JP2012000556A - Anaerobic treatment method and anaerobic treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the dissolution and outflow of granules in a reaction vessel, when introducing evaporated condensate water discharged from a pulp manufacturing process to the reaction vessel holding granule sludge and executing anaerobic treatment.SOLUTION: Absorbance of visible light with the wavelength in the range of 380-780 nm is measured for treated water from the reaction vessel, and at least one of the introducing flow rate of water to be treated to the reaction vessel, the addition amount of nutrients and the addition amount of a polymeric flocculant is controlled on the basis of the measured value. By measuring the absorbance of the visible light with the wavelength in the range of 380-780 nm for the treated water from the reaction vessel, the amount of suspended solids (SS) contained in the treated water is quickly detected, and by executing required control according to the change of the SS concentration, the dissolution and outflow of the granule sludge are prevented.

Description

  The present invention relates to a method and an apparatus for performing anaerobic treatment by introducing evaporative condensed water discharged in a pulp manufacturing process into a methane fermentation reaction tank in which granule sludge is retained.

  As an anaerobic treatment method of organic substance-containing water, a UASB (Upflow Anaerobic Sludge Blanket) method capable of a high load treatment and an EGSB (Expanded Granular Sludge Bed) method capable of a higher load treatment than the UASB method are known.

  In these UASB method and EGSB method, granular sludge in which anaerobic microorganisms are granulated is used, and sludge containing anaerobic microorganisms is maintained and propagated in a granular state in a reaction tank. Since the biological treatment method using granular sludge can obtain a higher sludge retention concentration than a fixed bed or a fluidized bed in which microorganisms are held on a carrier, high-load operation is possible. In addition, granule sludge has a high microbial concentration and is excellent in sedimentation, so that solid-liquid separation between treated water and sludge is easy. Furthermore, if the granular sludge in the reaction tank that is already in operation is extracted as excess sludge and put into the new reaction tank, the newly installed reaction tank can be started up in a short period of time and can perform stable treatment. It is also recognized as the most efficient anaerobic treatment method.

  In the UASB method using granular sludge, etc., the greatest point for stably and satisfactorily treating organic substance-containing water is to maintain and propagate the granular sludge in the reaction vessel. If the granule sludge cannot be maintained and propagated in the reaction tank, the treatment performance gradually decreases and may eventually become untreatable.

  Granule sludge is formed as a framework of acetic acid-assimilating microorganisms of the genus Methanosaeta, and constitutes a kind of ecosystem in which hydrogen-utilizing methane bacteria, acetic acid-producing bacteria, acid-producing bacteria, etc. coexist. Among these microorganisms, acid-producing bacteria break down sugars, lipids, proteins, etc., and produce mucilage, so that the binding force between the bacteria is strengthened. Therefore, the strongest granular sludge is formed by using a culture solution of a sugar substrate.

  By the way, the papermaking process for producing paper can be roughly 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 processed 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. Along with distillation of the cooking liquor, a waste liquid called evaporative condensed water (evaporator condensate or evaporator drain) is generated.

The amount of evaporative condensed water generated in the pulp manufacturing process reaches about 5 to 7 times the amount of kraft pulp produced. Moreover, the organic substance density | concentration of this evaporation condensate water is 3,000-10,000 mg / L, and it is organic substance containing water which has methanol as a main component (70 mass% or more of all COD _Cr ) unlike normal organic substance containing water. Methanosarcina genus and Methanobacterium genus grow as main microorganisms.

  However, since Methanosarcina and Methanobacterium methane bacteria are difficult to form granule sludge, the anaerobic treatment of evaporative condensed water mainly consisting of these microorganisms reduces the production of slime organisms in the sludge. The sludge does not grow well and its strength is insufficient. For this reason, if the evaporative condensed water discharged from such a pulp manufacturing process is continuously operated as a liquid to be treated in a reaction tank holding granule sludge for a long period of time, the granule sludge becomes easy to dismantle and become finer. The sludge that has been discharged flows out of the reaction tank, and the processing efficiency is lowered.

