JP4684064B2 - Accelerated oxidized water treatment method and apparatus - Google Patents

Description

  The present invention relates to an accelerated oxidized water treatment method and apparatus for performing oxidative decomposition of a hardly decomposable substance in water by using ozone gas and hydrogen peroxide together, and more particularly to an injection control method and apparatus for ozone gas and hydrogen peroxide.

  Ozone has a strong oxidizing power, and water treatment that performs sterilization, decolorization, deodorization, oxidation removal of organic substances or inorganic substances by diffusing ozone gas into water is widely performed. In particular, in the suburbs of urban areas, the damage of off-flavors caused by the water intake is spreading, and the strong oxidizing power of ozone described above exerts a great effect on the removal of off-flavors. The introduction of advanced processing using is being promoted.

  In recent years, an accelerated oxidation method with higher oxidizing power has been used particularly for the purpose of decomposing a hardly decomposable substance. The accelerated oxidation method is a combination of ozone, ultraviolet irradiation, hydrogen peroxide addition, etc., which promotes the self-decomposition of ozone and promotes the generation of hydroxy radicals (OH radicals) generated at that time. This is a technique for increasing the oxidizing power and efficiently decomposing substances that are difficult to decompose with ozone alone.

  The inventors of the present application have found an economical and efficient method for controlling the injection of ozone gas and hydrogen peroxide in the accelerated oxidation treatment using both ozone and hydrogen peroxide, and have filed patent applications regarding the related art (for example, patent Application No. 2005-102864). The basic configuration is that an accelerated oxidation treatment tank that mixes and injects ozone gas and hydrogen peroxide is placed in series behind the ozone contact tank in which ozone gas and water to be treated are in contact, and the dissolved ozone concentration value in the ozone contact tank in the previous stage Accordingly, the ozone injection amount and the hydrogen peroxide injection amount to the subsequent accelerated oxidation treatment tank are controlled. The basic configuration is substantially the same except for an apparatus (FIG. 1) for carrying out the accelerated oxidized water treatment method of the present invention, which will be described later, and an injection control function of ozone gas and hydrogen peroxide in the control apparatus.

  By the way, ozone treatment has a problem of producing bromate ions that are considered to be carcinogenic substances. Therefore, according to the water quality standard enforced from April 2004, the maximum allowable limit of bromate ion concentration in drinking water was established, and the allowable limit was defined as 10 μg / L. In the accelerated oxidation treatment method using ozone gas and hydrogen peroxide, it is possible to effectively remove the ozone decomposable substance, and depending on the injection amount of ozone gas and hydrogen peroxide, the formation of bromate ions can be performed. (For example, refer to Patent Documents 1 and 2).

For example, Patent Document 1 recognizes the following description. That is, the paragraph [0007] of the paragraph states that “bromate has recently been designated as an estimated carcinogen and USEPA has set a maximum level of 10 μg / L for drinking water”, paragraph [0009] In the paragraph, it is stated that “the residual ozone concentration is minimized and the hydrogen peroxide concentration is maximized to suppress the formation of bromate”, and the paragraph [0043] is referred to as “ozone gas and hydrogen peroxide. Is introduced in the range of 0.5 to 6.0 between about 0.1 to 10 of the total molar ratio of H ₂ O ₂ / O ₃ , and the paragraph [0044] is further described as “Minimum residual ozone concentration To control hypobromite formation ".

In Patent Document 2, as in Patent Document 1, “M ₂ H ₂ O ₂ / O ₃ molar ratio is about to be set against the background of USEPA setting the maximum bromate level to 10 μg / L for drinking water”. There is a description of “between 0.1 and 10” (see claim 4). The bromate has various salts depending on the cation species (K, Na, Mg, etc.), but dissociates in water and exists as ions, so the maximum level of 10 μg / L is bromine. It is a value based on acid ion concentration.
JP 2001-516633 A Special Table 2002-514134

  However, the methods for controlling the injection of ozone gas and hydrogen peroxide disclosed in Patent Documents 1 and 2 above are directed to an "accelerated oxidation treatment apparatus of a system that pressurizes and mixes ozone gas and hydrogen peroxide into a water stream to be treated". 1, and an optimum control method applied to the accelerated oxidation treatment apparatus having the configuration of FIG. 1, that is, the “promoted oxidation treatment apparatus having a configuration in which an accelerated oxidation treatment tank is arranged in series at the subsequent stage of the ozone contact tank”. Whether or not is unknown.

