Method and apparatus for treating potable water in municipal and similar water tanks

Abstract

Method and apparatus for treating potable water in municipal and similar tanks to reduce and remove undesirable disinfectant byproducts such as trihalomethanes from the water by providing a water circulation system to create circulation patterns in the tank water and an air flow system for creating an air flow pattern in the headspace region of the enclosed tank above the water surface. In operation, a portion of the tank water is drawn-up a draft tube from the tank floor to above the water surface and sprayed through a nozzle outwardly about a vertical axis and slightly downwardly toward the surface of remaining tank water. The air flow system creates and directs a high volume of air through the tank above the water surface to volatize undesirable trihalomethanes in the drawn-up water portion to gaseous state to enter the air flow pattern and exit the tank into ambient air.

We claim: 
     
         1 . A method for treating water laden with trihalomethanes (THM) in liquid state in an enclosed tank having a ceiling, floor, and side walls extending between the ceiling and floor to contain the water therein with the surface of the water spaced at least a first distance below the ceiling of the tank to create an air gap region between the ceiling and the surface of the water therebelow, said method including the steps of:
 (a) providing a water circulation system for creating a circulation pattern of the water laden with THM in said tank (1) by continuously moving up a portion of the water from the depths of the tank into an inlet of a draft tube and up through said draft tube to a first location above the surface of the remaining water and (2) by thereafter spraying the upwardly moved portion of the water into the air gap region in a spray pattern (i) outwardly above the surface of the remaining water in the tank about a vertical axis toward the side walls of the tank and (ii) with at least a portion of said spray pattern directed slightly downwardly toward the surface of the remaining water thereby continuously circulating the remaining water in the tank radially outwardly of and about said vertical axis adjacent the surface of the water in the tank toward said tank side walls, downwardly along the tank side walls, and inwardly across the floor toward the inlet to the draft tube with said portion thereof moved upwardly through said draft tube to said first location above the surface of the remaining water in the tank and sprayed outwardly into said air gap region toward the surface of the remaining water wherein the upwardly moved water portion laden with THM sprayed into the air gap region is exposed to the air in said air gap region and the THM in liquid state therein volatized by the air exposure to a gaseous state in said air gap region and   (b) providing an air flow system for creating a continuous air flow pattern directed above and across the surface of the remaining water in the tank from ambient, atmospheric air outside of the tank continuously through the tank from an inlet in the tank into the air gap region above the surface of the remaining water in the tank and back out of the air gap region above the surface of the remaining water in the tank through an air outlet in the tank into the ambient, atmospheric air by establishing a pressure differential between the air inlet and the air outlet of the tank, and further including the step that said provided air flow system is further capable of directing at least a portion of said air flow pattern toward and into the spray pattern of step (a)(2) of the upwardly moved water portion above the surface of the remaining water in the tank wherein the THM in liquid state upwardly moved through the draft tube and volatized to gaseous state in the air gap region above the surface of the remaining water in the tank enters the air flow pattern in the tank above the surface of the remaining water in the tank and exits the tank with the air flow pattern through the air outlet of the tank.   
     
     
         2 . The method of  claim 1  wherein the provided water circulation system is further capable of maintaining said first location of said upwardly moved portion of the water at a predetermined distance above the surface of said remaining water. 
     
     
         3 . The method of  claim 1  wherein the provided water circulation system is further capable of varying the distance of the surface of the remaining water in the tank below the ceiling of the tank and maintaining said first location of said upwardly moved portion of the water at a predetermined distance above the surface of said remaining water. 
     
     
         4 . The method of  claim 1  wherein the provided water circulation system further includes a flotation platform capable of supporting the draft tube with said first location of the upwardly moved water portion therethrough at a predetermined distance above the surface of the remaining water in the tank. 
     
     
         5 . The method of  claim 1  wherein the provided water circulation system is further capable of directing substantially all of the upwardly moved water portion downwardly in step (a)(2). 
     
     
         6 . The method of  claim 1  wherein the provided water circulation system is further capable of directing the spray pattern of step (a)(2) downwardly about the vertical axis substantially in the shape of an inverted cone. 
     
