In this research we analyse the steady-state operation of a continuous flow bioreactor, with or without recycle, and an idealised, or non-idealised, continuous flow membrane reactor. The reaction is assumed to be governed by, the well-known, Monod growth kinetics. We show that a flow reactor with idealised recycle has the same performance as an idealised membrane reactor and that the performance of a non-idealised membrane reactor is identical to an appropriately defined continuous flow bioreactor with non-idealised recycle. The performance of all three reactor types can therefore be obtained by analysing a flow reactor with recycle. The steady-states of the recycle model are found and their stability determined as a function of the residence time. The performance of the reactor at large residence times is obtained. In the limit as the residence time becomes very large, all three reactor configurations have identical performances. Thus the main advantage of using a membrane reactor, or a flow reactor with recycle, for the treatment of industrial wastewaters and slurries is to improve the performance at low residence times. This is quantified for the case of an ideal membrane reactor.