JP2023149241A - Wastewater treatment device, and wastewater treatment method - Google Patents

Abstract

To provide a wastewater treatment device and a wastewater treatment method capable of decreasing the amount of alkali to be used for pH adjustment and preventing the wastewater treatment efficiency and the recovery rate of useful biogas generated in a treatment process from declining, in a wastewater treatment using an anaerobic treatment.SOLUTION: There are provided a wastewater treatment device that comprises a decarboxylation tank into which raw water is introduced, an acid generation tank, and a reactor carrying out an anaerobic treatment and returns treated water treated in the reactor to the decarboxylation tank, and a wastewater treatment method using the device. According to the present invention, the decarboxylation tank and the acid generation tank are separately provided, and the decarboxylation tank is disposed upstream relative to the acid generation tank, and thereby decline of the treatment efficiency resulting from over-aeration in the acid generation tank and decline of the recovery rate of biogas generated in the acid generation tank can be prevented. The amount of alkali to be used for adjusting pH of the treated water can be decreased by returning water treated in the reactor to the decarboxylation tank to allow the same to function as a pH adjusting agent.SELECTED DRAWING: Figure 1

Description

The present invention relates to a wastewater treatment device and a wastewater treatment method. In particular, the present invention relates to a wastewater treatment device and a wastewater treatment method that involve anaerobic treatment.

Biological treatment using various microorganisms is generally known as a method for treating wastewater containing organic matter. There are two main types of biological treatment: aerobic treatment and anaerobic treatment. Among these, anaerobic treatment can be broadly divided into two types: methane fermentation treatment and denitrification treatment. Among these, methane fermentation treatment has many advantages, such as almost no surplus sludge being generated.

Methane fermentation treatment is an anaerobic treatment that decomposes organic matter in wastewater into methane and carbon dioxide through the action of anaerobic microorganisms in an anaerobic environment. Widely used.

Methane fermentation treatment includes an acid production process in which acid-producing bacteria are brought into contact with organic matter in wastewater to produce acid, and a methane production process in which methane-producing bacteria are brought into contact with the acid-generated treatment liquid to produce methane. It will be done. Since the acid production step and the methane production step have different suitable progress conditions, a two-phase system in which the processes are performed in separate treatment tanks (an acid production tank and a methane fermentation tank) is widely used.

For example, Patent Document 1 describes an anaerobic treatment device including an acid generation tank and a methane fermentation tank for anaerobic treatment of wastewater containing organic matter. Further, Patent Document 1 describes an anaerobic treatment method including an acid generation step in an acid generation tank, a methane generation step in a methane fermentation tank, and a return step of returning a part of the treated water of the methane generation step to the acid generation step. , it is described that by aerating the liquid to be treated in the acid generation step, decarboxylation can be performed and the amount of alkali used for pH adjustment can be reduced.

Japanese Patent Application Publication No. 5-277486

As described in Patent Document 1, it is known that in anaerobic treatment, the amount of alkali used for pH adjustment can be reduced by performing decarboxylation through aeration.
On the other hand, in the anaerobic treatment described in Patent Document 1, aeration is performed in an acid generation tank, so if the amount of wastewater treated or the amount of treatment load is reduced, an overaerated state will occur, resulting in a decrease in the activity of acid-producing bacteria and methanogens. There are concerns that this could lead to Furthermore, in the anaerobic treatment described in Patent Document 1, gases from aeration are mixed into the useful biogas generated in the acid generation tank, resulting in a decrease in the recovery rate as biogas.

The problem of the present invention is to reduce the amount of alkali used for pH adjustment in wastewater treatment involving anaerobic treatment, and to suppress a decrease in wastewater treatment efficiency and a decrease in the recovery rate of useful biogas generated during the treatment process. It is an object of the present invention to provide a wastewater treatment device and a method for treating wastewater.

