Cleaning in membrane filtration systems

Abstract

A method of cleaning permeable, hollow membranes in an arrangement of the type wherein a pressure differential is applied across the walls of the permeable, hollow membranes immersed in a liquid suspension, the liquid suspension being applied to the outer surface of the porous hollow membrane to induce and sustain filtration through the membrane walls. The method of cleaning comprises the steps of applying a cleaning solution to one side of the membrane wall; applying a pressure differential across the membrane wall to cause flow of the cleaning solution through the wall from the one side of the membrane wall to the other side of the membrane wall and applying a reverse pressure differential across the membrane wall to cause flow of the cleaning solution through the wall from the other side of the membrane wall back to the one side of the membrane wall.

What is claimed is: 
     
         1 . A method of controlling a chemical clean of a membrane, the method comprising:
 measuring a pH and/or a membrane resistance of a membrane for at least a portion of the clean; and   ceasing the chemical clean when the pH and/or membrane resistance attains a predetermined value.   
     
     
         2 . The method of  claim 1 , wherein the membrane is a microfiltration or ultrafiltration membrane. 
     
     
         3 . A method of controlling a chemical clean of a membrane, the method comprising:
 measuring a pH and/or a membrane resistance of a membrane for at least a portion of the clean;   measuring an elapsed time of the clean;   calculating a rate of change of pH with respect to time (dpH/dt) and/or a rate of change of membrane resistance (dR/dt) with respect to time; and   ceasing the chemical clean when dpH/dt and/or dRldt attains a predetermined value.   
     
     
         4 . The method of  claim 3 , wherein the membrane is a microfiltration or ultrafiltration membrane. 
     
     
         5 . A method of controlling the chemical cleaning of a filtration system, the method comprising:
 measuring a membrane resistance of a membrane for at least a portion of the clean;   measuring an elapsed time of the clean;   calculating a rate of change of membrane resistance (dR/dt) with respect to time; and   using dR/dt to calculate a duration for completion of the clean.   
     
     
         6 . A method of controlling a chemical clean of a membrane, the method comprising:
 increasing the amount of chemical cleaning agent present during the clean;   measuring membrane resistance of a membrane for at least a portion of the clean; and   ceasing the increase in chemical cleaning agent when membrane resistance attains a predetermined value.   
     
     
         7 . The method of  claim 6 , wherein the amount of cleaning agent is increased incrementally. 
     
     
         8 . The method of  claim 6 , wherein the predetermined value approximates a steady-state value of membrane resistance. 
     
     
         9 . The method of  claim 6 , wherein the membrane is a microfiltration or ultrafiltration membrane.