Capacitive electrostatic process for inhibiting the formation of biofilm deposits in membrane-separtion systems

Abstract

A high-voltage capacitive electrostatic device is used to improve the performance of membrane-separation processes, particularly reverse-osmosis units, wherein species of a given ionic polarity are separated from water. The device is immersed in the water flowing across the membranes and is operated continuously at very high voltages, preferably greater than 30,000 volts DC. The charge on the wetted surface of the suspended particles is altered by the electrostatic field so generated and is found to reduce biofilm formation, thereby materially enhancing the performance of the membrane-separation system. The application of high-voltage electrostatic fields is also found to reduce corrosion of metallic surfaces in the system.

What is claimed is:  
     
         1 . A method for inhibiting the formation of biofilm deposits on a membrane of a water treatment unit, comprising the steps of: 
 providing a capacitive electrostatic generator adapted to create a capacitive electrostatic field;    immersing said capacitive electrostatic generator in a body of flowing water fed to the membrane of the water treatment unit, the flowing water being electrically grounded relative to an electromotive force available for energizing the capacitive electrostatic generator; and    energizing said capacitive electrostatic generator with said electromotive force at a voltage greater than 10,000 volts DC, such that a corresponding capacitive electrostatic field is created between said generator immersed in the flowing water and said electrical ground without a measurable current leakage in the body of flowing water.    
     
     
         2 . The method of  claim 1 , wherein said water treatment unit comprises a reverse-osmosis membrane.  
     
     
         3 . The method of  claim 1 , wherein said water treatment unit comprises an ultrafiltration membrane.  
     
     
         4 . The method of  claim 1 , wherein said water treatment unit comprises a nanofiltration membrane.  
     
     
         5 . The method of  claim 1 , wherein said capacitive electrostatic generator comprises a dielectric tube of unibody construction having an integrally-sealed end defining an inner cavity with an inner wall; conductive material contained within said inner cavity and disposed in intimate contact with said inner wall; electrically-insulated sealing means for providing hermetic closure to said inner cavity; and electrical means for energizing said conductive material with a static electromotive force.  
     
     
         6 . The method of  claim 1 , wherein said voltage is greater than about 30,000 volts DC.  
     
     
         7 . The method of  claim 5 , wherein said voltage is greater than about 30,000 volts DC.  
     
     
         8 . A method for reducing corrosion of metallic surfaces in a water treatment system by inhibiting the formation of biofilm deposits on said metallic surfaces, comprising the steps of: 
 providing a capacitive electrostatic generator adapted to create an electrostatic field;    immersing said electrostatic generator in a body of flowing water fed to the water treatment system, said metallic surfaces in the water treatment system being connected to an electrical ground relative to an electromotive force available for energizing the electrostatic generator; and    energizing said electrostatic generator with said electromotive force at a voltage greater than 10,000 volts DC, such that a corresponding electrostatic field is created between said generator immersed in the water and said electrical ground without measurable current leakage in the body of flowing water.    
     
     
         9 . The method of  claim 8 , wherein said water treatment system comprises a reverse-osmosis membrane.  
     
     
         10 . The method of  claim 8 , wherein said water treatment system comprises an ultrafiltration membrane.  
     
     
         11 . The method of  claim 8 , wherein said water treatment system comprises a nanofiltration membrane.  
     
     
         12 . The method of  claim 8 , wherein said capacitive electrostatic generator comprises a dielectric tube of unibody construction having an integrally-sealed end defining an inner cavity with an inner wall; conductive material contained within said inner cavity and disposed in intimate contact with said inner wall; electrically-insulated sealing means for providing hermetic closure to said inner cavity; and electrical means for energizing said conductive material with a static electromotive force.  
     
     
         13 . The method of  claim 8 , wherein said voltage is greater than about 30,000 volts DC.  
     
     
         14 . The method of  claim 12 , wherein said voltage is greater than about 30,000 volts DC.  
     
     
         15 . Membrane separation apparatus comprising: 
 a membrane separation unit;    means for feeding a body of water through said membrane separation unit;    a capacitive electrostatic generator immersed in the body of water;    an electrical ground connected to the body of water; and    a power supply for energizing the electrostatic generator to create an electrostatic field without measurable current leakage in the body of water by application of an electromotive force greater than 10,000 volts DC.    
     
     
         16 . The apparatus of  claim 15 , wherein said membrane separation unit comprises a reverse-osmosis membrane.  
     
     
         17 . The apparatus of  claim 15 , wherein said membrane separation unit comprises an ultrafiltration membrane.  
     
     
         18 . The apparatus of  claim 15 , wherein said membrane separation unit comprises a nanofiltration membrane.  
     
     
         19 . The apparatus of  claim 15 , wherein said capacitive electrostatic generator comprises a dielectric tube of unibody construction having an integrally-sealed end defining an inner cavity with an inner wall; conductive material contained within said inner cavity and disposed in intimate contact with said inner wall; electrically-insulated sealing means for providing hermetic closure to said inner cavity; and electrical means for energizing said conductive material with a static electromotive force.  
     
     
         20 . The apparatus of  claim 15 , wherein said voltage is greater than about 30,000 volts DC.  
     
     
         21 . The apparatus of  claim 19 , wherein said voltage is greater than about 30,000 volts DC.  
     
     
         22 . A method for reducing the formation of biofilm deposits on a wall in a water system comprising the steps of: 
 providing a capacitive electrostatic generator adapted to create an electrostatic field;    immersing said electrostatic generator in a body of water in the water system, the water system being connected to an electrical ground relative to an electromotive force available for energizing the electrostatic generator; and    energizing said electrostatic generator with said electromotive force at a voltage greater than 10,000 volts DC, such that a corresponding electrostatic field is created between said generator immersed in the water system and said electrical ground without measurable current leakage in the body of water.    
     
     
         23 . The method of  claim 22 , wherein said capacitive electrostatic generator comprises a dielectric tube of unibody construction having an integrally-sealed end defining an inner cavity with an inner wall; conductive material contained within said inner cavity and disposed in intimate contact with said inner wall; electrically-insulated sealing means for providing hermetic closure to said inner cavity; and electrical means for energizing said conductive material with a static electromotive force.  
     
     
         24 . The method of  claim 22 , wherein said voltage is greater than about 30,000 volts DC.  
     
     
         25 . The method of  claim 22 , wherein said voltage is greater than about 30,000 volts DC.