  Conventionally, as a method of preventing the disintegration of granular sludge in the anaerobic treatment of evaporative condensed water, a method of adding nitric acid or nitrous acid to a reaction tank (Patent Document 1), the reaction tank contains starch discharged from the papermaking process A method of adding starch-containing waste liquid (Patent Document 2) and a method of adding carbohydrate to a reaction tank (Patent Document 3) have been proposed.

  In addition, as a high load anaerobic treatment method of evaporative condensed water, after removing sulfur components contained in evaporative condensed water, a method of performing anaerobic treatment in a methane fermentation tank using water mixed with polymer carbohydrate as treated water, There has been proposed a method of performing anaerobic treatment in a methane fermentation tank after coagulating and removing an inhibitory substance that inhibits methane fermentation by lowering the pH of evaporated condensed water (see, for example, Patent Documents 4 and 5).

JP 2008-279383 A JP 2008-279384 A JP 2008-279385 A Japanese Patent No. 3174364 Japanese Patent Laid-Open No. 61-97096

  Prior to the anaerobic treatment, the methods described in Patent Documents 4 and 5 require the treatment of the evaporative condensed water and have the disadvantage that the treatment process becomes complicated.

  The methods described in Patent Documents 1 to 3 can simply prevent the disintegration and outflow of granule sludge simply by adding an additive to evaporative condensed water, but regardless of the dismantling tendency of the granule sludge, Since the additive is always added in a predetermined amount, the additive may be excessively added.

  If these additives are added only when there is a tendency to dismantle the granular sludge in the reaction tank immediately and there is a tendency to disassemble the granular sludge, this waste can be saved. However, in the past, no technology has been proposed to immediately grasp the signs of granule sludge demolition.

  In the present invention, when anaerobic treatment is performed by introducing the evaporated condensed water discharged in the pulp manufacturing process into the reaction tank in which the granular sludge is retained, the signs of the demolition of the granular sludge are immediately detected, By taking measures to prevent the dismantling of the granular sludge, the method and apparatus for preventing the disassembly of the granular sludge in the reaction tank and the outflow from the reaction tank in advance and stably performing high-load high-speed treatment for a long period of time. The purpose is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have measured the absorbance of visible light in the wavelength range of 380 to 780 nm for the treated water from the reaction tank, thereby suspending the suspended matter contained in the treated water. It has been found that the amount of (SS) can be detected quickly, and the granule sludge can be prevented from being dismantled and outflowed by performing necessary control according to the change in the SS concentration.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] In a method for introducing an treated water containing evaporative condensed water discharged in a pulp manufacturing process to an anaerobic treatment in a reaction tank in which granule sludge is held, about the treated water from the reaction tank, An anaerobic treatment method comprising measuring the absorbance of visible light in the wavelength range of 380 to 780 nm and controlling one or more of the following (1) to (3) based on the measured value of the absorbance: .
(1) Introduction flow rate of water to be treated into the reaction tank (2) Amount of nutrient added to the reaction tank (3) Amount of polymer flocculant added to the reaction tank

[2] The anaerobic treatment method according to [1], wherein the nutrient contains one or more selected from the group consisting of nitric acid, nitrous acid, sugar, coating waste liquid, calcium compound, and iron salt. .

[3] A reaction tank in which granular sludge is retained, means for introducing treated water containing evaporated condensed water discharged from the pulp manufacturing process into the reaction tank, means for taking out treated water from the reaction tank, Means for measuring the absorbance of visible light in the wavelength range of 380 to 780 nm of the treated water, and means for controlling one or more of the following (1) to (3) based on the measured value of the absorbance: An anaerobic treatment apparatus characterized by comprising.
(1) Introduction flow rate of water to be treated into the reaction tank (2) Amount of nutrient added to the reaction tank (3) Amount of polymer flocculant added to the reaction tank

[4] The anaerobic treatment apparatus according to [3], wherein the nutrient contains one or more selected from the group consisting of nitric acid, nitrous acid, sugar, coating waste liquid, calcium compound, and iron salt. .

