light transmittance is
mazin (see 9.2.3), and styrenedivinylbenzene (SDVB) (see related to the size, shape, and composition of the particles in
9.2.4). These standards may be used to calibrate the instrument. the water, and also to the wavelength of the incident light.
Calibration standards may be instrument specific.
4.2 This test method is based upon a comparison of the
3.2.2 calibration verification standards, n—defined stan-
intensity of light scattered by the sample with the intensity of
dards used to verify the accuracy of a calibration in the
light scattered by a reference suspension. Turbidity values are
measurement range of interest.
determined by a nephelometer, which measures light scatter
3.2.2.1 Discussion—These standards may not be used to
from a sample in a direction that is at 90° with respect to the
perform calibrations, only calibration verifications. Included centerline of the incident light path.
standards are opto-mechanical light scatter devices, gel-like
5. Significance and Use
standards, or any other type of stable liquid standard. Calibra-
tion verification standards may be instrument specific.
5.1 Turbidity is undesirable in drinking water, plant effluent
waters, water for food and beverage processing, and for a large
3.2.3 nephelometric turbidity measurement, n—the mea-
number of other water-dependent manufacturing processes.
surement of light scatter from a sample in a direction that is at
Removal is often accomplished by coagulation, settling, and
90° with respect to the centerline of the incident light path.
filtration. Measurement of turbidity provides a rapid means of
3.2.3.1 Discussion—Units are NTU (nephelometric turbid-
process control for when, how, and to what extent the water
ity units); when ISO 7027 technology is employed units are in
must be treated to meet specifications.
FNU (formazin nephelometric units).
5.2 This test method is suitable to turbidity such as that
3.2.4 ratio turbidity measurement, n—the measurement de-
found in drinking water, process water, and high purity
rived through the use of a nephelometric detector that serves as
industrial water.
the primary detector and one or more other detectors used to
compensate for variation in incident light fluctuation, stray
5.3 When reporting the measured result, appropriate units
light, instrument noise, or sample color.
should also be reported. The units are reflective of the
technology used to generate the result, and if necessary,
3.2.5 reference turbidity standard, n—a standard that is
provide more adequate comparison to historical data sets.
synthesized reproducibly from traceable raw materials by the
5.3.1 Table 1 describes technologies and reporting results
user.
(see also Refs (1-3)). Those technologies listed are appropriate
3.2.5.1 Discussion—All other standards are traced back to
for the range of measurement prescribed in this test method.
this standard. The reference standard for turbidity is formazin
Others may come available in the future. Fig. X5.1 provides a
(see 9.2.2).
flow chart to aid in selection of the appropriate technology for
3.2.6 seasoning, n—the process of conditioning labware
low-level static turbidity applications.
with the standard to be diluted to a lower value.
5.3.2 If a design that falls outside of the criteria listed in
3.2.6.1 Discussion—The process reduces contamination and
Table 1 is used, the turbidity should be reported in turbidity
dilution errors. See Appendix X2 for the suggested procedure.
units (TU) with a subscripted wavelength value to characterize
3.2.7 stray light, n—all light reaching the detector other than
the light source that was used.
that contributed by the sample.
6. Interferences
3.2.7.1 Discussion—Examples: ambient light leakage, inter-
nal reflections and divergent light in optical systems.
6.1 For this application, bubbles, color, and large particles,
3.2.8 turbidimeter, n—an instrument that measures light although they cause turbidity, may result in interferences in
scatter caused by particulates within a sample and converts the measured turbidity as determined by this test method. Bubbles
measurement to a turbidity value. cause a positive interference and color typically causes a
negative interference. Dissolved material that imparts a color
3.2.8.1 Discussion—The detected light is quantitatively
converted to a numeric value that is traced to a light-scatter to the water may cause errors in pure nephelometric readings,
unless the instrument has special compensating features to
standard.
reduce these interferences. Certain turbulent motions also
3.2.9 turbidity, n—an expression of the optical properties of
create unstable reading conditions of nephelometers.
a sample that causes light rays to be scattered and absorbed
rather than transmitted in straight lines through the sample.
6.2 Color is characterized by absorption of specific wave-
3.2.9.1 Discussion—Turbidity of water is caused by the lengths of light. If the wavelengths of incident light are
presence of suspended and dissolved matter such as clay, silt, significantly absorbed, a negative interference will result un-
finely divided organic matter, plankton, other microscopic less the instrument has special compensating features.
organisms, organic acids, and dyes.
