JP5184658B2 - Anaerobic treatment system and anaerobic treatment method - Google Patents

Description

  The present invention relates to an anaerobic treatment system and an anaerobic treatment method for organic wastewater.

  As a method for treating organic wastewater containing organic matter, the UASB (Upflow Anaerobic Sludge Blanket) method and the EGSB (Expanded Granular Sludge Bed) method using granulated anaerobic sludge are known. These methods consist of granulated anaerobic sludge (hereinafter also simply referred to as “granule sludge”) with high density and good sedimentation in an upflow anaerobic treatment tank included in the anaerobic treatment device. The organic wastewater is anaerobically treated through the organic wastewater from the bottom to the top of the anaerobic treatment tank.

  However, in anaerobic treatment with granular sludge, granule sludge becomes excessively large and sedimentation is caused by long-term continuous operation or high load treatment with a BOD load of more than a dozen kg / m3 / day. May decrease. The main reason for the decrease in sedimentation is considered to be that gas accumulates inside the granular sludge and the specific gravity of the granular sludge decreases. Granule sludge having lowered sedimentation surfaced on the water surface in the anaerobic treatment tank and flows out of the anaerobic treatment tank together with the treated water. Thereby, the quantity of the granular sludge in an anaerobic processing tank reduces gradually, and processing capacity falls. When the amount of granulated sludge in the anaerobic treatment tank is large, it may be necessary to newly add granule sludge to the anaerobic treatment tank.

As a method for recovering the sedimentation property of granular sludge, for example, methods described in Patent Documents 1 to 4 are known. In these methods, granulated sludge that has floated up or granulated sludge that has become easy to float is crushed by a crushing device such as a grinder pump or mixer, and then the anaerobic treatment tank is released. It has returned to.
JP-A-6-182382 JP-A-8-103794 Japanese Patent Laid-Open No. 8-103795 JP-A-8-132091

  However, since the methods described in Patent Documents 1 to 4 all use a crushing device, there is a problem that granule sludge is excessively crushed and finely divided. If the granule sludge is refined, the granule sludge may easily rise due to the attachment of bubbles and conversely flow out. In addition, it takes a certain time to obtain granulated sludge suitable for the treatment of organic wastewater by granulating the refined sludge again.

  Therefore, the present invention can restore the sedimentation property of granule sludge having a decreased sedimentation property without reducing the granularity, and maintain a high concentration of anaerobic sludge in the anaerobic treatment tank. An object of the present invention is to provide an anaerobic processing system and method capable of improving the processing efficiency.

  The anaerobic treatment system of the present invention contains granule sludge formed by granulating anaerobic sludge, and the organic wastewater is anaerobically treated by flowing the organic waste water upward and bringing it into contact with the granule sludge. An anaerobic treatment tank, a collecting device that collects the floating granular sludge that has floated inside the anaerobic treatment tank, and the floating granule that has been degassed without crushing the floating granular sludge collected by the collecting device. A deaeration treatment device for discharging the gas contained in the sludge, and a return means for returning the granular sludge degassed in the deaeration treatment device to the anaerobic treatment tank. It is a cleaning device.

  In the anaerobic treatment system of the present invention, the gas contained in the floating granule sludge (hereinafter also referred to as “encapsulated gas”) is obtained by deaeration treatment without crushing the floating granule sludge collected by the collecting device. Discharge out of the floating granule sludge. Therefore, the sedimentation property of the granular sludge can be recovered without making the floating granule sludge fine. In addition, the concentration of anaerobic sludge in the anaerobic treatment tank is increased by returning the granulated sludge, which has been deaerated and recovered in sedimentation, to the anaerobic treatment tank and reused it. Processing efficiency is improved. The inclusion gas is a gas mainly composed of carbon dioxide gas and methane gas generated by decomposition of organic waste water or decomposition of microbial sludge killed inside granule sludge.

  In the anaerobic treatment system of the present invention, a cleaning device using fresh water is adopted as the deaeration treatment device. When deaeration treatment of the floating granule sludge is performed using a cleaning device using fresh water, the inclusion gas can be sufficiently discharged without crushing the floating granule sludge.

