JP2013126665A - Apparatus and method for treating organic wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for treating organic wastewater which allow application of methane fermentation treatment even when temperature of low concentration organic wastewater is low.SOLUTION: The apparatus for treating organic wastewater 101 is provided with: a solid-liquid separation device 10 which separates the low concentration organic wastewater 1 into solid and liquid and into solid-liquid separated water 2 and first concentrated sludge 3; an acid fermentation tank 20 which is kept at a prescribed temperature and carries out acid fermentation treatment of the first concentrated sludge 3; a mixing tank 30 which mixes the solid-liquid separated water 2 and the acid fermentation treatment water 4 treated in the acid fermentation tank 20 and separates fermentation gas contained in the mixed water; and a methane fermentation treatment tank 40 which carries out methane fermentation treatment of mixing tank outlet water 5 from which the fermentation gas is separated.

Description

  The present invention relates to an organic wastewater treatment apparatus equipped with an acid fermentation tank and an organic wastewater treatment method for subjecting low-concentration organic wastewater such as domestic wastewater and sewage to methane fermentation.

Compared to the technology that treats organic wastewater with methane fermentation, compared to the technology that treats organic wastewater to aerobic organisms, (1) less sludge is generated, and (2) electricity costs such as a blower are not required, so running costs are low. In recent years, organic effluents having a CODcr concentration of 2000 to 3000 mg / L or more have become widespread. For the methane fermentation treatment, a methane fermentation treatment method such as UASB (abbreviation of Up-flow Anaerobic Sludge Blanket) method, fixed bed method, fluidized bed method or the like is used. In particular, the UASB method uses a self-granulating function of anaerobic microorganisms to hold granulated sludge with excellent sedimentation at a high concentration in the tank, so that the CODcr load is 10 to ³⁰ kg / m ³ / d. Such a high load can be applied. For the above reasons, the UASB method is most popular as a method for methane fermentation treatment of domestic and foreign organic wastewater.

  On the other hand, in warming areas such as Brazil, India, Southeast Asia, etc., pretreatment of aerobic biological treatment (specifically activated sludge treatment) for organic wastewater with a CODcr concentration of 400 to 1000 mg / L such as sewage As shown in FIG.

  However, in an area where the temperature in winter falls to 0 to 10 ° C. as in Japan, the temperature of sewage to be treated is as low as 5 to 15 ° C. Therefore, when sewage is treated with UASB, the temperature in the UASB tank becomes as low as 5 to 15 ° C., and the activity of anaerobic bacteria in the tank is suppressed. In addition, suspended substances (suspended solids, hereinafter referred to as SS) accumulate in the UASB tank, and the UASB process cannot be performed. In addition, the block diagram of the conventional methane fermentation processing apparatus is shown in FIG.

  In addition, when organic wastewater with a CODcr concentration of 400 to 1000 mg / L such as sewage is subjected to UASB treatment, a large amount of energy is required for heating the UASB tank, and organic wastewater with a CODcr concentration of 1000 to 3000 mg / L or more is required. Less economical than processing. For these reasons, in a cold region, methane fermentation treatment cannot be applied to organic wastewater having a CODcr concentration of 400 to 1000 mg / L such as sewage. For this reason, the activated sludge treatment method has been applied to the treatment of organic wastewater such as sewage. Thus, in the prior art, running costs such as an electric bill such as a blower in the activated sludge treatment, and sludge treatment costs are required.

  By the way, in order to carry out UASB treatment with good contact efficiency and a large load, Patent Document 1 is given as an example of solid separation of solid components in waste water, solubilization treatment of separated sludge, and methane fermentation treatment. Patent Document 1 discloses an anaerobic digestion treatment apparatus for high-concentration organic wastewater (generally CODcr concentration of 2000 to 3000 mg / L or more) such as starch factory waste liquid, beer factory waste liquid, and acid fermentation waste liquid. And an anaerobic digestion processing apparatus provided with the solubilization tank is indicated. In this device, organic wastewater is solid-liquid separated in a sedimentation tank, and the precipitated solid concentrate containing the separated organic solids is solubilized and solubilized in a solubilization tank at high temperature (50 to 90 ° C.). The treatment liquid and the supernatant of the precipitation tank are introduced into an anaerobic treatment apparatus (methane fermentation treatment tank) (paragraph 0008, FIG. 3). Further, methane gas generated in the anaerobic treatment apparatus is combusted, and the solubilization tank is heated by the generated heat (paragraph 0011).

  However, when organic wastewater with a CODcr concentration of 400 to 1000 mg / L, such as sewage, is treated with methane fermentation, the amount of methane gas generated is larger than when organic wastewater with a CODcr concentration of 2000 to 3000 mg / L is treated with methane fermentation. Less is. Moreover, in order to maintain granule sludge, there is a limit to the water flow rate, and it is not possible to take the organic matter load in the UASB tank. In addition, part of the generated methane gas exists as dissolved methane in the organic waste water, and as a result, the amount of methane gas that can be recovered is further reduced. For this reason, even if it is going to process organic wastewater, such as sewage, using the anaerobic digestion processing device indicated by patent documents 1, a solubilization tank is maintained at high temperature conditions (50-90 ° C) only with collected methane gas. Can not. In order to maintain the high temperature condition, additional heat energy is required, which is not preferable because of high cost.

Japanese Patent Laid-Open No. 9-1179

  Therefore, the present invention is an organic wastewater treatment apparatus equipped with an acid fermentation tank for methane fermentation of low-concentration organic wastewater, and the organic wastewater to which methane fermentation treatment can be applied even when the organic wastewater has a low water temperature. An object is to provide a treatment apparatus and an organic wastewater treatment method. The “low water temperature” is a water temperature in the methane fermentation treatment tank, and means a water temperature of 20 ° C. or less, particularly 10 to 15 ° C.

