JPH1099878A - Water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To put strong oxidizing action to practical use to treat a pollutant and to effectively utilize an oxidizing agent thoroughly, in a water treatment method adding ozone to water to be treatred to dissolve the same therein and adding hydrogen peroxide thereto, by detecting the absorbancy of water to be treated to control an amt. of ozone. SOLUTION: Piping 2 for water to be treated, hydrogen peroxide piping 3 and ozone-containing air piping 4 are connected to a treatment tank 1 and an air diffusion pipe 5 is arranged on the bottom part of the tank 1. Ozone is added to water to be treated within the treatment tank 1 to be dissolved therein and hydrogen peroxide is added to perform water treatment. In this case, the concn. of ozone in exhaust gas is measured by an ozone gas concn. detector (ultraviolet absorbancy method) 6 and a flow rate of ozone gas to be blown in is changed, for example, so that the measured concn. of excessive ozone gas becomes 10g/Nm<3> (1/10 initial concn.). The addition of ozone is performed by an air diffusion system or an ejector system and the control of an addition amt. of ozone is performed by controlling the amt. or concn. of ozone gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a water treatment method using hydrogen peroxide and ozone. More specifically, disinfecting, disinfecting, discoloring, deodorizing, decomposing organic substances, improving the transparency, improving the clarity of sewage or human waste secondary treatment water, industrial effluent or waste landfill leachate or the secondary treatment water etc. The present invention relates to a water treatment method for reducing BOD and COD. In the present invention, the term "treatment" means water purification, and refers to an operation for disinfecting, sterilizing, decolorizing, deodorizing water, or decomposing organic substances in water, improving transparency, and reducing BOD / COD. Say.

[0002]

2. Description of the Related Art In recent years, water resources are limited as well as energy, and the importance of recycling wastewater is being recognized. On the other hand, the contamination of the tap water source by trace contaminants has become a problem. In addition to the conventional advanced treatment for removing nitrogen and phosphorus, treatment for the purpose of deodorization, decolorization, sterilization, removal of trace contaminants, etc. Methods are being introduced. In such a social situation, activated carbon treatment, ozone treatment, membrane treatment, and the like have been put into practical use as methods for reusing water and removing trace pollutants. However, activated carbon treatment can remove organic pollutants by adsorption, but has no bactericidal action, and requires replacement of activated carbon. Ozone treatment has excellent decolorization, deodorization, and sterilization effects, but has a low effect of decomposing pollutants. Membrane treatment is excellent from the viewpoint of water treatment, but has the problem of generating waste.

In contrast to the above processing method, Japanese Patent Publication No. 60-67
No. 18 and Japanese Patent Publication No. 60-41999 disclose a method of treating ozone and hydrogen peroxide by adding ozone and hydrogen peroxide to wastewater as a treatment method capable of comprehensively solving the above problems. In the above-mentioned treatment method, OH radicals having a very strong oxidizing power are generated by adding ozone and hydrogen peroxide to wastewater, and the OH radicals are used to treat wastewater. OH radicals are stronger oxidizing agents than ozone, and can also decompose and remove pollutants in wastewater that could not be decomposed by ozone alone, have high decomposition efficiency of pollutants, and have deodorizing, decolorizing and sterilizing effects. It is an effective treatment method that is excellent and does not generate secondary waste.

[0004]

However, the method of using ozone and hydrogen peroxide in combination has a strong oxidizing effect, but it cannot always efficiently use an expensive oxidizing agent, resulting in a high cost treatment. It was a means. The inventor of the present invention completed the present invention with a problem of treating pollutants by utilizing a strong oxidizing action using ozone and hydrogen peroxide in combination, and effectively using an oxidizing agent to be added without exhaustion. is there.

[0005]

Means for Solving the Problems As a result of research, the present inventor has
Although it is a value that is affected by the concentration and type of pollutants in the water to be treated, it has been found that the concentration of ozone and hydrogen peroxide in the water to be treated, especially the ozone concentration, has a great effect on the effective use of oxidizing agents. . That is, if the amount of added ozone is changed following the fluctuation of the concentration of the water to be treated, the treatment efficiency is greatly increased, and the optimum addition amount of hydrogen peroxide has a small change with respect to the concentration change of the water to be treated. Was found. The present invention is a water treatment method of adding and dissolving ozone to water to be treated, and adding hydrogen peroxide, wherein the amount of ozone to be added is controlled by detecting the absorbance of the water to be treated. A featured water treatment method is provided.