  In the anaerobic treatment method of the present invention, the organic waste water is made to flow upward in an anaerobic treatment tank containing granulated sludge formed by granulating anaerobic sludge and brought into contact with the granular sludge. Anaerobic treatment process for anaerobic treatment of waste water, collection process for collecting floating granular sludge that has floated in the anaerobic treatment tank, and deaeration treatment without crushing the floating granular sludge obtained through the collection process A deaeration process step for discharging the encapsulated gas of the floating granule sludge, and a return step for returning the granulated sludge subjected to the deaeration process to the anaerobic treatment tank. It is characterized by a cleaning treatment with fresh water.

  In the anaerobic treatment method of the present invention, the floating granule sludge collected in the collecting step is degassed without being crushed, so that the gas contained in the floating granule sludge is discharged out of the floating granule sludge. . Therefore, the sedimentation property of the granular sludge can be recovered without making the floating granule sludge fine. In addition, the concentration of anaerobic sludge in the anaerobic treatment tank is increased by returning the granulated sludge, which has been deaerated and recovered in sedimentation, to the anaerobic treatment tank and reused it. Processing efficiency is improved.

  According to the present invention, it is possible to recover the sedimentation property without reducing the granular sludge having a lowered sedimentation property, and maintain a high concentration of anaerobic sludge in the anaerobic treatment tank. It is possible to provide an anaerobic processing system and method capable of improving the processing efficiency.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted.

(First embodiment)
FIG. 1 is a schematic diagram showing the configuration of an embodiment of an anaerobic treatment system according to the present invention. An anaerobic treatment system 1 shown in FIG. 1 has an upflow type anaerobic treatment device 10 for anaerobically treating organic wastewater by flowing the organic wastewater upward and passing it through granular sludge.

  The anaerobic treatment apparatus 10 includes an acid generation tank 11 that receives organic wastewater that has passed through the raw water inflow pipe L1. The acid generation tank 11 decomposes organic substances contained in the organic wastewater into acetic acid and the like by acid-producing bacteria. Moreover, it is also preferable to add an alkali agent (for example, sodium hydroxide) as a neutralizing agent in the acid generation tank 11. A water supply pipe L2 is connected to the acid generation tank 11, and organic waste water in the acid generation tank 11 flows into the upward flow anaerobic treatment tank 12.

  The anaerobic treatment tank 12 is composed of a rectangular parallelepiped container as shown in FIG. 2, and an inflow portion 13 that communicates with the water supply pipe L <b> 2 at the lower portion thereof to allow organic wastewater to flow into the anaerobic treatment tank 12. Is provided. The inflow portion 13 is, for example, a water pipe that is provided with holes uniformly in the longitudinal direction. In addition, a sludge blanket layer 14 containing granular sludge for anaerobically treating organic wastewater is formed in the lower part of the anaerobic treatment tank 12.

  In the anaerobic treatment tank 12, the organic waste water is introduced into the inside through an inflow portion 13 provided in the lower portion thereof to cause upward flow, and the organic waste water is passed through the sludge blanket layer 14 to make the organic waste water anaerobic. To process. Thereby, the liquid layer 15 containing the organic waste water (treated water) subjected to the anaerobic treatment is formed on the upper part of the sludge blanket layer 14. The treated water of the liquid layer 15 includes floating granular sludge that has floated from the sludge blanket layer 14 and gas (for example, methane gas) generated by anaerobic treatment. The floating granule sludge is one in which the granule sludge floats. For example, the gas sludge floats on the granule sludge or the gas is encapsulated therein.

  A cover 16 for sealing the anaerobic treatment tank 12 is provided on the upper part of the anaerobic treatment tank 12. The cover 16 is disposed above the liquid surface of the liquid layer 15 and below the upper end of the side wall 17 of the anaerobic treatment tank 12. At the center of the cover 16, a separation tank 18 for separating the gas from the treated water containing the floating sludge and the gas has an upper end protruding from the cover 16 and a lower end thereof included in the liquid layer 15. Is arranged.

  An inlet for introducing treated water into the separation tank 18 is formed at the lower end of the separation tank 18. In order to guide the treated water to the introduction port, introduction plates 19 are provided along the bottom of the separation tank 18 below the separation tank 18 and on both sides of the introduction port. The introduction plates 19 are inclined opposite to each other with respect to the vertical direction. The introduction plate 19 is formed with a return port for returning the treated water that has not been introduced to the introduction port to the lower side below the introduction port.

