Wastewater treatment apparatus and wastewater treatment method

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

Technical Field

[0001] The present invention relates to a wastewater treatment apparatus and a wastewater treatment method. In particular, the present invention relates to a wastewater treatment apparatus and a wastewater treatment method involving anaerobic treatment.

Background Art

[0002] Generally, as a method for treating wastewater containing organic substances, biological treatment using various microorganisms is known. Biological treatment is roughly classified into two types: aerobic treatment and anaerobic treatment. Among these, anaerobic treatment is further roughly classified into two types: methane fermentation treatment and denitrification treatment. Among these, methane fermentation treatment has high merits in terms of, for example, hardly generating excess sludge.

[0003] Methane fermentation treatment is an anaerobic treatment that decomposes organic substances in wastewater into methane and carbon dioxide by the action of anaerobic microorganisms in an anaerobic environment, and is widely used as anaerobic treatment from the viewpoints of treatment cost and usefulness of the generated gas.

[0004] Methane fermentation treatment includes an acid generation step of bringing acid-forming bacteria into contact with organic substances in wastewater to generate acid, and a methane generation step of bringing methane-forming bacteria into contact with the treated liquid in which acid has been generated to generate methane. Since the suitable progress conditions for the acid generation step and the methane generation step are different, a two-phase system in which treatment is performed in separate treatment tanks (acid generation tank and methane fermentation tank) is widely used.

[0005] For example, Patent Document 1 describes an anaerobic treatment apparatus including an acid generation tank and a methane fermentation tank as anaerobic treatment of wastewater containing organic substances. Further, Patent Document 1 describes that, in 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 in the methane generation step to the acid generation step, decarboxylation is performed by aerating the liquid to be treated in the acid generation step, and the amount of alkali used for pH adjustment can be reduced.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-277486 [Overview of the project] [Problems that the invention aims to solve]

[0007] 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 by aeration. On the other hand, in the anaerobic treatment described in Patent Document 1, aeration is performed in the acid production tank, so if the amount of wastewater treated or the treatment load is reduced, it may result in over-aeration, which is a concern as it may lead to a decrease in the activity of acid-producing bacteria and methane-producing bacteria. In addition, in the anaerobic treatment described in Patent Document 1, gas from aeration is mixed with the useful biogas generated in the acid production tank, which reduces the biogas recovery rate.

[0008] The object of the present invention is to provide a wastewater treatment apparatus and wastewater treatment method that can reduce the amount of alkali used for pH adjustment in wastewater treatment involving anaerobic treatment, while suppressing a decrease in wastewater treatment efficiency and a decrease in the recovery rate of useful biogas generated during the treatment process. [Means for solving the problem]

[0009] As a result of diligent research into the above-mentioned problems, the inventors of the present invention have found that in anaerobic treatment, after decarbonation is performed in a decarbonation tank into which the raw water to be treated is introduced, anaerobic treatment involving acid generation and methane generation is performed, and the treated water after anaerobic treatment is returned to the decarbonation tank, it is possible to reduce the amount of alkali used for pH adjustment, as well as suppress the decrease in wastewater treatment efficiency and the decrease in the recovery rate of useful biogas generated in the treatment process, and have completed the present invention. In other words, the present invention relates to the following wastewater treatment apparatus and wastewater treatment method.

[0010] The wastewater treatment apparatus of the present invention, which solves the above problems, comprises a decarbonation tank for decarbonation treatment, an acid generation tank, and a reaction unit for anaerobic treatment downstream of the acid generation tank, and is characterized in that raw water is introduced into the decarbonation tank, and the treated water after anaerobic treatment in the reaction unit is returned to the decarbonation tank. The wastewater treatment apparatus of the present invention separates the decarbonation tank and the acid generation tank, eliminating the need for decarbonation treatment in the acid generation tank. This makes it possible to suppress the decrease in treatment efficiency due to excessive aeration caused by decarbonation treatment in the acid generation tank, and the decrease in the recovery rate of useful biogas generated in the acid generation tank. Furthermore, by providing a decarbonation tank before the acid generation tank, the water to be treated introduced from the decarbonation tank to the acid generation tank is deaerated of gases other than carbon dioxide (especially oxygen). Here, since the acid generation treatment is a reaction that proceeds under anaerobic conditions, placing the decarbonation tank before the acid generation tank makes it possible to improve the acid generation treatment efficiency of the water to be treated introduced into the acid generation tank. Furthermore, the treated water after anaerobic treatment in the reaction section contains dissolved carbon dioxide generated during the anaerobic treatment. By returning this treated water to the decarbonation tank, the pH can be lowered in the decarbonation tank without the use of chemicals. At this time, performing the decarbonation treatment in the decarbonation tank with a lowered pH makes it possible to increase the efficiency of the decarbonation treatment. In addition, by using the treated water after anaerobic treatment as a pH adjuster in the decarbonation tank, it is possible to reduce the amount of pH-adjusting chemicals (alkali) used in the treated water.