  According to the present invention, in the anaerobic treatment of the evaporative condensed water discharged from the pulp manufacturing process in which granules are difficult to form, the signs of the disintegration of the formed granule sludge are detected immediately, and the disassembly of the granule sludge is performed. By performing precise control for prevention, it is possible to reliably prevent granule sludge from being disassembled in the reaction tank and sludge outflow from the reaction tank, and to perform high-load high-speed treatment stably over a long period of time. .

It is a systematic diagram which shows embodiment of the anaerobic processing apparatus of this invention. It is a systematic diagram which shows other embodiment of the anaerobic processing apparatus of this invention. It is a graph which shows the time-dependent change of the average particle diameter of the granular sludge in a reaction tank in Examples 1-3 and the comparative example 1. FIG. It is a graph which shows the time-dependent change of the sludge interface height of the granular sludge layer in the reaction tank in Examples 1-3 and Comparative Example 1.

  Embodiments of an anaerobic treatment method and an anaerobic treatment apparatus of the present invention will be described below in detail with reference to the drawings.

  1 and 2 are system diagrams showing an embodiment of the anaerobic treatment apparatus of the present invention.

  1 and 2, reference numeral 1 denotes a reaction tank, and the reaction tank 1 is filled with granular sludge 2. A gas-solid-liquid separator (GSS) 3 is provided at the upper part of the reaction tank 1. The top of the GSS 3 protrudes from the liquid level in the reaction tank 1, and the treated water extraction pipe 13 communicates with the inside of the GSS 3. The treated water extraction pipe 13 is connected to the treated water tank 5, and the treated water tank 5 communicates with the adjustment tank 6 and the lower part, and the adjusted tank 6 further communicates with the pH adjustment tank 7 and the lower part. The treated water introduction pipe 11 is in communication with the adjustment tank 6. The pH adjustment tank 7 is connected to the lower part of the reaction tank 1 by a adjustment water introduction pipe 8. The water to be treated is diluted and adjusted in the adjustment tank 6 with the treated water in the communicating treatment water tank 5, and the pH is adjusted in the pH adjustment tank 7 to which the pH adjuster C (acid or alkali) is added. It is introduced into the reaction tank 1 by a pump P provided in the pipe 8 and flows in the reaction tank 1 in an upward flow. A gas discharge pipe 12 is connected to the upper part of the reaction tank 1.

  In the reaction tank 1, the inside of the GSS 3 is a gas-solid separation part, and the lower part is a reaction part where the granular sludge 2 is developed. In the reaction part, the granule sludge 2 develops to form a sludge blanket. Granule sludge 2 is a sludge that is granulated by self-granulating microorganisms including anaerobic microorganisms, and has a relatively high density and excellent sedimentation.

  Due to the anaerobic treatment of the water to be treated in the reaction tank 1, the mixed liquid containing the gas generated in the reaction tank 1 and the proliferated sludge is gas-solid-liquid separated inside the GSS 3, and the gas reacts from the gas discharge pipe 12. It is taken out of the tank 1 and stored in the gas holder 4. In addition, the liquid that is separated and clarified from the sludge is taken out from the treated water extraction pipe 13 to the treated water tank 5 and discharged out of the system through the treated water discharge pipe 16. This treated water may be further treated by an aerobic biological treatment apparatus (not shown) provided at a later stage.

  In this way, in order to adjust the ascending flow rate in the reaction tank 1 and appropriately expand the granular sludge 2, part of the treated water from the treated water tank 5 is circulated to the reaction tank 1 together with the treated water. be introduced.