The organic wastewater treatment apparatus 101 according to the first aspect of the present invention for solving the above-described problem is, for example, as shown in FIG. A solid-liquid separation device 10 for dividing the first concentrated sludge 3; an acid fermentation tank 20 that performs acid fermentation treatment of the first concentrated sludge 3; a solid-liquid separation water 2 and an acid fermentation tank 20; A mixing tank 30 for mixing the acid-fermented treated water 4 treated with the above, and separating the fermentation gas contained in the mixed water; and a methane fermentation treatment tank 40 for subjecting the mixing tank outlet water 5 from which the fermentation gas has been separated to methane fermentation. With.
In the present specification, “low-concentration organic wastewater” refers to organic wastewater having a CODcr value of 1000 mg / L or less. The “predetermined temperature” is preferably 20 to 35 ° C., and more preferably 20 to 25 ° C. as judged from the sewage water temperature and the heat energy of the generated gas. “Acid fermentation” means that polysaccharides, proteins, and lipids in organic substances are first hydrolyzed into monosaccharides, amino acids, and other unit constituent molecules, and then volatile fatty acids such as acetic acid and propionic acid. And a series of treatments that are decomposed into alcohols such as ethanol, lactic acid, succinic acid, and ethanol, hydrogen, carbon dioxide and the like. Microorganisms involved in acid production are facultative anaerobes. “Methane fermentation treatment” refers to an anaerobic biological treatment performed in an ORP range of −330 mV or less. “Fermentation gas” is mainly CO ₂ gas and partially contains H ₂ gas.

  If comprised in this way, the sludge contained in a low concentration organic wastewater can be isolate | separated and concentrated by a solid-liquid separator. Therefore, in the heating of the concentrated sludge in the acid fermentation tank maintained at a predetermined temperature, the energy required for heating can be reduced compared to the case of directly heating the organic waste water. Furthermore, in the acid fermenter, a part of the solid matter (SS content) contained in the concentrated sludge is converted into soluble organic matter (acetic acid, propionic acid, etc.) through hydrolysis and organic acid fermentation. Therefore, the activity of methane bacteria is maintained by the presence of such substances, and methane fermentation treatment can be performed satisfactorily even with organic wastewater with a low water temperature. Moreover, the fermentation gas generated in the acid fermentation tank can be separated from the mixed water in the mixing tank. Therefore, fermentation gas can be prevented from flowing into the methane fermentation treatment tank and generating scum. That is, since the sludge concentration in the acid fermentation tank is as high as 10,000 mg / L to 20000 mg / L, part of the fermentation gas is accompanied with the sludge. Therefore, if it is mixed with solid-liquid separated water in that state and put into the UASB tank, it will cause scum in the UASB tank. Therefore, when mixed with solid-liquid separated water or inflow sewage in the mixing tank, it is necessary to separate the fermentation gas accompanying the acid fermentation treatment sludge.

  The organic waste water treatment apparatus 102 according to the second aspect of the present invention is, for example, as shown in FIG. 3, subjected to acid fermentation treatment of the second concentrated sludge 7 discharged from the methane fermentation treatment tank 40, at a predetermined temperature. The acid fermentation tank 20 maintained; and the mixing tank 30 that mixes the low-concentration organic waste water 1 and the acid fermentation treated water 4 ′ treated in the acid fermentation tank 20 and separates the fermentation gas contained in the mixed water; A methane fermentation treatment tank 40 that performs methane fermentation treatment on the mixing tank outlet water 5 ′ from which the fermentation gas has been separated is provided.

  If comprised in this way, even if it is a case where SS content accumulates in a methane fermentation processing tank by the water temperature of low concentration organic waste water, and the interface of sludge rises, the rise of an interface will be carried out by discharging concentrated sludge in a tank. Can be prevented. Further, in the acid fermentation tank, a part of the solid matter (SS content) contained in the concentrated sludge is converted into soluble organic matter (acetic acid, propionic acid, etc.) through hydrolysis and organic acid fermentation. Therefore, the activity of methane bacteria is maintained by the presence of such substances, and methane fermentation treatment can be performed satisfactorily even with organic wastewater with a low water temperature. Moreover, the fermentation gas generated in the acid fermentation tank can be separated from the mixed water in the mixing tank. Therefore, fermentation gas can be prevented from flowing into the methane fermentation treatment tank and generating scum.

  In the organic wastewater treatment method according to the third aspect of the present invention, for example, as shown in FIG. 1, the low-concentration organic wastewater 1 is solid-liquid separated and divided into solid-liquid separated water 2 and first concentrated sludge 3. A separation step; an acid fermentation step in which the first concentrated sludge 3 is subjected to an acid fermentation treatment at a predetermined temperature; a solid-liquid separation water 2 and an acid fermentation treated water 4 treated in the acid fermentation step are mixed, and the mixed water A mixing step for separating the fermentation gas contained in the vessel; and a methane fermentation treatment step for subjecting the mixing tank outlet water 5 from which the fermentation gas has been separated to methane fermentation.

  If comprised in this way, the sludge contained in a low concentration organic waste water can be isolate | separated and concentrated by a isolation | separation process. Therefore, in the heating of the concentrated sludge in the acid fermentation process in which the acid fermentation process is performed at a predetermined temperature, the energy required for heating can be reduced as compared with the case of directly heating the organic waste water. Furthermore, in the acid fermentation process, a part of the solid matter (SS content) contained in the concentrated sludge is converted into soluble organic matter (acetic acid, propionic acid, etc.) through hydrolysis and organic acid fermentation. Therefore, the activity of methane bacteria is maintained by the presence of such substances, and methane fermentation treatment can be performed satisfactorily even with organic wastewater with a low water temperature. Moreover, the fermentation gas generated in the acid fermentation process can be separated from the mixed water in the mixing process. Therefore, fermentation gas can be prevented from flowing into the methane fermentation treatment process and generating scum.

  In the organic wastewater treatment method according to the fourth aspect of the present invention, for example, as shown in FIG. 3, acid fermentation is performed by subjecting the second concentrated sludge 7 discharged from the methane fermentation treatment step to an acid fermentation treatment at a predetermined temperature. A mixing step of mixing the low-concentration organic waste water 1 and the acid fermentation treated water 4 'treated in the acid fermentation step, and separating the fermentation gas contained in the mixed water; and a mixing tank in which the fermentation gas is separated A methane fermentation treatment step for subjecting the outlet water 5 'to a methane fermentation treatment.

If comprised in this way, even if it is a case where SS content accumulates in the methane fermentation treatment process by the water temperature of the low concentration organic waste water and the sludge interface rises, it is possible to prevent the rise of the interface by discharging the concentrated sludge. it can. In the acid fermentation process, part of the solid matter (SS content) contained in the concentrated sludge is converted into soluble organic matter (acetic acid, propionic acid, etc.) through hydrolysis and organic acid fermentation. Therefore, the activity of methane bacteria is maintained by the presence of such substances, and methane fermentation treatment can be performed satisfactorily even with organic wastewater with a low water temperature. Moreover, the fermentation gas generated in the acid fermentation process can be separated from the mixed water in the mixing process. Therefore, fermentation gas can be prevented from flowing into the methane fermentation treatment process and generating scum.

