Decoloring method of colored waste liquid and production method of food raw material or food

Abstract

To provide a decoloring method of a colored waste liquid which can reduce the chromaticity of the waste liquid while preventing excessive increase in electric conductivity in the waste liquid, and a production method of a food raw material or food including a step of performing such a decoloring method.SOLUTION: A decoloring method of a colored waste liquid includes: performing flocculation treatment in which a chloride flocculant in such an amount that a concentration in a raw waste liquid is 0.010 to 0.1 mass% and a hydroxide flocculant in such an amount that the concentration is 0.3 to 1.0 mass% are added to the raw waste liquid which is a colored waste liquid having an absorbance at a wavelength of 420 nm of 1.0 or less when diluted by 10 times, and solid-liquid separation is performed so as to obtain a treatment liquid of a liquid phase portion; and performing oxidation treatment on the treatment liquid after the flocculation treatment by oxidatively decomposing a component in the treatment liquid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for decolorizing a colored waste liquid, and a method for producing a food ingredient or a food product, which includes a step of carrying out the method. [Background technology]

[0002] Molasses discharged from sugar refineries is widely used as an inexpensive fermentation raw material for the production of ethanol, amino acids, and baker's yeast because it contains nutrients such as amino acids and vitamins, as well as sucrose as its main component. After being used as a fermentation raw material, most of the useful nutrients in the molasses are consumed, and a dark brown colored waste liquid containing molasses pigments derived from the molasses (for example, washing waste liquid generated when washing the cells separated from the culture medium of useful microorganisms such as yeast) is discharged. The main components of molasses pigments are melanoidin, caramel, and polyphenols, which are difficult to biodegrade, and since it is difficult to decolorize them by biological treatment, most of them have been disposed of by ocean dumping. In recent years, ocean dumping has been completely prohibited due to the coming into force of an international treaty, so there is a need to develop a technology to decolorize such colored waste liquid to a level that can be economically reused.

[0003] It has been reported that ozone oxidation treatment is effective as a method for decolorizing colored wastewater (Non-Patent Documents 1 and 2). For example, Non-Patent Document 1 discloses a method of ozone treatment of a biological treatment liquid (a treatment liquid obtained by diluting raw wastewater discharged from a sugar factory in Okinawa Prefecture 250 times and then treating it with a batch activated sludge treatment method). Non-Patent Document 1 also discloses a method of decolorizing a treatment liquid obtained by diluting raw wastewater 400 times by performing only ozone treatment, and also discloses that in this case, a decolorization effect of about 90% was obtained by oxidizing the colored wastewater with ozone for 60 minutes.

[0004] Patent Document 1 discloses a method for treating wastewater containing COD components, which is characterized in that, in a flocculation treatment step using a flocculant carried out prior to an oxidation treatment step, an inorganic flocculant is added to the water to be treated and then an organic flocculant is added to the water to be treated, and activated carbon is added when the inorganic flocculant is added so that the inorganic flocculant and activated carbon coexist in the treatment.

[0005] Although it is not a technology for decolorizing colored waste liquid derived from molasses, Patent Document 2 describes a method for decolorizing molasses itself, which is characterized by filtering molasses and its contents treated with invertase using an ultrafiltration membrane or a reverse osmosis membrane. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-214020 A [Patent Document 2] JP-A-63-207400 (Patent No. 2516006) [Non-patent literature]

[0007] [Non-Patent Document 1] Hiroyasu Ichikawa et al., "Treatment of Molasses Wastewater by Combined Ozone Oxidation and Biological Treatment", Journal of the Japan Society on Water Environment, 1996, Vol. 19, No. 12, pp. 1004-1008 [Non-Patent Document 2] Taira, Naohide et al., "Study on decolorization of colored wastewater by a new chemical oxidation method (2)", Okinawa Industrial Technology Center Research Report, Okinawa Prefectural Industrial Technology Center, 1998, No. 1, 23-42 Summary of the Invention [Problem to be solved by the invention]

[0008] Considering the reuse of the treatment liquid obtained by the decolorization treatment of colored waste liquid, it is desirable to reduce the color of the waste liquid until the absorbance at a wavelength of 420 nm (OD420) when diluted 10 times is 0.005 or less.

[0009] In the decolorization method of Non-Patent Document 1, which only performs ozone treatment, it is described that ozone oxidation treatment was performed on colored wastewater diluted 400 times, and the absorbance (OD400) at a wavelength of 400 nm was about 0.1 (page 59, "3.4 Direct ozone oxidation of molasses wastewater", Figure 6). The color index used in the present invention is OD420 when the wastewater is diluted 10 times. Although OD400 and OD420 are strictly different, they are approximated to show the same degree of absorbance, and when the dilution degree in Non-Patent Document 1 is converted to the dilution degree in the present invention, the color after oxidation treatment is about 0.14. This level of decolorization is insufficient for reuse.

[0010] Non-Patent Document 1 discloses a method for decolorizing colored wastewater by combining ozone oxidation and biological treatment, but even this method does not achieve sufficient decolorization.

[0011] The present inventors have noticed that the molecular weights of the pigments (coloring substances) in the colored wastewater that are difficult to biodegrade have a wide distribution from high to low molecular weights, and have thought that the chromaticity can be efficiently reduced by removing the high molecular weight pigments by coagulation treatment and then decomposing the low molecular weight pigments by oxidation treatment such as ozone treatment. However, they have found that simply performing coagulation treatment using a base such as calcium hydroxide on the colored wastewater causes a problem of excessive increase in electrical conductivity in the treated wastewater. If the electrical conductivity is excessively high, the treated wastewater is not suitable for reuse even if the chromaticity is low. In addition, the increase in electrical conductivity is caused by an increase in the amount of salt derived from the coagulant in the wastewater, and a desalination process or the like must be added in a subsequent process to reduce the electrical conductivity, which may increase costs. Considering the reuse of the treated wastewater as process water, it is desirable to reduce the chromaticity of the colored wastewater and suppress an excessive increase in electrical conductivity.