  In the present invention, treated water is mainly used for adjusting the concentration of treated water, and further treated water such as city water, industrial water, well water, river water, and other treated water other than treated water. Water having a lower organic concentration than water may be used as dilution water, and this dilution water may be introduced into the adjustment tank 6 from the dilution water introduction pipe 15 via the flow rate adjustment valve 15V. By using the diluted water together, the organic matter concentration of the water introduced into the reaction tank 1 can be adjusted stably. In particular, when the quality of treated water deteriorates, if only treated water is used as dilution water, the circulation rate of treated water increases and the amount of dilution water is adjusted so that the rising flow rate in the reaction tank is within a predetermined range. It can be difficult to adjust. In such a case, it is preferable to use the treated water in combination with other dilution water having a stable organic substance concentration, or to use only another dilution water having a stable organic substance concentration.

  The treated water tank 5 is provided with a control device 9 that measures the absorbance of treated water and outputs a control signal based on the measured value.

  In the anaerobic treatment apparatus of FIG. 1, a valve 11 </ b> V for adjusting the introduction flow rate of the treated water is provided in the treated water introduction pipe 11 in conjunction with the control device 9. The introduction flow rate of the water to be treated into the adjustment tank 6 is controlled based on the turbidity or SS concentration of the water to be treated obtained from the measurement value or the measurement value of the absorbance.

  The anaerobic treatment apparatus of FIG. 2 includes a medicine storage tank 10 that stores a nutrient or a polymer flocculant, and a medicine injection pipe 14 for injecting medicine in the medicine storage tank 10 into the adjustment water introduction pipe 8 A valve 14V linked to the control device 9 is provided, and is introduced into the reaction tank 1 based on the measured value of the absorbance of the treated water or the turbidity or SS concentration of the treated water obtained from the measured value of the absorbance. It is comprised so that the chemical injection quantity of the nutrient or polymer flocculent to adjustment water may be controlled.

In this way, the absorbance of the treated water is measured, and the turbidity of the treated water, that is, the SS concentration, is detected based on the measured value, and the signs of the dismantling of the granular sludge in the reaction tank can be detected.
That is, as described above, when an evaporative condensed water mainly composed of methanol is subjected to anaerobic treatment, Methanosarcina genus and Methanobacterium genus methane bacteria grow as main microorganisms. Since these methane bacteria are difficult to form granules, there is a problem that if the operation is continued for a long period of time, the strength of the granules gradually decreases and the granules are disassembled and refined and flow out of the reaction tank. . When the granule is refined and flows out of the reaction vessel, the SS concentration in the treated water is significantly increased than usual. Therefore, by monitoring the SS concentration, it is possible to grasp the signs of granule refinement, but this SS concentration is correlated with the turbidity of the treated water, and the turbidity of the treated water is Since there is a correlation with the absorbance of visible light in the wavelength range of 380 to 780 nm, the SS concentration of treated water can be detected by measuring the absorbance of treated water.

In the present invention, one or more of the following (1) to (3) is controlled based on the measured value of the absorbance of the treated water or the turbidity or SS concentration of the treated water obtained from the measured value. As a result, dismantling and outflow of granular sludge in the reaction tank is prevented.
(1) Flow rate of water to be treated into reaction tank (2) Amount of nutrient added to reaction tank (3) Amount of polymer flocculant added to reaction tank

  Since the measurement of the absorbance of the treated water and the conversion of the treated water turbidity or SS concentration based on this measured value can be performed in a short time, according to the present invention, there is no indication of the dismantling of the granular sludge in the reaction tank. The controls (1) to (3) described above for detecting immediately and preventing the dismantling of the granular sludge can be performed quickly, and sludge outflow due to control delay can be prevented.

In addition, a spectrophotometer, a turbidimeter, a sludge concentration meter etc. can be used for the measurement of the light absorbency of treated water.
The absorbance of the treated water may be measured continuously or intermittently, for example, once every 1 to 24 hours.
To determine the turbidity or SS concentration of the treated water from the measured value of the absorbance of the treated water, prepare a test water with a known turbidity or SS concentration, and prepare it in advance from the relationship between the absorbance of the sample water and the turbidity or SS concentration This can be done according to a calibration curve or calculation formula.
Moreover, without performing these conversions, the relationship between the absorbance of the treated water and the sign of the dismantling of the granular sludge can be examined in advance, and direct control can be performed from the measured value of the absorbance of the treated water.

