The invention relates to an effluent treatment installation which can be used to improve the filtration capacity of membranes and to reduce water losses without increasing the floor area thereof. For said purpose, the invention comprises a pulsed sludge blanket settling tank (1) containing membrane filtration modules (10) which are submerged in or above the sludge blanket, and the system (11) for extracting the treated effluents is connected upstream of said filtration modules (10). The invention also relates to a method for clarification by means of coagulation/flocculation/decantation and for filtration using said installation.