The present invention also relates to a water treatment method for adding and dissolving ozone to water to be treated and adding hydrogen peroxide, wherein the ozone is added by detecting the concentration of dissolved ozone in the water to be treated. A water treatment method characterized by controlling the amount of ozone is provided. Usually, it is preferable to control the amount of ozone to be added so that the concentration of dissolved ozone in the water to be treated falls within the range of 0.1 to 10 mg / liter.

Further, there is provided a water treatment method in which ozone is added to and dissolved in water to be treated, and hydrogen peroxide is added,
A water treatment method characterized by controlling the amount of ozone to be added by detecting the concentration of excess ozone in exhaust gas generated in the process of treating water to be treated. Generally, the excess ozone concentration in the exhaust gas is 1 to 10% of the initial concentration.
By controlling the amount of ozone to be added to be within the range of
Efficient use of ozone can be expected. In the above-mentioned water treatment method, by detecting the absorbance of the water to be treated, the concentration of dissolved ozone in the water to be treated and / or the concentration of excess ozone in the exhaust gas, and controlling the amount of hydrogen peroxide to be added, more efficient treatment is achieved. Can be expected.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described in detail. In the present invention, the amount of ozone added to the water to be treated is detected by detecting the absorbance of the water to be treated, the concentration of dissolved ozone in the water to be treated, and the concentration of excess ozone in the exhaust gas generated in the process of treating the water to be treated. And oxidatively decompose pollutants efficiently. The present invention decomposes pollutants in the water to be treated by OH radicals generated by contact between ozone and hydrogen peroxide. The OH radicals react with ozone and hydrogen peroxide to cause strong oxidation. Dissipate power. In other words, if the concentration of ozone or hydrogen peroxide is too low, the generation of OH radicals is small. Conversely, if the concentration of ozone or hydrogen peroxide is too high, the generated OH radicals do not oxidize the pollutants and ozone or peroxide It is thought that it disappears by reacting with hydrogen and the expected treatment is not performed in any case. Since the reaction rate between OH radicals and ozone is much faster than the rate at which ozone moves from the gas phase to the liquid phase, the concentration of dissolved ozone in the water to be treated is usually low, and the It is considered that dissolved ozone rarely hinders the treatment, but rather the treatment reaction often does not proceed because the concentration of dissolved ozone in the liquid phase is too low.

For this reason, when a certain amount of ozone gas is injected into the water to be treated, the following situation occurs. That is, if the concentration of pollutants in the water to be treated is too high, ozone is reduced due to the reaction with the pollutants in the water to be treated, and the dissolved ozone concentration cannot be maintained at a high level. The chance of generating OH radicals is reduced. Therefore, the effect is almost the same as that of the treatment using ozone alone, or the reaction is inhibited by hydrogen peroxide. Conversely, if the concentration of pollutants in the water to be treated is too low, the dissolved concentration of ozone in the water to be treated is maintained at a high level, making it difficult for ozone to be absorbed. As a result, ozone is used or wasted at very low efficiency.

On the other hand, the concentration of hydrogen peroxide can be easily adjusted because it can be added to the water to be treated in a liquid state. However, when the concentration is high, the oxidation reaction of pollutants is inhibited. However, even if the concentration of pollutants in the water to be treated fluctuates,
The change in the optimal amount of hydrogen peroxide added to pollutants is relatively small, so even if the amount of added hydrogen peroxide is constant and the constant value is close to the optimal value, it is sufficient to supply ozone sufficiently. Processing is performed almost appropriately.