[0011] Furthermore, in one embodiment of the wastewater treatment apparatus of the present invention, the decarbonation tank is characterized by performing an acid generation treatment in conjunction with the decarbonation treatment. This feature allows for decarbonation and acid generation treatment to be performed first in a decarbonation tank. Combined with degassing of the water to be treated before it is introduced into the subsequent acid generation tank, this makes it possible to adjust the pH of the water to be treated to a pH suitable for acid generation (weakly acidic) without adding strong acids such as hydrochloric acid. This reduces the amount of chemicals used for pH adjustment, regardless of the pH of the raw water introduced, while promoting acid generation in the acid generation tank, thereby improving wastewater treatment efficiency and biogas recovery rate.

[0012] Furthermore, one embodiment of the wastewater treatment apparatus of the present invention is characterized in that the decarbonation tank is equipped with a heating means. This feature makes it possible to improve the efficiency of the decarbonation process in the decarbonation tank. Furthermore, when performing acid generation treatment in the decarbonation tank, it is possible to not only improve the efficiency of the decarbonation process but also to accelerate the acid generation process.

[0013] Furthermore, one embodiment of the wastewater treatment apparatus of the present invention is characterized in that the treated water, after anaerobic treatment in the reaction section, is returned from the top of the decarbonation tank. This feature allows for deaeration by introducing treated water containing carbon dioxide into the decarbonation tank from the top of the tank, using the impact of the falling water. This makes it possible to save energy compared to decarbonation treatments that use drive devices such as aeration.

[0014] Furthermore, the wastewater treatment method of the present invention, which solves the above problems, comprises a decarboxylation step of performing decarboxylation treatment, an acid generation step, and a reaction step of performing anaerobic treatment after the acid generation step, wherein raw water is introduced into the decarboxylation step, and the treated water after the reaction step is returned to the decarboxylation step. The wastewater treatment method of the present invention makes it possible to suppress the decrease in the recovery rate of useful biogas generated in the acid generation step by separating the decarbonation step and the acid generation step. Furthermore, by providing a decarbonation step before the acid generation step, it is possible to improve the efficiency of acid generation treatment of the water to be treated in the acid generation step. By returning the treated water after the reaction step to the decarbonation step, the decarbonation step can perform decarbonation treatment with the pH reduced without using chemicals, thereby enhancing the decarbonation treatment efficiency. Further, by allowing the treated water after the reaction step to act as a pH adjuster in the decarbonation step, it becomes possible to reduce the amount of chemicals (alkali) used for pH adjustment with respect to the treated water generated in the reaction step.

Advantages of the Invention

[0015] According to the present invention, there can be provided a wastewater treatment apparatus and a wastewater treatment method capable of reducing the amount of alkali used for pH adjustment, suppressing a decrease in wastewater treatment efficiency, and suppressing a decrease in the recovery rate of useful biogas generated in the treatment process, in wastewater treatment involving anaerobic treatment.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic explanatory view of a wastewater treatment apparatus in a first embodiment of the present invention. [Figure 2] It is a schematic explanatory view of a wastewater treatment apparatus in a second embodiment of the present invention. [Figure 3] It is a schematic explanatory view showing another aspect of the wastewater treatment apparatus in a second embodiment of the present invention.

Modes for Carrying Out the Invention

[0017] 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) capable of anaerobic treatment. Specific examples of raw water include, for example, industrial wastewater discharged from various factories such as food factories, chemical factories, and paper pulp factories, and domestic wastewater such as sewage.