  Further, below the introduction plate 19, a rectifying plate 20 is provided for adjusting the flow of treated water returned through the return port of the introduction plate 19.

  The treated water flowing upward through the sludge blanket layer 14 is caused to flow in the direction of arrow A by the introduction plate 19, and into the introduction path 21 formed between the introduction plate 19 and the separation tank 18. 15 flows from the liquid surface side. At that time, since the gas contained in the treated water comes out between the cover 16 and the liquid surface, the space defined by the separation tank 18, the cover 16, the side wall 17, and the liquid surface is a gas reservoir 22. Function as. The gas accumulated in the gas reservoir 22 may be discharged out of the anaerobic treatment tank 12 from the side wall 17 side, for example.

  Part of the treated water that has passed through the introduction path 21 flows in the direction of arrow B and flows into the separation tank 18 from the introduction port, and the other part flows in the direction of arrow C and flows down from the return port of the introduction plate 19. It is designed to flow to the side.

  The treated water that has flowed into the separation tank 18 overflows from the side wall of the separation tank 18 and accumulates in an area formed by the separation tank 18, the cover 16, and the side wall 17, so that area becomes the treated water reservoir 23. ing. A treated water return path L3 for returning a part of the treated water to the acid generation tank 11 (see FIG. 1) and a drain pipe L4 for draining the other part are connected to the treated water reservoir 23.

  Also, an overflow type collecting tank (collecting device) 30 that collects floating sludge contained in the treated water is provided in the vicinity of the top of the inlet of the treated water in the separation tank 18. . In the separation tank 18, a partition wall 24 is provided between the side wall of the separation tank 18 and the collection tank 30 to prevent the treated water flowing from the introduction port from flowing directly into the treated water reservoir 23. Yes. The collection tank 30 as a collection device has an inverted triangular cross section, and floating sludge in the vicinity of the surface of the treated water collected in the separation tank 18 flows into the collection tank 30 and is collected. The collection tank 30 communicates with the sludge discharge pipe L5 that introduces the collected floating sludge into the deaeration processing device 40.

  Referring to FIG. 1, the deaeration device 40 performs a deaeration process on the floating granule sludge collected in the collection tank 30 and releases the gas contained in the floating granule sludge. The deaeration device 40 is not particularly limited as long as it can release the inclusion gas from the floating granule sludge, and various devices can be used. For example, a decompression device that depressurizes a container in which floating granule sludge is contained and releases the inclusion gas, a centrifugal separator that releases inclusion gas by centrifugal force, and makes the floating granule sludge contact with clean water to release the inclusion gas. Examples thereof include a cleaning device and an ultrasonic cleaning device that releases the inclusion gas by ultrasonic vibration. In addition, these apparatuses may be used individually by 1 type, and may use 2 or more types together. Among the above devices, a decompression device and a centrifugal separator are preferable, and a decompression device is more preferable, from the viewpoint of more efficiently and sufficiently releasing the inclusion gas.

  The deaeration device 40 is in communication with a granule sludge return pipe (return means) L6 for returning the granulated sludge subjected to the deaeration process to the anaerobic treatment tank 12. The tip of the granule sludge return pipe L6 is connected to the water supply pipe L2.

  Next, a method for treating organic wastewater using the anaerobic treatment system 1 will be described.

  The organic waste water is caused to flow into the acid generation tank 11 through the raw water inflow pipe L1, and the organic waste water is stored in the acid generation tank 11. The organic waste water stored in the acid generation tank 11 is decomposed by acid-producing bacteria. At that time, it is preferable to add a neutralizing agent. The organic waste water stored in the acid generation tank 11 is caused to flow into the anaerobic treatment tank 12 from the inflow portion 13 through the water supply pipe L2.

  Here, with reference to FIG. 2, the anaerobic process in the anaerobic process tank 12 is demonstrated. The organic waste water that has flowed in from the inflow portion 13 disposed in the lower part of the anaerobic treatment tank 12 flows upward and passes through the sludge blanket layer 14. Thereby, an organic wastewater is anaerobically processed (anaerobic treatment process).

