JPH0691258A - Method for removing hydrogen peroxide - Google Patents

Abstract

PURPOSE:To remove surely hydrogen peroxide and to attempt to improve simplicity and versatility on application by a method wherein a waste water contg. hydrogen peroxide is brought into contact with a particulate activated carbon suspended at a specified ratio, and then, it is separated therefrom and the separated particulate activated carbon is returned to a contacting process. CONSTITUTION:A treating tank 1 has a double tank structure divided into an inside contacting part 11 and an outside sedimentation part 12 and a waste water feeding inlet 3 is provided on the bottom and the waste water contg. hydrogen peroxide is fed into an upward stream. In addition, a metal net 5 with a fine mesh is provided on the lower part and a particulate activated carbon suspended with a ratio of 1-35% of the effective vol. of the tank is filled thereon and another waste water feeding hole 4 is opened on the neighborhood of the upper part of the net 5 from which a waste water contg. hydrogen peroxide is fed along the side face of the contacting part 11 in the tangent direction to make the activated carbon-suspended water flow in the contacting part 11 and to stir it. In addition the activated carbon settled and accumulated on the bottom of the sedimentation part 12 is returned to the contacting part 11 from the opening 6 of the sedimentation part with the waste water from the waste water feeding hole 4 and the treated water which has been separated into a solid and a liq. is made flow out of a discharge pipe 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for effectively removing hydrogen peroxide from industrial wastewater containing a relatively low concentration of hydrogen peroxide, such as semiconductor manufacturing wastewater, metal surface treatment wastewater and plating wastewater. It is a thing.

[0002]

Hydrogen peroxide is a cleaning agent, an oxidizing agent, a decolorizing agent,
It is widely used industrially as a bactericide, etc., and is stable when it is discharged to wastewater at a relatively low concentration (tens to thousands of mg / liter), and it cannot be removed efficiently. It's not easy.

As a method for removing hydrogen peroxide in waste water, a treatment of reducing hydrogen peroxide in waste water with sodium bisulfite (NaHSO ₃ ) is well known. In this method, sulfuric acid is produced as a reaction product and the pH shifts to the acidic side, so that pH monitoring and alkali injection control are required. Further, in this method, whether or not the decomposition of hydrogen peroxide is completed is usually monitored by monitoring the redox potential (ORP) and controlling the chemical injection of sodium bisulfite. ORP is defined as the concentration ratio of oxidizing substances and reducing substances, but in a multi-component system such as wastewater, it cannot always be an index indicating the completion of decomposition of hydrogen peroxide, and the chemical injection control becomes insufficient. easy. As described above, in the reduction method using sodium bisulfite, the control system is complicated and it is difficult to perform a reliable operation.
The running cost also increases because a lot of chemicals have to be used.

A method of decomposing and removing by adjusting the pH of an aqueous solution containing hydrogen peroxide to 10 or more and passing the aqueous solution through a granular activated carbon filling tank in a downward flow is disclosed in JP-A-62-270.
No. 90 publication. In this method, the pH of the liquid
The requirement is to increase the hydrogen peroxide removal rate to 10 or more, but from a different perspective, neutralization of the pH is required when the liquid after hydrogen peroxide removal is released to public areas. Is self-evident, and therefore the control system is complicated and the amount of chemicals used is large. On the other hand, even if the pH is set to be high, hydrogen peroxide cannot be completely decomposed in the surface layer of the activated carbon filling tank, so that means for degassing is required and the apparatus becomes complicated.

[0005]

SUMMARY OF THE INVENTION The present invention was devised to solve the above-mentioned drawbacks of the prior art.
It is possible to reliably decompose hydrogen peroxide in waste water without using chemicals such as acids and reducing agents or a control device, and to provide a method that is simple and highly versatile in practice.

