Methods and systems for determining free chlorine concentration in water based on dissolved oxygen

Abstract

A method and system for analyzing water that includes free chlorine. The method includes adding hydrogen peroxide into the water to react with free chlorine present in the water to produce dissolved oxygen, measuring an amount of dissolved oxygen produced in the water from a reaction between the hydrogen peroxide and the free chlorine in the water, and determining a concentration of free chlorine in the water based on the measured amount of dissolved oxygen produced in the water. The system includes a hydrogen peroxide infusion device and a dissolved oxygen sensor.

Description

METHODS AND SYSTEMS FOR DETERMINING FREE CHLORINE CONCENTRATION IN WATER BASED ON DISSOLVED OXYGENTECHNICAL FIELD

[0001] The present disclosure relates generally to methods and systems for determining free chlorine concentration based on dissolved oxygen content measured in water.BACKGROUND

[0002] Chlorine is commonly used as a disinfectant in water systems and wastewater treatment processes. Measuring and monitoring free chlorine is important for ensuring safe drinking water and meeting environmental regulatory requirements for wastewater and industrial streams. Commonly used methods for measuring free chlorine in water include colorimetric assays and amperometric methods.

[0003] In colorimetric methods, an indicator such as N,N-Diethyl-p-phenylenediamine (DPD), and a buffer are added to the water. The indicator reacts with the free chlorine in the water to produce a color having an absorbance proportional to the concentration of free chlorine. The absorbance at a particular wavelength can be measured to determine the free chlorine concentration. The buffer adjusts the pH of the water to a range that is optimum for measurement of free chlorine. However, colorimetric methods can suffer from errors due to color and turbidity, which are common to wastewater streams and interference from other oxidants, such as chlorine dioxide, monochloramine, chlorite, ozone, and the like. Excess alkalinity and high and low pH can also affect the results of colorimetric techniques. Furthermore, local regulations may require specific disposal of the waste output of many colorimetric analyzers and therefore may limit use of those analyzers in certain locations.

[0004] Amperometric methods use a chlorine-selective electrode to detect and quantify free chlorine in the water by measuring the electric current over time. However, amperometric methods may be unreliable, are often susceptible to electrode fouling, and require constant flow. Additionally, amperometric probes and other electrochemical sensors may suffer from signal drift as, for example, electrolyte degrades, membranes age, and electrodes polarize, which causes readings to become inaccurate over time. Therefore, the probes may need to be calibrated frequently (e.g., monthly or even more frequently) to restore accuracy. Calibration may be amanual, labor-intensive process performed by a technician. For each calibration, the technician has to travel to the location of the probe, which may be installed at a remote location. When frequent calibration is combined with hard-to-reach installation points, the result is high maintenance burden, involving more travel time, more safety exposure, and higher risk that calibrations are deferred, leading to long periods of inaccurate measurements. Additionally, amperometric probes can also have a long warm-up time (e.g., 24 hours after powering on).

[0005] There is a need for an improved free chlorine measurement method that can accurately measure free chlorine in a water system without suffering from the above drawbacks.SUMMARY

[0006] In view of the above, an object of the present disclosure is to provide a method of analyzing water that includes free chlorine that reduces or eliminates the common drawbacks of colorimetric and amperometric methods.

[0007] Disclosed herein are a method and system for analyzing water that includes free chlorine. The method includes adding hydrogen peroxide into the water to react with free chlorine present in the water to produce dissolved oxygen, measuring an amount of dissolved oxygen produced in the water from a reaction between the hydrogen peroxide and the free chlorine in the water, and determining a concentration of free chlorine in the water based on the measured amount of dissolved oxygen produced in the water.

[0008] The system includes a hydrogen peroxide infusion device for introducing hydrogen peroxide into the water to react with free chlorine present in the water to produce dissolved oxygen; and a dissolved oxygen sensor for measuring an amount of dissolved oxygen in the water.BRIEF DESCRIPTION OF THE FIGURES

[0009] FIG. l is a graph showing the concentration of dissolved oxygen over time in water samples including hypochlorite (CIO') with hydrogen peroxide being added after about 10-20 seconds.

[0010] FIG. 2 is a graph showing the concentration of dissolved oxygen over time in samples including chlorite (CIO2) with hydrogen peroxide being added after about 10-20 seconds.

[0011] FIG. 3 is a graph showing the concentration of dissolved oxygen over time in samples including chlorine dioxide (CIO2) with hydrogen peroxide being added after about 10-20 seconds.

[0012] FIG. 4 is a graph showing the concentration of dissolved oxygen over time in samples including monochloramine (NH2CI) with hydrogen peroxide being added after about 10-20 seconds.DETAILED DESCRIPTION OF EMBODIMENTS

[0013] In the following description, numerous details are set forth to provide an understanding of the present disclosure. However, it may be understood by those skilled in the art that the systems and methods of the present disclosure may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.

[0014] Broadly speaking, the present disclosure provides a method of analyzing water that includes free chlorine. The method involves adding hydrogen peroxide to the water, where the hydrogen peroxide reacts with the free chlorine in the water to generate a stoichiometric amount of dissolved oxygen. The change in the amount of dissolved oxygen can be measured, and the amount of free chlorine can be calculated from the change in the amount of dissolved oxygen.

[0015] The described method can overcome the drawbacks of current methods. Indeed, the disclosed method is free from many of the interferences of the DPD and amperometric methods. For example, the disclosed method can accurately and reliably measure the amount of free chlorine without interference due to color and turbidity. The disclosed method can be used to measure the amount of free chlorine in turbid and dark colored water, even water that is too turbid and dark colored to effective zero out the interference for colorimetric tests, such as DPD. Moreover, the disclosed method is specific to free chlorine (for example, hypochlorite ions (OCF)) and thus does not suffer from interferences from other oxidants, such as chlorine dioxide, chlorite, ozone, and monochloramine. Furthermore, hydrogen peroxide is less of an environmental concern than DPD. The disclosed method is also more reliable than amperometricmethods and does not require constant flow. Tn some embodiments, a dissolved oxygen sensor, such as a dissolve oxygen probe, can be used to measure the change in the dissolved oxygen concentration, which may facilitate free chlorine measurement in difficult industrial environments, such as wastewater streams and the like. In this regard, such probes can accurately measure the dissolved oxygen concentration even in heavy fouling conditions.

