Fluorescence moieties as a surrogate for residual chlorine in three drinking water networks

Several factors play a role in chlorine consumption in drinking water networks such as microbial contamination and dissolved organic matter (DOM). This study investigated the simultaneous impacts of seasonal variations on chlorine consumption and DOM composition for a year-long period in three different full-scale water distribution networks in a southern city of China. Efforts were made to determine the association between different fluorescence moieties in DOM of finished water and chlorine consumption through excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC). The chlorine consumption was also found to be directly related to N-Nitrosodimethylamine (NDMA) and NDMA-formation potential (NDMA-FP), presenting consequence of excess residual chlorine. The wet season with high rainfall showed elevated consumption of chlorine on the opposite of dry season. During wet season, humic-like component in finished water was dominant than protein-like features and its abundance decreased in dry season. Results proved that chlorine consumption was season dependent and highly influenced by DOM composition in the finished water. Unlike the bulk quality parameters and protein-like component, fluorescence moieties related to humic substances acted as a surrogate for the chlorine consumption. Based on humic-like component, a single excitation based fluorescence peak, I-245/410 or I-335/410, was also extracted from EEMs of finished water samples and validated on different water distribution networks. These two single peaks well-explained the trends of residual chlorine and have the potential for on-line monitoring and portable purposes. This field-based study demonstrated application of fluorescence spectroscopy in designing chlorine dose to obtain optimal residual chlorine at consumer's tap.

Automated summary

This study investigated the impacts of seasonal variations on chlorine consumption and DOM composition, finding a direct relationship between chlorine consumption and N-Nitrosodimethylamine, with elevated consumption in the wet season and dominance of humic-like components. Fluorescence moieties related to humic substances acted as a surrogate for chlorine consumption, and single fluorescence peaks showed potential for on-line monitoring and portable purposes. This field-based study demonstrated the application of fluorescence spectroscopy in designing chlorine dose for optimal residual chlorine at consumer's tap.