JPH07171561A - Hydrogen peroxide removal method using granular activated carbon packed tower - Google Patents

Abstract

PURPOSE:To treat an aqueous solution containing hydrogen peroxide efficiently and stably by a method wherein an aqueous solution containing hydrogen peroxide is passed through preceding and succeeding stages and when the concentration of hydrogen peroxide in treated water in a tower in the preceding stage has reached a predetermined range, the preceding tower is back-washed to remove bubbles, and thereafter the solution is passed again through the preceding and succeeding stages. CONSTITUTION:A preceding stage tower 4 and a succeeding stage tower 7, as granular activated carbon packed towers, are installed so that an aqueous solution containing hydrogen peroxide is passed downwardly through the tower 4 and tower 7 in series, In this case, the solution to be treated comes into contact with a preceding stage granular activated carbon layer 5 packed in the tower 4 so that the hydrogen peroxide in the solution is decomposed and removed. And when the hydrogen peroxide concentration in the solution of the tower 4 has become about 1mg/L, the tower 4 is back washed to remove bubbles in the layer 5 and thereafter the solution is passed again through the tower 4 and tower 7 in series, in this order. As a result, aqueous solution containing hydrogen peroxide of high concentration can be treated efficiently and stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently removing hydrogen peroxide from an aqueous solution containing hydrogen peroxide in a relatively high concentration, for example, waste liquid in a semiconductor manufacturing factory.

[0002]

2. Description of the Related Art In the electronic industry for manufacturing semiconductors, so-called ultrapure water is used for cleaning products, in which impurities such as fine particles, live bacteria and TOC are removed to the limit, as well as various ions.

Such ultrapure water is produced by making full use of various techniques such as filtration, ion exchange treatment, reverse osmosis membrane treatment, ultraviolet sterilization, etc. In order to maintain the purity of the ultrapure water,
The pipe for transferring ultrapure water is regularly cleaned. The cleaning of the pipe is especially required to remove slime deposited in the stagnant part of the pipe,
It is carried out for sterilization of the entire liquid contact part, and as the cleaning agent, an aqueous solution containing 0.15% by weight to 0.25% by weight of hydrogen peroxide is usually used. After that, the aqueous solution containing hydrogen peroxide used for the cleaning is collected for the purpose of periodically discharging it as waste liquid, reducing the cost of using the undiluted solution, and saving the amount of water required at the factory. Sometimes it is reused.

When the aqueous solution containing hydrogen peroxide is discharged as a waste liquid, the aqueous solution containing hydrogen peroxide cannot be discharged as it is because of the problem of COD regulation. When the aqueous solution containing hydrogen peroxide is collected and reused, the collected water is usually subjected to coagulation / precipitation treatment, ion exchange treatment, reverse osmosis membrane treatment, and the like.

In the above treatment process, if the recovered aqueous solution contains hydrogen peroxide even at a low concentration, for example, when the recovered liquid is subjected to a coagulation treatment, the polymer added in the aggregating step The coagulant is destroyed, the coagulation effect is reduced, and when the ion exchange treatment is performed, the hydrogen peroxide contained in the recovery liquid deteriorates the ion exchange resin. Further, the reverse osmosis membrane treatment has a problem that the membrane itself is deteriorated by hydrogen peroxide which is an oxidant.

For this reason, the waste liquid containing hydrogen peroxide is subjected to hydrogen peroxide removal treatment both when it is discharged and when it is recovered. A conventional method is to add a reducing agent such as sodium sulfite to the waste liquid to neutralize the oxidizing power of hydrogen peroxide.

However, in the neutralization reaction by the addition of sodium sulfite, the reaction time of hydrogen peroxide and sodium sulfite is relatively long as 2 to 3 hours, and therefore the reaction tank also becomes large, and when the amount of the waste liquid is large, the reaction tank is large. Requires a large installation area, and even if hydrogen peroxide remains in the treatment liquid, or conversely, sodium sulfite remains, it becomes unsuitable for discharge, and compared with the neutralization reaction of acid and alkali. The allowable range of discharge is extremely narrow, neutralization of redox is technically difficult, and its control is relatively complicated when it is automated. Therefore, the equipment cost of the reactor equipped with such a reaction tank, automatic control mechanism, and stirring mechanism is relatively high, and a reducing agent such as sodium sulfite is constantly required, resulting in high running cost. Have

As a method for removing hydrogen peroxide from an aqueous solution, in addition to the above-mentioned conventional method, a method of passing an aqueous solution containing hydrogen peroxide through an activated carbon packed tower to decompose and remove the hydrogen peroxide is used. There is.

