Adsorption and denitrification in nitrifying trickling filters

Step and pulse response experiments carried out on large pilot-scale nitrifying trickling filters show that adsorption and desorption of ammonium, as well as denitrification, may occur in the biofilm. These phenomena should then be taken into account when modeling the fast reactor dynamics. The observed adsorption and desorption cause the transients of the effluent ammonium concentration to become significantly slower than expected from measured residence time distributions. Sampling for measurements of stationary nitrification rates should then be carried out several mean residence times after changes in operating conditions. A physically based model of simultaneous nitrification, denitrification, adsorption and desorption in the biofilm is presented. Simulated responses to changes in influent concentrations agree with the experimental data. From the simulations it is also evident that the effects of adsorption on the responses are considerable although the actual amounts of adsorbed ammonium are small relative to amounts observed for activated sludge.