JP3173827B2 - Purification booth water treatment method - 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 purifying water to be treated in a coating booth, in which water to be treated in a wet coating booth is separated into paint scum and treated water, and the treated water can be used repeatedly.

[0002]

2. Description of the Related Art In a wet coating booth, a spray treatment is performed in which sprayed paint mist is collected in water, separated into paint scum and treated water, and then treated water is repeatedly used. Since many paints dissolve or disperse in water, such as aqueous paints, it is often difficult to separate the water to be treated into paint scum and treated water. In order to facilitate the solid-liquid separation of the water to be treated, various treatment agents have been developed.

[0003] As the treating agent, those which agglomerate paint scum to flocs to facilitate separation are mainly used, and aluminum sulfate, polyaluminum chloride, iron chloride, iron sulfate and the like are generally used. For example, JP-A-52-59
No. 67, Japanese Patent Application Laid-Open No. 52-72538 and the like disclose the optimum conditions when these coagulants are used.

Japanese Patent Application Laid-Open No. 51-96163 discloses that
A method is disclosed in which an acid agent of phosphoric acid or sulfuric acid and an alkali agent such as calcium hydroxide or barium hydroxide are added to form an insoluble or hardly soluble salt, and a paint residue is adsorbed to precipitate and separate. Furthermore, not only the above-mentioned inorganic treating agents but also organic treating agents have been used in recent years. For example, Japanese Patent Application Laid-Open No. 61-74607 discloses a method of treating with a treating agent containing polyethyleneimine as an active ingredient. JP-A-63-42706 discloses a method of adding and treating a cationic organic polymer flocculant and an anionic organic polymer flocculant.

[0005]

However, when an inorganic treatment agent is added to the water to be treated mixed with the water-based paint, a mat ball-like aggregate is locally formed. The aggregates are sticky, and when leaked from the processing apparatus, problems such as blockage of pipes, sedimentation and accumulation, and blockage of the venturi portion occur. In an automobile metallic paint booth, aluminum powder is mixed into the water to be treated. However, since this aluminum powder is contained in the aggregate, the specific gravity of the aggregate is large and the sedimentation is large. Therefore, it is difficult to separate the aggregates by a solid-liquid separation method using a pressurized flotation device, a diffused flotation device, or the like. Then, there is a problem that the resin component having poor coagulation remains in the treated water, and the treated water becomes cloudy, so that clear treated water cannot be obtained. Further, when the treatment system is acidic, there is a problem that aluminum reacts to generate hydrogen gas.

[0006] A treating agent containing polyethyleneimine as an active ingredient has an effect of precipitating and aggregating resin and the like even when added in a very small amount. However, since the range of the optimum addition ratio is narrow, it is very difficult to set the addition amount. In addition, since the suspended particles agglomerate and precipitate the resin particles in the alkaline region, the floc particles have no core and are unstable and easily broken. Therefore, in particular, in the case of continuous treatment, clear treated water having a transparency of 30 cm or more cannot be obtained at present, and has not been put to practical use.

Further, the anionic polymer coagulant is used at a concentration of about 0.05 to 1.0%, but is decomposed in a short period of time by hydrolysis or the like. There is a large number of man-hours for dilution work.
As the cationic polymer flocculant, a polyamine-based acidic one is used. Although this is preferable because the range of the optimum addition ratio is wide, it is uneconomical because of excessive use in a low paint concentration region. Then, the excess cationic polymer flocculant remains in the circulating water, and forms flocculated floc at the paint mixing location in the coating booth. Therefore, there is a problem that sludge is deposited at the venturi portion, and finally, the pipe is blocked.

The present invention has been made in view of such circumstances, and it is an object of the present invention to eliminate the above-mentioned various problems and to easily perform solid-liquid separation.

[0009]

According to the present invention, there is provided a method for purifying water to be treated in a coating booth, comprising the steps of: an alkalizing step for adjusting the pH to 9.5 to 11, a neutralizing step for adjusting the pH of the water to be treated to 6 to 8 by adding an acidic flocculant, and separating flocculated floc from the water to be treated. Separation process to make treated water and paint slag sludge,
It is characterized by consisting of.

