JP2005334873A - Method for treating waste water from elemental chlorine free bleaching process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating waste water from an elemental chlorine free ECF bleaching process of a paper pulp production process for simply and effectively removing an organic component and a coloring component at a low cost by a combined use of an activated sludge treatment and an adsorption treatment using incineration ash. <P>SOLUTION: This method is for treating the waste water from the ECF bleaching process for effectively removing the organic component and the coloring component in the waste water by mixing the waste water with ash discharged from a boiler or an incinerator, and thereafter by treating the waste water via the activated sludge treatment. The specific surface of the ash is preferably 2,000 cm<SP>2</SP>/g or more. The pH of the ECF bleaching waste water during the treatment is preferably not less than 8. The used ash can be reused after incinerating at 800°C or higher. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for treating organic components and coloring components contained in wastewater discharged from pulp factory wastewater, particularly wastewater discharged from a so-called ECF (Elemental Chlorine Free) bleaching process that does not use elemental chlorine.

In order to use lignocellulosic material as a papermaking raw material in many applications, after pulping by chemical action such as cooking, or pulping by mechanical action using a refiner etc., the resulting pulp is bleached by chemicals. Need to be bleached to increase whiteness. For example, kraft pulp is usually subjected to alkaline oxygen bleaching, except when used for applications that require strength such as packaging materials, and then atomic chlorine, hypochlorite, chlorine dioxide, hydrogen peroxide, oxygen, It is generally used as bleached kraft pulp after being bleached with a bleaching agent such as ozone or caustic soda and a bleaching aid, and lignin, which is a color-causing substance contained in the pulp, is removed. In addition, mechanical pulp is usually bleached in one or two stages using chemicals such as hydrogen peroxide and hydrosulfite.

In recent years, so-called ECF (Elemental Chlorine Free), which does not use elemental chlorine for the purpose of suppressing organic chlorine compounds, is in progress in Japan. Usually, as bleaching using chlorine, as described above, atomic chlorine (C), caustic soda / oxygen (E / O), hypochlorite (H), chlorine dioxide (D), etc. are used. It is said that the 4-stage sequence of -E / O-H-D is advantageous from the viewpoint of bleaching cost. In addition, in order to convert this sequence to ECF, it is necessary to substitute chlorine and hypochlorite with other chemicals. However, as a chemical substitute for chlorine, the reactivity is similar and the current reaction Chlorine dioxide that can be substituted in the tower is used, and hydrogen peroxide (P) is often used as an alternative to hypochlorite as well.

Wastewater from the ECF bleaching process is decolorized using coprecipitation with iron hydroxide in addition to biological treatment and coagulation sedimentation treatment after being mixed with wastewater from single or other processes to remove organic components and coloring components. It is processed by combining various methods such as adsorption treatment and ozone oxidation.

There is a method of using a polymer flocculant, sulfuric acid sulfate or polyaluminum chloride in the coagulation sedimentation treatment of waste water. Also, as in Japanese Patent Publication No. 31-4636 (see Patent Document 1), in wastewater treatment in the bleaching process, iron waste is dissolved in acidic wastewater generated from the chlorine stage, mixed with alkaline wastewater, etc., and slaked lime is added. A treatment method is also known in which the pH is adjusted to produce iron hydroxide, and the organic components and colored components of the waste water are adsorbed and coagulated and precipitated in this floc, but it is not suitable for the treatment of ECF bleaching waste water with less chlorine ions in the waste water. It is.

In addition, when switching from a normal bleaching sequence (CE / O-HD etc.) to an ECF bleaching sequence (D1-E / OPPD2 etc.), Japanese Patent Laid-Open No. 2002-186975 (see Patent Document 2) Although there is a method of substituting ferrous chloride as in (1), there is a problem that the treatment cost is high in addition to increasing the amount of chloride ions in the wastewater sludge.

