Control of ozone dosing using bioelectrochemical sensors.

Abstract

The water treatment system has an ozonation unit (12), a biological sensor (16) and an optional biological treatment unit (14). The biological sensor (16) measures the biodegradability of organic contaminants after ozonation. The biological sensor (16) can be a bioelectrochemical sensor that produces an electrical signal related to the metabolic activity of bacteria at the electrodes of the sensor. The biological sensor (16) can be connected to a controller (18) adapted to regulate one or more operating parameters of the ozonation unit (12), or the biological treatment unit (16), or both. Methods of treating water and controlling a water treatment process using the biological sensor to measure the biodegradability of the water are further described. The measurements can be used to regulate an upstream ozonation process or a downstream biological treatment process. These systems and methods can be used to remove sparingly soluble organic compounds or organic micropollutants from secondary or tertiary effluents from municipal or industrial wastewater plants.

Description

[Technical field]

[0001] This application claims the benefit of French Patent Application No. 2106452, filed June 17, 2021, which is incorporated herein by reference.

[0002] This document relates to wastewater treatment including controlled ozone dosing in a wastewater treatment system, optionally in combination with biological treatment. [Background technology]

[0003] US Patent No. 10,287,182, Regulating Method for a Water Treatment Installation Using Measured Parameters and Control of an Ozonisation Device, describes a method for controlling a water treatment installation having an ozonation stage, a transfer stage and a biological filter. The method involves controlling the amount of ozone delivered in relation to measurements of contaminant concentrations in the influent water, the transfer stage water and the effluent water. The contaminant concentrations are measured using a fluorescent sensor or a UV / Vis sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Pat. No. 10,287,182 [Patent Document 2] US Patent Application Publication No. 2020 / 0283314 [Patent Document 3] US Patent Application Publication No. 2020 / 0003754 [Patent Document 4] US Patent Application Publication No. 2014 / 0353170 Summary of the Invention [Means for solving the problem]

[0005] The following summary is intended to introduce the reader to the invention and the detailed description that follows, but is not intended to limit or define the scope of the claims.

[0006] The present specification describes a water treatment system using an ozonation unit (optionally referred to as an ozone contactor) and a biological sensor (optionally referred to as a biosensor). The biological sensor is adapted to measure a metabolic parameter related to the extent to which organic contaminants in the water treatment process stream have become biodegradable after contacting with ozone. For example, the biological sensor may produce or enable a measurement or signal related to metabolic activity, such as carbon bio-degradation (CBD) or carbon consumption rate (CCR), of a bacterial population. In some examples, the biological sensor is a bioelectrochemical sensor adapted to measure metabolic activity, such as carbon consumption rate, by producing an electrical signal related to bacterial metabolic activity at an electrode of the sensor. The biological sensor is optionally connected to a controller adapted to regulate the rate of ozone delivery to the wastewater. In some examples, a biological treatment unit, such as a biologically active filter (BAF), is provided downstream of the ozonation unit. Optionally, measurements or signals from the biosensors may be used to adjust operating parameters of the biological processing unit.

[0007] The present specification also describes a method of treating water and controlling a water treatment process using a biological sensor. The biological sensor contacts the water contacted with ozone. The biological sensor measures the extent to which organic contaminants in the water have become biodegradable. For example, the biological sensor may measure the metabolic activity, such as the carbon consumption rate, of organisms exposed to the ozonated water. In some examples, the biological sensor is a bioelectrochemical sensor that provides an electrical signal corresponding to the metabolic activity of a bacterial population at the electrodes of the biosensor. Optionally, a voltage and / or current can be delivered across the electrode pairs of the biosensor. The measurements or signals from the biosensor are used to adjust the rate of ozone delivery to the wastewater. Contaminants in the wastewater can be biologically degraded after contacting with ozone. For example, the wastewater can be treated in a biologically active filter (alternatively referred to as a biologically activated filter, or biological filter, or biofilter). Optionally, the measurements or signals from the biosensor can be used to adjust the operating parameters of the biological degradation process.