As a result of intensive study on the above-mentioned issues, the present inventor has determined that in anaerobic treatment, after decarboxylation is performed in a decarboxylation tank into which raw water to be treated is introduced, anaerobic treatment accompanied by acid generation treatment and methane generation is performed. By returning the treated water after anaerobic treatment to the decarbonation tank, in addition to reducing the amount of alkali used for pH adjustment, it also suppresses a decrease in wastewater treatment efficiency and a decrease in the recovery rate of useful biogas generated during the treatment process. The present invention was completed by discovering that this is possible.
That is, the present invention provides the following wastewater treatment apparatus and wastewater treatment method.

A wastewater treatment device of the present invention for solving the above problems includes a decarboxylation tank that performs decarboxylation treatment, an acid generation tank, and a reaction section that performs anaerobic treatment downstream of the acid generation tank. Raw water is introduced into the reactor, and after being subjected to anaerobic treatment in the reaction section, the treated water is returned to the decarbonation tank.
In the wastewater treatment apparatus of the present invention, by separating the decarboxylation tank and the acid generation tank, there is no need to perform decarboxylation treatment in the acid generation tank. This makes it possible to suppress a decrease in treatment efficiency due to overaeration caused by decarboxylation in the acid generation tank and a decrease in the recovery rate of useful biogas generated in the acid generation tank. Additionally, by providing a decarboxylation tank before the acid generation tank, the water to be treated that is introduced from the decarboxylation tank to the acid generation tank is deaerated from gases other than carbon dioxide (especially oxygen). . Since the acid production process is a reaction that proceeds under anaerobic conditions, placing the decarboxylation tank before the acid production tank improves the acid production efficiency of the water to be treated that is introduced into the acid production tank. It becomes possible to do so.
The treated water after anaerobic treatment in the reaction section contains dissolved carbon dioxide generated during the anaerobic treatment, and by returning this treated water to the decarbonation tank, chemicals can be used in the decarbonation tank. pH can be lowered. At this time, by performing the decarboxylation treatment with the pH lowered in the decarboxylation tank, it is possible to improve the decarboxylation treatment efficiency. Furthermore, by using the treated water after anaerobic treatment as a pH adjuster in the decarbonation tank, it is possible to reduce the amount of chemicals (alkali) used for adjusting the pH of the treated water.

Further, in one embodiment of the wastewater treatment apparatus of the present invention, the decarboxylation tank is characterized in that it performs acid generation treatment in conjunction with decarboxylation treatment.
According to this feature, by first performing decarboxylation treatment and acid generation treatment in the decarboxylation tank, strong acids such as hydrochloric acid can be added in addition to degassing the water to be treated that is introduced into the acid generation tank in the subsequent stage. Therefore, it is possible to set the pH of the water to be treated, which is introduced into the subsequent acid generation tank, to a pH (weakly acidic) suitable for acid generation treatment. This makes it possible to reduce the amount of chemicals used for pH adjustment, regardless of the pH of the raw water introduced, and to promote acid generation treatment in the acid generation tank, improving wastewater treatment efficiency and biogas recovery. This makes it possible to improve the rate.

Moreover, one embodiment of the wastewater treatment apparatus of the present invention is characterized in that the decarboxylation tank is equipped with a heating means.
According to this feature, it becomes possible to increase the decarboxylation processing efficiency in the decarboxylation tank. Furthermore, when acid generation treatment is performed in the decarboxylation tank, in addition to increasing the decarboxylation treatment efficiency, it is also possible to promote the acid generation treatment.

Furthermore, an embodiment of the wastewater treatment apparatus of the present invention is characterized in that the treated water that has been subjected to anaerobic treatment in the reaction section is returned from the upper part of the decarbonation tank.
According to this feature, by introducing treated water containing carbon dioxide into the decarbonation tank from the top of the tank, deaeration can be performed by the impact of falling water. This makes it possible to save energy compared to decarbonation treatment using a drive device such as aeration.