From the above findings, it is possible to perform an efficient treatment by making the amount of added ozone follow the change in the concentration of pollutants in the water to be treated. As a method for controlling the amount of ozone added, the absorbance of the water to be treated is measured, or the concentration of dissolved ozone or excess ozone in the exhaust gas is detected, and the concentration difference is compared with a target value determined by the concentration and type of the pollutant. The feedback control of adding ozone so as to cancel out is effective. However, other control methods that can make the amount of added ozone follow the change in the concentration of pollutants,
For example, feedforward control can be adopted. When controlling the amount of added ozone using the absorbance of the water to be treated, the wavelength at which the absorbance is measured is a problem, but different wavelengths are suitable depending on the properties of the water to be treated and the target treatment level. In many cases, in practice, it is sufficient to experimentally select a wavelength that exhibits a behavior that matches the water pollution index.

Specific target values of the absorbance, the dissolved ozone concentration and the surplus ozone concentration are as follows:
It is difficult to specify all together depending on the type and concentration of coexisting substances, processing equipment, gas-liquid contact status, and the like. For example, when controlling the amount of ozone added using the absorbance of the water to be treated,
The absorbance of the water to be treated having a wavelength of 420 nm is measured, and the amount of ozone added is changed according to the rate of change.
The absorbance in nm may be measured for both the treated water and the treated water, and the amount of ozone added may be changed so that the treated water becomes higher. The concentration of dissolved ozone in the water to be treated is 0.1
The surplus ozone concentration in the exhaust gas generated in the process of treating the water to be treated is preferably set within the range of 1 to 10% of the initial concentration. By controlling the amount of ozone added, it is possible to treat water to be treated at a certain concentration or higher, which is difficult to treat only by controlling the concentration of hydrogen peroxide, and to supply ozone in an amount that can cover the entire fluctuation range of the concentration of treated water. Useless consumption of ozone due to uniform addition can be prevented.

The control of the amount of added ozone may be performed by controlling the amount of gas or by controlling the concentration of ozone. Further, the amount of generated ozone may be controlled by controlling the ozone generator itself. However, in reality, it is often easier to control the gas flow rate. It is desirable that the dissolved ozone concentration in the water to be treated and the excess ozone concentration in the exhaust gas can be measured instantaneously in order to increase the response speed, and an ultraviolet absorption type densitometer or the like can be used.

As a method of adding ozone, any form such as a diffuser type and an ejector type is not particularly limited. However, when the concentration of the pollutant is high, there is a limit to the absorption of ozone by a single bubble column. Therefore, it is preferable to arrange the treatment apparatus in multiple stages. The residence time of the water to be treated in the ozone dissolving tank is usually in the range of 1 to 60 minutes, preferably about 5 to 25 minutes.

Ozone is usually supplied using various types of ozone generators such as a silent discharge method, but there is no particular limitation on the type or method of supply. However, the higher the concentration of ozone contained in one liter of gas, the more the dissolution of ozone in the water to be treated is promoted.
0 mg, preferably 50 mg or more of ozone may be contained. It is more preferable that the content is 100 mg or more.
Air, oxygen-enriched air, and other gases can be used as the gas serving as the ozone medium. Further, the ozone-containing exhaust gas discharged from the treatment tank can be blown into the water to be treated as pretreatment. The average diameter of the supplied ozone gas bubbles depends on the properties of the water to be treated.
The range of up to 10,000 μm is preferred, especially 10 to 1 μm.
The range of 000 μm is suitable because the consumption of the dispersion energy is small in spite of the large gas-liquid contact area.

In the water treatment method of the present invention, by controlling the addition amount of hydrogen peroxide in addition to the control of the addition amount of ozone, more efficient treatment and treatment can be achieved as compared with the case where only the addition amount of ozone is controlled. More precise control becomes possible. The concentration of hydrogen peroxide contained in the water to be treated depends on the type and concentration of the substance to be treated contained in the water to be treated, the type and concentration of coexisting substances, the treatment equipment, the amount of ozone used, and the gas-liquid contact conditions. Although not specified, usually 0.1 to 100 mg, preferably 0.5 to 100, per liter of water to be treated
It is in the range of 50 mg. In general, there is an optimum value for the concentration of hydrogen peroxide in the water to be treated. Therefore, the optimum amount of hydrogen peroxide to be added may be determined experimentally.

Although the method for adding hydrogen peroxide is not particularly specified, since the treatment reaction by OH radicals is inhibited at a high concentration, the hydrogen peroxide inlet may be divided into a plurality of portions or a plurality of times at a low concentration. It is preferable to add it in divided portions, add it continuously, or add it while stirring sufficiently. The larger the contact area between the water to be treated and the ozone-containing gas, for example, the smaller the bubbles of the ozone-containing gas, the larger the optimum amount of added hydrogen peroxide tends to be.

