Impact of climate and atmospheric pressures on natural organic matter concentration and surface water treatment practices

For decades, there have been reported widespread increases in the concentration of natural organic matter (NOM) measured as dissolved organic carbon (DOC) throughout the Northern hemisphere, a phenomenon commonly referred to as brownification. Some of the main drivers of brownification are associated with anthropogenic pressures including the reversal of atmospheric acid (e.g., sulfate) deposition as a result of more stringent air emissions policies, and climate pressures (e.g., increasing frequency, intensity and duration of precipitation events, as well as warming temperature). Many studies have predicted that browning will continue considering climate pressures, even after sulfate deposition returns to background levels. Furthermore, browning of surface waters is expected to have a profound impact on drinking water treatment practices. For example, drinking water providers drawing from browning water supplies can expect to experience increased coagulant demand, reduced filter hydraulic performance and potential for elevated disinfection by-products (DBPs) if NOM removal is unoptimized. Inadequate removal of NOM during treatment may also result in elevated trace metal concentration in the distribution system, which can increase the ability of treated drinking water to transport contaminants such as lead. Drinking water treatment processes should be designed to accommodate for fluctuations in both NOM concentration and quality and a buffer between treated water quality and regulatory limits is critical.