Near Complete Removal of Total Mercury and Methylmercury from River Water during the Production of Municipal Drinking Water

We quantified, for the first time, how efficiently total mercury (THg) and methylmercury (MeHg) were removed from different treatment stages in a conventional drinking water treatment plant. For this, the municipal E.L. Smith Drinking Water Treatment Plant in Edmonton, Alberta, Canada drawing its water from the North Saskatchewan River (NSR) was used as a case study. The major treatment stages involved chemical flocculation and clarification, filtration, and ultraviolet disinfection prior to the processed water being stored in reservoirs for distribution. On average, 75% THg and 66% MeHg were removed from river water following chemical flocculation and clarification. A further 9.8% THg and 31.8% MeHg was removed during filtration, while 1.5% THg and 0.8% MeHg was removed during ultraviolet disinfection. We also examined how open water season (1 May to 31 October) yields of THg and filtered THg changed along the NSR as it flowed from its glacial headwaters through a large reservoir, various ecological subregions (foothills, mixedwood, parkland), and agriculturally dominated land to where it was sourced for drinking water production in Edmonton 534 kms downriver, highlighting value in the protection of source watersheds.