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• Six Gaussian bands comprise differential absorbance spectra of all examined waters. • Bands A1-A4 in the spectra of chlorinated compounds show dependence of conjugation. • Spectral parameters from long wavelength have high correlation with DBPs formation. This study compared chlorination-induced changes of the properties of natural organic matter (NOM) represented by standard humic substances and NOM present in pristine and anthropogenically-affect reservoirs, rivers, groundwater and seawater. The chlorination-induced changes of NOM properties were quantified using the differential absorbance spectra (DAS) which were processed via numeric deconvolution. Six Gaussian bands were found to comprise the DAS of all examined waters. These bands (denoted as A0, A1, A2, A3, A4 and A5, respectively) have maxima located at ca. 200, 240, 276, 316, 385 and 547 nm. The bands A1-A4 were observed in the DAS of representative model chlorinated compounds. Quantum chemical (QC) calculations were carried out to examine the intrinsic nature of these bands and electronic transitions associated with them. QC data demonstrate that bands A1 and A2 are present in almost all aromatic organic species, A3 is likely to be associated with acetophenone- and/or styrene-like groups. A4 can be attributed to the engagement of m-hydroxyaromatic and flavone-type groups typical for the polyphenolic moiety in NOM and known to be the key precursors of disinfection by-product (DBP) formation. Thus, the intensity of band A4 is predicted to be an especially strong predictor of DBP formation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Thermodynamic and kinetic aspects of the formation of trihalomethanes and haloacetic acids determined based on the quantum chemical (QC) simulations were compared in this study with the experimental data generated using the differential spectroscopy approach in chlorination and chloramination. The ratios of the slopes of the correlations between -DlnA 350 values and individual DBPs concentrations (S NH2Cl /S HOCl) were observed to be linearly correlated with the ratios of the Gibbs free energies (ΔG NH2Cl /ΔG HOCl) of the corresponding reactions of chloramine and chlorine with acetaldehyde which was used as a model DBP precursor in QC simulations. Further QC examination of the kinetics of chlorination and chloramination of the model compound acetoacetic acid showed that the activation energy of reactions between monochloramine that directly participates in substitution reactions to form mono-, di and tri-halogenated intermediates are 2–3 times higher than those of HOCl formed via the hydrolysis monochloramine. This result confirms that the interactions of chloramine with NOM and ensuing DBP formation are primarily mediated by the free chlorine released as a result of the hydrolysis of monochloramine while direct halogenation of NOM by monochloramine is likely to provide a small contribution to DBP formation. Image 1 • -DlnA 350 is linear with most of individual DBPs yields in chlor(am)ination. • Ratio of slopes (S NH2Cl /S HOCl) for individual DBPs are linear with ΔG NH2Cl /ΔG HOCl. • Direct halogenation of NOM by NH 2 Cl contribute to small fraction of DBP formation. • The activation energy of NOM reaction with NH 2 Cl is higher than HOCl. • Tri-chlorinated HAAs and THMs are suppressed in chloramine due to trace level HOCl. [ABSTRACT FROM AUTHOR]