The present invention is a method and system for removal of volatile contaminants from water. More specifically, it is a method and system for using spray aeration for removing trihalomethanes and radon from a water supply.
Volatile Organic Compounds (VOCs) are organic chemicals that have a high vapor pressure, or volatility, at ordinary, room-temperature conditions. Their volatility results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and enter the surrounding air or water. VOCs are numerous, varied, and ubiquitous. They include both man-made and naturally occurring chemical compounds. VOCs can be present in ground water and be of environmental concern, or VOCs can be present in drinking water and be a public health issue. For example, one group of VOCs is Trihalomethanes (THMs), which are disinfection byproducts (DBPs) found in drinking water. The present invention applies to the removal of VOCs from water, in general, but for simplicity the present invention will be discussed in reference to THMs and radon in drinking water.
Trihalomethanes (THMs) are formed as a by-product when chlorine or bromine is used to disinfect water for drinking. Trihalomethanes are chemical compounds in which halogens replace three of the four hydrogen atoms of methane (CH4). Halogen is an element from the group that includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Some of the common trihalomethanes .found in water are Choloform (tricholoromethane CHCl3), Dibromochloromethane (CHBr2Cl−), Bromodichloromethane (CHBrCl2), and Bromoform (tribromomethane CHBr3).
There have been some studies such as a California study that suggest a link between miscarriages and disinfection by-products (DBP) of THM in drinking water. The U.S. Environmental Protection Agency (EPA) in recent years has increased the standard related to THM therein reducing the amount of THM in parts per billion (ppb).
The EPA describes radon as an odorless, tasteless and invisible gas produced by the decay of naturally occurring uranium in soil and water. Radon is a form of ionizing radiation and a proven carcinogen. Luna cancer is the only known effect on human health from exposure to radon in air. According to a report on radon released in 1998 by the National Academy of Sciences there about 168 cancer deaths per year: 89% from lung cancer caused by breathing radon released to indoor air from water and 11% from stomach cancer caused by consuming water containing radon. Drinking water that comes from underground sources, as opposed to surface water, is a greater concern since the dissolved radon gas does not have an opportunity to escape into the outside air before it arrives at the tap.
Water systems, such as public water systems, need to balance several, factors in the treatment of water. Some water systems, such as small public water systems, may obtain water from neighboring systems resulting in the water being in the distribution system for longer time periods. This longer time period may result in more disinfection by-products (DSP) such as THMs.
In contrast to conventional systems, the system and method of the instant invention reduces the level of trihalomethanes at minimum cost including both operation and maintenance costs, works well in both large scale and small scale systems, and can take an existing system and modify without requiring major infrastructure expansion.
According to the invention, a method of treating water to reduce the level of trihalomethanes or other volatile contaminants includes spraying the water through a nozzle to aerate the water to be treated to increase the air/water interface therein reducing the level of trihalomethanes in the water.
One aspect of the present invention is a method of treating water to reduce the level of volatile contaminants comprising: spraying water into a tank constructed to contain water, wherein the water is sprayed through a nozzle to aerate the water to be treated thereby increasing the air/water interface and reducing the level of volatile contaminants in the water.
One embodiment of the method of treating water to reduce the level of volatile contaminants is wherein the volatile contaminant is radon.
One embodiment of the method of treating water to reduce the level of volatile contaminants is wherein the volatile contaminant is a trihalomethane.
One embodiment of the method of treating water to reduce the level of volatile contaminants further comprises the step of positioning the nozzle above the surface of the water contained in the tank to create a distance over which the air/water interface occurs thereby further increasing the air/water interface and reducing the level of volatile contaminants in the water.
One embodiment of the method of treating water to reduce the level of volatile contaminants is wherein the distance between the nozzle and the surface of the water in the tank is greater than about four meters.
One embodiment of the method of treating water to reduce the level of volatile contaminants is wherein the nozzle has an orifice of about ⅛ inch to about 2 inches.
One embodiment of the method of treating water to reduce the level of volatile contaminants further comprises the step of adjusting the pressure of the water to be treated thereby creating a droplet size of the water exiting the nozzle that is less than 5000 microns SMD.
One embodiment of the method of treating water to reduce the level of volatile contaminants is wherein the droplet size of the water exiting the nozzle is less than 2000 microns SMD.
One embodiment of the method of treating water to reduce the level of volatile contaminants is wherein the droplet size of the water exiting the nozzle is less than 1000 microns SMD.
One embodiment of the method of treating water to reduce the level of volatile contaminants is wherein the droplet size of the water exiting the nozzle is less than 400 microns SMD.
One embodiment Of the method of treating water to reduce the level of volatile contaminants is wherein the droplet size of the water exiting the nozzle is less than 150 microns SMD.
