JP2947675B2 - Method for treating wastewater containing fluorine ions and hydrogen peroxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater containing fluorine ions and hydrogen peroxide such as wastewater from a wafer process in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art Various inorganic compounds and organic compounds are contained in the wastewater from a wafer process in a semiconductor manufacturing process, and it is particularly characterized that they contain fluorine ions and hydrogen peroxide.

In the semiconductor manufacturing process, hydrofluoric acid is used in a wafer etching process, and a large amount of hydrogen peroxide is used for the purpose of sterilization and bleaching. Of hydrogen peroxide.

[0004] Hydrogen peroxide contained in the wastewater of the wafer process is naturally decomposed in the step of removing coagulated sediment such as fluorine ions to generate gaseous oxygen. The gaseous oxygen resulting from the natural decomposition of hydrogen peroxide becomes microbubbles in the internal voids of the floc, or adheres to the surface of the floc.
Flock floats out. Further, hydrogen peroxide itself has toxicity, which adversely affects the subsequent activated sludge treatment step and the external environment.

As a method for decomposing and removing hydrogen peroxide in wastewater which adversely affects the subsequent steps and the external environment, a method of reductive decomposition using a reducing agent such as sodium sulfite, sodium bisulfite, hydrazine or the like is generally used. It is being done.

However, in order to decompose hydrogen peroxide,
It is necessary to add these reducing agents in the same amount as hydrogen peroxide. Therefore, when the concentration of hydrogen peroxide in the wastewater is high, a large amount of a reducing agent must be added. Further, if the amount of the reducing agent is excessive, it has an adverse effect on the environment due to toxicity of the reducing agent itself.

In recent years, a method of treating wastewater from a wafer process using catalase, which decomposes hydrogen peroxide, has been proposed instead of the chemical reduction method (JP-A-63-2705).
No. 95). That is, in the wafer process wastewater, after adding an alkaline calcium-containing compound to convert the fluoride ions in the wastewater, which is a catalyst poison of catalase, into calcium fluoride, catalase was added at pH 5 to 9,
In this method, hydrogen peroxide is decomposed and then separated into solid and liquid.

Catalase is safe because it is an enzyme derived from a living organism, and has the advantage that it can be used in a small amount because it catalytically decomposes hydrogen peroxide.

[0009] However, this treatment with catalase generates oxygen during decomposition of hydrogen peroxide.
Fine oxygen bubbles are generated, and flocs are caused to float and flow out, causing a problem in the precipitation separation process.

[0010] As a method for preventing the floating and outflow of flocs due to the use of catalase, the sludge that has been solid-liquid separated after the addition of catalase is returned to the wastewater before the solid-liquid separation and mixed, and the absolute amount of flocs in the coagulation process is determined. An improved method has been proposed in which the effect of oxygen on floc generated during the decomposition of hydrogen peroxide by catalase is reduced by increasing the amount (JP-A-2-222773).

[0011] However, this improved method has a drawback in that the concentration and amount of the sludge to be returned have to be appropriately controlled, which involves technical complexity.

[0012]

In general, flocs generated in the treatment of wastewater from a wafer process have a particle size of 5 mmφ or more, and the porosity in the flocs is often large due to flocculation of the flocs. For this reason, the apparent specific gravity becomes small, so that the fluid may flow due to a small amount of water flow, bubbles may be easily held in voids in the floc, and precipitation in solid-liquid separation may not be sufficiently achieved. This is remarkable particularly when the floc floats and flows out in the sedimentation tank due to generation of gaseous oxygen due to decomposition of hydrogen peroxide and gasification of dissolved substances in water due to temperature change or the like. Therefore, it is effective to form the fine flocs to increase the apparent specific gravity in order to prevent the floating outflow of the flocs.

Further, if a catalyst substance such as catalase which promotes a reaction for generating gaseous oxygen is added before the solid-liquid separation step, it is dangerous because oxygen bubbles are attached to the flocs.

The present invention has been completed based on the above technical background, and an object of the present invention is to provide a flocculant for treating wastewater containing fluorine ions and hydrogen peroxide such as wafer process wastewater. It is an object of the present invention to provide a wastewater treatment method capable of preventing the floating outflow of water and efficiently removing fluorine ions and hydrogen peroxide.

[0015]

That is, according to the present invention, an alkaline calcium-containing compound is added to waste water containing fluoride ions and hydrogen peroxide to convert the fluoride ions into calcium fluoride, and then the colloid equivalent value is -2. 0.0 to -8.0 meq / g of an anionic polymer flocculant to form fine flocs, followed by solid-liquid separation, followed by the addition of catalase to decompose hydrogen peroxide. And a method for treating wastewater containing hydrogen peroxide.

