JP5873736B2 - Organic wastewater treatment method and treatment apparatus - Google Patents

Description

  The present invention relates to a treatment method and a treatment apparatus for low-concentration organic wastewater such as domestic wastewater and sewage.

  Examples of organic wastewater treatment methods include aerobic biological treatment and anaerobic biological treatment. Among the anaerobic biological treatments, the methane fermentation treatment is a biological treatment method that decomposes organic substances into methane gas, carbon dioxide gas, etc. by utilizing the metabolic reaction of anaerobic microorganisms that grow in an anaerobic environment without oxygen.

  The methane fermentation treatment has less sludge generation than the aerobic biological treatment, and does not require an electricity bill such as a blower (aeration), so it does not require running costs. In addition, since there is a merit that the generated methane gas can be used effectively, it has recently become widespread in fields such as sewage treatment, human waste treatment, and industrial wastewater treatment.

As types of methane fermentation treatment, for example, UASB (abbreviation of Upflow Anaerobic Sludge Blanket) method, methane fermentation treatment method such as fixed bed method, fluidized bed method and the like are known. Above all, the UASB method can maintain a high concentration of granular sludge with excellent sedimentation in the tank by utilizing the self-granulating function of anaerobic microorganisms, such as a CODcr load of 10 to ³⁰ kg / m ³ / d. It is a method that is widely used in Japan and overseas as a method for treating organic wastewater.

Compared to aerobic biological treatment, methane fermentation treatment not only requires aeration, but has low operating power costs, and has the advantage that the generated methane gas can be used as fuel for various power generation facilities. . On the other hand, only the methane fermentation treatment has a demerit that it cannot be purified to water quality that can be discharged directly into rivers because organic matter remains.
For this reason, it is proposed that after the methane fermentation treatment, an aerobic biological treatment such as an activated sludge method is performed to purify the water quality so as to satisfy the discharge standard, and then discharge to the river.

  As a treatment combining methane fermentation treatment and aerobic biological treatment, for example, Patent Document 1 discloses that wastewater discharged from a factory or the like is decomposed into methane gas in an anaerobic treatment step using anaerobic microorganisms. After reusing as fuel, inorganic substances such as phosphorus and nitrogen are removed in the aerobic biological treatment process using aerobic microorganisms, and chemical substances that adversely affect the environment are removed and released. A method is disclosed.

  Patent Document 2 discloses an organic wastewater treatment method in which treated water is subjected to methane fermentation treatment, and the digested liquid after treatment is subjected to an aerobic biological treatment by an activated sludge method, wherein the organic matter concentration of the treated water is a set concentration. If it is above, the methane fermentation process is performed, and when the said setting density | concentration is not reached, the aerobic biological process with the said digestive liquid is disclosed, The organic waste water treatment method characterized by the above-mentioned is disclosed.

  In Patent Document 3, in the wastewater treatment method in which an acid generation process, a methane fermentation process, and an aerobic biological treatment process are sequentially performed on wastewater, the wastewater supplied to the acid generation process is terminated with the methane fermentation process. And the wastewater processing method characterized by preheating by carrying out heat exchange with the treated water sent to the said aerobic biological treatment process is disclosed.

  By combining methane fermentation treatment and aerobic biological treatment in this way, it is possible not only to purify organic wastewater to a quality that meets discharge standards, but also to recover methane that can be used as fuel. This has advantages in both environmental and economic benefits. However, in the post-process aerobic biological treatment method, microorganisms oxidize and decompose some of the organic matter taken in, and the remaining organic matter is converted into sludge and discharged as surplus sludge. The problem was that sludge was generated in large quantities.

  Therefore, conventionally, as a treatment method for reducing the volume of such excess sludge, for example, excess sludge is extracted from an aeration tank or a sedimentation tank, and this extracted sludge is modified by ozone treatment, heat treatment, acid or alkali treatment, etc. There has been proposed a method in which a biodegradability is improved by treatment, and the modified sludge is returned to an aeration tank for biodegradation (for example, Patent Document 4).

JP 2003-71486 A Japanese Patent Laid-Open No. 2004-25051 JP 2008-173614 A Japanese Unexamined Patent Publication No. 7-116687

  The present invention relates to a method for treating organic wastewater as water to be treated first by methane fermentation treatment, followed by aerobic biological treatment to sufficiently purify the treated water. It is intended to provide a new organic wastewater treatment method and treatment apparatus that can reduce the volume of sludge and further increase the energy recovery rate.

The present invention, as shown in FIG. 1, methane fermentation treatment of water to be treated using anaerobic organisms, a generated gas containing methane gas, methane fermentation treated water, and methane fermentation treated sludge to obtain methane fermentation treated sludge; An aerobic biological treatment step for obtaining an aerobic biologically treated water and an aerobic biologically treated sludge by biologically oxidizing and decomposing the methane fermentation treated water using an aerobic organism, and a part of the aerobic biologically treated sludge or and all acid fermentation process to acid fermentation sludge acid fermentation process to obtain the process, the acid fermentation sludge, after fermentation gas is separated in the mixing degassing vessel, the inlet side of the methane fermentation step, the methane And a process for supplying organic effluent in order to suppress generation of scum in the fermentation process .

According to the organic wastewater treatment method proposed by the present invention, an aerobic biological treatment sludge generated from aerobic biological treatment, that is, an organic acid that is easily subjected to methane fermentation by supplying a hardly dewaterable excess sludge to an acid fermentation treatment step. Since it can return to a methane fermentation treatment process after converting into etc., the volume reduction of the sludge finally discharged | emitted out of the system can be aimed at. In addition, since the hardly dewaterable surplus sludge is then returned to the methane fermentation step, methane as an energy source can be recovered from the surplus sludge, and the energy recovery rate can be further increased.
Moreover, compared with the conventional treatment method mentioned above, ie, the treatment method which first treats water to be treated with acid fermentation, then performs methane fermentation treatment and aerobic biological treatment, in the present invention, the treatment to be treated in the acid fermentation treatment step. Since the amount is small, the amount of heating energy for heating the water to be treated is remarkably small, and the energy consumption and treatment cost of the whole treatment process can be suppressed.

In the present invention, the acid fermentation treated sludge generated in the acid fermentation process is not directly returned to the methane fermentation treatment process, but passed through a gas separation tank for separating the fermentation gas in the acid fermentation treated sludge, and then the acid fermentation It is also proposed to return the treated sludge to the methane fermentation process.
Fermentation gas is contained in the acid fermentation treatment sludge. If this acid fermentation treatment sludge is returned to the methane fermentation treatment step as it is, sludge thorn below the reaction tank will rise in the reaction tank due to the fermentation gas, and the upper layer Scum will be generated in the part. Therefore, the generation of scum can be suppressed by returning to the methane fermentation treatment step after passing through the gas separation tank for separating the fermentation gas in the acid fermentation treatment sludge.

