Start-up of biofilter for nitrification and effect of filtration rate on the ammonium removal efficiency in drinking water treatment on pilot plant

Biological filtration is a process that can be used for ammonia removal from water. The removal of ammonia is based on the nitrification process. Nitrification depends on many factors, such as water quality and filtration process parameters. To investigate the influence of filtration rate on the nitrification efficiency, nitrifying biofilters were formed at the pilot plant in the industry for drinking water production from surface water. The new biological filters were started under optimal conditions for biofilm formation. After the biofilm formation, the influence of the filtration rate on nitrification was examined over 3 months (from November to January). The time required for the spontaneous growth of nitrifying bacteria on the new filters was around 70 days. The operating conditions at the start-up period were the continuous flow of water containing γ(NH4+) ≈ 1mg/L, dissolved oxygen in a concentration >9 mg/L, filtration rate <1 m/h, inlet water temperature >12 °C and pH from 7.8 to 8. After the complete formation of the nitrifying biofilm, the percentage of NH4+ removal was greater than 95% for all tested filtration rates, from 0.5 to 8.4 m/h, at γ(NH4+) from 1 to 2.5 mg/L and raw water temperature from 13 to 7°C.