Abstract:
This invention is directed to a method and apparatus for controlling and optimizing the feed of two or more oxidizers to an aqueous stream, thereby providing a synergistic effect. The system combines the use of amperometric or ORP based sensor technology with amperometric sensor technology employing a gas permeable membrane, thereby providing definitive control of each oxidizer feed stream.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the control of multiple oxidizer levels in water treatment processes, and particularly relates to the use of a combination of sensors including at least one amperometric sensor isolated by a gas permeable membrane.  
           [0002]    1. Background of the Invention  
           [0003]    In the areas of both pool water and waste water treatment, there has been an increased trend toward combining oxidizers to achieve a synergistic effect, thereby exceeding the performance of the individual oxidizers. Although there is no question as to the benefits provided by the use of synergistic oxidizer chemistry, the ability to control their concentrations, ratios, and optimize their feed rate in real world applications has proven to be a difficult task. This often leads to overfeeding to ensure adequate results.  
           [0004]    Most oxidizer feed applications incorporate either ORP (Oxidation Reduction Potential) or wet chemistry methods which use color change reagents,. e.g. DPD, to indicate the presence and concentration of the oxidizer. ORP has become increasing popular due to its ability to control the feed of oxidizer based on the oxidizer demand.  
           [0005]    In many water treatment applications the demand for oxidizer can change over time. In pools for example, as bathers enter the pool water, organic contaminants are introduced to the water that impose a demand on the oxidizer (usually chlorine). In order to maintain the same oxidation potential, the ORP controller would increase the concentration of chlorine in the water. This process ensures enough oxidizer has been added to not only satisfy the organic demand, but also to ensure sufficient residual oxidizer is available to effectively sanitize the water.  
           [0006]    In the pool example, chlorine is the sanitizer and therefore must be maintained in sufficient concentrations to effectively provide for a safe bathing environment. However, if another oxidizer is added to the pool water to enhance oxidation of organic contaminants, the ORP based control system can be compromised since either chlorine or the second oxidizer can satisfy the ORP setting.  
           [0007]    Should chlorine feed be compromised, the second oxidizer could be fed in sufficient concentrations to meet the ORP set-point. In this instance, sanitation of the water could be compromised. Also, because chlorine concentrations are reduced, the synergistic effects provided by the combined effect of the two oxidizers would also be compromised.  
           [0008]    2. Description of the Prior Art  
           [0009]    U.S. Pat. No. 5,239,257 to Muller et al teaches an amperometric probe with a gas permeable membrane. The patent fails to teach or disclose a measuring system for controlling oxidizers in a water treatment process by combining multiple sensors inclusive of at least one gas permeable membrane enclosed amperometric sensor.  
           [0010]    U.S. Pat. No. 5,902,751 to Godec et al teaches a method for the measurement of dissolved carbon employing a gas permeable membrane dividing deionized water from the oxidized sample water and a pair of micro-conductivity and temperature sensors.  
           [0011]    U.S. Pat. No. 6,030,842 to Peachey-Stoner teaches a method for determining free halogens in aqueous fluids utilizing an azine indicator material and a benzidine type catalyst material impregnated into a matrix carrier.  
           [0012]    The prior art fails to teach or suggest a system for determining and controlling the amounts of free oxidizer in a multiple oxidizer system.  
         SUMMARY OF THE INVENTION  
         [0013]    Many water treatment applications incorporate two oxidizers that together provide a synergistic effect. For example, Advanced Oxidation Technologies (AOTs) can employ ozone with peroxide to produce hydroxyl free radicals (hydroxyl radicals). In yet another similar application, hydrogen peroxide is converted to hydroxyl free radicals using ultra violet radiation. While one oxidizer is predominant, the production of hydroxyl radicals makes for a two-oxidizer application. There are other similar processes used in AOTs with the results being to produce hydroxyl free radicals.  
           [0014]    In yet another water treatment application, a halogen based oxidizer such as chlorine is used in combination with peroxygen based oxidizers such as potassium monopersulfate to effectively eliminate the formation of volatile halogenated nitrogen based compounds into the air of indoor aquatic facilities. In this application, both chlorine and monopersulfate are fed to the pool water based on ORP based control.  
           [0015]    Although these applications take advantage of the synergistic properties which flow from the use of two oxidizers, they nevertheless fail to optimize the control and/or optimize the feed or production of each oxidizer based, on program performance, e.g. oxidizer demand.  