[0006]

The above object can be achieved by the method for removing hydrogen peroxide of the present invention. That is, 1) After contacting the waste water containing hydrogen peroxide with the granular activated carbon suspended at a ratio of 1 to 35% of the effective volume of the tank in the contact step of keeping in a fluidized stirring state, the granular activated carbon and the treated water are contacted with each other. A method for removing hydrogen peroxide, characterized in that the mixed water is separated in a sedimentation step, and the separated granular activated carbon is returned to the contact step. 2) Waste water containing hydrogen peroxide having a tank effective capacity is used. 1-35
% Of the particulate activated carbon suspended in the contact step of maintaining the fluidized stirring state, and the granular activated carbon and treated water are separated by a screen at the outflow portion of the contact step to remove hydrogen peroxide. Is the way

3) In a treatment tank having a contact portion and a sedimentation portion, a waste water containing hydrogen peroxide is suspended in the contact portion at a ratio of 1 to 35% of the effective volume of the contact portion and kept in a state of fluidized stirring with granular activated carbon. While making contact, the mixed water of the granular activated carbon and the treated water overflows from the upper part of the contact portion to the sedimentation portion, and the granular activated carbon and the treated water are separated by sedimentation in the sedimentation portion, and the separated granular activated carbon is treated water. And a part of the treated water is discharged from the upper part of the sedimentation part to the outside of the system.

To keep the waste water containing hydrogen peroxide in a state of fluidized stirring with the granular activated carbon suspended at a ratio of 1 to 35% of the effective volume of the tank means that the waste water filled in the mixing tank and the granular activated carbon are kept. It means that the weight of the granular activated carbon in the tank effective volume occupied by and is 1 to 35%.

[0009] One method of the present invention is characterized in that (1) solid-liquid separation of hydrogen peroxide-containing wastewater and activated carbon is performed by a sedimentation method in an adjacent step, and another method of the present invention is ( 2) The solid-liquid separation of the hydrogen peroxide-containing wastewater and the granular activated carbon is carried out by filtering with a screen in the same step, and the third method of the present invention is (3) the hydrogen peroxide-containing wastewater and the activated carbon. The solid-liquid separation of (1) is performed by a sedimentation method in the circulation process of mixed water, and the activated carbon that has sedimented can be recycled. Particularly, in the third method, both of them are mixed and contacted very well in order to efficiently remove hydrogen peroxide from the hydrogen peroxide-containing wastewater, and the control thereof is easy.

In any of the above methods (1), (2) and (3), the method of the present invention selects an extremely wide range of mixing ratio of waste water and activated carbon in the hydrogen peroxide decomposition tank (contact tank). However, this is a method that can efficiently maintain the hydrogen peroxide decomposition reaction at the contact interface between the waste water and activated carbon, and enables reliable decomposition and removal of hydrogen peroxide.

It is said that hydrogen peroxide is unstable under alkaline conditions and easily decomposes into water and oxygen, but it is often stable for a long period of time when it has a low concentration and a substance such as an organic acid coexists. Although metal oxides, noble metal dust, activated carbon, and the like are known as decomposition catalysts used for catalytic decomposition capable of efficiently decomposing low-concentration hydrogen peroxide, granular activated carbon was used in the present invention. The reason for selecting activated carbon is that it is industrially available and that the decomposition reaction of hydrogen peroxide occurs efficiently due to the large specific surface area per unit weight. Activated carbon reacts with hydrogen peroxide to change into CO and CO ₂ , but basically it is a catalyst, and the loss in the decomposition reaction of hydrogen peroxide is negligible. However, it is necessary to replenish the damage lost by the outflow from the system caused by the destruction due to the collision during the mixing and stirring.

In the catalytic decomposition method using activated carbon as a catalyst, the hydrogen peroxide-containing wastewater comes into contact with the activated carbon in the contact tank, and the hydrogen peroxide is decomposed at the active points on the surface of the activated carbon to change into water and oxygen. Oxygen generated by decomposition grows into fine bubbles on the surface of activated carbon, but is released into the atmosphere because it desorbs when the shearing force generated by mixing exceeds the adhesive force of bubbles. Therefore, the reaction interface is not lost due to the adhesion of bubbles, and the hydrogen peroxide decomposition reaction proceeds sequentially. Therefore, in order to efficiently proceed the treatment of hydrogen peroxide-containing wastewater by the activated carbon catalytic decomposition method and to maintain the activity, it is necessary to desorb the generated oxygen fine bubbles from the activated carbon surface and to remove the desorbed oxygen into the atmosphere. Good radiation is important. Therefore, it is preferable that the contact system between the waste water and the activated carbon be in a stirring state and open to the atmosphere.