  Since the anaerobically treated organic wastewater is flowing upward, it flows in the direction of arrow A in FIG. 2 and flows into the introduction path 21 between the introduction plate 19 and the separation tank 18. At that time, the gas generated by the anaerobic treatment exits from the liquid surface, so that the gas content in the treated water flowing into the introduction path 21 is reduced. The gas that has come out from the liquid level is accumulated in the gas reservoir 22 and is exhausted from the anaerobic treatment tank 12.

  A part of the treated water passing through the introduction path 21 flows into the separation tank 18 from the introduction port formed at the lower end of the separation tank 18, but the other part passes through the return port of the introduction plate 19 and is on the sludge blanket layer 14 side. Will be returned.

  A part of the treated water flowing into the separation tank 18 is discharged from the side wall to the treated water reservoir 23. The treated water collected in the treated water reservoir 23 is returned to the acid generation tank 11 (see FIG. 1) through the treated water return path L3 and drained through the drain pipe L4. In addition, after further performing an aerobic process etc. as needed with respect to the treated water drained through the drain pipe L4, the to-be-processed water is drained to a river etc.

  Referring to FIG. 1, floating granular sludge floating on the surface of treated water stored in the separation tank 18 is caused to flow into the collection tank 30, and the floating sludge is collected by the collection tank 30 (collection process). The floating sludge collected in the collection tank 30 is introduced into the deaeration processing device 40 (see FIG. 1) through the sludge discharge pipe L5. And the deaeration process is performed with respect to the floating granular sludge in the deaeration unit 40 (deaeration process).

  When the deaeration process is performed by a decompression device, the floating granular sludge from the collection tank 30 is accommodated in a decompression container, and the interior of the container is decompressed by a vacuum pump connected to the container. The pressure (gauge pressure) in the container is preferably −10 kPa or less, and more preferably −20 to −100 kPa. By depressurizing the inside of the container, the gas contained in the floating granular sludge is released to the outside through voids and surface holes existing inside the sludge. Further, the bubbles attached to the floating granular sludge are easily removed from the granular sludge by reducing the pressure.

  When the deaeration process is performed by a centrifugal separator, the floating granular sludge is put into the centrifugal separator, and the inclusion gas is degassed by applying a centrifugal force. The centrifugal force to be applied is preferably 500 to 3000G. Since the floating granule sludge is crushed by centrifugal force, the inclusion gas is released to the outside. Moreover, since the centrifugal force which a granule sludge receives and the bubble adhering to this differs, the adhering bubble is isolate | separated from a granule sludge.

  When the deaeration process is performed by a cleaning device, the floating granule sludge is put into a cleaning container together with fresh water, and the encapsulated gas is deaerated by bringing the floating granule sludge into contact with the fresh water. As the fresh water to be brought into contact with the floating granule sludge, it is preferable to use water in which the amount of dissolved gas such as carbon dioxide or methane gas is small (more preferably, water in which the gas is not dissolved). By bringing such fresh water and floating granule sludge into contact, some of the gas (carbon dioxide, methane gas, etc.) adhering to the granule sludge dissolves in water, and the other part is granule sludge. Is removed as bubbles.

  When the adhering gas is removed, the partial pressure of the gas phase on the surface of the granular sludge is lowered, so that the inclusion gas moves to the surface through the voids existing inside the sludge. The gas that has moved to the surface of the granular sludge is dissolved in fresh water or released from the surface as bubbles. In this case, the deaeration process can be performed more effectively by providing a stirring blade in the cleaning container and stirring the fresh water and the floating granule sludge. In order to easily remove the gas from the floating granule sludge, it is preferable to use fresh water at around 50 ° C. in which methanogenic bacteria and the like are not inactivated.

  It is difficult to release the contained gas sufficiently by stirring to such an extent that the floating granule sludge is not crushed. By adopting the above-described method using a decompression device, a centrifugal separator or a washing device, the floating granule sludge The inclusion gas can be effectively released. Thereby, the sedimentation property of the granular sludge can be recovered. Compared with the conventional method of crushing granular sludge using a pump with rotating blades or rotating blades or a mixer with rotating blades, deaeration treatment can be carried out under mild conditions. Can be prevented.

  The granular sludge from which the encapsulated gas has been released by the deaeration device 40 is returned to the water supply pipe L2 through the granule sludge return pipe L6 (returning step). Since the water pipe L2 communicates with the inflow portion 13, the granular sludge is returned to the anaerobic treatment tank 12 by returning it to the water pipe L2.

