JP2020000969A - Method and device of treating aqueous ink effluent - Google Patents

Abstract

To provide a method of efficiently precipitating and flocculating resin components and colorant components of various aqueous inks.SOLUTION: There are provided a device of treating aqueous ink comprising a reaction tank 10 for mixing and heating effluent containing aqueous ink, an acid, and an oxidizer to flocculate a solid component of the ink, a filtration tank 70 comprising a filter, and a pipeline 60 for transferring a liquid that contains the agglomerate prepared in the reaction tank 10 to the filtration tank 70, and a method of treating aqueous ink effluent, which is characterized by flocculating the solid component of aqueous ink by adding an acid and an oxidizing agent to effluent that contains aqueous ink, and heating the effluent.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating a waste liquid containing an aqueous ink.

  Inks used in flexographic printing machines, gravure printing machines, and the like have often been oily inks. In recent years, aqueous inks have been developed to reduce the use of volatile organic solvents (VOCs), and the amount of aqueous inks used has been increasing. Aqueous flexographic inks and gravure inks have a composition in which a colorant component (organic pigment or inorganic pigment) is dispersed in an aqueous solution or aqueous emulsion of a resin called a vehicle component, and further a stabilizer component such as an emulsifier is added.

  The water-based ink has an advantage that the apparatus can be washed with water when changing colors of a printing press or an accessory device. However, the washing waste liquid generated at the time of washing with water is a colored suspension in which about 1 g / L to 500 g / L of solid components are dispersed, and therefore cannot be discharged as it is. Further, the solid component in the colored suspension has a very high filtration specific resistance, and it is difficult to perform solid-liquid separation using a filtration device.

  For this reason, the washing waste liquid containing the water-based ink is entirely industrial waste, or a coagulant is added to coagulate and precipitate solid components such as a resin and a colorant component, and pressure filtration is performed by a filter press or the like. The processing is thus performed. However, in the method using a flocculant, the flocculant effect differs greatly depending on the properties of the resin, the coexisting polar solvent component, the stabilizer component, and the like, and the flocculation becomes incomplete with a high concentration liquid having a solid component of 50 g / L or more. There was a problem that a clear filtrate could not be obtained. Further, the collected solid component has a high viscosity and contains a large amount of bound water, so that there is a problem that handling is difficult and a waste amount is increased.

  As a coagulation-sedimentation filtration method, a method has been proposed in which either or both of an acid and a metal salt are added and heated to precipitate and coagulate a resin component, and the resulting mixture is separated by filtration (Patent Document 1). This method may be effective as long as the vehicle component is an alkali-soluble resin having a carboxyl group as a hydrophilic group, but is stabilized by a surfactant or an emulsifier that is currently generally used. It is often not effective for emulsion type resins and colloidal dispersion type resins.

  A method has been proposed in which the coagulation-sedimentation filtration method is improved, a processing agent such as a strong cationic dicyandiamide condensate is added instead of an acid to precipitate a resin component, and further coagulation with a polymer coagulant (Patent) Reference 2). However, in terms of adding a flocculant, the problem of increasing the amount of waste has not been solved.

  As more general methods for treating organic wastewater, a Fenton method, an electrolytic Fenton method (for example, Patent Document 3), an accelerated oxidation method (AOP method) (for example, Patent Document 4), and the like are known. However, the Fenton method and the electrolytic Fenton method require the addition of an iron salt in order to generate OH radicals, and there is a problem that a large amount of iron hydroxide is generated during neutralization and the amount of waste increases. Further, when the processing target is a waste liquid containing an aqueous ink, there is a problem that a large amount of an oxidizing agent or electric power is required for complete decomposition due to a high concentration of the organic substance. The accelerated oxidation method is a method of generating OH radicals by combining ozone, hydrogen peroxide, and UV irradiation. Like the Fenton method, in the case of a waste liquid containing an aqueous ink, a large amount of an oxidizing agent is used to decompose organic substances. In addition, UV irradiation is not effective because the waste liquid containing the aqueous ink is opaque.

