MASS-TRANSFER COEFFICIENTS FOR AN AUTOTROPHIC AND A HETEROTROPHIC BIOFILM SYSTEM

To evaluate the mass transfer coefficients at the interface bulk/biofi lm two biofilm systems with autotrophic and heterotrophic microbes wer e investigated with oxygen microelectrodes over a longterm period (1 y ear). To determine the transfer coefficient the oxygen profiles were s imulated with a mass transfer model and compared with the measured sub strate flux. The oxygen profiles at flow velocities >10 cm/(s) yielded concentration layers of about 100 mu m and transfer coefficients >10( 4) m/(s). These evaluated transfer coefficients were one magnitude hig her than those known from hydrodynamics without biofilm reactions. Thu s, the assumption, which determines the transfer coefficient as a quot ient of the diffusion coefficient through the thickness of the laminar sublayer is oversimplified.