  The organic waste water treatment apparatus 103 according to the fifth aspect of the present invention is separated by the solid-liquid separation apparatus 10 in the organic waste water treatment apparatus 101 according to the first aspect of the present invention, for example, as shown in FIG. A first opening / closing device 51 for opening and closing the flow path in a flow path for transferring the first concentrated sludge 3 thus produced to the acid fermentation tank 20, and an acid for the second concentrated sludge 7 discharged from the methane fermentation treatment tank 40 A second opening / closing device 52 for opening and closing the flow path; a temperature measuring device for measuring the temperature in the methane fermentation tank 40; and the height of the sludge interface in the methane fermentation tank 40. A height measuring device for measuring; the first opening / closing device 51 and the second opening / closing device 52 are opened and closed based on the measured values of the temperature measuring device and the height measuring device.

  If comprised in this way, both the 1st concentration sludge and the 2nd concentration sludge can be acid-fermented in an acid fermentation tank. Moreover, the water temperature in the methane fermentation tank 40 and the water temperature in the methane fermentation tank 40 are selected by selecting the sludge to be acid-fermented in consideration of the water temperature in the methane fermentation tank 40 and the height of the sludge interface in the methane fermentation tank 40. Methane fermentation can be performed according to the height of the sludge interface.

  The organic wastewater treatment method according to the sixth aspect of the present invention is the organic wastewater treatment method according to the third aspect of the present invention, for example, as shown in FIG. 5, discharged from the methane fermentation treatment step. Based on the acid fermentation process in which the second concentrated sludge 7 is subjected to an acid fermentation treatment at a predetermined temperature; the treatment temperature in the methane fermentation treatment process; and the height of the sludge interface in the methane fermentation treatment process. A step of transferring the concentrated sludge 3 or the second concentrated sludge 7 to the acid fermentation step.

  If comprised in this way, both the 1st concentration sludge and the 2nd concentration sludge can be acid-fermented in an acid fermentation process. In addition, by selecting the sludge for acid fermentation treatment in consideration of the treatment temperature in the methane fermentation treatment process and the height of the sludge interface, the methane fermentation matched to the treatment temperature in the methane fermentation treatment process and the height of the sludge interface. Processing is possible.

  ADVANTAGE OF THE INVENTION According to this invention, a solid acid fermentation process and a methane fermentation process are combined, and a low concentration organic wastewater can be applied to a methane fermentation process also at low water temperature. Therefore, compared with the case where low-concentration organic wastewater is treated with activated sludge alone, it has become possible to significantly reduce the running costs such as the electricity bill of the equipment and sludge treatment costs.

It is a block diagram of the organic waste water treatment equipment 101 which concerns on the 1st Embodiment of this invention. It is the schematic of the mixing tank 30 and the UASB tank 40 with which the organic waste water treatment apparatus 101 is provided. It is a block diagram of the organic waste water treatment equipment 102 which concerns on the 2nd Embodiment of this invention. It is the schematic of the mixing tank 30 and the UASB tank 40 with which the organic waste water treatment apparatus 102 is provided. It is a block diagram of the organic waste water treatment equipment 103 which concerns on the 5th Embodiment of this invention. FIG. 9 is a flowchart showing a criterion for selecting each device in FIGS. 1, 3, 5, and 8. FIG. It is a block diagram of organic waste water treatment equipment 101 'which added the dissolved methane collection tank 60 to organic waste water treatment equipment 101. It is a block diagram of the conventional methane fermentation processing apparatus. It is a figure which shows the table | surface (Table 1) of the raw | natural water state used in Example 1, 2, 3, 4 and Comparative Examples 1, 2, 3, and 4. FIG. It is a figure which shows the table | surface (Table 2) of the specification of the apparatus used in Example 1, 2, 3, 4 and Comparative Examples 1, 2, 3, and 4. FIG. It is a figure which shows the table | surface (Table 3) of the experimental conditions of Examples 1, 2 and Comparative Examples 1, 2. It is a figure which shows the table | surface (Table 4) of the experimental result of Example 1, 2 and Comparative Example 1,2. It is a graph which shows the experimental result of Run1. It is a graph which shows the experimental result of Run2. It is a figure which shows the table | surface (Table 5) of the experimental result of Example 3, 4 and the comparative examples 3 and 4. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same or similar reference numerals, and redundant description is omitted. Further, the present invention is not limited to the following embodiments. In particular, any of the UASB method, the fixed bed method, and the fluidized bed method can be applied to the methane fermentation treatment. In the following embodiments, a UASB method that is most suitable for methane fermentation treatment will be described as an example.

  The organic wastewater treatment apparatus and the organic wastewater treatment method of the present invention include an acid fermentation tank (acid fermentation step) for the purpose of applying methane fermentation treatment even when the low-concentration organic wastewater has a low water temperature. Realized by.

  With reference to FIG. 1, the organic waste water treatment equipment 101 which concerns on the 1st Embodiment of this invention is demonstrated. The organic waste water treatment apparatus 101 includes a solid-liquid separation apparatus 10, an acid fermentation tank 20, a mixing tank 30, and a UASB tank 40 as a methane fermentation treatment tank. As shown in FIG. 1, the sewage 1 as the low-concentration organic wastewater enters the solid-liquid separation device 10, and the SS component with good sedimentation in the wastewater settles, so that the solid-liquid separation water 2 and the first concentrated sludge are settled. Separated into three. The first concentrated sludge 3 is supplied to the acid fermentation tank 20 and subjected to acid fermentation. The acid fermentation treated water 4 subjected to the acid fermentation treatment and the solid-liquid separated water 2 are supplied to the mixing tank 30 and mixed. The mixed tank outlet water 5 is supplied to the UASB tank 40 and subjected to methane fermentation. The flow path through which the sewage 1, the solid-liquid separation water 2, the concentrated sludge 3, the acid fermentation treated water 4, the mixing tank outlet water 5, the methane fermentation treated water 6 and the like pass is a pipe that can transport these, for example, a pipe Can be used.

  The solid-liquid separator 10 is preferably a solid-liquid separator such as a sedimentation basin, a centrifuge, a screen, or a screw press. For solid-liquid separation of solids with a large amount of water such as sewage and low SS concentration without chemical injection, it is easy to scale up from the viewpoint of equipment and maintenance, and running costs are low, so maintenance management A sedimentation basin is suitable because of its ease. Therefore, when the organic waste water to be treated is sewage with a large amount of water, a sedimentation basin is particularly preferable. That is, the solid-liquid separator 10 may be an initial sedimentation basin used in conventional activated sludge treatment.