Further, the wastewater treatment method of the present invention for solving the above problems includes a decarboxylation step for performing decarboxylation treatment, an acid generation step, and a reaction step for performing anaerobic treatment after the acid generation step, Raw water is introduced into the decarboxylation step, and the treated water after the reaction step is returned to the decarboxylation step.
In the wastewater treatment method of the present invention, by separating the decarboxylation step and the acid generation step, it is possible to suppress a decrease in the recovery rate of useful biogas generated in the acid generation step. Further, by providing the decarboxylation step before the acid generation step, it is possible to improve the acid generation treatment efficiency of the water to be treated in the acid generation step.
By returning the treated water after the reaction step to the decarboxylation step, decarboxylation can be performed in a state where the pH is lowered without using chemicals in the decarboxylation step, increasing the decarboxylation efficiency. can. Furthermore, since the treated water after the reaction step acts as a pH adjuster in the decarboxylation step, it is possible to reduce the amount of chemicals (alkali) used for adjusting the pH of the treated water generated in the reaction step.

According to the present invention, in wastewater treatment involving anaerobic treatment, it is possible to reduce the amount of alkali used for pH adjustment, and to suppress a decrease in wastewater treatment efficiency and a decrease in the recovery rate of useful biogas generated in the treatment process. It is possible to provide a wastewater treatment device and a method for treating wastewater.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic explanatory drawing of the wastewater treatment apparatus in the 1st embodiment of this invention. It is a schematic explanatory view of the wastewater treatment device in the 2nd embodiment of this invention. It is a schematic explanatory drawing which shows another aspect of the wastewater treatment apparatus in the 2nd embodiment of this invention.

The wastewater to be treated in the present invention (hereinafter referred to as "raw water") is not particularly limited as long as it contains substances (organic substances) that can be treated anaerobically. Specific examples of raw water include industrial wastewater discharged from various factories such as food factories, chemical factories, and pulp and paper factories, and domestic wastewater such as sewage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a wastewater treatment device and a wastewater treatment method according to the present invention will be described in detail with reference to the drawings. Regarding the wastewater treatment method in the present invention, the description of the operation of the wastewater treatment device according to the present invention shall be substituted.
Note that the wastewater treatment apparatus and wastewater treatment method described in the embodiments are merely exemplified to explain the wastewater treatment apparatus according to the present invention and the wastewater treatment method using the wastewater treatment apparatus according to the present invention. It is not limited to.

[First embodiment]
FIG. 1 is a schematic explanatory diagram of a wastewater treatment apparatus according to a first embodiment of the present invention.
As shown in FIG. 1, the wastewater treatment apparatus 1A in this embodiment includes a decarbonation tank 2 into which raw water W0 is introduced, an acid generation tank 3 which performs acid generation treatment on the water W1 to be treated from the decarbonation tank 2, and It is equipped with a reaction section 4 that performs anaerobic treatment on the water to be treated W2 from the generation tank 3. Furthermore, a line L1 which is an introduction pipe for introducing raw water W0 into the decarbonation tank 2, a line L2 which introduces the water to be treated W1 discharged from the decarbonation tank 2 into the acid generation tank 3, and an acid generation A line L3 that introduces the treated water W2 discharged from the tank 3 into the reaction section 4, and a line L4 that is a return piping for returning a part of the treated water W3 treated in the reaction section 4 to the decarbonation tank 2. and a line L5 which is a discharge pipe for discharging treated water W3 discharged from the reaction section 4 to the outside of the system. Note that the thick arrows in FIG. 1 indicate the flow of water.

The wastewater treatment apparatus 1A in this embodiment starts from the decarbonation tank 2 into which raw water W0 is introduced via the line L1, and then processes the wastewater in the order of the acid generation tank 3 and the reaction section 4. Further, a part of the treated water W3 treated in the reaction section 4 is returned to the decarbonation tank 2 via the line L4, and in the decarbonation tank 2, the mixed liquid of the raw water W0 and the treated water W3 is decarboxylated. becomes.