           [0016]    For example in the pool, while ORP initiates oxidizer feed based on demand for the oxidizer(s), this method of control does not clearly differentiate between the oxidizers. Oxidizers are fed proportional to one another. Using this control scheme, dynamic optimization of oxidizer ratios, and verification of individual oxidizer feed is not possible. Similar inefficiencies exist with AOTs.  
           [0017]    Accordingly, it is an objective of the instant invention to teach a method of operation and apparatus for performing the method which combines the use of either ORP or amperometric sensor technology, along with at least one amperometric sensor that employs a gas permeable membrane to provide superior process control in two oxidizer systems. The gas permeable membrane described in this application will have the ability to allow gases and/or nonionic compounds to permeate while restricting ionic particles from permeating.  
           [0018]    It is a further objective of the instant invention to teach a process wherein the combination of sensor technologies can, in many two oxidizer applications, independently control the oxidizers, verify concentration or presence of both oxidizers, and enhance the optimization of oxidizers(s) feed rates in dynamic systems.  
           [0019]    Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0020]    [0020]FIG. 1 is a block diagram and flow-sheet of a typical testing device in accordance with the present invention;  
         [0021]    [0021]FIG. 2 is a graphical analysis of the relative concentration of chlorine versus pH;  
         [0022]    [0022]FIG. 3 is a graph of the increase in the amperometric value as Hydrogen peroxide is incrementally added to the solution.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    In the application employing a halogen-based oxidizer with a peroxygen-based oxidizer, the invention is comprised of at least one amperometric sensor incorporating a gas permeable membrane in conjunction with one or more of ORP, pH, and temperature sensor technologies. These sensors serve as data inputs to a microprocessor or analog based computer. The computer employs some mode of control utilizing Time Based Proportional (TBP), Proportional (P), Proportional Integral (PI), Proportional Integral Differential (PID) and/or on/off control for controlling chemical(s) feed.  
         [0024]    To further improve control, the computer can be programmed utilizing either Fuzzy logic or Boolean logic protocols to provide the system with the ability to make changes to various settings or feed adjustments based on evaluation of input data.  
         [0025]    In yet another application of the invention, AOT applications employ at least one amperometric sensor utilizing a gas permeable membrane that separates the amperometric electrode from the treated water, along with one or more standard amperometric sensors (no gas permeable membrane). These sensors serve as data inputs to a microprocessor or analog based computer. The computer employs some mode of control utilizing Time Based Proportional (TBP), Proportional Integral (PI), Proportional Integral Differential (PID) and/or on/off control for controlling chemical feed.  
         [0026]    To further improve control, the computer can be programmed utilizing Fuzzy logic or Boolean logic to make changes to various settings or feed adjustments based on evaluation of input data.  
         [0027]    Halogen/Peroxygen Test  
         [0028]    In this test, chlorine in the form of sodium hypochlorite was used in combination with potassium monopersulfate.  
         [0029]    The amperometric sensor incorporated a gas permeable membrane used to prevent dissolved solids from influencing the amperometric sensor. Therefore, only dissolved chlorine in the form of hypochlorous acid can permeate the membrane and influence the amperometric sensor. The sensor was calibrated for use with chlorine. The amperometric sensor and supporting hardware employ pH and temperature inputs for accurate determination of free chlorine. An ORP sensor was incorporated to measure water ORP values.  
         [0030]    A circulating system with a 10-gallon reservoir was used for testing purposes (FIG. 1)  
         [0031]    The circulating pump was turned on, the water was treated with sodium bypochlorite, and the pH was adjusted. Free chlorine concentration was verified using standard DPD methods with a HACH DR-2000 spectrophotometer. The amperometric controller was standardized, then allowed to track while samples where periodically tested using DPD free chlorine test. The solution ORP was recorded periodically throughout the test period.  
         [0032]    After ensuring the sensors had achieved equilibrium (stabilized readings), the solution was treated with various concentrations of potassium monopersulfate by addition into the top reservoir. After each addition of monopersulfate, the effect on both the amperometric reading and ORP reading were measured and recorded (Table 1).  
