JP2008279384A - Anaerobic treatment apparatus for paper industry sewage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a stably anaerobic treatment of an evaporated water condensate exhausted from a paper industry process with a granule sludge for a long time at a high load and rate. <P>SOLUTION: The evaporated water condensate is introduced into a reaction vessel 20 through a treating liquid path 31. A coating waste liquid exhausted from the coating process part 71 is added to a mid flow of the treating liquid path 31 or to the reaction vessel 20. The granule sludge is brought in contact with a sludge blanket 24 expanded from the granule sludge for methane fermentation with the granule sludge formed by self-granulating from a methane producing bacteria retained in the reaction vessel 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an anaerobic treatment apparatus for wastewater generated in a paper mill, and more particularly to a treatment apparatus for anaerobically biotreating papermaking wastewater into a reaction tank that holds granular sludge.

  The papermaking process for producing paper can be broadly divided into a pulping process, a papermaking process, a coating process, and a finishing process. For example, in the pulping process, wood is mainly used as a raw material, which is treated by a mechanical method, a chemical method, or both to extract fibers to obtain a pulp raw material. In the paper making process, the pulp raw material produced in the pulping process is beaten with a machine called a refiner, and chemicals are added to make paper. In the coating process, the paint is applied to a paper base that has been made and dried, and finishes such as glazing are performed, and this is cut in the finishing process to obtain a product.

  In such a papermaking process, waste liquids having various properties are discharged. For example, as a pulp manufactured in the pulping process, a chemical pulp in which raw materials are chemically processed to extract fibers is generally used. In particular, a chemical pulp manufactured by a kraft method (craft pulp) is manufactured. Often.

  Kraft pulp is obtained by heating (cooking) chips obtained by pulverizing wood in a chemical solution containing alkali and sodium sulfide. The liquid (distilled liquid) obtained by this cooking is distilled to recover the alkali content. As the cooking liquor is distilled, a waste liquid called evaporative condensed water (evaporator / condenser) is generated.

  The amount of evaporating condensed water reaches about 5 to 7 times the amount of kraft pulp produced, and the organic substance concentration reaches 3,000 to 10,000 mg / L. The organic matter-containing water is generally treated by an aerobic biological treatment method called an activated sludge method, but evaporative condensed water is not suitable for treatment by the activated sludge method because the organic matter concentration is high.

  On the other hand, according to the anaerobic treatment in which organic matter is methane-fermented by anaerobic microorganisms, water containing high concentration organic matter can be treated without diluting. ing. However, the evaporated condensed water contains a sulfur compound derived from sodium sulfide contained in the chemical solution, which may inhibit methane fermentation.

Thus, a method has been developed in which an inhibitory substance that inhibits methane fermentation is aggregated and removed by lowering the pH of the evaporated condensed water and then supplied to a reaction tank for methane fermentation to perform anaerobic treatment (Patent Document). 1).
JP-B-2-32958

By the way, as an anaerobic treatment method of organic substance-containing water, a UASB (Upflow Anaerobic Sludge Blanket) method capable of high-load high-speed treatment, and an EGSB method capable of higher-load high-speed treatment than the UASB method. (Expanded Granule Sludge
Blanket) is known. In the UASB method and the EGSB method, the organic substance-containing water is introduced into a reaction tank holding granule sludge having a high density and a large sedimentation property, and the upward circulation liquid is used to develop the granules and perform high-load high-speed treatment.

Granule sludge is granular sludge formed by self-granulation of anaerobic microorganisms. UA
The greatest point of stably performing the anaerobic treatment by the SB method and the EGSB method is to maintain and propagate the granular sludge. If granule sludge cannot be maintained and propagated in the reaction tank, the treatment performance gradually decreases and may eventually become untreatable.

  Here, the evaporated condensed water is an organic substance-containing water whose main component is methanol (approximately 70% by mass or more of the total CODcr). Therefore, when the evaporated condensed water is anaerobically treated, the Methanosaeta genus (formerly Methanothrix genus), the Methanosarcina genus, And microorganisms such as Methanobacterium grow. Although these bacteria assimilate methanol to produce methane, it is difficult to form granular sludge.