  By the way, in Japan, when the temperature of winter sewage falls to less than 18 ° C., if such low temperature sewage is treated with methane fermentation, the activity of anaerobic bacteria in the tank will decrease, and suspended matter will remain in the tank. (Suspended Solids, hereinafter referred to as SS) accumulates, methane fermentation does not proceed, and the sludge interface in the fermenter rises and eventually overflows. At this time, in order to heat the sewage as the water to be treated, a large amount of energy is required due to a large amount of water flow, which is not realistic.

Therefore, in the present invention, for example, when the water temperature of the water to be treated is 13 ° C. or higher and lower than 18 ° C. (note that the water temperature of the water to be treated is substantially the same as the water temperature in the methane fermentation tank), It is proposed to supply a part or all of the treated sludge to the entrance side of the acid fermentation treatment process.
In this way, if a part or all of the methane fermentation treatment sludge is extracted from the methane fermentation tank and supplied to the acid fermentation treatment step, the rise of the sludge interface in the fermentation tank can be suppressed, and the acid Since the methane fermentation treated sludge can be converted into an organic acid that can be easily methane fermented in the fermentation treatment process and returned to the methane fermentation treatment process, the methane fermentation treatment can be performed even if the water temperature is low and the activity of the anaerobic bacteria is reduced. Can be promoted.

In addition, the present invention provides, for example, as an appropriate treatment method when the water temperature of the water to be treated is less than 13 ° C., the water to be treated is subjected to solid-liquid separation to obtain separated water and separated sludge, and the separated sludge or the separated sludge is concentrated. It is proposed that the acid-separated sludge is acid-fermented with part of the aerobic biologically-treated sludge to obtain acid-fermented sludge, and the acid-fermented sludge is supplied to the inlet side of the methane fermentation process with the separated water. To do.
When the water temperature of to-be-processed water is less than 13 degreeC, the activity of anaerobic bacteria will fall further. Therefore, the water to be treated is firstly solid-liquid separated, and the separated sludge or the concentrated separated sludge obtained by concentrating the separated sludge is supplied to the acid fermentation treatment step to convert it into an organic acid or the like that is easily methane-fermented, and then the methane fermentation treatment. By supplying to the process, the methane fermentation treatment can be promoted even if the water temperature is lower and the activity of the anaerobic bacteria is further reduced.

It is the figure which showed the apparatus and process of the processing method of the organic waste_water | drain which concerns on an example of this invention. It is the figure which showed the apparatus and process of the processing method A of the organic waste_water | drain which concerns on an example of embodiment of this invention. It is the figure which showed the apparatus and process of the processing method B of the organic waste_water | drain which concerns on an example of embodiment of this invention. It is the figure which showed the apparatus and process of the processing method C of the organic waste_water | drain which concerns on an example of embodiment of this invention. It is the figure which showed an example of the UASB apparatus which can implement an upflow anaerobic sludge filter bed method (UASB) as an example of a methane fermentation processing apparatus. It is the figure which showed the other example of the UASB apparatus. It is the figure which showed the further another example of the UASB apparatus. It is the top view which looked at the upper part of the methane fermentation tank in the UASB apparatus shown in FIG. 7 from upper direction. It is the figure which showed the process of the evaluation reference | standard processing method performed in order to evaluate an Example and a comparative example, ie, the normal sewage processing method currently performed.

<This processing method A>
FIG. 2 is a diagram illustrating an example of an apparatus and a process of an organic wastewater treatment method A (referred to as “the present treatment method A”) according to an example of the present embodiment.

  This treatment method A is a method of mixing acid fermentation treated sludge supplied from an acid fermentation treatment step and water to be treated (raw water), and removing the fermentation gas in the acid fermentation treated sludge to obtain degassed mixed water. Degassing step, methane fermentation treatment of degassed mixed water, methane fermentation treatment step to obtain generated gas containing methane gas, methane fermentation treatment water and methane fermentation treatment sludge, and aerobic biological treatment of methane fermentation treatment water, An aerobic biological treatment process for obtaining aerobic biological treatment water and an aerobic biological treatment sludge; and an excess sludge concentration process for concentrating a part of the aerobic biological treatment sludge (excess sludge) to obtain a concentrated surplus sludge. Acid fermentation treatment sludge obtained by acid fermentation treatment of aerobic biological treatment sludge or concentrated surplus sludge, and acid fermentation treatment step of supplying the acid fermentation treatment sludge to the mixed degassing step. It is a processing method.

As an apparatus for carrying out this processing method A, for example, a mixed degassing tank 1, a methane fermentation treatment apparatus 2, an aerobic biological treatment apparatus 3 and an acid fermentation treatment apparatus 4 are provided and treated water (raw water). To be treated is connected to the inlet side of the mixed degassing tank 1, and the methane fermentation treatment apparatus 2 is connected to the outlet side of the mixed degassing tank 1 via the mixed water supply pipe 6. A generated gas discharge pipe 7, a methane fermentation treated water supply pipe 8 and a methane fermentation treated sludge discharge pipe 9 are connected to the outlet side of the fermentation treatment tank 2, and the generated gas discharge pipe 7 is connected to the generated gas processing apparatus 10, The methane fermentation treated water supply pipe 8 is connected to the inlet side of the aerobic biological treatment apparatus 3, the methane fermentation treated sludge discharge pipe 9 is connected to the dehydrator 11, and the aerobic biological treatment apparatus 3 is connected to the outlet side. The aerobic biological treatment liquid discharge pipe 12 is connected The aerobic biological treatment liquid discharge pipe 12 is connected to the inlet side of the solid-liquid separator 13, and an aerobic biological treatment water discharge pipe 14 and an aerobic biological treatment sludge supply pipe 15 are connected to the outlet side of the solid-liquid separator 13. The aerobic biological treatment sludge supply pipe 15 is branched in the middle, and one is connected to the inlet side of the aerobic biological treatment apparatus 3 and the other is connected to the concentration apparatus 16. An acid fermentation treatment sludge supply pipe 18 is connected to the inlet side of the acid fermentation treatment apparatus 4, and an acid fermentation treatment sludge supply pipe 18 is connected to the outlet side of the acid fermentation treatment apparatus 4. An apparatus having a configuration connected to the side can be mentioned.
However, the concentrator 16 may be installed as necessary and is not always necessary.

  Hereinafter, each process and the equipment for implementing it will be described in detail.

(Raw water)
As the water to be treated (raw water), low-concentration organic wastewater, specifically, organic wastewater having a CODcr value of 1000 mg / L or less, particularly 300 mg / L or more or 600 mg / L or less is suitable for this treatment method.
Incidentally, sewage is generally low-concentration organic wastewater with a CODcr concentration of 400 to 1000 mg / L.