JP-A-48-57470 JP 2007-14934 A JP 2017-60942 A JP 2017-202465 A

  The waste liquid containing the aqueous ink (hereinafter also referred to as “aqueous ink waste liquid”) contains a wide variety of aqueous inks such as an alkali-soluble type, an emulsion type, and a colloidal dispersion type, so that the conventional processing method is sufficient. Processing could not be performed. For example, in the method described in Patent Document 1, since a different ink causes a different chemical reaction, a component that does not agglomerate is contained, and a sufficient aggregating process cannot be performed. In the methods described in Patent Literatures 3 and 4, although aggregation occurs, OH radicals are generated and UV irradiation is indispensable, so that it is not practical as a treatment for aqueous ink waste liquid. As described above, a method for efficiently depositing and aggregating the resin component and the colorant component of a variety of aqueous inks has not been established. Further, the treatment method by adding a metal salt or a coagulant has a problem that the amount of solid waste increases. In addition, high-concentration aqueous ink waste cannot be subjected to coagulation treatment. SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide an efficient method and apparatus for treating aqueous ink waste liquid.

  The inventors of the present invention have conducted intensive studies to solve the above-described problems. As a result, the acid functional group was added to the aqueous ink waste liquid to make it non-dissociated, and a small amount of an oxidizing agent was added thereto, followed by heating. It has been found that by partially decomposing the stabilizer component, the hydrophobic resin component and the pigment component having no ionic group can be efficiently aggregated and removed without using a metal salt or a coagulant. The invention has been completed.

Embodiments of the present invention are as follows.
[1] A method for treating an aqueous ink waste liquid comprising adding an acid and an oxidizing agent to a waste liquid containing the aqueous ink, and heating the resultant to agglomerate solid components of the ink.
[2] The method for treating an aqueous ink waste liquid according to [1], wherein the aqueous ink is an aqueous flexographic ink or an aqueous gravure ink.
[3] The treatment method according to [1] or [2], wherein the oxidizing agent is selected from the group consisting of ozone, hydrogen peroxide, chloric acid, chlorate, persulfate, and persulfate. .
[4] An acid and an oxidizing agent are added to the waste liquid containing the aqueous ink, and the solid components of the ink are aggregated by heating, and then the pH is adjusted to neutral by adding an alkali or bicarbonate. The treatment method according to any one of [1] to [3], wherein the aggregate is filtered from the mixture.
[5] a reaction tank for mixing a waste liquid containing an aqueous ink, an acid, and an oxidizing agent and heating the mixture to aggregate the solid components of the ink;
A filtration tank having a filter;
A pipe for sending a liquid containing the aggregate prepared in the reaction tank to the filtration tank,
A processing apparatus for implementing the aqueous ink waste liquid treatment method according to any one of [1] to [4], further comprising:

  That is, in the present invention, the acid is added to the aqueous ink waste liquid to make acidic functional groups such as carboxyl groups into a non-dissociated state (H type) to lose hydrophilicity, and at the same time, increase the oxidation-reduction potential of the oxidizing agent to oxidize. By increasing the power and heating in this state, the hydrophilic structure such as a polyether chain of a surfactant or an emulsifier can be partially decomposed, and the function as a stabilizer for a resin or a pigment component can be destroyed. Due to the combined action of the two reactions of the acid and the oxidizing agent under this heating, even if the aqueous ink waste liquid contains a high concentration of a solid component (derived from resin), the solid component can be efficiently aggregated, and the solid component can be easily coagulated. The solid component can be separated by filtration.

  As the oxidizing agent to be added, it is preferable to use an oxidizing agent having a relatively low oxidation-reduction potential that does not generate OH radicals. Preferably, at least one oxidizing agent selected from the group consisting of ozone, hydrogen peroxide, chloric acid, chlorate, persulfuric acid, and persulfate can be used. The oxidizing agent having a relatively low oxidation-reduction potential is consumed by partially decomposing the hydrophilic structure of the emulsifier and the surfactant present on the surface and the interface of the resin component and the organic pigment component in the aqueous ink waste liquid. Since it does not have enough oxidizing power to oxidize the hydrophobic skeleton of the resin components, organic pigments, emulsifiers and surfactants in the ink waste liquid, it functions as a stabilizer by attacking hydrophilic groups on the surface. Can be reduced efficiently, and waste of oxidizing power can be avoided.