[0018] Hereinafter, embodiments of the wastewater treatment apparatus and the wastewater treatment method according to the present invention will be described in detail with reference to the drawings. The wastewater treatment method in the present invention shall be replaced by the description of the operation of the wastewater treatment apparatus according to the present invention. Note that the wastewater treatment apparatus and the wastewater treatment method described in the embodiments are merely examples for explaining the wastewater treatment apparatus according to the present invention and the wastewater treatment method using the wastewater treatment apparatus according to the present invention, and are not limited thereto.

[0019] [First Embodiment] FIG. 1 is a schematic explanatory view 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 the present embodiment includes a decarboxylation tank 2 for introducing raw water W0, an acid generation tank 3 for subjecting the treated water W1 from the decarboxylation tank 2 to acid generation treatment, and a reaction section 4 for subjecting the treated water W2 from the acid generation tank 3 to anaerobic treatment. Further, a line L1 which is an introduction pipe for introducing raw water W0 to the decarboxylation tank 2, a line L2 for introducing the treated water W1 discharged from the decarboxylation tank 2 to the acid generation tank 3, a line L3 for introducing the treated water W2 discharged from the acid generation tank 3 to the reaction section 4, a line L4 which is a return pipe for returning a part of the treated water W3 treated in the reaction section 4 to the decarboxylation tank 2, and a line L5 which is a discharge pipe for discharging the 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.

[0020] The wastewater treatment apparatus 1A in the present embodiment starts from the decarboxylation tank 2 into which raw water W0 is introduced via the line L1, and performs wastewater treatment 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 decarboxylation tank 2 via the line L4, and the decarboxylation tank 2 performs decarboxylation treatment on the mixed liquid of the raw water W0 and the treated water W3.

[0021] The decarboxylation tank 2 is a tank for performing a decarboxylation treatment (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 decarboxylation tank 2 via the line L1 from the supply source of the raw water W0, and the treated water W3 treated in the reaction section 4 is introduced via the line L4. Note that although lines L1 and L4 are shown as separate entities in Figure 1, the system is not limited to this configuration. For example, lines L1 and L4 may be merged, and the raw water W0 and treated water W3 may be mixed in the merged piping before being introduced as a mixture into the decarbonation tank 2.

[0022] The specific means for the decarbonation treatment carried out in the decarbonation tank 2 are not particularly limited. One example of the decarbonation means 21 in this embodiment is to provide an aeration mechanism that includes a diffuser pipe 22 and a blower 23 that supplies gas to the diffuser pipe 22, as shown in Figure 1. Other examples of the decarbonation means 21 include providing a stirring mechanism in the decarbonation tank 2 or providing a depressurization mechanism to reduce the pressure inside the decarbonation tank 2. This decarbonation means 21 allows for aeration treatment of the raw water W0 and treated water W3 in the decarbonation tank 2, thereby enabling the discharge of dissolved carbon dioxide from the tank. At this time, the gas discharged from the decarbonation tank 2 contains not only carbon dioxide but also odorous gases derived from the raw water W0 or treated water W3. Therefore, it is preferable to transfer the gas discharged from the decarbonation tank 2 to a deodorization facility and perform deodorization treatment.

[0023] In this embodiment, treated water W3 is supplied to the decarbonation tank 2 from the reaction unit 4 via line L4. As will be described later, the treated water W3 contains microbial cells (anaerobic bacteria such as acid-producing bacteria and methane-producing bacteria) used in anaerobic treatment. Therefore, especially when the pH of the raw water W0 is on the alkaline side, the acid production reaction proceeds in the decarbonation tank 2 when the raw water W0 and the treated water W3 containing acid-producing bacteria are mixed. This acid generation reaction makes the pH of the solution in the decarboxylation tank 2 more acidic, thereby increasing the efficiency of decarboxylation by aeration, and also improving the efficiency of the acid generation process in the subsequent acid generation tank 3. The treated water W1, which has been treated in the decarbonation tank 2, is then introduced into the acid generation tank 3 via line L2.

[0024] In cases where the main components of the raw water W0 are high concentrations of lower alcohols and organic acids, and there are few substances to be decomposed by acid-producing bacteria, or when the pH of the raw water W0 is acidic, the treatment performed in the decarboxylation tank 2 is sufficient with only decarboxylation treatment by the decarboxylation means 21.

