EXPLORING DECADAL INCREASES IN THE CONCENTRATION OF NATURAL ORGANIC MATTER AND THE IMPACT ON SURFACE DRINKING WATER TREATMENT PROCESSES

Abstract

Natural organic matter (NOM) is prevalent in surface waters and impacts all aspects of drinking water treatment. In recent decades, there have been reports of increasing NOM concentration (often referred to as brownification) in the northern hemisphere and reduced atmospheric deposition has been identified as a potential driver. The objectives of this thesis were to 1) provide a comprehensive review of surface water quality responses to decreased acid deposition with a focus on NOM dynamics, and identify the potential impacts of these responses on water treatment infrastructure, 2) quantify the impact of decreased deposition and its effect on NOM concentration and subsequent surface water treatment practices in Atlantic Canada, 3) investigate the relationship between NOM and metal colloids (Fe, Al, Mn) in lakes representing a range of DOC levels in a region where surface waters are browning significantly, and 4) evaluate the use of granular activated carbon (GAC) adsorption as a robust adaptation strategy for enhancing NOM removal.

This work identified the primary drivers of brownification to be a combination of reductions in atmospheric deposition and climate change, where climate impacts will have a more pronounced impact as acid deposition stabilizes. This work also showed that in Atlantic Canada, reductions in atmospheric sulfate deposition was a primary driver of brownification and was responsible for up to 3.8-fold increases in lake color and corresponding alum dosing at the treatment facilities drawing from browning lakes. This resulted in compromised filter performance at a direct filtration facility and revealed that treatment facilities may be under designed as a result. This work highlighted the importance of colloid characterization in drinking water supplies challenged with brownification, as opposed to the convention of quantifying dissolved material via separation through a 0.45 m filter adopted by industry. Finally, this work determined that GAC is a robust adaptation strategy, however it can release significant quantities of dissolved Mn when potassium permanganate is used. The source water complexities that are anticipated through brownification and the need for considering robust adaptation water treatment solutions that consider many factors in addition to NOM, including Mn and Fe, were highlighted.