In addition, by partially decomposing the stabilizer, the filtration specific resistance and the viscosity are greatly reduced, so that filtration can be performed even under a release condition without pressurization, and a filtered product having good dehydration properties can be obtained.
The acid to be added is preferably a strong acid having a small acid dissociation constant in order to convert an organic acid such as a carboxyl group into an H-form. For example, sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, oxalic acid, methanesulfonic acid and the like are preferable. Used. The acidic condition is preferably pH 6.58 or less, which is the pKa of maleic acid, and more preferably pH 4.35 or less, which is the pKa of acrylic acid.

  The oxidizing agent added in the present invention does not need to have strong oxidizing power, and does not need to be used in combination with a metal salt such as an iron salt that generates an OH radical. From the viewpoint of reducing the waste of the oxidizing agent and the waste, an oxidizing agent having a weak oxidizing power and having a volatile property is preferable. As the oxidizing agent used in the present invention, for example, ozone, hydrogen peroxide, hypochlorous acid, hypochlorite, chloric acid, chlorate, perchloric acid, perchlorate, persulfate, persulfate, It can be selected from potassium monopersulfate double salt and the like. These oxidizing agents may be supplied as a chemical, or may be supplied by generating or regenerating in situ using an electrolytic oxidation reaction. Among these oxidizing agents, ozone and hydrogen peroxide do not remain as salts after the reaction, and therefore are preferably used from the viewpoint of reducing the amount of waste. When a chlorine-based oxidizing agent is used, it is necessary to pay attention to ventilation since chlorine gas may be generated by a reaction with an acid.

  The heating temperature in the present invention can be appropriately set in consideration of the combination of the type of the stabilizer contained in the aqueous ink to be treated and the oxidizing agent to be added. For example, it can be set to 40 ° C. or higher, preferably about 40 ° C. to 50 ° C. Further, the coagulation action is gradually improved by raising the temperature to about 70 ° C., but it is preferable to perform the treatment at about 50 ° C. from the viewpoint of reducing heat energy. The heating time is, for example, about 10 to 30 minutes, and a sufficient coagulation effect can be obtained. As a heat source for heating, a throw-in heater or the like may be provided, and it is also preferable to use, for example, waste heat from a drying process of a printing press from the viewpoint of energy efficiency.

  Aqueous inks to be treated in the present invention include, for example, aqueous flexographic inks and aqueous gravure inks, but are not limited thereto, and include polar solvent components containing water, vehicle components, and colorants. Any ink can be applied as long as the ink is composed of a component and a stabilizer component. Examples of the vehicle component resin for an aqueous ink include a natural resin, an acrylic resin, a styrene-acrylic resin, a styrene-maleic acid-acrylic resin, and a styrene-maleic acid resin.

  Since the agglomerate obtained by the present invention has a very low filtration specific resistance, the agglomerate is filtered not only using a pressurized filtration device such as a closed bag filter and a filter press but also using a non-pressurized open filtration device. Separation is also possible, and operation costs can be suppressed.

FIG. 1 is a schematic view showing an embodiment of an apparatus (batch type) for carrying out the method for treating aqueous ink waste liquid of the present invention. FIG. 2 is a schematic view showing one embodiment of an apparatus (continuous type) for performing the aqueous ink waste liquid treatment method of the present invention. FIG. 3 is a schematic view showing an embodiment of an apparatus (neutralization type after filtration) for performing the aqueous ink waste liquid treatment method of the present invention. 9 is a photograph showing a state of a processing solution according to Example 3 and Comparative Example 3.

Embodiment

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.
[First Embodiment]
FIG. 1 shows an embodiment of a batch processing apparatus for performing the processing method of the present invention.

  The processing apparatus shown in FIG. 1 mixes an aqueous ink waste liquid, an acid, and an oxidizing agent, and heats the reaction tank 10 to form and precipitate aggregates. A filtration tank 70 having a filter for filtering the liquid containing the aggregate into the aggregate and the separated water, and a pipe 60 for sending the liquid containing the aggregate prepared in the reaction tank 10 and the supernatant water to the filtration tank 70 are provided. . The pipe 60 is connected to the reaction tank 10 so that a liquid containing the aggregate and supernatant water prepared in the reaction tank 10 flows out from the lower part of the reaction tank 10 to the pipe 60.

