Method and apparatus for decolorizing colored wastewater

Abstract

To provide a safe, simple, and low-cost decolorization method and apparatus for colored wastewater generated when manufacturing products using plant materials, particularly colored wastewater generated in the manufacturing process of olive-based foods such as freshly pickled olives. [Solution] By mixing colored wastewater with at least one additive selected from the group consisting of reducing agents and chelating agents, colored wastewater can be decolorized safely, easily, and at low cost.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for decolorizing colored wastewater.

Background Art

[0002] Wastewater generated in a food factory or the like may be colored by dyes or the like contained in the raw materials. However, the color of the wastewater is not subject to the regulations of the Water Pollution Control Law. If the wastewater is discharged into public water areas without sufficient decolorization treatment, it may cause complaints from surrounding residents.

[0003] Regarding the decolorization of colored wastewater, it is often difficult to remove by biological treatment methods such as the activated sludge method, which is a general wastewater treatment method. Therefore, oxidation treatment methods using oxidants such as highly exposed powders, adsorption separation methods using activated carbon or the like, and coagulation precipitation methods using coagulants are generally used as decolorization methods. Further, as decolorization methods using reducing agents, Patent Document 1 discloses a method of using sulfite together with hydrosulfite in colored wastewater, and Patent Document 2 discloses a method of simultaneously adding a peroxide and a reducing agent to colored wastewater for treatment.

[0004] The decolorization effect when these decolorization methods are applied to colored wastewater is not uniform depending on the coloring components contained in the wastewater, and the safety of the chemicals used, the treatment cost, etc. also differ. Specifically, the oxidants used in the oxidation treatment method and the peroxides used in combination with reducing agents may fall under the category of dangerous goods in the Fire Service Act, and the reducing agent hydrosulfite decomposes over time in the air and is unstable. Therefore, highly specialized knowledge is required to safely handle these chemicals and control the decolorization treatment. In addition, the disposal cost of the spent carbon or sludge generated after using the activated carbon commonly used in the adsorption separation method and the coagulant used in the coagulation precipitation method becomes a problem. For example, in the decolorization of wastewater from the production of freshly pickled olives, sodium percarbonate, a hazardous substance, is often used. However, this decolorization requires a large amount of chemicals, and because the treated wastewater is strongly alkaline, a separate neutralization process using highly toxic acids such as sulfuric acid is essential. This raises concerns about the safety of the work and the complexity of the treatment process. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 54-028452 [Patent Document 2] Japanese Patent Application Publication No. 09-085265 [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention has been made in view of the problems of the prior art described above, and its purpose is to provide a safe, simple, and low-cost decolorization method and apparatus for colored wastewater generated in food factories and the like. [Means for solving the problem]

[0006] As a result of diligent research to solve the above problems, the inventors of the present invention have discovered that colored wastewater can be decolorized safely, simply, and at low cost by adding at least one additive selected from the group consisting of reducing agents and chelating agents to colored wastewater, and have completed the present invention.

[0007] In other words, the gist of the present invention is as follows: (1) A method for decolorizing colored wastewater, characterized by decolorizing the colored wastewater generated when manufacturing a product using plants as raw materials by mixing the colored wastewater with at least one additive selected from the group consisting of reducing agents and chelating agents. (2) The method for decolorizing colored wastewater according to (1), wherein the reducing agent is at least one selected from the group consisting of pyrosulfite, sulfite, bisulfite, thiosulfite, ascorbic acid, and isoascorbic acid, and salts thereof. (3) The method for decolorizing colored wastewater according to (2), wherein the reducing agent is a pyrosulfite. (4) The method for decolorizing colored wastewater according to (1), wherein the chelating agent is at least one selected from the group consisting of hydroxycarboxylic acid chelating agents, ethylenediaminetetraacetic acid, and diethyldithiocarbamic acid. (5) The method for decolorizing colored wastewater according to (4), wherein the chelating agent is at least one selected from the group consisting of citric acid, tartaric acid, lactic acid, glycolic acid, and malic acid, and salts thereof. (6) The method for decolorizing colored wastewater according to (5), wherein the chelating agent is citric acid. (7) A decolorizing agent composition for decolorizing colored wastewater from freshly pickled olives, comprising a reducing agent and a chelating agent. (8) A decolorizing agent composition for decolorizing colored wastewater from freshly pickled olives, comprising pyrosulfite and citric acid. (9) A decolorizing apparatus for decolorizing colored wastewater generated when manufacturing products using plants as raw materials, comprising: a reaction tank for decolorizing colored wastewater generated when manufacturing products using plants as raw materials; a transfer unit for transferring the wastewater to the reaction tank; and an additive unit for adding at least one additive selected from the group consisting of reducing agents and chelating agents to the reaction tank. [Effects of the Invention]