[0012] The present invention has been made in view of the above problems, and aims to provide a method for decolorizing a colored waste liquid, which can reduce the color of the waste liquid and suppress an excessive increase in the electrical conductivity of the waste liquid. In addition, the present invention aims to provide a method for producing a food material or a food product, which includes a step of carrying out the above-mentioned decolorizing method. [Means for solving the problem]

[0013] The present inventors have found that the chromaticity of the wastewater can be reduced and an excessive increase in electrical conductivity can be suppressed by adding a chloride coagulant in an amount that results in a concentration of 0.010 to 0.1 mass% and a hydroxide coagulant in an amount that results in a concentration of 0.3 to 1.0 mass% to a raw wastewater that is a colored wastewater with an absorbance of 1.0 or less at a wavelength of 420 nm when diluted 10 times, and then carrying out a coagulation treatment, and then carrying out an oxidation treatment for oxidizing and decomposing the components in the treated liquid after the coagulation treatment, thereby achieving the above-mentioned object. The present invention is as follows. <1> A chloride flocculant and a hydroxide flocculant are added to the raw waste liquid, which is a colored waste liquid having an absorbance of 1.0 or less at a wavelength of 420 nm when diluted 10 times, in an amount such that the concentration in the raw waste liquid is 0.010 to 0.1 mass %, and a hydroxide flocculant is added to the raw waste liquid in an amount such that the concentration in the raw waste liquid is 0.3 to 1.0 mass %, and the raw waste liquid is subjected to solid-liquid separation to perform a flocculation treatment to obtain a treated liquid of the liquid phase portion; The treatment liquid after the coagulation treatment is subjected to an oxidation treatment for oxidatively decomposing components in the treatment liquid. A method for decolorizing colored waste liquid. <2> The concentration ratio of hydroxide coagulant to chloride coagulant (concentration of hydroxide coagulant / concentration of chloride coagulant) is 15-60; <1> The method according to <3> After the coagulation treatment, a bubbling treatment is performed in which carbon dioxide gas is brought into contact with the treatment liquid. <1> or <2> The method according to <4> The oxidation treatment is a treatment using at least one of ozone, hydrogen peroxide, and UV. <1> ~ <3> 2. The method according to claim 1 , <5> The chloride flocculant comprises polyaluminum chloride; <1> ~ <4> 2. The method according to claim 1 , <6> The hydroxide flocculant comprises an alkaline earth metal hydroxide; <1> ~ <5> 2. The method according to claim 1 , <7> The alkaline earth metal is calcium; <6> The method according to <8> The colored waste liquid is a washing waste liquid of yeast cells cultured in a medium containing blackstrap molasses. <1> ~ <7> 2. The method according to claim 1 , <9> The concentration ratio of hydroxide coagulant to chloride coagulant (concentration of hydroxide coagulant / concentration of chloride coagulant) is 15 to 60; After the coagulation treatment, a bubbling treatment is performed in which carbon dioxide gas is brought into contact with the treatment liquid, The oxidation treatment is a treatment using at least one of ozone, hydrogen peroxide, and UV light, the chloride flocculant comprises polyaluminum chloride; the hydroxide flocculant comprises an alkaline earth metal hydroxide; The alkaline earth metal is calcium, The colored waste liquid is a washing waste liquid of yeast cells cultured in a medium containing blackstrap molasses. <1> The method according to <10> <1> ~ <9> 2. A method for producing a food ingredient or a food product, comprising carrying out any one of the methods described above. Effect of the Invention

[0014] According to the method for decolorizing colored waste liquid of the present invention, the color of the waste liquid can be reduced to a level that allows reuse, and an excessive increase in the electrical conductivity of the waste liquid can be suppressed. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a graph showing the relationship between oxidation treatment (ozone treatment) time and chromaticity in one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <How to decolorize colored waste liquid> The method for decolorizing a colored waste liquid of the present invention comprises the steps of: A chloride flocculant and a hydroxide flocculant are added to the raw waste liquid, which is a colored waste liquid having an absorbance of 1.0 or less at a wavelength of 420 nm when diluted 10 times, in an amount such that the concentration in the raw waste liquid is 0.010 to 0.1 mass %, and a hydroxide flocculant is added to the raw waste liquid in an amount such that the concentration in the raw waste liquid is 0.3 to 1.0 mass %, and the raw waste liquid is subjected to solid-liquid separation to perform a flocculation treatment to obtain a treated liquid of the liquid phase portion; The treatment liquid after the coagulation treatment is subjected to an oxidation treatment for oxidatively decomposing the components in the treatment liquid.

[0017] According to the present invention, most of the colored substances (particularly high molecular weight components) in the colored wastewater are removed by the coagulation treatment using a chloride coagulant and a hydroxide coagulant in combination, and the remaining colored substances (particularly low molecular weight components) are decomposed by the subsequent oxidation treatment, so that the color can be reduced to a high level. In particular, in the present invention, the amounts of the chloride coagulant and hydroxide coagulant added are adjusted so that the concentrations in the raw wastewater are within a specific range that is sufficient to reduce the color and does not increase the electrical conductivity (EC) excessively. As a result, the increase in EC caused by the addition of the chloride coagulant and hydroxide coagulant can be suppressed while sufficiently reducing the color. In addition, since the amounts of the chloride coagulant and hydroxide coagulant added are appropriately adjusted, the materials and time used during the oxidation treatment can be reduced, so that the present invention can provide an energy-saving decolorization method for colored wastewater.