  The reaction tank 10 is provided with means for mixing and heating the aqueous ink waste liquid, the acid and the oxidizing agent. In the embodiment of FIG. 1, the reaction tank 10 is provided with a heater 20, a stirrer 40, and an acid and oxidant supply means 30.

  In the embodiment of FIG. 1, the reaction tank 10 further adjusts the pH of a liquid containing an aggregate obtained by mixing and heating an aqueous ink waste liquid, an acid, and an oxidizing agent and supernatant water. An agent supply unit 50 is provided. A process in which a pH adjusting agent is added using the pH adjusting agent supply means 50 to adjust the pH of the aggregate and the supernatant water, and then filtered in a filtration tank 70 to obtain a clear and neutralized pH. You can get water.

  As the supply means 30 for the acid and the oxidizing agent, a chemical tank for the acid and the oxidizing agent and a chemical pump are generally provided. Alternatively, an oxidizing solution produced in the anode compartment can be supplied as an acid and an oxidizing agent by installing a small diaphragm electrolytic cell. In this case, the alkaline solution produced in the cathode compartment can be used as a pH adjuster.

Next, a method for treating aqueous ink waste liquid of the present invention using the treatment apparatus shown in FIG. 1 will be described.
The processing apparatus of the present invention is installed in a place where waste liquid and washing waste water accompanying color change and washing of a printing machine and attached equipment can be received, and the aqueous ink waste liquid is received in the reaction tank 10. The solid concentration of the aqueous ink waste liquid to be received is not particularly limited, but the solid concentration is preferably 300 g / L or less in order to secure the fluidity at the time of adding the acid, and the solid concentration is higher than 300 g / L. When the aqueous ink waste liquid is received, the filtered water obtained by the treatment method of the present method can be added to the reaction tank 10 and appropriately diluted.

  While stirring the aqueous ink waste liquid using the stirrer 40 in the reaction tank 10, an acid is added from the acid supply unit 30 to adjust the pH of the aqueous ink waste liquid in the reaction tank 10 to 4.35 or less. The aqueous ink waste liquid is heated to about 50 ° C. using the heater 20, and an oxidant is added from the oxidant supply unit 30. The addition amount of the oxidizing agent and the heating reaction time should be appropriately adjusted depending on the properties of the aqueous ink waste liquid, but the oxidizing agent is about 1.5 g / L as hydrogen peroxide, and the heating time of 10 minutes is sufficient. An aggregation effect can be obtained.

  When the agglutination reaction in the reaction tank 10 is completed, a liquid containing the formed and precipitated agglomerates and supernatant water is introduced into the filtration tank 70 using the pipe 60, and filtered. The transfer of the liquid from the reaction tank 10 to the filtration tank 70 can be performed by pumping water using a pump or by natural flow utilizing a height difference between the tanks. As a filtration method in the filtration tank 70, squeezing using a closed bag filter, a filter press, or the like may be performed, but filtration using natural filtration using an open bag filter or the like is also possible. A sufficiently clear filtrate can be obtained even if the pore size of the filter is as large as about 5 to 10 μm.

  In the embodiment of FIG. 1, the pH adjusting agent is supplied before the liquid containing the aggregate and the supernatant water obtained by mixing and heating the aqueous ink waste liquid, the acid, and the oxidizing agent and heating the filtrate. The pH is adjusted using the means 50. As the pH adjuster supplied by the pH adjuster supply means 50, sodium hydroxide, sodium bicarbonate, calcium hydroxide and the like are preferably used. These are preferably supplied as a powder or an aqueous solution. Alternatively, when a diaphragm electrolytic cell is used as the acid and oxidizing agent supply means, a cathode compartment solution can be used as a pH adjuster. It is preferable that the pH of the treated water is in the range of 5.8 to 8.6 specified in the uniform wastewater standard value.

  Depending on the composition of the received aqueous ink waste liquid, a suspension or precipitate may be generated in the liquid after pH adjustment. In such a case, as described above, the pH is adjusted before filtration to generate a suspension or precipitate in advance, and then filtration is performed to treat the filtered water whose pH has been neutralized and clear. Can be drained as water.

