Ammonium removal of drinking water at low temperature by activated carbon filter biologically enhanced with heterotrophic nitrifying bacteria

We sought to confirm whether use of Acinetobacter strains Y7 and Y16, both strains of heterotrophic nitrifying bacteria, was practical for removing ammonium (NH₄ ⁺-N) from drinking water at low temperatures. To test this, ammonium-containing drinking water was treated with strains Y7 and Y16 at 8 and 2 °C. Continuous ammonium treatment was conducted in order to evaluate the performance of three biologically enhanced activated carbon (BEAC) filters in removing ammonium. The three BEAC filters were inoculated with strain Y7, strain Y16, and a mixture of strains Y7 and Y16, respectively. A granular activated carbon (GAC) filter, without inoculation by any strains, was tested in parallel with the BEAC filters as control. The results indicated that NH₄ ⁺-N removal was significant when a BEAC filter was inoculated with the mixture of strains Y7 and Y16 (BEAC-III filter). Amounts of 0.44 ± 0.05 and 0.25 ± 0.05 mg L⁻¹ NH₄ ⁺-N were removed using the BEAC-III filter at 8 and 2 °C, respectively. These values were 2.8–4.0-fold higher than the values of ammonium removal acquired using the GAC filter. The synergistic effect of using strains Y7 and Y16 in concert was the cause of the high-ammonium removal efficiency achieved by using the BEAC-III filter at low temperatures. In addition, a high C/N ratio may promote NH₄ ⁺-N removal efficiency by improving biomass and microbial activity. This study provides new insight into the use of biofilters to achieve biological removal of ammonium at low temperature.