Japanese Patent Laid-Open No. 10-249327 (see Patent Document 3) discloses a method for treating pulp wastewater in which fly ash generated from a coal boiler is added, mixed, and settled. It is intended for pulp wastewater after the secondary treatment and takes time for sedimentation separation.
Japanese Patent Publication No. 31-4636 JP 2002-186975 A JP-A-10-249327

An object of the present invention is to treat organic components and colored components at low cost simply and efficiently by using an ECF bleaching wastewater in a paper pulp manufacturing process in combination with an adsorption treatment using incinerated ash and an activated sludge treatment.

According to the present invention, it is possible to easily and efficiently treat ECF bleaching wastewater at low cost, and it is possible to use various incineration ash generated in a paper mill.

In order to achieve the above-mentioned problems, the present inventors have earnestly studied the treatment of ECF bleaching process wastewater and obtained the following knowledge. That is, after mixing the ash discharged from the boiler or the incinerator with the bleaching effluent, it was found that organic components and coloring components in the effluent can be efficiently removed by treating with activated sludge, and the present invention was completed. It was.

The present invention encompasses the following inventions.
(1) No elemental chlorine used in the paper pulp manufacturing process (ECF) A method of treating ECF bleaching process wastewater in which activated sludge is treated after mixing the ash discharged from the boiler or incinerator with the wastewater generated from the bleaching process.
(2) The method for treating ECF bleaching process waste water according to (1), wherein the specific surface area of the ash is 2000 cm ² or more.
(3) The method for treating ECF bleaching waste water according to (1) or (2), wherein the ash has a particle size of 2 to 80 μm.
(4) The ECF wastewater treatment method according to any one of (1) to (3), wherein the ash is mixed with wastewater in a range of 0.01% by mass to 5.0% by mass.
(5) The method for treating ECF bleaching process waste water according to any one of (1) to (4), wherein mixing of ash and waste water is performed at a pH of 8 or more.
(6) The method for treating ECF bleaching process waste water according to any one of (1) to (5), wherein the ash is combusted at 800 ° C. or higher after being mixed with waste water and reused.

The mechanism of removing organic components and colored components from the bleaching process wastewater by treating the activated sludge after mixing the ash discharged from the boiler or the incinerator with the wastewater generated from the ECF bleaching process is considered as follows. In the first treatment using incinerated ash, organically difficult-to-decompose organic coloring components such as lignin contained in the bleaching process wastewater are adsorbed and removed by unburned carbon adhering to the incinerated ash surface. On the other hand, in the subsequent activated sludge treatment, the organic components are decomposed and the incinerated ash is agglomerated and separated by a viscous substance produced by the fungus body, thereby obtaining a clear treated water.

Activated sludge and coagulation sedimentation are often used together with wastewater treatment in the bleaching process, but the organic matter concentration and chromaticity after activated sludge treatment are reduced by placing adsorption treatment with incinerated ash before activated sludge treatment. In addition, the load on the subsequent process can be reduced, and the wastewater treatment cost can be reduced.

In the present invention, ash generated in a paper mill is used as ash to be added to and mixed with wastewater generated from the ECF bleaching step.
Most of them are generated from boilers and incinerators, and incinerators include fluidized bed furnaces and stalker furnaces. The generated ash is roughly divided into fly ash that turns to the exhaust gas side (fly ash) and fuel shells (clinker ash) that remain in the furnace bottom. In the present invention, any ash discharged from the above-described boiler and incinerator can be used.
Of the ash, those with less unburned carbon can be used effectively for building materials, and those with less disturbing components such as chlorine can be used effectively as cement raw materials. There has been a lot of effort and cost to process.

In the present invention, ash having a specific surface area of 1000 cm ² / g or more is preferable, and ash having a specific surface area of 2000 cm ² / g or more is used. Those having a specific surface area of less than 2000 are not preferred because of their low adsorption capacity. The larger the specific surface area, the higher the adsorption capacity, which is preferable. However, the ash generated in the boiler or the like is about 8000 cm ² / g at most.