[0016] Free chlorine is often introduced into water, such as industrial water, municipal water, and wastewater, for disinfection. Monitoring of free chlorine levels in water is important for maintaining safe potable water, and ensuring that discharge water from wastewater plants, for example, retains a safe chlorine level since chlorine can be highly toxic to aquatic life. Too little chlorination presents the risk of microbial growth, and over-chlorination can be toxic and lead to the formation of chlorinated byproducts that are mutagenic.

[0017] Free chlorine can refer to all chlorine present in the water as Ch(g), HOCl(aq) and OCfi(aq). Free chlorine can be introduced into water, such as industrial water, municipal water, and wastewater, in various forms, for example, in the form of hypochlorite (OCF) or chlorine gas (CI2). The hypochlorite can be in the form of a powder or a liquid such as chlorine bleach (e.g., a solution of sodium hypochlorite in water). When chlorine gas is added to water, it reacts with the water to form hypochlorous acid (HOC1), which ionizes into hypochlorite ions (OCF). The three forms of free chlorine (dissolved CI2 gas, HOC1, and OC1 ) can exist together in equilibrium, with their relative proportions influenced by the pH of the water. At the neutral to alkaline pH of most water systems, hypochlorite may be predominantly present.

[0018] For example, the water may have a pH in a range of approximately 6 to approximately 10, approximately 6.5 to 9, or approximately 7 to 8. The method can also include adding a buffer to adjust the pH of the sample before adding the hydrogen peroxide. The pH can be adjusted to a pH of about 6 to about 12, about 6.5 to about 11, about 7 to about 10, or about 7 to about 9.

[0019] Free chlorine dosed in the water can also react with inorganic and organic compounds, such as ammonia and nitrate, present in the water to produce chloramines, including monochloramine, dichloramine, and trichloramine. These chlorine species, which may not have the same disinfecting power as free chlorine, can interfere with colorimetric techniques for measuring free chlorine. However, the disclosed method is specific for free chlorine e.g.,hypochlorite) and does not suffer from interferences from such chloramines or other oxidants, such as chlorite and chlorine dioxide.

[0020] In the disclosed method, hydrogen peroxide is added into the water or a water sample. The hydrogen peroxide may be added to the water in any suitable amount, for example, in an amount in a range of 1 ppm to 30 ppm, 5 ppm to 25 ppm, or 10 ppm to 15 ppm. The hydrogen peroxide reacts with the free chlorine (e.g., hypochlorite) present in the water to produce dissolved oxygen in situ. In particular, the hydrogen peroxide may react with hypochlorite according to the below reaction:OC1 + H2O2 Cl + H2O + O2The reaction is nearly instantaneous and free of many of the interferences in the DPD methods. For example, the disclosed method is specific to free chlorine (e.g., hypochlorite) and does not suffer from interferences from chloramines, such as monochloramine, or other oxidants, such as chlorine dioxide and chlorite.

[0021] By adding hydrogen peroxide into the water containing free chlorine, a stoichiometric amount of oxygen is solution is generated. The change in the concentration of dissolved oxygen can be used to calculate the concentration of free chlorine in the water. The concentration of free chlorine can be calculated stoichiometrically based on the following equation:71-S-rCl2AO2ppm x — — = Free Chlorine as ppm Cl232mol2In the above equation, 71 g / mol and 32 g / mol are the approximate molecular weights of Ch and O2, respectively. More accurate values with more decimal places could be used in the above equation. For example, a molecular weight of 70.906 g / mol could be used as the molecular weight of CI2 instead of 71 g / mol in the above equation. Similarly, a molecular weight of 31.999 g / mol could be used as the molecular weight of O2 instead of 32 g / mol. These molecular weights can be used to calculate a more accurate value of the free chlorine.

[0022] The amount of dissolved oxygen produced by the reaction can be proportional, for example, directly proportional, to the amount of free chlorine (e.g., hypochlorite) in the water. The disclosed method is specific to free chlorine (e.g., hypochlorite) and does not suffer from interferences from chloramines, such as monochloramine, or other oxidants, such as chlorine dioxide and chlorite. In other words, as shown in the examples, the amount of oxygenproduced in the water after the addition of hydrogen peroxide is attributable to the amount of hypochlorite in the water, and not attributable to other oxidants, such as chlorite and monochloramine.

[0023] The amount of dissolved oxygen produced by the reaction of hydrogen peroxide and free chlorine is determined by determining the change in the amount of dissolved oxygen in the water. As such, the amount of dissolved oxygen in the water can also be measured before introducing the hydrogen peroxide into the water to provide a baseline amount of dissolved oxygen. However, it may not be necessary to measure the amount of dissolved oxygen before introducing the hydrogen peroxide if the amount of the dissolved oxygen in the water is known and relatively constant. For example, the amount of dissolved oxygen in the water before introducing the hydrogen peroxide can be less than about 10 mg / L. The dissolved oxygen concentration before addition of the hydrogen peroxide also be in a range of from about 0.1 to about 50 mg / L, about 1 to about 25 mg / L, about 1 to about 15 mg / L, about 1 to about 9 mg / L, or about 3 to about 7 mg / L.

[0024] The amount of dissolved oxygen produced in the water can be measured one or more times after the hydrogen peroxide has been added to the water. In this way, the increase in the dissolved oxygen concentration in the water after the addition of the hydrogen peroxide may be determined. Because the reaction is nearly instantaneous, the dissolved oxygen concentration can be measured shortly after the hydrogen peroxide has been added to the water. In other words, the dissolved oxygen concentration can be measured after the reaction is completed even when the measurement is performed shortly after adding the hydrogen peroxide to the water. For example, the dissolved oxygen concentration can be measured one or more times in a range of from about 5 seconds to an hour after the hydrogen peroxide has been added to the water. For example, the measurement can be made about 10 seconds to 30 minutes, 20 seconds to 15 minutes, 30 seconds to 10 minutes, or 1 to 5 minutes after the hydrogen peroxide has been added to the water.