A conventional method for treating an aqueous solution containing hydrogen peroxide with activated carbon is, for example, JP-A-62-27090.
There is a method disclosed in Japanese Patent Publication No. 5-7075. According to JP-A-62-27090,
An aqueous solution containing hydrogen peroxide whose pH was adjusted to 10 or more was made to flow down into a column composed of two upper and lower packed beds of granular activated carbon and a space attached to the lower part thereof, and the reducing power of the granular activated carbon was used. , A method of decomposing and removing hydrogen peroxide in an aqueous solution has been proposed.

According to this method, when the pH becomes 10 or more,
Since the decomposition rate of hydrogen peroxide becomes faster, it decomposes in the relatively upper part of the granular activated carbon packed bed, the amount of bubbles generated in the packed bed is extremely small, and the channeling phenomenon of hydrogen peroxide can be prevented. ing. However, p
A step of H adjustment is required, and for this reason a special pH
Since the adjustment tank and the neutralization after the treatment are required, the pH adjustment tank and the control system associated therewith cause a cost increase, and there are drawbacks such as an economical burden for adjusting the pH and an increase in salts in the wastewater. .

According to Japanese Examined Patent Publication No. 5-7075, a method is proposed in which the aqueous solution is passed through the granular activated carbon layer in an upward flow to bring the granular activated carbon into a fluidized bed for fluid contact. In this method, since the contact is made in the fluidized bed, the reduction of hydrogen peroxide by the activated carbon is carried out while constantly exposing the new surface of the activated carbon, so that the activity of the activated carbon slows down and the pH of the activated carbon is changed by the acid or alkali. It is said that no complicated adjustment is required.

However, in this method, when the activated carbon particles are fluidized as a property of the fluidized bed, a part of the activated carbon particles are crushed by contact with each other or with the tower wall to be fine particles, and these are fluidized. Since it shifts to the upper part of the tank and is discharged out of the tower together with the waste water, it is necessary to replenish or replace the granular activated carbon, and the granular activated carbon is relatively expensive, which leads to high cost. Further, in the fluidized bed, when the flow velocity of the fluid is increased, the fluidized bed expands and activated carbon particles flow out, so that the flow velocity has an upper limit and it is impossible to process at a flow velocity higher than a set value. Further, since the contact occurs in the fluidized bed, it is difficult to form an adsorption zone, and therefore it is doubtful whether the hydrogen peroxide concentration of the treated water can be constantly maintained at a low concentration level.

[0013]

The present invention has been made to solve these drawbacks and provides a method for efficiently and stably treating an aqueous solution containing hydrogen peroxide at a high concentration in a granular activated carbon packed tower. The purpose is to provide.

[0014]

Means for Solving the Problems That is, according to the present invention, when an aqueous solution containing hydrogen peroxide is passed through a granular activated carbon packed column to remove hydrogen peroxide, the granular activated carbon packed column is
At least two towers, a first tower and a second tower, are installed, and the above aqueous solution is passed in a downward flow in series in the order of the first tower and the second tower, and the hydrogen peroxide concentration of the treated water in the first tower becomes around 1 mg / L. Then, by backwashing the former column, the bubbles in the granular activated carbon layer are removed, and then the former column and the latter column are passed again in series in this order.

[0015]

[Function] The method of removing hydrogen peroxide by activated carbon is to decompose and remove hydrogen peroxide in an aqueous solution using the reducing power of granular activated carbon. However, the problem is that when the aqueous solution comes into contact with the granular activated carbon layer, Immediately a decomposition reaction occurs and oxygen is generated, which becomes bubbles and is trapped in the packed bed,
It can be mentioned that the bubbles cause a short path (channeling phenomenon) of the aqueous solution in the packed bed, which causes early leakage of hydrogen peroxide of the processing solution. Therefore, conventionally, it is inevitable to perform backwashing of the packed bed frequently to remove the bubbles, and a sufficient amount of water for backwashing must be secured.

