JP4511881B2 - Wastewater treatment method - Google Patents

Description

  The present invention relates to a method for treating various hydrogen peroxide-containing wastewater such as semiconductor manufacturing wastewater and food container washing wastewater, and in particular, treatment of hydrogen peroxide-containing wastewater that decomposes hydrogen peroxide contained in wastewater using a catalyst. Regarding the method.

  Hydrogen peroxide is an excellent cleaning and sterilizing effect, and is a clean chemical that decomposes into oxygen and water after the reaction. Therefore, it is widely used as a cleaning agent and sterilizing agent in the manufacturing process. For example, a semiconductor device manufacturing factory is used for cleaning wafers in various processes.

  Hydrogen peroxide used for cleaning and sterilization is discharged from the manufacturing process as waste liquid (hydrogen peroxide-containing waste water). Since this waste liquid has a sterilizing power and becomes a causative substance of COD (Chemical Oxygen Demand), it is not preferable to discharge it directly into public water areas.

  Conventionally, as a treatment method for hydrogen peroxide-containing wastewater, treatment using a reducing agent such as sodium sulfite and an enzyme agent such as peroxidase has been performed, but there are problems such as a large amount of chemicals used and high running costs. Met.

  On the other hand, a technique is known in which hydrogen peroxide is decomposed into water and oxygen using a catalyst such as activated carbon, a manganese-supported catalyst, or a platinum-supported catalyst. By using these catalyst treatment methods, the running cost required for treatment of hydrogen peroxide-containing wastewater can be reduced. In particular, activated carbon is suitable as a catalyst used for the treatment of wastewater containing hydrogen peroxide because it has a low market price and low risk of elution of harmful substances.

  Treatment of hydrogen peroxide-containing wastewater using activated carbon as a catalyst has the above-mentioned advantages, but the oxygen gas generated by the decomposition of hydrogen peroxide accumulates in the catalyst packed bed, so that contact between the wastewater and the catalyst occurs. As a result, there was a problem that the decomposition rate of hydrogen peroxide decreased.

  As a method for solving the above-mentioned problem, for example, in Japanese Patent Publication No. 6-61541 (Patent Document 1), after adjusting the raw water pH to 10 or more, by passing the liquid downward from the upper part of the activated carbon catalyst, Most hydrogen peroxide is decomposed at the upper part of the catalyst, and as a result, gas generation inside the catalyst can be suppressed.

  Japanese Patent Publication No. 1-203094 (Patent Document 2) proposes a method for preventing oxygen gas from accumulating in the activated carbon layer by using an upward flow as a water flow method and flowing the activated carbon layer. ing.

Japanese Examined Patent Publication No. 6-61541 Japanese Patent Publication No. 1-203094

  However, in the method of Patent Document 1, a large amount of pH adjusting agent is required to adjust the pH of the waste water to 10 or more, resulting in an increase in running cost.

  Moreover, in the method of patent document 2, when an activated carbon layer is made to flow, an activated carbon catalyst will flow out easily and it will be easy to lead to the deterioration of treated water quality. Moreover, since the activated carbon catalyst flows out, it is necessary to replenish the activated carbon catalyst, resulting in an increase in running cost.

  In the present invention, hydrogen peroxide-containing wastewater and a catalyst are brought into contact with each other, while preventing accumulation of oxygen gas in the catalyst layer and suppressing an increase in running cost due to addition of a pH adjuster or catalyst replenishment. This is a wastewater treatment method for decomposing hydrogen peroxide in wastewater.

The present invention is a wastewater treatment method in which hydrogen peroxide-containing wastewater is brought into contact with a catalyst to decompose hydrogen peroxide in the wastewater, wherein the catalyst has an equality factor of 1.4 or less and has a circularity. Is a spherical activated carbon having an average of 0.95 to 1.0 .

  Further, in the wastewater treatment method, the wastewater is brought into contact with the catalyst in a state where a fluidized bed of the catalyst is formed by passing the wastewater from above the catalyst layer filled with the catalyst by an upward flow. It is preferable to make it.

