Membrane processes differ from traditional filtration processes in the fact that the phase to be separated does not accumulate at a surface forming the well-known filter cake, but that the concentration takes place in the liquid itself. Emulsified oil and possibly existing solids are collected in a closed circuit until they reach the desired concentration. The greatest advantage of cross-flow filtration consists in the conversion of a traditional discontinuous filtration process into a continuous one which runs automatically and without monitoring.