Further, in order to facilitate the management of the treatment of hydrogen peroxide-containing wastewater by the activated carbon catalytic decomposition method, it is easy to control the amount of wastewater supplied to the contact tank, and it is possible to recycle the granular activated carbon. Is an important factor. For example, if a large amount of wastewater containing hydrogen peroxide is discharged irregularly, a temporary storage tank will be prepared, and the wastewater will overflow from the contact tank and the activated carbon will also overflow at the same time. The structure is such that the suspension can be circulated in the contact tank so that it can be controlled, and conversely, a structure that can treat a small amount of waste water is also adopted.

The treatment efficiency of hydrogen peroxide-containing wastewater by activated carbon seems to depend on the amount of activated carbon filled in the treatment tank and the time during which the wastewater contacts the activated carbon. In the method for removing hydrogen peroxide of the present invention, the weight of the activated carbon filled in the contact tank is used in the range of 1 to 35% of the effective tank capacity as described above, but in consideration of various factors, the contact tank is usually used. 5 to 2 of the volume of
It is expedient to charge in a weight of 0% of granular activated carbon. In addition, the time for keeping the wastewater containing hydrogen peroxide in the contact tank while keeping it in a fluidized agitated state is usually appropriate in the range of 10 to 60 minutes.

It has been found that the decrease in the concentration of hydrogen peroxide in the contact tank has a good correlation with the value of the parameter x · t described below. Here, when x is the weight w of the activated carbon charged in the effective capacity V of the contact tank, x = (w /
V)%, and t is a value representing the time during which the wastewater stays in the contact tank in minutes. When the above-mentioned conditions of the present invention are represented by the above x and t, x is 1 to 35 and t is 10
Values of .about.60, therefore the preferred treatment conditions for the removal of hydrogen peroxide according to the invention are values of the parameter x.multidot.t of 20.
It can be said that the range is up to 2100. However, removal of hydrogen peroxide has effects on wastewater properties such as initial concentration, pH, and water temperature, and the performance of activated carbon, and it is practically preferable that the range of the parameter x · t for removing hydrogen peroxide is 50 to 30.
It can be said that it is between 0.

As a stirring method for placing the contact system of waste water and activated carbon in a stirring state, the waste water is flowed into a contact tank and kept in a fluidized stirring state by a water flow in the tank, and the bottom of the contact tank is kept from outside the system. Various methods such as a method of blowing a gas such as compressed air to maintain a fluidized stirring state and a method of mechanically stirring a contact system of wastewater and activated carbon can be used.
However, the mixed state of the waste water and the activated carbon does not need to be uniform, and the activated carbon concentration in the upper part of the contact tank may be sparse and the lower part may be dense. Depending on the granular distribution of the granular activated carbon, the concentration of activated carbon will inevitably be sparse or dense, but the wastewater will come into turbulent contact with activated carbon without strong mixing to make it uniform. If stirring is carried out to such an extent that it does not settle on the bottom, there is practically no problem. Further, for the decomposition of hydrogen peroxide, one of the important factors is to use the activated carbon in a weight corresponding to 1 to 35% of the effective tank capacity, but maintaining the fluidized stirring state is also an important factor. .

The first method of maintaining the fluidized stirring state with the granular activated carbon for suspending the wastewater containing hydrogen peroxide in the contact tank is a method of mechanically stirring with a stirrer. In this case, granular activated carbon is put in a tank having a volume corresponding to the amount of waste water, and the waste water is supplied to the tank by either a batch system or a continuous system, and the parameter x · t is, for example, 50 to 3
Hydrogen peroxide can be removed by treating the wastewater under conditions between 00. FIG. 4 shows a specific example of the case where waste water is continuously supplied and mechanically stirred for treatment.
In FIG. 4, the waste water is supplied to the contact tank 21 by the supply pump 2.
The waste water is supplied from the waste water supply pipe 20, and the granular activated carbon and the waste water are stirred and contacted by the stirrer 22 in the contact tank 21, and the waste water is treated under the condition that the parameter x · t is 130 for a certain period of time. After the contact treatment, mixed water of treated water and activated carbon is introduced into the settling tank 8 through the water supply pipe 9, and the activated carbon is allowed to settle in the settling tank 8 to be separated from the treated water. Treated water is treated water outlet 7
And the activated carbon is returned to the contact tank 21 by the return pipe 10.

