Low energy reverse osmosis process

Abstract

We provide a system and method for reverse osmosis treatment of water, including seawater and brackish water. Methods and systems of embodiments of the invention may include, for example, ultrafiltration followed by biofoulant removal, both of which precede reverse osmosis. In preferred embodiments the system is run at a low flux. For example, a flux of 6-8 GFD may be used with seawater. Additional embodiments may provide the above process in conjunction with a reverse-osmosis membrane cleaning system. The membrane cleaning system is a “clean in place” system that includes use of the natural pressure differential in the reverse osmosis system to remove biofoulants and their precursors.

1 - 20 . (canceled) 
     
     
         21 . A method for removal of biofoulants from water, comprising:
 filtering water through an ultrafiltration membrane, thereby removing turbidity including bacteria and viruses from the water;   filtering the water for biofoulant removal, thereby removing biofoulants, additional bacteria, and additional viruses from the water, wherein the step of filtering the water through an ultrafiltration membrane precedes the step of filtering the water for biofoulant removal.   
     
     
         22 . The method of  claim 21 , wherein the removal of biofoulants occurs prior to a membrane purification of the water, and wherein the removal of biofoulants decreases fouling of at least one membrane in the membrane purification. 
     
     
         23 . The method of  claim 21 , wherein said ultrafiltration membrane reduces SDI of the feed stream to less than 3-5 SDI. 
     
     
         24 . The method of  claim 21 , wherein said ultrafiltration membrane reduces turbidity of the feed stream to less than 0.1. 
     
     
         25 . The method of  claim 21 , wherein said biofoulant removal step reduces turbidity to less than 0.08. 
     
     
         26 . The method of  claim 21 , wherein said removal of biofoulants is conducted using a member of the group consisting of ion exchange materials, positively charged media, electrochemical removal, and electrode-based removal. 
     
     
         27 . The method of  claim 21 , wherein said cleaning is conducted based on a preset increase in differential pressure or numbers of hours of operation of the reverse osmosis membrane. 
     
     
         28 . The method of  claim 21 , wherein said method excludes addition of chlorine upstream of the UF membrane, and wherein the method may include addition of chlorine during a backwash to avoid ingress of chlorine in feed water to be desalinated. 
     
     
         29 . A method for removal of impurities from water, comprising:
 filtering water through an ultrafiltration membrane, thereby removing turbidity including bacteria and viruses from said feed stream;   treating the water to remove biofoulants, additional bacteria, and additional viruses from the water, wherein the step of filtering the water through an ultrafiltration membrane is conducted prior to the step of treating the water to remove biofoulants, additional bacteria, and additional viruses from the water; and   treating the water by reverse osmosis, wherein the reverse osmosis is conducted at an operating flux, wherein the operating flux results in an energy consumption, and wherein conducting the reverse osmosis at a flux lower than the operating flux does not reduce the energy consumption by more than 10%; and   cleaning at least one reverse osmosis membrane used in treating the water by reverse osmosis, comprising, for a reverse osmosis membrane having a feed side and a permeate side:   maintaining a concentration differential by adding reverse osmosis concentrate to the feed side of the reverse osmosis membrane, thereby allowing the reverse osmosis concentrate to remain in the feed side and causing a flow of permeate water from the permeate side to the feed side due to the concentration differential.   
     
     
         30 . The method of  claim 29 , wherein said removal of biofoulants is conducted using a member of the group consisting of ion exchange materials, positively charged media, electrochemical removal, and electrode-based removal. 
     
     
         31 . The method of  claim 29 , wherein said cleaning is conducted based on a preset increase in differential pressure or numbers of hours of operation of the reverse osmosis membrane. 
     
     
         32 . The method of  claim 29 , wherein said method excludes addition of chlorine upstream of the UF membrane, and wherein the method may include addition of chlorine during a backwash to avoid ingress of chlorine in feed water to be desalinated. 
     
     
         33 . A method for in situ cleaning of a reverse osmosis membrane for treating water, comprising, for a reverse osmosis membrane having a feed side and a permeate side:
 maintaining a concentration differential by adding reverse osmosis concentrate to the feed side of the reverse osmosis membrane;   allowing the reverse osmosis concentrate to remain in the feed side; and   causing a flow of permeate water from the permeate side to the feed side due to the concentration differential, thereby cleaning the reverse osmosis membrane.   
     
     
         34 . A method for regenerating a biofoulant filter, comprising treating the biofoulant filter with a cleaning method selected from the group consisting of chemical cleaning and electrochemical cleaning. 
     
     
         35 . The method of  claim 34 , wherein the cleaning method is chemical cleaning. 
     
     
         36 . The method of  claim 34 , wherein the cleaning method is electrochemical cleaning.