Compact spiral-wound filter elements, modules and systems

A filter system, comprising:

• two or more filter modules, each of the two or more filter modules comprising:
• a housing, a spiral-wound filter element comprised of a spiral-wound membrane having an interior, said spiral-wound membrane wrapped around and attached to a perforated core having an interior, with the interior of a single leaf spiral-wound membrane in fluid communication with the interior of the perforated core, said interior of the single leaf spiral-wound membrane and interior of the perforated core forming a permeate channel, and a feed stream inlet located on the housing external to the spiral-wound membrane, wherein said two or more modules are in fluid communication in series such that retentate of a first filter module becomes the feed stream of a second filter module or the permeate of the first filter module becomes the feed stream of the second filter module and the feed channel flow cross section changes between at least two successive modules and wherein the outermost feed channel of the spiral-wound filter element is blocked.