Nitrification potential and population dynamics of nitrifying bacterial biofilms in response to controlled shifts of ammonium concentrations in wastewater trickling filters

► We studied nitrifying bacteria in wastewater nitrifying trickling filters. ► Nitrification potentials reacted to shifts in wastewater ammonium concentrations. ► Nitrification potentials often correlated with relative amounts of nitrifiers. ► Nitrosomonas oligotropha dominated the ammonium oxidizers in all ammonium regimes. ► Ammonium feed strategies can be used to optimize treatment plant performance.