  Each control method will be described below.

[Control of flow rate of water to be treated into reaction tank]
When controlling the flow rate of water to be treated into the reaction tank, for example, the measured value of the absorbance of the treated water increases, the turbidity of the treated water, that is, the SS concentration increases, When the sign of dismantling is detected, the flow rate of the treated water into the reaction tank is reduced to prevent sludge growth inhibition by microorganisms in the treated water.
Decreasing the flow rate of treated water into the reaction tank, improving the tendency to disassemble granular sludge, decreasing the measured value of absorbance of treated water, and reducing the turbidity of treated water, that is, SS concentration If it is, the introduction flow rate of the water to be treated into the reaction tank is returned to the original value.

  As the control method, for example, when the measured value of the absorbance of the treated water is increased and the SS concentration of the treated water is increased by a predetermined value or more, for example, 20% or more, the treated water is introduced into the reaction tank. Decrease the flow rate within a predetermined range, for example, 5 to 10%; preset the introduction flow rate of the water to be treated with respect to the measured value of the absorbance of the treated water (or treated water turbidity or SS concentration). A control method such as controlling the flow rate of the treated water based on the set value can be employed.

[Control of the amount of nutrients added to the reaction tank]
When controlling the amount of nutrient added to the reaction tank, for example, the measured value of the absorbance of the treated water is increased, the turbidity of the treated water, that is, the SS concentration is increased, and the granular sludge is disassembled. Is detected, the nutrient is added to the reaction tank or the amount of the nutrient added to the reaction tank is increased to promote the growth of sludge in the reaction tank.
In addition, it was determined that the addition of nutrients or an increase in the amount added improved the tendency of the granular sludge to disassemble, decreased the measured value of the absorbance of the treated water, and lowered the turbidity of the treated water, that is, the SS concentration. If so, the amount of the nutrient added is returned to the original value, or the addition of the nutrient is stopped.

  In this control method, for example, when the measured value of the absorbance of the treated water is increased and the SS concentration of the treated water is increased by a predetermined value or more, for example, 20% or more, the addition amount of the nutrient is set within a predetermined range, For example, the amount is increased in the range of 5 to 10%; the amount of the nutrient added is set in advance for the measured value of the absorbance of the treated water (or the treated water turbidity or SS concentration), and the nutrition based on this set value It is possible to adopt a control method such as controlling the amount of agent added.

As the nutrient, one or more selected from the group consisting of nitric acid, nitrous acid, saccharides, coating waste liquid, calcium compound, and iron salt can be used, and the amount of nutrient added is COD _{Cr in the} treated water. It is preferable to be within a range of 0.01 to 10% by mass, particularly 0.02 to 5% by mass with respect to the concentration.
Nitric acid or nitrous acid as a nutrient is not limited to a nitric acid solution or the like, and a substance that releases nitrate ions or nitrite ions when added to water to be treated, such as nitrate or nitrite, may be used.
Moreover, a nutrient may be introduce | transduced and added to a reaction tank with to-be-processed water by adding with respect to to-be-processed water in the front | former stage of a reaction tank, and may be added directly to a reaction tank. Moreover, a nutrient may be added continuously or intermittently.
When a nutrient is added intermittently, the addition amount can be controlled by changing the addition frequency.

[Control of amount of polymer flocculant added to reaction vessel]
When controlling the amount of the polymer flocculant added to the reaction tank, for example, the measured value of the absorbance of the treated water is increased, the turbidity of the treated water, that is, the SS concentration is increased, and the granular sludge is increased. When a sign of disassembly is detected, the polymer flocculant is added to the reaction tank or the amount of the polymer flocculant added to the reaction tank is increased to prevent the sludge in the reaction tank from being dismantled.
In addition, the addition of the polymer flocculant or an increase in the amount added improves the tendency of the granular sludge to dismantle, reduces the measured value of the absorbance of the treated water, and lowers the turbidity of the treated water, that is, the SS concentration. If it is determined that the polymer flocculant is added, the addition amount of the polymer flocculant is returned to the original value, or the addition of the polymer flocculant is stopped.