The hydrogen peroxide to be added may be a commercially available aqueous hydrogen peroxide solution or may be directly supplied from a hydrogen peroxide production device. An aqueous solution of hydrogen peroxide electrolytically produced using a sodium hydroxide aqueous solution as an electrolytic solution can also be used. The concentration of hydrogen peroxide in the hydrogen peroxide solution used for mixing with the water to be treated is not particularly limited, but the amount of hydrogen peroxide added,
The concentration may be easily controlled by the pump performance and the like.

The temperature at which the treatment is carried out is not particularly limited as long as the water to be treated retains a liquid phase. The higher the temperature of the water to be treated, the higher the reaction rate, but the rate of self-decomposition of ozone and hydrogen peroxide also increases. Therefore, an optimum temperature suitable for the treatment may be set as appropriate. As a specific embodiment of the present invention, FIG. 1 schematically shows an example of a single-tank circulation process, and FIG. 5 schematically shows an example of a continuous process using a continuous multi-tank method.

[0020]

EXAMPLES Various embodiments of the present invention will be described below with reference to examples. In Examples and Comparative Examples, the treatment efficiency was determined by the following equation using the water pollution index before and after the treatment. Treatment efficiency = (1−C / C ₀ ) × 100 where C: Water pollution index after treatment of treated water C ₀ : Water pollution index before treatment of treated water The water pollution index depends on the purpose. , COD, B
Various things such as OD and TOC are used.

Example 1 This is an experiment in which actual wastewater was used and the pollutant concentration was changed according to the actual situation. The ozone concentration in the exhaust gas was measured by the ozone gas concentration detector 6 (ultraviolet absorbance method) using the flow-type experimental apparatus shown in FIG. 1, and the measured excess ozone gas concentration was 10 g / Nm ³ (1/1 of the initial concentration). 1
The flow rate of the ozone gas to be blown was changed so as to be 0). Further, the water to be treated is changed at regular intervals to a liquid obtained by mixing the leachate of waste landfill and water at the weight ratio shown in Table 1,
A processing test was performed. The COD, the amount of added ozone, and the amount of added hydrogen peroxide were measured at regular intervals. FIG.
FIGS. 3 and 4 show the relationship between the treatment efficiency (hereinafter referred to as COD treatment efficiency) and the treatment time using D as the water pollution index, and the relationship between the treatment time and the ozone addition amount and hydrogen peroxide addition amount, respectively. The amount is shown in% by weight based on the amount (the amount of ozone added is 120 mg / liter and the amount of hydrogen peroxide added is 10 mg / liter).

Example 2 An experiment was conducted using the same experimental apparatus as used in Example 1 and in the same manner as in Example 1, except that the amount of hydrogen peroxide added was changed in addition to the flow rate of the ozone gas to be blown. Was. The COD, the amount of added ozone, and the amount of added hydrogen peroxide were measured at regular intervals. FIG. 2 shows the relationship between the COD treatment efficiency and the treatment time, and FIGS. 3 and 4 show the relationship between the ozone addition amount and the hydrogen peroxide addition amount and the treatment time, respectively, as the initial amount (the ozone addition amount 120 mg / liter, (% Of hydrogen peroxide added: 10 mg / liter).

Comparative Example 1 An experiment was conducted in the same manner as in Example 1 to compare with the present invention. However, only a fixed amount of ozone gas was injected while changing only the amount of added hydrogen peroxide so that the concentration of surplus ozone gas in the exhaust gas to be measured was 10 g / Nm ³ (1/10 of the initial concentration). The COD and the amount of hydrogen peroxide added were measured at regular intervals. FIG. 2 shows the relationship between the COD treatment efficiency and the treatment time, and FIGS. 3 and 4 show the relationship between the ozone addition amount and the hydrogen peroxide addition amount and the treatment time, respectively, as the initial amount (ozone addition amount 120 mg / liter). , Hydrogen peroxide added amount of 10 mg / liter).