  The acid fermentation tank 20 may be any tank capable of stirring sludge. For stirring, a stirrer may be installed, or a gas such as air may be aerated. The acid fermentation tank 20 includes an external heat source. As a heat source for heating, methane gas g1 recovered from the UASB tank 40 can be converted into steam by a boiler and used. The temperature in the acid fermenter 20 is preferably 20 to 35 ° C., more preferably 20 to 25 ° C. as judged from the sewage temperature and the heat energy of the generated gas. Thus, the 1st concentration sludge 3 which flowed into the acid fermentation tank 20 is heated to 20 degreeC or more with an external heat source, and is acid-fermented. In the acid fermenter 20, solids (SS content) contained in the organic waste water that cannot be decomposed by microorganisms as they are are subjected to organic acid fermentation by acid-producing bacteria, and soluble organic matter (propionic acid, acetic acid, etc.) ).

The HRT (Hydraulic Retention Time) of the acid fermenter 20 in which the acid fermentation treatment is performed is a soluble organic matter concentration (S-CODcr) and a volatile fatty acid concentration such as acetic acid / propionic acid / lactic acid (Volatile Fatty). Acid, hereinafter abbreviated as VFA). That is, the HRT when the CODcr solubilization ratio (S-CODcr / CODcr) and the VFA (asCODcr) / S-CODcr ratio show constant values is set as the optimum HRT.
For example, in the case of the first sedimentation basin sludge, if the HRT in the acid fermentation treatment is 2 days, the acid fermenter temperature is 20 ° C., the S-CODcr / CODcr ratio is 0.15 to 0.20 (−), and VFA (asCODcr ) / S-CODcr ratio is 0.3 to 0.4, acid fermenter temperature is 25 ° C., S-CODcr / CODcr ratio is 0.15 to 0.20 (−), VFA (asCODcr) / S-CODcr Becomes 0.55 to 0.65. On the other hand, in the case of UASB concentrated sludge, if the HRT in the acid fermentation treatment is 2 days, the acid fermenter temperature is 20 ° C., the S-CODcr / CODcr ratio is 0.10 to 0.20 (−), VFA (asCODcr ) / S-CODcr ratio is 0.13-0.20, acid fermenter temperature is 25 ° C., S-CODcr / CODcr ratio is 0.10-0.20 (−), VFA (asCODcr) / S-CODcr The ratio is 0.35 to 0.45. Thus, since the activity of acid-producing bacteria increases when the temperature of the acid fermenter increases in both the initial sedimentation basin sludge and the concentrated sludge in the UASB tank, the HRT is shortened, and the optimum HRT is 2 to 3 days at a water temperature of 20 ° C. The optimum HRT is 1 to 2 days at 25 ° C, and the optimum HRT is 0.5 to 1.5 days at a water temperature of 30 ° C. The concentrated sludge in the UASB tank is the one after the organic matter in the wastewater has been partially decomposed by anaerobic bacteria in the UASB tank. The / S-CODcr ratio is a smaller value for the concentrated sludge in the UASB tank.

  The concentrated sludge in the acid fermentation tank 20 is preferably stirred continuously or intermittently. Since the MLSS concentration in the acid fermenter 20 is as high as 20000 to 40000 mg / L, power for uniformly stirring the sludge is applied. However, when the agitation is strong, the generated organic acid is volatilized or oxidized to decrease. Therefore, the acid fermenter is stirred intermittently. It is preferable to perform intermittent stirring for 5 to 15 minutes at intervals of 1 to 2 hours.

  In FIG. 2, after mixing the solid-liquid separation water 2 and the acid-fermentation treated water 4 in the mixing tank 30, a mode that the mixing tank exit water 5 is passed through the UASB tank 40 is shown. In the mixing tank 30, as shown in FIG. 2, the mixed water is temporarily retained in the distribution tank 30 serving as a mixing tank and is brought into contact with the atmosphere to separate the fermentation gas generated by the acid fermentation treatment from the mixed water. . In the distribution tank 30, the fermented gas contained may be separated by diverting the mixed water, naturally flowing, overflowing, or the like. Moreover, the mixing tank 30 may be equipped with a stirrer inside. By separating the fermentation gas, the generation of scum by the fermentation gas in the UASB tank 40 can be suppressed, and the UASB process can be performed satisfactorily.

  The UASB tank 40 has a GSS 41 (gas-solid-liquid separator) and a sludge bed 42 inside. Furthermore, it has a flow path, for example, piping, for transferring the concentrated sludge (second concentrated sludge) in the sludge bed 42 to the dewatering step. In UASB treatment, organic substances contained in low-concentration organic wastewater, soluble organic substances produced by acid fermentation, and organic acids such as acetic acid and propionic acid are converted into methane and carbon dioxide by anaerobic bacteria in the UASB tank 40. Disassembled.

In addition, since sewage is generally a low-concentration organic wastewater having a CODcr concentration of 400 to 1000 mg / L, the CODcr volumetric load in the methane fermentation treatment tank (UASB tank) is as low as 1 kg / m ³ / d. Therefore, the amount of generated methane gas is small compared to methane fermentation treatment of high concentration organic wastewater such as food production wastewater. In the methane fermentation treatment of low-concentration organic wastewater, 40 to 60% of the methane gas generated in the methane fermentation treatment tank is dissolved in the methane fermentation treatment water and discharged out of the system. Therefore, the amount of heat energy from methane gas obtained by methane fermentation treatment of low-concentration organic wastewater is limited. The SS concentration of sewage is usually 200 mg / L. In this state, it is difficult to raise the water temperature even if the gas generated by methane fermentation is converted into steam by a boiler and used as heating energy. In that respect, if SS is solid-liquid separated and concentrated to about 100 to 200 times as a concentrated sludge concentration (20,000 to 40000 mg / L), the temperature in the acid fermenter can be increased by 5 to 10 ° C. Therefore, in order to set the temperature of the acid fermentation tank to 20 ° C. or higher, it is preferable that the temperature of the first sedimentation basin or the methane fermentation treatment tank as a solid-liquid separator in the methane fermentation process is 10 to 15 ° C. or higher.