  According to the anaerobic treatment system 1 of the present embodiment, the release of floating granule sludge gas flowing out from the anaerobic treatment tank 12 can be performed by deaeration treatment without crushing the granule sludge. . Therefore, the granular sludge maintains its size sufficiently even after the deaeration treatment. Therefore, since the sedimentation rate of the granular sludge is sufficiently high, returning it to the anaerobic treatment tank 12 increases the concentration of the granule sludge in the tank and improves the treatment efficiency of organic wastewater. To do. In addition, since the granular sludge after the deaeration treatment is sufficiently maintained in size, it is not necessary to granulate the sludge again, and the apparatus and process for that purpose can be omitted.

(Second Embodiment)
FIG. 3 is a schematic explanatory diagram of a configuration of the anaerobic processing system 2 according to the second embodiment. The anaerobic treatment system 2 shown in the figure does not have a collection tank in the separation tank 18, and is a subsequent stage of the anaerobic treatment tank 12, and a solid-liquid separation apparatus as a collection apparatus in front of the deaeration treatment apparatus 40. It differs from the anaerobic processing system 1 in that 50 is arranged.

  The solid-liquid separator 50 separates the floating granular sludge and the treated water contained in the treated water flowing from the treated water reservoir 23 through the water supply pipe L8. The solid-liquid separation device 50 includes a floating separation tank 52 that stores treated water from the water supply pipe L8, and a skimmer 55 that scrapes the floating granular sludge that has floated on the liquid surface of the floating separation tank 52. The skimmer 55 rotates in the direction of arrow D shown in FIG. 3 and can scrape the floating granular sludge. As the skimmer 55, a conventionally known skimmer can be used as long as it can scrape scum and oil floating on the liquid surface.

  The floating separation tank 52 is connected to a floating granule sludge discharge pipe L10 for introducing the floating granular sludge raked by the skimmer 55 to the degassing processing device 40. Further, a drain pipe L9 for draining the treated water from which the floating granular sludge has been separated is connected to the floating separation tank 52.

  The anaerobic treatment method of organic wastewater using the anaerobic treatment system 2 is an anaerobic treatment system 1 in that the treated water flowing from the treated water reservoir 23 to the water supply pipe L8 is solid-liquid separated by the solid-liquid separation device 50. It is different from the case of using. In the anaerobic treatment system 2, the treated water that has been anaerobically treated in the anaerobic treatment tank 12 flows into the separation tank 18 from the inlet formed in the lower end of the separation tank 18, and then the treated water reservoir 23. Flow into. A part of the treated water in the treated water reservoir 23 is returned to the acid generation tank 11 through the treated water return path L3.

  The treated water that has not been returned to the acid generation tank 11 among the treated water is introduced into the solid-liquid separator 50 through the water supply pipe L8, and the floating granular sludge contained in the treated water is scraped by the skimmer 55. And separated. A deaeration treatment device 40 performs a deaeration process on the floating granular sludge separated by the solid-liquid separation device 50. Then, similarly to the anaerobic treatment system 1, the granular sludge is returned to the anaerobic treatment tank 12 through the granule sludge return pipe L 6 and the water supply pipe L 2. In the case of the first embodiment, the granular sludge in the anaerobic treatment tank 12 is increased by returning the granular sludge subjected to deaeration treatment, and the treatment efficiency of organic waste water is improved. It is the same.

  The solid-liquid separator 50 is not limited to the one provided with the floating separation tank 52 as described above, but may be one provided with a filtration tank, a membrane separation tank, a liquid cyclone, or the like.

  As mentioned above, although preferred embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to the said embodiment. For example, although the anaerobic treatment apparatus includes an acid generation tank, it does not necessarily have an acid generation tank. Moreover, in the said embodiment, although the granule sludge in which the deaeration process was performed is introduce | transduced into the water pipe L2 through the granule sludge return pipe L6, it introduce | transduces directly into the anaerobic processing tank 12. May be. Furthermore, in the first embodiment, an overflow-type collection tank is exemplified as the collection device, but a collector equipped with a skimmer as exemplified in the second embodiment may be used.

  Hereinafter, a degassing treatment for granular sludge having lowered sedimentation will be specifically described with reference to experimental examples.