  For this reason, when evaporative condensed water is used as the liquid to be treated and the operation is continued for a long time, the granular sludge is disassembled to reduce the particle size, and the amount of sludge in the reaction tank is reduced. For this reason, conventionally, it has been difficult to treat evaporative condensed water by an anaerobic treatment method using granular sludge.

  In view of the above problems, an object of the present invention is to provide an anaerobic treatment apparatus that enables high-load and high-speed treatment of papermaking wastewater mainly composed of evaporated condensed water using granular sludge. Another object of the present invention is to improve the efficiency of the entire wastewater treatment in the papermaking process while stably and efficiently treating evaporative condensed water by anaerobic treatment using granular sludge.

  The present invention provides the following.

(1) A reaction tank in which granule sludge is retained and methane fermentation is carried out, a treated liquid path for introducing evaporative condensed water discharged from the pulp manufacturing process into the reaction tank, and starch containing starch discharged from the papermaking process An anaerobic treatment apparatus for papermaking wastewater, comprising: a starch waste liquid path for supplying a contained waste liquid in the middle of the reaction tank or the liquid path to be treated.
(2) The anaerobic treatment apparatus according to (1), wherein the starch waste liquid path is a coating waste liquid path that supplies a coating waste liquid as the starch-containing waste liquid.

  According to the present invention, the granule sludge can be prevented from collapsing. Therefore, conventionally, high-load high-speed treatment using evaporative condensed water, which has been difficult to maintain and multiply granular sludge, as the liquid to be treated can be stably continued over a long period of time.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view of a paper mill in which an anaerobic treatment apparatus (hereinafter simply referred to as “treatment apparatus”) 1 for organic substance-containing water according to a first embodiment of the present invention is arranged. Here, a papermaking process using kraft pulp as a raw material is shown, and the process is roughly divided into a pulping process, a papermaking process, a coating process, and a finishing process.

  In the pulp process, the chip 51 is put into the feeder 53, mixed with a chemical solution containing alkali and sodium sulfide, heated in the digester 55, and the fibers are extracted to produce kraft pulp. Kraft pulp is temporarily stored in the pulp storage tank 57 and then sent to the paper making process. In the paper making process, pulp slurry prepared from kraft pulp is made by the wire part 61. The papermaking sheet is press dehydrated by the wire part 63 and dried by the dryer part 65. The dried paper base is coated with a coating liquid by a coating machine 71 in a coating process, polished, and then cut with a cutting machine (not shown) to obtain a paper product.

From the digester 55, the digested liquid (black liquor) from which the lignin and the like contained in the chips are eluted is discharged. The cooking liquor collects alkali by distillation with a distiller 59. At this time, the evaporated condensed water containing methanol as a main component is discharged as a waste liquid. The distiller 59 is connected to the reaction tank 20 of the anaerobic treatment apparatus 1 by the liquid passage 31 to be treated, and the evaporated condensed water discharged from the distiller 59 is sent to the reaction tank 20.

  The reaction tank 20 is filled with granular sludge. The liquid path 31 to be treated is connected to the lower part of the reaction tank 20. The organic substance-containing water is introduced into the reaction tank 20 by a pump P provided in the liquid passage 31 to be treated and flows through the reaction tank 20 in an upward flow. In addition, a gas-solid-liquid separator (GSS) is provided in the upper part of the reaction tank 20. The top of the GSS protrudes from the liquid level in the reaction vessel 20. The gas path 33 is connected to the upper part of the reaction tank 20. The processing liquid path 32 communicates with the inside of the GSS.

  In the reaction tank 20, the inside of the GSS is a gas-solid separation part, and the lower part thereof is a reaction part 22 where the granular sludge is developed. In the reaction part 22, the granular sludge is developed to form a sludge blanket 24. Granule sludge is sludge in which anaerobic microorganisms are self-granulated into granules having an average particle size of about 0.5 to 1.0 mm, and the density is about 1.02 to 1.1 kg / L. There is excellent sedimentation. The liquid in the reaction unit 22 is gas-solid-liquid separated inside the GSS, and the treatment liquid separated from the granular sludge is taken out from the treatment liquid path 32.