[0018] The Fenton reaction is known as an effective method for reducing color, but according to the present invention, color can be sufficiently reduced without using the Fenton reaction in the coagulation treatment. The Fenton reaction requires iron chloride and hydrogen peroxide, but iron remains in the treatment liquid. From the viewpoint of environmental conservation, it is necessary to remove iron, but the treatment is very costly. In the present invention, the amount of chloride coagulant and hydroxide coagulant added is balanced in the coagulation treatment, and an oxidation treatment is further combined, so that color can be sufficiently reduced without using iron chloride. In addition, the decolorization method of the present invention does not require an adsorbent such as activated carbon.

[0019] The colored wastewater is not particularly limited as long as it is colored to a degree that the absorbance at a wavelength of 420 nm when diluted 10 times (hereinafter, simply referred to as "diluted OD420") is 1.0 or less. By having a diluted OD420 of 1.0 or less, the color can be sufficiently reduced without using a large amount of flocculant, and the overall cost of treatment can be kept within a practical range. Since the smaller the diluted OD420 is, the easier it is to decolorize, the diluted OD420 may be 0.9 or less, or 0.8 or less. The lower limit of the diluted OD420 is not particularly limited, but in terms of reducing the effort of dilution and suppressing an increase in the amount of treatment due to an increase in the amount of wastewater, it is, for example, 0.5 or more or 0.6 or more in practice. The diluted OD420 may be 1.0 or less at the discharge stage (before dilution), or may be 1.0 or less at the stage diluted after discharge. In other words, the colored waste liquid used as the raw waste liquid in the decolorization method of the present invention may be a waste liquid whose OD420 when diluted is 1.0 or less as discharged, or it may be a waste liquid that has been diluted after discharge so that its OD420 when diluted is 1.0 or less.

[0020] The decolorization method of the present invention is suitable for use with wastewater containing colored substances with a wide range of molecular weights from high to low. Examples of the types of wastewater include wastewater from food and beverage manufacturing plants, paper mills, petrochemical plants, and farms. In particular, the present invention is suitable for use with wastewater discharged during the production of fermentation microbial products, and is even more suitable for use with wastewater from washing yeast cells cultured in a medium containing blackstrap molasses.

[0021] The chloride flocculant is a chloride having an effect of flocculating suspended solids in a suspension, and a known material can be used. The chloride flocculant preferably contains polyaluminum chloride (PAC), and more preferably is PAC. The amount of the chloride flocculant added is adjusted so that the concentration in the raw waste liquid is 0.010 to 0.1 mass%. By adjusting the amount of the chloride flocculant added in this way, the chromaticity of the waste liquid can be reduced and an excessive increase in the electrical conductivity in the waste liquid can be suppressed. The amount of the chloride flocculant added is preferably adjusted so that the concentration in the raw waste liquid is 0.06 mass% or less, 0.05 mass% or less, 0.04 mass% or less, or 0.03 mass% or less. Furthermore, the amount of the chloride flocculant added is preferably adjusted so that the concentration in the raw waste liquid is 0.011 mass% or more, 0.012 mass% or more, 0.013 mass% or more, or 0.014 mass% or more.

[0022] The hydroxide flocculant is a hydroxide having the effect of flocculating suspended matter in a suspension, and known materials can be used. The hydroxide flocculant preferably contains a hydroxide of an alkaline earth metal. Examples of alkaline earth metals include magnesium, calcium, strontium, and barium. The alkaline earth metal is preferably calcium because of its good reactivity with carbon dioxide. In particular, the hydroxide flocculant preferably contains calcium hydroxide, and more preferably calcium hydroxide. The amount of the hydroxide flocculant added is adjusted so that the concentration in the raw waste liquid is 0.3 to 1.0 mass%. By adjusting the amount of the hydroxide flocculant added in this way, the chromaticity of the waste liquid can be reduced and an excessive increase in the electrical conductivity in the waste liquid can be suppressed. The amount of the hydroxide flocculant added is preferably adjusted so that the concentration in the raw waste liquid is 0.9 mass% or less, 0.8 mass% or less, 0.7 mass% or less, or 0.65 mass% or less. Furthermore, the amount of hydroxide coagulant added is preferably adjusted so that the concentration in the raw waste liquid is 0.40 mass% or more, 0.45 mass% or more, 0.50 mass% or more, or 0.55 mass% or more. It is preferable to keep the amount of chloride coagulant and hydroxide coagulant added small within an effective range in order to reduce the burden of subsequent treatment.

[0023] By adding a hydroxide coagulant to the chloride coagulant, it is possible to adjust the pH of the reaction liquid and facilitate coagulation. The timing of adding the added chloride coagulant and hydroxide coagulant is not particularly limited. The chloride coagulant may be added first, the hydroxide coagulant may be added first, and the chloride coagulant and the hydroxide coagulant may be added simultaneously. After adding the coagulant, it is preferable to thoroughly stir the raw waste liquid. The concentration ratio of the hydroxide coagulant to the chloride coagulant (concentration of the hydroxide coagulant / concentration of the chloride coagulant) is preferably 15 to 60. By having the concentration ratio in the above range, the balance between the reduction in the chromaticity of the waste liquid and the suppression of the increase in EC can be further improved. The concentration ratio is preferably 50 or less, more preferably 45 or less, and even more preferably 40 or less. In addition, the concentration ratio is preferably 20 or more, more preferably 23 or more, and even more preferably 25 or more.

[0024] In the decolorization method of the present invention, after adding the chloride flocculant and the hydroxide flocculant, a polymer flocculant can be added. By adding the polymer flocculant, the primary flocs flocculated by the addition of the chloride flocculant and the hydroxide flocculant can be flocculated to generate secondary flocs with larger diameters, making solid-liquid separation easier. The polymer flocculant is not particularly limited, and may be any of cationic, anionic, amphoteric, and nonionic flocculants. The polymer flocculant is preferably an anionic polymer, and more preferably an anionic polyacrylamide.