  Although the treated water obtained by the method of the present invention is clear without solids and colorants, depending on the composition of the received aqueous ink waste liquid, it contains a water-soluble organic component and the COD concentration becomes high. May be. If this poses a problem, it is also preferable to perform a post-treatment of decomposing organic components by further adding an oxidizing agent to the treated water or performing electrolytic oxidation treatment.

[Second embodiment]
FIG. 2 shows an embodiment of a continuous processing apparatus for carrying out the processing method of the present invention.
The processing apparatus shown in FIG. 2 includes a reaction tank 10 in which an aqueous ink waste liquid, an acid, and an oxidizing agent are mixed and heated to form an aggregate, and an outflow including the aggregate prepared in the reaction tank 10 and supernatant water. A pH adjusting tank 80 having a pH adjusting agent supply means 50 for adjusting the pH of the liquid, a filtration tank 70 having a filter for filtering the effluent after the pH adjustment into aggregates and separated water, and a reaction tank 10 A pipe 60 for sending the effluent containing the aggregate and the supernatant water prepared in the above to the pH adjustment tank 80, and a pipe 62 for sending the effluent containing the aggregate and the supernatant water after the pH adjustment from the pH adjustment tank 80 to the filtration tank 70. And The pipe 60 is connected to the reaction tank 10 so that the effluent adjusted in the reaction tank 10 flows out from the lower part of the reaction tank 10, and the pipe 62 connects the effluent after pH adjustment from the lower part of the pH adjustment tank 80. It is connected to the pH adjusting tank 80 so as to flow out.

  The reaction tank 10 is provided with means for mixing and heating the aqueous ink waste liquid, the acid and the oxidizing agent. In the embodiment of FIG. 2, the reaction tank 10 is provided with a heater 20, a stirrer 40, and an acid and oxidant supply means 30.

  In the embodiment of FIG. 2, a pH adjusting tank 80 is separately provided between the reaction tank 10 and the filtration tank 70, and adjusts the pH of the effluent containing the aggregate and the supernatant water from the reaction tank 10. The pH adjusting tank 80 is provided with a pH adjusting agent supply means 50. In the pH adjusting tank 80, a pH adjusting agent is added to adjust the pH of the effluent including the aggregates and the supernatant water, and then the filtrate is filtered in the filtration tank 70, whereby the clarified and neutralized pH is obtained. Treated water can be obtained.

  As the supply means 30 for the acid and the oxidizing agent, a chemical tank for the acid and the oxidizing agent and a chemical pump are generally provided. Alternatively, an oxidizing solution produced in the anode compartment can be supplied as an acid and an oxidizing agent by installing a small diaphragm electrolytic cell. In this case, the alkaline solution produced in the cathode compartment can be used as a pH adjuster.

Next, a method for treating aqueous ink waste liquid of the present invention using the treatment apparatus shown in FIG. 2 will be described.
The processing apparatus of the present invention is installed in a place where waste liquid and washing waste water accompanying color change and washing of a printing machine and attached equipment can be received, and the aqueous ink waste liquid is received in the reaction tank 10. The solid concentration of the aqueous ink waste liquid to be received is not particularly limited, but the solid concentration is preferably 300 g / L or less in order to secure the fluidity at the time of adding the acid, and the solid concentration is higher than 300 g / L. When the aqueous ink waste liquid is received, the filtered water obtained by the treatment method of the present method can be added to the reaction tank 10 and appropriately diluted.

  While stirring the aqueous ink waste liquid using the stirrer 40 in the reaction tank 10, an acid is added from the acid supply unit 30 to adjust the pH of the aqueous ink waste liquid in the reaction tank 10 to 4.35 or less. The aqueous ink waste liquid is heated to about 50 ° C. using the heater 20, and an oxidant is added from the oxidant supply unit 30. The addition amount of the oxidizing agent and the heating reaction time should be appropriately adjusted depending on the properties of the aqueous ink waste liquid, but the oxidizing agent is about 1.5 g / L as hydrogen peroxide, and the heating time of 10 minutes is sufficient. An aggregation effect can be obtained.

