Biological Ammonia Removal for Small Systems

摘要

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