[0025] Measuring the amount of dissolved oxygen in the water or a sample thereof can be performed by any suitable method. The dissolved oxygen concentration can be directly or indirectly measured. For example, in one embodiment, an amount of dissolved oxygen produced by the reaction is directly measured by measuring a change in an amount of dissolved oxygen in the water after the introduction of the hydrogen peroxide. The change in the amount of dissolvedoxygen in the water is measured by directly measuring an amount of dissolved oxygen in the water after the introduction of the hydrogen peroxide, and comparing the measured amount of dissolved oxygen in the water to the baseline amount of dissolved oxygen in the water before the hydrogen peroxide was introduced. The baseline amount of dissolved oxygen in the water before the hydrogen peroxide is introduced may be known, or the method may further include directly measuring an amount of dissolved oxygen in the water before introducing the hydrogen peroxide into the fluid. The dissolved oxygen concentration can be directly measured by a sensor, such as a dissolved oxygen probe, for example, a luminescent dissolved oxygen probe, an electrochemical sensor, including a galvanic sensor and polarographic sensor, or an optical oxygen sensor. The dissolved oxygen concentration may be measured in an open or closed system.

[0026] In some embodiments, the dissolved oxygen sensor can be used in combination with an electrochemical sensor. For example, the method can include measuring, via the dissolved oxygen sensor, a concentration of free chlorine in the water and outputting a first signal to a processor; measuring, via an electrochemical sensor, a concentration of free chlorine in the water and outputting a second signal to the processor; and outputting, via the processor, a measurement of the concentration of the free chlorine in the water based on at least one of the first signal and the second signal. The electrochemical sensor can be an amperometric sensor or any other suitable chlorine sensor.

[0027] By this method, whichever of the first signal and / or second signal is the most useful at a given time can be used. For example, during warm-up of the electrochemical sensor, only the first signal from the dissolved oxygen sensor can be used. That is, for an initial time period after powering on the electrochemical sensor, the processor can output the measurement of the free chlorine concentration based on the first signal only.

[0028] The processor can be configured to output the measurement based on both the first signal and the second signal, for example, after the warm-up period. For example, the measurement that is output can be calculated as a mean of the first signal and the second signal. This could provide a more accurate measurement in some instances.

[0029] The processor can be configured to calibrate the second signal from the electrochemical sensor based on the first signal from the dissolved oxygen sensor. That is, the dissolved oxygen sensor can be used to calibrate (e.g, periodically) the electrochemical sensor,such as an amperometric sensor, to compensate for drifts in signal from the electrochemical sensor. This can eliminate or reduce the need to manually calibrate the electrochemical sensor.

[0030] The free chlorine concentration can be measured less frequently by the dissolved oxygen sensor than by the electrochemical sensor in some embodiments. That is, the first signal can be output to the processor less frequently than the second signal. For example, the first signal may be output once per every 5, 10, or 20 times that the second signal is output to the processor (or any other suitable output ratio). This can reduce the amount of the hydrogen peroxide reagent needed, while allowing for calibration of the electrochemical sensor.

[0031] The free chlorine concentration can be measured simultaneously or nearly simultaneously by the dissolved oxygen sensor and the electrochemical sensor such that the first and second signals are substantially simultaneous. This can enable a high degree of correlation. Alternatively, the free chlorine concentration can be measured by the dissolved oxygen sensor at different times than the electrochemical sensor so that the first and second signals do not coincide. This can allow filtering of possible errors with simultaneous measurements or outputs.

[0032] The method can additionally or alternatively include monitoring, for example, via one or more processors, a difference between the first signal and the second signal. For example, the processor(s) can monitor a difference between an amplitude of the first signal and the second signal. The processor(s) can periodically, intermittently, or occasionally calculate the difference between the first signal and the second signal. When the difference exceeds a predetermined threshold, the processor(s) can be configured to output a signal that the predetermined threshold has been exceeded. For example, the system can include an audio and / or visual alarm that is activated by the processor when the threshold is exceeded, or the processor(s) can be configured to send an alert signal to an external alarm when the threshold has been exceeded.

[0033] An alarm that the threshold has been exceeded can be indicative of an error in the functioning of the electrochemical sensor, the dissolved oxygen sensor, the processor, and / or some other component of the system. The alarm can prompt the user to check that the system including, e.g., the electrochemical sensor and / or dissolved oxygen sensor, has been set up and is functioning correctly. In some cases, the processor can be configured to only output the free chlorine measurement if the difference is less than or equal to the threshold.

[0034] The predetermined threshold can be suitably set by those skilled in the art. For example, the predetermined threshold can be the highest acceptable difference between the first and second signal, e.g., the highest difference that is not indicative of an error in functioning of one or more components of the system. For example, the threshold can be set based on known drift of the electrochemical sensor.

[0035] By using both the dissolved oxygen sensor and an electrochemical sensor, such as an amperometric sensor, the dissolved oxygen sensor can be used to calibrate e.g., periodically, intermittently, or occasionally) the electrochemical sensor to compensate for drifts in signal from the electrochemical sensor. Thus, the problems associated with manual calibration and warm-up time of the electrochemical sensor can be eliminated or significantly reduced. The relative strengths of the dissolved oxygen sensor and the electrochemical sensor can be synergistically combined while negating the weaknesses of each, and avoiding the disposal concerns associated with DPD methods.

[0036] The method may further include adjusting the concentration of free chlorine in the water based on the determined concentration of free chlorine. For example, the free chlorine concentration may be adjusted to be within a predetermined range based on the determined concentration of free chlorine. The predetermined range may be a range for achieving sufficient disinfection. For example, if the determined free chlorine concentration is below the predetermined range, the free chlorine concentration may be adjusted by introducing more chlorine into the water to increase the concentration of free chlorine in the water to a value within the predetermined range, and if the determined free chlorine concentration is greater than the predetermined range, dechlorination methods may be performed to decrease the concentration of free chlorine in the water to a value within the predetermined range. The determined free chlorine concentration may be compared to one or more threshold values. For example, the determined free chlorine concentration may be compared to a first threshold value, which may be a minimum free chlorine concentration necessary for disinfection, a value just above the minimum free chlorine concentration necessary for disinfection, or any other suitable value. If the determined free chlorine concentration is below the threshold value, then more chlorine can be introduced into the water to increase the free chlorine concentration to a value greater than the threshold value. The determined free chlorine concentration may also or alternatively be compared to a second threshold value, which may be a value of a desiredmaximum free chlorine concentration in the water or any other suitable value. If the determined free chlorine concentration is greater than the second threshold, then dechlorination methods may be performed to decrease the free chlorine concentration in the water to a value below the second threshold.

