JP3537995B2 - Wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wastewater treatment method using ozone and hydrogen peroxide. More specifically, the present invention relates to a wastewater treatment method for treating secondary treatment water of sewage or night soil, industrial wastewater or leachate of landfill waste, or secondary treatment water thereof using ozone and hydrogen peroxide. In the present invention, the term "treatment" means purification of wastewater, and disinfects, sterilizes, decolorizes, and deodorizes wastewater, or decomposes organic matter in wastewater, improves transparency, improves BOD, CO2
An operation for reducing D.

[0002]

2. Description of the Related Art In recent years, the importance of purifying wastewater for reuse has increased. As part of reuse, conventional nitrogen
In addition to advanced treatment for phosphorus removal, deodorization, decolorization,
Introduction of treatment methods for the purpose of sterilization, removal of trace contaminants, and the like has been promoted. Specifically, treatment methods such as activated carbon treatment, ozone treatment, and film treatment are being implemented. Among these treatment methods, activated carbon treatment can adsorb and remove organic pollutants, but has no bactericidal action, and requires replacement of activated carbon. The ozone treatment has excellent decolorization, deodorization and sterilization effects, but has a low function of decomposing pollutants. Membrane treatment is excellent from the viewpoint of water treatment, but has a problem of producing waste.

Therefore, Japanese Patent Publication No. Sho 60-6718, Japanese Patent Publication No. Sho 60-41999, and Japanese Patent Application Laid-Open No. 58-55088 are disclosed.
Japanese Patent Application Publication No. JP-A-2006-13312 describes a method of treating wastewater by adding ozone and hydrogen peroxide to the wastewater as a means for comprehensively solving the problems of the treatment method. The treatment method described above is to add ozone and hydrogen peroxide to wastewater to generate OH radicals having extremely strong oxidizing power, and treat the wastewater with the generated OH radicals. O
H radicals are stronger oxidizing agents than ozone, and can decompose and remove pollutants in wastewater that cannot be decomposed by ozone alone. It is an effective treatment method that has excellent deodorizing, decoloring and sterilizing effects and does not generate secondary waste.

[0004]

However, the above-mentioned wastewater treatment method using ozone and hydrogen peroxide together has a strong oxidizing effect, and is capable of cleanly treating pollutants which are difficult to treat by other methods. Although it has excellent features, it does not sufficiently utilize the added expensive oxidizing agent, especially ozone, and thus has a disadvantage of increasing the processing cost, and has not been widely used. Another problem is that ozone remains in the treated water unless some measures are taken after the treatment. The inventor of the present invention treats many pollutants by utilizing the strong oxidizing power of the combined use of ozone and hydrogen peroxide, and seeks to reduce the treatment cost by using the expensive ozone to be added as effectively as possible. As an object, the present invention has been completed.

[0005]

Means for Solving the Problems As a result of the research by the present inventor,
Although the value is affected by the concentration and type of pollutants in the water to be treated, it has been clarified that the concentration of ozone and hydrogen peroxide in the water to be treated has a significant effect on the effective use of oxidizing agents, especially the concentration of ozone. Was. That is, a certain linear relationship is established between the amount of added ozone and the concentration of dissolved ozone, and if the concentration of dissolved ozone is maintained at a constant level, the efficiency of use of ozone is increased and stable treatment is possible. I found it.

