Water filtration using immersed membranes

Abstract

A process for operating filtering membranes submerged in a tank involves, in one aspect, periodically deconcentrating the tank by partially emptying and refilling the tank with fresh water. The emptying and refilling may be performed generally simultaneously or sequentially. In another embodiment, the membrane modules are arranged in a series of filtration zones between a feed water inlet and a retentate outlet of a tank and the zone adjacent the outlet is emptied and refilled.

1 . A process for treating water comprising the steps of: 
 a) providing one or more membrane modules in a generally vertically oriented flow channel;    b) flowing feed water into the flow channel from above the one or more membrane modules to immerse the one or more membrane modules;    c) applying a suction to the one or more membrane modules to withdraw permeate; and,    d) removing unpermeated water from the flow channel from below the one or more membrane modules.    
   
   
       2 . The process of  claim 1  further comprising a step of providing gas bubbles to scour the one or more membrane modules.  
   
   
       3 . The process of  claim 1  wherein steps (b), (c) and (d) are performed simultaneously and continuously over a period of time.  
   
   
       4 . The process of  claim 3  further comprising a step of scouring the one or more membrane modules during the period of time.  
   
   
       5 . The process of  claim 3  wherein the rate of feed flow is between 1.3 to 5.2 times the rate of permeate flow during the period of time.  
   
   
       6 . An apparatus for treating water comprising; 
 a) a tank;    b) one or more membrane modules in the tank;    c) a non-porous casing surrounding the one or more membrane modules and defining a generally vertical flow channel containing the one or more membrane modules;    d) a source of suction in communication with the one or more membrane modules;    e) an inlet to the tank; and,    f) an outlet from the tank,    wherein,    g) the apparatus is configured such that water in the tank flows into the top of the casing and out of the bottom of the casing.    
   
   
       7 . The apparatus of  claim 6  wherein  80 % or more of the footprint of the tank is covered with membrane modules.  
   
   
       8 . The apparatus of  claim 6  having a plurality of non-porous casings each defining a vertical flow channel containing one or more membrane modules, the apparatus configured such that water in the tank flows into the top of each casing and out from the bottom of each casing.