Example 3 An experiment was conducted using the continuous processing apparatus shown in FIG. However, first, the absorbance of the water to be treated at a wavelength of 420 nm was measured by the absorbance meter 507a, and the amount of ozone gas added to the reaction tube 501a was increased or decreased by the increase or decrease. The initial value of the amount of ozone added at this time was 60 mg / liter. The amount of hydrogen peroxide added was kept constant at 5 mg / liter. Further, the dissolved ozone concentration was measured by a dissolved ozone concentration meter 507b, and the amount of ozone added to the reaction tube 501b was controlled so that the dissolved ozone concentration in the water to be treated was 0.5 mg / liter. The amount of hydrogen peroxide added at this time was kept constant at 3 mg / liter. Other conditions were the same as in Example 1, and the COD and the amount of added ozone were measured at regular intervals. FIG. 6 shows the relationship between the COD treatment efficiency and the treatment time, and FIG. 7 shows the relationship between the ozone addition amount and the treatment time.
Indicated by

Comparative Example 2 An experiment was conducted in the same manner as in Example 3 except that the amount of added ozone was kept constant, and the COD and the amount of added ozone were measured at regular intervals. FIG. 6 shows the relationship between the COD treatment efficiency and the treatment time, and FIG. 7 shows the relationship between the ozone addition amount and the treatment time in terms of% by weight with respect to the initial amount (ozone addition amount 120 mg / liter).

[0026]

[Table 1]

[0027]

According to the present invention, efficient treatment can always be carried out in response to a change in the concentration of the water to be treated, and the treatment efficiency with added hydrogen peroxide and ozone per unit amount is improved. . The amount of ozone and hydrogen peroxide added can be reduced, and running costs can be kept low.

[Brief description of the drawings]

FIG. 1 is a schematic view of a distribution processing mode according to the present invention (Example 1, Embodiment 1).
2, Comparative Example 1).

FIG. 2 shows a relationship between COD processing efficiency and processing time (Examples 1, 2 and Comparative Example 1).

FIG. 3 shows the relationship between the ozone addition amount and the processing time with respect to the initial addition amount (Examples 1, 2 and Comparative Example 1).

FIG. 4 shows the relationship between the amount of hydrogen peroxide added to the initial amount added and the processing time (Examples 1, 2 and Comparative Example 1).

FIG. 5 is a schematic diagram of a continuous processing embodiment of the present invention.

FIG. 6 shows the relationship between COD processing efficiency and processing time (Example 3, Comparative Example 1).

FIG. 7 shows the relationship between the ozone addition amount and the processing time with respect to the initial addition amount (Example 3, Comparative Example 1).

[Explanation of symbols]

1: treatment tank 2, 502: treated water pipe 3, 503: hydrogen peroxide water pipe 4, 504: ozone-containing gas pipe 5, 505: diffuser pipe 6, 506: surplus ozone concentration detector 7, ozone gas concentration detector 8, 9, 508, 5
09: Flow control valve 10, 510: Processing liquid discharge pipe 11, 511: Exhaust pipe 501a: Reaction tube 501b: Processing tank 507a: Absorbance meter 507b: Dissolved ozone concentration meter

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/50 540 C02F 1/50 540A 540B 550 550L 1/72 1/72 Z

Claims (4)

[Claims] 1. A water treatment method for adding and dissolving ozone to water to be treated and adding hydrogen peroxide, wherein the amount of ozone to be added is controlled by detecting the absorbance of the water to be treated. A water treatment method characterized by the above-mentioned. 2. A water treatment method for adding and dissolving ozone to water to be treated and adding hydrogen peroxide, wherein the amount of ozone to be added is controlled by detecting the concentration of dissolved ozone in the water to be treated. A water treatment method, comprising: 3. A water treatment method for adding and dissolving ozone to water to be treated, and adding hydrogen peroxide, wherein a concentration of excess ozone in exhaust gas generated in the process of treating the water to be treated is detected. Water treatment method characterized by controlling the amount of ozone to be added. 4. The amount of hydrogen peroxide to be added is further controlled by detecting the absorbance of the water to be treated, the concentration of dissolved ozone in the water to be treated and / or the concentration of excess ozone in the exhaust gas. The water treatment method according to claim 1, 2, or 3.