A second method of maintaining the fluidized stirring state with the granular activated carbon for suspending the wastewater containing hydrogen peroxide in the contact tank is a method of stirring the wastewater by supplying the wastewater to the contact tank. As a method of supplying the wastewater to the contact tank, there is a method of inflowing the wastewater from the bottom of the tank and causing the wastewater in the contact tank together with the granular activated carbon to generate a water flow for treatment. As another method, there is a method of forming a layer of granular activated carbon in the contact tank, supplying wastewater in an upward flow from below the support plate, and treating through the layer of granular activated carbon. In this case, it is also possible to strengthen the contact between the wastewater and the granular activated carbon by inflowing the wastewater from the middle stage of the tank and superimposing a spiral flow on the upward flow of the activated carbon / wastewater mixture system by the wastewater flow. . As a method for forming the granular activated carbon layer, a known method may be used with or without a supporting plate provided below.

Further, as a third stirring method, there is a method using aeration. In this case, an air lift pipe or air diffuser pipe is provided in the contact tank to bring granular activated carbon into contact with wastewater containing hydrogen peroxide, so that gas bubbles such as air are supplied to maintain a good fluid agitation state by aeration. You can

When actually designing the hydrogen peroxide removal apparatus, the factors such as the tank capacity, the stirring method, the amount of activated carbon, and the particle size of activated carbon are not particularly limited in their numerical values, and can be freely selected in consideration of individual circumstances such as contact means and site area. Various choices are possible. However, it is desirable to carry out an experiment in advance in order to perform a lean design.

Regardless of which stirring method is used, if the wastewater and the activated carbon are placed in a sufficiently good contact with each other, the activated carbon will overflow from the contact tank. In order to prevent this overflow and separate the granular activated carbon from the wastewater, as shown in FIG. 2, a screen 13 having an opening corresponding to the granularity of the activated carbon is provided at the wastewater outflow portion above the contact tank 21.
The screen 13 may be a wire mesh, but is preferably of a type having a clogging prevention means.

As another solid-liquid separation method of waste water and granular activated carbon, as shown in FIG. 3, mixed water of treated water and granular activated carbon discharged from the contact tank 21 is granulated by a mixed water feed pipe 9. Water may be sent to the settling tank 8 for activated carbon, and the granular activated carbon may be settled in the settling tank 8 for solid-liquid separation. The granular activated carbon settled in the settling section is returned to the contact tank 21 by the activated carbon return pipe 10 and reused. This type of treatment method is more complicated than the one-tank treatment method using a screen for solid-liquid separation, but does not affect the removal efficiency of hydrogen peroxide, and does not have the same effect as when a screen is used. There is an advantage that it is not necessary to use a clogging prevention means.

It is also possible to use a treatment tank including the sedimentation section as a single tank. That is, as shown in FIG. 1, the treatment tank 1 has a double structure, and the mixed water of the treated water and the granular activated carbon overflowed from the inner contact portion 11 is guided to the outer tank (settling portion) 12 and allowed to stay there for a while. To settle the granular activated carbon,
The supernatant water is a method of discharging the treated water from the treated water discharge pipe 7. In this case, the settled granular activated carbon can be naturally returned to the inner contact portion 11. Also, it may be forcibly returned. Further, the single-tank treatment tank shown in FIG. 1 has a double structure, but the treatment tank does not need to have a completely double structure and sediments between the contact portion 11 and the treated water discharge pipe 7. It suffices that there is a portion 12 in which the activated carbon settles and the settled activated carbon returns to the contact portion 11.

[0024]

EXAMPLES The method for removing hydrogen peroxide of the present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

(Embodiment 1) FIG. 2 shows an embodiment 1 of the present invention.
An example is shown. In FIG. 2, the contact tank 21 has an effective capacity of 10 liters. Below the contact tank 21, a wire net 5 having a finer opening than the particle size of the granular activated carbon is provided, and the granular activated carbon is filled thereon. There are wastewater supply ports 3 and 4 opening near the bottom of the contact tank 21 and the upper part of the wire net 5, respectively, and a wastewater supply pipe 20 is connected to each of the wastewater supply ports 3 and 4, and the wastewater supply pipe 20 is supplied through them. Waste water containing hydrogen peroxide is supplied to the contact tank 21 by the pump 2. At this time, the inflow of the waste water from the waste water supply port 4 is carried out along the side surface of the tank 1, and the water flow causes the inflow of the tank 2
The activated carbon suspension water in 1 is stirred.

