JP2012192331A - Treatment method for aqueous coating material waste liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment method for aqueous coating material waste liquid, which can simplify treatment steps of waste liquid including an aqueous coating material, reduce treatment cost and recycle the treated waste liquid as plant water for washing or the like of a coating booth.SOLUTION: The waste liquid including the aqueous coating material is recycled as plant water for the coating booth through a reaction step 1 for performing neutralization treatment by adding acid to the waste liquid including the aqueous coating material and then adding alkali, a filtering step 2 for removing a solid content from the treated liquid obtained by the step 1, and an adsorption step 3 for removing water-soluble organic components by adsorbent by means of a merry-go-round method.

Description

  The present invention relates to a method for treating an aqueous paint waste liquid that makes it possible to recycle a waste liquid containing an aqueous paint used as a material for automobile painting as water for a painting booth.

  Conventionally, paints using organic solvents have been used in painting processes such as automobile manufacturing. However, from the viewpoint of environmental protection, volatile organic compounds (VOC) emissions have been required to be reduced. It has become common to use water-based paints that do not use solvents, or that are significantly reduced in the amount of organic solvents replaced with water.

However, water-based paints are water-soluble organic substances and reducing substances that increase the BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), and SS (Floating Substance) content, which are standard water quality. Therefore, it has been difficult to separate and remove organic components once dissolved in water.
For this reason, in the treatment of aqueous paint waste liquid, conventionally, a method of agglomerating and removing organic components by adding an additive has been employed (for example, see Patent Document 1).

In FIG. 2, the outline | summary of an example of the process of the processing method of the conventional water-based paint waste liquid is shown.
In the method shown in FIG. 2, in the primary flocculation step 11, the coating component, which is an organic component, is solidified by the addition of the flocculating agent and precipitates at the bottom of the treatment tank. Since these coagulant and aggregated coating component deposits adhere to the bottom of the treatment tank and accumulate, it was necessary to manually remove the sludge after extracting the treated water.
In addition, since the organic component is not sufficiently removed from the treated water, the sludge is further removed through the secondary agglomeration step 12 and the neutralization step 13, and then the microorganism treatment step 14 is performed in the aeration tank. It was considered as factory wastewater.

  In addition, in the primary flocculation step, instead of adding a flocculant, a method has been proposed in which an acid is added to solidify a paint component and neutralize, and then the solid content is removed (see Patent Document 2). .

Japanese Patent Publication No. 52-45139 JP 2001-219176 A

However, the method using an additive such as an aggregating agent as described in Patent Document 1 is expensive in the cost of an aggregating agent such as an additive, and the labor cost for collecting a precipitate is high. Was necessary. Moreover, it is necessary to treat sludge containing 80% or more of sewage (aqueous paint waste liquid).
In addition, in order to obtain factory wastewater, the agglomeration process has to be performed twice, microbial treatment is necessary, and the number of treatment processes is large and complicated.
Furthermore, in the microbial treatment, the surfactant could not be sufficiently removed, so problems such as foaming occurred, and the wastewater after the microbial treatment could not be recycled as factory water for washing the painting booth. .

On the other hand, as described in Patent Document 2, in the method of adding an acid and an alkali, an inexpensive flocculant is not used, an inexpensive acid and alkali are used, and pH adjustment is fully automated. In addition, since the reaction can be performed in the same tank, there is an advantage that the processing can be simplified and the cost can be reduced.
However, in this method as well, unreacted organic components, particularly non-volatile components such as alcohol compounds such as organic solvents, polymer carboxylic acids, and other additives remain in the waste liquid. In order to obtain wastewater, it was necessary to go through a secondary aggregation process, a neutralization process, a microorganism treatment process, and the like. In addition, as described above, when the microbial treatment process is performed, the surfactant is not sufficiently removed, and problems such as foaming occur. Therefore, the waste water after the microbial treatment is washed in the coating booth. It was not possible to recycle it as industrial water.

  The present invention has been made in order to solve the above technical problem, simplifying the treatment process of waste liquid containing water-based paint, reducing the treatment cost, and cleaning the waste liquid after treatment to the paint booth. It aims at providing the processing method of the water-based paint waste liquid which makes it possible to recycle as industrial water.

The treatment method of the aqueous paint waste liquid according to the present invention includes a reaction step of adding an alkali to the waste liquid containing the aqueous paint, and then neutralizing by adding an alkali, and a filtration step of removing solids from the treatment liquid by the above step And an adsorption process for removing water-soluble organic components with an adsorbent, and the waste liquid containing the water-based paint is recycled as paint booth water.
According to such a process, it is not necessary to perform microbial treatment on the waste liquid containing the water-based paint, and the treatment process can be simplified and the treatment cost can be reduced.