[0008] The systems and methods described herein are useful for treating secondary or tertiary effluents from municipal or industrial wastewater treatment plants, among other examples. These systems and methods serve to reduce the concentration of one or more poorly soluble compounds or micro-pollutants prior to discharge of the treated effluent or direct or indirect reuse of the treated wastewater. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a wastewater treatment system and a process flow diagram of a wastewater treatment process. [Diagram 2] 2 is a schematic graph of total organic carbon (TOC) and carbon consumption rate over time for wastewater being treated in the wastewater treatment system or process of FIG. 1; [Diagram 3] FIG. 1 illustrates a method for controlling O3 in a wastewater treatment system using biological sensors. [Figure 4] 1 is a schematic graph illustrating the relationship between a TOC effluent / TOC influent comparison or ratio and metabolic activity, for example, CCR. [Diagram 5] 1 is a schematic graph of metabolic activity, e.g., CCR, as a function of the O3 / TOC influent ratio, where Ozone is the amount of ozone added to the ozone contactor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The systems and methods described herein use biological sensors, e.g., bioelectrochemical sensors, to control the operating conditions of a wastewater treatment system or process. The wastewater treatment system includes an ozonation unit and optionally includes a downstream biological treatment unit, such as a biologically active filter. The wastewater treatment system is optionally located in a municipal or industrial wastewater treatment plant downstream of the plant's second or third level treatment. The biological sensor contacts the ozonated effluent, e.g., near or downstream of the end of the ozonation unit, or in an intermediate zone between the ozonation unit and the biological treatment unit, or is incorporated within the biological treatment. For example, the biological sensor may be located above the media in the BAF, or may be embedded a short distance, e.g., about 2 to about 3 inches, below the top of the media. The biological sensor is preferably downstream of sodium sulfite injection, e.g., to avoid the adverse effects of O3 neutralization on the biological sensor. The biological sensor directly or indirectly measures the biological availability of organic carbon compounds in the ozonated effluent. At least some of these biodegradable compounds are created by ozonation of poorly soluble organic compounds or micropollutants in the ozonation unit. In some examples, the biological sensor measures electron transport through a biofilm-impregnated electrode. Measuring the rate of uptake of biodegradable compounds in real time may allow control of the ozonation unit. In one example, a sudden drop or increase in the rate of uptake of biodegradable compounds may indicate an operational problem. The operational problem may be related to a sudden fluctuation in ozone dosage or nutrients, which may need to be accommodated, for example, by adapting the operation of the BAF or controlling the ozone dosage.Alternatively or additionally, measuring the rate of uptake of biodegradable compounds in combination with an algorithm may allow control of the ozonation unit, optionally performed by an operator or computer, optionally based on historical data from the same or similar wastewater treatment plant. For example, the ozone injection rate in the ozone contactor may be controlled to provide one or more of: a maximum concentration of readily biodegradable organic compounds; at least a minimum concentration of readily biodegradable organic compounds; and an optimal concentration of readily biodegradable organic compounds according to a function including one or more factors such as minimum conversion, power consumption, target water quality, ozone consumption, and biological treatment factors. Increasing the biodegradability of the pollutants may improve the performance of an optional downstream biological treatment unit. Optionally, one or more operating parameters of the biological treatment parameters may be adjusted based on measurements provided by the biological sensor. Optionally, a second biological sensor may be provided in communication with the influent wastewater such that background concentrations of readily biodegradable organic compounds may be differentiated from readily biodegradable organic compounds created by the conversion of less soluble compounds by ozonation.

[0011] Ozone production in a wastewater treatment plant may be controlled using one or more relationships between TOC effluent, TOC influent, metabolic activity, e.g., as determined by a biological sensor, and ozone. These relationships may be created, for example, by one or more of calculations, modeling, or historical data of plant operation. Historical data may be collected from one or more similar plants, i.e., plants having ozone contactors and BAFs. In some examples, historical data is collected from the same wastewater treatment plant that is being controlled to create a location-specific O3 dosage control algorithm. The word "algorithm" is used herein to indicate a method that includes steps, some or all of which are optionally computer-implemented. In one example, a plant may be started with a predefined algorithm from a previous application in a similar plant or based on a calculated or modeled relationship. Historical data, including metabolic activity, e.g., CCR measurements, may be collected through the first few months (i.e., 1-8 months) of operation, and then an algorithm may be created or refined. Optionally, the algorithm may be further refined based on the collected historical data, e.g., through the first year of operation of the plant, or longer. In one example, the algorithm may be constantly updated with data collected by one or more biological sensors and other relevant operational data to continue to refine the algorithm in a plant-specific manner. An O3 control algorithm is used in combination with real-time biological sensor readings to control ozone production. Optionally, other inputs are also input to the algorithm, such as TOC or nitrogen data collected from the influent TOC and / or target effluent TOC.