At the upper part of the contact tank 21, there is a treated water discharge pipe 7 equipped with a screen 13, and the uppermost part of the contact tank 21 is opened to disperse the generated gas. Furthermore, on the upper part of the screen 13, a rotating brush 1 for preventing clogging is provided.
4 is installed, and the opening of the screen 13 is ensured while gently rotating from the inside to the outside of the contact tank 21. The activated carbon suspension water, which has been stirred in the contact tank 21 and has been sufficiently retained to decompose and remove hydrogen peroxide, is subjected to solid-liquid separation by the screen 13, and then flows out from the treated water discharge pipe 7 as treated water.

Table 1 and FIG. 5 show the results of treating the metal surface treatment wastewater with the apparatus shown in FIG. First
In the table R. T. Represents the residence time (t) in the contact tank 21, and x represents the amount of activated carbon used in the contact tank 21. In Example 1, the activated carbon used was crushed carbon of 10 to 16 mesh. The pH of the reaction water was neutral.

[0028]

[Table 1]

When the amount of activated carbon used was 2.0%, the retention time of the waste water was 40 min, and when the amount of the activated carbon used was 5.0%, the hydrogen peroxide could be completely decomposed and removed in the retention time of the waste water 20 min.

(Embodiment 2) FIG. 1 shows another embodiment of the present invention. In FIG. 1, the processing tank 1 has a double tank structure in which an inner contact portion 11 and an outer sedimentation portion 12 are divided into inner and outer tanks. The lower part of the treatment tank 1 has a narrowed inverted trapezoidal shape, a waste water supply port 3 is provided at the bottom, and waste water containing hydrogen peroxide goes upward from the waste water supply port 3 through a waste water supply pipe 20. Supplied in flow. In addition, a wire net 5 having a finer opening than the particle size of the granular activated carbon is provided in the lower part of the processing tank 1, and the granular activated carbon is filled thereover. Another wastewater supply port 4 is opened near the upper part of the wire net 5, and wastewater containing hydrogen peroxide is supplied in a tangential direction along the side surface of the inner contact portion 11 through the wastewater supply pipe 20, and the inner side is formed by the water flow. The activated carbon suspension water in the contact portion 11 of is agitated.

In addition, in the vicinity of the opening of the wastewater supply port 4, there is a settling part opening 6 at the bottom of the outer settling part 12, and the activated carbon that has settled and accumulated is tangentially supplied from the wastewater supply port 4. It is refluxed into the inner tank. The treated water treated with the suspended activated carbon in the inner contact portion 11 once flows into the tank of the outer sedimentation portion 12, and the activated carbon sediments and accumulates in the lower portion. The treated water in which the activated carbon has settled and solid-liquid separated flows out from the treated water outlet 7. Further, the activated carbon deposited on the lower portion is refluxed into the contact portion 11 from the sedimentation portion opening 6 as described above.

Table 2 and FIG. 6 show the results of treating semiconductor manufacturing wastewater containing a higher concentration of hydrogen peroxide using the same apparatus as in Example 2. In this Example 2, the amount of activated carbon used was 5.0% and the pH of the reaction water was 7%.
However, there was no big difference in the decomposition rate between the two, and in each case, hydrogen peroxide could be almost completely decomposed and removed with the retention time of the waste water of 30 minutes. Further, the effect was the same even when the supply port 4 was closed, the supply port 3 was opened, and the waste water was supplied from the supply port 3.

[0033]

[Table 2]

(Embodiment 3) FIG. 3 shows another embodiment of the present invention. In FIG. 3, the contact tank 21 is filled with granular activated carbon. Waste water containing hydrogen peroxide is supplied from the bottom of the contact tank 21 through the waste water supply pipe 20 by the supply pump 2, and is contacted with the granular activated carbon layer to be treated. The air lift pipe 1 installed in the center of the contact tank 21 for stirring the granular activated carbon suspended water inside the contact tank 21.
9 is provided, and air is blown from the air supply pipe 16. A mixed water feed pipe 9 for discharging the mixed water is provided at the upper part of the contact tank 21, and the upper part thereof is opened to disperse the generated gas.