  Further, in the wastewater treatment method, it is preferable that the water treated with the catalyst is circulated to the lower part of the catalyst layer to give the catalyst layer a water flow rate sufficient for the catalyst to flow.

  In the present invention, when hydrogen peroxide containing wastewater and a catalyst are brought into contact with each other to decompose hydrogen peroxide in the wastewater, a spherical activated carbon having a uniform particle diameter is used as a catalyst, so that oxygen gas is accumulated in the catalyst layer. In addition, an increase in running cost can be suppressed.

  Hereinafter, embodiments of the present invention will be described.

  In a wastewater treatment method according to an embodiment of the present invention, in which a hydrogen peroxide-containing wastewater and a catalyst are brought into contact with each other to decompose hydrogen peroxide in the wastewater, spherical activated carbon having a uniform particle diameter is used as the catalyst.

  Activated carbon is widely used not only as a catalyst but also as an excellent adsorbent, and generally used granular activated carbon has a non-uniform particle size and particle shape, and many particle shapes are flat. When such activated carbon is used as a catalyst for the treatment of hydrogen peroxide-containing wastewater, the voids between the particles are non-uniform, so that a pool of generated oxygen gas is easily formed. Further, when the particle shape is flat, it is easy to prevent the generated oxygen gas bubbles from rising and induce the generation of gas pools. Therefore, by using spherical activated carbon with a uniform particle size as the catalyst, the voids between the particles become uniform and the oxygen gas bubbles rise smoothly, and as a result, the occurrence of gas accumulation can be suppressed.

  As a raw material of the spherical activated carbon used in the wastewater treatment method according to the present embodiment, it is preferable to use coal that is inexpensive and easy to form, but other raw materials such as coconut shells can also be used.

  The average particle diameter of the spherical activated carbon can be arbitrarily selected, but is preferably in the range of 0.2 mm to 5 mm, and more preferably in the range of 0.5 mm to 2 mm. When the particle diameter is smaller than 0.2 mm, the packing density increases, and the effect of promoting gas loss due to the use of a spherical shape may be reduced. Further, when the particle diameter is larger than 5 mm, the packing density is lowered, and the contact efficiency may be lowered.

  Here, the “particle size” of the spherical activated carbon refers to the major axis of the particle on the microscope image (maximum value between any two points on the particle outline) when the particle is observed with a microscope. The “average particle size” is obtained by first measuring 30 particle sizes on a microscope image, and obtaining the number of measurements with a probability of 90% or more and an accuracy of 5% from the results, and then calculating the average value of the measured numbers. And

  Further, “spherical” is represented by a circularity F obtained by the following method. The circularity F is defined as a value (F = L / K) obtained by dividing the circumference L of a circle equal to the projected sectional area of the particle on the microscope image when the particle is observed with a microscope by the projected contour length K of the particle. In the case of a true sphere, F = 1, and when the shape is flat, the value is smaller than 1. The spherical activated carbon in this embodiment preferably has an average circularity F in the range of 0.8 to 1.0, more preferably in the range of 0.9 to 1.0. More preferably, it is in the range of 95 to 1.0. The circularity F can be obtained by image analysis or the like based on a microscope image.

  Further, the “uniform particle size” is represented by a uniformity coefficient shown in JIS-K1474. The particles are sieved by a sieve specified in JIS-K1474, and the sieve opening m (mm) when 10% of the particles have passed, and the sieve opening n (mm) when 60% of the particles have passed, The uniformity coefficient U = n / m. It shows that the particle size of particle | grains is uniform, so that the uniformity coefficient U is small. The uniformity coefficient U is preferably 2.0 or less, and more preferably 1.4 or less.

  An example of the waste water treatment apparatus 1 used in the waste water treatment method according to the embodiment of the present invention is shown in FIG. A catalyst (granular activated carbon) layer 12 filled with a catalyst (granular activated carbon) is formed in the tank 10 opened at the top. The pump 14 feeds raw water to be treated from the lower part of the tank 10 by an upward flow without causing the catalyst to flow. The treated water that has been treated with the spherical activated carbon that is the catalyst and from which hydrogen peroxide has been removed flows out from the upper part of the tank 10.