                                                                     TABLE 1                       Persulfate   Approx.           HACH Free       Amperometric       Addition   Time lapsed           Chlorine   Amperometric   Free Chlorine       (ppm)   (minutes)   ORP mv   pH   (ppm)   HOCl (ppm)   (ppm)                                0   0   53   0.3   5.2   2.77   5.2       9   5   62   0.3   n/a   2.78   5.2       9   15   64   0.3   n/a   2.83   5.2       26   30   70   0.2   n/a   2.9   5.1       26   50   82   0.1   5.1   2.95   5.1                  
 
         [0033]    With the addition of the acid based monopersulfate, slight changes in pH induced a change in the measured hypochlorous acid (FIG. 2). However, the calculated free chlorine value remained stable since the monopersulfate exists as an ionized salt that cannot permeate the gas permeable membrane.  
         [0034]    It is evident from the results of this test that free chlorine concentration was accurately measured by the amperometric sensor while the ORP value was significantly influenced by the presence of the second oxidizer (potassium monopersulfate). Even with concentrations of monopersulfate magnitudes higher than that applied in actual application such as the pool example, free chlorine residual was accurately measured by the amperometric sensor.  
         [0035]    By incorporating this sensor technology into this dual oxidizer application, verification and optimization of chlorine feed would be achieved even in the presence of the second oxidizer. Therefore, in a pool application where chlorine is used as the sanitzer, implementation of this control technology would ensure that low levels of chlorine would not occur due to the satisfied ORP value measured by the ORP controller.  
         [0036]    Yet another benefit of this invention is the improved performance achieved through the optimized proportioning of the oxides. For instance, if sufficient chlorine is available to ensure sanitation and support its role in the oxidation processes, the second oxidizer could be selected and fed independent of the chlorine. Boolean logic or Fuzzy logic can be effectively included to maximize performance through optimized proportioning of the oxidizers whether fed together or independently.  
         [0037]    AOT Test 1  
         [0038]    An amperometric sensor combined with a readout display was calibrated to report the measured value of hydrogen peroxide as Chlorine (Cl 2 ). Hydrogen peroxide was incrementally added to the solution. The increase in the amperometric value is illustrated in FIG. 3. Based on these results, it is evident that amperometric technology can effectively detect the presence of hydrogen peroxide.  
         [0039]    The same test was performed using an amperometric sensor incorporating a gas permeable membrane. For the 90 ppm active concentration of hydrogen peroxide, the displayed value was 0.1 ppm as Cl 2 .  
         [0040]    Based on these two tests, it is evident the employing these two types of amperometric methods of measure could allow for an accurate measure of oxidizers independently in a two oxidizer environment.  
         [0041]    In AOT applications hydrogen peroxide is converted to form hydroxyl free radicals, the second most powerful oxidizer known. This process incorporates combining hydrogen peroxide with ozone, or contacting the hydrogen peroxide with UV radiation.  
         [0042]    Hydroxyl free radicals rapidly react with many organic and inorganic contaminants found in many water treatment applications. However, if the concentration of hydroxyl radicals is to be optimized based on demand for the oxidizer, an accurate means of measuring this oxidizer in the presence of the second oxidizer must be employed.  
         [0043]    ORP sensors do not provide an accurate method for measuring hydrogen peroxide. Amperometric sensor technology can be applied as previously reviewed. However, hydroxyl radicals can interfere with the amperometric sensor if present with the hydrogen peroxide. In order to adjust the concentration of hydroxyl radicals, independent measure of hydroxyl radicals must be made while in the presence of residual hydrogen peroxide.  
         [0044]    Like hypochlorous acid, hydroxyl radicals are nonionic. This enables them to permeate through gas permeable membranes like that employed in the previous test. Hydrogen peroxide on the other hand possesses a strong anionic charge.  
         [0045]    An amperometric sensor calibrated to report the oxidizer concentration as chlorine (Cl 2 ) incorporated a gas permeable membrane.  
         [0046]    A sample of water was treated with 600 ppm of active hydrogen peroxide by adding 30% laboratory grade hydrogen peroxide to distilled water. A sample of solution was placed on a magnetic stirrer, the sensor with the membrane was immersed into a sample of the solution, the stirrer was activated, and the sensor was allowed to equilibrate for approximately 30-minutes.  
         [0047]    Another equal volume of sample was placed in a reaction vessel, in which a UV lamp was placed. The sample with the lamp was periodically immersed in a swirling ice bath to maintain temperature at 23° C. (±1° C.). The solution was exposed for approximately 30 minutes.  