Another aspect of the present invention is a method of treating water to reduce the level of volatile contaminants in water, comprising: pumping the water to be treated in a pipe from a reservoir to a nozzle located in a tank which is constructed to contain water; adjusting the pressure of the water to be treated thereby creating a droplet size of the water exiting the nozzle that is less than 150 microns SMD; and positioning the nozzle at a distance greater than about four meters from the surface of the water in the tank, thereby increasing the air/water interface and reducing the level of volatile contaminants in the water.
Another aspect of the present invention is a drinking water treatment system for reducing the level of volatile contaminants in water, comprising a reservoir for containing water to be treated; a nozzle for spraying the water to be treated; a pipe for carrying the water to be treated from the reservoir to the nozzle; a tank for receiving the treated water; and a pump for pumping the water from the reservoir through the nozzle, wherein the nozzle that is located in the tank has an orifice which produces a droplet size of the water exiting the nozzle that is less than 2000 microns SMD, thereby increasing the air/water interface and reducing the level of volatile contaminants in the water.
One embodiment of the drinking water treatment system for reducing the level of volatile contaminants in water is wherein the droplet size of the water exiting the nozzle that is less than 1000 microns SMD.
One embodiment of the drinking water treatment system for reducing the level of volatile contaminants in water is wherein the droplet size of the water exiting the nozzle that is less than 400 microns SMD
One embodiment of the drinking water treatment system for reducing the level of volatile contaminants in water is wherein the nozzle is at a distance greater than about four meters from the surface of the water in the tank.
One embodiment of the drinking water treatment system for reducing the level of volatile contaminants in water is wherein the volatile contaminant is radon.
One embodiment of the drinking water treatment system for reducing the level of volatile contaminants in water is wherein the volatile contaminant is a trihalomethane.
One embodiment of the drinking water treatment system for reducing the level of volatile contaminants in water is wherein the nozzle has an orifice of about ⅛ inch to about 2 inches.
These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims and accompanying drawings.
The foregoing and other objects, features, and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
The present invention is a system 20 and a method for treating water to reduce levels of trihalomethanes. Referring to
In a prototype, various operating conditions and design variables were tested. Table I and Table II show the variables.
Referring to
All THM concentration analysis was conducted using the modified version of EPA method 551.1. The electron capture gas chromatograph used in analysis was an Agilent Technologies 6890N GC-ECD, fitted with an Agilent 7683 Series auto sampler and auto injector. Included with each batch of samples was a lab-created spiked sample for calibration. The squared correlation coefficient (R2) for spiked samples (provided by the lab) was greater than 0.99 for all four species of THMs, indicating satisfactory analytical accuracy.
Referring to
In order to design a spray aeration system based on operating conditions and treatment objectives, several diffused aeration models based on a minimum air to water ratio were evaluated. Diffused aeration is where bubbles of air, pass through liquid versus spray aeration where droplets of liquid pass through air. The one that best matched experimental results is shown in Equation 1. Predicted and empirical results are shown in
While the first round of testing was done with diffused aeration, diffused and spray aeration rely on the same mechanisms for mass transport; a concentration gradient drives the THMs through an interfacial surface area, moving the THMs from a liquid phase to a gas phase. The key difference between diffused and spray aeration is that the bubbles created in diffused aeration have a finite volume and can reach saturation rapidly. This means that THM removal may only occur for the first few feet of bubble contact. Because bubbles have a small volume, the gas concentration of THMs inside the bubbles increases over time, lessening the concentration gradient that provides the driving force for mass transfer. Spray aeration offers a larger, air volume, greatly lessening the effect of a decreasing concentration gradient, and therefore offering the potential for a more efficient THM removal using an aeration strategy. Like a diffused aeration apparatus, a spray aerator could be placed in a water tower or a clear well chlorine contact chamber.
Finally, spray aeration requires water pressure to make an air/water interface, while diffused aeration requires air pressure. Because water pressure is already required for filling a water tank, the instant invention recognizes that some systems 20 may require nothing more than a redesign of the water tank influent piping and the addition of a spray nozzle 26 in order to realize significant THM reductions. Other systems will require an additional pump or set of pumps to re-circulate the water in the tank through the one or more spray nozzles.
The spray aeration pilot scale experiments focused on an assessment of operating and design variables affecting THM removal rates with an emphasis on gathering enough information to accurately create a model which could be utilized to design and build an actual spray aeration apparatus in the field. With that goal in mind, all design and operating variables were chosen to either reflect likely worst case operating conditions, or design variables identified as likely to influence THM removals. Design and operating variables for the spray aeration pilot scale optimization trails are summarized in Table III.