The waste water is mixed and stirred with the granular activated carbon by the flow of the waste water and aeration in the contact tank 21 and, after passing through the settling tank 8 enough to decompose and remove the hydrogen peroxide, the treated water discharge pipe 7 Is discharged as treated water. At this time, the granular activated carbon flowing out from the contact tank 21 together with the treated water is sent as mixed water to the activated carbon settling tank 8 through the mixed water feed pipe 9. The granular activated carbon is settled in the settling tank 8, and the activated carbon is returned to the contact tank 21 by the activated carbon return pipe 10.

[0036]

As described above, in the method for removing hydrogen peroxide of the present invention, the apparatus having a simple structure is used to decompose and remove the hydrogen peroxide contained in the wastewater and effectively remove the gas as the reaction product. It is possible to remove as much as possible and to perform solid-liquid separation of activated carbon and treated water. Further, since it is not necessary to use chemicals or control equipment, and the amount of activated carbon and the particle size thereof, which are important factors in operation, can be set in a wide range, the method for removing hydrogen peroxide of the present invention is Easy to manage,
This is an extremely practical method.

[Brief description of drawings]

FIG. 1 is a process flow diagram illustrating an example of a method for removing hydrogen peroxide using a double structure treatment tank by water flow stirring according to the present invention.

FIG. 2 is a process flow chart for explaining another example of the method for removing hydrogen peroxide by water flow stirring according to the present invention.

FIG. 3 is a process flow diagram illustrating an example of a method for removing hydrogen peroxide by aeration stirring according to the present invention.

FIG. 4 is a process flow diagram illustrating an example of a method for removing hydrogen peroxide by mechanical stirring according to the present invention.

FIG. 5 is a graph showing an example of reduction of residence time of waste water and concentration of hydrogen peroxide.

FIG. 6 is a graph showing another example of retention time of waste water and reduction of hydrogen peroxide concentration.

[Explanation of symbols]

 1 Treatment Tank 12 Settling Section 2 Pump 13 Screen 3 Waste Water Supply Port 14 Rotating Brush 4 Waste Water Supply Port 15 Blower 5 Wire Mesh 16 Air Supply Pipe 6 Settling Port Opening 17 Baffle 7 Treated Water Discharge Pipe 18 Activated Carbon 8 Settling Tank 19 Air Blow Pipe 9 Mixed water feed pipe 20 Waste water supply pipe 10 Activated carbon return pipe 21 Contact tank 11 Contact part 22 Stirrer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Abe 378, Oguni-machi, Oguni-cho, Nishiokitama-gun, Yamagata Prefecture Inside the Oguni Factory of Toshiba Ceramics Co., Ltd. (72) Makoto Yano 378, Oguni-cho, Oguni-cho, Nishiokitama-gun, Yamagata Prefecture Inside Toshiba Corporation Oguni Factory

Claims (3)

[Claims] 1. Waste water containing hydrogen peroxide is contacted with granular activated carbon suspended at a ratio of 1 to 35% of the effective volume of a tank in a contact step of keeping in a fluidized stirring state, and then the granular activated carbon and treated water are contacted with each other. The method for removing hydrogen peroxide, characterized in that the mixed water of 1. is separated in the sedimentation step, and the separated granular activated carbon is returned to the contact step. 2. Waste water containing hydrogen peroxide is contacted with granular activated carbon suspended at a ratio of 1 to 35% of the effective volume of a tank in a contact step of keeping in a fluidized stirring state, and the granular activated carbon and treated water are treated as described above. A method for removing hydrogen peroxide, characterized in that it is separated by a screen at the outflow portion of the contact step. 3. A granular activated carbon in which a wastewater containing hydrogen peroxide is suspended in the contact portion of a treatment tank having a contact portion and a sedimentation portion at a ratio of 1 to 35% of the effective volume of the contact portion and kept in a fluidized stirring state. While making contact, the mixed water of the granular activated carbon and the treated water overflows from the upper part of the contact portion to the sedimentation portion, and the granular activated carbon and the treated water are separated by sedimentation in the sedimentation portion, and the separated granular activated carbon is treated water. I sent it back to the contact part with a part of
A method for removing hydrogen peroxide, characterized in that a part of the treated water is discharged from the upper part of the sedimentation part to the outside of the system.