JP2002018483A - Method for treating pulp wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lighten a load on environment by enabling an adsorptive organic halogen to be reduced and remarkaly colored wastewater discharged especially from a bleaching process to be decolored in a pulp manufacturing process. SOLUTION: When a dye decoloring filiform fungus, especially Geotrichum candidum is inoculated to pulp wastewater, for example, wastewater after oxygen bleaching or decoloration after alkali-extraction, soluble lignin or adsorptive organic halogen being a colored constituent in the wastewater is decomposed, and a load of the wastewater on environment is lightened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention decomposes wastewater from a pulp manufacturing process, in particular, coloring components and adsorptive organic halogens (AOX) of bleaching effluent during a kraft pulp manufacturing process to reduce the load on the environment. How to do it.

[0002]

2. Description of the Related Art In the process of producing pulp from lignocellulosic material, wastewater is colored brown because coloring components derived from lignin and hemicellulose are eluted in cooking effluent and bleaching effluent.

[0003] In pulping by the Kraft method, 100% of lignin present in wood is not removed, but 1-4% remains. If the intended end product is high grade paper, bleaching is performed to remove this residual lignin. Most of the remaining lignin is removed in the alkaline extraction step in the bleach plant. The residual lignin is solubilized in the bleaching step, and the solubilized lignin becomes a coloring component having a conjugate bond formed by an unsaturated bond with a quinoid moiety formed during the oxidation step of the bleaching plant. The bleach plant effluent is colored because it contains this coloring component. There are other sources of color in the paper mill effluent, but when bleaching, the effluent is the primary cause of the effluent color. In the kraft bleached pulp mill, the effluent from the alkali extraction step accounts for the majority of the effluent color.

[0004] These colored wastes significantly resist biological oxidation and are not largely removed in biological treatment plants. Here, available technologies already exist, such as the alkaline extraction step of a bleach plant, which can remove more than 90% of the color from a separate wastewater stream before, during or after biological treatment. I have. These technologies include chemical treatment (eg, alum, ferric, lime polyelectrolyte), biological processes (wood rot fungi), and physical processes (eg, ultrafiltration, ion exchange, carbon adsorption). .

[0005] Further, white rot bacteria are acclimated in advance in wastewater to be treated, and the bacteria are added to a reaction tank into which actual wastewater flows,
There is a method of adding hydrogen peroxide from the outside and oxidatively decomposing colored substances and hardly decomposable substances in actual wastewater using a hydrogen peroxide decomposing enzyme (peroxidase) generated by the white rot fungus (Japanese Patent Laid-Open No. Hei 10 (1998)). -286589).

Further, the pulp is treated with a reducing agent such as sodium bisulfite, hydrosulfite, sodium persulfate or the like which can inactivate chromophores contained in pulp wastewater,
A method of treating the waste water with an epichlorohydrin-dimethylamine polymer capable of decolorizing the waste water (JP-A-7-155)
774), fly ash mainly composed of SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , and MgO generated by combustion of a coal boiler in the pulp wastewater is 3% by weight to 7% by weight based on the pulp wastewater. Pulp wastewater is decolorized by addition and sedimentation (see JP-A-10-249327), and a water-soluble amphoteric copolymer and a polyamine in an amount effective for decolorization are combined to coagulate the pigment contained in the wastewater. To remove aggregated dyes from wastewater (Japanese Patent Laid-Open No.
However, none of these methods enjoys widespread use because they are not economical.

Further, the colored wastewater is passed through a three-phase fluidized-bed biological treatment apparatus filled with a decolorizing bacteria-immobilized carrier and activated sludge or coagulated sludge to treat the wastewater. A method for removing a pigment by acting on a captured indigenous decolorizing bacterium (JP-A-10-27754)
No. 0), a method in which only the decolorizing effective bacterial species are separated from the bacterial flora in the activated sludge, grown and immobilized, and the dye in the wastewater is removed using the decolorizing bacteria-immobilized carrier (Japanese Unexamined Patent Application Publication No.
-323185)), and the like,
There is no known example of immobilizing microorganisms capable of decolorizing bleaching wastewater by these methods.