In the present invention, if the particle size is 2 to 80 μm, ash containing unburned carbon and interference components to some extent as described above is also effective. After separation after sludge treatment and incineration at 800 ° C. or higher, unburned carbon and interfering components disappear, and can be effectively used as a cement raw material, building material raw material, ceramic raw material, roadbed material, and soil improvement material. Considering the energy spent for auxiliary combustion and the life of the furnace, it is sufficient to burn at 800 to 850 ° C.
A particle size of less than 2 μm is not preferable because it has a small adsorption capacity and is difficult to separate. Moreover, the thing larger than 80 micrometers is unpreferable because the specific surface area is small.
Incinerated ash may be humidified for the purpose of preventing scattering during transportation, but either dry ash or humidified ash can be used in this treatment method, but it is preferable that the amount of humidification is small.

The amount of ash added to the bleaching wastewater is preferably 0.01% by mass to 5.0% by mass with respect to the bleaching wastewater. If the amount of ash added is large, the amount of organic and colored components adsorbed will also increase, but the residual concentration of incinerated ash in the wastewater will increase, and it will take time to settle, and the burden on the activated sludge that follows will be large. In the end, the efficiency is lowered, and more preferably 0.05% by mass to 2% by mass.
When a large amount of ash is used exceeding 5.0% by mass, a step of separating and removing the incinerated ash adsorbed before the activated sludge treatment from the wastewater by natural sedimentation or the like is required.

The ECF wastewater discharged from the bleaching process may be any sequence as long as it is discharged from the ECF sequence. For example, D (chlorine dioxide) -E / OD, Ez (xylanase enzyme treatment) -DE / OD, DE / OP (hydrogen peroxide) -D, DE / OP- ECF sequences such as D, Z (ozone) -E / OD, A (acid treatment) -ZE / OD, Z / DE / OD, ADE / OD Or chlorinated bleaching chemicals such as ZE / OP, AZE / OP, E / OP-X (chelate treatment) -E / OP, E / OXP-E / OXP It can also be used in waste water from a multi-stage bleaching sequence that does not use any, and there is no particular limitation as long as it is ECF. Further, for example, waste water from a single-stage bleaching process such as P stage, D stage, and Z stage may be used, and the number of stages is not limited.

The drainage load discharged from a general bleaching sequence (DE / OPD) varies depending on the reached whiteness, chemical addition rate, etc., but COD is 5 kg / ADT to 35 kg / ADT per pulp ton, BOD is 2 kg / ADT to 25 kg / ADT per pulp ton, color 2 kg / ADT to 35 kg / ADT, acidic drainage pH is 1.5 to 6.0, and alkaline drainage pH is 9.0 to 12.5. Although it can be used for drainage of any region, it is preferable to adjust pH to 8 or more when heavy metals contained in ash are eluted.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
(Measurement of specific surface area)
Shimadzu specific surface area measuring device Measured with SS-100 type
(Measurement of particle size)
Measured with Nikkiso Microtrac Particle Size Analyzer 9300HRA.
(Measurement of COD)
The measurement was carried out in accordance with JIS K-0102 “Oxygen consumption by potassium permanganate at 100 ° C. (CODMn)”. The COD cut rate was calculated by the following formula.
COD cut rate (%) = ((COD before treatment) − (COD after treatment)) / (COD before treatment) × 100

(Measurement of chromaticity)
This was carried out in accordance with JIS K-0101 “Platinum / Cobalt Chromaticity” measurement method. The chromaticity cut rate was calculated by the following equation.
Chromaticity cut rate (%) = ((chromaticity before processing) −chromaticity after processing)) / (chromaticity before processing) × 100

In the adsorption treatment using incinerated ash, 1 liter of waste water is put into a 1 liter beaker, a predetermined amount of incinerated ash is added thereto, and the mixture is stirred at 100 rpm for 3 minutes using a jar tester.

In the activated sludge treatment, 1 liter of waste water and 0.5 liter of returned sludge from the actual waste water treatment facility were placed in a 3 liter beaker placed in a 35 ° C. water bath, stirred for 3 hours while blowing air, and then allowed to stand for 30 minutes. The supernatant liquid is treated water.