  Further, water may be passed by a downward flow as shown in FIGS. In this case, it is only necessary that the inlet of the raw water flow is located above the catalyst layer 12. In addition, when water is passed by downward flow, the tank 10 is sealed as shown in FIG. 2 to provide a gas escape mechanism 16, or the upper part of the tank 10 is opened as shown in FIG. Just do it. In either case, the treated water flows out from the lower part of the tank 10.

  In hydrogen peroxide decomposition using activated carbon, the concentration of hydrogen peroxide in raw water, reaction pH, water flow rate (flow rate per unit time), water flow rate (flow rate per unit time divided by the catalyst bed bottom area) ), Activated carbon layer height, etc. are influential factors on the processing efficiency. Although this point is the same in this embodiment, all these factors are taken into consideration by the apparatus designer considering the quality of the water to be treated, the treatment target, the properties of the carrier to be used (particle size, specific gravity, reaction efficiency), etc. It can be arbitrarily planned, and is not particularly limited in this embodiment. However, when the upward flow is used, it is preferable to design the water line speed within a range in which the activated carbon does not flow out regardless of the flow. At this time, even if the water passage speed is the same, the higher the concentration of hydrogen peroxide in the raw water, the more the catalyst layer swings due to the air lift effect of the oxygen gas generated during hydrogen peroxide decomposition, leading to the outflow of the catalyst, etc. Therefore, it is preferable to design the water passage speed in consideration of the concentration of hydrogen peroxide in the raw water.

  As described above, when the catalyst is not flowed, any of an upward flow type and a downward flow type can be used as a flow form of the drainage to the catalyst, but the oxygen gas pool in the catalyst layer 12 can be used. In order to suppress the outflow of the catalyst into the treated water, while using spherical activated carbon with a uniform particle size as the catalyst, the waste water is passed upward from the bottom of the catalyst layer 12, It is preferable to contact the waste water and the catalyst in a state where the catalyst forms a fluidized bed.

  FIG. 4 shows an example of the waste water treatment apparatus 1 when the catalyst is flowed. The tank 10 with the upper part opened is filled with a catalyst (granular activated carbon), and the pump 14 supplies raw water to be treated from the lower part of the tank 10 in an upward flow to cause the catalyst to flow, thereby the catalyst (granular activated carbon). ) The fluidized bed 18 is formed. The treated water that has been treated with the spherical activated carbon as the catalyst and from which hydrogen peroxide has been removed flows out from the upper part of the tank 10 into the treatment liquid recovery tank.

  It is effective to use a fluidized bed as a method for more reliably suppressing the occurrence of gas accumulation in the catalyst layer 12. However, if the particle size and particle shape of the catalyst used are not uniform, the flow state of each particle varies. Further, if the particle shape is flat, even in the individual particles, the flow method varies depending on the direction of the particles. As a result, the catalyst particles are likely to flow out. However, if a spherical catalyst having a uniform particle diameter is used as in this embodiment, the variation in the flow state due to the above reason can be prevented, so that the occurrence of gas accumulation in the catalyst layer is almost completely suppressed, and the catalyst Can reduce spillage.

  Further, as a measure for causing the catalyst to flow, it is more preferable to provide the catalyst layer with a water flow rate sufficient to cause the catalyst to flow by circulating the catalyst-treated water treated with the catalyst to the lower part of the catalyst layer.

  FIG. 5 shows an example of the waste water treatment apparatus 1 when the treated water is circulated to form a fluidized bed of the catalyst. The tank 10 with the upper part opened is filled with a catalyst (granular activated carbon), and the pump 14 supplies raw water to be treated from the lower part of the tank 10 in an upward flow to cause the catalyst to flow, thereby the catalyst (granular activated carbon). ) The fluidized bed 18 is formed. The treated water that has been treated with the spherical activated carbon as the catalyst and from which hydrogen peroxide has been removed flows out from the upper part of the tank 10 into the treatment liquid recovery tank 20. Thereafter, the treated water is circulated by the pump 22 and flows again from the lower part of the tank 10. When the treated water is not circulated, the raw water inflow rate may be increased so that an equivalent water passage speed can be obtained.

