The water treatment plant (WTP), in the Town of St. Walburg, Saskatchewan, is currently experiencing difficulty in maintaining stable free chlorine residuals within the potable water storage reservoir and the clearwell due to the presence of high ammonia levels (1.8-2.0 mg/L) in the well water supply. The Saskatchewan Ministry of Environment (MOE) regulates that a minimum of 4-log inactivation of viruses through disinfection be provided for groundwater treatment plants. In order to maintain adequate free chlorine residuals, high doses of free chlorine were required. Such high doses in the presence of high ammonia levels resulted in high total chlorine levels. The Town investigated methods of improving the disinfection, in order to demonstrate compliance with the minimum 4-log virus inactivation primary disinfectant requirement. Some methods assessed included switching to an alternate primary disinfectant, such as chlorine dioxide, ozone or UV; and removing the ammonia through treatment modifications, thus allowing the use of free chlorine as the primary disinfectant. The preliminary assessment suggested that removing ammonia from the raw water supply was the most cost-effective approach. As such, pilot tests were conducted to determine effective ammonia removal technologies applicable to small systems. Various biological filtration (BF) media and ion exchange (IX) media were pilot tested. In order to minimize regenerant waste from the ion exchange process and to eliminate start-up lag time for seeding of BF, a pilot system consisting of a hybrid IX-BF system was also tested. The pilot study also evaluated the biofilter configuration using fixed bed and fluidized flows, as well as various media such as GAC, sand, and walnut shell. This paper describes the pilot test results of ammonia removal from groundwater in a small water treatment system.
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