The alkaline agent added in the alkalizing step includes sodium hydroxide, potassium hydroxide, sodium carbonate, an aluminate aqueous solution containing these,
An aqueous solution of polyethyleneimine or the like can be used.
In the alkalizing step, the pH of the water to be treated is adjusted to 9.5 to 11 by adding the alkali agent. As a result, the surface charge of the fine suspended particles or the resin colloid particles is reduced, and the hydrophilic groups of the resin and the like are blocked, so that precipitation and aggregation occur. When the water to be treated contains aluminum powder, the aluminum powder is converted into an aluminate and dissolved in the water to be treated. If the pH is lower than 9.5, precipitation and aggregation become difficult, and pH 10 to 11 is optimal for chemically converting aluminum into aluminate in a short time. p
If H exceeds 11, the effect is saturated and an excess alkali agent is excessive, and an extra acidic coagulant for neutralizing the excess alkali agent in the next neutralization step is required, resulting in cost reduction. Causes problems.

In the neutralization step, an acidic coagulant is added to the water to be treated which has been made alkaline in the alkalizing step. Here, as the acidic coagulant, an inorganic coagulant such as aluminum sulfate, polyaluminum chloride, and iron sulfate, and an anionic polymer coagulant such as polyacrylic acid and polyacrylamide are used. Aluminum sulfate which is inexpensive and has a large clarifying effect on treated water is particularly preferred. The addition amount of the inorganic coagulant is appropriately 2 to 10%, and the addition amount of the polymer coagulant is 1 to
10 ppm is appropriate.

In the neutralization step, the pH of the water to be treated is adjusted to a range of 6 to 8 by adding the above-mentioned coagulant. This forms a strong and stable aggregate floc. When the pH becomes lower than 6 and becomes acidic, the amount of paint sludge increases, and a neutralizing agent for neutralizing the treated water is required. pH 8
In a larger alkaline region, flocculated floc is weak, and clarification of treated water becomes difficult.

The separation step is a step of separating flocculated flocs from the water to be treated to produce treated water and paint sludge. This separation step can be performed in the same manner as in the related art using a pressure flotation device, a diffused flotation device, or the like. In the treatment method of the present invention, the flocculated floc is strong, stable and soft, so that it can be easily floated and separated.

[0014]

In the purification treatment method of the present invention, the water to be treated is first adjusted to pH 9.5 to 11 in the alkalizing step. As a result, the surface charge of the fine suspended particles or the resin colloid particles is reduced, and the hydrophilic groups of the resin and the like are blocked, so that precipitation and aggregation occur. Then, in the next neutralization step, an acidic flocculant is added to the water to be treated. This forms a strong and stable aggregate floc.

Here, the case where sodium hydroxide is used as an alkali agent in the alkalizing step and aluminum sulfate is used as the coagulant will be described. In the neutralizing step, aluminum sulfate reacts with sodium hydroxide as shown in equation (1). I do. Al ₂ (SO ₄ ) ₃ + 6NaOH → 2Al (OH) ₃ + 3Na ₂ SO ₄ (1) Water-insoluble resins, pigments, etc. are precipitated together with the aluminum hydroxide generated by this reaction, and the aluminum hydroxide is a strong core. To form stable flocculated flocs.

If the water to be treated contains aluminum powder, the reaction of the formula (2) occurs in the alkalizing step, and sodium aluminate is produced. Al + 2NaOH → NaAlO ₂ + Na ⁺ + H ₂ (2) The sodium aluminate undergoes hydrolysis in the neutralization step as shown in equation (3) to produce aluminum hydroxide.

NaAlO ₂ + H ₂ O + H ⁺ → Al (OH) ₃ + Na ⁺ (3) The aluminum hydroxide also becomes a core of the flocculated floc and forms a stable flocculated floc. That is, since the aluminum powder contained in the water to be treated eventually functions as a coagulant, the coagulant can be saved.

[0018]

The present invention will be specifically described below with reference to examples. (Example 1) Topcoat water-based paint for automobile ("NWB-13
0 "manufactured by Nippon Paint Co., Ltd.) was diluted with industrial water to a concentration of 1% by weight to prepare a sample water. Table 1 shows the properties of this sample water.
Shown in

[0019]