[0037] In an embodiment, the concentration of free chlorine in the water can be continuously monitored and controlled to, for example, remain within defined target levels or ranges. For example, the method may involve measuring the dissolved oxygen concentration following (and optionally immediately before) the addition of the hydrogen peroxide to continuously monitor the concentration of free chlorine in the water, and making the appropriate adjustments to the concentration of free chlorine as needed. For example, the free chlorine concentration may be adjusted by introducing more chlorine into the water to increase the concentration, or performing dechlorination methods to decrease the free chlorine concentration. Suitable dechlorination methods may include, but are not limited to, passing chlorinated water through activated carbon and ensuring sufficient contact time for effective chlorine removal. In addition, or the alternative, chemicals such as sodium bisulfite, sodium sulfite, or sulfur dioxide may be used on-site in, for example, wastewater treatment or sewage facilities. Also, tablets of sodium bisulfate may be placed in a contact basin to treat chlorine containing wastewater effluent. Electrochemical reduction is another technique that may be performed at ambient temperature and pressure to minimize or avoid toxic byproducts. Continuous monitoring enables the concentration of free chlorine in the water to be controlled to be within a desired predetermined range.

[0038] For example, the method may include measuring the dissolved oxygen concentration, and introducing a predetermined amount of the hydrogen peroxide into the water or a sample thereof automatically at predetermined intervals. For example, an initial dissolved oxygen concentration may be automatically measured every 5 minutes, 15 minutes, 30 minutes, hour, 2 hours, or any other suitable interval. Then, a predetermined amount of the hydrogen peroxide may automatically be introduced into the water or a sample thereof. Then, after a predetermined period of time, the dissolved oxygen concentration can be automatically measured again to determine the change in the oxygen concentration for the purpose of calculating the free chlorine concentration. Then, the free chlorine concentration may be adjusted as needed to be within a predetermined range based on the calculated free chlorine concentration in the water.

[0039] The pH of the water or any other measurable property may also be monitored and controlled to be within a desired range. In this respect, pH levels can affect the effectiveness of chlorine to disinfect the water. For example relatively higher pH levels can reduce the ability of chlorine to disinfect, whereas relatively lower pH levels can cause chlorine to rapidly dissipate, which can make it less effective over time. For example, the pH may be controlled to be within any of the predetermined ranges discussed above, such as a range of about 6.5 to about 11. For example, the pH may also be continuously measured at predetermined time intervals. Those measurements may be compared to a predetermined pH range. If the measured pH is outside of the predetermined range, then a buffer may be introduced into the fluid for adjusting the pH of the fluid to be within the predetermined range. The pH may be continuously measured until the pH is determined to be within the predetermined range or until a predetermined time interval has passed.

[0040] The present disclosure also relates to a system for analyzing water that includes free chlorine. The system can include a hydrogen peroxide infusion device configured to introduce hydrogen peroxide into the water to react with hypochlorite present in the water to produce dissolved oxygen, and a dissolved oxygen sensor configured to measure an amount of dissolved oxygen in the sample.

[0041] The hydrogen peroxide infusion device can be configured to introduce hydrogen peroxide in any suitable amount into the water or a sample thereof. The hydrogen peroxide infusion device can be any suitable device for introduce hydrogen peroxide into the water or a sample thereof, such as an injection device or pump or the like.

[0042] The dissolved oxygen sensor can be any suitable sensor that can measure an amount of dissolved oxygen in water. For example, the sensor can be a dissolved oxygen probe, such as a luminescent dissolved oxygen (LDO) probe. The probe may have, for example, a sensor head that takes the measurement. The sensor can also include an electrochemical sensor, including a galvanic sensor and polarographic sensor, or an optical oxygen sensor, or any other suitable sensor for measuring an amount of dissolved oxygen in water. The dissolved oxygen sensor, such as the LDO probe, can include an integrated processor, such as a microprocessor, which can determine the free chlorine concentration of the water from the measured amount of dissolved oxygen. Alternatively, the dissolved oxygen sensor can output a signal correspondingto the measured amount of dissolved oxygen to a separate or different processor to calculate the free chlorine concentration.

[0043] The system can further include a sample collector configured to collect a sample of water. The sample collector may be any suitable device for collecting a sample of the fluid. For example, the sample collector may be a pipe or other vessel for collecting a sample directly from water. A portion of the water may be diverted into pipe or vessel for analysis. The sample collector may be an open or closed system. The hydrogen peroxide infusion device can be configured to introduce hydrogen peroxide into the water or into a sample of water collected by the sample collector. Similarly, the dissolved oxygen sensor can be configured to measure an amount of dissolved oxygen in the water or in a sample of water collected by the sample collector.

[0044] The system can further include an electrochemical sensor that is configured to measure a concentration of chlorine (e. ., free chlorine) present in the water. The electrochemical sensor can be any suitable sensor that can measure a concentration of free in the water. For example, the electrochemical sensor can be an amperometric sensor. The electrochemical sensor, such as an amperometric sensor, can provide “reagentless” monitoring of free levels in water. An amperometric sensor can operate, for example, applying a constant voltage across two or three electrodes immersed in electrolyte to detect an electric current generated by the reduction of chlorine, which is directly proportional to the chlorine concentration in the water. Similarly to the dissolved oxygen sensor, the electrochemical sensor can also include an integrated processor, such as a microprocessor. The system can further include one or more processors. As mentioned above, the one or more processors can include processor(s) integrated in other components of the system, such as the dissolved oxygen sensor and / or electrochemical sensor. The one or more processors include at least one processor that is configured to determine an amount of the free chlorine in the water based on the measured amount of oxygen produced by the reaction. The one or more processors can also control an amount of free chlorine in the water. The processor(s) can be a microprocessor, CPU, controller, or any other suitable device for receiving, processing, analyzing, and recording signals and information, including measurement results from the sensor(s) and any other device, and transmitting instructions and / or command signals to other devices based on the received information.

[0045] The system can also include a chlorine infusion device configured to introduce chlorine into the water, a buffer infusion device configured to introduce a buffer into the water or a sample thereof, a chlorine neutralization device configured to treat the water to decrease the chlorine concentration (e.g., by introducing a chlorine neutralizer into the water, filtering the water to remove chlorine, or any other suitable treatment), and any other infusion device for introducing any substance into the water or a sample thereof.