[0025] The solid-liquid separation of the raw waste liquid after the addition of the flocculant can be carried out by known methods such as a static method, a filtration method, and a centrifugation method. In the case of the static method, the static time is preferably, for example, 30 minutes to 24 hours, and may be 1 to 10 hours. In the case of the filtration method, a filter cloth or diatomaceous earth can be used. In the case of the centrifugation method, the rotation speed is preferably, for example, 100 to 5000 rpm, and may be 150 to 3000 rpm. The processing time of the centrifugation is preferably, for example, 3 to 60 minutes, and may be 5 to 30 minutes.

[0026] After the coagulation treatment, a treated liquid with a certain degree of reduced color is obtained. In the decolorization method of the present invention, from the viewpoint of finally reducing the color (OD420 when diluted) to 0.005 or less by the oxidation treatment, the color of the treated liquid after the coagulation treatment is preferably 0.050 or less, more preferably 0.045 or less, and even more preferably 0.040 or less. The color of the treated liquid is further reduced by the oxidation treatment, for example, to about 1 / 10. Usually, the EC in the treated liquid after the coagulation treatment increases due to the coagulant in the coagulation treatment, but the amount of the increase is suppressed by appropriately adjusting the amount of the chloride coagulant and hydroxide coagulant added. In the decolorization method of the present invention, a treatment for reducing the color is also carried out after the coagulation treatment.

[0027] Specifically, in the decolorization method of the present invention, the treatment liquid after the coagulation treatment is subjected to an oxidation treatment for oxidatively decomposing the components in the treatment liquid. The oxidation treatment decomposes the colored components in the treatment liquid, thereby reducing the chromaticity.

[0028] The oxidation treatment is not particularly limited as long as it is a treatment that can oxidatively decompose the colored substances in the treatment liquid that could not be removed by the coagulation treatment, and can be carried out by a known method. The oxidation treatment is preferably a treatment using at least one of ozone, hydrogen peroxide solution, and UV. In particular, the oxidation treatment is preferably a treatment using ozone. The aeration rate of the ozone gas is, for example, preferably 0.3 to 0.8 L / min, and more preferably 0.4 to 0.6 L / min, per 10 L of liquid. The gas density is, for example, about 50 g / m 3 It is.

[0029] In the present invention, from the viewpoint of removing ions derived from the coagulant as precipitates (e.g., calcium carbonate) and reducing EC, it is preferable to further carry out a bubbling treatment in which carbon dioxide gas is brought into contact with the treatment liquid. The bubbling treatment also has the effect of adjusting (lowering) the pH value. The bubbling treatment is not particularly limited as long as it is a treatment that can reduce EC, and can be carried out by a known method. Examples of the method of bringing carbon dioxide gas into contact with the treatment liquid include a method of injecting air into the treatment liquid, a method of injecting exhaust gas from a heat engine such as a boiler or a spray dryer into the treatment liquid, and a method of injecting dry ice or gas from a carbon dioxide cylinder into the treatment liquid. In the bubbling treatment, the more gas with a higher concentration of carbon dioxide gas is used, the more quickly EC can be reduced. However, the method of injecting dry ice or gas from a carbon dioxide cylinder increases the material cost required for the bubbling treatment. It is preferable to utilize exhaust gas from a heat engine, but if not, injection of air is sufficient. The aeration rate of the injected gas is preferably 40 to 70 mL / min for a liquid volume of 500 mL, and more preferably 50 to 60 mL / min. The time of the bubbling process can be appropriately adjusted according to the carbon dioxide gas concentration in the injected gas and the aeration rate. For example, if the aeration rate for 1 L of liquid is 110 mL / min, the time is, for example, 2 to 4 days (e.g., 3 days) for air, 5 to 7 hours (e.g., 6 hours) for exhaust gas from a heat engine, and 15 to 30 minutes (e.g., 20 minutes) for dry ice or gas from a carbon dioxide gas cylinder.

[0030] The order of the bubbling treatment and the oxidation treatment is not particularly limited, and the bubbling treatment may be performed first, or the oxidation treatment may be performed first. The precipitate generated in the bubbling treatment can be removed by filtration using a filter cloth or diatomaceous earth, or by centrifugation.

[0031] As a result of the decolorization method of the present invention, water is obtained in which the chromaticity of the waste liquid is reduced to a level that allows reuse, and an excessive increase in the electrical conductivity of the waste liquid is suppressed. The chromaticity of the water can be achieved to 0.005 or less, and can also be achieved to 0.004 or less, 0.003 or less, or 0.002 or less. The EC of the water can be achieved to 10.0 mS / cm or less, and can also be achieved to 8.0 mS / cm or less, 5.0 mS / cm or less, or 4.0 mS / cm or less. The pH of the water may be approximately neutral, for example, 6 to 9.

[0032] <Food ingredients or food manufacturing methods> The method for producing a food raw material or food of the present invention includes a step of carrying out the above-mentioned decolorization method. In the method for producing a food raw material or food, including a step of carrying out a decolorization method for a colored waste liquid includes, for example, a case where water treated by the decolorization method is used as process water in the production of a food raw material or food.

[0033] According to the present invention, since the colored waste liquid can be reused, it is expected that the effect of reducing the burden on the environment can be achieved. EXAMPLES

[0034] The present invention will be described in more detail below with reference to examples. The materials, amounts, ratios, processing contents, and processing procedures shown in the examples can be appropriately changed within the scope of the invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[0035] <Verification 1: Combination of flocculants> The effect of changing the combination of flocculants on the decolorization effect was verified. A flocculation treatment was carried out on the raw waste liquid sample using the formula below, and the color, electrical conductivity, and pH of the treated sample (treated liquid) were measured using the measurement methods below. The raw waste liquid was prepared by cultivating baker's yeast in a medium using blackstrap molasses, and washing water was added to the bacteria separated from the medium by centrifugation. The washing waste liquid was then separated by further centrifugation, and activated sludge treatment was carried out to prepare the sample.