[0025] On the other hand, if the main components of the 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 if the pH of the raw water W0 is alkaline, it is preferable to perform acid generation treatment in conjunction with decarbonation treatment in the decarbonation tank 2. As described later, in the treatment in the acid generation tank 3, it is preferable that the pH of the solution to be treated (treated water W1) be weakly acidic. Therefore, by performing acid generation treatment on some components in the decarbonation tank 2, it is possible to make the pH of the treated water W1 more acidic without adding strong acids such as hydrochloric acid, and thus promote the acid generation treatment in the subsequent acid generation tank 3. In addition, by partially carrying out the acid generation treatment in the decarbonation tank 2, it is possible to improve the wastewater treatment efficiency for the raw water W0 in conjunction with the acid generation treatment in the acid generation tank 3.

[0026] The acid production treatment in the decarbonation tank 2 may be carried out by adding acid-producing bacteria to the decarbonation tank 2 from outside the system, but it is also possible to perform the acid production treatment using the bacterial cells contained in the treated water W3. Specifically, this may involve providing a means to add nutrients required by the acid-producing bacteria to the decarbonation tank 2, or using an oxygen-free gas introduced from the diffuser pipe 22 or using a decarbonation means 21 other than aeration in order to create an anaerobic or microaerophilic atmosphere inside the decarbonation tank 2.

[0027] In this case, the acid generation treatment in the decarbonation tank 2 only needs to be able to neutralize or slightly acidify the pH of the raw water W0, and does not need to completely carry out the acid generation treatment on the raw water W0. For this reason, it is preferable to set the residence time of the solution (raw water W0 and treated water W3) in the decarbonation tank 2 to be shorter than the residence time of the solution (treated water W1) in the acid generation tank 3. More specifically, this can be achieved by making the volume of the decarbonation tank 2 smaller than the volume of the acid generation tank 3, or by adjusting the flow rates in each line L1 to L3 so that the amount of solution introduced into the decarbonation tank 2 is less than the amount of solution introduced into the acid generation tank 3.

[0028] Furthermore, the decarbonation tank 2 in this embodiment may be equipped with various additional facilities. For example, the decarbonation tank 2 may be equipped with a means for adjusting the internal water temperature. In particular, it is preferable to provide a heating means in the decarbonation tank 2. The heating means can be any means that can raise the temperature of the solution (raw water W0 and treated water W3) in the decarbonation tank 2, and its specific structure is not particularly limited, and it may be provided either inside or outside the decarbonation tank 2. This makes it possible to increase the decarbonation treatment efficiency in the decarbonation tank 2. Furthermore, by providing a temperature control (temperature adjustment) function in the heating means and maintaining the temperature inside the decarbonation tank 2 at a temperature suitable for acid generation treatment, it is possible to improve the decarbonation treatment efficiency and promote the acid generation treatment in the decarbonation tank 2. Note that the heating means itself also functions as a decarbonation means 21, but by combining it with the other decarbonation means 21 described above, it is possible to further improve the decarbonation treatment efficiency.

[0029] The acid generation tank 3 is a tank for performing an acid generation treatment (acid generation step) in which organic matter in the water to be treated W1 is decomposed by acid-producing bacteria, which are facultative anaerobic bacteria, under an anaerobic atmosphere without dissolved oxygen, and organic acids are produced. As shown in Figure 1, the water to be treated W1 is supplied to the acid generation tank 3 via line L2. In the acid generation tank 3, the components contained in the water to be treated W1 are decomposed by the acid-producing bacteria contained inside. It is desirable that the acid generation tank 3 be a closed system and that an anaerobic environment be maintained. One example of decomposition by acid generation treatment is the decomposition of high molecular weight organic substances such as polysaccharides and proteins contained in the treated water W1 into low molecular weight organic substances such as monosaccharides, amino acids, and lower fatty acids (hydrolysis), and further decomposition of these low molecular weight organic substances into lower alcohols, acetic acid, hydrogen, methane, carbon dioxide, etc. (acid fermentation).

[0030] The treated water W2 after the acid generation treatment is discharged from the acid generation tank 3 via line L3 and introduced into the reaction section 4. The biogas G1 generated by the acid generation treatment is discharged outside the acid generation tank 3 via line L6. In order to effectively utilize the biogas G1 (mainly hydrogen and methane) discharged from the acid generation tank 3, it is preferable that line L6 be connected to means for the recovery, purification, and storage of biogas G1 (hydrogen and methane).