[0046] The chlorine infusion device can be configured to introduce a predetermined amount of chlorine into the water when it is determined that the amount of free chlorine in the water is below a predetermined range or a threshold. For example, the processor(s) (e.g., controller(s)) may instruct the chlorine infusion device to introduce a predetermined amount of the chlorine into the water when the processor(s) determines that the amount of the free chlorine in the water is below the predetermined range or threshold based on the measured oxygen production in the water or sample of water. For example, the chlorine infusion device can include a chlorine injector or pump for introducing a chlorine solution, a device for introducing chlorine gas into the water, or a dry pellet chlorinator for introducing a compressed chlorine tablet or powder into the water. The chlorine infusion device can be used to introduce known amounts of chlorine into a water sample for testing purposes to determine, for example, that the system is accurately determining the amount of free chlorine in the water.

[0047] The chlorine neutralization device can treat the water to decrease the free chlorine concentration. For example, the chlorine neutralization device can introduce a chlorine neutralizer into the water to decrease the free chlorine concentration, can filter the water to remove chlorine, or any perform any other suitable treatment for decreasing the chlorine concentration. The neutralization device can be configured to introduce any suitable chlorine neutralization agent into the water for chemically reducing the concentration of free chlorine in the water. The neutralization device can be a filtration device, which can include, for example, carbon filters, reverse osmosis (RO) systems, kinetic degradation fluxion (KDF) filters, activated alumina filters, and ultraviolet filters. The filtration device may remove chlorine from the water if chlorine levels are determined to be excessive. In one embodiment, the neutralization device can be configured to divert the water stream to solid media containing a chlorine neutralization agent, or to a filtration device for decreasing the chlorine concentration in the water.

[0048] Each of the infusion devices can be any suitable device for introducing an accurate amount of the relevant fluid, for example, hydrogen peroxide, buffer, chlorine, chlorine neutralizer, and the like into the water or a sample of the water collected by the sample collector. For example, one or more of the infusion devices can be a pump connected to a container or reservoir that meters an accurate amount of the relevant fluid (e.g, hydrogen peroxide, buffer, chlorine, chlorine neutralizer, and the like) into the water via conduits and valves that can be controlled. Any suitable device capable of introducing the water or a sample thereof to hydrogen peroxide, buffer, chlorine, chlorine neutralizer, and / or any other suitable agent or substance and configurations thereof can be used.

[0049] The one or more processors (e.g, controlled s)) can control pump additions, timing, and recirculation, and can include memory for recording readings from the dissolved oxygen sensor for determining the amount of free chlorine in the water. In one aspect, the processor(s) can determine the amount of the free chlorine in the water or a sample thereof based on the measured amount of dissolved oxygen after addition of hydrogen peroxide. For example, the processor( s)candetermine the amount of free chlorine in the water based on an increase in the amount of the dissolved oxygen after hydrogen peroxide is introduced into the water or a sample thereof to react with the free chlorine present in the water.

[0050] The processed s)canalso control the amount of hydrogen peroxide that is introduced into the water or a sample thereof. The processed s)canalso record the measured amount(s) of dissolved oxygen in the memory and determine a change in the dissolved oxygen concentration for determining the amount of the free chlorine in the water or water sample. For example, the processor(s) can be configured to determine the concentration of free chlorine based on a difference between a baseline amount of dissolved oxygen measured by the dissolved oxygen sensor before hydrogen peroxide is introduced into the water or water sample and an amount of dissolved oxygen measured by the dissolved oxygen sensor after the hydrogen peroxide has been introduced into the water or water sample.

[0051] The memory can store the stoichiometric equation for determining the free chlorine concentration based on the change in dissolved oxygen: equation :71-S-7C12AO2ppm x — — = Free Chlorine as ppm Cl232 - mo rlO?z

[0052] The processor(s)can use the stoichiometric equation stored in the memory to calculate the free chlorine concentration based on the measured change (e.g., increase) in dissolved oxygen, and can send instructions for modifying the process conditions based on the calculated quantity. For example, the processor(s)can instruct the chlorine infusion device to add more chlorine into the water if the calculated free chlorine concentration is below a threshold or predetermined range. If the calculated free chlorine concentration is above a threshold or predetermined range, then the processor(s)can instruct the chlorine neutralization device to treat the water to decrease the free chlorine concentration in the water to below the threshold and / or within the predetermined range.

[0053] The processor(s)can control an amount of chlorine that is added to the water based on the determined amount of free chlorine in the water, and control an amount of a neutralizing agent that is added to the water (or other neutralization treatment performed on the water) based on the determined amount of free chlorine in the water. In this regard, the chlorine solution can be kept in a container or tank and connected to the water system via a conduit with a valve that be controlled by instructions from the processor(s)to increase or decrease the concentration of free chlorine in the water. Similarly, the hydrogen peroxide and any chlorine neutralization agent can also be kept in containers or tanks connected to the water system via a conduit with a valve that can be controlled by instructions from the processor(s)to increase or decrease the concentrations thereof in the water.

[0054] The system can also include a memory for storing data. For example, the stoichiometric equation for determining the free chlorine concentration in the water based on the change in the dissolved oxygen can be stored in the memory. As mentioned above, the memory can also store the measured amounts of dissolved oxygen for determining the amount of free chlorine in the water. The memory can also store the determined amount of free chlorine. The memory may be in the form of any computer data storage, such as random-access memory or flash memory.

[0055] Systems that employ these methods can include a feedback control connected to the chlorine infusion device that introduces chlorine into the water. The feedback control loop can also be connected to a chlorine neutralization device that introduces any neutralizing agent into the water stream to neutralize the free chlorine present in the water. The feedback controlloop can also be connected to a valve or diverter that sends a portion of the water stream to a fixed media or a filtration device to remove or neutralize excess chlorine.

[0056] The system can employ a monitoring display that shows the real-time amount of dissolved oxygen and the corresponding amount of free chlorine, as well as the control steps that are being employed, e g., the amount of chlorine or neutralizing agent being added to the water, and any other information to the user. The display may be, for example, a liquid crystal display (LCD) or any suitable display. The system can provide alerts (e.g., visual and / or audio alerts) if the system values deviate from expected or desired values, such as when the free chlorine concentration exceeds a threshold level in the system. In some processes, for example, the free chlorine may only need to be neutralized by introducing a neutralizing agent into the water or directing the process stream to fixed media or filtration device when the concentration exceeds a threshold value. The processor(s)may automatically instruct the neutralization device to introduce a neutralization agent into the water or automatically direct the process to fixed media containing a neutralization agent or a filtration device when, for example, the free chlorine values exceed threshold levels in the system. An operator may also manually adjust the amount of the neutralization agent, hydrogen peroxide, and / or chlorine being added to the water or water sample.

