We consider a control problem for a single bioreaction occuring in a continuous and well mixed bioreactor, assuming that the bioreaction's kinetics is not represented by a validated model. We develop a nonlinear controller and prove the global asymptotic stability of the closed loop system towards the equilibrium corresponding to the set point. Since this control law needs the knowledge of some parameters, we derive an adaptive version of the nonlinear controller and prove again the global asymptotic stability of the closed loop system. Finally, we show the relevance of our approach on a real life wastewater treatment plant. Key words: Nonlinear adaptive control, continuous bioprocesses, unknown kinetics, wastewater treatment.