Monochloramine loss mechanisms and dissolved organic matter characterization in stormwater

• Published in: The Science of the total environment Vol. 631-632; pp. 745 - 754
• Main Authors: Zhang, Qianyi, Davies, Evan G.R., Bolton, James R., Liu, Yang
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.08.2018
• Subjects: Dissolved organic matter; Monochloramine dissipation; Stormwater; Monochloramine dissipation; Dissolved organic matter; Stormwater
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2018.02.335

Monochloramine (NH2Cl) is widely used for secondary disinfection by water utilities. However, Edmonton field stormwater sampling results have shown that NH2Cl, because of its long-lasting property, can cause stormwater contamination through outdoor potable water uses during the summer season. To protect water sources, it is important to understand NH2Cl dissipation mechanisms in stormwater. Natural organic matter (NOM) is the dominant species that contributes to NH2Cl decay in stormwater. In this research, it is proposed that NOM reacted with both NH2Cl and free chlorine through rapid and long-term reactions during NH2Cl dissipation. Based on this assumption, a kinetic model was developed and applied to estimate the NH2Cl decay in real stormwater samples, and the modeling results matched experimental data well under all the conditions. Further, the stormwater dissolved organic matter (SWDOM) collected from different neighborhoods was analyzed by Fourier transform infrared (FTIR) and fluorescence excitation-emission matrix (EEM) techniques. Humic substances were found to be dominant in SWDOM, and the samples from different neighborhoods had similar organic constituents. After reaction with excess NH2Cl, 25%–41% SWDOM fluorophores converted to inorganic components, while most of DOM remained in organic form. Humic substances as the major components in SWDON, are the dominant precursors of disinfection by-products in chloramination. Therefore, the potential reaction products of stormwater humic substances with NH2Cl should also be of concern. This research provided a useful method to estimate the NH2Cl dissipation in stormwater, and the methodology can also be applied for stormwater NH2Cl decay studies in other cities. Further, it is believed the SWDOM analysis in this research will contribute to future studies of NH2Cl NOM reaction mechanisms in both storm sewers and drinking water distribution systems. [Display omitted] •Active chlorine concentration was high in stormwater and can contaminate fresh water.•Model was built to describe the monochloramine (NH2Cl) decay in stormwater.•Natural organic matter led to rapid and slow reactions with free chlorine and NH2Cl.•Humic substances were dominant in stormwater dissolved organic matter.