A feature of the present invention is that a specific anionic polymer flocculant is used to form fine flocs, and further, catalase is added to solid-liquid separated fine flocs to decompose hydrogen peroxide. .

The wastewater to be treated according to the present invention is wastewater containing fluorine ions and hydrogen peroxide. A typical example thereof is a wafer process wastewater, but is not limited to the wafer process wastewater. .

In the present invention, the anionic polymer flocculant used to form the fine floc is, for example, a copolymer of sodium acrylate and acrylamide, a copolymer of acrylamide and sulfonate of allylamide, and a copolymer of acrylamide and acrylic. copolymer of sodium and sulfonated acrylamide etc., colloidal those
The amount is -2.0 meq / g or less, preferably -2.0 to -8.0 meq / g. In addition, colloid
When the equivalent value is -2.0 meq / g or more, the floc grows excessively and becomes large, so that the floating of the floc easily occurs due to the adhesion of bubbles, and the colloid equivalent value is -8.0 m.
On the other hand, if it is less than eq / g, on the contrary, the floc becomes extremely fine, so that solid-liquid decomposition becomes difficult. Further, polyaluminum chloride, aluminum sulfate and / or a cationic polymer flocculant may be used as an auxiliary.

In the present invention, the fine floc refers to a fine floc having a floc particle size of 1 to 2 mmφ and a small void in the floc. By reducing the particle size and increasing the apparent specific gravity, the particles are less susceptible to a slight flow of water, and are less likely to hold bubbles in the voids in the flocs. Therefore, sedimentation can be sufficiently achieved in the solid-liquid separation step.

[0020] The alkaline calcium-containing compound used in the present invention is not particularly limited as long as the fluoride ion is hardly soluble calcium fluoride, and examples thereof include slaked lime and quick lime.

The catalase used in the present invention is
It is an enzyme present in almost all living organisms other than anaerobic bacteria, can be easily obtained, and its origin is not particularly limited. The amount of catalase to be added is sufficient as a catalytic amount. For example, when using catalase having a titer of 50,000 units, the weight ratio to the amount of hydrogen peroxide in the waste water is 1: 1 to 1: 0. A range of 1 (H ₂ O ₂ : catalase) is preferred. Since the enzyme activity of catalase is maximized near neutrality, it is necessary to adjust the pH of the waste water to 7 to 8 before adding catalase.

In the present invention, catalase is added after the solid-liquid separation step. However, if the treated water in the solid-liquid separation step merges with the wastewater of another system after the solid-liquid separation step, In order to reduce the influence of drainage from the system, it is preferable to add catalase immediately after the precipitation tank.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments.

Example 1 As a wastewater containing fluorine ions and hydrogen peroxide, wastewater treatment was performed on wastewater from the wafer process shown in Table 1 using the wastewater treatment apparatus shown in FIG.

[0025]

[Table 1]

The wastewater from the wafer process in the raw water tank 1 is transferred to the first reaction tank 2 and calcium hydroxide of 10% by weight slurry is added at 0.7 m ³ / hr (a in FIG. 1), and the fluorine ions in the wastewater are added. Was converted to insoluble calcium fluoride, transferred to a second reaction tank, adjusted to pH 7 to 8 with 35% hydrochloric acid, and a 200 mg / L sulfate band was added as an auxiliary flocculant (b in FIG. 1). ), transferred to a flocculation tank 5, a copolymer of sodium acrylate and acrylamide (colloidal those
(Amount of -2.9 meq / g, addition amount of 10 mg / L) was added (c in FIG. 1) to aggregate calcium fluoride.
In FIG. 1, reference numeral 4 denotes a stirrer attached to each of the first and second reaction tanks and the flocculation tank.

After coagulation, the mixture is transferred to the sedimentation tank 6 to perform solid-liquid separation, and the catalase (enzyme titer: 50, 0) is added to overflow water.
(00 unit / ml, addition amount: 20 mg / L) (d in FIG. 1), and then introduced into a reaction tank / treatment water tank to complete the decomposition reaction of hydrogen peroxide in the wastewater. In addition,
In FIG. 1, reference numeral 8 denotes a treatment water transfer pump, and reference numeral 9 denotes a partition wall provided inside the reaction tank / treatment water tank 7. The floc solid-liquid separated in the sedimentation tank was a fine floc having a particle size of 1 to 2 mm, was easily solid-liquid separated, and the floc did not float up or down.