(Experimental example 1)
Using the anaerobic treatment system 1 of the first embodiment, a beer factory wastewater having a chemical oxygen demand (CODcr) of about 25000 mg / L is converted into CODcr load 20 kg-CODcr / m3 / day and the initial granular sludge. The treatment was performed at a concentration of about 40,000 mg-VSS / L. Granule sludge that floated on the surface of the anaerobic treatment tank during the treatment under the above conditions was collected in a separation tank.

  In this experimental example, the collected granular sludge was degassed by a decompression method using a decompression device. That is, 100 mL of floating granule sludge (solid content: about 10 g / L) was accommodated in a 1 L vacuum container. Thereafter, the inside of the container was reduced to -300 mmHg (gauge pressure) with a vacuum pump, and the floating granular sludge was deaerated for 10 minutes under this pressure condition.

(Experimental example 2)
The granular sludge that floated under the anaerobic treatment conditions similar to those of Experimental Example 1 was subjected to deaeration treatment by a centrifugal separation method using a centrifuge. That is, 50 ml of floating granule sludge (solid content: about 10 g / L) was collected in a centrifuge tube, and this centrifuge tube was attached to a centrifuge (manufactured by Kokusan Co., Ltd.). The centrifuge was operated for 1 minute under the condition of centrifugal force of 1600 G, and the floating granule sludge was deaerated.

(Experimental example 3)
The granular sludge that floated under the anaerobic treatment conditions similar to those of Experimental Example 1 was subjected to deaeration treatment by a cleaning method in which the floating granular sludge and fresh water were brought into contact with each other. That is, 100 mL of floating granule sludge (solid content: about 10 g / L) and 500 ml of water were placed in a 1 L beaker, and the floating granule sludge was degassed by stirring gently for about 10 minutes.

(Evaluation of sedimentation after deaeration)
Each granule sludge degassed by the decompression method (Experimental Example 1), the centrifugal separation method (Experimental Example 2), and the cleaning method (Experimental Example 3) was charged with methane fermentation treated water collected from the anaerobic treatment tank. Each was introduced into a graduated cylinder, and the sedimentation property of the granular sludge was visually observed. As a result, it was found that the depressurization method had the highest effect of recovering the sedimentation property of the granular sludge, and hereinafter, the order of the centrifugal separation method and the washing method was followed. In addition, by visual observation, neither sludge pulverization nor fine granulation was observed in any degassing treatment method.

It is a schematic explanatory drawing of the structure of the anaerobic processing system of 1st Embodiment. It is a schematic explanatory drawing of the structure of an anaerobic processing tank. It is a schematic explanatory drawing of the structure of the anaerobic processing system of 2nd Embodiment.

DESCRIPTION OF SYMBOLS 1, 2 ... Anaerobic processing system, 10 ... Anaerobic processing apparatus, 12 ... Anaerobic processing tank, 30 ... Separation tank (collection apparatus), 40 ... Deaeration processing apparatus, 50 ... Solid-liquid separation apparatus (collection apparatus), L6: Granule sludge return pipe (return means).

Claims (2)

An anaerobic treatment tank that contains granulated sludge formed by granulating anaerobic sludge and anaerobically treats the organic waste water by causing the organic waste water to flow upward and contact with the granular sludge, and
A collecting device for collecting the floating granular sludge that has floated inside the anaerobic treatment tank;
A degassing treatment device for discharging the gas contained in the floating granule sludge by degassing the flocculated granule sludge collected by the collecting device without crushing;
Returning means for returning granule sludge degassed in the degassing treatment device to the anaerobic treatment tank,
The anaerobic treatment system, wherein the deaeration treatment device is a cleaning device using fresh water. In an anaerobic treatment tank containing granulated sludge formed by granulating anaerobic sludge, the organic waste water is anaerobically treated by flowing the organic waste water upward and bringing it into contact with the granular sludge. Anaerobic treatment process;
A collecting step of collecting the floating granule sludge that has floated inside the anaerobic treatment tank;
A deaeration treatment step for discharging the gas contained in the floating granule sludge by deaeration treatment without crushing the floating granule sludge obtained through the collecting step;
A return step of returning the granulated sludge subjected to the deaeration treatment to the anaerobic treatment tank, and
The anaerobic treatment method, wherein the deaeration treatment is a washing treatment with fresh water.

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