[0031] The acid-producing bacteria contained in the acid-producing tank 3 may be added to the acid-producing tank 3 from outside the system, or they may be collected from the anaerobic microbial layer M in the reaction unit 4, which will be described later. More specifically, the acid-producing treatment may be carried out using the 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-producing tank 3 in the same state as they are contained in the water to be treated W1, so these bacterial cells can be used. Alternatively, a line may be provided connecting the reaction unit 4 and the acid-producing tank 3, and a portion of the treated water W3 may be supplied to the acid-producing tank 3.

[0032] The acid-producing tank 3 in this embodiment may be equipped with various additional facilities. For example, the acid-producing tank 3 may be equipped with means for adjusting the internal water temperature and means for adding metals such as nitrogen, phosphorus, cobalt, and nickel, which are nutrients required by the acid-producing bacteria. Alternatively, the acid-producing tank 3 may use a carrier that holds the acid-producing bacteria.

[0033] The reaction unit 4 is for performing a reaction step in which the water to be treated W2, which has been treated in the acid generation tank 3, is subjected to anaerobic treatment. As shown in Figure 1, the reaction unit 4 is equipped with a methane fermentation tank 41 and a separation device 42 located in the upper part of the methane fermentation tank 41 for separating biogas G2 (mainly methane), treated water W3, and solid components.

[0034] The methane fermentation tank 41 is for performing methane fermentation, which generates methane from the carbon source contained in the treated water W2 treated in the acid production tank 3. Methane fermentation is a type of anaerobic treatment carried out in an anaerobic atmosphere without dissolved oxygen by methane-producing bacteria maintained in the methane fermentation tank 41 by methods such as the suspension method, fixed bed method, fluidized bed method, UASB method, and EGSB method. It is essential that the methane fermentation tank 41 is a closed system and that an anaerobic environment is maintained. Examples of reactions in methane fermentation include the decomposition of organic matter (mainly acetic acid) into methane and carbon dioxide, and the production of methane from carbon dioxide and hydrogen. The methane produced at this time is separated and recovered as biogas G2 by the separation device 42, but a high proportion of carbon dioxide remains dissolved in the treated water W3.

[0035] The methane-producing bacteria retained in the methane fermentation tank 41 are not particularly limited. For example, isolated microorganisms may be used, or seed sludge from other anaerobic treatment facilities may be used. Alternatively, anaerobic microorganisms contained in the raw water W0 (water to be treated W2) may be utilized.

[0036] The form of the methanogenic bacteria that form the layer (anaerobic microbial layer M) is not particularly limited, but for example, granules of microorganisms with a diameter of about 0.3 to 3 mm, called granules, can be used. Granules are microbial masses that utilize self-immobilization, and it is possible to maintain a high concentration of microbial cells. Therefore, by using granules, an anaerobic microbial layer M with a high concentration of methanogenic bacteria is formed in the methane fermentation tank 41. Furthermore, instead of the granule layer, a carrier layer consisting of a carrier holding methanogenic bacteria may be used as the anaerobic microbial layer M.

[0037] It is preferable to provide means for recovering or reusing the biogas G2 (methane), treated water W3, and solid components separated by the separation device 42. For example, it is preferable to transfer the methane to a means for recovery, purification, and storage via line L7 in order to effectively utilize it as biogas G2. In addition to being discharged outside the system via line L5, the treated water W3 is returned to the decarbonation tank 2 via line L4 to adjust the pH of the raw water W0 in the decarbonation tank 2 and the pH of the treated water W3 itself. Furthermore, since the solid components contain methane-producing bacteria, it is preferable to retain them in the methane fermentation tank 41 using the separation device 42 to prevent them from flowing outside the system. A portion of the solid components may be supplied to the decarbonation tank 2 or the acid production tank 3 and used as seed sludge for acid-producing bacteria.

[0038] The reaction unit 4 in this embodiment may be further equipped with various auxiliary facilities. For example, the reaction unit 4 may be equipped with means for adjusting the internal water temperature and means for adding metals such as nitrogen, phosphorus, cobalt, and nickel, which are nutrients required by methane-producing bacteria.