[0008] According to the present invention, a safe, simple, and low-cost decolorization method and apparatus can be provided for colored wastewater generated in food factories and the like. Furthermore, while the reducing agent and chelating agent of the present invention can be used individually to achieve a decolorizing effect, a higher decolorizing effect can be obtained by using them in combination. Moreover, the decolorization method using the non-salt chelating agent of the present invention does not require a neutralization step after decolorization, is easy to perform due to the short processing steps and reaction time, and is safe because it does not use hazardous or poisonous substances.

Brief Description of the Drawings

[0009] [Figure 1] Figure 1 is a schematic diagram of the decolorization device used in the method of the present invention.

Modes for Carrying Out the Invention

[0010] Next, a preferred embodiment for carrying out the present invention will be described, but the present invention is not limited thereto.

[0011] plant The plants are not particularly limited, and examples include olive, camphor tree, etc.

[0012] Colored wastewater The colored wastewater includes the colored wastewater generated in food factories, processing factories, etc. that use plants as raw materials. The colored wastewater includes, in particular, the production wastewater of products using olives as raw materials, such as olive new pickles and olive oil (hereinafter referred to as "olive wastewater"). The production wastewater generated in a state where it is not exposed to air as much as possible can obtain a higher decolorization effect.

[0013] Figure 1 shows one embodiment of the decolorization device for colored wastewater according to the present invention, but is not limited thereto.

[0014] As shown in Figure 1, the colored wastewater generated in the manufacturing process is transferred to the reaction tank 1 by the pump 2. In the reaction tank 1, there are provided a chemical tank 3 for adding at least one additive selected from the group consisting of a reducing agent and a chelating agent, a pump 4 for feeding the chemical, and a stirring blade 5 for mixing the colored wastewater and the chemical. The wastewater after the decolorization treatment is drained by the pump 6.

[0015] additives The additive includes a reducing agent, or / and a chelating agent.

[0016] Reducing agent The reducing agents used in the present invention are not particularly limited, and examples thereof include ascorbic acid, isoascorbic acid, pyrosulfurous acid, sulfurous acid, bisulfite, thiosulfuric acid, and salts thereof. Examples of the salts include alkali metal salts such as sodium and potassium; alkaline earth metal salts such as calcium. These reducing agents may be used alone or in combination of two or more, and are not particularly limited.

[0018] Chelating agents The chelating agents used in the present invention are not particularly limited, and examples thereof include citric acid, tartaric acid, lactic acid, glycolic acid, malic acid, ethylenediaminetetraacetic acid, diethyldithiocarbamic acid, and salts thereof. Examples of the salts include alkali metal salts such as sodium and potassium; alkaline earth metal salts such as calcium and magnesium. These chelating agents may be used alone or in combination of two or more, and are not particularly limited.

[0019] The reducing agent and the chelating agent used in the present invention may be added sequentially or simultaneously. In order to perform the present invention efficiently, it is preferable to stir the treatment liquid during the decolorization treatment. As the stirring method for mixing the colored wastewater with the reducing agent and the chelating agent, any method may be used as long as it can be stirred, such as a stirring blade, a magnetic stirrer, or gas bubbling.

[0020] The method for confirming the coloring state of the wastewater is not particularly limited, and examples thereof include visual confirmation or confirmation using a measuring instrument such as a spectrophotometer. As a method for visually confirming the coloring, for example, there is a method of pouring the wastewater into a container such as a beaker and qualitatively determining the coloring state by allowing it to stand on white paper. Further, as a method for quantitatively confirming the degree of coloring visually, there is a dilution method (PPM, Vol. 21, No. 2, pp8-12 (1990)). This method uses a transparency meter with a water depth of 30 cm to compare the test water with distilled water, and numerically displays the dilution ratio at which the distinction is no longer possible as the coloring degree.

