Simplified and Monod kinetics in one-dimensional biofilm reactor modelling: a comparison

A theoretical study supported by some experimental tests has been carried o ut with the aim of comparing one-dimensional (I-D) biofilm reactor models t hat use simplified (zero- and first-order) and Monod kinetics. Two differen t situations have been compared: one rate-limiting substrate with or withou t liquid film diffusion. The results obtained show that the use of a simpli fied kinetic approach compared to the Monod kinetic approach determines (1) an unjustified overestimate of the removal rate, especially for thin biofi lms, and (2) an excessive overestimate of the liquid film layer thickness n ecessary to justify high kinetic orders. Even if recent research projects s how that biofilm structure is more complicated than the one assumed in the modelling approach used in this study, nevertheless 1-D models still now co ntinue to be the only ones that can reasonably support process engineers in biofilm reactor design, due to their intrinsic simplicity and the need for small sets of input data and parameters that can be obtained theoretically or often empirically.