Moreover, in the UASB process of low concentration organic wastewater such as sewage, the CODcr volumetric load is 1 kg / m ³ / d. On the other hand, in the UASB treatment of high concentration organic wastewater such as food industry wastewater, the CODcr volumetric load is 10 to 20 kg / m ³ / d. That is, the low-concentration organic wastewater has a lower organic load of 1/10 to 1/20 than the high-concentration organic wastewater, the density of anaerobic bacteria is low, and the particle size of the granular sludge in the sludge bed is 0.00. It becomes as small as 1 to 0.5 mm. The difference between the sedimentation rate of granulated sludge and the sedimentation rate of inflow SS is smaller than the conventional UASB granule sludge applied to high-concentration organic wastewater. The occurrence of scum in the UASB tank increases, and it may be difficult to maintain the sludge in the UASB tank. For these reasons, the mixed water after mixing the solid-liquid separated water 2 and the acid fermentation treated water 4 preferably has an SS concentration of 2000 mg / L or less, particularly preferably 1000 mg / L or less.

With reference to FIG. 3, the organic waste water treatment apparatus 102 which concerns on the 2nd Embodiment of this invention is demonstrated. The organic waste water treatment apparatus 102 includes an acid fermentation tank 20, a mixing tank 30, and a UASB tank 40 as a methane fermentation treatment tank. As shown in FIG. 3, sewage 1 as low-concentration organic waste water is supplied to a mixing tank 30. On the other hand, the second concentrated sludge 7 discharged from the UASB tank 40 is supplied to the acid fermentation tank 20 and subjected to an acid fermentation process. The treated acid fermentation treated water 4 ′ is supplied to the mixing tank 30. In the mixing tank 30, the sewage 1 and the acid fermentation treated water 4 ′ are mixed, and the mixing tank outlet water 5 ′ is supplied to the UASB tank 40 and subjected to methane fermentation.
For the same reason as described for the organic waste water treatment apparatus 101, the mixed water after mixing the influent sewage 1 and the acid fermentation treated water 4 ′ preferably has an SS concentration of 2000 mg / L or less. In particular, it is preferably 1000 mg / L or less.

  FIG. 4 shows how the mixing tank outlet water 5 ′ is passed through the UASB tank 40 after mixing the sewage 1 and the acid fermentation treated water 4 ′ in the mixing tank 30. In FIG. 4, the flow path for supplying the second concentrated sludge 7 discharged from the UASB tank 40 to the acid fermentation tank 20 is branched from the flow path for transferring the second concentrated sludge 7 to the dehydration step. These flow paths may be provided separately.

  If the temperature of the sewage 1 falls to 15 to 20 ° C. or lower in winter or the like, the activity of anaerobic bacteria in the UASB tank 40 decreases. Among the anaerobic bacteria, particularly when acid-producing bacteria are affected by the water temperature, the SS content in the sewage 1 becomes difficult to undergo acid fermentation, and much SS content accumulates in the sludge bed, and the interface of the sludge bed rises. For this reason, in the organic waste water treatment apparatus 102, as shown in FIG. 3, sludge is discharged from a portion (MLSS 20,000 to 40,000 mg / L) having a high sludge concentration at the lower part of the UASB tank 40 and supplied to the acid fermentation tank 20. To do. In the acid fermentation tank 20, sludge is heated to 20 ° C. or higher using an external heat source, and acid fermentation treatment is performed. The acid fermentation treated water 4 ′ is mixed with the sewage 1 and supplied to the UASB tank 40. Acid fermentation produces organic acids such as soluble organic substances and acetic acid / propionic acid. These organic substances are decomposed into methane and carbon dioxide by anaerobic bacteria in the UASB tank 40.

In areas where the outside air temperature is low throughout the year (for example, Hokkaido in Japan, Germany and Denmark in northern Europe, etc.), when sewage is subjected to methane fermentation, the temperature of the methane fermentation tank (for example, UASB tank) is 15 to 20 ° C. In many cases, the amount of inflow SS increases in the methane fermentation treatment tank. Therefore, in such an area, the organic waste water treatment apparatus 101 (FIG. 1) according to the first embodiment is applied.
On the other hand, in warming areas where the outside temperature is 15 ° C or higher throughout the year (for example, southern Shikoku, southern Kyushu, etc. in Japan, and Southeast Asia, India, Brazil, etc. overseas), when sewage is treated with methane fermentation, For example, the temperature of the UASB tank) is often 15 to 20 ° C. or more, and the accumulation of sludge in the methane fermentation treatment tank is reduced. However, even in such a region, there may be a case where sludge accumulates in the UASB tank due to a sudden drop in temperature in winter or a change in inflow SS concentration due to changes in weather conditions. Further, for the purpose of increasing the amount of gas generated in the methane fermentation treatment, it is an effective method to subject the organic matter remaining in the UASB tank to a part of the acid fermentation. In such a case, the organic waste water treatment apparatus 102 (FIG. 3) according to the second embodiment is applied.

  With reference to FIG. 5, the organic waste water treatment apparatus 103 which concerns on the 3rd Embodiment of this invention is demonstrated. In the organic waste water treatment apparatus 103, the second concentrated sludge 7 is discharged from the UASB treatment tank 40 by the transfer device 63 (transfer destination: acid fermentation tank 20) in the organic waste water treatment apparatus 101 shown in FIG. It is supplied to the fermenter 20 and subjected to acid fermentation. That is, it has the structure of both the organic waste water treatment apparatus 101 (FIG. 1) and the organic waste water treatment apparatus 102 (FIG. 3). Furthermore, in the organic waste water treatment device 103, the first concentrated sludge 3 separated by the solid-liquid separation device 10 is supplied to the acid fermentation 20 by the transfer device 61 (transfer destination: acid fermentation tank 20) and subjected to acid fermentation treatment. The The flow path from the solid-liquid separator 10 to the acid fermentation tank 20 includes a valve 51 as a first opening / closing apparatus that opens and closes the flow path, and the second concentrated sludge 7 discharged from the UASB tank 40. The flow path to 20 is provided with a valve 52 as a second opening / closing device that opens and closes the flow path. In addition, a flow path from the sewage 1 that is low-concentration organic waste water to the solid-liquid separator 10 and a branch from the flow path in front of the solid-liquid separator 10 bypass the solid-liquid separator 10 to the mixing tank 30. Each flow path includes a valve 53 as a third opening / closing device and a valve 54 as a fourth opening / closing device. Furthermore, a thermometer as a temperature measuring device that measures the temperature in the UASB tank 40 and a height measuring device that measures the height of the sludge interface in the UASB tank 40 are provided.