Moreover, although this processing method A has the characteristics which can be implemented effectively even with a relatively low water temperature, when the water temperature in the methane fermentation tank is 18 ° C. or higher, particularly 20 to 25 ° C. or higher. It is particularly preferred to carry out.
From the same viewpoint, the water to be treated (raw water) is particularly preferably 18 ° C. or higher, particularly 20 to 25 ° C. or higher.

(Mixed degassing process and equipment)
In the mixed degassing step, the water to be treated (raw water) supplied to the mixed degassing tank 1 through the treated water supply pipe 5 and the mixed degassing tank 1 from the acid fermentation treatment process through the acid fermentation treated sludge supply pipe 18. The acid fermentation treated sludge that has been supplied is mixed in the mixed degassing tank 1, the fermentation gas in the acid fermentation treated sludge is withdrawn, and the resulting degassed mixed water is subjected to methane fermentation treatment through the mixed water supply pipe 6. Supply to device 2.

The mixed degassing tank 1 preferably includes a gas separation means for separating the fermentation gas. Fermentation gas is mainly CO ₂ gas and is a gas partially containing H ₂ gas. When the fermentation gas flows into the methane fermentation treatment apparatus 2, the sludge floats up, so that the sludge rises before the sludge and the anaerobic organisms are in sufficient contact with each other. Occurrence is encouraged. Therefore, the scum generation in the methane fermentation treatment apparatus 2 can be suppressed by separating and removing the fermentation gas in the acid fermentation treatment sludge in advance before the methane fermentation treatment step.

  Here, as a gas separation means for separating the fermentation gas, for example, the mixed water is temporarily retained in a mixing tank for mixing the water to be treated (raw water) and the acid fermentation treated sludge, and is brought into contact with the atmosphere. In addition, a configuration in which the fermentation gas can be separated and removed from the mixed water can be exemplified. Further, the separation of the fermentation gas contained may be promoted by diverting the mixed water, flowing naturally, overflowing, or the like. Moreover, you may make it provide a stirrer inside a mixing tank.

(Methane fermentation process and equipment)
In the methane fermentation treatment process, the degassed mixed water supplied from the mixed degassing tank 1 is subjected to methane fermentation treatment in the methane fermentation treatment device 2 to obtain generated gas containing methane gas, methane fermentation treated water, and methane fermentation treated sludge, While supplying the generated gas to the generated gas treatment device 10 through the generated gas discharge pipe 7, the methane fermentation treated water is supplied to the aerobic biological treatment device 3 through the methane fermentation treated water supply pipe 8, and the methane fermentation treated sludge is supplied. Is supplied to the dehydrator 11 through the methane fermentation treatment sludge discharge pipe 9.

  Here, the methane fermentation treatment is an anaerobic biological treatment performed in an ORP range of −400 mV or less, and an organic substance is decomposed into methane gas and carbon dioxide by anaerobic microorganisms, and the generated methane gas can be effectively used as energy. It is processing to do.

  As the methane fermentation treatment method of the present treatment method A, for example, a known method such as an upward flow anaerobic sludge bed method (UASB), a fixed bed method, a fluidized bed method can be appropriately employed. Among them, it is preferable to employ the upward flow anaerobic sludge filter bed method (UASB).

The upflow anaerobic sludge filtration method (UASB) uses agglomeration action of anaerobic microorganisms to granulate highly active cells (granular sludge with a diameter of 2 to 3 mm, filamentous acetic acid assimilating methane) It is a method that retains a large amount in the reaction tank as a dense floc (mainly produced bacteria), and injects wastewater (treated water) from the bottom of the reaction tank to decompose organic substances in the wastewater in an anaerobic state. is there.
The upflow anaerobic sludge filter bed method (UASB) uses the self-granulating function of anaerobic microorganisms to maintain highly settled granular sludge in the tank at a high concentration, thus increasing the CODcr load. Can do. Moreover, compared to ordinary anaerobic treatment, it can be applied to wastewater with a relatively low concentration, and high-speed treatment is possible and aeration is not required. Can be generated. On the other hand, in the case of low-concentration wastewater, it is necessary to supply a large amount of wastewater into the tank in order to increase the CODcr load, and the sludge bed in the methane fermentation tank flows out of the system by this wastewater flow. May end up. Therefore, in order to maintain the sludge bed in the methane fermentation tank at a high concentration, it is preferable to limit the amount of water flow to the methane fermentation tank. In order to maintain the granular sludge in the UASB tank, the water flow rate is preferably 0.5 to 2.0 m / h, more preferably 0.75 to 1.5 m / h. .
Therefore, when the UASB method is applied to low-concentration wastewater having a CODcr of 1000 mg / L or less, it is necessary to reduce the water flow rate, so the CODcr load is reduced to 1 to 2 kg / m ³ / d.

As a preferable example of the methane fermentation treatment apparatus 2, a methane fermentation tank 30 (also referred to as “UASB apparatus 30”) capable of performing the upward flow anaerobic sludge filter bed method (UASB) as shown in FIG. 5 is given. be able to.
The methane fermentation tank 30 includes a sludge bed 32, a gas-solid-liquid separator (GSS) 33, and an overflow weir 34 that separates methane fermentation treated water, and a cover 35 that covers the top of the methane fermentation tank 30. Furthermore, a mixed water supply pipe 6 for supplying degassed mixed water from the mixed degas tank 1 is connected to the bottom of the methane fermentation tank 30, and a methane fermentation treatment sludge discharge pipe 9 for transferring sludge is provided in the methane fermentation tank 30. A methane fermentation treated water supply pipe 8 connected to the lower portion and supplying methane fermentation treated water flowing into the overflow weir 34 to the aerobic biological treatment device 3 is connected to the overflow weir 34 and the generated gas is treated with the generated gas treatment device. The generated gas discharge pipe 7 to be supplied to 10 is connected to a gas-solid-liquid separator (GSS) 33.

  In the methane fermentation tank 30, the degassed mixed water from the mixed degassing tank 1 flows from the lower part of the methane fermentation tank 30 and is uniformly diffused into the sludge bed 32, that is, the granule layer precipitated in the lower part, Organic substances contained in the water to be treated, soluble organic substances produced by acid fermentation, and organic acids such as acetic acid / propionic acid are decomposed into methane gas and carbon dioxide gas by anaerobic bacteria in the methane fermentation tank 30. The generated gas and granule float together with the treated water, and are separated into the generated gas, methane fermentation treated sludge (granule), methane fermented treated water, and the like by the gas-solid-liquid separator (GSS) 33. The generated gas is supplied to the generated gas processing apparatus 10 through the generated gas discharge pipe 7 and used as an energy source. The methane fermentation treated water is supplied to the aerobic biological treatment device 3 through the methane fermentation treated water supply pipe 8, and the methane fermentation treated sludge is supplied to the dehydrator 11 through the methane fermentation treated sludge discharge pipe 9 to reduce the volume. Are discharged outside the system.

