Back-flushable spiral wound filter and methods of making and using same

A method of operating a spiral wound membrane element which includes periodic back-flushing, which method comprises:

• placing a spiral wound membrane element, having a feed spacer sheet, a membrane filter layer sheet and a permeate carrier sheet, generally vertically in a tank containing an aqueous feed solution, said element being confined to a generally cylindrical configuration and being open to inflow at a lower end and open to outflow at an upper end thereof;
• creating a pressure differential between the permeate carrier sheet in said element and the feed solution within the tank so that water passes through the membrane sheet into the permeate carrier;
• introducing on a periodic basis a pressurized back-flush fluid into the permeate carrier sheet of the element to cause reverse flow through said membrane sheet into said feed spacer sheet to dislodge feed solution solids being retained on the membrane filter layer sheet;
• and
• providing bubbles below the open lower end of the element which rise upward and flow through the element so as to create a convective flow of the feed solution into the open lower end of the element and out the open upper end and to promote turbulence at a surface of the membrane filters layer sheet to reduce a boundary layer at the surface of the membrane filter layer sheet, said bubbling rising flow causing feed solution within the element and permeate flowing in reverse through the membrane sheet to exit from the open upper end and carry with it dislodged solids.

A system for operating a spiral wound membrane element that includes the step of periodically back-flushing, which system comprises:

• a feed tank holding a volume of feed solution;
• a spiral wound membrane element having a permeate carrier sheet, a feed spacer sheet, and a membrane filter layer sheet, which element is aligned generally vertically within said feed tank,
• means confining said spiral wound membrane to a generally cylindrical configuration with said element being open to axial flow at both ends thereof;
• means for creating a vacuum in said permeate carrier sheet within said element to create driving pressure across said membrane sheet that results in permeate flow into said permeate carrier sheet and flow of feed solution upward into said element in said feed spacer sheet;
• and
• means for periodically applying pressurized back-flush fluid to said permeate carrier sheet to back-flush the element by creating fluid flow from said permeate carrier sheet through said membrane sheet and into said feed spacer sheet.

A system for operating a back-flushable spiral wound membrane cross flow filtration element comprising:

• a spiral wound membrane cross flow filtration element;
• means for supplying feed solution to the filtration element which includes a feed pump for pumping and pressurizing the feed solution and a feed pipe through which the pressurized feed solution flows to the element;
• said element including a pressure tube having a first outlet through which a first portion of the feed solution which permeates the membrane exits as permeate, and a second outlet where a portion of the feed solution that does not permeate the membrane exits the element as concentrate;
• a feed diverter valve for controlling flow in the feed pipe leading to the element to direct flow either to an inlet to the element or to drain;
• a concentrate diverter valve for controlling flow of concentrate from second outlet of the pressure tube;
• means for supplying back flushing fluid to the first outlet of the membrane filtration element to create reverse flow through the membrane;
• and
• means for adjusting the feed and concentrate diverter valves during back flushing to allow the back flush fluid to exit through the feed pipe and flow to drain, and for adjusting said concentrate diverter valve to halt the flow of concentrate out of the second outlet of the pressure tube.