Figure 10.4 Graphic representation of
the Monod type reaction rate model
and its two limiting cases (first order
and zero order).
where km is the external mass transfer coefficient, and S and Si are the substrate
concentrations in the bulk liquid and at the biofilm-liquid interface, respectively, then:
(14)In biofilm reactors, it is more common to calculate the “surface reaction rate”, rA
(kgsubstrate.m−^2 .s−^1 ), that is the substrate consumption rate per unit area of biofilm. This
variable is related to rf through:
(15)where Lf is the thickness of the microbial layer and η is the overall efficiency of the
biofilm (see below).
The following integrated expressions may be obtained to estimate the substrate
consumption rate per unit surface area of biofilm:
a) First order intrinsic reaction:
(16)The “biofilm internal efficiency” (ηi) represents the ratio between the actual substrate
consumption rate and the substrate consumption rate that the biofilm would display if
there were no internal diffusional limitations. This parameter is given by:
Biofilm reactors 305