The decarboxylation tank 2 is a tank for performing a decarboxylation process (decarboxylation step) for removing carbon dioxide contained in the raw water W0 and the treated water W3 returned from the reaction section 4. As shown in FIG. 1, raw water W0 is introduced into the decarbonation tank 2 from a source of raw water W0 through a line L1, and treated water W3 that has been treated in the reaction section 4 is introduced through a line L4. be done.
Note that although the lines L1 and L4 are shown as being independent in FIG. 1, the line L1 and the line L4 are not limited to this. For example, the line L1 and the line L4 may be merged, and the raw water W0 and the treated water W3 may be mixed in the merged pipe and introduced into the decarbonation tank 2 as a mixed liquid.

There are no particular limitations on the specific means for the decarboxylation treatment performed in the decarboxylation tank 2. As an example of the decarboxylation means 21 in this embodiment, for example, as shown in FIG. 1, an aeration mechanism including an aeration pipe 22 and a blower 23 that supplies gas to the aeration pipe 22 may be provided. Further, other examples of the decarboxylation means 21 include providing a stirring mechanism in the decarboxylation tank 2, and providing a pressure reducing mechanism for reducing the pressure inside the decarboxylation tank 2.
This decarbonation means 21 performs aeration treatment on the raw water W0 and treated water W3 in the decarbonation tank 2, thereby making it possible to discharge dissolved carbon dioxide to the outside of the tank.
At this time, the gas discharged from the decarbonation tank 2 contains carbon dioxide as well as odorous gases derived from the raw water W0 or the treated water W3. It is preferable to transfer it to a deodorizing treatment.

The decarboxylation tank 2 in this embodiment is supplied with the treated water W3 from the reaction section 4 via the line L4, but as described later, the treated water W3 is supplied with bacterial bodies (acid-producing bacteria and anaerobic bacteria such as methanogens).
Therefore, especially when the pH of the raw water W0 is on the alkaline side, the acid production reaction progresses in the decarbonation tank 2 by mixing the raw water W0 and the treated water W3 containing acid-producing bacteria.
By making the pH of the solution in the decarboxylation tank 2 more acidic through this acid production reaction, it is possible to increase the decarboxylation efficiency by aeration, and the acid production process in the acid production tank 3 in the subsequent stage can also be made more efficient. It becomes possible to increase the
The water to be treated W1 treated in the decarbonation tank 2 is then introduced into the acid generation tank 3 via the line L2.

Here, if the main components contained in the raw water W0 are high-concentration lower alcohols or organic acids, and there are few targets for decomposition by acid-producing bacteria, or if the pH of the raw water W0 is acidic, decarboxylation tank 2 is used. The decarboxylation process performed by the decarboxylation means 21 alone is sufficient.

On the other hand, when the main components contained in raw water W0 are high molecular weight organic substances such as polysaccharides and proteins, and there are many targets for decomposition by acid-producing bacteria, or when the pH of raw water W0 is alkaline, decarboxylation tank 2 is used. As for the treatment to be performed, it is preferable to perform an acid generation treatment in conjunction with a decarboxylation treatment. As will be described later, in the treatment in the acid generation tank 3, it is preferable that the pH of the solution to be treated (the water to be treated W1) is weakly acidic. Therefore, in the decarboxylation tank 2, some of the components are subjected to acid generation treatment, making it possible to make the pH of the water to be treated W1 more acidic without adding strong acids such as hydrochloric acid. It becomes possible to accelerate the acid generation process in the acid generation tank 3. In addition, by partially proceeding with the acid production process in the decarbonation tank 2, together with the acid production process in the acid production tank 3, it becomes possible to improve the wastewater treatment efficiency for the raw water W0.

The acid production process in the decarboxylation tank 2 may be performed by adding acid-producing bacteria to the decarboxylation tank 2 from outside the system, but the acid production process is performed using bacterial bodies contained in the treated water W3. This can be mentioned. Specifically, the decarboxylation tank 2 is provided with a means for adding nutrients required by acid-producing bacteria, and an aeration pipe is installed to create an anaerobic or microaerobic atmosphere inside the decarboxylation tank 2. Examples include using a gas that does not contain oxygen as the gas introduced from 22, or using decarbonation means 21 other than aeration.