[0057] The processor(s)and / or display may include navigational control pad including any input interface that allows a user to input commands and / or interact with the system and / or processor(s). For example, the control pad may be in the form of a keypad. The control pad may, for example, allow an operator to enter variables, set parameters, access menu items, and the like. For example, the control pad may enable an operator to input threshold values or desired ranges of, for example, free chlorine concentrations and pH values.

[0058] For example, the processor(s)and / or display may include inputs to control the oxygen sensor and / or any other sensor or probe locally, or to locally control any other device that is connected to the processor(s). The processor(s)may also receive commands or other information from another controller or processor to remotely control the oxygen probe and / or any other sensor or device connected thereto. For example, other devices, such as a buffer infusion device, a chlorine infusion device, a hydrogen peroxide infusion device, and / or a chlorine neutralization device can also be (wired or wirelessly) connected to the processor(s).

[0059] The processor(s)may be connected to a wireless router and a distributed control system (DCS). The oxygen measurements can be sent to the processor(s)from the dissolved oxygen sensor. These measurements and / or any other information may also be displayed on the display. The processor(s)can transmit the measurement and / or any other information via either a wired or wireless connection to another controller and / or processor within the DCS. For example, the information can be transmitted via wireless router. The processor(s)can include local processor(s)and / or remote processor(s)and can receive the measurements from the sensors, calculate a change in the dissolved oxygen concentration, and determine the amount of free chlorine in the water based on the change in dissolved oxygen and / or whether the determined amount is within prescribed limits. If the amount of the free chlorine is not within prescribed limits, the local or remote processor(s)can send a command signal to increase or decrease the amount of the free chlorine in the water. The processor(s)can also cause the display to display a warning to an operator that the amount of free chlorine is not within the prescribed limits. An operator can also manually adjust the amount of the chlorine in the water.

[0060] In embodiments including both the dissolved oxygen sensor and the electrochemical sensor, the one or more processors can be configured to receive the first signal and / or the second signal from the dissolved oxygen sensor and the electrochemical sensor, respectively, and output a measurement of the concentration of the free chlorine in the water based on at least one of the first signal and the second signal. As mentioned above, the at least one processor configured to determine the free chlorine concentration based on the measured dissolved oxygen can be integrated into the dissolved oxygen sensor or can be external to the sensor. Similarly, the one or more processors can also include at least one processor configured to determine the free chlorine concentration from the raw output of the electrochemical sensor. Such a processor can be integrated into the electrochemical sensor or external to the sensor.

[0061] The processor configured to determine the free chlorine concentration based on the measured dissolved oxygen can be the same or different from the processor that is configured to receive the second signal and / or output the measurement based on the first and second signal. For example, the dissolved oxygen sensor can include an integrated processor that is configured to determine the free chlorine concentration based on the measured amount of dissolved oxygen and output a first signal (corresponding to the determined free chlorine concentration) to a different processor(s). The electrochemical sensor can similarly include an integrated processorthat is configured to receive the raw output of the sensor to determine the free chlorine concentration and output a second signal (corresponding to the determining free chlorine concentration) to the different processor(s). The different processor(s) can include output a measurement of the concentration of the free chlorine in the water based on at least one of the first signal and the second signal. Alternatively, the dissolved oxygen sensor and / or electrochemical sensor can output to one or more processors (e.g., external to the sensors or not integrated within the sensors) first and second signals, respectively, corresponding to raw measurement data by the sensors. The one or more processors can process the raw measurement signals to correspond to the free chlorine concentration measurements by the dissolved oxygen and / or electrochemical sensors, and then output the measurement based on at least one of the processed first and second signals.

[0062] The measurement can be output to, for example, a display and / or another processor, such as a controller, which in turn can control one or more devices of the system, such as the chlorine infusion device and / or chlorine neutralization device, based on the measurement. For example, when the measurement based on at least one of the first and second signals is greater than a threshold, the controller can control the neutralization device to decrease the amount of chlorine in the water, as described above. Alternatively, when the measurement based on at least one of the first and second signals is less than a threshold, the controller can control the chlorine infusion device to increase the amount of chlorine in the water, as described above.

[0063] The one or more processors can be configured to output the measurement of the concentration of the free chlorine in the water based on at least one of the first signal and the second signal, according to any of the methods described above. For example, the one or more processors can output the measured based on the first signal during an initial period after the electrochemical sensor is powered on to allow the electrochemical sensor to sufficiently warmup. The one or more processors can be configured to output the measurement as a mean of the first and second signals. The one or more processors can be configured to calibrate the second signal by using the first signal to compensate for drift in signal of the electrochemical sensor. The one or more processors can also be configured to monitor a difference between the first signal and the second signal and output a signal when the difference exceeds a threshold, as described above.

[0064] The system can further include an alarm, such as an audio or visual alarm. For example, an alarm message can be output to the display and / or an alarm sound can be activated when the one or more processors determines that the difference between the first and second signals exceeds a threshold.

[0065] The memory can further store, for example, the first signal output by the dissolved oxygen sensor and / or the second signal output by the electrochemical sensor. The memory can be accessed by the one or more processors. For example, in embodiment where the first signal is output less frequently than the second signal, the one or more processors can access the memory to obtain the first signal when the second signal is received by the one or more processors in order to output the measurement using both the first and second signals, including, for example, calibrating the second signal based on the first signal, and determining a difference between the first and second signals, as described above. The memory can further store differences between the first and second signals over time.