         [0048]    After equilibrating for approximately 30 minutes, the amperometric reading was recorded followed by the ORP, and temperature. After recording, the UV sample was given a final ice water bath to stabilize the solution temperature. The lamp was disengaged, and the amperometric w/gas membrane sensor was immersed into the solution. The magnetic stirrer was initiated and the sensor was allowed to equilibrate.  
         [0049]    After approximately 60 seconds, the measured value on the display increased significantly and in approximately 3-minutes reached a value of 8.38 as CL 2  as illustrated the following table. The pH, ORP and temperature were also recorded.  
                                                   Temperature   Amperometric               Sample Name   ° C.   w/membrane   ORP   pH                   Control   23   0.37   245   7.25       UV radiated   23   8.38   240   7.25                  
 
         [0050]    AOT Test 2  
         [0051]    To further demonstrate the ability to differentiate oxidizers and provide superior process control, a 500 ml sample of tap water was treated with 1 ml of 30% hydrogen peroxide. 50 ml of solution was removed and radiated with UV for 30 minutes. The remaining 450 ml of peroxide solution was stirred using a magnetic stirrer with the membrane amperometric sensor immersed.  
         [0052]    After 30 minutes and temperature adjustment with an ice bath, the UV radiated solution was reintroduced to the starting 600 ppm solution. Because both solutions began with 600 ppm of active hydrogen peroxide, addition of the solution would not affect the concentration of peroxide and thereby induce interference to the reading. In fact, it is reasonable to assume it would reduce the peroxide concentration since some of the peroxide had been consumed in the production of hydroxyl radicals.  
         [0053]    The results clearly demonstrate the membrane-amperometric based technology has the ability to insulate electrode from significant interferences induced by the presence of hydrogen peroxide, thereby allowing effective detection and measurement of hydroxyl radicals.  
                                                           Temperature   Amperometric           Sample Name   ° C.   w/membrane                           Control   22   1.1           Treated   22   8.3                      
 
         [0054]    Including gas permeable membrane based amperometric technology with conventional amperometric technology provides superior process control of two oxidizers in two oxidizer systems.  
         [0055]    One example is to maintain sufficient hydrogen peroxide in a body of water, such as a pool, for sanitation with use of a standard amperometric sensor. Then enhancing oxidation of organics with hydroxyl radicals by applying the gas membrane amperometric sensor technology to measure residual hydroxyl radicals directly, or by difference between the two gas membrane amperometric readings, one taken before and one after hydroxyl radicals are employed. This application could effectively be applied to pools as well as other water treatment applications where oxidation using hydroxyl free radicals would effectively assist in the reduction of organic and other oxidizable inorganic substances.  
         [0056]    To further illustrate other potential performance benefits offered by this process control system, with increased concern of cryptosporidium contamination of water, and the high chlorine tolerance of said organisms, the ability to control hydroxyl free radical concentrations offers the ability to destroy the protective lipid layer of the Cryptosporidium Oocyst by inoculating the water with effective doses of hydroxyl free radicals. Application of this technology with additional treatment and/or on-line monitoring could further improve water safety and quality.  
         [0057]    The hydroxyl measurement can be used as part of a feedback control by which adjusting the introduction of hydroxyl radicals into the water to be treated, or by increasing the production rate of hydroxyl radicals by increasing or decreasing the ozone concentration or UV intensity and/or contact with the supporting oxidizer (peroxide or ozone) is controlled.  
         [0058]    Yet another method of applying this technology to improve the effectiveness and efficiency of 2-oxidizer systems when utilizing a halogen oxidizer is to measure the free halogen concentration with the gas permeable membrane amperometric sensor, while also measuring the solution pH and ORP. An algorithm is used to correlate the concentration of oxidizer demand based on the required free halogen concentration needed to achieve the measured ORP for a given measured pH.  
         [0059]    For a given water quality, it will require a specific concentration of free halogen oxidizer at a given pH to achieve a targeted ORP value. This concentration of halogen will not change unless the demand for the oxidizer changes (at a constant pH). If the measured free halogen concentration needed to achieve a targeted ORP increases, the demand in the water has increased. By using an algorithm to identify the presence of this demand, a second oxidizer can be employed to effectively address this demand. For example, the feed rate or production rate of hydroxyl radicals can be adjusted in real-time utilizing this form of control to maximize the performance of the treatment program.  
         [0060]    It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement of parts herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and drawings.