Dynamic behaviour of a fixed-bed biofilm reactor: analysis of the role of the intraparticle convective flow under biofilm growth

The influence of the intraparticle convective flow on the dynamic response of a fixed-bed biofilm reactor is evaluated theoretically for a stepwise in crease in substrate concentration in the feed line. Dimensionless transient mass balance equations for the substrate within the bulk liquid biofilm an d support phases are derived considering a substrate inhibition kinetic mod el (Haldane equation) and biofilm growth. Governing equations are simultane ously solved for phenol biodegradation by finite element collocation method s to yield the bed response, in terms of dimensionless phenol concentration at outlet against a reduced time (breakthrough curves), for two different bulk flow rates. The results reported in this study, for different intrapar ticle velocities, show that the major beneficial effect of the intraparticl e convective flow on the production of a good effluent quality is expressed by the occurrence of later breakthrough curves, due to the improvement of intraparticle mass transfer by convection, particularly when higher diffusi onal limitations are present inside the biofilm and support. Thus, bioreact ors must be operated under such conditions that liquid how occurs within bi ofilms. (C) 1998 Elsevier Science S.A. All rights reserved.