[0036] Measurement method (1) Chromaticity Chromaticity is an index of the color tone of a sample. The chromaticity was measured using a V-630 spectrophotometer (manufactured by JASCO Corporation) and the absorbance (OD420) value at a wavelength of 420 nm when diluted 10 times was used. The lower the chromaticity, the more transparent the sample is. The target value for chromaticity is 0.005 or less. The chromaticity can be reduced to about 1 / 10 by the oxidation treatment described below, so the target chromaticity after the aggregation treatment is about 0.05 or less. (2) Electrical conductivity (EC) EC is also an indicator of the amount of salt in a sample. EC was measured using an EC meter EC20 (manufactured by Appella Instruments). The target value for EC is 10.0 mS / cm or less, and preferably 4.0 mS / cm or less. (3) pH The pH was measured using a pH meter HM-30G (manufactured by DKK-TOA Corporation). The pH was targeted to be 6 to 9.

[0037] Treatment Method (1) As an alkaline flocculant, a predetermined amount of sodium hypochlorite (NaClO) aqueous solution (concentration: 30 mass%) shown in Table 1 was added to the raw waste liquid, stirred, and allowed to stand for 24 hours. The supernatant liquid after standing was taken out as a measurement sample.

[0038] (2) As an alkaline flocculant, a specific amount of calcium hydroxide (Ca(OH)2) shown in Table 1 was added to the raw waste liquid, stirred, and allowed to stand for 24 hours. The supernatant liquid after standing was taken out as a measurement sample.

[0039] (3) As an alkaline flocculant, a specific amount of calcium hydroxide shown in Table 1 was added to the raw waste liquid and stirred. An appropriate amount of dry ice was then added to the raw waste liquid to lower the pH to 6.5, and the liquid was allowed to stand for 24 hours. The supernatant liquid after standing was taken out as a measurement sample.

[0040] (4) A specific amount of polyaluminum chloride (PAC) aqueous solution (concentration 10% by mass) shown in Table 1 was added as an acidic flocculant to the raw waste liquid, stirred, and allowed to stand for 24 hours. The supernatant liquid after standing was taken out as a measurement sample.

[0041] (5) A specific amount of PAC aqueous solution (concentration 10% by mass) shown in Table 1 was added as an acidic flocculant to the raw waste liquid sample, and the sample was stirred. Then, a specific amount of NaClO aqueous solution (concentration 30% by mass) shown in Table 1 was added to the sample, and the sample was stirred and left to stand for 24 hours. The supernatant liquid after standing was taken out as a measurement sample.

[0042] (6) As an acidic flocculant, a specific amount of PAC aqueous solution (concentration 10% by mass) shown in Table 1 was added to the raw waste liquid sample, which was then stirred, and then a specific amount of calcium hydroxide shown in Table 1 was added to the sample, which was then stirred and allowed to stand for 24 hours. The supernatant liquid after standing was taken out as a measurement sample.

[0043] (7) As an acidic flocculant, a specific amount of PAC aqueous solution (concentration 10% by mass) shown in Table 1 was added to the raw waste liquid sample and stirred, and then a specific amount of calcium hydroxide shown in Table 1 was added to the sample and stirred. Furthermore, dry ice was added to the sample under the same conditions as in (3). The supernatant liquid after standing was taken out as a measurement sample.

[0044] (8) As an acidic flocculant, 2 mL of a PAC aqueous solution (concentration 10% by mass) was added to the raw waste liquid sample, which was then stirred, and an additional amount of PAC aqueous solution was added to the sample so that the total amount was 40 mL, and the sample was stirred and left to stand for 24 hours. The supernatant liquid after standing was taken out as a measurement sample.

[0045] The measurement results of the raw waste liquid and the samples (treated liquids) of treatments 1 to 8 are shown in Table 1. The amounts added in Table 1 indicate the amounts added per 1 L of raw waste liquid.

[0046] [Table 1]

[0047] Explanation of the results of Test 1 The color, EC and pH of the raw wastewater were 0.48 (when diluted 10 times), 2.97 mS / cm and 8.33, respectively.

[0048] When an aqueous NaClO solution was added to the raw wastewater (Process 1), the color decreased, indicating that decolorization was possible, but the EC was high, indicating that the salt content in the wastewater was high, and the pH was alkaline. This suggests that further desalination treatment is necessary to reuse or discard the treated liquid from Process 1. In Process 1, it takes about 12 hours for complete decolorization, and it is expected that the treatment costs will be high.

[0049] When calcium hydroxide was added to the raw waste liquid (treatment 2), the EC showed a high value and the pH showed an alkaline value, but the color was sufficiently reduced. Furthermore, when an appropriate amount of dry ice was added to the treatment liquid of treatment 2 and a bubbling treatment was performed to react with the carbon dioxide in the dry ice (treatment 3), the color increased, but it was found that the EC could be reduced and the pH could be adjusted to within the target range.

[0050] When only PAC was added to the raw effluent (Treatment 4), the color slightly decreased, and the EC slightly increased, but within the acceptable range.

[0051] When PAC and NaClO were added to the raw wastewater (Treatment 5), the color showed a low value below the target value at a smaller amount than when PAC was not added (Treatment 1). The EC and pH showed high values, similar to those of Treatment 1. This EC value is at a level that is difficult to reduce to the target value even by the subsequent oxidation treatment.

[0052] When PAC and calcium hydroxide were added to the raw waste liquid (treatment 6), the EC showed a high value and the pH was alkaline, just as in the case when PAC was not added (treatment 2), but the chromaticity was sufficiently low with a smaller amount than in treatment 2. When an appropriate amount of dry ice was added to the treatment liquid of treatment 6 and a bubbling treatment was performed to react with the carbon dioxide in the dry ice (treatment 7), it was found that the EC could be lowered and the pH could be adjusted to within the target range while maintaining a sufficiently low chromaticity.