[Table 1] One liter of this sample water was collected in a beaker and treated by the treatment method of the present invention shown in FIG. (1) Alkalinization Step A beaker containing sample water was placed on a jar tester rotating at a speed of 200 rpm, and a 5% by weight sodium hydroxide solution was added to the sample water to adjust the pH to 11. (2) Neutralization Step To the sample water of pH 10 was added 10% by weight of liquid aluminum sulfate (manufactured by Sumitomo Chemical Co., Ltd.) at a concentration of 8% by weight as Al ₂ O _3.
00 ppm was added. The pH at this time is 7.1.
And an anionic polymer coagulant (“Haktron A27-
1000 ppm of an aqueous solution of 30M (manufactured by Hakuto Co., Ltd.) having a concentration of 0.1% by weight was added to further increase the flocculated floc. The pH at this time is 7.1. (3) Separation Step Next, 700 ml of the sample water after the neutralization step was collected in a 1-liter graduated cylinder, and 3 kg / cm ^{2 of} air-saturated pressurized water was added.
After adding 00 ml, the mixture was shaken up and down for 30 seconds and allowed to stand.
Then, in about 30 seconds, all the aggregated flocs were separated by floating with fine bubbles. Table 2 shows the results of measuring the properties of the remaining treated water after removing the aggregated flocs.
Incidentally, perspective degree measured according to the perspective of the JlSK-0102, SV ₃₀ was measured by measuring cylinder method. (Comparative Example 1) Using the same sample water as in Example 1, 1 liter was similarly collected in a beaker. And it processed by the conventional processing method shown in FIG. That is, first, 10% of liquid aluminum sulfate (manufactured by Sumitomo Chemical Co., Ltd.) having a concentration of 8% by weight was added to the sample water.
00 ppm was added. The pH at this time is 4.3.
Next, a sodium hydroxide solution having a concentration of 5% by weight was added and the pH was adjusted.
The solution was adjusted to 7.5, and 1000 ppm of an aqueous 0.1% by weight aqueous solution of an anionic polymer coagulant ("Haktron A27-30M" manufactured by Hakuto Co., Ltd.) was added for coagulation.

[0020] Then, 700
and pressurized water saturated with 3 kg / cm ² air 300 ml
It was charged, shaken up and down for 30 seconds, and allowed to stand. Some flock floated and separated, but most flock settled. Next, the supernatant of the treated water was collected, and the properties were measured in the same manner as in Example 1. Table 2 shows the results.

[0021]

[Table 2] From Table 2, it is clear that the treatment of Example 1 significantly improves the clarity of treated water as compared with Comparative Example 1 which is a conventional treatment method. (Test Example) Using the same coating material as in Example 1, the concentration of 0.5% by weight, 1.0% by weight and 2.0% by weight in industrial water was used.
Three types of sample water were prepared by adjusting the types. Then, a continuous purification experiment was performed on each sample water using a pressurized flotation device (“Type FS15” manufactured by Unitika Ltd.). The treating agent and method used for the purification treatment are exactly the same as in Example 1 and Comparative Example 1.

As a result, the treatment method of Example 1 was able to treat any sample water without any problem. However, in the processing method of Comparative Example 1, there was a problem that granular flocs were deposited in the flocculation tank with the sample water having a paint concentration of 1% or more, and the processing could not be performed unless it was removed. (Example 2) Topcoat water-based paint for automobile ("TWX-10
0 "(Kansai Paint Co., Ltd.) was diluted with industrial water to a concentration of 1% by weight to prepare a sample water. Table 3 shows the properties of this sample water.
Shown in

[0023]

[Table 3] One liter of this sample water was collected in a beaker and treated by the treatment method of the present invention shown in FIG. (1) Alkalinization Step A beaker containing sample water was placed on a jar tester rotating at a speed of 200 rpm, and a polyethyleneimine-based coagulant (manufactured by Hakuto K.K.) was added at 120 ppm. The pH at this time is 10.5. (2) Neutralization Step To the sample water having a pH of 10.5, 500 ppm of liquid aluminum sulfate (manufactured by Sumitomo Chemical Co., Ltd.) having a concentration of 8% by weight was added. The pH at this time is 6.8. (3) Separation Step After standing, the flocculated floc and treated water were separated. This separation was easy. The properties of the treated water were measured in the same manner as in Example 1, and the results are shown in Table 4. In addition, the foaming property evaluated the foaming state when the treated water was put into a test tube and shaken. (Comparative Example 2) Using the same sample water as in Example 2, 1 liter was similarly collected in a beaker. And it processed by the conventional processing method shown in FIG. That is, 10 wt% of liquid aluminum sulfate (manufactured by Sumitomo Chemical Co., Ltd.) having a concentration of 8 wt%
00 ppm was added. The pH at this time is 4.3.
Next, a sodium hydroxide solution having a concentration of 5% by weight was added, and the pH was adjusted.
The concentration was adjusted to 7.0, and 2,000 ppm of a 0.1% by weight aqueous solution of an anionic polymer flocculant ("Haktron A27-30M" manufactured by Hakuto Co., Ltd.) was added for flocculation.