[0008]

The coloring of the wastewater from a pulp mill impairs the landscape of the rivers and waters discharged, and there is a concern about the effects on the ecology such as a decrease in light transmittance. Is required. Further, since the organic components in the bleaching wastewater are discharged as AOX, it is required to reduce the amount. An object of the present invention is to perform decolorization or AOX reduction of pulp wastewater including bleached wastewater by a novel treatment method using bacteria.

[0009]

Means for Solving the Problems In the study of wastewater treatment by microorganisms, the present inventors have focused on Geotricum candidam, which is considered to be effective for decolorization of dyes, and reached the present invention. Geotrichum can
didum ) is isolated as a microorganism that degrades any of reactive dyes, acid dyes, and disperse dyes, and a method of decolorizing the dye by using this microorganism or this extracellular secretion is known (J.
Ferment. Bioeng., 79, [6] 601-607 (1995), Bioindustry, 13 [2], 27-35 (1996)), and its decomposition rate is known to be high (Japanese Unexamined Patent Publication No. 9-173051). Reference).

That is, in order to solve the above-mentioned problems, the present invention employs the following configuration. 1. A method for treating pulp wastewater, comprising reducing the color and / or organic halogen in the pulp wastewater by inoculating the pulp wastewater with a dye-decolorizing filamentous fungus. 2. The method for treating pulp wastewater according to the first aspect, wherein the pulp wastewater is wastewater from a pulp bleaching process. 3. The method for treating pulp wastewater according to 1 or 2, wherein the dye-decolorizing filamentous fungus is a filamentous fungus belonging to the genus Geotrichum. 4. The method for treating pulp wastewater according to any one of the above-mentioned items 1 to 3, further comprising an organic substance capable of being used by the filamentous fungus in the pulp wastewater. 5. The method for treating pulp wastewater according to claim 4, wherein the organic matter that can be assimilated by the filamentous fungus is glucose.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In this specification, waste liquid discharged from a pulp digestion step, waste liquid discharged from a bleaching step,
Alternatively, a mixture of wastewater or service water discharged from these and another process is indicated as “pulp wastewater” and is an object of the present invention.

As the pulp bleaching wastewater, any of wastewater after oxygen exposure and alkali extraction wastewater after the chlorine stage can be decolorized. For both hardwood and softwood species, the pulp bleaching wastewater can be decolorized. AOX (adsorptive organic halogen) can be decomposed in any wastewater. The measurement of AOX can be performed using an AOX analyzer.

The dye-decolorizing filamentous fungus used in the present invention is not particularly limited as long as it is a filamentous fungus capable of decolorizing dyes such as azo dyes, but is preferably a filamentous fungus belonging to the genus Geotricum, and more preferably. Is used as Geotricum Candidam. In particular, Geotricum candidam Dec1 having high decolorization ability (separated strain FERM P-15348 deposited by National Institute of Biotechnology and Industrial Technology) is suitable.

When the Geotricum candidam Dec1 strain is used, the strain is cultured on an agar medium such as potato dextrose agar medium for about 2 to 10 days, and the cells are suspended in sterile distilled water and filtered with gauze or the like. A method for preparing a spore suspension is simple. By adding the suspension to pulp wastewater and treating it with stirring for at least one day, preferably at least three days, decolorization or AOX reduction can be achieved.

The temperature of the treatment is not particularly limited as long as it is a temperature suitable for the growth of the dye-decolorizing filamentous fungus to be used, but it is preferably from 10 to 40 ° C., more preferably from 15 to 3 ° C.
5 ° C.

Addition of an organic substance which can be assimilated by dye decolorizing bacteria as a carbon source to pulp wastewater promotes decolorization. Examples of the organic substance include sugars such as glucose and starch, and ammonium salts such as ammonium sulfate and ammonium tartrate, urea, yeast extract, malt extract, and soybean protein as nitrogen sources. Among them, the decolorizing effect is particularly high when glucose is added. When glucose is added, a high correlation is seen between the decrease in glucose concentration in the wastewater and the decolorization. If necessary, decolorization can be further promoted by adding a necessary amount of a phosphate, potassium salt, magnesium salt or the like as an inorganic salt.