[0066] Although some embodiments of the invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the disclosed embodiments.Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the claims. For example, although the above disclosure relates to determining free chlorine concentration in water, the methods are not limited to free chlorine, and can be used to determine any free halogen concentration, such as free bromine. The foregoing is further illustrated by reference to the following examples, which are presented for purposes of illustration and are not intended to limit the scope of the present disclosure.EXAMPLES

[0067] Water samples were prepared by adding 1.6 mL of 0.2M NaHPCL and 0.4 mL of 0. IM Citric acid stock solution 198 mL RO water to create 200 mL of water samples buffered at pH = 7.0 in a 250 mL beaker.Example 1 - Measurement of free chlorine in water sample including hypochlorite

[0068] 12.5% bleach was added to one of the 200 mL water samples prepared as described above to target 1-2 ppm CE.

[0069] 50 mL of the water sample was extracted for DPD Free and DPD Total measurement.

[0070] A Hach IntelliCAL LBOD101 Luminescent / Optical Dissolved Oxygen (LDO) Probe was submerged into and kept within the remaining 150 mL water sample for 30 seconds for probe to equilibrate and start recording. After approximately 10 to 20 seconds, a baseline reading of dissolved oxygen in the sample was taken by the LDO Sensor. Next, 20 ppm of hydrogen peroxide (H2O2) (0.010 mL of 30% H2O2 to 150 mL of sample) was added to the sample. The change in dissolved oxygen levels were recorded by the probe over a 180 second interval. The testing was repeated as necessary. Free chlorine as ppm CI2 in the sample was calculated based on multiplying change in dissolved oxygen by the stoichiometric ratio of CI2 to O2 according to the stoichiometric equation disclosed herein. The CI2 was calculated from the max dissolved oxygen after 30 seconds and the baseline dissolved oxygen at the beginning of the test.

[0071] As shown in FIG. 1, the was a sharp increase in the amount of dissolved oxygen in water after the hydrogen peroxide was added (at about 10-20 seconds), showing that the hypochlorite in the water reacted quickly with the hydrogen peroxide to produce oxygen.

[0072] The results of the DPD Free, DPD Total, and Dissolved Oxygen tests are shown in Table 1 below.Table 1Measured CI2 ppm Test 1 Test 2 Test 3 Average No H2O2 Only H2O2 DPD Free 1.56 1.50 1.48 1.51 1.48 0.0 DPD Total 1.67 1.68 1.65 1.67 1.61 0.0 DO method 1.62 1.60 1.62 1.61 0.07 0.04

[0073] The results shown in Table 1 demonstrate that the described dissolved oxygen based method is specific to hypochlorite and can therefore be used for accurately measuring Ch ppm and achieve results comparable to the DPD Free and DPD Total methods. Reactions between hydrogen peroxide and hypochlorite produced a strong stoichiometric response where the amount of oxygen produced as directly proportional to the amount of hypochlorite in solution, such that the described dissolved oxygen method was able generate very consistent results (e.g., Tests 1-3) compared the DPD method.

[0074] The "No H2O2" and "Only H2O2 tests both represent controls against which the other experimental results were compared. In the "No H2O2" tests, measured Ch (ppm) was determined without adding hydrogen peroxide. In the "Only H2O2" test, measured Ch (ppm) was determined in water samples that contained hydrogen peroxide without any added chlorine.Example 2 - Measurement of free chlorine in water sample including chlorite

[0075] 7.5% chlorite stock was added to one of the 200 mL water samples. 50 mb of the water sample was extracted for DPD Free and DPD Total measurement. The remaining 150 mL water sample was analyzed by adding hydrogen peroxide and using the dissolved oxygen probe in the same manner as described in Example 1. FIG. 2 shows the dissolved oxygen concentration measured by the oxygen probe over time in the chlorite-containing sample. As shown in FIG. 2, the dissolved oxygen concentration did not change over time, even after the hydrogen peroxide was added (at about 10-20 seconds). This shows that the chlorite in the water sample did not react with the hydrogen peroxide to produce oxygen.

[0076] The results of the DPD Free, DPD Total, and Dissolved Oxygen tests are shown in Table 2 below.Table 2Measured Ch ppm Test 1 Test 2 Average No H2O2 Only H2O2 DPD Free 0.00 0.00 0.00 0.00 0.0 DPD Total 0.01 0.00 0.01 0.00 0.0 DO method 0.02 0.07 0.04 0.09 0.04

[0077] The results shown in Table 2 demonstrate that chlorite did not show a strong response compared to its control.Example 3 - Measurement of free chlorine in water sample including chlorine dioxide

[0078] 3000 ppm CIO2 was added to one of the 200 mL water samples. 50 mL of the water sample was extracted for DPD Free and DPD Total measurement. The remaining 150 mL water sample was analyzed by adding hydrogen peroxide and using the dissolved oxygen probe in the same manner as described in Example 1. FIG. 3 is a graph showing the concentration of dissolved oxygen over time in the samples including chlorine dioxide (CIO2) with hydrogen peroxide being added after about 10-20 seconds.

[0079] The results of the DPD Free, DPD Total, and Dissolved Oxygen tests are shown in Table 3 below.Table 3Measured CI2 Test 1 Test 2 Test 3 Average No H2O2 No H2O2 Only ppm (after H2O2180seconds)DPD Free 1.68 1.74 1.89 1.77 1.89 1.28 0.0 DPD Total 1.67 1.73 1.82 1.74 1.93 1.34 0.0 DO method 0.40 0.27 0.18 0.28 0.24 0.58 0.04

[0080] Based on the results shown in Table 3, the unstable natural of chlorine dioxide appears to have generated oxygen during its breakdown. While the test at a pH of 7.0 did not show a significant response upon addition of hydrogen peroxide, reaction between hydrogen peroxide and of chlorine dioxide is known to occur at higher pH levels. During the control without addition of hydrogen peroxide, the tested sample was measured again with the DPD methods, e.g., DPD Free and DPD Total, after 180 seconds elapsed. The loss in measured CI2 was proportional to the Ch calculated from the change in dissolved oxygen possibly resulting from the breakdown of chlorine dioxide in solution.Example 4 - Measurement of free chlorine in water sample including monochloramine

[0081] 1000 ppm monochloramine was added to one of the 200 mL water samples. 50 mL of the water sample was extracted for DPD Free and DPD Total measurement. The remaining 150 mL water sample was analyzed by adding hydrogen peroxide and using the dissolved oxygen probe in the same manner as described in Example 1. FIG. 4 is a graphshowing the concentration of dissolved oxygen over time in samples including monochloramine (NH2CI) with hydrogen peroxide being added after about 10-20 seconds.