[0053] When a total of 20 times the amount of PAC was added compared to treatment 4 (treatment 8), the color was reduced, but not to a sufficient level, and the EC was high and the pH was acidic.

[0054] The above results indicate that it is possible to sufficiently reduce color and EC by performing coagulation treatment using a combination of chloride coagulants and hydroxide coagulants. When chloride coagulants and hydroxide coagulants are used alone, it is expected that it is not easy to achieve both reduction in color and suppression of excessive increases in EC. For example, when each coagulant is used alone, a large amount of each must be added to reduce the color to the target value after coagulation treatment (0.05 or less). As a result, when PAC is added alone to reduce EC, desalination treatment is required, and when Ca(OH)2 is added alone, a large amount of CO2 is required. By adjusting the amounts of chloride coagulants and hydroxide coagulants to specific ranges, the overall time of the decolorization method can be shortened (especially by balancing the times of bubbling and oxidation treatments).

[0055] <Verification 2: Concentration of chloride coagulant> The effect of changing the PAC concentration on the decolorization effect was examined. The raw wastewater was prepared in the same manner as in Experiment 1. Treatment Method An aqueous PAC solution (concentration: 10% by mass) was added to 500 mL of the raw waste liquid to give the concentration shown in Table 2, and the mixture was stirred and allowed to stand for 30 minutes. Thereafter, the chromaticity, EC, and pH of the supernatant liquid were measured.

[0056] [Table 2]

[0057] Explanation of the results of Test 2 As the amount of PAC added increased, the color decreased, but the EC increased and the pH shifted to the acidic side. When the PAC concentration was 1.0 mass% (0.1 mass% in terms of solid content) or less, the EC was at a level that could be sufficiently reduced in a reasonable processing time in the subsequent processing.

[0058] <Verification 3: Concentration of hydroxide coagulant> The effect of changing the calcium hydroxide concentration on the decolorization effect was examined. The raw wastewater was prepared in the same manner as in Experiment 1. Treatment Method Calcium hydroxide was added to 500 mL of the raw waste liquid to the concentration shown in Table 3, and the mixture was stirred and allowed to stand for 6 hours. The color, EC, and pH of the supernatant liquid were then measured.

[0059] [Table 3]

[0060] Explanation of the results of Test 3 As the amount of calcium hydroxide added increased, the color decreased, but the EC increased and the pH shifted to the alkaline side. When the calcium hydroxide concentration was 1.0 mass% or less, the EC was at a level that could be sufficiently reduced in a reasonable treatment time in the subsequent treatment.

[0061] <Verification 4: Combination conditions of chloride coagulant and hydroxide coagulant> The effect of changing the combination of chloride and hydroxide coagulants on the decolorization effect was examined. The raw wastewater was prepared in the same manner as in Verification 1.

[0062] Treatment Method (9)~(12) A PAC aqueous solution (concentration: 10% by mass) was added to the raw waste liquid sample to give the specified concentration shown in Table 4, and the sample was stirred and left to stand for 30 minutes. Calcium hydroxide was then added to the sample to give the specified concentration shown in Table 4, and the sample was stirred and left to stand for 6 hours. The supernatant was then recovered by centrifugation to obtain a new sample. After that, an appropriate amount of dry ice was added under the same conditions as in (3), and the chromaticity, EC, and pH of the sample were measured.

[0063] (13) Calcium hydroxide was added to the raw waste liquid sample to give the specified concentration shown in Table 4, and the sample was stirred and left to stand for 6 hours. Furthermore, a PAC aqueous solution (concentration: 10% by mass) was added to the sample to give the specified concentration shown in Table 4, and the sample was stirred and left to stand for 30 minutes, and the supernatant was collected by centrifugation to obtain a new sample. Thereafter, the chromaticity, EC, and pH of the sample were measured.

[0064] (14) Calcium hydroxide was added to the sample, which was the raw waste liquid, to a prescribed concentration shown in Table 4, and the mixture was stirred and left to stand for 6 hours. Furthermore, an aqueous PAC solution (concentration: 10% by mass) was added to the sample to a prescribed concentration shown in Table 4, and the mixture was stirred and left to stand for 30 minutes, and the supernatant was collected by centrifugation to obtain a new sample. After that, an appropriate amount of dry ice was added under the same conditions as in (3), and the chromaticity, EC, and pH of the sample were measured.

[0065] (15) A PAC aqueous solution (concentration 10% by mass) and calcium hydroxide were simultaneously added to the raw waste liquid sample to give the specified concentrations shown in Table 4, and the mixture was stirred and allowed to stand for 6 hours, after which the supernatant was collected by centrifugation to obtain a new sample. The chromaticity, EC, and pH of the sample were then measured.

[0066] (16) A PAC aqueous solution (concentration 10% by mass) and calcium hydroxide were simultaneously added to the raw waste liquid sample to the prescribed concentrations shown in Table 4, stirred, allowed to stand for 6 hours, and then centrifuged to recover the supernatant to obtain a new sample. After that, an appropriate amount of dry ice was added under the same conditions as in (3), and the chromaticity, EC, and pH of the sample were measured.

[0067] [Table 4]

[0068] Explanation of the results of Test 4 In the cases of treatments 9 to 12, the samples became red and turbid when calcium hydroxide was added. By adding an appropriate amount of dry ice to these samples, the floating precipitate settled, and a supernatant with sufficiently reduced color and EC was obtained. The pH was also within the target range. In particular, when the concentration of the PAC aqueous solution was 0.15 to 0.2 mass% (0.015 to 0.02 mass% in terms of solid content) and the concentration of calcium hydroxide was 0.6 mass%, a supernatant with significantly reduced color and EC was obtained (treatments 10 and 11). When the treatments were performed in the same manner as treatments 9 to 12, except that the bubbling treatment was not performed, the results were similar to those of treatment 13.

