The microbial mineralization of EDTA in waste water by a mixed culture was studied with suspended and immobilized cells. Efficient degradation of EDTA could be achieved, though the chelator is stated not to be biodegradable. A complete set of kinetic parameters was determined that enables the modelling of EDTA degradation and, related to this, bacterial growth, ammonium release, maintenance requirement as well as oxygen uptake. In order to obtain important technical scale-up parameters, the microorganisms were immobilized on different carrier particles and employed in continuously operated three-phase airlift-loop reactors. The reactors could be operated at a dilution rate up to D = 1.2 h(-1) (D much greater than mu(max)) that, at an EDTA concentration of 450 mg dm(-3), led to EDTA degradation rates up to 12.8 kg m(-3) day(-1). The extent of EDTA degradation remained constant at 95-99% with increasing values of D. Achieved kinetic parameters of the biofilm systems were compared with those which were obtained from experiments with suspended cells.