Tables 2 and 3 show changes in the concentration of hydrogen peroxide, SS in the treated water, and evaluation. As is clear from the results in Tables 2 and 3, the wastewater treatment method of the present invention can efficiently decompose and remove hydrogen peroxide and reduce the SS concentration in treated water by the effect of preventing the floating and outflow of flocs. It could be kept, and the evaluation of the treated water was good.

Example 2 The wastewater from the wafer process was treated in the same manner as in Example 1 except that a copolymer of sodium acrylate and acrylamide having a colloid equivalent value of -5.0 meq / g was used. Tables 2 and 3 show changes in the concentration of hydrogen peroxide, SS in the treated water, and evaluation. As is clear from the results in Tables 2 and 3, as in Example 1, the evaluation of the treated water was good.

Comparative Example 1 For comparison with the conventional method (Japanese Patent Application Laid-Open No. 63-270595), the wafer process wastewater from the raw water tank 1 was transferred to the first reaction tank 2 and 10% by weight slurry calcium hydroxide was added to 0.1 wt%.
After adding 7 m ³ / hr (a in FIG. 1) to convert the fluoride ions in the wastewater into insoluble calcium fluoride, the solution was transferred to the second reaction tank, and the pH was adjusted to 7 to 8 with 35% hydrochloric acid. Further, a sulfuric acid band of 200 mg / L was added as an auxiliary flocculant (b in FIG. 1), transferred to the flocculation tank 5, and catalase (enzyme titer: 50,000 unit / ml, added amount: 20 mg / l)
L) to decompose hydrogen peroxide, and then copolymerize sodium acrylate and acrylamide (colloid equivalent value-
2.9 meq / g, 0.1% by weight, added amount 10 mg / g
L) was added (c in FIG. 1) and transferred to the precipitation tank 6 to perform solid-liquid separation. The flocs in the sedimentation tank 6 contained oxygen bubbles during the decomposition of hydrogen peroxide, and some of them overflowed.

Tables 2 and 3 show changes in the concentration of hydrogen peroxide, SS in the treated water, and evaluation. From the results in Tables 2 and 3,
Although effective in decomposing and removing hydrogen peroxide, the SS concentration in the treated water increased due to the floating and outflow of flocs, and the evaluation of the treated water was low.

Comparative Example 2 In order to compare with an anionic polymer flocculant having a colloid equivalent value outside the range of the present invention, a colloid equivalent value of -1.0 meq /
The wastewater from the wafer process was treated in the same manner as in Example 1, except that g of the copolymer of sodium acrylate and acrylamide was used. The floc in the settling tank 6 has a particle size of 5 to 6 m.
m, embracing oxygen bubbles during hydrogen peroxide decomposition,
Some overflowed.

Tables 2 and 3 show changes in the concentration of hydrogen peroxide, SS in the treated water, and evaluation. From the results shown in Tables 2 and 3, although effective for decomposing and removing hydrogen peroxide, the SS concentration in the treated water increased due to the floating outflow of flocs, and the evaluation of the treated water was low.

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

As is clear from the above embodiments, the effects of the present invention are as follows.

(1) By using a specific anionic polymer flocculant, a fine floc can be formed, the apparent specific gravity of the floc can be increased, and the floc can be easily separated into solid and liquid. The SS concentration in the treated water can be reduced by preventing the floating and outflow of flocs.

(2) Since the addition of catalase is performed after the solid-liquid separation step, oxygen generated by the decomposition of hydrogen peroxide does not adhere to the flocs, and the floating of the flocs can be prevented.

(3) Since catalase is used, hydrogen peroxide can be safely decomposed. (4) There is no need for a complicated operation such as the conventional method of returning the sludge solid-liquid separated after the addition of catalase to the wastewater before the solid-liquid separation and mixing.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating the flow of a wafer process wastewater treatment apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Raw water tank 2 ... 1st reaction tank 3 ... 2nd reaction tank 4 ... Stirrer 5 ... Coagulation tank 6 ... Sedimentation tank 7 ... Reaction tank and treatment water tank 8 ... Water discharge pump

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshinobu Imahama 1-4-9, Kawagishi, Toda City, Saitama Prefecture Inside the Organo Research Institute (56) References JP-A-2-222773 (JP, A) ( 58) Field surveyed (Int.Cl. ⁶ , DB name) C02F 1/52-1/78

Claims (1)

(57) [Claims] 1. A wastewater containing fluorine ions and hydrogen peroxide, to which an alkaline calcium-containing compound is added to convert the fluorine ions into calcium fluoride, and then a colloid equivalent
A fine floc is formed by adding an anionic polymer flocculant having a value of -2.0 to -8.0 meq / g, followed by solid-liquid separation, followed by addition of catalase to decompose hydrogen peroxide. Of wastewater containing fluorine ions and hydrogen peroxide.