Purpose: The ADMI (American Dye Manufacturers Institute) Color Index was developed to monitor the color of wastewater effluent as an indicator of water quality. ADMI is a single metric based on the Adams Nickerson (ANLab) color difference between water and the visual Pt-Co liquid color standards that is independent of hue. This metric is used to quantify the residual color of wastewater due to the presence of colored minerals and dyes, humic breakdown substances and iron.

Up to 12% of the synthetic dyes used in textile manufacturing operations can be found in dye wastewater effluent. After being processed in treatment plants, 20% of those dye losses will enter the environment. The same mechanism that allows these colorants to bind so well with textile fibers also causes hydrolysis reactions with other wastewater components, or reduction in anaerobic sediments to produce obnoxious by-products.

The dispersed dyes tend to remain resident in the environment for some time. The half-life of these dyes depends on the pH, temperature and surrounding medium (natural water or anaerobic sediment). The dominant hue of these colored effluents tends to be blue [1].

The Adams Nickerson Chromatic Value formula was an attempt to transform CIE tristimulus color space into a visually uniform color space through the use of a single metric color difference value. It is based on the premise that if two colors of different hues, A and B, are perceived to be visually different to the same degree from a colorless water reference point, then the vector distance (originally calculated as a ANLab delta E) from the colorless point to A or B will be the same in the Adams Nickerson color difference space.

In the case of the ADMI scale, the APHA/Pt-Co liquid color standards [2] serve as a set of physical reference standards against which the dye effluent is rated using a total color difference correlation. For example, if a blue dye effluent is visually perceived to differ from distilled water to the same magnitude as a light yellow APHA/Pt-Co 100 standard solution from the same colorless water standard, then the blue effluent is assigned an ADMI rating of 100.

HunterLab has replaced this subjective visual judgment as to which APHA/Pt-Co standard solution the bluish effluent sample matches with an objective, colorimetric method using a dE* total color difference correlation to the APHA/Pt-Co liquid color standards. This correlation to assigns equivalent ADMI values to samples of textile wastewater effluent.

Prior to measurement, the bluish effluent sample is filtered or centrifuged to remove suspended colloidal particles until judged to be visually clear. The samples are brought to room temperature. As the color varies with pH, the pH is adjusted to 7.6 using H2SO4 or NaOH as necessary.

Here's how HunterLab meets ADMI Color Measurement of Wastewater

• ColorQuest XT with standard ADMI Color Applet
• Or ColorQuest XE with Touch Screen with standard ADMI Color Applet
• Or ColorQuest XE with EasyMatch QC in which the ADMI-10mm and ADMI-50mm metrics are standard under Indices.
• C02-1005-481 Transmission Cell Holder
• 13-8573-40 Transmittance cell 10 mm cell or 13-8573-20 Transmission cell 50 mm.

The HunterLab ColorQuest XT or XE sphere spectrophotometer is standardized in Total Transmittance using a 10 mm or 50 mm cell filled with distilled water for low chroma liquid samples are being measured for ADMI-50mm color. If the wastewater liquid is highly chromatic or dens, use the 10 mm cell and ADMI correlation.

As a PQ Performance Qualification step, measure back the water-filled cell as a Standard or Sample with an ADMI value of 0, within tight tolerances, being expected if the instrument is set up correctly and ready to measure.

As a further PQ qualification, an APHA/Pt-Co/Hazen liquid color standard in the same ADMI range as the wastewater samples can then be measured as an independent application diagnostic with an ADMI value expected that is equivalent to that assigned to the APHA/PtCo/Hazen liquid color standard. This can be tracked over time to verify long-term repeatability of the instrument in reading a stable, liquid sample similar in ADMI to the wastewater being measured.

Proceed to measure the ADMI Color of wastewater samples. An ADMI value of 0 represents distilled water. A higher ADMI value indicates more dye or colorant in the waster effluent.

Use of 10 mm or 50 mm path length transmittance cell for measuring ADMI Color scale of Wastewater

The literature references both a 10 mm and 50 mm pathlength cell being used with ADMI. Which one is correct?

From the literature references, the spectrophotometric correlation to the visual ADMI scale recommends use of a 10-mm pathlength cell for ADMI values greater than 250 and the use of a 50-mm path length cell for ADMI values less than 250. Think of it as using the 50 mm path length cell for low chroma; 10 mm for high chroma samples.

Both cell pathlengths will work for the entire range, but if no pathlength preference is stated, use a 50-mm pathlength transmittance cell for ADMI measurement.

References for ADMI Color

APHA 2120E 1995 Visual ADMI Color Method for the Examination of Water and Wastewater

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