     
         7 . The method of  claim 1  wherein the provided water circulation system is further capable of directing the spray pattern of step (a)(2)(ii) downwardly substantially between 25 and 35 degrees to the horizontal. 
     
     
         8 . The method of  claim 1  wherein the provided water circulation system in step (a)(2) includes the further limitations of providing a perforated sheet configured in an inverted, substantially conical shape with the sides of the cone inclined upwardly and outwardly relative to the vertical axis and the provided water circulation system is capable of spraying the upwardly moved water portion of step (a)((2)(ii) slightly downwardly toward the surface of the remaining water through the perforations of the sheet. 
     
     
         9 . The method of  claim 8  wherein the provided water circulation system is further capable of spraying the upwardly moved water portion through said perforations slightly downwardly in step (a)(2)(ii) between 25 and 35 degrees to the horizontal. 
     
     
         10 . The method of  claim 8  wherein the provided sheet is about 0.1 inches thick and has between 5,000 and 30,000 perforations therethrough of about 0.01 inches in diameter. 
     
     
         11 . The method of  claim 1  wherein the upwardly moved water portion of the provided water circulation system is capable of being drawn into the inlet of the draft tube substantially radially across the tank floor. 
     
     
         12 . The method of  claim 1  wherein the inlet to the draft tube of the provided water circulation system is capable of being positioned less than a foot from the tank floor. 
     
     
         13 . The method of  claim 1  wherein the volume of the upwardly moved water portion per minute of the provided water circulation system is capable of being less than one thousandth the volume of the water in the tank. 
     
     
         14 . The method of  claim 1  wherein the pump of the provided water circulation system is driven by a motor positioned in the draft tube in the upwardly moved water portion wherein the upwardly moved water portion of the provided water circulation system is capable of cooling the motor and conversely heating the upwardly moved water portion to aid in the rate and efficiency of the subsequent volatilization of the THM. 
     
     
         15 . The method of  claim 1  wherein the provided air flow system is capable of directing said portion of the air flow pattern downwardly through a hose toward and into the spray pattern of step (a)(2). 
     
     
         16 . The method of  claim 1  wherein the provided air flow system further includes a hose capable of depending downwardly to adjacent the surface of the remaining water in said tank and the provided air circulation system is capable of directing said portion of the air flow pattern through said hose downwardly toward said surface. 
     
     
         17 . The method of  claim 16  wherein the provided air flow system is further capable of depending said hose downwardly from the ceiling of the tank. 
     
     
         18 . The method of  claim 16  wherein the provided air flow system is further capable of depending said hose downwardly substantially along and about said vertical axis of said spray pattern. 
     
     
         19 . The method of  claim 16  wherein the provided air flow system is further capable of depending said hose downwardly to a second location closer to said tank ceiling than said first location of said drawn-up water portion of step (a)(1) of the provided water circulation system. 
     
     
         20 . The method of  claim 1  wherein the provided air flow system is further capable of establishing said pressure differential between the air inlet of the tank and the air outlet of the tank by pressuring the ambient air entering the air inlet to above atmospheric. 
     
     
         21 . The method of  claim 1  wherein the provided air flow system is capable of having the air flow of step (b) in cubic feet per minute between the tank inlet and outlet to be between 15 and 30 times the flow of the upwardly moved water portion of step (a)(1) of the provided water circulation system in cubic feet per minute. 
     
     
         22 . The method of  claim 1  wherein the provided water circulation system is further capable of maintaining said first location of said upwardly moved portion of water at a predetermined, fixed distance below the ceiling of the tank. 
     
     
         23 . The method of  claim 1  wherein the provided water circulation system is further capable of varying the distance of the surface of the remaining water in the tank and maintaining said first location of said upwardly moved portion of water at a predetermined, fixed distance below the ceiling of the tank. 
     
     
         24 . The method of  claim 1  wherein the provided water circulation system further includes a perforated hose substantially concentrically surrounding said draft tube substantially at said first location and the provided air flow system is capable of directing said air portion of step (b) into the space between the draft tube and surrounding, perforated hose.