Therefore, the present invention solves the above-mentioned problems by providing a first step of adding ozone to wastewater for treatment, and adding ozone and hydrogen peroxide to the water to be treated treated in the first step. A wastewater treatment method comprising the steps of: (a) controlling the amount of ozone added to the first step so that the concentration of dissolved ozone in the water to be treated on the inlet side of the second step is maintained at a predetermined value; And a method for treating wastewater. A wastewater treatment method comprising a first step of adding ozone to wastewater for treatment, and a second step of adding ozone and hydrogen peroxide to the treated water treated in the first step for treatment. A wastewater treatment method characterized by controlling the amount of ozone added to the second step so that the concentration of dissolved ozone in the water to be treated at the outlet of the second step is maintained at a predetermined value. Further, by combining the above two wastewater treatment methods, a first step in which ozone is added to wastewater for treatment and a treatment in which ozone and hydrogen peroxide are added to water to be treated treated in the first step. A wastewater treatment method comprising the second step, wherein the amount of ozone added to the first step is controlled so that the concentration of dissolved ozone in the water to be treated on the inlet side of the second step is maintained at a predetermined value, and A wastewater treatment method is provided, wherein the amount of ozone added to the second step is controlled so that the concentration of dissolved ozone in the water to be treated at the outlet of the second step is maintained at a predetermined value. Into the second step
The dissolved ozone concentration in the water to be treated on the mouth side is 0.1 to 1
In the first step to maintain the range of 0mg / liter
It is desirable to control the amount of ozone to be added. Also before
The concentration of dissolved ozone in the water to be treated at the outlet of the second step is
So that it is maintained at 0.1 to 2 mg / liter.
It is preferable to control the amount of ozone added to the two steps.
And preferably, measure the dissolved ozone concentration of the water to be treated.
To control the amount of ozone added
0.1-100mg of hydrogen per liter of water to be treated
To control. In these wastewater treatment methods, it is preferable that the water to be treated treated in the second step is aerated to remove remaining ozone and hydrogen peroxide in the water to be treated.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The wastewater treatment method of the present invention will be specifically described in detail. In the present invention, first, ozone is independently added to wastewater in the first step for treatment, and the resulting water to be treated is treated in the second step using both ozone and hydrogen peroxide. During this, the first step and / or the second step
The dissolved ozone concentration in the water to be treated at the process outlet is detected, and the first and / or the third step is performed so as to maintain a predetermined dissolved ozone concentration.
Alternatively, the pollutant can be efficiently oxidatively decomposed by controlling the amount of ozone added to the second step. The ozone is injected and added to the wastewater or the water to be treated together with the accompanying gas.

The present invention decomposes pollutants in the water to be treated by OH radicals generated by the reaction between ozone and hydrogen peroxide. On the other hand, OH radicals react with ozone and hydrogen peroxide. Then the strong oxidizing power disappears.
That is, if the concentration of ozone or hydrogen peroxide is too low, OH
The generation of radicals is small, and if the concentration of ozone or hydrogen peroxide is too high, the generated OH radicals react with ozone or hydrogen peroxide without oxidizing pollutants and disappear,
In either case, the expected processing is not performed. 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 Dissolved ozone rarely hinders the treatment. Rather, the treatment reaction often does not proceed because the concentration of dissolved ozone in the liquid phase is too low.

Therefore, if the amount of ozone added to the wastewater or the water to be treated is too small relative to the amount of the pollutants, the ozone is consumed by the reaction with the pollutants in the water to be treated, and the dissolved ozone concentration can be kept high. And no opportunity to generate OH radicals upon contact with hydrogen peroxide. As a result, the effect is almost the same as the treatment with ozone alone, or the reaction with hydrogen peroxide is inhibited. Therefore, in the initial stage of wastewater treatment, it is rather necessary to use ozone alone and carry out the treatment until the required residual ozone concentration can be maintained. Conversely, if the wastewater contains too little pollutants,
Since the residual ozone concentration in the water to be treated becomes high and ozone is hardly absorbed, the rate of wasteful use of the added ozone is increased and the use efficiency of ozone is reduced. It is more advantageous to add hydrogen peroxide to OH to generate OH radicals and to treat the OH radical.

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, if the concentration is too 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 the pollutants is relatively small. If the value is close to the above, the treatment can be performed almost properly as long as ozone is sufficiently supplied.

From the above findings, a wastewater treatment method comprising a first step of treating pollutants by adding ozone alone to wastewater and a second step of adding both ozone and hydrogen peroxide to the water to be treated. Monitoring the concentration of ozone remaining in the water to be treated at the process outlet and controlling the amount of ozone added so as to maintain the concentration within the required range, thereby changing the concentration of pollutants in the wastewater or water to be treated. It is possible to perform an efficient process that follows. The amount of ozone added may be controlled by detecting the concentration of ozone remaining in the water to be treated, and in accordance with a target value determined in advance by experiments and experiences and determined by the concentration and type of pollutants in the wastewater. In the second step, by detecting the residual ozone concentration, it is possible to stabilize the generation amount of OH radicals, and it is possible to perform processing that is stabilized with respect to the target level of wastewater purification.