[0012] Biological sensors measure one or more aspects of water based on biological responses to one or more aspects. In some examples, biosensors, optionally referred to as bioelectrochemical sensors, can be based on microbial fuel cells or another bioelectrochemical system. Bioelectrochemical sensors can sense electrical signals produced by electroactive microorganisms growing on the electrodes of the sensor. One aspect of the signal can be related to the metabolic processes of the microorganisms, which in turn can be related to one or more aspects of the water in contact with the sensor. Optionally, the concentration of readily biodegradable compounds can be measured from a signal from the biological sensor that is related to or interpreted as carbon consumption rate (CCR).

[0013] The system and method are further described below in the context of an example wastewater treatment system, but they can be used or adapted to other systems and methods. An exemplary system has an ozone contactor upstream of a biologically active filter. This type of system has been used to remove poorly soluble chemical oxygen demand (COD), total organic carbon (TOC) or micropollutants from the effluent of conventional municipal or industrial wastewater treatment plants, such as activated sludge plants or membrane bioreactor (MBR) systems. In the municipal sector, the combination of an ozone contactor unit and a biologically active filter product is mainly applied for the removal of TOC and micropollutants before the discharge of the effluent or for indirect- or direct- potable reuse (IPR / DPR) treatment methods.

[0014] In an ozone contact and biologically active filtration system, each treatment step has its own purpose. Ozonation converts poorly soluble organic compounds into more biodegradable species, and biologically active filtration biodegrades the converted organic compounds. From an operating cost (OPEX) perspective, the ozone treatment step accounts for the majority of the utilities of the combined system, e.g., 80% or more. The utilities are mainly electricity and oxygen. However, most ozone treatment systems are installed because the effluent from the upstream plant does not meet the desired parameters, e.g., regulated limits for TOC concentration. Thus, some usefulness must be consumed to reach the desired level of treatment.

[0015] Balancing the desire to minimize oxygen and power consumption with the desire to reach a desired level of treatment requires control to optimize the ozonation unit. Control of the ozonation unit may be performed by adjusting the amount of ozone injected into the ozone contactor, optionally with respect to the water flow rate or unit volume of water being treated. If insufficient ozone is injected into the ozone contactor, the biologically active filter will not remove enough organic compounds and will fall short of the overall removal goal, e.g., TOC concentration in the biologically active filter effluent. If too much ozone is injected into the ozone contactor, ozone and power consumption will be unnecessarily increased. In addition, too much ozone can result in excessive conversion of organic compounds. This can potentially create less biodegradable species, thereby preventing the biologically active filter from working efficiently. Injecting too much ozone leads to increased OPEX and, potentially, the formation of undesirable chemical by-products. Thus, there is an optimal ozone dosage to be injected into the ozone contactor for a) maximum conversion of poorly soluble compounds by ozonation, b) maximum removal of poorly soluble compounds in the combined product, c) minimization of formation of undesirable by-products, or d) minimum OPEX required to reach the goal of conversion of poorly soluble compounds by ozonation or in the combined product. Measurements from the biological sensors are used to control the ozonation unit or the combined product to achieve one or more of these objectives.

[0016] Measurement of biodegradable species is usually done by analysis of biochemical oxygen demand (BOD). However, direct measurement of BOD production by an ozone contactor is impractical for real-time control of optimal ozone dosing rates. Analysis of BOD can take hours to days, which is too slow for effective control of the ozone treatment process. In addition, readings at very low BOD levels (i.e., less than a few mg / l) cannot be achieved with sufficient accuracy to control the ozone dosing rate.