At this time, the acid generation treatment in the decarboxylation tank 2 may be any process that can neutralize or slightly acidify the pH of the raw water W0, and does not completely advance the acid generation treatment on the raw water W0. For this reason, the residence time of the solution (raw water W0 and treated water W3) in the decarbonation tank 2 is preferably set to be shorter than the residence time of the solution (to-be-treated water W1) in the acid generation tank 3. More specifically, the volume of the decarboxylation tank 2 is made smaller than the volume of the acid generation tank 3, and the amount of solution introduced into the decarboxylation tank 2 is made smaller than the amount of solution introduced into the acid generation tank 3. For example, the flow rate may be adjusted in each of the lines L1 to L3 so that the flow rate becomes less than the above.

Moreover, the decarbonation tank 2 in this embodiment can further be provided with various accompanying equipment. For example, the decarbonation tank 2 may be provided with an internal water temperature adjusting means.
In particular, it is preferable that the decarboxylation tank 2 is provided with a heating means. The heating means may be anything that can raise the temperature of the solution (raw water W0 and treated water W3) in the decarboxylation tank 2, and the specific structure is not particularly limited. It may be provided on either side. Thereby, it becomes possible to improve the decarboxylation processing efficiency in the decarboxylation tank 2. In addition, by providing a temperature control (temperature adjustment) function as a heating means and maintaining the inside of the decarboxylation tank 2 at a temperature suitable for acid generation treatment, the decarboxylation process efficiency is improved and the inside of the decarboxylation tank 2 is It becomes possible to accelerate acid generation treatment. Note that the heating means itself also functions as the decarboxylation means 21, but by combining it with the other decarboxylation means 21 described above, it becomes possible to further improve the decarboxylation processing efficiency.

The acid generation tank 3 performs acid generation treatment (acid generation step) in which organic matter in the water to be treated W1 is decomposed by acid generation bacteria, which are facultative anaerobic bacteria, to generate organic acids in an anaerobic atmosphere without dissolved oxygen. ). As shown in FIG. 1, water to be treated W1 is supplied to the acid generation tank 3 via a line L2. In the acid-producing tank 3, the components contained in the water to be treated W1 are decomposed by the acid-producing bacteria housed therein. Note that it is desirable that the acid generation tank 3 be a closed system and maintain an anaerobic environment.
As an example of decomposition by acid generation treatment, for example, high-molecular organic substances such as polysaccharides and proteins contained in the water to be treated W1 are decomposed into low-molecular organic substances such as monosaccharides, amino acids, and lower fatty acids (hydrolysis), Further examples include those in which this low-molecular organic substance is decomposed into lower alcohols, acetic acid, hydrogen, methane, carbon dioxide, etc. (acid fermentation).

The water to be treated W2 after the acid generation treatment is discharged from the acid generation tank 3 via the line L3 and introduced into the reaction section 4. Moreover, the biogas G1 generated by the acid generation process is discharged to the outside of the acid generation tank 3 via the line L6. At this time, in order to effectively utilize the biogas G1 (mainly hydrogen and methane) discharged from the acid generation tank 3, the line L6 is connected to a means for collecting, refining and storing the biogas G1 (hydrogen and methane). It is preferable to do so.

The acid-producing bacteria accommodated in the acid-producing tank 3 may be added to the acid-producing tank 3 from outside the system. One example is collecting and using. More specifically, acid production treatment may be performed using bacterial cells contained in the treated water W3. In this embodiment, the bacterial cells contained in the treated water W3 introduced into the decarboxylation tank 2 are supplied to the acid generation tank 3 while being contained in the water to be treated W1 as they are. can be used. Alternatively, a line connecting the reaction section 4 and the acid generation tank 3 may be provided to supply a portion of the treated water W3 to the acid generation tank 3.

The acid generation tank 3 in this embodiment can further be provided with various accompanying equipment. For example, the acid generation tank 3 may be equipped with an internal water temperature adjustment means and a means for adding metals such as nitrogen, phosphorus, cobalt, and nickel, which are nutrients required by acid-producing bacteria. Further, in the acid-producing tank 3, a carrier holding acid-producing bacteria may be used.