The specific target value of the dissolved ozone concentration is difficult to specify unconditionally according to the type and concentration of the substance to be treated, the type and concentration of the coexisting substance, the processing apparatus, the gas-liquid contact state, and the like. It is preferable to determine it empirically.
In general, at the inlet of the second step, 0.1 to 10mg /
A liter. If the concentration is less than 0.1 mg / l, the concentration of dissolved ozone is too low to perform the treatment in the second step sufficiently. Increase. At the outlet of the second step, 0.1 to 2 mg /
Liters, preferably in the range of 0.3 to 1 mg. Should be maintained. If it is less than 0.1 mg / liter, control becomes difficult, and if it is more than 2 mg / liter, useless surplus ozone will be discharged out of the system. By controlling the amount of ozone added by the above means, it is possible to treat water to be treated containing high-concentration pollutants, which is difficult to treat only by controlling the concentration of hydrogen peroxide. It is possible to prevent wasteful consumption of ozone by uniformly adding an amount of ozone that can cover the entire fluctuation range.

The control of the amount of added ozone may be performed by controlling the total amount of gas including the accompanying gas, or by controlling the concentration of ozone in the gas. Further, the amount of ozone generated may be controlled by adjusting the ozone generator itself. Generally, it is 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.

There is no particular limitation on the method of adding ozone, and for example, a diffuser type or an ejector type can be adopted. However, when the concentration of the pollutants is high, there is a limit to the absorption of ozone by a single bubble column. The residence time of the water to be treated in the ozone dissolving tank is generally in the range of 1 to 60 minutes, preferably 5 to 25 minutes.
Minutes.

Ozone can be supplied using various types of ozone generators including a silent discharge method, and there is no particular limitation. However, as the concentration of ozone contained in the gas is higher, the dissolution of ozone in the water to be treated is promoted, so that at least 20 mg, preferably 50 mg, per liter of gas is used.
It is good to contain more than mg of ozone. 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. The average diameter of the supplied ozone gas bubbles depends on the properties of the water to be treated.
m is preferable, and a range of 10 to 1000 μm is particularly preferable because the consumption of the dispersion energy is small in spite of the large gas-liquid contact area. Exhaust gas containing ozone can be added to wastewater as a pretreatment.

In the water treatment method of the present invention, by controlling the amount of hydrogen peroxide in addition to the control of the amount of ozone added, more efficient treatment and more precise processing than when only the amount of ozone is controlled. Control becomes possible. The concentration of hydrogen peroxide to be added to the water to be treated cannot be specified unconditionally according to the type and concentration of the substance to be treated and the coexisting substance contained in the water to be treated, the concentration, the treatment equipment, the amount of ozone used, and the gas-liquid contact conditions. Usually, 0.1 to 1 liter of treated water
100 mg, preferably in the range of 0.5 to 50 mg. In general, there is an optimum value for the concentration of hydrogen peroxide in the water to be treated. Therefore, it is preferable to experimentally and empirically determine the optimum amount of hydrogen peroxide to be added.

Although the method of adding hydrogen peroxide is not particularly limited, the treatment reaction with OH radicals is inhibited even at a high concentration locally. Add it in multiple portions at different concentrations,
It is preferable to add continuously or to be sufficiently stirred. 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 optimal amount of hydrogen peroxide tends to be.

The hydrogen peroxide to be added may be a commercially available hydrogen peroxide solution or may be directly supplied from a hydrogen peroxide production device. Hydrogen peroxide water electrolytically produced using an aqueous solution of sodium hydroxide as an electrolytic solution can also be used. There is no particular limitation on the concentration of the hydrogen peroxide solution added to the water to be treated, and the concentration may be easily controlled in consideration of the amount added, pump performance, and the like. The treatment temperature may be any range as long as the water to be treated retains a liquid phase, but is usually at room temperature. 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.

A specific embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a view schematically showing an example of a continuous multi-tank type wastewater treatment. The waste water is sent from the pipe 6 to the reaction tank 1a in the first step by the pump 3. Ozone is injected into the reaction tank 1a together with the accompanying gas from the pipe 7 through the flow controller 5a. At the inlet side of the reaction tank 1b, an ozone concentration meter 4a
And the dissolved ozone concentration is measured, and the amount of injected ozone is controlled by the flow controller 5a so that the measured value becomes a predetermined value. The water to be treated treated in the reaction tank 1a is introduced into the reaction tank 1b in the second step together with the hydrogen peroxide solution supplied from the pipe 8. At the outlet side of the reaction tank 1b, an ozone concentration meter 4b was attached to measure the dissolved ozone concentration.
The amount of injected ozone is controlled by the flow controller 5b so that the measured value becomes a predetermined value. The water to be treated, which has been treated in the reaction tank 1b, is introduced into the retention tank 2 and aerated with air blown from the pipe 9, and is taken out as treated water. Further, the exhaust gas discharged from the reaction tanks 1a and 1b in the first step and the second step and the retention tank 2 is sent to an ozonizer (not shown) through a pipe 10 and is discharged.

