Abstract: A modular membrane filtration device is provided with replaceable membrane elements. The device is designed for ease of cleaning or replacing the membrane elements during filtration of a feed liquid to remove suspended solids. The cleaning may be effected by continuous aeration or by application of air as intermittent pressurized pulses. The device preferably has two headers, at least one of which is a permeate collection header having receptacles for a plurality of membrane elements, each of which is a potted hollow fiber membrane bundle. The potted hollow fiber membrane bundles are distinct entities which may be inserted into the receptacles, preferably in rows of circular slots, on the permeate collection header(s), and may be easily removed for maintenance, such as for replacement of the hollow fiber membrane elements.