[0069] Even when the order of addition of the PAC aqueous solution and calcium hydroxide was reversed (treatments 13 and 14), the decolorization effect was similar to that of treatments 9 to 12. Even when the PAC aqueous solution and calcium hydroxide were added to the raw wastewater simultaneously (treatments 15 and 16), the decolorization effect was similar to that of treatments 9 to 12. In addition, by performing the bubbling treatment, the EC was reduced to the same extent as in treatments 9 to 12 (treatments 14 and 16).

[0070] It was found that by using an appropriate combination of coagulants in the coagulation treatment, it is possible to reduce the color to about 1 / 10 to 1 / 30 while maintaining the EC at 10.0 mS / cm or less. If the color is 0.05 or less and the EC is 10.0 mS / cm or less at this stage before the oxidation treatment, then a sufficient decolorization effect can be expected from the subsequent oxidation treatment. From the results of verification 4, it can be predicted that if the concentration of the chloride coagulant is 0.010 to 0.1 mass% converted to solids, and the concentration of the hydroxide coagulant is 0.3 to 1.0 mass%, then the color and EC can be sufficiently reduced in a reasonable treatment time in the subsequent oxidation treatment.

[0071] <Verification 5: Combined use of coagulation and oxidation treatment> The decolorization effect of combining coagulation and oxidation treatments was verified. Raw waste liquid was prepared in the same manner as in Test 1, and the following coagulation and bubbling treatments were carried out on this raw waste liquid. Then, the following oxidation treatment using ozone was carried out, and the color, EC, and pH of the obtained sample were measured.

[0072] Coagulation treatment A PAC aqueous solution (concentration 10% by mass) was added to the raw waste liquid sample to a concentration of 0.2% by mass (0.02% by mass in terms of solid content), and the mixture was stirred for 30 minutes. After that, calcium hydroxide was added to the sample to a concentration of 0.6% by mass, and the mixture was stirred for 6 hours. Furthermore, a PP355 (anionic polyacrylamide polymer, manufactured by ANHUI JUCHENG FINE CHEMICALS CO., LTD., China) solution (concentration 0.1% by mass) was added to the sample to a concentration of 17 ppm by mass, and coagulated flocs were precipitated in the sample. The precipitates were removed from the sample by filtering the sample through a screen mesh (opening 600 μm), and the filtrate thus obtained was filled into a high-density polyethylene container.

[0073] Bubbling process The filtrate filled in the vessel was reacted with carbon dioxide by bubbling air through the vessel under conditions of aeration rate of 55 mL / min per 500 mL of liquid for 3 days.

[0074] Oxidation Treatment The sample after bubbling treatment was circulated at a flow rate of about 10 L / min, and ozone gas was mixed with the sample through an ejector, to perform ozone treatment. Ozone gas was generated at a flow rate of about 0.5 L / min and a concentration of about 50 g / m using an ozone generator (Fabozone 5, Ecodesign Co., Ltd.) that generates ozone from oxygen supplied from an oxygen cylinder. 3 The gas was supplied at a gas density of 1000 MPa for 60 minutes.

[0075] The relationship between the treatment time of the oxidation treatment, the color, EC and pH is shown in Table 5. Figure 1 is a graph showing the relationship between the treatment time of the oxidation treatment (ozone treatment) and the color.

[0076] [Table 5]

[0077] Explanation of the results of Test 5 By carrying out the oxidation treatment, the color of the sample reached the target value of 0.005 or less in about 15 minutes, and reached 0.002 (1 / 10 of the initial value) after 60 minutes. The EC was sufficiently reduced by the bubbling treatment before the oxidation treatment, and did not exceed the initial value during the oxidation treatment, remaining at a sufficiently low value. There was no significant change in pH during the oxidation treatment, and it remained near neutral.

[0078] From the results of verifications 1 to 5, it was found that by carrying out coagulation treatment using a chloride coagulant and a hydroxide coagulant in combination and oxidation treatment on colored wastewater, it is possible to suppress an excessive increase in EC and reduce the color to 0.005 or less while maintaining the pH at a value close to neutral. As explained in the background art, it is known that oxidation treatment has a certain degree of decolorization effect on molasses-derived wastewater, but oxidation treatment alone cannot achieve sufficient decolorization to the extent that it can be discarded or reused. For example, in the method of Non-Patent Document 1, the color reaches only about 0.14 (converted value at the index OD420 adopted in the present invention) after 60 minutes of ozone treatment. In contrast, the method of the present invention can significantly reduce the color of colored wastewater derived from molasses. In particular, it was found that the increase in EC can be further suppressed by also carrying out a bubbling treatment using carbon dioxide gas.

[0079] In addition, since the chromaticity is already reduced to a certain degree before the oxidation treatment, and the time required for the oxidation treatment is relatively short, it is expected that the initial cost and running cost of the oxidation treatment can be reduced.

[0080] <Verification 6: Residual amount of contaminants in processing solution> The amount of residual contaminants in the treated liquid was confirmed by a simple fouling test. The raw waste liquid was prepared in the same manner as in Verification 1. Fouling Test A membrane filter with a pore size of 0.22 μm or 0.45 μm was attached to the tip of a 10 mL syringe, and the syringe was placed in a 50 mL Falcon tube, and a Falcon tube assembled in this manner was prepared for each treatment liquid. 10 mL of treatment liquid was injected into each syringe, and the Falcon tube was attached to a centrifuge (HITACHI himac CF98DL, Hitachi, Ltd.), centrifuged at 500 rpm for 5 minutes, and the amount of liquid remaining in the syringe was measured. The smaller the amount of remaining liquid, the less likely it was to cause clogging, and the greater the amount of passing liquid, indicating that there was less residual contaminant.

