This study examined interactions between dissolved organic matter (DOM) and chloramine in the presence of varying concentrations of iodide. To gain insight into mechanisms and kinetics of these interactions, changes of DOM properties caused by DOM halogenation were quantified using the methods of absorbance and excitation emission matrixes (EEM). These measurements showed the existence of features in the absorbance spectra of reaction mixtures (e.g., a conspicuous peak at 225 nm) associated with the presence of iodide. Changes of the intensity of this peak were concluded to reflect the consumption of iodine species during DOM chloramination. Other features in the absorbance spectra of the examined system were also detected; they appear to correspond to the formation of transient species of iodine generated in the DOM/chloramine/iodine system. Fluorescence of DOM was affected by chloramine but its behaviour had specific features associated with varying iodide concentrations. In the absence of iodide, the intensity of EEM of DOM increased immediately after the start of chloramination, following which it decreased. In contrast, it decreased immediately, sometimes very significantly, after the start of chloramination at high iodide concentration. The non-monotonic behaviour of EEM intensity was concluded to be caused by two different processes. Initial increases of EEM intensity are likely to be associated with the breakdown of DOM molecules in the presence of chloramine but this effect is counter-balanced by iodide incorporation into the organic substrate and ensuing decrease of fluorescence due to heavy atoms effect. The extent of iodide consumption during chloramination was observed to be strongly correlated with the changes of DOM emission. These results show that DOM-iodine interactions, incorporation of iodine into DOM molecules and ultimately the generation of iodine-containing disinfection by-products can be probed using in situ methods.

Interactions between dissolved organic matter and iodine during chloramination: Examination based on spectroscopic data

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.