  In the present processing method A, as described above, since the fermentation gas in the acid fermentation treatment sludge is separated and removed in advance in the mixed degassing tank 1, generation of scum (floating waste) in the methane fermentation tank 30 is prevented. Can be suppressed.

When UASB treatment is performed on low-concentration organic wastewater such as sewage, the water flow rate is limited in order to secure a sludge bed (sludge zone), so the CODcr volume load is as low as 1 kg / m ³ / d. It becomes a load. On the other hand, in UASB treatment of high-concentration organic wastewater such as food industry wastewater, the CODcr volumetric load is as high as 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, the density of anaerobic bacteria is lower than the high-concentration organic wastewater, and the particle size of the granular sludge in the sludge bed is 0. .1 to 0.5mm and small.
Thus, when low concentration organic wastewater is treated with UASB, the difference between the sedimentation rate of granular sludge and the sedimentation rate of inflow SS is the conventional UASB granule sludge applied to high concentration organic wastewater. Therefore, the amount of scum generated in the methane fermentation tank 30 may increase depending on the concentration of SS flowing in and the nature of the wastewater, and it may be difficult to maintain the sludge in the methane fermentation tank 30.
For these reasons, the SS concentration of water to be treated for methane fermentation, that is, degassed mixed water, is preferably 2000 mg / L or less, and particularly preferably 1000 mg / L or less. And it is preferable to make SS density | concentration of degassed mixed water below 2000 mg / L, especially below 1000 mg / L.

When the UASB method is applied to low-concentration wastewater as described above, the particle size of the granular sludge in the sludge bed is reduced to 0.1 to 0.5 mm, and the sedimentation speed is also reduced, so that it is easily affected by the inflow SS concentration. Become. Therefore, it is preferable to employ one of the following two improvement methods. However, it does not necessarily have to be adopted.
(1) A carrier such as sand, zeolite, activated carbon or the like having a particle size of 0.1 mm to 1.0 mm, preferably 0.2 mm to 0.7 mm with good sedimentation, is 1 to 10% with respect to the sludge bed capacity, preferably Add to sludge bed at 5-7% rate.
(2) Fe salt is preferably added to the water to be treated derived from organic waste water at a ratio of preferably 1 to 20 mg / L (asFe), and more preferably 5 to 10 mg / L (asFe).

In the method (1), it is possible to increase the proportion of anaerobic bacteria in the sludge bed by attaching anaerobic bacteria to the carrier.
In the method (2), a Ca salt or the like can be applied in addition to the Fe salt.

The water temperature in the methane fermentation tank 30 is preferably 18 ° C or higher, particularly 20 ° C or higher, and particularly preferably 20 to 30 ° C.
In addition, methanogenic bacteria that play a central role in the stage of methanogenesis prefer a pH in the vicinity of neutrality, so it is preferable to adjust to pH 6-8.

  Moreover, although methanogenic bacteria are classified into several types according to the activation temperature, it is preferable to use methanogens having an activation temperature of 20 to 30 ° C. in this processing method A.

FIG. 6 is a view showing a methane fermentation tank 40 as a modification of the methane fermentation treatment apparatus.
Compared with the methane fermentation tank 30 shown in FIG. 5, the methane fermentation tank 40 does not include a gas-solid-liquid separation part (GSS) 33 inside the methane fermentation tank 40, and is a roof material 41 made of a material that does not transmit gas. The upper part of the fermenter 30 is hermetically covered, and a gas exhaust port 42 is provided at a connection portion between the roof material 41 and the methane fermenter 30, and the generated gas exhaust pipe 7 can be connected to the gas exhaust port 42 to discharge the reaction gas. This is a device having the configuration described above.
However, the position where the gas exhaust port 42 is provided can be arbitrarily designed. For example, you may provide in either of the roofing materials 41, and you may provide in the upper part of the methane fermentation tank 30.

When the water to be treated (raw water) is sewage, it is generally low-concentration organic wastewater with a CODcr concentration of 400 to 1000 mg / L as described above, so that the CODcr volumetric load in the methane fermentation treatment tank (UASB tank) The amount of generated gas is small compared to methane fermentation treatment of high-concentration organic wastewater such as food production wastewater, which is as low as 1 kg / m ³ / d. Therefore, the generated gas can be recovered and discharged without providing the gas-solid-liquid separator (GSS) 33 as in the apparatus shown in FIG.

FIG. 7 is a view showing a methane fermentation tank 50 as a further modification of the methane fermentation treatment apparatus.
Compared with the methane fermenter 40 shown in FIG. 6, the methane fermenter 50 is the same height as the superfluid weir 34 inside the methane fermenter 50, and scum collects scum at the inner portion of the superfluid weir 34. This is an apparatus having a configuration in which a collection frame 51 is provided.

  As shown in FIG. 8, the scum collection frame 51 may be fixed over the opposing inner walls of the methane fermentation tank 50, and the scum collection frame 51 is provided with an elevating means 52, and is necessary. Accordingly, the scum collection frame 51 can be arranged at the same height as the super-flow weir 34 or arranged above the liquid level.

(Aerobic biological treatment process and equipment)
In the aerobic biological treatment process, the methane fermentation treated water supplied through the methane fermentation treated water supply pipe 8 is subjected to biological oxidative decomposition treatment using the aerobic organism in the aerobic biological treatment device 3. The obtained aerobic biological treatment water and aerobic biological treatment sludge mixed treatment liquid is supplied to the solid-liquid separation device 13 through the aerobic biological treatment liquid discharge pipe 12. Separated into treated water and aerobic biological treated sludge, the former aerobic biological treated water is discharged out of the system through the aerobic biological treated water discharge pipe 14, and the latter aerobic biological treated sludge is supplied to the aerobic biological treated sludge A part thereof is returned to the inlet side of the aerobic biological treatment apparatus 3 through the pipe 15, and the other (referred to as “excess sludge”) is supplied to the concentration apparatus 16 or the acid fermentation treatment apparatus 4.

The aerobic biological treatment is a method in which an organic substance, ammonia nitrogen, and the like are oxidatively decomposed by an aerobic microorganism in an environment where dissolved oxygen is sufficient.
Examples of the aerobic treatment method that can be adopted by this treatment method A include a method of biologically oxidizing and decomposing an organic substance in a state where a biological floc is suspended by aeration (represented by the activated sludge method), and a microorganism as a carrier. Any known method such as a method (represented by a biofilm method) in which a biofilm is formed by adhering to and growing in contact with wastewater and biologically oxidatively decomposed can be employed.
Among these, in the present treatment method A, the activated sludge method is preferable from the viewpoint of suitably treating low-concentration organic wastewater such as sewage. The activated sludge method is a treatment method using gelatinous flocs made of various aerobic microorganisms called organic sludge, organic substances and inorganic substances.

