ASTM D7725-12
(Test Method)Standard Test Method for the Continuous Measurement of Turbidity Above 1 Turbidity Unit (TU)
Standard Test Method for the Continuous Measurement of Turbidity Above 1 Turbidity Unit (TU)
SIGNIFICANCE AND USE
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 of suspended matter is accomplished by coagulation, settling, and filtration. Measurement of turbidity provides a rapid means of process control to determine when, how, and to what extent the water must be treated to meet specifications.
This test method is suitable for the on-line monitoring of turbidity such as that found in drinking water, process water, and high purity industrial waters.
The instrumentation used must allow for the continuous on-line monitoring of a sample stream.
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.
Table 1 describing technologies and reporting results. Those technologies listed are appropriate for the range of measurement prescribed in this method are mentioned, though others may come available. Figure X3–1 from Appendix 3 contains a flowchart to assist in technology selection.
For a specific design that falls outside of these reporting ranges, the turbidity should be reported in turbidity units (TU) with a subscripted wavelength value to characterize the light source that was used.
Ratio White Light Turbidimeters are common as bench top instruments but not as a typical process instrument. However, if fitted with a flow-cell they meet the criteria of this method.
SCOPE
1.1 This test method covers the online and inline determination of high-level turbidity in water that is greater than 1.0 turbidity units (TU) in municipal, industrial and environmental usage.
1.2 In principle there are three basic applications for on-line measurement set ups. This first is the slipstream (bypass) sample technique. For the slipstream sample technique a portion of sample is transported out of the process and through the measurement apparatus. It is then either transported back to the process or to waste. The second is the in-line measurement where the sensor is brought directly into the process (see Figure 8). The third basic method is for in-situ monitoring of sample waters. This principle is based on the insertion of a sensor into the sample itself as the sample is being processed. The in-situ use in this method is intended for the monitoring of water during any step within a processing train, including immediately before or after the process itself.
1.3 This test method is applicable to the measurement of turbidities greater than 1.0 turbidity unit (TU). The absolute range is dictated by the technology that is employed.
1.4 The upper end of the measurement range is left undefined because different technologies described in this method can cover very different ranges of turbidity.
1.5 Many of the turbidity units and instrument designs covered in this method are numerically equivalent in calibration when a common calibration standard is applied across those designs listed in Table 1. Measurement of a common calibration standard of a defined value will also produce equivalent results across these technologies. This method prescribes the assignment of a determined turbidity values to the technology used to determine those values. Numerical equivalence to turbidity standards is observed between different technologies but is not expected across a common sample. Improved traceability beyond the scope of this method may be practiced and would include the listing of the make and model number of the instrument used to determine the turbidity values.
1.5.1 In this method, calibration standards are often defined in NTU values, but the other assigned turbidity units, such as those in Table 1 are equivalent. For example, a 1 NTU formazin standard is also a 1 FNU, a 1 FAU, a 1 BU, and so forth.
1.6 This sta...
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Designation: D7725 − 12
Standard Test Method for the
Continuous Measurement of Turbidity Above 1 Turbidity
1
Unit (TU)
This standard is issued under the fixed designation D7725; 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 Improved traceability beyond the scope of this method may be
practiced and would include the listing of the make and model
1.1 This test method covers the online and inline determi-
number of the instrument used to determine the turbidity
nation of high-level turbidity in water that is greater than 1.0
values.
turbidity units (TU) in municipal, industrial and environmental
1.5.1 In this method, calibration standards are often defined
usage.
in NTU values, but the other assigned turbidity units, such as
1.2 In principle there are three basic applications for on-line
those in Table 1 are equivalent. For example,a1NTU
measurement set ups. This first is the slipstream (bypass)
formazin standard is alsoa1FNU,a1FAU,a1BU,andso
sample technique. For the slipstream sample technique a
forth.
portion of sample is transported out of the process and through
1.6 This standard does not purport to cover all available
themeasurementapparatus.Itistheneithertransportedbackto
technologies for high-level turbidity measurement.
the process or to waste. The second is the in-line measurement
where the sensor is brought directly into the process (see Fig. 1.7 Thistestmethodwastestedondifferentwaters,andwith
8). The third basic method is for in-situ monitoring of sample standards that will serve as surrogates to samples. It is the
waters. This principle is based on the insertion of a sensor into user’s responsibility to ensure the validity of this test method
the sample itself as the sample is being processed. The in-situ for waters of untested matrices.
use in this method is intended for the monitoring of water
1.8 Those samples with the highest particle densities typi-
during any step within a processing train, including immedi-
cally prove to be the most difficult to measure. In these cases,
ately before or after the process itself.
the process monitoring method can be considered with ad-
1.3 This test method is applicable to the measurement of equate measurement protocols installed.
turbidities greater than 1.0 turbidity unit (TU). The absolute
1.9 This standard does not purport to address all of the
range is dictated by the technology that is employed.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
1.4 The upper end of the measurement range is left unde-
priate safety and health practices and determine the applica-
fined because different technologies described in this method
bility of regulatory limitations prior to use. Refer to the MSDSs
can cover very different ranges of turbidity.
for all chemicals used in this procedure.
1.5 Many of the turbidity units and instrument designs
1.10 This international standard was developed in accor-
covered in this method are numerically equivalent in calibra-
dance with internationally recognized principles on standard-
tion when a common calibration standard is applied across
ization established in the Decision on Principles for the
those designs listed in Table 1. Measurement of a common
Development of International Standards, Guides and Recom-
calibration standard of a defined value will also produce
mendations issued by the World Trade Organization Technical
equivalent results across these technologies. This method
Barriers to Trade (TBT) Committee.
prescribes the assignment of a determined turbidity values to
the technology used to determine those values. Numerical
2. Referenced Documents
equivalence to turbidity standards is observed between differ-
2
2.1 ASTM Standards:
ent technologies but is not expected across a common sample.
D1129 Terminology Relating to Water
D2777 Practice for Determination of Precision and Bias of
1
This test method is under the jurisdiction of ASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.03 on Sampling Water and
2
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, For referenced ASTM standards, visit the ASTM website, www.astm.org, or
On-Line Water Analysis, and Surveillance of Water. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Jan. 1, 2012. Published June 2012. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7725-12. the ASTM website.
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