  Furthermore, there are the following problems in addition to the problem of the difference in the above methods. That is, the trihalomethane production ability (THMFP) may be increased only by the control method of the accelerated oxidation treatment for the purpose of suppressing the formation of bromate. Like bromate, trihalomethane is a carcinogenic substance and its reduction is desired. Depending on the quality of treated water (raw water), reduction of trihalomethane may be more important than bromate.

  The present invention has been made in view of the above points. An object of the present invention is to remove the ozone decomposable substance of the water to be treated while suppressing the production of bromic acid, and to improve the quality of the raw water. An object of the present invention is to provide an accelerated oxidation water treatment method and apparatus for reducing the trihalomethane production ability (THMFP).

In order to solve the above-mentioned problems, the present invention performs ozone treatment on water to be treated by contacting and mixing with ozone gas in an ozone contact tank, and then mixing ozone gas and hydrogen peroxide in an accelerated oxidation treatment tank. In the accelerated oxidation water treatment method in which accelerated oxidation treatment is performed by injection, the amount of ozone gas injected into the ozone contact tank is within a preset range in which the dissolved ozone concentration value at the ozone contact tank outlet is 0.95 mg / L or less. Further, the hydrogen peroxide injection amount into the accelerated oxidation treatment tank is set to a predetermined molar ratio (H ₂ O ₂ / O ₃ mol) with respect to the ozone gas injection amount in the accelerated oxidation treatment step. The H ₂ O ₂ / O ₃ molar ratio is 2 or more (Claim 1).

  Further, the invention of the device is preferably the invention of claim 2 below. That is, an apparatus for carrying out the accelerated oxidation water treatment method according to claim 1, wherein the ozone contact tank, the accelerated oxidation treatment tank provided in the subsequent stage, and the dissolved ozone concentration monitoring apparatus provided at the ozone contact tank outlet And an ozone generation device, a hydrogen peroxide injection device, and ozone gas and hydrogen peroxide injection amount control means.

  That is, the present invention determines the dissolved ozone concentration at the ozone contact tank outlet to the extent that the production of bromic acid satisfies the water quality standard, and further sets the injection ratio of hydrogen peroxide and ozone into the accelerated oxidation treatment tank to a predetermined value. Thus, it is characterized in that it suppresses the formation of bromate ions, removes ozone-degradable substances, and reduces the trihalomethane generating ability (THMFP). Details will be described later.

  According to the present invention, it is possible to remove the ozone decomposable substance of the treated water while suppressing the production of bromic acid, and to reduce the trihalomethane generating ability (THMFP) according to the quality of the raw water, It is possible to perform optimal ozone injection control and hydrogen peroxide injection control based on the dissolved ozone feedback control similar to the conventional one.

  An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a system diagram of an accelerated oxidized water treatment apparatus according to an embodiment of the present invention. In FIG. 1, 1 is an inlet for water to be treated, 2 is an ozone contact tank, 3 is an ozone generator, 4 is an air diffuser (1), 5 is an accelerated oxidation treatment tank, 6 is an air diffuser (2), 7 is a hydrogen peroxide injection device, 8 is an outlet for treated water, 9 is a control device, and 10 is a dissolved ozone concentration monitoring device.

  In FIG. 1, the water to be treated is introduced into the ozone contact tank 2 from the introduction port 1 by natural flow or by pumping water, and the ozone gas generated in the ozone generator 3 passes through the ozone diffuser (1) 4 to the first stage. It is introduced into the ozone contact tank 2. In the ozone contact tank 2, the organic components in the water to be treated are decomposed to some extent, and unreacted ozone is detected as residual ozone at the same time.