  In this control method, for example, when the measured value of the absorbance of the treated water is increased and the SS concentration of the treated water is increased by a predetermined value or more, for example, 20% or more, the addition amount of the polymer flocculant is set to a predetermined value. Increase within a range, for example, 5 to 10%; the amount of polymer flocculant added in advance to the measured value of the absorbance of the treated water (or treated water turbidity or SS concentration), and this set value A control method such as controlling the addition amount of the polymer flocculant based on the above can be adopted.

As the polymer flocculant, the kind of flocculant to be added is not limited as long as it can increase the strength of the granular sludge by adhering to the surface of the granular sludge in the reaction tank. Those suitable for treatment systems such as cationic, anionic and amphoteric systems can be used. Preferred examples of the polymer flocculant include polyacrylamide and polyethylene oxide as nonionic flocculants. Examples of the cationic system include polyaminoalkyl acrylate, polyaminoalkyl methacrylate, polyethyleneimine, halogenated polydiallylammonium, chitosan, urea-formalin resin, and the like. Examples of the anionic system include sodium polyacrylate, polyacrylamide partial hydrolyzate, partially sulfomethylated polyacrylamide, poly (2-acrylamide) -2-methylpropane sulfate, and the amphoteric system includes acrylamide and aminoalkyl methacrylate. Examples include sodium acrylate copolymer. These may be used alone or in combination of two or more.
The addition concentration of the polymer flocculant is preferably controlled within a range of about 0.01 to 100 mg / L, particularly about 0.1 to 50 mg / L.

The polymer flocculant may be introduced into the reaction tank together with the water to be treated by adding it to the water to be treated before the reaction tank, or may be added directly to the reaction tank. Further, the polymer flocculant may be added continuously or intermittently.
When the polymer flocculant is added intermittently, the addition amount can be controlled by changing the addition frequency.

In the present invention, two or more control items (1) to (3) described above may be adopted.
When adding a nutrient and a polymer flocculant, either may be added to the water to be treated introduced into the reaction tank first, or may be added simultaneously. One may be added directly to the water to be treated introduced into the reaction vessel, the other may be added directly to the reaction vessel, or both may be added to the reaction vessel.

In the present invention, normal conditions can be adopted as the conditions for the anaerobic treatment. For example, the organic load on the reaction tank is 5 to 30 kg-COD _Cr / m ³ / day, particularly 8 to 20 kg-COD _Cr / m ³ / day is preferable, oxygen is not supplied into the reaction vessel, anaerobic conditions are set, the temperature is 25 to 40 ° C., particularly 30 to 38 ° C., and the pH is 6.0 to 8.0. preferable.
In particular, in order to perform stable treatment by the UASB method, a blanket of granular sludge having an average particle size of 0.5 to 3.0 mm, preferably about 0.8 to 1.5 mm is formed in the reaction tank. In the case of the EGSB method, it is preferable 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 vessel.

  In the UASB method in which a sludge blanket with a height of about 3 to 5 m is deployed in a reaction tank with a height of about 5 to 7 m, the treatment is performed at an ascending flow rate of about 0.3 to 1.5 m / hr in the reaction tank. In the EGSB method in which a sludge blanket having a height of about 5 to 18 m is developed in a reaction tank of about 7 to 20 m, it is preferable to perform high-speed processing at an ascending flow rate of about 2 to 5 m / hr in the reaction tank.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

  In addition, the anaerobic reaction tank used in the following Examples and Comparative Examples has an inner diameter of 6 cm and a height of 1.2 m, the capacity of the reaction part excluding the part where the GSS is installed is 3 L, and the capacity of the part including the GSS part Is 4L. This reaction tank was filled with 1.0 L of granular sludge taken out from a UASB type reaction tank of a food factory, and a load operation was started.