  In this way, in the processing apparatus 1, the evaporative condensed water is passed through the reaction tank 20 holding the granule sludge in an upward flow to develop the granule sludge, and the sludge blanket 24 is formed. As a result, the contact efficiency between the evaporative condensed water and the granular sludge increases, so in the UASB in which a sludge blanket having a height of about 3 to 5 m is deployed in a reaction tank having a height of about 5 to 7 m, a sludge load of 0.1 High load high speed processing of about 0.7 kg-CODcr / kg-VSS / d and an ascending flow rate in the reaction tank of about 0.3 to 1.5 m / h is possible. In EGSB where a sludge blanket with a height of about 5 to 18 m is deployed in a reaction tank with a height of about 7 to 20 m, a sludge load of 0.1 to 1.0 kg-CODcr / kg-VSS / d, an increase in the reaction tank The flow rate can be about 3 to 10 m / h.

  However, the preferable sludge load for the UASB type reaction tank is 0.2 to 0.6 kg CODcr / kg-Vss / d, and the preferable ascending flow rate is 0.5 to 1.0 m / h. Moreover, if it is an EGSB type reaction tank, a suitable sludge load is 0.2-0.7 kgCODcr / kg-Vss / d, and a suitable ascending flow rate is 2-5 m / h.

Evaporated condensed water introduced into the reaction tank 20 generally contains an organic substance having a concentration of 3,000 to 10,000 mg / L as CODcr, and most (80 to 90% by mass) is methanol. The organic load on the reaction tank 20 is preferably 5 to 30 kg-CODcr / m ³ / d, and particularly preferably 8 to 20 kg-CODcr / m ³ / d. Moreover, it is preferable to set it as anaerobic conditions without supplying oxygen in the reaction tank 20, and to make temperature into 25-40 degreeC, especially 30-38 degreeC.

  The reaction tank 20 holds about 20 to 50% of the granular sludge having the above properties per reaction tank volume in advance. Granule sludge can be formed spontaneously by anaerobic treatment of the liquid to be treated, and promotes self-granulation by adding a flocculant etc. to the reaction tank holding floating anaerobic sludge. The floating sludge can be self-granulated. However, it takes time to form naturally occurring granular sludge. Moreover, when a flocculant is added and floating sludge is granulated, the density of the formed granular sludge may become low.

On the other hand, if the granular sludge discharged as surplus sludge from the existing UASB or EGSB type reaction tank is filled in the reaction tank and the organic substance-containing water containing the substrate for growing the granular sludge is supplied, The reaction tank can be started up in a short time (that is, a reaction tank holding a necessary amount of granular sludge can be obtained). This is because granule sludge grows in the reaction tank and is crushed by the flow of water and gas generated in the reaction tank. It is said that sludge is formed.

  In order to perform a stable treatment with UASB, granule sludge having an average particle size of 0.5 to 3.0 mm, preferably about 0.8 to 1.5 mm, and the sludge blanket 24 described above are provided in the reaction tank 20. Maintain to form. In the case of EGSB, it is necessary to stably hold granular sludge having an average particle diameter of 0.5 to 3.0 mm, preferably about 1.0 to 1.5 mm, in the reaction tank 20.

However, if the evaporative condensed water treatment is continued, the granular sludge is destroyed. Therefore, in the present invention, the starch-containing waste liquid is supplied to the reaction tank 20. Starch-containing waste liquid discharged from the papermaking process includes coating waste liquid (coater wastewater) discharged from the coating process, and waste liquid (DIP) discharged from the deinked pulp manufacturing process (not shown). System wastewater) and papermaking waste liquid containing a sizing agent discharged from the papermaking process and used in the papermaking process.

  For example, in the case of a coating solution applied to the paper surface after papermaking, generally 10 to 20 parts of an adhesive and 1 to 5 minutes of an auxiliary agent such as a dispersant or a dye with respect to 100 parts of a pigment such as kaolin or calcium carbonate. Including degree. Therefore, these substances are contained in the waste liquid discharged from the process of using such a coating liquid. As the starch-containing waste liquid, a coating waste liquid derived from a coating liquid containing a natural organic adhesive as an adhesive, particularly a starch-based adhesive is preferable.