The reaction section 4 is for performing a reaction step of anaerobically treating the water to be treated W2 treated in the acid generation tank 3. As shown in FIG. 1, the reaction section 4 includes a methane fermentation tank 41 and a separation device 42 in the upper part of the methane fermentation tank 41 that separates biogas G2 (mainly methane), treated water W3, and solids. ing.

The methane fermentation tank 41 is for performing a methane fermentation process that generates methane from the carbon source contained in the water to be treated W2 treated in the acid generation tank 3. Methane fermentation treatment is a type of anaerobic treatment performed in an anaerobic atmosphere free of dissolved oxygen using methane-producing bacteria maintained in the methane fermentation tank 41 by a floating method, fixed bed method, fluidized bed method, UASB method, EGSB method, etc. It is. Note that it is essential that the methane fermentation tank 41 be a closed system and maintain an anaerobic environment.
Examples of reactions in methane fermentation include decomposing organic matter (mainly acetic acid) into methane and carbon dioxide, and generating methane from carbon dioxide and hydrogen. Methane generated at this time is separated and recovered as biogas G2 by the separator 42, but a high proportion of carbon dioxide will be dissolved in the treated water W3.

The methane-producing bacteria held in the methane fermentation tank 41 are not particularly limited. For example, isolated microorganisms may be used, or seed sludge from other anaerobic treatment equipment may be used. Alternatively, anaerobic microorganisms contained in the raw water W0 (water to be treated W2) may be utilized.

The form of the methanogens that form the layer consisting of methanogens (anaerobic microorganism layer M) is not particularly limited, but for example, granules of microorganisms with a diameter of about 0.3 to 3 mm called granules are used. One example is that. Granules are microbial clusters that utilize self-immobilization and are capable of maintaining a high bacterial cell concentration. Therefore, by using the granules, an anaerobic microorganism layer M in which methane-producing bacteria are maintained at a high concentration is formed in the methane fermentation tank 41.
Moreover, as the anaerobic microorganism layer M, a carrier layer made of a carrier holding methanogens may be used instead of the granule layer.

It is preferable to provide means for recovering or reusing the biogas G2 (methane), treated water W3, and solids separated by the separation device 42, respectively. For example, in order to effectively utilize methane as biogas G2, it is preferable that methane be transferred to means for recovery, purification, and storage via line L7. Furthermore, in addition to being discharged outside the system via line L5, treated water W3 is returned to decarbonation tank 2 via line L4 to adjust the pH of raw water W0 in decarbonation tank 2, and to adjust the pH of raw water W0 in decarbonation tank 2. The pH of the product itself shall be adjusted. Further, since the solid content contains methane-producing bacteria, it is preferable to use a separation device 42 to keep it in the methane fermentation tank 41 so that it does not flow out of the system. Note that a part of the solid content may be supplied to the decarboxylation tank 2 or the acid production tank 3 and used as seed sludge for acid production bacteria.

The reaction section 4 in this embodiment can further be provided with various accompanying equipment. For example, the reaction section 4 may be equipped with an internal water temperature adjustment means and a means for adding metals such as nitrogen, phosphorus, cobalt, and nickel, which are nutrient sources required by methanogens.

In the wastewater treatment device 1A of this embodiment, the decarboxylation tank 2 and the acid generation tank 3 are separated, and the treated water W3 that has been anaerobically treated in the reaction section 4 is returned to the decarbonation tank 2 to form raw water W0. By mixing, it becomes possible to adjust the pH to a certain degree in each tank that performs wastewater treatment (decarbonation tank 2, acid generation tank 3, methane fermentation tank 41) without using chemicals for pH adjustment. .
On the other hand, it is known that there is a pH range suitable for acid generation treatment and methane generation treatment, and in order to further improve wastewater treatment efficiency, the acid generation tank 3 and methane fermentation tank 41 are The pH inside the acid generation tank 3 and the methane fermentation tank 41 may be adjusted by providing a means for measuring pH (pH meter) and a means for adding a pH adjusting chemical (pH adjuster). Note that as the pH adjuster, known substances such as acids and alkalis are used.