6.3 Scratches, finger marks, or dirt on the walls of the
sample cell may give erroneous readings. Sample cells should
4. Summary of Test Method
be kept scrupulously clean both inside and outside and dis-
carded when they become etched or scratched. The sample
4.1 The optical property expressed as turbidity is measured
by the scattering effect that suspended particulate material have
on light; the higher the intensity of scattered light, the higher
The boldface numbers in parentheses refer to the list of references at the end of
the turbidity. In samples containing particulate material, the this standard.
D6855 − 17 (2023)
TABLE 1 Applicable Technologies Available for Performing Static Turbidity Measurements Below 5 NTU
Design and Reporting Typical Instrument
Prominent Application Key Design Features Suggested Application
Unit Range
Nephelometric non- White light turbidimeters. Comply with Detector centered at 90° relative to the in- 0.020 to 40 Regulatory reporting of
ratio (NTU) U.S. EPA Method 180.1 (1) for low- cident light beam. Uses a white light spec- clean water
level turbidity monitoring. tral source.
Ratio white light turbidi- Complies with ISWTR regulations and Used a white light spectral source. Primary 0.020 to 10 000 Regulatory Reporting of
meters (NTRU) Standard Method 2130B. (2) Can be detector centered at 90°. Other detectors clean water
used for both low- and high-level mea- located at other angles. An instrument algo-
surement. rithm uses a combination of detector read-
ings to generate the turbidity reading.
Nephelometric, near-IR Complies with ISO 7027. The wave- Detector centered at 90° relative to the in- 0.012 to 1000 0–40 ISO 7027 regulatory
turbidimeters, non- length is less susceptible to color inter- cident light beam. Uses a near-IR reporting
ratiometric (FNU) ferences. Applicable for samples with (780–900 nm) monochromatic light source.
color and good for low-level monitoring.
Nephelometric near-IR Complies with ISO 7027. Applicable for Uses a near-IR monochromatic light source 0.012 to 10 000 0–40 ISO 7027 regulatory
turbidimeters, ratio samples with high levels of color and (780–900 nm). Primary detector centered reporting
metric (FNRU) for monitoring to high turbidity levels. at 90°. Other detectors located at other
angles. An instrument algorithm uses a
combination of detector readings to gener-
ate the turbidity reading.
Nephelometric turbidity Is applicable to EPA Regulatory Detectors are geometrically centered at 0 0.012 to 4000 0–40 reporting for EPA
multibeam unit (NTMU) Method GLI Method 2. (2) Applicable to and 90°. An instrument algorithm uses a and ISO compliance
drinking water and wastewater monitor- combination of detector readings, which
ing applications. may differ for turbidities varying magnitude.
mNTU Is applicable to reporting of clean wa- Nephelometric method involving a laser- 5 to 5000 mNTU or 0–5000 mNTU, for EPA
ters and filter performance monitoring. based light source at 660 nm and a high 0.005 to 5.000 NTU compliance reporting on
Very sensitive to turbidity changes in sensitivity photo-multplier tube (PMT) de- drinking water systems
low turbidity samples. (3) tector for light scattered at 90°.
1000 mNTU = 1 NTU
cells must not be handled where the light strikes them when interest must be performed using acceptable, defined verifica-
positioned in the instrument well. tion standards (see 12.2).
6.3.1 Sample cell caps and liners must also be scrupulously
NOTE 3—Consult manufacturer’s instructions for guidance associated
clean to prevent contamination of the sample.
with verification methods and verification devices.
6.4 Ideally, the same indexed sample cell should be used 7.2.1 Consult the manufacturer to ensure that your instru-
first for standardization followed by unknown (sample) deter- ment meets or exceeds the specifications of this test method.
mination. If this is not possible, then sample cells must be
7.3 Photoelectric Nephelometer:
matched. Refer to the instrument manual for instructions on
7.3.1 This instrument uses a light source for illuminating the
matching sample cells.
sample and a single photodetector with a readout device to
NOTE 1—Indexing of the sample cell to the instrument well is
indicate the intensity of light scattered at right angle(s) (90°) to
accomplished by placing a mark on the top of the sample cell and a similar
the centerline of the path of the incident light. The photoelec-
mark on the upper surface of the well so that the sample cell can be placed
tric nephelometer should be designed so that minimal stray
in the well in an exact position each time.
NOTE 2—Sample cells can be matched by first filling with dilution
light reaches the detector
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