[0081] Treatment Method (17) Treatment method for wastewater by coagulation treatment using iron chloride A 40% by mass iron chloride (III) (FeCl3) solution was added to the raw waste liquid sample to a concentration of 0.43% by mass (solid content 0.17% by mass) and stirred. Then, a 0.1% by mass PP355 solution was added to the sample to a final concentration of 23 ppm by mass, causing coagulated flocs to precipitate in the sample. The precipitates were removed from the sample using a sludge dewatering device to obtain a measurement sample.

[0082] (18) A method for treating wastewater by coagulation treatment using PAC and calcium hydroxide A PAC aqueous solution (concentration 10% by mass) and calcium hydroxide were simultaneously added to the raw waste liquid sample, which was then stirred and allowed to stand for 6 hours. The amount of PAC aqueous solution added was adjusted to a final concentration of 0.2% by mass, and the amount of calcium hydroxide added was adjusted to a final concentration of 2.6% by mass. Then, a 0.1% by mass PP355 solution was added to the sample to a final concentration of 17 ppm by mass, causing coagulated flocs to precipitate in the sample. The precipitates were removed from the sample using a sludge dewatering device to obtain a measurement sample.

[0083] (19) A method for treating wastewater by coagulation treatment using PAC and calcium hydroxide and ozone treatment A PAC aqueous solution (concentration 10% by mass) and calcium hydroxide were simultaneously added to the raw waste liquid sample, which was then stirred and allowed to stand for 6 hours. The amount of PAC aqueous solution added was adjusted to a final concentration of 0.2% by mass, and the amount of calcium hydroxide added was adjusted to a final concentration of 2.6% by mass. Then, a 0.1% by mass PP355 solution was added to the sample to a final concentration of 17 ppm by mass, causing coagulated flocs to precipitate in the sample. The precipitate was removed from the sample using a sludge dewatering device to obtain a new sample, which was then filled into a high-density polyethylene container. The sample in the container was circulated at a flow rate of about 10 L / min, and ozone gas was mixed with the sample through an ejector, to perform ozone treatment. Ozone gas was generated at a flow rate of about 0.5 L / min and a concentration of about 50 g / m3 using an ozone generator (Fabozone 5, Ecodesign Co., Ltd.) that generates ozone from oxygen supplied from an oxygen cylinder. 3 The gas was supplied at a gas density of 1000 MPa for 15 minutes.

[0084] The results of the fouling tests are shown in Table 6.

[0085] [Table 6]

[0086] Explanation of the results of Test 6 In both cases of 0.22 μm and 0.45 μm pore size, the method of the present invention (Process 19) was found to be able to reduce colored substances in the raw wastewater significantly compared to other methods. This result shows that, according to the present invention, the colored substances in the wastewater can be appropriately reduced in the coagulation treatment using a chloride coagulant and a hydroxide coagulant in combination, and the colored substances can be almost completely removed by the subsequent oxidation treatment.

[0087] The treated water obtained by treating colored wastewater using the decolorization method of the present invention has sufficiently reduced chromaticity and EC, which are at a level that does not place a burden on the environment and is even at a level that allows it to be reused as process water in factories. [Industrial Applicability]

[0088] The present invention can be used to treat wastewater containing colored substances having a wide distribution of molecular weights from high to low, particularly wastewater discharged during the manufacture of fermentation microbial products.

Claims

1. a chloride flocculant and a hydroxide flocculant are added to a raw waste liquid, which is a colored waste liquid having an absorbance of 1.0 or less at a wavelength of 420 nm when diluted 10 times, in an amount such that the concentration in the raw waste liquid is 0.010 to 0.1 mass %, and a hydroxide flocculant is added to a concentration in the raw waste liquid of 0.3 to 1.0 mass %, and the raw waste liquid is subjected to solid-liquid separation to perform a flocculation treatment to obtain a treated liquid of the liquid phase portion; The treatment liquid after the coagulation treatment is subjected to an oxidation treatment for oxidatively decomposing components in the treatment liquid. A method for decolorizing colored waste liquid.

2. 2. The method according to claim 1, wherein the concentration ratio of hydroxide flocculant to chloride flocculant (concentration of hydroxide flocculant / concentration of chloride flocculant) is 15-60.

3. 3. The method according to claim 1, further comprising the step of: after the coagulation treatment, carrying out a bubbling treatment in which carbon dioxide gas is brought into contact with the treatment liquid.

4. 3. The method according to claim 1, wherein the oxidation treatment is a treatment using at least one of ozone, hydrogen peroxide, and UV.

5. 3. The method of claim 1 or 2, wherein the chloride flocculant comprises polyaluminum chloride.

6. 3. The method of claim 1 or 2, wherein the hydroxide flocculant comprises a hydroxide of an alkaline earth metal.

7. 7. The method of claim 6, wherein the alkaline earth metal is calcium.

8. 3. The method according to claim 1 or 2, wherein the colored waste liquid is a waste liquid obtained by washing yeast cells cultured in a medium containing blackstrap molasses.

9. The concentration ratio of the hydroxide coagulant to the chloride coagulant (concentration of the hydroxide coagulant / concentration of the chloride coagulant) is 15 to 60; After the coagulation treatment, a bubbling treatment is performed in which carbon dioxide gas is brought into contact with the treatment liquid, The oxidation treatment is a treatment using at least one of ozone, hydrogen peroxide, and UV light; the chloride flocculant comprises polyaluminum chloride; the hydroxide flocculant comprises an alkaline earth metal hydroxide; The alkaline earth metal is calcium, 2. The method according to claim 1, wherein the colored waste liquid is a waste liquid obtained by washing yeast cells cultured in a medium containing molasses.

10. 13. A method for producing a food ingredient or food product, comprising carrying out the method according to claim 1.

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