By the way, the present inventor has conducted extensive studies and found that, for example, two granular activated carbon packed towers were provided and an aqueous solution containing a relatively large amount of hydrogen peroxide was passed in series to the packed tower. Bubbles are generated in the packed bed of the tower, but the period in which the bubbles are not generated in the packed bed of the latter tower is relatively long. The hydrogen peroxide concentration of the treated water in the former tower is 1
When it exceeds mg / L, in other words, when the hydrogen peroxide concentration of the inflow water of the latter stage column exceeds 1 mg / L, bubbles also start to be generated in the latter stage column. Therefore, even if air bubbles are generated in the packed bed of the pre-stage column, water continues to flow as it is, and when the hydrogen peroxide concentration in the treated water of the pre-stage column is around 1 mg / L, the pre-stage column is backwashed to remove bubbles. When the water is removed and water is again passed in series in the order of the former tower and the latter tower, bubbles will not be generated in the packed tower of the latter tower, and the hydrogen peroxide concentration of the treated water can be maintained at a low level. Moreover, it was found that when the front column was backwashed to remove bubbles and water flow was restarted, bubbles were generated again, but the hydrogen peroxide removal capability of the former column was restored.

The present invention is based on the above findings. The treated water is passed through two or more granular activated carbon packed towers in series to remove hydrogen peroxide in the treated water, and the packed bed of the pre-column is packed. Even if bubbles are generated therein, bubbles are not generated in the packed bed of the latter stage column so that the hydrogen peroxide concentration of the treated water is maintained at a low level.

[0018]

EXAMPLES Examples of the present invention will be described below. Figure 1
It is explanatory drawing which shows the Example of this invention.

(1) is a water tank to be treated, and (2) is an inflow pump. (3) is an inflow pipe, one end of which is connected to the treated water tank (1) and the other end of which is connected to the upper part of the pre-stage column (4).
(6) is a delivery pipe, one end of which communicates with the lower part of the front column (4) and the other end of which communicates with the upper part of the rear column (7). (9) is an outflow pipe, one end of which communicates with the lower part of the post-stage tower (7) and the other end of which communicates with the water storage tank (16). Further, (5) and (8) in the figure are the pre-stage granular activated carbon layer and the post-stage granular activated carbon layer, respectively. (10) is a water intake pipe, and (11) is a backwash pump used for backwashing. Also, (12),
(13) are the front-stage backwash pipe and the back-stage backwash pipe, respectively.
4) and (15) are the front tower backwash drain pipe and the rear tower backwash drain pipe, respectively. (30), (31), (32), (3
3), (34), and (35) show valves, respectively.

Next, the method for removing hydrogen peroxide according to the present invention will be described. The water to be treated flows down from the water tank to be treated (1) by the inflow pump (2) through the inflow pipe (3) in the former column (4) in a downward flow. At that time, the pre-stage granular activated carbon layer (5) filled in the pre-stage tower comes into contact with the liquid to be treated, whereby hydrogen peroxide in the liquid to be treated is decomposed and removed. After that, the pretreatment liquid flows down through the delivery pipe (6) connected to the lower part of the front column (4) from the upper part of the rear column (7) into the latter column (7) in a descending flow to form the second stage granular activated carbon. The treated water from the lower part of the latter-stage tower (7) passes through the layer (8), passes through the outflow pipe (9), and is sent to the water storage tank (16).

As the above-mentioned water flow is continued, bubbles are generated in the granular activated carbon layer (5) of the former column (4) due to the oxygen generated by the decomposition of hydrogen peroxide, but the water flow is continued as it is. To do.

The valve (31) is opened during the passage of the water, the outlet water of the pre-stage tower is sampled from the water intake pipe (10), and the hydrogen peroxide concentration of the pre-stage tower treated water is measured. Then, when the hydrogen peroxide concentration of the treated water in the former tower is around 1 mg / L (0.9 to 1.0 mg / L), the water flow is interrupted and the backwashing step of the former tower (4) is performed. There is. That is, the valves (30) and (35) are closed and the valve (3
2) and (34) are opened, and from the water storage tank (16) by the backwash pump (11) through the front stage backwash pipe (12),
By backwashing the former column (4), air bubbles generated in the former granular activated carbon (5) are removed.

