The limitation of the membrane bioreactors treating municipal wastewater to manage peak flux conditions have often led to conservative design, which negatively impacts on capital and operating costs. This paper discusses the effectiveness of an alternative operation mode, tested under various peaking conditions and different experimental unit sizes. In this mode, the initiation of the backwashing is regulated by a transmembrane set-point value, which determines the degree of membrane fouling permitted. At low peaking factor, results showed a suitable fouling control, comparable to that obtained with the conventional temporized mode, but with higher process productivity (14-16%). During the long-term tests, this control mode demonstrated its capability to achieve a sustainable operation at high peaking fluxes (J(p) = 70 L/h m(2)) and peak periods of 6 h.