  The starch waste liquid path may be configured to connect the waste liquid discharge source and the liquid path 31 to be treated (or the reaction tank 20). In this embodiment, a coating waste liquid path 34 that connects the coating part 71 and the liquid path 31 (or the reaction tank 20) is provided as a starch waste liquid path, and the coating waste liquid is disposed in the middle of the liquid path 31 (or Add to reaction vessel 20). A valve V may be provided in the middle of the coating waste liquid path 34 to adjust the amount of coating waste liquid added. It is preferable to add the coating waste liquid so that the CODcr concentration derived from the coating waste liquid is 0.1 to 10% with respect to the CODcr concentration of the evaporated concentrated water. The valve V provided in the middle of the coating waste liquid path opens and closes according to the starch concentration of the coating waste liquid as the starch-containing waste liquid, for example, the starch concentration of the coating waste liquid is somewhat high (for example, 100 mg / L or more). In some cases, the coating waste liquid may be used so as to be supplied to the liquid passage 31 (or the reaction tank 20).

  Moreover, when providing a coating waste liquid storage tank (not shown) in the middle of the coating waste liquid path 34, it is preferable that the residence time of the coating waste liquid in a coating waste liquid storage tank shall be 1 to 24 hours. Further, the coating waste liquid may be added at about 30 to 35 ° C., and the pH may be added at about 6.0 to 9.0. By increasing the temperature of the coating waste liquid, the microorganism substrate contained in the coating waste liquid can be made into a form that is easy to assimilate for the microorganisms that form the granule. Inferred.

  Moreover, you may make it add any one or more of inorganic ions, such as a flocculant, nitric acid or nitrous acid, calcium, or magnesium, to the front | former stage of the reaction tank 20, or the reaction tank 20. As the aggregating agent, nonionic, cationic, anionic or amphoteric polymer aggregating agents may be used. In the case of a polymer flocculant, the addition concentration of the flocculant is preferably about 0.01 to 2 mg / l, particularly about 0.01 to 1 mg / l.

  Nitric acid or nitrous acid is preferably added so that the nitrogen (N) concentration in the treatment target liquid after addition is 1 to 1,000 mg / L, particularly 1 to 100 mg / L. Nitric acid or nitrous acid may be added either continuously or intermittently. The order of adding the flocculant, nitric acid or nitrous acid, and inorganic ions is not limited.

  Preferred conditions for the anaerobic treatment in the reaction tank 20 are as described above. In the reaction tank 20, organic substances in the evaporative condensed water are decomposed by the action of the granular sludge, and a gas containing methane is generated. Granule sludge grows using organic substance-containing water as a substrate.

  The mixed liquid containing the gas generated in the reaction tank 10 and the grown sludge is gas-solid-liquid separated inside the GSS, and the gas is taken out of the reaction tank 20 from the gas path 33 and stored in the gas holder 30. Further, the liquid component separated and clarified from the sludge is taken out of the reaction tank 20 from the treatment liquid path 32. The treatment liquid may be further treated by an aerobic biological treatment apparatus (not shown) provided at a later stage.

<Example 1>
Hereinafter, the present invention will be described in more detail based on examples. In the example, an experimental apparatus simulating the processing apparatus 1 shown in FIG. 1 was created, and evaporated condensed water discharged from the pulping process was supplied to the reaction tank 20 at a liquid flow rate of 11 L / d. Moreover, the coating waste liquid path 34 was connected in the middle of the to-be-processed liquid path 31, and the coating waste liquid discharged | emitted from a coating process is added in the quantity of 4.2 L / d. Evaporated condensed water had an organic substance concentration of 2,700 mg / L as CDOcr, of which the methanol concentration was about 1,500 mg / L. The coating waste liquid contained an organic substance concentration as CODcr of about 700 mg / L and starch at a concentration of 100 to 200 mg / L. The coating waste liquid was added so that the CODcr ratio derived from the coating waste liquid in the CODcr was about 10% in the mixed liquid obtained after the addition to the evaporated condensed water.