In the organic waste water treatment apparatus 103, by providing the control device 50, the control device 50 also performs on / off control based on the measurement values of the thermometer and the height measurement device. The pump 62 for transferring the acid fermentation treated water 4 (4 ′) is on / off controlled by the liquid level (not shown) of the acid fermentation tank 20. That is, when the liquid level of the acid fermentation tank 20 reaches a certain level (high level), the transfer pump 62 is turned on, and the acid fermentation treated water 4 (4 ′) is transferred to the mixing tank 30. When the liquid level of the acid fermenter 20 reaches a certain level (low level), the transfer pump 62 is turned off.
In addition, the water temperature of the UASB tank is affected by the air temperature, and changes in a long span on a monthly basis. Therefore, the valve 51 as the first opening / closing device, the valve 53 as the third opening / closing device, and the valve 54 as the fourth opening / closing device do not always need to be automatically controlled and can be manually opened / closed. It may be. Similarly, the valve 52 as the second opening / closing device may be manually opened and closed as necessary.

Thus, in the organic waste water treatment apparatus 103, the sludge to be subjected to the acid fermentation treatment can be selected in consideration of the water temperature in the UASB tank 40 and the height of the sludge interface in the UASB tank 40. In addition, a flow path should just be able to transfer treated water and sludge, for example, can use piping.
Further, in the organic waste water treatment apparatus 101 (FIG. 1) and the organic waste water treatment apparatus 102 (FIG. 3), the valves 51, 52, 53 and the transfer pumps 61, 62, 63 are omitted.

FIG. 6 shows a supply case of concentrated sludge to the acid fermentation tank according to the temperature in the UASB tank and the height of the sludge interface in the UASB tank. When the temperature inside the UASB tank is appropriate and the sludge interface height inside the UASB tank is appropriate, there is no pretreatment (acid fermentation treatment) (FIG. 8). If the UASB tank temperature is appropriate but the UASB tank sludge interface height is not appropriate, a portion of the UASB tank sludge is acid-fermented and mixed with the influent raw water and the acid-fermented water into the UASB tank. Supply (FIG. 3). If the temperature in the UASB tank is not appropriate, but the sludge interface height in the UASB tank is appropriate, the inflow raw water is solid-liquid separated, the concentrated sludge is acid-fermented, and the solid-liquid separated water and the acid-fermented water are mixed before UASB It supplies to a tank (FIG. 1). If the temperature in the UASB tank is not appropriate and the sludge interface height in the UASB tank is not appropriate, the raw inflow water is solid-liquid separated, the concentrated sludge is acid-fermented, and the solid-liquid separated water and the acid-fermented water are mixed Supply to UASB tank. Further, a part of the UASB tank sludge is subjected to an acid fermentation process, and the solid-liquid separated water and the acid fermentation process water are mixed and then supplied to the UASB tank (FIG. 5).
Here, when the temperature inside the UASB tank is appropriate, the UASB water temperature is set to 15 ° C. or higher, preferably 20 ° C. or higher. When the effective water depth is 5 m, the appropriate sludge interface height in the UASB tank is 2.0 to 3.0 m (40 to 60% of the effective water depth). When the sludge interface height is 3.5 m (70% of the effective water depth) or more, it is necessary to subject the concentrated sludge to an acid fermentation treatment.
As for the temperature inside the UASB tank, it is preferable to determine whether or not the average temperature is within an appropriate temperature range by installing thermometers at two places 1.0 m from the tank bottom and 3 m from the tank bottom. The sludge interface height is measured using an MLSS densitometer (photoelectric type) or the like.

As shown in FIG. 7, the organic waste water treatment apparatus 101 according to the first embodiment of the present invention may include a dissolved methane recovery tank 70 downstream of the UASB tank 40. The same applies to the organic waste water treatment apparatuses 102 and 103.
Acid-producing bacteria involved in acid fermentation are facultative anaerobes. Therefore, as shown in FIG. 7, air g2 is blown in the acid fermentation tank 20 instead of sludge stirring, and the acid fermentation treatment is advanced simultaneously with the sludge stirring. Oxygen in the air is consumed by the acid fermentation treatment, and carbon dioxide is generated. The exhaust gas g3 from the acid fermentation tank 20 is blown into the dissolved methane recovery tank 70 arranged at the rear stage of the methane fermentation treatment tank 40, and the dissolved methane in the methane fermentation treated water 6 is driven out and recovered as a mixed gas g4 containing methane gas. A gas containing oxygen may be used instead of the air g2.

Examples of the present invention will be described below. However, the present invention is not limited to the following examples.
Table 1 in FIG. 9 shows the properties of raw water used in this example. Looking at the average values, the SS concentration was 162 mg / L, CODcr 402 mg / L, S-CODcr 96 mg / L, BOD 165 mg / L, and S-BOD 39 mg / L.
Table 2 in FIG. 10 shows the specifications of the apparatus used in this example. A UASB tank (effective capacity 940 L) was used for methane fermentation. An acid fermentation tank (effective capacity 60 L) was used for the acid fermentation. The UASB tank body is made of steel plate, and the GSS part is made of transparent PVC. The temperature in the UASB tank was adjusted using a band heater and a temperature controller. Stirring in the acid fermentation tank was performed with a stirrer. The temperature adjustment in the acid fermentation tank was performed using a band heater and a temperature controller in the same manner as in the UASB tank.

[Example 1 / Comparative Example 1]
Table 3 in FIG. 11 shows the conditions of Example 1 and Comparative Example 1. In both Example 1 and Comparative Example 1, the amount of raw water is 2.82 m ³ / d, UASB tank HRT 8h, UASB tank temperature 10-20 ° C. (Run 1-1: 20 ° C., Run 1-2: 15 ° C., Run 1-3: 10 The experiment was conducted under the condition of ° C. In Run 1-1 of Example 1 (UASB water temperature 20 ° C.), the processing flow of the organic waste water treatment apparatus 201 shown in FIG. 8 was used. In Run 1-2 (UASB water temperature 15 ° C.) and Run 1-3 (UASB water temperature 10 ° C.), the processing flow of the organic waste water treatment apparatus 101 shown in FIG. 1 was used. The water area load of the first sedimentation basin (solid-liquid separator) was 32.5 m ³ / m ² / d, the amount of concentrated sludge from the first sedimentation basin was 0.030 m ³ / d, and the concentrated sludge concentration was 20000 mg / L. . The temperature of the acid fermenter was 25 ° C. and HRT was 2d. In Run 1-1 to Run 1-3 of Comparative Example 1, the treatment flow of the organic waste water treatment apparatus 201 shown in FIG. 8 was used.