[0017] To solve the problem of direct BOD measurement, surrogate means such as fluorescence or UV / Vis measurements have been used. The conversion of some organic compounds from complex poorly soluble molecules to simpler, more bioavailable molecules can be expressed by the change in fluorescence or UV absorption before and after ozonation. However, only a small fraction of the converted organic compounds can be measured with fluorescence or UV / Vis measurements. Fluorescence or UV / Vis measurements do not provide information about organic components that do not fluoresce or have UV-sensitive functional groups, and UV absorption measurements can be subject to interference from inorganic UV-active species. Therefore, this method can produce erroneous results when treating some wastewater streams. In addition, fluorescence parameters or UV / Vis parameters such as UV254 follow a smooth, continuously decreasing curve as the water proceeds through a system that combines ozonation and biologically active filtration. There is no clear definition of the optimal UV254 that results in an optimized combined system performance after ozonation. Although in-line TOC measurements can provide the total concentration of all organic carbon species present in a sample, they do not provide insight into changes in the biodegradability of organic compounds within the sample due to ozone treatment.

[0018] In a system having an ozone contactor, such as an ozone contactor and biologically active filter system, a biological sensor is placed downstream of the ozone contactor. Metabolic activity, such as biofilm growth or organic carbon uptake, is sensed by the sensor. The sensor generates a measurement or signal at a sufficient rate, i.e., at least once per hour, that is useful for controlling an aspect of the ozone contactor, such as, for example, the ozone dosing rate. In some examples, the biological sensor can be a bioelectrochemical sensor. The bioelectrochemical sensor can generate a digital signal that is essentially continuous or in real time, such as a signal updated every 10 minutes or less. Optionally, the presence of biological activity on the sensor generates a flow of electrons that is interpreted as a measurement of the carbon consumption rate (CCR). The CCR measurement correlates with the biodegradability of contaminants in the water in contact with the sensor, and the extent to which the sparingly soluble organic matter became biodegradable after the ozonation step. With reference to FIG. 2, the CCR increases during ozonation and decreases during any optional biological treatment downstream. The peak CCR occurs at the end of the ozonation step or between the ozonation and biological treatment steps. Controlling the ozone dosage to produce the maximum CCR reading corresponds to the optimal ozone dosage rate in the ozone contactor to produce a non-soluble effluent. Alternatively, minimizing the ozone dosage to stay above a threshold or within a desired range of CCR allows for reduced power and ozone consumption while meeting effluent targets, or providing desired operating conditions in the biological treatment step, or both. The CCR threshold or range may be selected based on one or more of: optionally meeting effluent quality targets at minimal operating costs; desired inputs to downstream biological processes; and optimization functions including factors of effluent quality and operating costs. Alternatively, the system may be controlled to provide the maximum possible CCR.

[0019] An example of a commercially available bioelectrochemical sensor is the SENTRY, made by Island Water Technologies. TMThe bioelectrochemical sensor is a sensor. Examples of bioelectrochemical sensors are also described in US Patent Application Publication No. 2020 / 0283314, US Patent Application Publication No. 2020 / 0003754 and US Patent Application Publication No. 2014 / 0353170, all of which are incorporated herein by reference. Alternatively, other forms of biosensors can be used. For example, the production of biodegradable species after ozonation can be measured using a biofilm monitor or a biofilm thickness monitor.

[0020] FIG. 1 shows a water treatment system 10 having an ozone contacting unit 12 and a biologically active filter 14. The ozone contacting unit 12 includes a liquid oxygen tank 40, an oxygen evaporator 42, an ozone generator 30, an ozone flow control valve 32, a contact tank 36, a degassing system 38, an ozone destruction unit 44, such as a catalytic ozone destruction unit, and an ozone foam generator 46. Wastewater 48 enters and flows through the contact tank 36. Ozone dissolves in the wastewater 48 and reacts with organic compounds in the wastewater 48. After the wastewater has been ozonated, it flows from the contact tank 36 to a reactor 52 of the biologically active filter 14. The reactor 50 includes a media bed 50, which in this example is coated with a biofilm. Bacteria in the biofilm biodegrade the ozonated organic compounds in the wastewater.