[0020]

EXAMPLE An experiment and a comparative experiment of the present invention were conducted using a flow-type experimental apparatus comprising the first step and the second step having the same configuration as that shown in FIG. explain. The treatment efficiency in the examples and comparative examples 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 after the second step treatment C ₀ : water pollution index after supply of the first step, water pollution The COD value was used as an index.

Example 1 In order to match the actual situation, the supply water to the first step was adjusted in the following order along with the elapsed time, and the concentration of pollutants was changed.
The experiment was performed for 0 hours. Start of experiment-2 hours Supply of leachate secondary wastewater from waste landfill 2-4 hours Supply water is diluted 2 times with fresh water and supply 4-6 hours The supply water is further diluted 2 times Supply 6-8 hours Leachate from waste landfill Leachate secondary supply water 8-10 hours Dissolve ozone concentration in treated water on the inlet side of the second step during supply experiment by diluting the above supply water 4 times with fresh water Is measured by an ozone concentration meter 4a (ultraviolet absorption method),
The treatment was performed by controlling the amount of added ozone using the flow rate controller 5a so that the dissolved ozone concentration was 2 mg / liter.
During this time, the flow controller 5b controlled the flow rate to be constant. COD in the water to be treated at the outlet of the second process every hour
And the amount of added ozone was measured. C obtained from measurement results
FIG. 2 shows the relationship between the OD processing efficiency (%) and the elapsed time (hr).
The total amount of ozone added (initial amount (total ozone added 80 mg
/ Liter) and the elapsed time (hr) are shown in FIG.

Example 2 As in Example 1, except that the flow rate is controlled to be constant by the flow controller 5a, and the dissolved ozone concentration in the water to be treated at the outlet of the second step is measured by the ozone concentration meter 4b (ultraviolet absorbance method). Then, an experiment was performed by controlling the amount of added ozone using the flow controller 5b so that the measured dissolved ozone concentration was 0.5 mg / liter. Every hour, the COD and ozone addition amount in the water to be treated at the outlet of the second step were measured. As in Example 1, the relationship between the processing efficiency obtained from the measurement results and the elapsed time is shown in FIG. 2, and the relationship between the ozone addition amount and the elapsed time is shown in FIG.

Example 3 As in Example 1, except that the ozone concentration in the water to be treated at the outlet of the first and second steps was measured by the ozone concentration meters 4a and 4b, and the dissolved ozone concentration was 2 mg / liter at 4a. The experiment was performed by controlling the amount of ozone added using the flow controllers 5a and 5b so that the amount became 0.5 mg / liter at 4b. COD and the amount of added ozone were measured in the same manner as in Example 1. FIG. 2 shows the relationship between the processing efficiency and the elapsed time obtained from the measurement results, and FIG. 3 shows the relationship between the amount of added ozone and the elapsed time.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1 except that the amount of ozone added to the first step was controlled to be constant. COD as in the first embodiment
FIG. 2 shows the relationship between the processing efficiency and the elapsed time obtained from the measurement results, and FIG. 3 shows the relationship between the ozone addition amount and the elapsed time.

Comparative Example 2 As in Example 3, except that hydrogen peroxide was added to the wastewater supplied to the first step at a rate of 3 mg / liter. COD and the amount of added ozone were measured in the same manner as in Example 1. FIG. 2 shows the relationship between the processing efficiency and the elapsed time obtained from the measurement results, and FIG. 3 shows the relationship between the amount of added ozone and the elapsed time.

Example 4 Eight hours after the start of the experiment of Example 3, the concentrations of dissolved ozone and hydrogen peroxide in the water to be treated before and after the storage tank 2 were measured. As a result, the dissolved ozone concentration was 0.5 mg / liter and the hydrogen peroxide concentration was 0.3 mg / liter before the retention tank 2, whereas the dissolved ozone concentration was 0.1 mg / liter after the retention tank 2. Liter and the concentration of hydrogen peroxide were 0.1 mg / liter.