  In order to make the catalyst flow, the water flow rate to the catalyst layer 12 (the value obtained by dividing the flow rate per unit time by the catalyst layer bottom area) should be set to a certain value or more. When the hydrogen peroxide concentration in the wastewater increases even if the water flow speed is constant, the amount of oxygen gas generated per unit time in the unit volume of the catalyst layer also increases. Cannot be made constant, and in some cases, the catalyst flows out. Therefore, in the treatment method of the present embodiment, it is important to keep the hydrogen peroxide inflow per unit time in the unit area of the catalyst layer 12 below a certain value. That is, the above-described event can be solved by diluting the inflow hydrogen peroxide concentration at a set water passage speed so as to be a certain value or less. At this time, if the catalyst-treated water that does not substantially contain hydrogen peroxide is circulated as the dilution water used for diluting the hydrogen peroxide concentration, the increase in running cost due to the introduction of the dilution water can be avoided. Can do.

  In addition, in the treatment using the non-spherical activated carbon which is the prior art, when the flow rate is secured in the catalyst layer by circulating the treated water as in this embodiment, the activated carbon that has flowed into the treated water flows into the raw water side, that is, the lower part of the reaction tank. There is a risk that processing troubles such as blockage at the bottom of the reaction tank may occur. That is, this method is a more effective treatment method with less risk of treatment failure when spherical activated carbon having a uniform particle diameter is used.

  As described above, the wastewater treatment method according to the present embodiment can prevent the accumulation of oxygen gas in the catalyst layer and suppress an increase in running cost due to the addition of a pH adjuster or the replenishment of the catalyst. In addition, since it is possible to prevent a reduction in processing efficiency due to gas accumulation, and it is possible to suppress the occurrence of gas accumulation, it is possible to maintain a high decomposition rate for a long period of time. Furthermore, compared with the conventional method, it becomes possible to treat wastewater having a high concentration of hydrogen peroxide, and the size of the wastewater treatment apparatus can be made compact.

  The wastewater treatment method according to this embodiment can be suitably used for the treatment of various hydrogen peroxide-containing wastewater such as semiconductor manufacturing wastewater and food container washing wastewater.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail more specifically, this invention is not limited to a following example, unless the summary is exceeded.

Example 1
An embodiment in the case of using the apparatus shown in FIG. 1 and flowing water in an upward flow without flowing activated carbon will be described. The water flow conditions were set as shown in Table 1. As the granular activated carbon, coal-based activated carbon having an average particle diameter of 1 mm, an average circularity of 0.96, and a uniformity coefficient of 1.2 was used. FIG. 6 shows changes with time in the hydrogen peroxide decomposition rate.

Here, the hydrogen peroxide decomposition rate was determined as follows. A predetermined amount of raw water and treated water were collected periodically, and the respective hydrogen peroxide concentrations were quantified by a titration method (JIS K8230) using a potassium permanganate solution. The hydrogen peroxide decomposition rate was calculated from the measured raw water and treated water hydrogen peroxide concentrations according to the following equation.
Hydrogen peroxide decomposition rate (%) = (1− (treatment water hydrogen peroxide concentration / raw water hydrogen peroxide concentration)) × 100

(Comparative example)
The treatment was performed under the same conditions as in Example 1 except that coal-based activated carbon having an average particle diameter of 1 mm, an average circularity of 0.67, and a uniformity coefficient of 1.5 was used as the non-spherical activated carbon. FIG. 6 shows changes with time in the hydrogen peroxide decomposition rate.

