Disclosed is a filtration process for separating solid, sludge-like and dissolved constituents from effluent, comprising the steps of introducing under an elevated pressure the effluent into a tube-shaped filter having a closed end and an open end, the tube-shaped filter being comprised of a semi-permeable material, the point of introduction of the effluent being initially near the closed end of the filter; moving the point of introduction of the effluent away from the closed end and toward the open end of the filter; and adjusting the rate of introduction of the effluent into the filter to achieve a predetermined content of solids in the concentrate remaining inside the filter. Also disclosed is a device for carrying out this process.