The preferred aerobic biological treatment apparatus 3 includes a treatment tank attached with an aeration apparatus for supplying a large amount of oxygen consumed by oxidative decomposition of organic matter by microorganisms, and a sludge settling tank for separating sludge and treated water. Can be mentioned.
For example, an initial sedimentation basin for removing suspended solids in the treated water, an aeration tank that mixes with activated sludge and aerates and decomposes organic matter by microbial metabolism, and a sludge sedimentation tank for separating sludge and treated water The aerobic biological treatment apparatus 3 provided with can be illustrated. However, any known aerobic biological treatment apparatus can be employed.

  Next, examples of the solid-liquid separation device 13 include a solid-liquid separation device such as a sedimentation basin, a centrifugal separator, and a membrane separation. 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 For example, a sedimentation basin is suitable. The solid-liquid separator 13 may be an initial settling basin used in conventional activated sludge treatment.

  Further, in the normal aerobic biological treatment apparatus 3, since the aerobic organisms are washed out together with the aerobic biological treatment sludge, in the present treatment method A, the aerobic biological treatment water is used in the solid-liquid separation device 13. The aerobic biological treatment sludge is preferably separated and returned to the inlet side of the aerobic biological treatment apparatus 3 as shown in FIG.

(Excess sludge concentration process)
A part of the aerobic biologically treated sludge separated by the solid-liquid separator 13 (excess sludge) is supplied to the concentrator 16 as necessary, and concentrated in the concentrator 16 to obtain concentrated surplus sludge, and the concentrated sludge supply pipe 17 is supplied to the acid fermentation treatment apparatus 4.

  In addition, the said excess sludge concentration process is not necessarily a required process. For example, when a microfiltration membrane (MF membrane) or ultrafiltration membrane (UF membrane) is used instead of a sedimentation basin as in the membrane separation activated sludge method (Membrane Bioreactor: MBR), the MLSS concentration in the aeration tank is Since it becomes a high density | concentration to 5000-10000 mg / L, the excess sludge concentration process is not necessarily required. Usually, since a sedimentation basin is often used, it is preferable to supply the acid fermentation treatment step after concentrating excess sludge.

(Acid fermentation process and equipment)
In the acid fermentation treatment apparatus 4, an aerobic biological treatment sludge (excess sludge) or concentrated excess sludge is subjected to an acid fermentation treatment to obtain an acid fermentation treatment sludge, and the acid fermentation treatment sludge is mixed and removed through an acid fermentation treatment sludge supply pipe 18. Supply to the gas tank 1.

  In the acid fermentation treatment, a part of the organic matter in the aerobic biological treatment sludge or the concentrated excess sludge can be reduced in molecular weight to an organic acid such as acetic acid or propionic acid.

  In the acid fermentation treatment, the microorganisms involved in acid production are facultative anaerobes and are preferably grown in the range of ORP of −200 to 50 mV.

  It is preferable that the acid fermentation treatment apparatus 4 includes a means capable of stirring the sludge. As the stirring means, a stirrer may be installed, or a gas such as air may be aerated.

The acid fermentation treatment apparatus 4 is preferably equipped with means for heating the inside of the acid fermentation tank. At this time, as a heat source for heating, the methane gas g1 recovered from the methane fermentation tank 30 can be converted into steam by a boiler and used.
Heating the object to be treated in the acid fermentation treatment step can reduce the energy required for heating as compared to, for example, directly heating the water to be treated in the methane fermentation treatment apparatus 2. In addition, in acid fermenters, some of the solids (SS content) contained in the concentrated sludge is converted into soluble organic substances (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 having a low water temperature.

The temperature in the acid fermentation treatment apparatus 4 is preferably 20 to 35 ° C., and more preferably in the range of 20 to 25 ° C. as judged from the sewage water temperature and the heat energy of the generated gas.
Thus, it is preferable that the aerobic biological treatment sludge or concentrated surplus sludge that has flowed into the acid fermentation treatment apparatus 4 is heated to 20 ° C. or more by an external heat source and subjected to acid fermentation treatment. Thus, in the acid fermentation treatment apparatus 4, the solid matter (SS content) contained in the organic waste water that cannot be decomposed by microorganisms as it is is subjected to the organic acid fermentation by the acid-producing bacteria to dissolve the organic matter (propionic acid). , Acetic acid, etc.).

The optimum HRT (Hydraulic Retention Time) of the acid fermentation treatment tank in the acid fermentation treatment is the concentration of soluble organic substances (Soluble CODcr: abbreviated as S-CODcr) and organic substances such as acetic acid, propionic acid, and lactic acid. It is preferable to determine the amount of acid produced.
That is, the ratio of solubilized solid organic matter is defined as the solubilization ratio of CODcr (S-CODcr / CODcr), and the ratio of organic acid contained in the soluble organic acid CODcr is defined as (asCODcr) / S-CODcr ratio. In the case of the definition, it is preferable that the HRT when the solubilization ratio of CODcr and the organic acid (asCODcr) / S-CODcr ratio show a constant value is the optimum HRT.

For example, in the case of the first sedimentation basin sludge, the acid fermenter temperature is 20 ° C., HRT is 2 to 3 days, the S-CODcr / CODcr ratio is 0.15 to 0.20 (−), and the organic acid (asCODcr) / S— The CODcr ratio becomes 0.3 to 0.4, and the temperature of the acid fermenter is 25 ° C. and the HRT is 1 to 2 days, the S-CODcr / CODcr ratio is 0.15 to 0.20 (−), VFA (asCODcr) / S-CODcr is 0.55 to 0.65.
On the other hand, in the case of UASB concentrated sludge, the acid fermenter temperature is 20 ° C. and the HRT is 2 to 3 days, and the S-CODcr / CODcr ratio is 0.10 to 0.20 (−), VFA (asCODcr) / S-CODcr. The ratio is 0.13 to 0.20, the temperature of the acid fermenter is 25 ° C., and the HRT is 1 to 2 days, and the S-CODcr / CODcr ratio is 0.10 to 0.20 (−), VFA (asCODcr) / S The -CODcr 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. ) / S-CODcr ratio is smaller for the concentrated sludge in the UASB tank.

  The concentrated sludge in the acid fermentation treatment apparatus 4 is preferably stirred continuously or intermittently. Since the MLSS concentration in the acid fermentation treatment apparatus 4 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, it is preferable to stir the acid fermentation tank intermittently. For example, it is preferable to perform intermittent stirring such as stirring for 5 to 15 minutes after stirring is stopped for 1 to 2 hours.

