Adsorption and denitrification in nitrifying trickling filters

Step and pulse response experiments carried out on large pilot-scale nitrif ying trickling filters show that adsorption and desorption of ammonium, as well as denitrification. may occur in the biofilm. These phenomena should t hen be taken into account when modeling the fast reactor dynamics. The obse rved adsorption and desorption cause the transients of the effluent ammoniu m concentration to become: significantly slower than expected from measured residence time distributions. Sampling for measurements of stationary nitr ification rates should then be carried out several mean residence times aft er changes in operating conditions. A physically based model of simultaneou s nitrification, denitrification, adsorption and desorption in the biofilm is presented. Simulated responses to changes in influent concentrations agr ee with the experimental data. From the simulations it is also evident that the effects of adsorption on the responses are considerable although the a ctual amounts of adsorbed ammonium are small relative to amounts observed f or activated sludge. (C) 1999 Elsevier Science Ltd. All rights reserved.