[0021] A bioelectrochemical sensor 16 is provided in communication with the water flowing between the ozone contactor unit 12 and the biologically active filter 14. The bioelectrochemical sensor 16 is connected to a controller 18. The bioelectrochemical sensor 16 is downstream of the sodium sulfite injection 24. As shown, the controller 18 is connected only to the local controller 20 of the bioelectrochemical sensor. This allows, for example, for measurements to be displayed from the bioelectrochemical sensor to a system operator. The system operator may adjust the operation of the ozone contactor unit 12 or the biologically active filter 14 based on the displayed measurements, based on further calculations, or based on recommendations provided by the controller 18. Optionally, the controller 18 is also connected to one or more other local controllers in the system 10. For example, the controller 18 may be connected to one or more local controllers 20 associated with one or both of the ozone generator 30 or the ozone flow control valve 32. The controller 18 may be configured to control the amount of ozone delivered to the water based on the signal from the bioelectrochemical sensor 16, optionally in combination with signals from one or more other sensors, such as the influent flow sensor 34. Alternatively, or in addition, the controller 18 may be configured to control one or more operating parameters of the biologically active filter 14 based on the signal from the bioelectrochemical sensor 16, optionally in combination with signals from one or more other sensors.

[0022] FIG. 3 illustrates an example method 300 of controlling a wastewater treatment plant using one or more biological sensors, optionally including collecting data to generate a relationship (i.e., a mathematical function) to be used in an ozone generation control algorithm. In a preliminary step, the plant may be started up, allowing about one month for the biological sensors to acclimate to the plant environment. The biological sensors may then be used to collect data to determine a curve (i.e., function) relationship (step 302), e.g., CCR=f(O3 / TOC), based on the measured metabolic activity (i.e., CCR) over a range of O3 and influent TOC conditions. A relationship comparing TOC removal (i.e., the ratio or difference between the measured influent TOC and effluent TOC) to the measured CCR may be developed in parallel with step 302 or sequentially (step 304). For example, a curve (i.e., function) of f(CCR)=TOC effluent / TOC influent may be developed. If the BAF media in the system is adsorptive, it may take 3-6 months of waiting time from plant startup to construct the f(CCR)=TOC effluent / TOC influent curve to allow the BAF to transition from being adsorptive to performing the desired biological process. If the media is not adsorptive, the curve may be constructed from about 1 to about 6 months after plant startup. The relationships determined in steps 302 and 304 may then be used in the remainder of the ozone production control method. For example, a target TOC effluent may be set (step 306), for example, based on emission regulations. In step 308, a TOC effluent / TOC influent ratio may be calculated using the measured TOC influent and the target TOC effluent determined in step 306. In step 308, metabolic activity (i.e., CCR) may also be determined using the curve (or its inverse) constructed in step 304 and the TOC effluent / TOC influent ratio. The curve created in step 302 depicts metabolic activity (i.e., CCR) as a function of O3 / influent TOC, and thus this ratio (O3 / influent TOC) can be identified in step 310 using the inverse relationship.If multiple ratios of O3 / influent TOC correspond to metabolic activity (i.e., CCR), the smallest ratio is used. The amount of O3 dosage required may be determined from the O3 / influent TOC ratio based on the measured influent TOC in step 312. In some examples, the curve in step 302 is generated at a stable NO2 concentration or considering the influent NO2 concentration, since NO2 consumes ozone. For example, the relationship in step 302 may be based on ozone minus ozone consumed by NO2. Optionally, the O3 determined in step 312 may be determined based on the influent TOC and NO2, for example, by increasing the O3 determined using a relationship based on ozone minus ozone consumed by NO2 by the amount consumed by the influent NO2. The process may return to step 308 after step 312 to adjust the dosage of ozone at an appropriate time interval, for example, once every 10-120 minutes. Optionally, if the TOC effluent target is changed, for example due to regulatory changes, the process may return to step 306. Optionally, the process may return to step 302 to periodically update the functions or other relationships described herein.

[0023] Figure 4 shows sample curves illustrating TOC effluent / TOC influent ratio as a function of CCR that may be constructed in step 304. Figure 5 shows sample curves illustrating CCR as a function of O3 / TOC influent ratio that may be constructed in step 302. Each of these curves may be developed using one or more of calculations, modeling, historical data from similar plants, or historical data from the plant being controlled using the curve. Optionally, the curves are specific to the plant for which the historical data is collected to provide an O3 control algorithm specific to that plant.

Claims

1. An ozone treatment unit, and a biological sensor comprising a water treatment system, wherein the biological sensor is adapted to contact the effluent from the ozone treatment unit and measure the growth or metabolism of microorganisms associated with the biological sensor.

2. The system according to claim 1, wherein the biological sensor measures the biodegradable degree of organic pollutants in the effluent from the ozone treatment unit.