<This processing method B>
FIG. 3 is a diagram illustrating an apparatus and a process of an organic wastewater treatment method B (referred to as “the present treatment method B”) according to an example of the present embodiment.

  The apparatus for carrying out this treatment method B is the apparatus for carrying out this treatment method A shown in FIG. 2, branching off the methane fermentation treatment sludge discharge pipe 9 and connecting one of the branches to the dehydrator 11. The other branch pipe 20 is the same as the apparatus for carrying out the present processing method A shown in FIG. 2 except that the other branch pipe 20 is connected to the inlet side of the acid fermentation treatment apparatus 4.

  This treatment method B supplies a part or all of the methane fermentation treatment sludge generated in the methane fermentation treatment device 2 to the acid fermentation treatment device 4 through the branch pipe 20 in the above treatment method A, and the acid fermentation treatment device 4 In this method, except that a part or all of the methane fermentation treatment sludge and aerobic biological treatment sludge (excess sludge) or concentrated surplus sludge are mixed and the mixture is subjected to an acid fermentation treatment. Same as A.

When the temperature of sewage falls as in Japan in winter, when this treatment method A is carried out using low-temperature sewage as the treated water, the activity of anaerobic bacteria in the tank is reduced, and suspended substances (SS) are present in the tank. There is a possibility that the methane fermentation will not proceed and the sludge interface in the fermenter will rise and eventually overflow. At this time, in order to heat the sewage as the water to be treated, a large amount of energy is required due to a large amount of water flow, which is not realistic.
Therefore, as in this treatment method B, if a part or all of the methane fermentation treatment sludge is extracted from the methane fermentation tank and supplied to the acid fermentation treatment process, the rise in the sludge interface in the fermentation tank is suppressed. In addition, the methane fermentation treatment sludge can be converted into an acid that is easily fermented in methane fermentation in the acid fermentation treatment process, and returned to the methane fermentation treatment process again, so the water temperature is low and the activity of anaerobic bacteria is reduced. Can also promote the methane fermentation process.
Therefore, this treatment method B is particularly preferably performed when the water temperature of the water to be treated (raw water), preferably the water temperature in the methane fermentation tank is 13 ° C. or more and less than 18 ° C.

<This processing method C>
FIG. 4 is a diagram illustrating an apparatus and a process of an organic wastewater treatment method C (referred to as “the present treatment method C”) according to an example of the present embodiment.

  The apparatus for carrying out this treatment method C is the apparatus for carrying out this treatment method A shown in FIG. 2 and is provided with a solid-liquid separation device 21 on the upstream side of the mixed degassing tank 1 so that water to be treated ( Raw water) is connected to the inlet side of the solid-liquid separator 21, and the separated water supply pipe 22 connected to the outlet side of the solid-liquid separator 21 is connected to the mixed degassing tank 1. 2 except that the separation sludge supply pipe 23 connected to the outlet side of the solid-liquid separator 21 is connected to the inlet side of the acid fermentation treatment apparatus 4 while being connected to the inlet side. Similar to the apparatus for carrying out method A.

  In this treatment method C, water to be treated (raw water) is solid-liquid separated by the solid-liquid separation device 21, and the obtained separated water is supplied to the mixed degassing tank 1. While mixing with acid fermentation process sludge, the process which extracts the fermentation gas in acid fermentation process sludge is performed, and while supplying the obtained mixed water to the methane fermentation processing apparatus 2 through the mixed water supply pipe 6, solid-liquid separation apparatus The separated sludge obtained in 21 is supplied to the acid fermentation treatment apparatus 4 through the separated sludge supply pipe 23, and is subjected to an acid fermentation treatment together with the separated sludge and a part of the aerobic biological treatment sludge (excess sludge). The acid fermentation treatment sludge is the same as the treatment method A except that the acid fermentation treatment sludge is supplied to the mixed degassing tank 1.

  When the water temperature of to-be-processed water is less than 13 degreeC, the activity of anaerobic bacteria will fall further than the case mentioned above. Therefore, the water to be treated is firstly solid-liquid separated, and the separated sludge or the concentrated separated sludge obtained by concentrating the separated sludge is supplied to the acid fermentation treatment step to convert it into an acid that is easily methane-fermented, and then into the methane fermentation treatment step. By supplying, even if the water temperature is lower and the activity of the anaerobic bacteria is further lowered, the methane fermentation treatment can be promoted.

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. Moreover, the SS concentration of sewage is usually a low concentration of 200 mg / L. In this state (SS 200 mg / L), the gas generated by methane fermentation is converted into steam by a boiler and used as heating energy. It is difficult to raise the water temperature.
In that respect, SS is solid-liquid separated to obtain a concentrated sludge concentration (20,000 to 40,000 mg / L), and the amount of concentrated sludge concentrated about 100 to 200 times becomes a small volume. Therefore, an acid is generated using methane gas in the generated gas. It is possible to raise the temperature in the fermenter around 5 ° C.

<Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

  Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments described here.

  In Comparative Example 1 and Examples 1-4, the following low-concentration organic wastewater is used as raw water for each season (January to February, March to May, June to October, November to December). The treatment was performed while appropriately changing the treatment method, and the amount of the dehydrated cake obtained was compared.

(Raw water)
Table 1 shows properties of raw water treated in Examples and Comparative Examples, that is, low-concentration organic wastewater.

Example 1
In this example, in the organic wastewater treatment method A shown in FIG. 2, the treatment was performed without degassing the fermentation gas after the acid fermentation treatment, and the amount of dehydrated cake (dry weight) was measured every day. The amount of dehydrated cake per day was determined.
The processing period is the next period.
-Medium water temperature period: March to May and November to December (water temperature in the UABB tank is 13 ° C or higher and lower than 18 ° C)
・ High water temperature period: June to October (water temperature in the UABB tank is 18 ° C or higher and lower than 25 ° C)

  In addition, since the temperature of raw | natural water and the water temperature in a UABB tank were substantially the same temperature, only the water temperature in a UABB tank is described. This is the same in the examples and comparative examples described later.

Specifically, low-concentration organic waste water (raw water) and acid fermentation treatment sludge obtained by treatment with an acid fermentation treatment apparatus described later at a water flow rate of 0.5 m / h as shown in FIG. It supplied in the UASB tank (capacity | capacitance 900L), the CODcr load in this tank was 1.0 kg / m < ³ > / d, and the methane fermentation process was performed. In addition, the sludge which was accustomed for about one year by the UASB method was used for the seed sludge by using the middle temperature digested sludge of sewage as seed sludge.

