Organic wastewater treatment system and organic wastewater treatment method

Abstract

To provide an organic wastewater treatment system and an organic wastewater treatment method that can realize stable and efficient operation.SOLUTION: There is provided an organic wastewater treatment system 1 including an anaerobic wastewater treatment unit 5 including an anaerobic wastewater treatment tank 51 for methane fermentation of organic wastewater, a demethanation / carbonation unit 6, a methanation unit 8, and control means, the system including: biogas supply means for supplying methane and carbon dioxide generated in the anaerobic wastewater treatment tank 51 to the methanation unit 8; methane fermentation treated water supply means for supplying methane fermentation treated water generated in the anaerobic wastewater treatment tank 51 to the demethanation / carbonation unit 6 and the methanation unit 8; hydrogen supply means for supplying hydrogen gas to the demethanation / carbonation 6 to vaporize dissolved methane and dissolved carbon dioxide in the methane fermentation treated water; and demethanation / carbonation supply means for supplying vaporized methane, carbon dioxide, and hydrogen to the methanation unit 8. The system is configured to be able to perform methanation using carbon dioxide and hydrogen supplied to the methanation unit 8.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an organic wastewater treatment system and an organic wastewater treatment method for treating organic wastewater. [Background technology]

[0002] The upflow anaerobic sludge blanket (UASB) method is known as a method for producing biogas by methane fermentation (anaerobic treatment) of organic wastewater discharged from food and chemical factories.

[0003] The UASB method is a high-load treatment method in which raw water flows upward from the bottom of the reaction tank, and the sludge is blocked or granulated without using a carrier for bacterial adhesion to form a sludge blanket of granular sludge with a particle size of 1 to several mm, maintaining a high concentration of microorganisms in the reaction tank. Compared to the aerobic activated sludge method, this method has an organic matter load per reaction tank volume of 10 kg-CODCr / m 3 / day or more. Furthermore, it has other excellent features such as no need for energy for aeration, energy recovery possible in the form of methane gas, and little excess sludge generation.

[0004] Methane fermentation involves two pathways: one that breaks down acetic acid into methane, and the other that produces methane from carbon dioxide and hydrogen (biomethanation). As biomethanation progresses, the pH of the methane fermentation liquid increases, reducing the efficiency of methane gas production. To address this issue, the method described in Patent Document 1 has been proposed. In the method described in Patent Document 1, when the methanation reaction progresses and the sludge pH in the methane fermentation tank reaches 9.0 or higher, the increase in pH is suppressed by stopping the supply of hydrogen to the methane fermentation tank or by injecting biogas into the tank. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2024-002180 Summary of the Invention [Problem to be solved by the invention]

[0006] The linear velocity (Lv) of the wastewater supplied to the tank to retain the granules in the lower part of the tank is generally around 1 to 2 m / h. However, if hydrogen gas is supplied to the UASB tank to convert carbon dioxide in the biogas into methane for biomethanation, the linear velocity of the fluid (total of wastewater and hydrogen gas) increases significantly. In this case, the granules cannot be retained and multiplied in the lower part of the tank, which reduces the organic wastewater treatment capacity and may eventually lead to an inability to treat the wastewater.

[0007] The granules are composed of acetogenic methanogens, hydrogen-utilizing methanogens, etc. Acetogenic methanogens are important for maintaining the self-aggregation properties of the granules, but supplying hydrogen gas to the UASB tank increases the proportion of hydrogen-utilizing methanogens, which changes the composition of the bacteria that make up the granules and may affect the self-aggregation properties of the granules.

[0008] The UASB treated water discharged from the UASB tank contains dissolved methane. If the UASB treated water is released into the atmosphere, the dissolved methane will be released into the atmosphere as methane gas, causing a greenhouse effect.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an organic wastewater treatment system and an organic wastewater treatment method that can realize more stable and efficient operation than conventional systems. [Means for solving the problem]

