Development of Membrane Filter Colorimetry for Determining Tap Water Discoloration Using a Spectrocolorimeter

• Published in: Water (Basel) Vol. 15; no. 23; p. 4137
• Main Authors: Kim, Dong-Heon, Lee, Jong-Geum, Kwon, Jin-Hong, Kim, Sang-Woo, Jun, Hang-Bae
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.12.2023
• Subjects: Atoms & subatomic particles; Coloring matter; Decomposition; discoloration; Drinking water; Environmental research; filter color unit; Germany; iron; manganese; membrane filter colorimetry; Membrane filters; Plasma; Scanning electron microscopy; South Korea; spectrocolorimeter; Spectrum analysis; Test methods; Water pipes; Water quality; Water supply; Water treatment plants; South Korea; Germany; United Kingdom > UK; United States > US; Berlin Germany
• ISSN: 2073-4441; 2073-4441
• DOI: 10.3390/w15234137

In this study, we aimed to develop a novel method to quantify residual colorants in the water supply using a spectrocolorimeter. Cross-tests of color and turbidity showed that standard color solutions of 1–50 color units had a turbidity of ˂0.094 nephelometric turbidity unit (NTU) and turbidity standard solutions of 0.1–5 NTU had color measurements of 0 true color unit, indicating limitations in measuring colorants using conventional methods. Therefore, the samples were diluted stepwise to 1 L and filtered through a 0.45 μm cellulose membrane; then, the residuals colorants were measured using membrane filter colorimetry (MFC) with a spectrocolorimeter to determine the color difference. The color difference exhibited a high correlation with turbidity. Furthermore, scanning electron microscopy/energy-dispersive X-ray spectroscopy and inductively coupled plasma-optical emission spectrometry analyses of the same samples confirmed that the main components of the colorants were iron and manganese; the concentration of these substances in the samples was measured using MFC with the standards Fe2O3·H2O and MnO2. The results confirmed a high correlation between the color difference (△E*ab) and concentration of the samples and standard substances. Our findings suggest that MFC is a promising approach for measuring colorants in drinking water.