“…Our approach consist to provide an upper observer of the system and through theory of monotone dynamical systems, we prove global partial stabilization of the upper observer of substrate concentration s about s d and by the way keeping s ≤ s d . Many works are interested by similar problems where issues of : optimal control [12,13], observers [1,2,5,9,10,12,15], simulation [6,14], have been studied. Robust control has been also treated, [4,5,7,8], but without recycle biomass.…”