3. The system according to claim 1, wherein the biological sensor produces or enables a measurement value or signal related to the carbon consumption rate (CCR) or carbon biodegradation (CBD) of the bacterial population associated with the biological sensor.

4. The system according to claim 1, wherein the biological sensor is a bioelectrochemical sensor that produces an electrical signal related to the metabolic activity of bacteria at the electrodes of the sensor.

5. The system according to claim 4, wherein the bioelectrochemical sensor comprises a power supply unit for delivering voltage or current across the electrode pair of the biosensor.

6. The system according to any one of claims 1 to 5, wherein the biological sensor is connected to a controller adapted to adjust the operating parameters of the ozone treatment unit.

7. The system according to any one of claims 1 to 5, comprising a biological treatment unit downstream of the ozone treatment unit.

8. The system according to claim 7, wherein the biological treatment unit is a biological activated filter.

9. The system according to claim 7, wherein the biological sensor is connected to a controller adapted to adjust the operating parameters of the biological treatment unit.

10. The system according to any one of claims 1 to 5, connected to the outlet of the secondary treatment unit or the tertiary treatment unit of a municipal or industrial wastewater treatment plant.

11. A method of treating water or controlling a water treatment process, comprising: contacting water with ozone to produce ozone-treated effluent; contacting the ozone-treated effluent with a biological sensor.

12. The method according to claim 11, wherein the biological sensor measures the biodegradable degree of organic pollutants in the ozone-treated effluent.

13. The method according to claim 12, wherein the biological sensor measures the metabolic activity, optionally the carbon consumption rate, of organisms exposed to the ozone-treated effluent. ​

14. The method according to claim 13, wherein the biological sensor is a bioelectrochemical sensor that provides an electrical signal corresponding to the metabolic activity of a bacterial population at the electrodes of the biosensor.

15. The method according to claim 14, comprising applying a voltage or current across the electrode pair of the biosensor.

16. The method according to any one of claims 11 to 15, wherein the measurement or signal from the biosensor is used to adjust the rate of ozone delivery to the wastewater.

17. The method according to any one of claims 11 to 15, comprising the biological degradation of pollutants in the ozone-treated effluent.

18. The method according to claim 17, wherein the biological degradation occurs in a biological active filter.

19. The method according to claim 17, wherein measurements or signals from the biosensor can be used to adjust the operating parameters of the biological degradation treatment step.

20. The method according to any one of claims 11 to 15, wherein the water is secondary or tertiary effluent from a municipal or industrial wastewater treatment plant.

21. A method of operating a wastewater treatment system comprising an ozone contactor and a biological active filter, comprising: setting a target for total organic carbon (TOC) effluent; collecting metabolic activity data from one or more biological sensors located downstream of the ozone contactor; collecting TOC influent water data; determining a target ozone amount taking into account the metabolic activity data, the TOC influent water data, and the TOC effluent target; controlling the ozone injection into the ozone contactor according to the target ozone amount comprising the method.

22. determining a first relationship between (a) the metabolic activity and (b) a comparison, such as a ratio or difference, of the TOC influent water to the TOC effluent of the wastewater treatment system or a similar system; determining a second relationship between (a) the ratio of the ozone amount to the TOC influent water and (b) the metabolic activity of the wastewater treatment system or a similar system; determining a target ozone amount taking into account the first relationship and the second relationship comprising the method according to claim 21.

23. The method according to claim 22, comprising determining a desired metabolic activity taking into account the first relationship, the TOC effluent target, and the TOC influent water data.

24. The method according to claim 23, comprising determining a desired ratio of the ozone amount to the TOC influent water, taking into account the desired metabolic activity and the second relationship.

25. The method according to any one of claims 22 to 24, comprising generating a first relationship and / or a second relationship using historical data collected while operating a wastewater treatment plant.

26. The method according to claim 25, comprising collecting historical data during the first 1 to 6 months of operation of a wastewater treatment system.

27. Stable NO in influent water ２ Determining a first relationship at a concentration, or considering the NO concentration in influent water to a wastewater treatment system and determining a first relationship, the method according to any one of claims 22 to 24. ２ ​

28. NO of the inflowing water ２ The method according to claim 27, comprising adjusting the target ozone amount based on the concentration.

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