Example

[0018] <Test Example 1: Measurement of Color Degree> The degree of coloration was measured using the dilution method. Specifically, two transparency meters (Shibata Scientific Co., Ltd., product name: Standard Transparency Meter) with a water depth of 30 cm were prepared. The sample was poured into one transparency meter from the top up to the 30 cm mark, and distilled water was similarly poured into the other transparency meter. The colors of both were compared by looking through the top of the transparency meters, and the dilution ratio at which they could no longer be distinguished was expressed numerically as the degree of coloration. In evaluating the decolorization performance, a lower numerical value for the degree of coloration after treatment was considered to indicate a better effect. A degree of coloration of 3,000 or less is preferred, and 2,000 or less is more preferred.

[0019] Example 1 200 mL of olive wastewater, collected with minimal exposure to air, was gently poured into a beaker and left to stand in a 20°C constant temperature water bath. 2 g of ascorbic acid (L(+)-ascorbic acid, special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (1 w / v%) was added, and the mixture was stirred with a magnetic rotor for 10 minutes, after which it was left to stand for 24 hours. The discoloration level of the wastewater decreased from 10,000 before treatment to 2,400 after treatment.

[0024] Example 2 The reaction was carried out under the same conditions as in Example 1, except that 2g of sodium pyrosulfite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade sodium pyrosulfite) was added (1 w / v%), and then neutralized with sulfuric acid. The discoloration level of the wastewater was 13,000 before treatment, but decreased to 2,300 after treatment.

[0025] Example 3 The reaction was carried out under the same conditions as in Example 1, except that 2 g of sodium sulfite (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., anhydrous sodium sulfite, special grade) was added (1 w / v%), and then neutralized with sulfuric acid. The discoloration level of the wastewater was 19,000 before treatment, but decreased to 2,400 after treatment.

[0020] Example 4 The reaction was carried out under the same conditions as in Example 1, except that 2g of citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., citric acid) was added (1 w / v%) and allowed to stand for 2 hours. The discoloration level of the wastewater was 9,500 before treatment, but decreased to 1,900 after treatment.

[0021] Example 5 In the same manner as in Example 1, 180 mL of wastewater was gently poured into a beaker and left to stand in a 20°C constant temperature water bath. 0.36 g of sodium pyrosulfite and 1.8 g of citric acid were added (0.2 w / v% and 1 w / v%, respectively), and the mixture was stirred with a magnetic rotor for 10 minutes, after which it was allowed to stand. The color intensity of the wastewater was 9,400 before treatment, decreased to 510 after 2 hours of addition, and to 1,100 after 24 hours of addition.

[0022] Comparative Example 1 In the same manner as in Example 1, 200 mL of wastewater was gently poured into a beaker and left to stand in a 20°C constant temperature water bath. The color intensity of the wastewater was 10,000, but after stirring with a magnetic rotor for 1 hour, the color intensity of the wastewater was 33,000. Furthermore, after stirring for 4 hours and 24 hours, the color intensity of the wastewater was 21,000 and 9,100, respectively.

[0023] Comparative Example 2 240 mL of olive wastewater was gently poured into a beaker and left to stand in a 20°C constant temperature water bath. 3.6 g (1.5 w / v%) of sodium percarbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, and the mixture was stirred with a magnetic rotor for 24 hours before being neutralized with sulfuric acid. The discoloration level of the wastewater was 29,000 before treatment, decreased to 7,200 after 2 hours of addition, and was 2,300 after 24 hours of stirring and treatment with sulfuric acid.