For example, when using Geotricum candidam as a dye-decolorizing filamentous fungus, 5 to 30 g / L of glucose as a carbon source and 0.5 g of a nitrogen source in pulp wastewater.
/ L ammonium tartrate, 1 g / L potassium dihydrogen phosphate as an inorganic salt, and 0.5 g / L magnesium sulfate heptahydrate, and inoculate a spore suspension of Geotricum candidamum. At 120 ° C. with shaking at 120 ° C., decolorization was observed from the second day, and 75% at the third day.
%, About 90% decolorization on day 7. In this specification, liter is represented by L, mol is represented by M, and millimol is represented by mM.

The measurement of the decolorization rate is performed as follows. Wavelength 46
The absorbance at 5 nm (A ₄₆₅ ) is measured, and the color unit (CU) is calculated according to the following equation.

CU = 500 × A ₄₆₅ /0.132

In the case of a culture solution, the absorbance of the supernatant after centrifugation at 12,000 rpm for 5 minutes is measured. C immediately after inoculation
The decrement rate (%) is defined as the decrement (%) when U is set to 100.

As described in the prior art, the coloring of the pulp wastewater is considered to be a lignin modification, and it is considered that the pulp wastewater can be decolorized by peroxidase or the like that degrades lignin. On the other hand, in the study by Geotricum candidam on the decolorization of the above-mentioned dyes, the action of peroxidase and the like is also presumed.

However, the decolorization of the pulp wastewater of the present invention is as follows.
As shown in the examples described below, it is not linked to the activities of peroxidase, manganese peroxidase, and lignin peroxidase. That is, it was found that the mechanism of decolorization and AOX decomposition in the present invention was not due to a reaction mechanism involving peroxidase such as decolorization of a dye. Therefore, the action of other enzymes is presumed. The activity of peroxidase was measured by adding the enzyme sample in a 25 mM citrate buffer (pH 3.2) containing the dye Reactive Blue 5 as a substrate and containing 100 ppm of the substrate.
Was maintained at 30 ° C. with the addition of hydrogen peroxide as the start of the reaction, and the decrease in absorbance at 600 nm was measured over time. 1
The amount of the enzyme that reduced 1 μmol per minute was defined as 1 unit.

The activity of manganese peroxidase was determined using guaiacol as a substrate and 0.1 mM guaiacol,
The enzyme was added to a 0.1 M tartrate buffer (pH 5) containing 0.1 mM manganese sulfate, and the change with time in the absorbance at 465 nm was measured at 30 ° C. with the addition of 0.1 mM hydrogen peroxide as the start of the reaction. Then, the amount of the enzyme to be reacted at 1 μmol per minute was defined as 1 unit.

The activity of lignin peroxidase is determined by adding the enzyme to 50 mM tartrate buffer (pH 2.5) containing veratryl alcohol as a substrate and 2 mM veratryl alcohol, and adding 0.4 mM hydrogen peroxide. At the start of the reaction, the increase in the absorbance at 310 nm at 30 ° C. was measured over time, and the amount of enzyme reacted at 1 μmol per minute was defined as one unit.

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to the examples.

【Example】

<Embodiment 1> Geotricum candidam D
ec1 (Bio-Industrial Technology Research Institute deposited strain FERMP)
-15348) was cultured for 6 days in potato dextrose agar medium (manufactured by Nissui Pharmaceutical) was suspended the cells in sterilized distilled water to prepare a spore suspension was filtered through gauze 10 ^7.
0.5 g / L ammonium tartrate, 1 g / L potassium dihydrogen phosphate, 0.5 g / L magnesium sulfate heptahydrate were added, and the glucose concentration was increased to 5 g / L and 10 g / L.
The aqueous extract of hardwood alkaline extract of CU1500 containing g / L was inoculated with Geotricum candidam Dec1 (FERM P-15348 strain deposited by the Institute of Biotechnology, Industrial Technology) and cultured with shaking at 30 ° C. and 120 spm. Samples were taken daily and glucose levels and CU were measured. The results are as shown in FIG. 1, where significant bleaching was observed from the second day to the third day, and almost 75% on the third day and 87% on the seventh day.

