A critical assessment of the use of a variableorder,
power-law type surface reaction rate equation to
correlate biosorption kinetics is presented. The general
nth
order rate equation with three adjustable parameters was fit
to the kinetic data of lead uptake by inactivated cells of
Rhodotorula glutinis
using a genetic algorithm search
method. The uptake process was fast, with apparent equilibrium
reached in approximately 30 min. According to the
Akaike information criterion test, the three-parameter nth
order equation was superior to the much used pseudo
second order equation with two fitting parameters. However,
the strong fit of the former equation resulted in
unrealistic parameter estimates. Parametric sensitivity
analysis indicated that the available kinetic data with only
limited information content did not allow simultaneous
identification of three unknown parameters. As a result, the
three-parameter
nth order equation was found to be overparameterized
with highly correlated parameters. It was,
however, possible to retrieve meaningful parameter estimates
from the kinetic data when the number of fitting
parameters was reduced from 3 to 2.