  As shown in FIG. 6, when non-spherical activated carbon was used, the hydrogen peroxide decomposition rate was not stable, and the decomposition rate decreased significantly after 30 days of water flow. After that, the water flow was stopped only for the non-spherical activated carbon system, and the water flow was resumed after removing the gas reservoir intervening in the activated carbon layer by tapping (operation to tap the side of the column). The hydrogen oxide decomposition rate recovered. That is, it was confirmed that the gas reservoir intervening in the activated carbon layer inhibited the decomposition of hydrogen peroxide. In addition, in non-spherical activated carbon, the reason why the effect of the gas accumulation became remarkable after 30 days of water passage was long is that activated carbon pulverized by hydrogen peroxide decomposition is between the particles of activated carbon having a normal particle size. As a result, it can be considered that an activated carbon layer in which gas tends to accumulate is formed in about 30 days of water flow.

(Example 2)
Using the apparatus shown in FIG. 5, activated carbon was caused to flow by circulating the treated water. The water flow conditions were set as shown in Table 2. At this time, the raw water quality was the same as in Table 1. The results are shown in FIG. Compared with Example 1 in which the flow of the treatment results shown above is not performed, the hydrogen peroxide decomposition rate is slightly reduced due to the increase in the water passage speed, but the high decomposition rate is maintained for a long time. Recognize.

  In addition, in the case where the activated carbon is not flowed, the reason why the decomposition rate decreased after 45 days of water flow is that the activated carbon pulverized by hydrogen peroxide decomposition fills the space between the activated carbon particles of the normal particle size. It is conceivable that a so-called short path in which water does not disperse uniformly occurs, and that an activated carbon layer in which gas easily accumulates is formed as in the case of the non-spherical activated carbon.

  Thus, as shown in this example, in the treatment of hydrogen peroxide-containing wastewater with activated carbon, the use of spherical activated carbon with a uniform particle size as a catalyst allows oxygen gas generated during hydrogen peroxide decomposition to be reduced. As a result, the processing efficiency can be prevented from being lowered due to gas accumulation. In the examples, in the case of non-flowing, the high decomposition rate maintaining period could be extended by about 1.5 times compared to the conventional method. In the case of the flow method, a high decomposition rate retention period of 1.5 times or more of the non-flow method and twice or more of the conventional method was confirmed.

It is a figure which shows an example of the waste water treatment equipment which concerns on embodiment of this invention. It is a figure which shows another example of the waste water treatment equipment which concerns on embodiment of this invention. It is a figure which shows another example of the waste water treatment equipment which concerns on embodiment of this invention. It is a figure which shows another example of the waste water treatment equipment which concerns on embodiment of this invention. It is a figure which shows another example of the waste water treatment equipment which concerns on embodiment of this invention. It is a figure which shows the relationship between the elapsed days of the process in Example 1 and a comparative example of this invention, and a hydrogen peroxide decomposition rate. It is a figure which shows the relationship between the elapsed days of the process in Example 1 and Example 2 of this invention, and a hydrogen peroxide decomposition rate.

Explanation of symbols

  10 tanks, 12 catalyst (granular activated carbon) layer, 14, 22 pump, 16 gas escape mechanism, 18 catalyst (granular activated carbon) fluidized bed, 20 treatment liquid recovery tank.

Claims (3)

A wastewater treatment method for contacting hydrogen peroxide-containing wastewater with a catalyst to decompose hydrogen peroxide in wastewater,
The waste water treatment method according to claim 1, wherein the catalyst is a spherical activated carbon having a uniformity coefficient of 1.4 or less and an average circularity in a range of 0.95 to 1.0 . A wastewater treatment method according to claim 1,
Waste water treatment, wherein the waste water and the catalyst are brought into contact with each other in a state where a fluidized bed of the catalyst is formed by passing the waste water through an upward flow from a lower part of the catalyst layer filled with the catalyst. Method. A wastewater treatment method according to claim 2,
A wastewater treatment method characterized in that a water flow rate sufficient to allow the catalyst to flow is provided to the catalyst layer by circulating water treated with the catalyst to a lower portion of the catalyst layer.

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