Next, the effluent containing the aggregates and the supernatant water from the reaction tank 10 is sent to the pH adjusting tank 80, where the pH adjusting agent is added from the pH adjusting agent adding means 50 and neutralized. As the pH adjuster supplied by the pH adjuster supply means 50, sodium hydroxide, sodium hydrogen carbonate, calcium hydroxide and the like are preferably used. These are preferably supplied as a powder or an aqueous solution. Alternatively, in the case where a diaphragm electrolytic cell is used as the acid and oxidant supply means, a cathode compartment solution can be used as a pH adjuster. It is preferable that the pH of the treated water is in the range of 5.8 to 8.6, which is defined as a uniform drainage standard value.
The effluent containing the coagulated matter neutralized in the pH adjusting tank 80 and the supernatant water is introduced into the filtration tank 70 through the pipe 62, and is separated into the coagulated matter and separated water. Transfer of the separated water from the pH adjustment tank 80 to the filtration tank 70 can be performed by pumping using a pump or by natural flow utilizing a height difference between the tanks. As a filtration method in the filtration tank 70, squeezing using a closed bag filter, a filter press, or the like may be performed, but filtration using natural filtration using an open bag filter or the like is also possible. A sufficiently clear filtrate can be obtained even if the pore size of the filter is as large as about 5 to 10 μm.

  Although the treated water obtained by the method of the present invention is clear without solids and colorants, depending on the composition of the received aqueous ink waste liquid, it contains a water-soluble organic component and the COD concentration becomes high. May be. If this poses a problem, it is also preferable to perform a post-treatment of decomposing organic components by further adding an oxidizing agent to the treated water or performing electrolytic oxidation treatment.

[Third embodiment]
FIG. 3 shows another embodiment of a continuous processing apparatus for performing the processing method of the present invention.
The processing apparatus shown in FIG. 3 mixes an aqueous ink waste liquid, an acid, and an oxidizing agent and heats them to form aggregates, and the effluent containing the aggregates and supernatant water prepared in the reactor 10. A filtration tank 70 having a filter for filtering the liquid, a pH adjustment tank 80 having a pH adjusting agent supply means 50 for adjusting the pH of the filtered separated water, an aggregate prepared in the reaction tank 10 and supernatant A pipe 60 for sending an effluent containing water to a filtration tank 70, a pipe 64 for sending separated water filtered in the filtration tank 70 to a pH adjustment tank 80, and a part of the treated water neutralized in the pH adjustment tank 80 And a pipe 66 returning to the filtration tank 70.

  The pipe 60 is connected to the reaction tank 10 so that the effluent containing the aggregate and the supernatant water prepared in the reaction tank 10 flows out from the lower part of the reaction tank 10, and the pipe 64 is connected to the separated water from the filtration tank 70. Is connected to the filtration tank 70 so as to flow out from the lower part of the filtration tank 70, and the pipe 66 is connected to the pH adjustment tank 80 so that the neutralized treated water flows out from the lower part of the pH adjustment tank 80. .

  The reaction tank 10 is provided with means for mixing and heating the aqueous ink waste liquid, the acid and the oxidizing agent. In the embodiment of FIG. 3, the reaction tank 10 is provided with a heater 20, a stirrer 40, and an acid and oxidant supply means 30.

  In the embodiment of FIG. 3, a pH adjustment tank 80 is separately provided downstream of the filtration tank 70, and the pH of the separated water after the aggregation and the filtration is adjusted. The pH adjusting tank 80 is provided with a pH adjusting agent supply means 50. By adding a pH adjusting agent in the pH adjusting tank 80 to adjust the pH, clear and neutralized treated water can be obtained.

Part or all of the treatment water flowing out of the pH adjustment tank 80 is returned to the filtration tank 70 and can be filtered again in the filtration tank 70.
As the supply means 30 for the acid and the oxidizing agent, a chemical tank for the acid and the oxidizing agent and a chemical pump are generally provided. Alternatively, an oxidizing solution produced in the anode compartment can be supplied as an acid and an oxidizing agent by installing a small diaphragm electrolytic cell. In this case, the alkaline solution produced in the cathode compartment can be used as a pH adjuster.