In the prototype, for the spray aeration pilot scale optimization experimental trials, spray nozzles from nozzle manufacturer BETE Fog Nozzle, Inc. (Greenfield, Mass.) were selected. These nozzles 26 were chosen because the nozzles 26 are able to produce a wide variety of droplet sizes (based on nozzle type and operating pressure) but have only one nozzle orifice. This was considered a design advantage because the large opening should help to prevent nozzle clogging. The second design variable selected for this experiment was droplet travel distance; the distance a droplet travels after exiting the nozzle 26 before splashing down onto the water surface. This was considered an important variable because the time it takes the droplet to travel from the nozzle exit to the water surface 50 is the time in which mass transfer can occur. By varying the droplet travel distance while keeping the nozzle exit velocity and droplet SMD constant, an assessment of the influence of air to water contact time was evaluated. The experimental apparatus shown in
By comparing the volumetric ratio to the percent removals achieved, a set of design graphs for each species of THM,
in one embodiment of the present invention, the size of the nozzle orifice, the inner diameter, can vary to increase the air/water interface. In one embodiment the size of the nozzle orifice is from about 1/16 inch to about 3 inches. In one embodiment the size of the nozzle orifice is from about ⅛ inch to about 2 inches. In one embodiment the size of the nozzle orifice is from about 3/16 inch to about 1.5 inches. In one embodiment the size of the nozzle orifice is from about ¼ inch to about 1 inch. In one embodiment the size of the nozzle orifice is about 1/16 inch, about ⅛ inch, about 3/16 inch, about ¼ inch, about 5/16 inch, about ⅜ inch, about 7/16 inch, or about ½ inch. In one embodiment the size of the nozzle orifice is about 9/16 inch, about ⅝ inch, about 11/16 inch, about ¾ inch, about 13/16 inch, about ⅞ inch, about 15/16 inch, or about 1 inch. In one embodiment the size of the nozzle orifice is about 1 1/16 inches, about 1⅛ inches, about 1 3/16 inches, about 1¼ inches, about 1 5/16 inches, about 1⅜ inches, about 1 7/16 inches, or about 1½ inches. In one embodiment the size of the nozzle orifice is about 1 9/16 inches, about 1⅝ inches, about 1 11/16 inches, about 1¾ inches, about 1 13/16 inches, about 1⅞ inches, about 1 15/16 inches, or about 2 inches. In one embodiment the size of the nozzle orifice is about 2 1/16 inches, about 2⅛ inches, about 2 3/16 inches, about 2¼ inches, about 2 5/16 inches, about 23/8 inches, about 2 7/16 inches, or about 2½ inches. In one embodiment the size of the nozzle orifice is about 2 9/16 inches, about 2⅝ inches, about 2 11/16 inches, about 2¾ inches, about 2 13/16 inches, about 2⅞ inches, about 2 15/16 inches, or about 3 inches.
In one embodiment of the present invention, the droplet size of the water exiting the nozzle can vary to increase the air/water interface. In one embodiment, the droplet size of the water exiting the nozzle is less than about 5000 microns Sauter mean diameter (SMD). In one embodiment, the droplet size of the water exiting the nozzle is less than about 4000 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 3000 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 2000 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 1000 microns SMD.
In one embodiment, the droplet size of the water exiting the nozzle is less than about 900 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 800 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 700 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 600 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 500 microns SMD.
In one embodiment, the droplet size of the water exiting the nozzle is less than about 450 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 400 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 350 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 300 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 250 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 200 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 150 microns SMD. In one embodiment, the droplet size of the water exiting the nozzle is less than about 100 microns SMD.
In one embodiment of the present invention, the nozzle is positioned above the surface of the water contained in the tank to create a distance over which the air/water interface occurs. This distance can vary to increase the air/water interface. In one embodiment, the distance between the nozzle and the surface of the water in the tank is greater than about one meter. In one embodiment, the distance between the nozzle and the surface of the water in the tank is greater than about two meters. In one embodiment, the distance between the nozzle and the surface of the water in the tank is greater than about three meters. In one embodiment, the distance between the nozzle and the surface of the water in the tank is greater than about four meters. In one embodiment, the distance between the nozzle and the surface of the water in the tank is greater than about five meters. In one embodiment, the distance between the nozzle and the surface of the water in the tank is greater than about six meters.
While the principles of the invention have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the invention. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art arc considered to be within the scope of the present invention.
The present application is a continuation-in-part of U.S. patent application Ser. No. 13/135,666, tiled Jul. 12, 2011, which is incorporated herein by reference.
Number | Date | Country | |
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Parent | 13135666 | Jul 2011 | US |
Child | 13493117 | US |