The adsorbent is preferably any one selected from activated carbon, alumina, diatomaceous earth, silica gel, and zeolite.
According to the adsorbents made of these materials, additives and organic components remaining in the waste liquid can be suitably adsorbed and removed.

Moreover, it is preferable to perform the said adsorption | suction process by a merry-go-round system.
Thereby, the additive and organic component which remain | survived in a waste liquid can be removed efficiently simply and at low cost.

According to the method for treating an aqueous paint waste liquid according to the present invention, it is possible to simplify the process of treating the waste liquid containing the aqueous paint, and to reduce the treatment cost.
In addition, the treatment method according to the present invention eliminates the need for microbial treatment that has been carried out in the conventional method, and no organic components or additives remain, so that the waste liquid after treatment is reused as factory water for painting booth washing and the like. It can be used, and the use of washing water in the coating process with a water-based paint can be closed.

It is process drawing which shows the outline | summary of the waste-liquid processing method which concerns on this invention. It is process drawing which shows the outline | summary of the conventional waste liquid processing method.

Hereinafter, the present invention will be described in more detail.
FIG. 1 shows an outline of the processing steps of the water-based paint waste liquid processing method according to the present invention.
As shown in FIG. 1, in the treatment method according to the present invention, after adding an acid to a waste liquid containing a water-based paint, a reaction step 1 in which an alkali is added and neutralized, and a solid content from the treatment liquid in the above step. A filtration step 2 for removing water and a step 3 for adsorbing an adsorption step for removing water-soluble organic components with an adsorbent.
That is, the treatment method according to the present invention is characterized in that the waste liquid containing the water-based paint is treated with the adsorbent in the final step without being treated with microorganisms.

Hereinafter, the processing method according to the present invention will be described in detail in the order of each step.
In the reaction step 1, first, an acid is added to the waste liquid to make it acidic.
The waste liquid here may contain water-based paint, and the water-based paint is not particularly limited to water-based paint for automobile painting.

The acid added to the waste liquid can be a general inorganic acid, and is not particularly limited, and examples thereof include hydrochloric acid, nitric acid, sulfuric acid and the like. The acid concentration is preferably a dilute acid from the viewpoints of safety and ease of pH adjustment.
It is preferable to adjust the acid so that the pH of the waste liquid is about 1 to 6 by adding dropwise with good stirring. In this way, the resin coating component can be solidified by acidifying the waste liquid.

After dropping the acid, it is preferable to heat the waste liquid in order to promote the reaction between the acid and the waste liquid.
The heating temperature at this time is preferably 30 to 100 ° C, more preferably 40 to 80 ° C.
If the heating temperature is too low, the resin coating component may not be cured. On the other hand, since the waste liquid is aqueous, the upper limit of the heating temperature is 100 ° C.

When heating as described above, the heating time is preferably 20 to 120 minutes, more preferably 30 to 60 minutes.
If the heating time is too short, the reaction between the acid and the waste liquid does not proceed sufficiently, and the resin coating component may not solidify. On the other hand, if the heating time is too long, the waste liquid and the acid azeotrope to evaporate and workability It is not preferable in terms of safety and environmental load.

Next, the waste liquid acidified as described above is neutralized by adding an alkali.
The alkali added here can be a general inorganic alkali, and is not particularly limited, and examples thereof include sodium hydroxide, potassium hydroxide, and calcium hydroxide. From these viewpoints, it is preferable to use a dilute alkali from the viewpoints of safety and ease of pH adjustment.

  Then, the resin coating component solidified through the reaction step with acid and alkali as described above is separated and recovered as waste sludge by mechanical dehydration. At the same time, some of the residual SS can also be captured and removed at this point.

The SS remaining without being removed is separately captured and removed in the next filtration step 2. Since the residual SS will lower the adsorption efficiency in the subsequent adsorption step 3, it is preferable to remove it as much as possible before the adsorption step 3.
The filtration method and filter material in the filtration step 2 are not particularly limited, and filter cloth, filter paper, and the like can be used, but sand filtration is preferable in terms of efficiency and cost.

Next, the waste liquid from which SS has been removed in the filtration step 2 is sent to the adsorption step 3. In this adsorption step 3, water-soluble organic components are removed.
The adsorbent used in the adsorption step 3 is not particularly limited, but is one selected from activated carbon, alumina, diatomaceous earth, silica gel, or zeolite from the viewpoint of adsorbing water-soluble organic components. It is particularly preferable to use activated carbon.