Next, a method for treating aqueous ink waste liquid of the present invention using the treatment apparatus shown in FIG. 3 will be described.
The processing apparatus of the present invention is installed in a place where waste liquid and washing waste water accompanying color change and washing of a printing machine and attached equipment can be received, and the aqueous ink waste liquid is received in the reaction tank 10. The solid concentration of the aqueous ink waste liquid to be received is not particularly limited, but the solid concentration is preferably 300 g / L or less in order to secure the fluidity at the time of adding the acid, and the solid concentration is higher than 300 g / L. When the aqueous ink waste liquid is received, the filtered water obtained by the treatment method of the present method can be added to the reaction tank 10 and appropriately diluted.

  While stirring the aqueous ink waste liquid using the stirrer 40 in the reaction tank 10, an acid is added from the acid supply unit 30 to adjust the pH of the aqueous ink waste liquid in the reaction tank 10 to 4.35 or less. The aqueous ink waste liquid is heated to about 50 ° C. using the heater 20, and an oxidant is added from the oxidant supply unit 30. The addition amount of the oxidizing agent and the heating reaction time should be appropriately adjusted depending on the properties of the aqueous ink waste liquid, but the oxidizing agent is about 1.5 g / L as hydrogen peroxide, and the heating time of 10 minutes is sufficient. An aggregation effect can be obtained.

  Next, the effluent containing the aggregates and the supernatant water from the reaction tank 10 is sent to the filtration tank 70 and filtered. The transfer of the effluent from the reaction tank 10 to the filtration tank 70 may be carried out by pumping using a pump or by natural flow utilizing a height difference between the tanks. As a filtration method in the filtration tank 70, squeezing using a closed bag filter, a filter press, or the like may be performed, but filtration using natural filtration using an open bag filter or the like is also possible. A sufficiently clear filtrate can be obtained even if the pore size of the filter is as large as about 5 to 10 μm.

Next, the separated water filtered is sent to the pH adjusting tank 80, and the pH adjusting agent is added from the pH adjusting agent adding means 50 to be neutralized. As the pH adjuster supplied by the pH adjuster supply means 50, sodium hydroxide, sodium bicarbonate, calcium hydroxide and the like are preferably used. These are preferably supplied as a powder or an aqueous solution. Alternatively, when a diaphragm electrolytic cell is used as the acid and oxidizing agent supply means, a cathode compartment solution can be used as a pH adjuster. It is preferable that the pH of the treated water is in the range of 5.8 to 8.6 specified in the uniform wastewater standard value.
Depending on the composition of the received aqueous ink waste liquid, a suspension or precipitate may be generated in the liquid after pH adjustment. In such a case, the pH-adjusted liquid is returned to the filtration tank 70 via the pipe 66 and filtered again to obtain a clear and neutralized treatment liquid. Although the treated water obtained by the method of the present invention is clear without solids and colorants, depending on the composition of the received aqueous ink waste liquid, it contains a water-soluble organic component and the COD concentration becomes high. May be. If this poses a problem, it is also preferable to perform a post-treatment of decomposing organic components by further adding an oxidizing agent to the treated water or performing electrolytic oxidation treatment.

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.
[Examples 1 to 4]
An aqueous ink waste liquid containing various types of ink was treated using the batch type treatment apparatus shown in FIG. Table 1 shows the test conditions and test results of Examples 1 to 4. In Examples 1 to 4, actual wastewater of an aqueous flexographic printing press for paper bags was used, and in Example 5, actual wastewater of an aqueous gravure printing press for paper packaging materials was used.

  In each of the examples, a clear filtrate was obtained, and the air-dried weight of the filtered product naturally filtered was about 1.1 to 1.4 times the solid concentration in the waste liquid. Example 4 is a condition in which the reaction temperature and the reaction time are increased under the same chemical solution conditions as in Example 3, and the effect that the particle size of the aggregate is larger than the condition of Example 3 and the filtration specific resistance is further reduced. Obtained.

  The filtrate could be discharged as neutral clear water by adjusting the pH with sodium hydroxide. However, when the pH of only the filtrate of Example 2 was neutralized, the separated solution became turbid, and a yellow-brown precipitate was generated. This is considered to be because trace amounts of iron salts and calcium were dissolved in the waste liquid, and a clear filtrate could be discharged by performing cake filtration together with the aggregates.

