Patent ID: 8632682

Claim:
A method for operating a tapered flow pressure driven arrangement containing a plurality of membrane modules, which comprises positioning said membrane modules in at least two successively arranged flow stages, such that the number of membrane modules operating in parallel in a given flow stage is greater than their number in the consecutive flow stage, passing a feed stream through a flow stage to generate a permeate and a concentrate, directing said concentrate to the consecutive flow stage and passing said concentrate therethrough, while periodically replacing one or more of the membrane modules belonging to said consecutive flow stage with one or more membrane modules belonging to the previous flow stage, wherein the periodicity of said replacement is such that the surface of membranes disposed in said consecutive flow stage is exposed to super-saturation conditions associated with the passage of said concentrate for a period of time that is shorter than the time required for said concentrate to precipitate therefrom one or more sparingly soluble salts and/or minerals, onto the surface of the membranes in said consecutive flow stage under said super-saturation conditions, or before deposit of organic substances can occur in the first of said two or more successively arranged flow stages.