  The water to be treated after the reaction flowing out from the ozone contact tank 2 was introduced into the subsequent accelerated oxidation treatment tank 5 and injected by the ozone supplied from the air diffuser (2) 6 and the hydrogen peroxide injector 7. Reacts with hydrogen peroxide. After the decomposition of the hardly decomposable components in the accelerated oxidation treatment tank 5, the remaining hydrogen peroxide is decomposed in a biological activated carbon tower or the like (not shown) and drained out of the system from the discharge port 8 as highly treated water. The

At this time, the control device 9 detects the value of the dissolved ozone concentration monitoring device 10 provided at the outlet of the ozone contact tank 2 to control the amount of ozone injected into the ozone contact tank 2 and at the same time the accelerated oxidation treatment tank 5. The amount of ozone gas supplied to the gas generator is controlled, and the hydrogen peroxide injection device 7 is controlled so that the amount of hydrogen peroxide injected is equal to the amount of ozone gas injected and a preset injection ratio. The injection ratio is controlled so that the H ₂ O ₂ / O ₃ molar ratio is 2 or more. Furthermore, the amount of ozone gas injected into the ozone contact tank 2 is controlled so that the dissolved ozone concentration value at the ozone contact tank outlet is 0.95 mg / L or less.

Next, an embodiment relating to control of the ozone injection amount, the hydrogen peroxide injection amount, and the like will be described with reference to FIGS. Figure 2 shows the relationship between the dissolved ozone concentration (mg / L) and bromate ion concentration (μg / L) at the ozone contact tank outlet, and Figure 3 shows the dissolved ozone concentration (mg / L) at the ozone contact tank outlet. It is a figure which shows the relationship with a THMFP reduction rate (%). FIG. 4 is a diagram showing the relationship between the ozone injection rate (mg / L) and the THMFP reduction rate (%) when the dissolved ozone concentration at the ozone contact tank outlet in FIG. 3 is 0 mg / L. That is, the ozone injection rate at which the dissolved ozone concentration is detected differs depending on the water quality, but up to a certain ozone injection rate, there are more components decomposed by ozone, so all ozone is consumed without remaining as dissolved ozone. It will be in a state to be. This shows the relationship between the ozone injection rate and the THMFP reduction rate when all of the injected ozone is consumed and the dissolved ozone concentration becomes 0 mg / L. FIG. 5 is a diagram showing the relationship between the molar ratio of H ₂ O ₂ / O ₃ in the accelerated oxidation treatment tank and the removal rate (%) of 1,4-dioxane, which is an ozone decomposable substance, and FIG. 6 shows the accelerated oxidation treatment. it is a diagram showing a relationship between the molar ratio and the bromate ion concentration of _{H 2 O 2 / O 3 (} μg / L) in the bath.

  As is apparent from FIG. 2, bromate ions are generated by ozone treatment, but are hardly generated where the dissolved ozone concentration is low. Also, from FIG. 3, the THMFP reduction rate is reduced to some extent by ozone injection as to whether or not the dissolved ozone concentration can be detected. From FIG. 4, even when the dissolved ozone concentration is 0 mg / L, the higher the ozone injection rate, that is, the state where the ozone injected into the water to be treated is injected with an appropriate amount necessary for ozone decomposition during the treatment. In this case, the THMFP reduction rate becomes high. This is because THMFP is reduced although the residual ozone is 0 mg / L because the organic matter component in the water to be treated contains a certain amount of components showing THMFP. That is, it is desirable to control to the extent whether the dissolved ozone concentration is detected.