Example 5 A treatment test was carried out in the apparatus shown in FIG. 1 using sewage secondary treated water. However, the flow controllers 5a and 5b were respectively changed so that the dissolved ozone concentration in the dissolved ozone concentration meter 4a was 2 mg / liter and the dissolved ozone concentration in the dissolved ozone concentration meter 4b was 0.5 mg / l. FIG. 4 shows the amount of ozone added per liter of water to be treated (mg / liter) and the change over time (hr) in COD treatment efficiency in the first step and the second step.

COMPARATIVE EXAMPLE 3 Under the same conditions as in Example 5, but without changing the settings of the flow controllers 5a and 5b according to the detection values of the dissolved ozone concentration meters 4a and 4b, Process 15mg / liter, 2nd process 10m
g / liter). FIG. 5 shows the changes over time in the dissolved ozone concentration (mg / liter) and the COD treatment efficiency measured by the ozone concentration meters 4a and 4b.

[0029]

According to the present invention, it becomes possible to add an appropriate amount of ozone in response to a change in the concentration of the water to be treated, and the treatment efficiency with ozone is improved. The amount of ozone added can be reduced, and the processing cost can be kept low.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an example of a distribution processing mode according to the present invention.

FIG. 2 shows the relationship between COD processing efficiency and elapsed time.

FIG. 3 shows the relationship between the total amount of added ozone and the elapsed time.

FIG. 4 shows the relationship between the amount of ozone added, COD treatment efficiency, and elapsed time (Example 4).

FIG. 5 shows the relationship between dissolved ozone concentration and COD treatment efficiency and elapsed time (Comparative Example 3).

[Explanation of symbols]

1: reaction tank (a: first step, b: second step) 2:
Retention tank 3: Water pump 4: Ozone concentration meter 5: Ozone flow controller 6: Treated water pipe 7: Ozone supply pipe 8: Hydrogen peroxide water supply pipe 9: Air pipe 10: Exhaust gas pipe

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-55-149688 (JP, A) JP-A-55-56889 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/78 C02F 1/20 C02F 1/72

Claims (7)

(57) [Claims] 1. A wastewater treatment method comprising: a first step of adding ozone to wastewater for treatment; and a second step of adding ozone and hydrogen peroxide to the treated water treated in the first step for treatment. Wherein the amount of ozone added to the first step is controlled so that the concentration of dissolved ozone in the water to be treated on the inlet side of the second step is maintained at a predetermined value. 2. A wastewater treatment method comprising: a first step of adding ozone to wastewater for treatment; and a second step of adding ozone and hydrogen peroxide to the treated water treated in the first step for treatment. Wherein the amount of ozone added to the second step is controlled so that the concentration of dissolved ozone in the water to be treated at the outlet of the second step is maintained at a predetermined value. 3. A wastewater treatment method comprising: a first step of adding ozone to wastewater for treatment; and a second step of adding ozone and hydrogen peroxide to the treated water treated in the first step for treatment. Controlling the amount of ozone added to the first step so that the concentration of dissolved ozone in the water to be treated on the inlet side of the second step is maintained at a predetermined value, and So that the dissolved ozone concentration of
A wastewater treatment method comprising controlling the amount of ozone added to a process. 4. Dissolved water in the water to be treated on the inlet side of the second step.
Dzon concentration is maintained between 0.1 and 10 mg / l
To control the amount of ozone added to the first step
The wastewater treatment method according to claim 1, 2, or 3. 5. A method for dissolving dissolved water in the water to be treated at the outlet of the second step.
Dzon concentration is maintained between 0.1 and 2 mg / l
Thus, controlling the amount of ozone added to the second step
Wastewater treatment method according to any one of claims 1 to 4, characterized in that:
Law. 6. Addition by measuring the dissolved ozone concentration of the water to be treated.
The amount of ozone to be added is controlled, and the amount of hydrogen peroxide
Control to 0.1 to 100 mg per liter of treated water
The method according to any one of claims 1 to 5, wherein
Water treatment method. 7. The wastewater treatment method according to claim 1 , wherein the treated water treated in the second step is aerated to remove dissolved ozone in the treated water. .