At this time, the water to be treated W1 introduced from the decarboxylation tank 2 to the acid production tank 3 needs to be weakly acidic to be suitable for acid production treatment. The water to be treated W2 needs to be neutral enough to be suitable for methane generation treatment.
As mentioned above, the water W1 to be treated in the decarbonation tank 2 can be easily made weakly acidic without using a pH adjuster depending on the nature of the raw water W0. For the treated water W1, the amount of pH adjuster used can be significantly reduced or no pH adjuster can be used. On the other hand, regarding the water to be treated W2 introduced from the acid generation tank 3 to the methane fermentation tank 41, acid is generated by the acid generation treatment, so the pH of the water to be treated W2 is lowered. Therefore, in order to perform neutralization suitable for methane generation treatment, it is preferable to provide the acid generation tank 3 with means for adding an alkali as a pH adjuster. At this time, by allowing part of the acid generation treatment to proceed in the decarboxylation tank 2, the amount of pH adjuster used is to suppress the pH drop in the acid generation tank 3 and neutralize the water to be treated W2. It becomes possible to reduce the

As described above, with the wastewater treatment device 1A of this embodiment and the wastewater treatment method using this wastewater treatment device 1A, by performing separate treatment in the decarboxylation tank 2 and the acid generation tank 3, the acid generation tank 3 There is no need to perform decarboxylation treatment. This makes it possible to suppress a decrease in treatment efficiency due to overaeration caused by decarboxylation in the acid generation tank and a decrease in the recovery rate of useful biogas generated in the acid generation tank. Here, since the acid generation treatment is a reaction that proceeds under microaerobic and anaerobic conditions, by arranging the decarboxylation tank 2 before the acid generation tank 3, the water to be treated that is introduced into the acid generation tank 3 is Appropriate dissolved oxygen in W1 improves acid generation treatment efficiency, making it possible to increase the recovery rate of biogas G1.

[Second embodiment]
FIG. 2 is a schematic explanatory diagram of a wastewater treatment apparatus 1B according to a second embodiment of the present invention.
As shown in FIG. 2, the wastewater treatment device 1B according to this embodiment includes a return pipe (line L4) that returns treated water W3 from the reaction section 4 (methane fermentation tank 41) to the decarboxylation tank 2 as the decarboxylation means 21. ) is connected to the upper part of the decarboxylation tank 2, and the treated water W3 is introduced into the decarboxylation tank 2 from the upper part of the decarboxylation tank 2.
Note that, among the configurations of the wastewater treatment device 1B in this embodiment, descriptions of those that are the same as the configurations of the wastewater treatment device 1A in the first embodiment will be omitted.

In the wastewater treatment device 1B of this embodiment, a return pipe (line L4) for returning treated water W3 that has been subjected to anaerobic treatment in the reaction section 4 to the decarbonation tank 2 is connected to the decarbonation tank 2 as the decarboxylation means 21. By setting the position at the upper part of the decarbonation tank 2, decarbonation (deaeration) is performed by the impact when the treated water W3 is dropped into the decarbonation tank 2 through the line L4. This makes it possible to save energy compared to decarbonation treatment using a drive device such as aeration.

As for the decarboxylation means 21 of this embodiment, the connection point between the return pipe (line L4) and the decarboxylation tank 2 may be the upper part of the decarboxylation tank 2, for example, the ceiling of the decarboxylation tank 2 or the decarboxylation tank 2. An example is the upper side of tank 2.
In addition, regarding the piping shape, opening shape, and opening direction of the line L4 that connects to the decarbonation tank 2, when the treated water W3 falls into the decarbonation tank 2, decarbonation (deaeration) is possible. There are no particular limitations on the specific structure, as long as it can apply a sufficient impact to achieve this. For example, the line L4 may have a structure that allows what is called a waterfall drop.