In Comparative Examples 1 to 4 below, comparative tests were performed using the same flexo ink actual wastewater as used in Example 3.
[Comparative Example 1]
In Comparative Example 1, a conventional treatment with a flocculant was attempted. Table 2 shows the test conditions and test results of Comparative Example 1. Aqua Nature AL-ST01 manufactured by Nextry was used as a flocculant for the aqueous flexographic ink. The state of aggregation was observed by changing the amount of addition from 5,000 mg / L to 30,000 mg / L. However, no aggregation occurred at up to 10,000 mg / L, and partial aggregation was observed under the addition of 30,000 mg / L. Although agglomeration occurred, no precipitation occurred, and filtration was difficult, and the solution was not clarified but remained colored and turbid. The wastewater was diluted 20-fold with water to a solids concentration of 4.9 g / L, and when the coagulant AL-ST01 was added to 1,200 mg / L, coagulation sedimentation occurred and a clear filtrate was obtained. (Not shown in the table). From this, it was confirmed that the waste liquid having a high solid content concentration cannot be treated by the conventional method.

[Comparative Examples 2 to 4]
Table 3 summarizes the test conditions and test results of Comparative Examples 2 to 4. In Comparative Examples 2 to 4, the effects of omitting one condition from each of the three conditions of acid addition, oxidizing agent addition, and heating, which were the treatment conditions in Example 3, were evaluated.

  In Comparative Example 2, only the acid addition and the heating were performed without adding the oxidizing agent. In order to promote the reaction, the heating temperature was increased and the heating time was increased as compared with Example 3, but no significant aggregation and precipitation occurred. The method of Comparative Example 2 was also based on the method of Patent Document 1, and it was suggested that the aqueous flexo ink waste liquid to be treated in this test was difficult to treat by the method of Patent Document 1.

  In Comparative Example 3, only an oxidizing agent was added and heating was performed without adding an acid. As in Comparative Example 2, the heating temperature and the heating time were increased as compared with the Example, but no aggregation occurred. Since the pH was in the neutral range of 7.8, the acidic functional groups of the resin were maintained in a dissociated state, and aggregation was not caused due to the fact that the oxidation-reduction potential of the oxidizing agent did not increase. Can be

  In Comparative Example 4, an acid and an oxidizing agent were added, and the test was performed under the condition that heating was not performed. The reaction was observed overnight at a water temperature of about 20 ° C. Aggregation occurred slightly due to the addition of the acid, but no significant precipitation occurred, and a clear liquid was not obtained.

  In order to facilitate understanding, FIG. 4 shows a comparison of photographs of the aggregated state of Example 3 and Comparative Example 3. In Example 3, aggregates precipitate and can be clearly distinguished from separated water, but in Comparative Example 3, aggregates and precipitates do not occur while suspended.

  From the above results, it can be confirmed that an efficient coagulation treatment is achieved by combining the three conditions of the method of the present invention, namely, addition of an acid, addition of an oxidizing agent, and heating.

According to the aqueous ink waste liquid treatment method of the present invention, an aqueous ink waste liquid containing a wide variety of inks can be efficiently coagulated and settled and easily filtered. The present invention promotes the transition from oil-based inks to water-based inks in the packaging material printing industry and the like, and contributes to addressing environmental problems in the industry.

Claims (5)

A method for treating an aqueous ink waste liquid, comprising adding an acid and an oxidizing agent to the aqueous ink-containing waste liquid and heating the same to aggregate the solid components of the ink. The method according to claim 1, wherein the aqueous ink is an aqueous flexographic ink or an aqueous gravure ink. 3. The method according to claim 1, wherein the oxidizing agent is selected from the group consisting of ozone, hydrogen peroxide, chloric acid, chlorate, persulfuric acid, and persulfate. An acid and an oxidizing agent are added to the waste liquid containing the aqueous ink, and the solid components of the ink are aggregated by heating, and then the pH is adjusted to neutral by adding an alkali or bicarbonate, and then the aggregate is formed. The treatment method according to any one of claims 1 to 3, wherein the water is filtered. A reaction tank that mixes the waste liquid containing the aqueous ink, the acid and the oxidizing agent and heats them to aggregate the solid components of the ink;
A filtration tank having a filter;
A pipe for sending a liquid containing the aggregate prepared in the reaction tank to the filtration tank,
A processing apparatus for implementing the aqueous ink waste liquid processing method according to any one of claims 1 to 4, further comprising: