In this work, we study a model of the chemostat where the species are present
in two forms, isolated bacteria and under an aggregated form like attached
bacteria or bacteria in flocks. We show that our general model contains a lot
of models which were previously considered in the literature. Assuming that
flocculation and deflocculation dynamics are fast with respect to the growth of
the species, we construct a reduced chemostat-like model in which both the
growth functions and the apparent dilution rate depend on the density of the
species. We also show that such a model involving monotonic growth rates may
exhibit bistability, while it may only occur in the classical chemostat model
when the growth rate in non monotonic