The backwash water is discharged out of the system through the front tower backwash water discharge pipe (14). After the backwash is completed, the valve (30) is opened, the valves (32) and (34) are closed, and the water flow is restarted. During the backwashing of the front tower (4), the water to be treated in the water tank (1) is passed through the rear tower (7) directly through a pipe (not shown) for a short time. No bubbles are generated in the latter tower. Therefore, water may be passed through the rear tower during the backwashing of the front tower.

In addition, when the suspension tower (7) is clogged with suspended matters or the like after a long period of use and the pressure loss increases, the backwash pump (11) passes through the backwash pipe (13) to the backwash pipe (13). It is safe to backwash the tower (7).

FIG. 2 shows the concentration of hydrogen peroxide in the treated water of the pre-stage column when raw water containing hydrogen peroxide at a concentration of 100 mg / L was passed in series to the pre-stage column and the post-stage column packed with the same amount of granular activated carbon. It is a relationship diagram of water passage time. Although not shown in FIG. 2, the hydrogen peroxide concentration of the treated water in the latter column is 0.0 mg / l when the hydrogen peroxide concentration of the treated water in the former column is up to 1 mg / l.
It is L. As can be seen from FIG. 2, since the conventional method is a single-column treatment, the hydrogen peroxide concentration in the outlet water of the treatment column becomes 0.1 mg / L after 6 days, and it was necessary to enter the backwashing washing step of the packed column. However, by installing the latter-stage column as in the present invention, 1.0
Water can be passed up to mg / L. Therefore, the water flow time before backwashing can be greatly extended to about 290 days, and the operation time until backwashing can be made about 30 times longer than the conventional one.

[0026]

As described above, in the method of the present invention, hydrogen peroxide can be removed only by passing the stock solution through the granular activated carbon layer, so that a large reaction tank unlike the conventional method is not required and the installation area of the apparatus can be reduced. Therefore, the equipment cost of the apparatus can be made lower than that of the conventional one, and since it is not necessary to use the reducing agent, the running cost can be significantly reduced.

Furthermore, at least two towers, a front tower and a rear tower, are installed as the granular activated carbon packed tower, and the water to be treated containing hydrogen peroxide is passed in series in the order of the front tower and the rear tower, and the inlet of the latter tower is covered. By keeping the hydrogen peroxide concentration of the treated water at 1 mg / L or less at all times, the treatment is performed without bubbles in the packed bed of the latter stage column, so the hydrogen peroxide concentration of the latter stage treated water is always kept at a low level. Since it can be maintained, and moreover, the front-stage tower can continue to pass water until the hydrogen peroxide concentration of the treated water reaches 1 mg / L, the backwash interval is about 30 times longer than that of the conventional one-column treatment method. It can be extended and the amount of backwash water can be significantly reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a flow of an example of an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the water passage time in the former column and the concentration of hydrogen peroxide in treated water.

[Explanation of symbols]

 1. Water tank to be treated 2. Inflow pump 3. Inflow pipe 4. Front tower 5. Pre-stage granular activated carbon layer 6. Delivery pipe 7. Rear tower 8. Second stage granular activated carbon layer 9. Outflow pipe 10. Intake pipe 11. Backwash pump 12. Pre-stage backwash tube 13. Post-stage backwash tube 14. Front tower backwash water discharge pipe 15. Back tower backwash water discharge pipe 16. Water storage tank

Claims (1)

[Claims] 1. An aqueous solution containing hydrogen peroxide is passed through a granular activated carbon packed column to remove hydrogen peroxide, and at least two columns, a pre-column and a post-column, are installed as the granular activated carbon packed column. The above-mentioned aqueous solution was passed in a descending flow in series in the order of the pre-column and the post-column, and when the hydrogen peroxide concentration of the treated liquid in the pre-column was around 1 mg / L, the pre-column was back-washed to obtain granular activated carbon. A method for removing hydrogen peroxide by means of a granular activated carbon packed tower, characterized in that air bubbles in the bed are removed, and then the first-stage column and the second-stage column are passed again in series.