Further, the absorbance of the treated water was measured using a spectrophotometer “Spectro :: lyser” manufactured by Sugawara Jitsugyo Co., Ltd., and the absorbance of light having a wavelength of 660 nm was measured. The SS concentration of the treated water was determined from a measured value of absorbance using a calibration curve prepared in advance using the absorbance of the test water with a known SS concentration.
The absorbance measurement and SS concentration detection of this treated water were performed at a frequency of once every 12 hours.

The water to be treated is evaporated condensed water discharged from the pulp manufacturing process, and the water quality is 7000 mg / L of organic matter as COD _Cr , of which the methanol concentration is 3800 mg / L (5700 mg / L as COD _Cr). )Met.
The water to be treated was passed while circulating the treated water so that the ascending flow rate in the reaction tank was 3 m / hr, and granular sludge was developed in the reaction tank to form a sludge blanket. The temperature in the reaction vessel was maintained at 30 to 35 ° C., and the pH was adjusted to be pH 7.0. The pH adjustment was performed by adding pH adjuster C (acid or alkali) to the pH adjusting tank. Under these conditions, in any of the following Examples 1 to 3 and Comparative Example 1, the organic matter load on the reaction tank is 10 to 15 kg-COD _Cr / m ³ / day, and the sludge load is 0.4 to 0.7 kg- It was set within the range of COD _Cr / kg-VSS / day.

<Example 1>
The SS concentration was monitored from the measured value of the absorbance of the treated water taken out from the reaction tank, and the flow rate of the treated water flowing into the reaction tank was controlled in accordance with the variation of the SS concentration. The treatment load was controlled in the range of sludge load 0.4 to 0.7 kg-COD _Cr / kg-VSS / day.
Specifically, the treated water flow rate is 0.65 L / hr when the treated water SS concentration is 80 mg / L or less, the treated water flow rate is 0.6 L / hr when the treated water SS concentration exceeds 80 mg / L and is 100 mg / L or less, When the treated water SS concentration exceeded 100 mg / L and 120 mg / L or less, the treated water flow rate was 0.55 L / hr, and when the treated water SS concentration exceeded 120 mg / L, the treated water flow rate was 0.5 L / hr.

As a result, at the sludge interface where the granular sludge is deployed, there is no sudden drop in height due to the outflow / reduction of sludge, and during the 90-day experiment period, the sludge interface exceeds the amount of granular sludge at the start of treatment. The amount could be maintained in the reaction vessel. In addition, the average particle size was not reduced due to the dismantling and refinement of the granular sludge in the reaction tank.
FIGS. 3 and 4 show the change over time in the average particle diameter of the granular sludge in the reaction tank and the change over time in the sludge interface height in the reaction tank, respectively.

<Example 2>
The SS concentration was monitored from the measured value of the absorbance of the treated water taken out from the reaction tank, and the amount of sodium nitrate solution added to the treated water was changed according to the variation of the SS concentration. The amount of sodium nitrate aqueous solution added was within a range in which the concentration of nitrate ions (hereinafter simply referred to as “nitric acid concentration”) after mixing the sodium nitrate aqueous solution and the water to be treated was 500 mg / L or less.
Specifically, when the treated water SS concentration is 80 mg / L or less, the nitric acid concentration is 130 mg / L, and when the treated water SS concentration exceeds 80 mg / L and is 100 mg / L or less, the nitric acid concentration is 200 mg / L, and the treated water SS concentration is 100 mg / L. The concentration of nitric acid was 250 mg / L and the treated water SS concentration was more than 120 mg / L, and the nitric acid concentration was 300 mg / L.

As a result, at the sludge interface where the granular sludge is deployed, the height of the sludge is not reduced due to the outflow / decrease of the sludge. It could be maintained in the reaction vessel. In addition, the average particle size was not reduced due to the dismantling and refinement of the granular sludge in the reaction tank.
FIGS. 3 and 4 show the change over time in the average particle diameter of the granular sludge in the reaction tank and the change over time in the sludge interface height in the reaction tank, respectively.