Next, FIG. 5 will be described. The accelerated oxidation treatment using ozone and hydrogen peroxide is effective in removing ozone-degradable substances such as 1,4-dioxane, and the hydrogen peroxide injection rate relative to the ozone injection rate (injection ratio: H ₂ O ₂ / O ₃ is defined here as a ratio of the mol concentration), to be effective than ozone treatment with _{H 2 O 2 / O 3 =} 0.5 or higher, seen from Fig. Therefore, from FIG. 5, it is desirable that the molar ratio of H ₂ O ₂ / O ₃ is at least 0.5.

Next, FIG. 6 will be described. FIG. 6 shows the relationship between the molar ratio of H ₂ O ₂ / O ₃ and the bromate ion concentration (μg / L) in the accelerated oxidation treatment tank. According to FIG. 6, H ₂ O ₂ / O ₃ = In 0.5, the bromate ion concentration (μg / L) is extremely high compared to the molar ratio before and after that, and in order to suppress the formation of bromate ions, H ₂ O ₂ / O ₃ = 2 The above is desirable.

As described above, when H ₂ O ₂ / O ₃ = 2 or more, the bromate ion concentration (μg / L) in the accelerated oxidation treatment tank is 2 μg / L. Therefore, in order to satisfy the maximum allowable limit of 10 μg / L of bromate ion concentration in drinking water, the bromate ion concentration allowed at the ozone contact tank outlet is 8 μg / L. In order to satisfy this, it is necessary to make the dissolved ozone concentration at the ozone contact tank outlet 0.95 mg / L or less from FIG.

  Further, from the viewpoint of reducing trihalomethane, the dissolved ozone concentration needs to be 0.95 mg / L or less from FIGS.

  As described above, it is possible to perform optimal ozone injection control and hydrogen peroxide injection control for the purpose of suppressing the formation of bromate ions, the decomposition of ozone-degradable substances, and the reduction of THMFP.

The system system | strain diagram of the accelerated oxidation water processing apparatus in connection with the Example of this invention. The figure which shows the relationship between the dissolved ozone density | concentration and bromate ion density | concentration of an ozone contact tank exit. The figure which shows the relationship between the dissolved ozone concentration of an ozone contact tank exit, and a THMFP reduction rate. The figure which shows the relationship between the ozone injection rate when the dissolved ozone concentration of an ozone contact tank exit is 0 mg / L, and a THMFP reduction rate. Diagram showing the relationship between the molar ratio of 1,4-dioxane removal rate of H ₂ O ₂ / O ₃ in promoting the oxidation treatment tank. Diagram showing the relationship between the molar ratio and the bromate ion concentration of H ₂ O ₂ / O ₃ in promoting the oxidation treatment tank.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Introduction port, 2 Ozone contact tank, 3 Ozone generator, 4 Air diffuser (1), 5 Promote oxidation treatment tank, 6 Air diffuser (2), 7 Hydrogen peroxide injection device, 8 Outlet, 9 Control device 10 Dissolved ozone concentration monitoring device.

Claims (2)

Oxidized water treatment that treats water to be treated with ozone gas in an ozone contact tank and performs ozone treatment by mixing and injecting ozone gas and hydrogen peroxide in the accelerated oxidation tank In the method
The amount of ozone gas injected into the ozone contact tank is controlled so that the dissolved ozone concentration at the ozone contact tank outlet is a value within a preset range of 0.95 mg / L or less, and further to the accelerated oxidation treatment tank. The hydrogen peroxide injection amount is controlled so as to have a predetermined molar ratio (H ₂ O ₂ / O ₃ molar ratio) with respect to the ozone gas injection amount in the accelerated oxidation treatment step, and the H ₂ O ₂ An accelerated oxidized water treatment method characterized in that the / O ₃ molar ratio is 2 or more. It is an apparatus which implements the accelerated oxidation water treatment method of Claim 1, Comprising: The ozone contact tank, the accelerated oxidation process tank provided in the back | latter stage, the dissolved ozone concentration monitoring apparatus provided in the ozone contact tank exit, ozone An accelerated oxidized water treatment apparatus comprising: a generator, a hydrogen peroxide injection device, and ozone gas and hydrogen peroxide injection amount control means.

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