[0030] <Result> When comparing the degree of discoloration of wastewater after decolorizing olive wastewater using a reducing agent and / or chelating agent for Examples 1 to 5, the lowest level was 510 in Example 5, i.e., 2 hours after adding sodium pyrosulfite and citric acid, and a good decolorization effect was obtained even after 24 hours, at 1,100. Examples 1-3 are all experimental cases in which only a reducing agent was added to olive wastewater. The color intensity of Examples 1-3 24 hours after adding the reducing agent was similar to that of Examples 2,300-2,400, and was higher than the result of Example 5 (color intensity of 1,100 after 24 hours). Example 4 is an experimental example in which only a chelating agent was added to olive wastewater. Two hours after adding the reducing agent, the color intensity of Example 4 was 1,900, which was higher than the result of Example 5 (color intensity of 510 after two hours). From these results, it was found that using a combination of reducing agents and chelating agents resulted in higher decolorization performance than using either one alone. Comparative Example 1 is a control experiment in which no reducing agent or chelating agent was added to the olive wastewater. In Comparative Example 1, the color intensity of the wastewater increased from 10,000 at the start of the experiment to 21,000 after 4 hours of stirring, and then to 9,100 after 24 hours. Therefore, Comparative Example 1 had a higher color intensity than any of the cases in Examples 1 to 5. Comparative Example 2 is an experimental example using an oxidizing agent (sodium percarbonate) that has been conventionally used as a decolorizing agent for olive wastewater. After adding sodium percarbonate to olive wastewater, the color intensity of Comparative Example 2 was 7,200 after 2 hours, which was considerably higher than the result of Example 5 (color intensity of 510 after 2 hours). Furthermore, after stirring for 24 hours and then neutralizing with sulfuric acid, the color intensity of Comparative Example 2 was 2,300, which was also higher than the result of Example 5 (color intensity of 1,100 after 24 hours). These results show that in Example 5, the degree of discoloration decreased significantly in a shorter time than in the conventional method using an oxidizing agent, indicating superior decolorization effect. Sodium percarbonate used in Comparative Example 2 is classified as a hazardous material, but the additive used in Example 5 is not classified as a hazardous material, offering the advantage of safe handling. Furthermore, in Comparative Example 2, neutralization using sulfuric acid is necessary, and since sulfuric acid is a highly toxic substance, careful handling is required. However, with the combination of reducing agent and chelating agent used in Example 5, the pH of the wastewater after treatment is neutral, eliminating the need for neutralization with sulfuric acid. This offers the significant advantage of safe, efficient, and low-cost treatment. [Explanation of symbols]

[0024] 1 Reaction vessel 2 pumps 3. Chemical tank 4 pumps 5. Agitator blades 6 pumps

Claims

1. A method for decolorizing colored wastewater, characterized by decolorizing the colored wastewater generated when manufacturing a product using plants as raw materials, by mixing the colored wastewater with at least one additive selected from the group consisting of reducing agents and chelating agents.

2. The method for decolorizing colored wastewater according to claim 1, wherein the reducing agent is at least one selected from the group consisting of pyrosulfite, sulfite, bisulfite, thiosulfite, ascorbic acid, and isoascorbic acid, and salts thereof.

3. The method for decolorizing colored wastewater according to claim 2, wherein the reducing agent is a pyrosulfite.

4. The method for decolorizing colored wastewater according to claim 1, wherein the chelating agent is at least one selected from the group consisting of hydroxycarboxylic acid chelating agents, ethylenediaminetetraacetic acid, and diethyldithiocarbamic acid.

5. The method for decolorizing colored wastewater according to claim 4, wherein the chelating agent is at least one selected from the group consisting of citric acid, tartaric acid, lactic acid, glycolic acid, and malic acid, and salts thereof.

6. The method for decolorizing colored wastewater according to claim 5, wherein the chelating agent is citric acid.

7. A decolorizing agent composition containing a reducing agent and a chelating agent for decolorizing the colored wastewater of freshly pickled olives.

8. A decolorizing agent composition containing pyrosulfite and citric acid for decolorizing the colored wastewater of freshly pickled olives.

9. A decolorization apparatus for decolorizing colored wastewater generated when manufacturing products using plants as raw materials, comprising: a reaction tank for decolorizing colored wastewater generated when manufacturing products using plants as raw materials; a transfer unit for transferring the wastewater to the reaction tank; and an additive unit for adding at least one additive selected from the group consisting of reducing agents and chelating agents to the reaction tank.

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