FIG. 12 shows a summary of the experimental results (1) and FIG. 13 shows the experimental results (1). In Comparative Example 1, as the water temperature of the UASB tank gradually decreases with Run 1-1 (UASB water temperature 20 ° C.), Run 1-2 (UASB water temperature 15 ° C.), and Run 1-3 (UASB water temperature 10 ° C.), the gas A significant decrease in the amount of generation was observed (60 days after the experiment: 192 L / d, 120 days after the experiment: 120 L / d, 180 days after the experiment: 60 L / d). This is because the methane fermentation treatment was affected by the water temperature, and as a result, the undecomposed SS content in the UASB tank increased and the rise of the sludge interface became significant (60 days after the experiment: 2.6 m, experiment) 120 days after the lapse: 3.3 m, 180 days after the experiment: 4.5 m).
On the other hand, in Example 1, from Run 1-2 (UASB water temperature 15 ° C.), raw water was supplied to a first sedimentation basin as a solid-liquid separator and subjected to solid-liquid separation, and concentrated sludge was supplied to an acid fermentation tank. The acid fermenter was subjected to an acid fermentation under conditions of a water temperature of 25 ° C. and HRT2d, and then mixed with the separated water of the solid-liquid separator and supplied to the UASB tank. As a result, even in the period when the temperature in the UASB tank was lowered to 10 to 15 ° C., the gas generation amount was not significantly reduced, and the methane fermentation treatment was performed well (60 days after the experiment progressed: 191 L / d, 120 days after the course of the experiment: 191 L / d, 180 days after the course of the experiment: 160 L / d). Furthermore, there was no increase in the undecomposed SS content in the UASB tank, and no increase in the sludge interface was observed (60 days after experiment: 2.7 m, 120 days after experiment: 2.7 m, after experiment) 180th day: 2.8 m).

[Example 2 / Comparative Example 2]
Table 3 in FIG. 11 shows the conditions of Example 2 and Comparative Example 2. In both Example 2 and Comparative Example 2, the amount of raw water is 2.82 m ³ / d, UASB tank HRT8h, UASB tank temperature 15 to 25 ° C. (Run 2-1: 25 ° C., Run 2-2: 20 ° C., Run 2-3: 15 The experiment was conducted under the condition of ° C. In Run 2-1 (UASB water temperature 25 ° C.) and Run 2-2 (UASB water temperature 20 ° C.) of Example 2, the processing flow of the organic waste water treatment apparatus 201 shown in FIG. 8 was used. In Run 2-3 (UASB water temperature 15 ° C.), the treatment flow of the organic waste water treatment apparatus 102 shown in FIG. 3 was used. The sludge in the UASB tank was discharged from the discharged sludge pipe located 1 m from the bottom of the UASB tank. The amount of concentrated sludge discharged from the UASB tank was 0.015 m ³ / d, and the concentrated sludge concentration was 40000 mg / L. The temperature of the acid fermenter was 25 ° C., and the HRT was 2d. In Run 2-1 to Run 2-3 of Comparative Example 2, the treatment flow of the organic waste water treatment apparatus 201 shown in FIG. 8 was used.

FIG. 12 shows the summary of experimental results (1) and FIG. 14 shows the experimental results (2). In Comparative Example 2, no decrease in gas generation was observed until Run 2-1 (UASB water temperature 25 ° C.) and Run 2-2 (UASB water temperature 20 ° C.). However, when Run 2-3 (UASB water temperature water temperature 15 ° C.) is reached, the gas generation rate decreases (60 days after the experiment: 211 L / d, 120 days after the experiment: 190 L / d, 180 days after the experiment: 130 L / d) was observed. This is because the methane fermentation treatment was affected by the water temperature. As a result, during this period, the undecomposed SS content in the UASB tank increased and the sludge interface increased (60 days after the experiment: 3.2 m). 120 days after the course of the experiment: 3.4, 180 days after the course of the experiment: 4.0 m).
On the other hand, in Example 2, when it became Run 2-3 (UASB water temperature 15 degreeC), 0.015 m < ³ > / d sludge was discharged | emitted from the position of 1.0 m from the UASB tank bottom part, and it supplied to the acid fermentation tank. The acid fermentation tank was subjected to an acid fermentation treatment under conditions of a water temperature of 25 ° C. and HRT2d, and then mixed with raw water and supplied to the UASB tank. As a result, even during the period when the temperature in the UASB tank was lowered to 15 ° C., no decrease in gas generation was observed, and the methane fermentation treatment was performed well (60 days after experiment: 230 L / d, experiment progress). 120 days after: 210 L / d, 180 days after the experiment: 198 L / d). Furthermore, there was no increase in the undecomposed SS content in the UASB tank, and no increase in the sludge interface was observed (60 days after the experiment: 3.1 m, 120 days after the experiment: 3.2 m, after the experiment) 180th day: 3.4 m).

  FIG. 15 shows a summary (2) of the experimental results. Hereinafter, FIG. 6 shows a case (Example 3) in which “FIG. 3: part of UASB tank sludge is subjected to acid fermentation treatment and mixed with inflow raw water and acid fermentation treated water and supplied to UASB tank” and FIG. "Fig. 5: Inflow raw water is solid-liquid separated, concentrated sludge is acid-fermented, solid-liquid separated water and acid-fermented water are mixed and then supplied to the UASB tank. A part of the sludge in the UASB tank is acid-fermented, A case (Example 4) in which solid-liquid separated water and acid fermentation treated water are mixed and then supplied to the UASB tank will be described.

[Example 3 / Comparative Example 3]
Since the temperature inside the UASB tank was 20 ° C., the treatment was performed with the treatment flow of the organic waste water treatment apparatus 201 shown in FIG. 8, but the allowable value of the sludge interface inside the UASB tank was exceeded (interface 4 m). 3, a part of the UASB tank sludge was subjected to an acid fermentation process, and the inflow raw water and the acid fermentation process water were mixed and then supplied to the UASB tank. That is, the second opening / closing device 52 shown in FIG. 5 is opened, and the transfer pump 63 for concentrated sludge (second concentrated sludge) in the UASB tank and the transfer pump 62 for acid fermentation treated water are turned on via the control device 50. An off-operation was performed. In Comparative Example 3, processing was performed with the processing flow of FIG.
On the 60th day after the start of the experiment, in Example 3, the sludge interface decreased from 4.0 m to 3.5 m and stabilized at a generated gas amount of 198 L / day. On the other hand, in Comparative Example 3, the sludge interface increased from 4.0 m to 4.5 m, the sludge flowed into the UASB treated water, and the treated water SS concentration was a high numerical value of 1000 mg / L or more. At the same time, scum accumulated in the GSS section and the generated gas piping was blocked, making it impossible to recover the gas from the GSS, and the generated gas was discharged out of the system together with the UASB treated water.