[0082] The results of the DPD Free, DPD Total, and Dissolved Oxygen tests are shown in Table 4 below.Table 4Measured Ch Test 1 Test 2 Test 3 Average No H2O2 Only H2O2 PPmDPD Free 0.01 0.01 0.02 0.01 0.03 0.0 DPD Total 1.04 1.03 1.02 1.03 1.02 0.0 DO method 0.09 0.04 0.02 0.05 0.07 0.04

[0083] The results shown in Table 4 demonstrate that monochloramine did not show a strong response compared to its control.

[0084] The below Table 5 summarizes the results of the above Examples.Table 5Product CI2 (ppm) Ch (ppm) CI2 (ppm)via DO via DPD via DPDFree TotalCIO' 1.61 1.51 1.65CIO2 0.28 1.80 1.79CIO2- 0.04 0.00 0.00CINH2 0.05 0.02 1.03

[0085] The results shown in Table 5 demonstrate that the described method to measure free chlorine showed specificity to hypochlorite (CIO') and provided accurate testing results when compared to DPD-based methods as shown by DPD Free and DPD Total. The observed reactions produced a strong stoichiometric response where the amount of oxygen produced was observed to be directly proportional to the amount of hypochlorite in solution. The described dissolved oxygen detection based method was able generate very consistent results compared the DPD Free and DPD Total methods.

[0086] Although some embodiments of the invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the disclosed embodiments.Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

WHAT TS CLAIMED TS1. A method of analyzing water that includes free chlorine, the method comprising: adding hydrogen peroxide into the water to react with free chlorine present in the water to produce dissolved oxygen;measuring an amount of dissolved oxygen produced in the water from a reaction between the hydrogen peroxide and the free chlorine in the water; anddetermining a concentration of free chlorine in the water based on the measured amount of dissolved oxygen produced in the water.

2. The method of claim 1, wherein the hydrogen peroxide reacts with hypochlorite in the water to produce the dissolved oxygen.

3. The method of claim 1, further comprising measuring an amount of dissolved oxygen in the water before the hydrogen peroxide is added to the water to determine a baseline amount of dissolved oxygen in the water.

4. The method of claim 3, further comprising measuring an amount of dissolved oxygen in the water after adding the hydrogen peroxide, wherein the amount of dissolved oxygen produced in the water from the reaction is measured as a difference between the baseline amount of dissolved oxygen and the amount of dissolved oxygen measured after adding the hydrogen peroxide.

5. The method of claim 1, further comprising collecting a sample of the water, wherein the hydrogen peroxide is added to the sample of the water, and the amount of dissolved oxygen produced is measured in the sample of the water.

6. The method of claim 1, further comprising adjusting the concentration of free chlorine in the water based on the determined concentration of free chlorine in the water.

7. The method of claim 6, wherein adjusting the concentration of free chlorine in the water comprises adding chlorine to the water if the determined concentration of free chlorine isbelow a first threshold or decreasing an amount of free chlorine in the water if the determined concentration of free chlorine is above a second threshold.

8. The method of claim 1, wherein the hydrogen peroxide is introduced into the water in an amount in a range of 5 ppm to 20 ppm.

9. The method of claim 1, wherein determining the concentration of free chlorine in the water comprises stoichiometrically calculating the concentration of free chlorine from the measured amount of dissolved oxygen produced in the water.

10. The method of claim 1, wherein the amount of dissolved oxygen produced by the reaction is directly proportional to an amount of hypochlorite in the water.

11. The method of claim 1, wherein the water further comprises chlorite and monochloramine.

12. The method of claim 1, wherein the water has a pH in a range of 6 to 10.

13. The method of claim 1, wherein the amount of dissolved oxygen produced by the reaction is measured by a dissolved oxygen probe that is submerged in the water.

14. A method of analyzing water that includes free chlorine, the method comprising: measuring, via a dissolved oxygen sensor, a concentration of free chlorine in the water and outputting a first signal, the concentration of free chlorine being measured based on a measured amount of dissolved oxygen produced in the water after adding hydrogen peroxide to the water to react with the free chlorine present in the water;measuring, via an electrochemical sensor, a concentration of free chlorine in the water and outputting a second signal; andreceiving, via one or more processors, the first signal and the second signal, and outputting a measurement of the concentration of the free chlorine in the water based on at least one of the first signal and the second signal.

15. The method of claim 14, wherein the electrochemical sensor is an amperometric sensor.

16. The method of claim 14, further comprising calibrating, via the at least one processor, the second signal using the first signal.

17. The method of claim 14, further comprising monitoring, via the at least one processor, a difference between the first signal and the second signal.

18. A system for analyzing water that includes free chlorine, the system comprising: a hydrogen peroxide infusion device configured to introduce hydrogen peroxide into the water to react with free chlorine present in the water to produce dissolved oxygen; anda dissolved oxygen sensor configured to measure an amount of dissolved oxygen in the water.

19. The system of claim 18, further comprisingat least one processor that is configured to determine a concentration of free chlorine in the water based on a measured amount of dissolved oxygen in the water.

20. The system of claim 19, wherein the at least one processor is configured to determine the concentration of free chlorine based on a difference between a baseline amount of dissolved oxygen measured by the dissolved oxygen sensor before hydrogen peroxide is introduced into the water and an amount of dissolved oxygen measured by the dissolved oxygen sensor after the hydrogen peroxide has been introduced into the water.

21. The system of claim 20, further comprising a chlorine neutralization device configured to treat the water to decrease the concentration of free chlorine in the water if the concentration of free chlorine determined by the at least one processor is above a threshold.

22. The system of claim 20, further comprising a chlorine infusion device configured to introduce chlorine into the water if the concentration of free chlorine determined by the at least one processor is below a threshold.

23. The system of claim 18, further comprising a sample collector configured to collect a sample of the water, wherein the hydrogen peroxide infusion device is configured to introduce hydrogen peroxide into the sample of water, and the dissolved oxygen sensor is configured to measure an amount of dissolved oxygen in the sample of water.

24. The system of claim 18, further comprising an electrochemical sensor configured to measure a concentration of free chlorine in the water.

25. The system of claim 24, further comprising:one or more processors configured to:receive a first signal from the dissolved oxygen sensor,receive a second signal from the electrochemical sensor, andoutput a measurement of the concentration of the free chlorine in the water based on at least one of the first signal and the second signal.

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