Use of log-transformed absorbance spectra for online monitoring of the reactivity of natural organic matter

• Raw, settled and filtered waters from two WTPs were sampled weekly for six months.
• Slopes of log-transformed absorbance spectra of all sampled waters were computed.
• Spectral slopes in the range 280 and 350 nm (S280–350) correlate with SUVA.
• S280–350 correlate with the yields of trihalomethanes and haloacetic acids.
• S280–350 can be measured in real time and used for online water quality monitoring.

This study examined the significance of water quality monitoring parameters obtained via logarithmic transformation of the absorbance spectra of raw and treated drinking water. The data were generated using samples of the influent, settled and filtered water acquired weekly over a six months period at two full scale treatment plants. Examination of the weekly plant samples combined with the data of laboratory fractionation and chlorination experiments showed that the slopes of the log-transformed spectra are correlated with typically reported water quality parameters (e.g., its specific absorbance at 254 nm, SUVA254); yet the determination of spectral slopes is considerably simpler and potentially information-rich. The spectral slopes determined for the range of wavelength 280–350 nm were shown to be correlated with the yields of trihalomethanes (THMs) and haloacetic acids (HAAs). These results support the notion that multi-wavelength monitoring of the absorbance spectra of drinking water and their interpretation via logarithmic transformation constitutes a promising practically implementable approach for online water quality monitoring.

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