For the past decade(s), many surface waters in the Northern hemisphere (e.g., Europe, Canada, United States) have exhibited widespread increases in natural organic matter (NOM) concentration measured as dissolved organic carbon (DOC) or colour in surface waters, a phenomenon commonly referred to as brownification. Some of the most reported drivers of browning include the reversal of atmospheric acid (e.g., sulphate) deposition, climate change (e.g., warming temperatures, precipitation events) and, in some circumstances, changing land use are expected to play a dominant role in controlling surface water NOM. The efficacy of drinking water treatment processes is dependent on the concentration and character of NOM present and brownification of drinking water supplies is expected to have a profound impact on treatment practices.<br/> <br/>Fluorescence spectroscopy has emerged in the last decade as a valuable tool for the characterization and monitoring of NOM in water treatment through the acquisition of 3D fluorescence excitation-emission matrices (EEMs). We used a large dataset containing over 10 years of raw water fluorescence EEM data from a browning drinking water supply to evaluate temporal changes in the character of NOM. Generalized additive models were used to model time series of the humic EEM region and significant temporal increases were observed for these components when seasonality was removed. This suggests that increases in NOM (e.g., DOC, color) are driven by terrestrially derived humic material. We confirmed these findings through resin fractionation, which is a conventional NOM characterization technique, revealing that increases in the proportion of hydrophobic or humic DOC contributed to a ~1 mg/L increase in DOC over the 10-year period.<br/> <br/>In conjunction with reversal of acidification (e.g., reduced sulphate deposition), climate trends in the drinking water supply over the past decade showed increasingly earlier and longer lasting higher temperature, as well as more intense precipitation events which together are contributing to humic-induced browning. Further, model forecasts suggest the humic component will continue to increase, which will cause operational challenges at the full-scale treatment facility drawing from this supply (e.g., coagulant dose increases, shorter filter run times). Accordingly, fluorescence-based monitoring in drinking water supplies will become a crucial part of climate change projections for water treatment.

Exploring decadal changes in natural organic matter quality in a browning drinking water supply using a large fluorescence dataset

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

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