Next, the methane fermentation treated water was subjected to biological oxidative decomposition treatment using activated sludge in an aerobic biological treatment apparatus. At this time, as the aerobic biological treatment apparatus 3, an aerobic biological treatment apparatus 3 having an initial sedimentation basin, an aeration tank, and a sludge sedimentation tank was used.
Then, the obtained aerobic biological treated water and aerobic biologically treated sludge mixed treatment liquid is supplied to a solid-liquid separation device, and separated into aerobic biologically treated water and aerobic biologically treated sludge. A part of the biologically treated sludge was returned to the inlet side of the aerobic biological treatment apparatus, while the remaining aerobic biological treatment sludge (excess sludge) was concentrated in a concentrator to obtain concentrated excess sludge.

Next, the concentrated surplus sludge obtained as described above is stirred in an acid fermentation treatment apparatus while the concentrated surplus sludge is heated to 25 ° C. and subjected to an acid fermentation treatment in the range of ORP of −200 to 50 mV. Fermentation-treated sludge was obtained, and the acid-fermented sludge was supplied to the mixed degassing tank.
At this time, as the acid fermentation treatment apparatus, an acid fermentation treatment tank (capacity 10 L), a means equipped with a means for stirring sludge, and a heating means are used, and the acid fermentation treatment tank is HRT 2 days. Stirring was carried out intermittently such that stirring was continued for 5 minutes after stopping stirring for 1 hour.

(Example 2)
In this embodiment, in the organic wastewater treatment method A shown in FIG. 2, the fermentation gas after acid fermentation treatment is degassed, the amount of dehydrated cake (dry weight) is measured daily, and the amount of dehydrated cake per day Asked.
The processing period is the next period.
-Medium water temperature period: March to May and November to December (water temperature in the UABB tank is 13 ° C or higher and lower than 18 ° C)
・ High water temperature period: June to October (water temperature in the UABB tank is 18 ° C or higher and lower than 25 ° C)

  Specifically, low-concentration organic wastewater (raw water) having a CODcr value of 315 to 520 mg / L is treated water. First, in the mixed degassing tank, the treated water and an acid fermentation treatment apparatus described later are used. In addition to mixing the acid-fermented sludge obtained in this way, the fermentation gas in the acid-fermented sludge was extracted to obtain degassed mixed water (SS concentration 500 to 15000 mg / L). Then, this degassed mixed water is supplied into the UASB tank (capacity 200 L) of the UASB apparatus as shown in FIG. 5 at a water flow rate of 0.5 m / h, and the subsequent steps are the same as in Example 2. Processed.

(Example 3)
This embodiment is an embodiment in which the fermentation gas after the acid fermentation treatment was degassed in the organic wastewater treatment method B shown in FIG.
The processing period is the next period.
・ Low water temperature period: January to February (water temperature in UABB tank is less than 13 ° C)
-Medium water temperature period: March to May and November to December (water temperature in the UABB tank is 13 ° C or higher and lower than 18 ° C)

In a present Example, in said Example 2, a part (5-30 mass%) of methane fermentation treatment sludge is supplied to an acid fermentation treatment apparatus, In an acid fermentation treatment apparatus, a part of said methane fermentation treatment sludge and the said The treatment was performed in the same manner as in Example 1 except that the concentrated excess sludge was mixed and the mixture was subjected to an acid fermentation treatment.
In addition, the mixing ratio of a part of methane fermentation treatment sludge and concentrated excess sludge was 1:10 to 1: 3 by mass ratio.

Example 4
In this example, the organic wastewater treatment method C shown in FIG. 4 is used to degas the fermentation gas after the acid fermentation treatment, measure the amount of dehydrated cake (dry weight) every day, and determine the amount of dehydrated cake per day. Asked.
The processing period is the next period.
・ Low water temperature period: January to February (water temperature in UABB tank is less than 13 ° C)

In this example, a solid-liquid separation device is arranged upstream of the mixed degassing tank in Example 2, and the water to be treated (raw water) is subjected to solid-liquid separation using the solid-liquid separation device. In the mixed degassing tank, the separation water and the acid fermentation treatment sludge are mixed and the fermentation gas in the acid fermentation treatment sludge is removed and the solid-liquid separation device obtains the mixture. The separation sludge thus obtained was supplied to an acid fermentation treatment apparatus, and the treatment was performed in the same manner as in Example 2 except that both the separation sludge and the concentrated excess sludge were subjected to an acid fermentation treatment.
In addition, the mixing ratio of separation sludge and concentrated excess sludge was 0.5: 1 to 2: 1 in mass ratio.

(Comparative Example 1)
Comparative Example 1 is an example in which there is no acid fermentation treatment step in the organic wastewater treatment method shown in FIG. 1, and the amount of dehydrated cake (dry weight) is measured every day to determine the amount of dehydrated cake per day. It was.
The processing period is the next period.
-Medium water temperature period: March to May and November to December (water temperature in the UABB tank is 13 ° C or higher and lower than 18 ° C)
・ High water temperature period: June to October (water temperature in the UABB tank is 18 ° C or higher and lower than 25 ° C)

Specifically, low-concentration organic wastewater (raw water) is supplied into a UASB tank (capacity 200 L) of a UASB apparatus as shown in FIG. 5 at a water flow rate of 0.5 m / h, and CODcr in the tank A methane fermentation treatment was performed at a load of 1 kg / m ³ / d to obtain generated gas containing methane gas, methane fermentation treated water, and methane fermentation treated sludge.

Next, the methane fermentation treated sludge obtained as described above was subjected to biological oxidative decomposition treatment using an aerobic organism in an aerobic biological treatment apparatus. At this time, as the aerobic biological treatment apparatus 3, an aerobic biological treatment apparatus 3 having an initial sedimentation basin, an aeration tank, and a sludge sedimentation tank was used.
Then, the obtained aerobic biological treated water and aerobic biologically treated sludge mixed treatment liquid is supplied to a solid-liquid separation device, and separated into aerobic biologically treated water and aerobic biologically treated sludge. A part of the biologically treated sludge was returned to the inlet side of the aerobic biological treatment apparatus, while the remaining aerobic biological treatment sludge (excess sludge) was concentrated in a concentrator to obtain concentrated excess sludge.

<Evaluation method>
The same low concentration organic wastewater (raw water) as in the above-mentioned examples and comparative examples is treated throughout the year by the treatment method shown in FIG. 9 (normal sewage activated sludge treatment not including methane fermentation treatment). The amount of dehydrated cake (dry weight) obtained by the treatment method was measured.
Then, the average amount of dehydrated cake (dry weight) per day obtained by this method was set as 100, and the evaluation was performed in comparison with the values of the Examples and Comparative Examples (Table 3).
Table 2 shows the use of the experimental apparatus shown in FIG.

