A remarkable feature of biological activated carbon (BAC) in drinking water treatment is nitrification. However, BAC has been empirically operated without sufficient understanding its ammonium removal potential. This study aims to reveal the impacts of low water temperature on ammonium removal potential of BAC. BAC samples were collected from a full-scale drinking water treatment plant from November 2018 to March 2019. Bench-scale column assay simulating actual hydraulic condition was used to determine volumetric removal rates (VRR) of BAC in synthetic medium or ozonated water from the same plant at 25 °C. In addition, VRRs were measured in ozonated water at actual water temperature on the sampling occasions. VRR in ozonated water at 25°C were always lower than those in synthetic medium at 25°C, possibly due to lack of some nutrients. As water temperature decreased from 18°C (November) to 5°C (January), VRR in ozonated water at actual water temperature decreased by 89%, while VRR in synthetic medium and ozonated water at 25°C decreased by only 25% and 12%, respectively. These results demonstrated that ammonium removal activity of BAC was very sensitive to low water temperature while removal potential of BAC was maintained with limited reduction.
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