ABSTRACT
In such a biofilm reactor wastewater either flows over a fixed bed of sup port material or the biofilm-coated medium is suspended in and stirred with the liquid, i.e., the wastewater. In both cases, the purification process is based on the transport of dissolved substances into the biofilm by diffusion and sorp tion onto the microbial cells where they can be metabolized (Harremoes, 1978; Bryers and Characklis, 1990). Therefore, the performance of biofilm systems is determined by the mass transfer of substrates from the bulk liquid to the biofilm and within the biofilm (external and internal transport, respectively) (Harremoes, 1978; Siegrist and Gujer, 1985).