When activated carbon is used as the adsorbent, the type, shape, and the like are not particularly limited. For example, pulverized, granular, powdery, etc. plant material having a particle size of about 0.1 to 100 mm, coal, What consists of raw materials, such as petroleum quality, can be used.
Moreover, it is preferable that the quantity is 0.05 to 50 weight% with respect to the amount of waste liquid to process, More preferably, it is 0.5 to 25 weight%.
When the amount of the activated carbon is less than 0.05% by weight, it is difficult to sufficiently remove hydrophilic organic components. On the other hand, when the amount exceeds 50% by weight, the adsorption effect corresponding to the amount larger than that is Since it is not obtained and the cost is increased, it is not preferable.

The adsorption step 3 is preferably performed by a merry-go-round method.
In the merry-go-round method, multiple towers filled with adsorbent are connected in series, and when the adsorption capacity of the first tower into which the waste liquid flows decreases, this tower is removed from the series and a new one is added to the final stage. A method of adding a tower filled with activated carbon.
By adopting such a system, it is possible to obtain a stable water quality treatment liquid with almost constant BOD, COD, etc. without performing aeration treatment or microbial treatment for removing organic components remaining in the waste liquid. Moreover, it is possible to reduce the total waste liquid treatment cost by about 1/3. Further, since conventional microbial treatment is not required, the control of the treatment becomes simple, and additives such as surfactants contained in the waste liquid can be removed.

  The waste liquid processed through the above-described steps does not contain any organic components or additives, and therefore can be recycled as factory water for cleaning a painting booth. According to such recycling, it becomes possible to close the use of the washing water in the coating process with the water-based paint.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.
[Example 1]
103.0 g of 62% nitric acid was added dropwise to 10.89 kg of the waste liquid containing the aqueous paint to adjust the pH to 1-2. After stirring for 30 minutes, the mixture was neutralized with 14.9 g of slaked lime and filtered through gauze.
100 g of the obtained filtrate was collected, 5.0 g of activated carbon (granular white birch XS7100-3 (manufactured by Nippon Enviro Chemicals Co., Ltd.)) was added, the temperature was raised to 50 ° C., and the mixture was stirred for 30 minutes. 99.7 g (yield 72.3%) was obtained.
SS in this treatment solution was 10 mg / L, and COD was less than 500 mg / L.

[Example 2]
4.9 g of 62% nitric acid was added dropwise to 500.1 g of a waste liquid containing an aqueous paint to adjust the pH to 1-2. After stirring for 30 minutes, the solution was filtered with a filter paper to obtain 364.2 g of a colorless and transparent filtrate.
The obtained filtrate was neutralized with 0.3 g of 50% aqueous sodium hydroxide solution and filtered through gauze.
To the obtained filtrate, 20.3 g of activated carbon (granular white birch WH2C8 / 32SS (manufactured by Nippon Enviro Chemicals)) was added, and the temperature was raised to 50 ° C. and stirred for 30 minutes, and then 364.5 g (yield) 72.8%).
SS in this processing liquid was 180 mg / L, and COD was less than 29000 mg / L.

[Comparative Example 1]
To 500.3 g of a waste liquid containing a water-based paint, 5.7 g of 62% nitric acid was dropped to adjust the pH to 2-3. After heating to 50 ° C. and stirring for 30 minutes, the mixture was neutralized with 1.6 g of 50% aqueous sodium hydroxide solution, filtered with gauze, further filtered with filter paper, and 351.2 g (yield) of a light brown filtrate. 70.2%).
SS in this filtrate (treatment liquid) was 1020 mg / L, and COD was less than 34000 mg / L.

  From the results of the above experimental examples, when the waste liquid was subjected to a reaction treatment with acid and alkali, followed by filtration and then adsorption treatment (Examples 1 and 2), compared with the treatment waste liquid not subjected to the adsorption treatment (Comparative Example 1). Thus, it was recognized that SS and COD can be effectively reduced, and it is possible to achieve a water quality level that can be recycled as cleaning water for the painting booth.

Claims (3)

  After adding acid to waste liquid containing water-based paint, neutralization treatment by adding alkali, filtration process to remove solids from the treatment liquid by the above process, and water-soluble organic components are removed by adsorbent A method for treating an aqueous paint waste liquid, wherein the waste liquid containing the aqueous paint is recycled as water for a coating booth through an adsorption step.   The method for treating an aqueous paint waste liquid according to claim 1, wherein the adsorbent is any one selected from activated carbon, alumina, diatomaceous earth, silica gel, and zeolite.   The water-based paint waste liquid treatment method according to claim 1, wherein the adsorption step is performed by a merry-go-round method.

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