The membrane bioreactor, with an increase of biomass concentration in the aeration tank, permit work with low F/M ratio and a reduction in sludge production. The membrane bioreactor potentialities have been tested on a laboratory pilot for domestic wastewater treatment. Various operating conditions (HRT, SRT) were applied to investigate organic and nitrogen removal as well as sludge production. Two modeling approaches were tested (maintenance phenomena, single sludge simulation process) with unsuccessfull predictions. Futher investigations are needed to better understand biological kinetics and phenomena in membrane bioreactor and to obtain higher flux on membrane processes.