  The objective of the paper is to evaluate the ability of reactive transport
models and their numerical implementations (such as MIN3P) to simulate simple
microbial transformations in conditions of chemostat or gradostat models, that
are popular in microbial ecology and waste treatment ecosystems. To make this
comparison, we first consider an abstract ecosystem composed of a single
limiting resource and a single microbial species that are carried by advection.
In a second stage, we consider another microbial species in competition for the
same limiting resource. Comparing the numerical solutions of the two models, we
found that the numerical accuracy of simulations of advective transport models
performed with MIN3P depends on the evolution of the concentrations of the
microbial species: when the state of the system is close to a non-hyperbolic
equilibrium, we observe a numerical inaccuracy that may be due to the
discretization method used in numerical approximations of reactive transport
equations. Therefore, one has to be cautious about the predictions given by the
models.