Moreover, as the decarboxylation means 21 in this embodiment, in addition to performing waterfall dropping by the arrangement of the line L4, a mechanism for further increasing the decarboxylation efficiency may be provided.
FIG. 3 is a schematic explanatory diagram showing another aspect of the wastewater treatment device 1B in this embodiment.
As shown in FIG. 3, another aspect of the wastewater treatment device 1B is to provide an air introduction section 24 on the line L4.
The air introduction section 24 is provided with pressurized air introduction means for forcibly supplying air to the treated water W3, and by adding pressurized air to the treated water W3, the treated water W3 is removed from the line L4. When introduced (discharged) into the carbonation tank 2, the pressure applied to the treated water W3 is released, thereby increasing the decarboxylation effect.
Note that the air introduction section 24 is not limited to forcibly supplying pressurized air to the treated water W3. Another example of the air introduction section 24 is to restrict a part of the line L4 and provide an air suction port, thereby functioning as a so-called aspirator that increases the speed of the fluid (treated water W3) flowing within the line L4. For example, it may have a structure that As a result, the inflow speed of the treated water W3 introduced (discharged) from the line L4 to the decarbonation tank 2 can be increased without using power such as a pump, and it is possible to further dissolve air in the treated water W3. , it becomes possible to further enhance the decarboxylation effect caused by the impact of falling into water.

Further, the decarboxylation means 21 in this embodiment may be provided with a structure with which the treated water W3 comes into contact while falling through the decarbonation tank 2. As a result, in addition to the impact of falling water, the treated water W3 is also subjected to impact due to contact with the structure, making it possible to improve decarboxylation efficiency.

As described above, the wastewater treatment device 1B in this embodiment and the wastewater treatment method using this wastewater treatment device 1B do not particularly require a drive device in the decarbonation process, so that energy saving of the wastewater treatment device 1B as a whole can be achieved. It becomes possible to achieve this goal.

In addition, the embodiment mentioned above shows an example of a wastewater treatment apparatus and a wastewater treatment method. The wastewater treatment device and the wastewater treatment method according to the present invention are not limited to the embodiments described above, and the wastewater treatment device and the wastewater treatment method according to the embodiments described above are applicable without changing the gist of the claims. May be deformed.

For example, a plurality of decarboxylation means shown in this embodiment may be combined. This makes it possible to increase the decarboxylation treatment efficiency in the decarboxylation tank.

The wastewater treatment device and wastewater treatment method of the present invention are suitably used for anaerobic treatment of wastewater containing organic matter.

1A, 1B wastewater treatment device, 2 decarboxylation tank, 21 decarboxylation means, 22 aeration pipe, 23 blower, 24 air introduction section, 3 acid generation tank, 4 reaction section, 41 methane fermentation tank, 42 separation device, L1 to L7 Line, G1, G2 Biogas, M Anaerobic microbial layer, W0 Raw water, W1, W2 Treated water, W3 Treated water

Claims (5)

A decarboxylation tank that performs decarboxylation treatment,
an acid generation tank;
a reaction section that performs anaerobic treatment downstream of the acid generation tank;
A wastewater treatment device, characterized in that raw water is introduced into the decarbonation tank, and treated water after being subjected to anaerobic treatment in the reaction section is returned to the decarbonation tank. The wastewater treatment apparatus according to claim 1, wherein the decarboxylation tank performs acid generation treatment in addition to decarboxylation treatment. The wastewater treatment apparatus according to claim 1 or 2, wherein the decarbonation tank includes a heating means. The wastewater treatment device according to any one of claims 1 to 3, wherein the treated water that has been subjected to anaerobic treatment in the reaction section is returned from an upper part of the decarbonation tank. a decarboxylation step for performing decarboxylation;
an acid generation step;
a reaction step of performing anaerobic treatment after the acid generation step,
A wastewater treatment method, characterized in that raw water is introduced into the decarboxylation step, and the treated water after the reaction step is returned to the decarboxylation step.