After standing, flocculated floc and treated water were separated. This separation was easy. The properties of the treated water were measured in the same manner as in Example 1, and the results are shown in Table 4. (Comparative Example 3) Using the same sample water as in Example 2, 1 liter was similarly collected in a beaker. Then, 500 ppm of a polyamine-based coagulant (manufactured by Hakuto Co., Ltd.) was added for coagulation.
After standing, flocculated floc and treated water were separated. This separation was easy. The properties of the treated water were measured in the same manner as in Example 1, and the results are shown in Table 4.

[0025]

[Table 4] Table 4 shows that according to the treatment method of Example 2, the effect of removing COD is improved and treated water with high clarity can be obtained. (Example 3, Comparative Example 4, Comparative Example 5) A sample water was prepared by diluting an automotive topcoat water-based paint ("TWX-200" manufactured by Idac Corporation) to a concentration of 1% by weight with industrial water. Table 5 shows the properties of the sample water.

[0026]

[Table 5] One liter of this sample water was collected in a beaker, treated in the same manner as in Example 2, Comparative Example 2 and Comparative Example 3, and the properties of the supernatant were measured in the same manner. The results are shown in Table 6.

[0027]

[Table 6] Table 6 shows that according to the treatment method of Example 3, the effect of removing COD is improved, and treated water with high clarity can be obtained. (Test Example) Using the same sample water as in Example 2, a continuous purification experiment was performed using a pressurized flotation device (“Type FS15” manufactured by Unitika Ltd.). The coagulant and method used for the purification treatment are exactly the same as in Example 2. As Comparative Example 6, after adding 300 ppm of a polyamine-based flocculant (manufactured by Hakuto Co., Ltd.) to coagulate, anionic polymer coagulant ("Haktron A27-30M" manufactured by Hakuto Co., Ltd.) was added.
A continuous purification experiment was performed in the same manner by adding 1000 ppm of a 1% by weight aqueous solution to cause aggregation.

The properties of the treated water after the continuous treatment for 2 hours were measured in the same manner as in Example 2, and the results are shown in Table 7.

[0029]

[Table 7] From Table 7, it can be seen that according to the processing method of Example 2, high purification processing performance can be obtained even in continuous processing.

[0030]

According to the method for purifying treated water of a coating booth according to the present invention, a strong, stable and soft flocculated floc is formed, so that floating separation is extremely easy and the clarity of the treated water is improved. The COD removal effect is improved.
In addition, since the cohesive floc has low adhesiveness, the problem due to the floc adhesion is eliminated.

Since the treated water is substantially neutral and has no excess coagulant, formation of coagulated flocs in the booth is avoided, and problems such as sludge accumulation in the venturi and blockage of the piping do not occur. Further, the generation of hydrogen gas due to the reaction between the aluminum powder and the acid is prevented, and the corrosion of the processing apparatus and the tank is also prevented. In addition, the foaming property of the treated water is reduced, and the problem of foaming in a paint slag or the like is eliminated.

[Brief description of the drawings]

FIG. 1 is a flowchart of a processing method of the present invention.

FIG. 2 is a flowchart of a conventional processing method.

FIG. 3 is a graph showing a relationship between an optimum addition concentration range of aluminum sulfate and a paint concentration of water to be treated.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Yamase 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Kazushige Seki 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Corporation ( 72) Inventor Koichi Nishioka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (72) Inventor Yukihisa Kobayashi, 6-6-9, also known as Yokkaichi City, Mie Prefecture. Jun 6-4-9, Yokkaichi City, Mie Prefecture, Central Research Laboratory of Hakuto Co., Ltd. (72) Inventor Kazuo Matsui 4-1 Hina Kitamachi, Okazaki City, Aichi Prefecture Unitika Engineering Division, (56) References JP 52 -1440547 (JP, A) JP-A-54-123245 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/52 C02F 1/54 C 02F 1/56

Claims (1)

(57) [Claims] An alkaline agent is added to water to be treated in a coating booth containing an aqueous paint to adjust the pH of the water to be treated to 9.5 to 9.5.
An alkalizing step of adjusting the pH of the water to be treated to 6 to 6 by adding an acidic coagulant;
8. A method for purifying water to be treated in a coating booth, comprising: a neutralizing step of adjusting to 8; and a separating step of separating flocculated floc from the treated water to form treated water and paint sludge.