[Example 4 / Comparative Example 4]
Since the temperature inside the UASB tank was 13 ° C., the inflow raw water was solid-liquid separated, the concentrated sludge (first concentrated sludge) was acid-fermented, and the solid-liquid separated water and the acid fermentation treated water were mixed and supplied to the UASB tank. (Processing flow of the organic waste water treatment apparatus 101 shown in FIG. 1: That is, the third switch 53 shown in FIG. 5 is opened, the fourth switch 54 is closed, the first switch 51 is opened, The second opening / closing device 52 is closed, the transfer pump 61 and the transfer pump 62 are on / off, and the transfer pump 63 is off). Since the allowable value of the sludge interface in the UASB tank exceeded 3.8 m, in Example 4, a part of the sludge concentrated sludge in the UASB tank (second concentrated sludge) was subjected to acid fermentation treatment, solid-liquid separation water and acid fermentation treatment After mixing with water, it was supplied to the UASB tank (that is, the second opening / closing device 52 was opened and the transfer pump 63 was turned on / off). In Comparative Example 4, processing was performed with the processing flow in FIG.
On the 30th day after the start of the experiment, in Example 4, the sludge interface decreased from 3.8 m to 3.3 m and stabilized at a generated gas amount of 157 L / day. On the other hand, in Comparative Example 4, the sludge interface increased from 3.8 m to 4.5 m, the sludge flowed into the UASB treated water, and the treated water SS concentration was a high value of 3000 mg / L or more. At the same time, scum accumulated in the GSS section and the generated gas piping was blocked, making it impossible to recover the gas from the GSS, and the generated gas was discharged out of the system together with the UASB treated water.

1 Low-concentration organic drainage, sewage 2 Solid-liquid separation water 3 First concentrated sludge
4, 4 'acid fermentation treated water
5, 5 'mixing tank outlet water
6 Methane fermentation treated water, UASB treated water
7 Second concentrated sludge 8 Methane recovery tank treated water
10 Solid-liquid separator
20 Acid fermenter
30 mixing tank, distribution tank 40 methane fermentation treatment tank, UASB tank 41 GSS (gas-solid-liquid separation unit)
42 Sludge bed
50 control device 51 first switchgear, valve 52 second switchgear, valve 53 third switchgear, valve 54 fourth switchgear, valve 61 transfer device (transfer pump for first concentrated sludge 3, transfer Previous: Acid fermenter 20)
62 Transfer device (transfer pump for acid fermentation treated water 4 (4 ′), transfer destination: mixing tank 30)
63 Transfer device (transfer pump for second concentrated sludge 7, transfer destination: acid fermentation tank 20)
70 Dissolved methane recovery tanks 101, 101 ′, 102, 103 Organic wastewater treatment apparatus 201 Conventional methane fermentation treatment apparatus g1 Methane gas g2 Air g3 Exhaust gas g4 Mixed gas h1 Effective water depth in UASB tank (h1 = h2 + h3 + h4)
h2 Pipe position for sending the concentrated sludge from the UASB tank to the acid fermentation tank (usually 1 m for an effective water depth of 5 m)
h2 + h3 Limit sludge interface height in UASB tank (when h3 = 2.5-3m, effective water depth 5m)
h4 Distance from the upper water surface of the UASB tank to the critical sludge interface (actual measurement when measured from the upper water surface of the UASB tank using a sludge interface meter)

Claims (6)

A solid-liquid separation device for solid-liquid separation of low-concentration organic wastewater having a CODcr value of 1000 mg / L or less, and separating it into solid-liquid separation water and first concentrated sludge;
An acid fermentation tank that is subjected to an acid fermentation treatment of the first concentrated sludge and maintained at a predetermined temperature;
A mixing tank for mixing the solid-liquid separated water and the acid fermentation treated water treated in the acid fermentation tank and separating the fermentation gas contained in the mixed water;
A methane fermentation treatment tank for methane fermentation treatment of the mixing tank outlet water from which the fermentation gas has been separated;
Organic wastewater treatment equipment. An acid fermentation tank maintained at a predetermined temperature for acid fermentation treatment of the second concentrated sludge discharged from the methane fermentation treatment tank;
A mixing tank for mixing a low-concentration organic waste water having a CODcr value of 1000 mg / L or less and acid-fermented water treated in the acid fermentation tank, and separating the fermentation gas contained in the mixed water;
A methane fermentation treatment tank that performs methane fermentation treatment of the mixing tank outlet water from which the fermentation gas has been separated;
Organic wastewater treatment equipment. A separation step in which a low-concentration organic wastewater having a CODcr value of 1000 mg / L or less is subjected to solid-liquid separation, and separated into solid-liquid separation water and first concentrated sludge;
An acid fermentation process in which the first concentrated sludge is subjected to an acid fermentation treatment at a predetermined temperature;
A mixing step of mixing the solid-liquid separated water and the acid fermentation treated water treated in the acid fermentation step, and separating the fermentation gas contained in the mixed water;
A methane fermentation treatment step of subjecting the mixing tank outlet water from which the fermentation gas has been separated to methane fermentation treatment;
Organic wastewater treatment method. An acid fermentation step of subjecting the second concentrated sludge discharged from the methane fermentation treatment step to an acid fermentation treatment at a predetermined temperature;
A mixing step of mixing a low-concentration organic waste water having a CODcr value of 1000 mg / L or less and acid-fermented water treated in the acid fermentation step, and separating the fermentation gas contained in the mixed water;
The methane fermentation treatment step of subjecting the mixing tank outlet water from which the fermentation gas has been separated to methane fermentation treatment;
Organic wastewater treatment method. A first opening / closing device that opens and closes the flow path to a flow path for transferring the first concentrated sludge separated by the solid-liquid separator to the acid fermentation tank;
A second opening / closing device for opening and closing the flow path in a flow path for transferring the second concentrated sludge discharged from the methane fermentation treatment tank to the acid fermentation tank;
A temperature measuring device for measuring the temperature in the methane fermentation tank;
A height measuring device for measuring the height of the sludge interface in the methane fermentation tank;
Opening and closing the first switchgear and the second switchgear based on the measured values of the temperature measuring device and the height measuring device;
The organic waste water treatment apparatus according to claim 1. An acid fermentation step of subjecting the second concentrated sludge discharged from the methane fermentation treatment step to an acid fermentation treatment at a predetermined temperature;
A step of transferring the first concentrated sludge or the second concentrated sludge to the acid fermentation step based on the treatment temperature in the methane fermentation treatment step and the height of the sludge interface in the methane fermentation treatment step. Prepare;
The organic waste water treatment method according to claim 3.

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