- Experiments were carried out on bench-scale activated sludge units operated continuously in the single-sludge model. A synthetic feed consisting of glucose, acetate, ammonium chloride and essential elements was used. The results served to examine the validity of various expressions for process modelling, and to derive several process parameters. For effluent ammonia of approximately 0.5 mg l-1 a specific nitrification rate of 0.75 · gNH4+-N · gVSS-1 day-1 was selected. The maximum nitrification rate was above 1.9 gNH4+-N · gVSS-1 day-1 and the maximum denitrification rate was 1.7 gNO3-N · gVSS-1 · day-1. The yield and decay coefficients were determined as 0.31 gVSS · gCOD-1 and 0.018 day-1 respectively, for the heterotrophs, and 0.246 gVSS · gNH4+-N-1 and 0.007 day-1, respectively, for the autotrophs. Microbial counts were in qualitative agreement with predicted values.