  In Comparative Example 1, when the water temperature of the methane fermentation tank was 13 ° C. or more and less than 18 ° C., sludge accumulated in the tank because the activity of the anaerobic bacteria decreased. It was necessary to perform sludge treatment frequently. For this reason, the measurement of the sludge generation amount was 80. Since the activity of anaerobic bacteria increased at a water temperature of 18 ° C. or higher and lower than 25 ° C. (medium water temperature period) in the methane fermentation tank, the amount of sludge generated was 60.

On the other hand, in Example 1, since the degassing tank was not provided, scum was generated in the methane fermentation tank in any temperature condition, the sludge bed concentration in the UASB tank was not stable, and the amount of sludge generated was in the middle water temperature period 78 and 58 in the high water temperature period.
In Example 2, by providing a degassing tank, the amount of sludge generated during the medium water temperature period was 72, and the amount of sludge generated during the high water temperature period was 55. However, the sludge accumulated in the methane fermentation tank because the activity of the anaerobic bacteria decreased during the middle water temperature period of less than 18 ° C. Therefore, it was necessary to perform sludge treatment frequently. Thus, in the high water temperature period of water temperature 18 degreeC or more, since the sludge density | concentration of the sludge bed in a UASB tank was stabilized by providing a degassing tank, the process became stable. However, the amount of sludge generated during the middle water temperature period tended to increase compared to the high water temperature period.

In Example 3, the amount of sludge generated during the intermediate water temperature period was 58 by subjecting part of the sludge in the UASB tank to acid fermentation. It became low compared with the amount of sludge generation 72 in the middle water temperature period of Example 2. On the other hand, when the water temperature period was lower than 13 ° C., the activity of the anaerobic bacteria further decreased, so that sludge in the methane fermentation tank accumulated. For this reason, it was necessary to perform sludge treatment frequently. The amount of sludge generated during the low water temperature period was 80, which was higher than that during the middle water temperature period.
In Example 4, the processing method C (FIG. 4) was applied. As a result, the sludge generation amount in the low water temperature period was 65, and the sludge generation amount was lower than that in the low water temperature period of Example 3.

DESCRIPTION OF SYMBOLS 1 Mixed degassing tank 2 Methane fermentation treatment apparatus 3 Aerobic biological treatment apparatus 4 Acid fermentation treatment apparatus 5 To-be-treated water supply pipe 6 Mixed water supply pipe 7 Generated gas discharge pipe 8 Methane fermentation treated water supply pipe 9 Methane fermentation treatment sludge discharge Tube 10 Generated gas treatment device 11 Dehydration device 12 Aerobic biological treatment liquid discharge tube 13 Solid-liquid separation device 14 Aerobic biological treatment water discharge tube 15 Aerobic biological treatment sludge supply tube 16 Concentration device 17 Concentrated sludge supply tube 18 Acid fermentation treatment Sludge supply pipe 20 Branch pipe 21 Solid-liquid separator 22 Separation water supply pipe 23 Separation sludge supply pipe 30 Methane fermentation tank (UASB apparatus)
32 Sludge bed 33 Gas-solid separation part (GSS)
34 Overflow weir 35 Cover lid 40 Methane fermentation tank (UASB device)
41 Roofing material 42 Gas exhaust port 50 Methane fermentation tank (UASB device)
51 Scum collection frame 52 Lifting means

Claims (11)

Methane fermentation treatment of the water to be treated using anaerobic organisms to obtain generated gas containing methane gas, methane fermentation treatment water and methane fermentation treatment sludge, and the methane fermentation treatment water using aerobic organisms An aerobic biological treatment step to obtain an aerobic biological treatment water and an aerobic biological treatment sludge by biological oxidative decomposition treatment, and acid fermentation treatment sludge by subjecting a part or all of the aerobic biological treatment sludge to acid fermentation treatment In order to suppress the occurrence of scum in the methane fermentation treatment process, after separating the fermentation gas in a mixed degassing tank, the acid fermentation treatment process and obtaining the acid fermentation treatment sludge method of treating organic waste water comprising process and, to be supplied to.   The processing method of the organic waste_water | drain of Claim 1 provided with the spin-drying | dehydration process which obtains spin-dry | dehydrated cake by carrying out the spin-drying | dehydration process of the methane fermentation process sludge.   It implements when the water temperature in a methane fermenter becomes 18 degreeC or more, The processing method of the organic waste water of Claim 1 or 2 characterized by the above-mentioned.   The organic wastewater treatment method according to claim 1 or 2, wherein a part or all of the methane fermentation treatment sludge is supplied to an inlet side of the acid fermentation treatment step.   It implements when the water temperature in a methane fermenter is 13 degreeC or more and less than 18 degreeC, The processing method of the organic waste water of Claim 4 characterized by the above-mentioned.   The treated water (raw water) is subjected to solid-liquid separation to obtain separated water and separated sludge, and the separated sludge or the concentrated separated sludge obtained by concentrating the separated sludge is subjected to an acid fermentation treatment together with a part of the aerobic biologically treated sludge. The processing method of the organic waste_water | drain of Claim 1 or 2 which obtains fermentation treatment sludge and supplies this acid fermentation treatment sludge with the said separated water to the entrance side of a methane fermentation treatment process.   It implements when the water temperature in a methane fermenter is less than 13 degreeC, The processing method of the organic waste water of Claim 6 characterized by the above-mentioned. From an aerobic biological treatment tank, an aerobic biological treatment tank, and an aerobic biological treatment tank that biologically oxidatively decomposes methane fermentation treated water discharged from the methane fermentation water tank After the acid fermentation treatment tank for acid fermentation treatment of a part of the aerobic biological treatment sludge that has come out and the acid fermentation treatment sludge that has come out of the acid fermentation treatment tank are supplied to the mixed degassing tank to separate the fermentation gas, An organic wastewater treatment apparatus comprising: a supply means for supplying scum in the methane fermentation treatment tank to suppress generation of scum in the inlet side of the methane fermentation treatment tank .   The processing apparatus of the organic waste_water | drain of Claim 8 provided with the dehydration processing apparatus which spin-dry | dehydrates part or all of the methane fermentation process sludge which came out of the methane fermentation processing tank, and obtains a dewatering cake.   The organic wastewater treatment apparatus according to claim 8 or 9, wherein a part or all of the methane fermentation treatment sludge discharged from the methane fermentation treatment tank is supplied to the entrance side of the acid fermentation treatment tank.   A solid-liquid separation device that separates treated water into solid and liquid to obtain separated water and separated sludge is placed on the inlet side of the upward flow sludge bed type methane fermentation water tank, and the separated sludge or the separated sludge is concentrated and separated. The sludge is supplied to the acid fermentation treatment tank together with a part of the aerobic biological treatment sludge, and the acid fermentation treatment sludge discharged from the acid fermentation treatment tank is supplied to the inlet side of the methane fermentation treatment tank together with the separated water. The processing apparatus of the organic waste_water | drain in any one of Claims 8-10.

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