Process for enhanced total organic carbon removal while maintaining optimum membrane filter performance

Abstract

One embodiment of a method to system for enhancing TOC removal while maintaining membrane filter performance is the implementation of a dual pH control system. This embodiment will enhance the ability to maximize TOC removal while maintaining optimum membrane filter performance. By adjusting pH, dosing a chemical coagulant and incorporating liquid-solids separation, a considerably higher degree of TOC removal is possible. By adjusting pH again after liquid-solids separation this embodiment can drastically increase the efficiency of the membrane microfiltration/ultrafiltration system. Thus pH control for soluble organic removal is critical. This pH level however may not be the ideal set point for minimizing membrane fouling which is the basis for this embodiment. An example: the pH set point for optimum soluble organic removal is designated to be 5.5. However, the optimum pH set point for optimum membrane performance is 7.0. This embodiment will show the reader that a two stage approach can accomplish the desired result. Stage 1 involves coagulant dosing, pH control, mixing and liquid-solids separation followed by Stage two which involves pH control, mixing and membrane filtration.

1 . (canceled) 
     
     
         2 . A membrane filtration system, comprising:
 a first treatment stage, comprising:
 a first mixing tank; 
 a first pH probe configured to measure a first pH level of water in the first mixing tank; 
 a metering system configured to disperse a coagulant into the water in the first mixing tank; 
 a first mechanical mixing device configured to mix the water in the first mixing tank; and 
 a liquid-solid separator device in fluid communication downstream of the first mixing tank for receiving water from the first mixing tank; 
   a second treatment stage, comprising:
 a second mixing tank, the second mixing tank in fluid communication downstream of the liquid-solid separator device, and configured to receive water that has passed through the liquid-solid separator device; 
 a second pH probe configured to measure a second pH level of the water in the second mixing tank; 
 a second mechanical mixing device configured to mix the water in the second mixing tank; and 
 a membrane filter in fluid communication downstream of the second mixing tank configured to receive water from the second mixing tank, 
 wherein the second treatment stage comprises no metering system for dispersing a coagulant into the second mixing tank; and 
   a pH set point control system in communication with the first and second pH probes and configured to:
 adjust the first pH level of the water in the first mixing tank, prior to the water being directed through the liquid-solid separator device, to a first pH set point selected for optimum TOC removal in response to a signal from the first pH probe, and to 
 adjust the second pH level of the water in the second mixing tank, prior to the water being directed through the membrane filter, to a second pH set point selected for optimum performance of the membrane filter in response to a signal from the second pH probe, the second pH set point being higher than the first pH set point. 
   
     
     
         3 . The membrane filtration system of  claim 2 , wherein the pH set point control system comprises a first acid/base dosing system in fluid communication with the first mixing tank and a second acid/base dosing system in fluid communication with the second mixing tank. 
     
     
         4 . The membrane filtration system of  claim 2 , wherein the first treatment stage further comprises a flow meter for determining a flow rate of water flowing into the first mixing tank, and wherein the metering system for dispersing the coagulant is configured to determine an amount of coagulant to dose based upon the flow rate of the water flowing into the first mixing tank. 
     
     
         5 . The membrane filtration system of  claim 2 , wherein the liquid-solid separator device is selected from the group consisting of a plate separator, a sedimentation tank, a solids-contact clarifier, an ion exchange unit and a dissolved air flotation unit. 
     
     
         6 . The membrane filtration system of  claim 2 , wherein the coagulant is an aluminum or iron metal salt based coagulant. 
     
     
         7 . The membrane filtration system of  claim 2 , wherein the first pH set point is about 5.0 to about 6.0, and wherein the second pH set point is neutral or about 7.0 or higher. 
     
     
         8 . The membrane filtration system of  claim 2 , wherein the membrane system comprises microfiltration or ultrafiltration membranes made of polymeric or ceramic materials. 
     
     
         9 . The membrane filtration system of  claim 2 , further comprising an ion exchange operation upstream of the first treatment stage. 
     
     
         10 . The membrane filtration system of  claim 2 , further comprising a disinfection or a granular activated carbon adsorption operation downstream of the second treatment stage. 
     
     
         11 . A process for treating water, comprising:
 dispersing an effective amount of coagulant into a volume of water in a first tank;   adjusting a pH level of the water in the first tank to a first pH set point selected for optimum total organic carbon removal;   mixing the water in the first tank;   directing the water at the first pH set point through a liquid-solid separator device and into a second tank downstream of the liquid-solid separator device;   adjusting a pH level of the water in the second tank to a second pH set point selected for optimum performance of a downstream membrane filter, the second pH set point being higher than the first pH set point;   mixing the water in the second tank; and   directing the water at the second pH set point through the membrane filter.   
     
     
         12 . The process of  claim 11 , wherein the dispersing step includes metering the coagulant based upon a signal which corresponds to a flow rate of water into the first tank. 
     
     
         13 . The process of  claim 11 , wherein the effective amount of coagulant is determined based upon the volume, TOC level and temperature of the water in the first tank. 
     
     
         14 . The process of  claim 11 , further comprising suppressing the pH level of the water prior to the coagulant dispersing step. 
     
     
         15 . The process of  claim 11 , wherein the first pH set point ranges from 5.0 to 6.0 standard units and the second pH set point is at least 7.0 standard units. 
     
     
         16 . The process of  claim 11 , further comprising performing an ion exchange operation upstream of the first tank. 
     
     
         17 . The process of  claim 11 , further comprising performing a disinfection or a granular activated carbon adsorption operation downstream of the membrane filter. 
     
     
         18 . A process for treating water, comprising:
 dispersing an effective amount of coagulant into a volume of water in a first tank;   adjusting a pH level of the water in the first tank to a first pH set point selected for optimum total organic carbon removal;   mixing the water in the first tank;   directing the water at the first pH set point through a liquid-solid separator device and into a second tank downstream of the liquid-solid separator device, wherein no coagulant is dispersed downstream of the liquid-solid separator device;   adjusting a pH level of the water in the second tank to a second pH set point selected for optimum performance of a downstream membrane filter;   mixing the water in the second tank; and   directing the water at the second pH set point through the membrane filter.   
     
     
         19 . The process of  claim 11 , wherein the effective amount of coagulant is determined based upon the volume, TOC level and temperature of water in the first tank. 
     
     
         20 . The process of  claim 2 , further comprising suppressing the pH level of the water prior to the coagulant dispersing step.