In Examples 1 to 7 and Comparative Examples 1 to 3, wastewater obtained by mixing acidic and alkaline wastewater generated from the D1-E / O-D2 sequence of the ECF bleaching process at a ratio of 4: 6 is used as raw water. The quality of raw water is pH 8.0, COD 631 mg / l, chromaticity 472 degrees.

Example 1
After adding 0.1% by mass of incinerated ash having a particle diameter of 45 μm and a specific surface area of 2000 cm ² / g collected to a mixed wastewater of the acidic wastewater and alkaline wastewater with a cyclone dust collector of a stalker furnace, the mixture was stirred for 3 minutes with a jar tester. Table 1 shows the COD, chromaticity, and respective cut rates of treated water obtained by treating the supernatant water that was allowed to stand for 30 minutes with activated sludge.

Example 2
The treatment was performed in the same manner as in Example 1 except that the amount of incinerated ash added was 0.05% by mass, and the COD and chromaticity of the treated water and the respective cut rates are shown in Table 1.

Example 3
The treatment was performed in the same manner as in Example 1 except that the amount of incinerated ash added was 0.8% by mass, and the COD and chromaticity of the treated water and the respective cut rates are shown in Table 1.

Example 4
The treatment was performed in the same manner as in Example 1 except that the amount of incinerated ash added was 2.0% by mass, and the COD and chromaticity of the treated water and the respective cut rates are shown in Table 1.

Example 5
The treatment was performed in the same manner as in Example 1 except that the amount of incinerated ash added was 4.0% by mass, and the COD and chromaticity of the treated water and the respective cut rates are shown in Table 1.

Example 6
After adding 0.1% by mass of incinerated ash having a particle size of 2 μm and a specific surface area of 4000 cm ² / g collected in an electric dust collector of a stalker furnace to the mixed wastewater of the acidic wastewater and alkaline wastewater, and stirring for 3 minutes with a jar tester, Table 1 shows the COD, chromaticity, and respective cut rates of treated water obtained by treating the supernatant water that was allowed to stand for 30 minutes with activated sludge.

Example 7
After adding 5000 ppm incinerated ash with a particle size of 70 μm and a specific surface area of 1200 cm ² / g collected by a cyclone dust collector in a stalker furnace to the mixed wastewater of the acidic wastewater and alkaline wastewater, the mixture is stirred for 3 minutes with a jar tester and left for 30 minutes. Table 1 shows the COD, chromaticity, and respective cut rates of treated water obtained by treating activated supernatant with the treated supernatant water.

Comparative Example 1
The treatment with incinerated ash was omitted, and the treatment was performed in the same manner as in Example 1 except that the treatment was performed with activated sludge alone.

Comparative Example 2
0.1% by mass of incinerated ash having a particle size of 45 μm and a specific surface area of 1800 cm ² / g removed from the smoke of the stalker furnace was added to the mixed wastewater of the acidic wastewater and alkaline wastewater, and stirred for 3 minutes with a jar tester. Table 1 shows the COD and chromaticity of the treated water that was allowed to stand for a minute, and the respective cut rates.

Comparative Example 3
Table 1 shows the COD, the chromaticity, and the respective cut rates except that ash was added to the wastewater after the activated sludge treatment.

The incinerated ash used in Examples 1 to 7 was burned at 800 to 850 ° C. in a fluidized bed furnace, so that it could be effectively used as a building material material.

Claims (5)

ECF bleaching process wastewater treatment characterized by mixing activated sewage after mixing ash discharged from boiler or incinerator with wastewater generated from bleaching process without using elemental chlorine in paper pulp manufacturing process (ECF) Method. The method for treating ECF bleaching wastewater according to claim 1, wherein the specific surface area of the ash is 2000 cm ² / g or more. The method for treating ECF wastewater according to claim 1 or 2, wherein the ash is mixed with wastewater in a range of 0.05 mass% to 5 mass%. The method for treating ECF bleaching process wastewater according to any one of claims 1 to 3, wherein the mixing of ash and wastewater is carried out at a pH of 8 or more. The method for treating ECF bleaching process wastewater according to any one of claims 1 to 4, wherein the ash is burned at 800 ° C or higher after being mixed with wastewater and reused.