USE OF A DYNAMIC GASSING-OUT METHOD FOR ACTIVITY AND OXYGEN DIFFUSION-COEFFICIENT ESTIMATION LN BIOFILMS

p-toluenesulphonic acid degradation by Comamonas testosteroni T-2 in m ulti-species biofilms was studied in a fixed bed biofilm reactor. The polypropylene static mixer elements (Sulzer Chemtech Ltd., Switzerland ) were used as a support matrix for biofilm formation. Biofilm respira tion was estimated using the dynamic gassing-out oxygen uptake method. A strong relation between oxygen uptake and reactor degradation effic iency was observed, because p-toluenesulphonate degradation is a stric tly aerobic process. This technique also allowed us to estimate the th ickness of the active layer in the studied system. The mean active thi ckness was in order of 200 mu m, which is close to maximum oxygen pene tration depth in biofilms. A transient mathematical model was establis hed to evaluate oxygen diffusitivity in non-steady-state biofilms. Bas ed on the DO concentration profiles, the oxygen diffusion coefficient and the maximum respiration activity were calculated. The oxygen diffu sion coefficient obtained (2 10(-10)-1.2 10(-9) m(2) s(-1)) is in good agreement with published values. The DO diffusion coefficient varied with biofilm development. This may be, mast likely, due to the biofilm density changes during the experiments. The knowledge of diffusivity changes in biofilms is particularly important for removal capacity est imation and appropriate reactor design. (C) 1998 IAWQ. Published by El sevier Science Ltd.