Comparative Example Geotricum Candidam De
Wastewater treatment was performed in the same manner as in Example 1 except that the c1 strain was not inoculated. That is, 0.5 g / L ammonium tartrate, 1 g / L potassium dihydrogen phosphate, and 0.5 g / L magnesium sulfate heptahydrate were added, and hardwood alkali extraction of CU 1500 containing 10 g / L of glucose was performed. The effluent was shake-cultured at 30 ° C. and 120 spm. Sampled daily and CU was measured. The results were as shown in FIG. 1 and no decolorization occurred.

Example 2 0.5 g / L ammonium tartrate, 1 g / L potassium dihydrogen phosphate, 0.5 g / L
L of magnesium sulphate heptahydrate and the concentration of glucose was adjusted to CU3 containing 5 g / L and 10 g / L, respectively.
The effluent after exposing 200 hardwood oxygen species was inoculated with Geotricum candidam Dec1 strain and cultured with shaking at 30 ° C. and 120 spm. Daily sampling, glucose level and CU
Was measured. The results are as shown in FIG. 2. When glucose was contained at 10 g / L, decolorization was 68% on the sixth day.

Example 3 0.5 g / L ammonium tartrate, 1 g / L potassium dihydrogen phosphate, 0.5 g / L
L of magnesium sulfate heptahydrate was added thereto, and Geotrichum candidum Dec1 strain was inoculated into a CU4100 conifer alkaline extraction wastewater containing a glucose concentration of 30 g / L, followed by shaking culture at 30 ° C. and 120 spm. Samples were taken daily and glucose levels and CU were measured. The result is FIG.
The decolorization rate was 73%, and AOX
Was reduced by 43%. Also, on the second and third days when decolorization is active, peroxidase, manganese peroxidase,
Lignin peroxidase activity was almost nonexistent, and the activity was detected on and after the fourth day after the decolorization activity had ceased. This result clearly indicates that these enzymes are not involved in decolorization.

[0030]

According to the present invention, Geotricum candidam is
With respect to the highly colored effluent generated from the bleaching step in the pulp production step, it is possible to remove the coloring and reduce the amount of adsorbable organic halogen. ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to reduce the load which the wastewater at the time of pulp production gives to an environment.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing a change over time in a decolorization rate and a sugar residual amount of a hardwood alkaline extraction wastewater (CU1500). The horizontal axis of the figure indicates the number of days, and the vertical axis indicates the decolorization rate (%) and the remaining sugar amount (g / L). The display in the figure is as follows. ○ Decolorization rate at 5 g / L of glucose □ Residual amount of sugar at 5 g / L of glucose ● Decolorization rate at 10 g / L of glucose ■ Residual amount of sugar at 10 g / L of glucose × Comparative example without bacteria Decolorization rate

FIG. 2 is a graph showing the change over time in the bleaching rate of a hardwood oxygen-exposed effluent (CU3200). In the figure, ○ indicates the decolorization rate when glucose 5 g / L and glucose 10 g / L were added to the wastewater. The horizontal axis represents the number of days, and the vertical axis represents the bleaching rate (%).

FIG. 3 is a graph showing a time-dependent change in the decolorization rate of a conifer alkaline extraction effluent (CU4100), the residual rate of AOX, and each peroxidase activity. The display in the figure is as follows. ○ Decolorization rate ● AOX residual rate ▲ Peroxidase activity □ Manganese peroxidase activity × Lignin peroxidase activity

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) (C12N 1/14 (C12N 1/14 C12R 1: 645) C12R 1: 645)

Claims (5)

[Claims] 1. A method for treating pulp wastewater, wherein the dye and / or organic halogen in the pulp wastewater is reduced by inoculating a dye-decolorizing filamentous fungus into the pulp wastewater. 2. The pulp wastewater treatment method according to claim 1, wherein the pulp wastewater is a pulp bleaching process wastewater. 3. The method for treating pulp wastewater according to claim 1, wherein the dye-decolorizing filamentous fungus is a filamentous fungus belonging to the genus Geotrichum. 4. The pulp wastewater contains an organic substance which can be assimilated by the filamentous fungus.
A method for treating pulp wastewater according to any one of the above. 5. The method for treating pulp wastewater according to claim 4, wherein the organic matter that can be assimilated by the filamentous fungus is glucose.