  The reaction tank 20 has an inner diameter of 6 cm, a height of 1.2 m, and the capacity of the reaction part 12 excluding the part where the GSS is installed is 3 L, and the capacity of the part including the GSS part is 4 L. The reaction tank 20 is filled with 1.0 L of granular sludge (density 1.03-1.1 mm, particle size 1.2-1.5 mm) taken out from the existing UASB-type reaction tank in the chemical factory. Thus, the experiment was started in a state where the start-up of the reaction vessel 20 was completed.

Waste water was passed through the reaction tank 20 at a CODcr load of 10 g-CODcr / L / d derived from evaporated condensed water and a sludge load of 0.4 to 0.7 g-CODcr / g-VSS / d. The waste liquid was passed while circulating the treated water so that the ascending flow rate in the reaction tank 20 was 3 m / h, and the sludge blanket was formed by developing the granular sludge. The temperature in the reaction vessel 20 was maintained at 30 to 35 ° C., and the pH was adjusted to be pH 7.0. The pH adjustment was performed by adding a pH adjuster (NaHO ₃ solution) stored in a pH adjuster tank (not shown) to the liquid channel 31 to be treated.

  The height of the upper end (sludge interface) of the sludge blanket formed by the development of the granule sludge in the reaction tank 20 increases, and during the 90-day experiment period, the amount is more than the amount of granule sludge at the start of treatment. The granular sludge could be maintained in the reaction tank 20. At this time, the average particle size of the granular sludge was increased, and the collapse of the granular sludge could be prevented.

<Example 2>
In Example 2, a sodium nitrate solution was further added to the liquid passage 31 to be treated. The amount of nitric acid added was such that the concentration of nitric acid after mixing the sodium nitrate solution and the liquid to be treated was 20 mg-N / L. Other than that, the experiment was conducted in the same manner as in Example 1. As a result, the amount of granular sludge in the reaction tank 20 increased and the average particle size also increased.

<Example 3>
In Example 3, a flocculant was added to the liquid passage 31 to be treated. As the flocculant, a cationic polymer flocculant (polyaminoalkyl acrylate) was used, and the amount added was adjusted to 0.1 mg / L after the flocculant and the liquid to be treated were mixed . Other than that, the experiment was conducted in the same manner as in Example 1. As a result, the amount of granular sludge in the reaction tank 20 increased and the average particle size also increased.

<Example 4>
As Example 4, nitric acid and a flocculant were further added to the liquid passage 31 to be treated. The types and addition amounts of nitric acid and flocculant were the same as in Example 2 and Example 3. Other than that, the experiment was conducted in the same manner as in Example 1. As a result, the amount of granular sludge in the reaction tank 20 increased and the average particle size also increased.

<Comparative example 1>
In Comparative Example 1, the coating waste liquid was not supplied to the reaction tank 20. Other than that, the experiment was performed under the same conditions as in Example 1. As a result, the amount of granular sludge in the reaction tank 20 was gradually decreased, and the particle size was also decreased.

  2 and 3 show the results of Examples and Comparative Examples. Thus, according to the invention, it has been shown that granulated sludge can be used to prevent the collapse thereof and evaporate condensed water can be processed at high load and high speed. Moreover, it was shown that the efficiency of the papermaking wastewater treatment can be improved by mixing the evaporated condensed water and the coating waste liquid.

  The present invention can be used for waste water treatment discharged from a paper mill.

The schematic diagram of the anaerobic processing apparatus which concerns on 1st Embodiment of this invention. The figure which shows the result of an Example and a comparative example. The figure which shows the result of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anaerobic processing apparatus 20 Reaction tank 22 Reaction part 24 Sludge blanket 30 Gas holder 31 Processed liquid path 32 Processed liquid path 33 Gas path 34 Coating waste liquid path (starch waste liquid path)

Claims (2)

A reaction tank in which granule sludge is retained and methane fermentation is carried out;
A treated liquid path for introducing evaporative condensed water discharged from the pulp manufacturing process into the reaction tank;
An anaerobic treatment apparatus for papermaking wastewater, comprising: a starch waste liquid path that supplies a starch-containing waste liquid that is discharged from the papermaking process and contains starch in the middle of the reaction tank or the liquid path to be treated.   The anaerobic treatment apparatus according to claim 1, wherein the starch waste liquid path is a coating waste liquid path that supplies a coating waste liquid as the starch-containing waste liquid.

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