<Example 3>
In Example 2, instead of the sodium nitrate aqueous solution, a cationic polymer flocculant (polyaminoalkyl acrylate) was used, and the amount added was changed in accordance with the change in the SS concentration of the treated water. The amount of the polymer flocculant added was controlled in a range where the concentration of the flocculant after mixing the flocculant and the water to be treated (hereinafter simply referred to as “flocculating agent concentration”) was 15 mg / L or less.
Specifically, when the treated water SS concentration is 80 mg / L or less, the flocculant concentration is 10 mg / L, and when the treated water SS concentration exceeds 80 mg / L and is 100 mg / L or less, the flocculant concentration is 11 mg / L and the treated water SS concentration is 100 mg. The coagulant concentration was set to 13 mg / L when the coagulant concentration was 12 mg / L exceeding 120 L / L and the treated water SS concentration exceeded 120 mg / L.

As a result, at the sludge interface where the granular sludge is deployed, the height of the sludge is not reduced due to the outflow / decrease of the sludge. It could be maintained in the reaction vessel. In addition, the average particle size was not reduced due to the dismantling and refinement of the granular sludge in the reaction tank.
FIGS. 3 and 4 show the change over time in the average particle diameter of the granular sludge in the reaction tank and the change over time in the sludge interface height in the reaction tank, respectively.

<Comparative Example 1>
The anaerobic treatment was performed under the condition that neither the control of the SS concentration of the treated water taken out from the anaerobic reaction tank nor the control based on the monitoring result was performed.
As a result, the granular sludge in the anaerobic reaction tank gradually decreased, and the average particle size became smaller.
FIGS. 3 and 4 show the change over time in the average particle diameter of the granular sludge in the reaction tank and the change over time in the sludge interface height in the reaction tank, respectively.

  From the following results, by controlling the flow rate of water to be treated into the reaction tank based on the absorbance of the treated water, the amount of nutrients added, or the amount of polymer flocculant added, the granular sludge dismantled in the reaction tank, It can be seen that sludge outflow from the reaction tank can be reliably prevented and high-load high-speed treatment can be stably performed over a long period of time.

DESCRIPTION OF SYMBOLS 1 Reaction tank 2 Granule sludge 3 Gas-solid-liquid separator 4 Gas holder 5 Treated water tank 6 Adjustment tank 7 pH adjustment tank 9 Control apparatus 10 Drug storage tank

Claims (4)

In a method of performing anaerobic treatment by introducing treated water containing evaporative condensed water discharged in a pulp manufacturing process into a reaction tank in which granule sludge is retained, the treated water from the reaction tank has a wavelength of 380 to 380. An anaerobic treatment method characterized by measuring the absorbance of visible light in the range of 780 nm and controlling one or more of the following (1) to (3) based on the measured value of the absorbance.
(1) Introduction flow rate of water to be treated into the reaction tank (2) Amount of nutrient added to the reaction tank (3) Amount of polymer flocculant added to the reaction tank   2. The anaerobic treatment method according to claim 1, wherein the nutrient contains one or more selected from the group consisting of nitric acid, nitrous acid, sugar, coating waste liquid, calcium compound, and iron salt. A reaction tank in which granule sludge is retained, means for introducing treated water containing evaporative condensed water discharged from the pulp production process into the reaction tank, means for taking out treated water from the reaction tank, and the treated water Means for measuring the absorbance of visible light in the wavelength range of 380 to 780 nm, and means for controlling one or more of the following (1) to (3) based on the measured value of the absorbance: An anaerobic treatment device characterized.
(1) Introduction flow rate of water to be treated into the reaction tank (2) Amount of nutrient added to the reaction tank (3) Amount of polymer flocculant added to the reaction tank   4. The anaerobic treatment apparatus according to claim 3, wherein the nutrient contains one or more selected from the group consisting of nitric acid, nitrous acid, sugar, coating waste liquid, calcium compound, and iron salt.

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