[0039] In the wastewater treatment apparatus 1A of this embodiment, the decarbonation tank 2 and the acid production tank 3 are separated, and the treated water W3, which has been anaerobically treated in the reaction unit 4, is returned to the decarbonation tank 2 and mixed with the raw water W0. This makes it possible to adjust the pH to a certain extent in each tank (decarbonation tank 2, acid production tank 3, methane fermentation tank 41) that performs wastewater treatment without using chemicals for pH adjustment. On the other hand, it is known that there is an optimal pH range for acid production treatment and methane production treatment. In order to further improve wastewater treatment efficiency, the acid production tank 3 and methane fermentation tank 41 may be equipped with means for measuring pH (pH meter) and means for adding pH adjusting chemicals (pH adjusting agents) to adjust the pH in the acid production tank 3 and methane fermentation tank 41. As pH adjusting agents, known substances should be used for both acids and alkalis.

[0040] At this time, the water to be treated W1 introduced from the decarbonation tank 2 to the acid generation tank 3 needs to be weakly acidic, suitable for acid generation treatment, while the water to be treated W2 introduced from the acid generation tank 3 to the methane fermentation tank 41 needs to be neutral, suitable for methane generation treatment. As described above, the treated water W1 processed in the decarbonation tank 2 can be easily made weakly acidic without using a pH adjuster, depending on the properties of the raw water W0. Therefore, the amount of pH adjuster used for the treated water W1 in the decarbonation tank 2 can be significantly reduced, or no pH adjuster can be used at all. On the other hand, the treated water W2 introduced from the acid generation tank 3 to the methane fermentation tank 41 will have its pH lowered because acid is generated during the acid generation process. Therefore, in order to neutralize the water in a way suitable for methane generation, it is preferable to provide a means for adding alkali as a pH adjuster in the acid generation tank 3. In this case, by allowing part of the acid generation process to proceed in the decarbonation tank 2, it is possible to suppress the decrease in pH in the acid generation tank 3 and reduce the amount of pH adjuster used to neutralize the treated water W2.

[0041] As described above, the wastewater treatment apparatus 1A of this embodiment and the wastewater treatment method using this wastewater treatment apparatus 1A separate the decarbonation tank 2 and the acid production tank 3, eliminating the need for decarbonation treatment in the acid production tank 3. This makes it possible to suppress the decrease in treatment efficiency due to excessive aeration caused by decarbonation treatment in the acid production tank, and the decrease in the recovery rate of useful biogas generated in the acid production tank. Here, since the acid production treatment is a reaction that proceeds under microaerobic and anaerobic conditions, by placing the decarbonation tank 2 before the acid production tank 3, the appropriate amount of dissolved oxygen in the water to be treated W1 introduced into the acid production tank 3 improves the efficiency of the acid production treatment and increases the recovery rate of biogas G1.

[0042] [Second Embodiment] Figure 2 is a schematic diagram illustrating a wastewater treatment apparatus 1B according to a second embodiment of the present invention. As shown in Figure 2, the wastewater treatment apparatus 1B according to this embodiment has a return pipe (line L4) connected to the upper part of the decarbonation tank 2 as a decarbonation means 21, which returns treated water W3 from the reaction unit 4 (methane fermentation tank 41) to the decarbonation tank 2, and introduces the treated water W3 into the decarbonation tank 2 from the upper part of the decarbonation tank 2. Note that the components of the wastewater treatment device 1B in this embodiment that are the same as those of the wastewater treatment device 1A in the first embodiment will not be described.

[0043] In this embodiment, the wastewater treatment device 1B uses a return pipe (line L4) that returns the treated water W3, which has been anaerobically treated in the reaction unit 4, to the decarbonation tank 2. The connection point of the return pipe (line L4) to the decarbonation tank 2 is located at the top of the decarbonation tank 2. Decarbonation (deaeration) is performed by the impact when the treated water W3 falls into the decarbonation tank 2 via line L4. This makes it possible to save energy compared to decarbonation treatments that use drive devices such as aeration.

[0044] In this embodiment, the decarbonation means 21 can be connected to the return piping (line L4) and the decarbonation tank 2 at any point on the upper part of the decarbonation tank 2, such as the ceiling of the decarbonation tank 2 or the upper side of the decarbonation tank 2. Furthermore, the piping shape, opening shape, and direction of the opening of line L4 connected to the decarbonation tank 2 are not particularly limited, as long as they can provide sufficient impact to enable decarbonation (deaeration) when the treated water W3 falls into the decarbonation tank 2. For example, line L4 may have a structure that allows for a so-called waterfall-like flow.

[0045] Furthermore, in addition to performing a waterfall-like cascading action by arranging line L4, the decarbonation means 21 in this embodiment may also include a mechanism to further enhance the decarbonation efficiency. Figure 3 is a schematic diagram illustrating another embodiment of the wastewater treatment device 1B in this embodiment. As shown in Figure 3, another embodiment 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. By adding pressurized air to the treated water W3, the pressure applied to the treated water W3 is released when the treated water W3 is introduced (discharged) from line L4 to the decarbonation tank 2, thereby enhancing the decarbonation effect. Furthermore, 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 a structure that functions as an aspirator, which increases the velocity of the fluid (treated water W3) flowing through line L4 by narrowing a portion of line L4 and providing an air intake. This increases the inflow velocity of the treated water W3 introduced (discharged) from line L4 to the decarbonation tank 2 without using power such as a pump, and also allows more air to be dissolved in the treated water W3, further enhancing the decarbonation effect associated with the impact of the falling water.

[0046] Furthermore, the decarbonation means 21 in this embodiment may include a structure that the treated water W3 comes into contact with as it falls through the decarbonation tank 2. This means that the treated water W3 is subjected not only to the impact of falling water but also to the impact of contact with the structure, thereby increasing the decarbonation efficiency.

[0047] As described above, in the wastewater treatment apparatus 1B and the wastewater treatment method using this wastewater treatment apparatus 1B in this embodiment, a drive device is not particularly required in the decarbonation treatment, making it possible to save energy for the wastewater treatment apparatus 1B as a whole.

[0048] The embodiments described above are merely examples of wastewater treatment apparatus and wastewater treatment methods. The wastewater treatment apparatus and wastewater treatment method according to the present invention are not limited to the embodiments described above, and the wastewater treatment apparatus and wastewater treatment method according to the embodiments described above may be modified without changing the gist of the claims.

[0049] For example, multiple decarbonation methods described in this embodiment may be combined. This makes it possible to improve the decarbonation treatment efficiency in the decarbonation tank. [Industrial applicability]

[0050] The wastewater treatment apparatus and wastewater treatment method of the present invention are suitably used for anaerobic treatment of wastewater containing organic matter. [Explanation of Symbols]

[0051] 1A, 1B Wastewater treatment device, 2 Decarbonation tank, 21 Decarbonation means, 22 Aeration pipe, 23 Blower, 24 Air inlet, 3 Acid generation tank, 4 Reaction unit, 41 Methane fermentation tank, 42 ​​Separation device, L1~L7 Lines, G1, G2 Biogas, M Anaerobic microbial layer, W0 Raw water, W1, W2 Treated water, W3 Treated water

Claims

1. A decarboxylation tank that performs decarbonation, deoxygenation, and acid generation treatments, An acid generation tank that generates acid downstream of the decarbonation tank, The system includes a reaction section that performs anaerobic treatment downstream of the acid production tank, Raw water is introduced into the decarbonation tank, and the treated water, after being subjected to anaerobic treatment in the reaction section, is returned to the decarbonation tank. A wastewater treatment apparatus characterized by the aforementioned decarbonation.

2. The wastewater treatment apparatus according to claim 1, characterized in that the decarbonation tank is equipped with a heating means.

3. A decarbonation tank for performing decarbonation treatment, An acid generation tank that generates acid downstream of the decarbonation tank, The system includes a reaction section that performs anaerobic treatment downstream of the acid production tank, The aforementioned decarbonation tank is equipped with a heating means, A wastewater treatment apparatus 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.

4. The wastewater treatment apparatus according to any one of claims 1 to 3, characterized in that the treated water, after being subjected to anaerobic treatment in the reaction section, is returned from the top of the decarbonation tank.

5. A decarboxylation step that performs deoxygenation and acid generation along with decarboxylation treatment, An acid generation step is performed after the decarboxylation step, The reaction step comprises an anaerobic treatment step following the acid production step, A wastewater treatment method characterized in that raw water is introduced into the decarbonation step, and the treated water after the reaction step is returned to the decarbonation step.

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