[0010] The organic wastewater treatment system according to the present invention for achieving the above object has the following characteristic configuration: An organic wastewater treatment system comprising: an anaerobic wastewater treatment unit having an anaerobic wastewater treatment tank in which an aggregate containing methanogens is provided in a lower portion and which performs methane fermentation of organic wastewater; a demethanization / carbonation unit; a methanation unit; and a control means for controlling operation, a biogas supply means for supplying methane and carbon dioxide generated by methane fermentation in the anaerobic wastewater treatment tank to the methanation unit; a methane fermentation treated water supply means for supplying methane fermentation treated water generated by methane fermentation in the anaerobic wastewater treatment tank to the demethanizer / carbonator and the methanation unit; a hydrogen supply means for supplying hydrogen gas to the demethanization / carbonation section to vaporize the methane and carbon dioxide dissolved in the methane fermentation treated water; a demethanizer / carbonator supply means for supplying the methane, carbon dioxide, and hydrogen vaporized in the demethanizer / carbonator to the methanation section, The feature is that methanation can be carried out using the carbon dioxide supplied by the biogas supply means and the carbon dioxide and hydrogen supplied by the demethanizer / carbonate supply means.

[0011] According to the above characteristic configuration, hydrogen gas is supplied to the demethanizer / carbonator section rather than the anaerobic wastewater treatment tank. Because only organic wastewater is supplied to the anaerobic wastewater treatment tank, the linear velocity of the fluid supplied to the anaerobic wastewater treatment tank is reduced, allowing aggregates containing methanogens to be retained at the bottom of the anaerobic wastewater treatment tank. Furthermore, the bacterial composition of the aggregates is prevented from becoming dominated by hydrogen-utilizing methanogens, which does not affect the self-aggregation properties of the aggregates. The hydrogen gas supplied by the hydrogen supply means can vaporize the methane and carbon dioxide dissolved in the methane fermentation treated water. The demethanizer / carbonate supply means can supply the vaporized methane, carbon dioxide, and hydrogen to the methanation section. This prevents methane dissolved in the methane fermentation treated water from escaping into the atmosphere. The methanation unit is configured to methanate using carbon dioxide supplied from the anaerobic wastewater treatment unit and carbon dioxide and hydrogen supplied from the demethanizer / carbonate unit, which allows for a greater amount of energy recovery in the form of methane gas than when organic wastewater is treated using the anaerobic wastewater treatment unit alone. Therefore, the above-described characteristic configuration can reduce the dissolved methane concentration after wastewater treatment. In addition, the efficiency of methane fermentation in anaerobic wastewater treatment is not adversely affected, and the carbon dioxide generated by methane fermentation can be converted into methane, increasing the amount of energy recovered, enabling more stable and efficient operation than conventional systems.

[0012] Further characteristic configurations of the organic wastewater treatment system according to the present invention include: The control means controls the hydrogen supply means so as to allow a portion of the hydrogen gas to be supplied to the methanation section.

[0013] When methane fermentation treated water flows down from the top of the demethanizer / carbonator, if the amount of methane fermentation treated water supplied to the demethanizer / carbonator is small and the amount of hydrogen gas supplied is large, it may be impossible to discharge the treated water. According to the above characteristic configuration, the control means is configured to be able to control the supply of some of the hydrogen gas to the methanation section as well. In this way, methanation, which converts carbon dioxide into methanation, can be performed in the methanation section, enabling more stable and efficient operation than conventional systems.

[0014] Further characteristic configurations of the organic wastewater treatment system according to the present invention include: The control means adjusts the amount of methane fermentation treated water supplied to the methanation section by the methane fermentation treated water supply means to a supply amount necessary for maintaining methane bacteria in the methanation section.

[0015] The methanation section contains methanogens that methanate the carbon dioxide and hydrogen supplied to it. Because methanation is a biological treatment process, unless the methanogens are maintained under appropriate nutrient concentrations and solution residence times, a sufficient methane production rate cannot be maintained stably. According to the above-described characteristic configuration, the control means adjusts the amount of methane fermentation treated water supplied to the methanation unit to the amount necessary to maintain methane bacteria in the methanation unit. The methane bacteria in the methanation unit utilize the nutrients contained in the methane fermentation treated water, allowing methane bacteria to be maintained at a high density in the methanation unit. Furthermore, because the methane fermentation treated water contains methane bacteria, it is possible to supply methane bacteria to the methanation unit. Therefore, according to the above characteristic configuration, it is possible to appropriately maintain methane bacteria in the methanation section, enabling more stable and efficient operation than conventional systems.

[0016] Further characteristic configurations of the organic wastewater treatment system according to the present invention include: The present invention is characterized in that it comprises, upstream of the anaerobic wastewater treatment unit, an acid production unit which performs acid fermentation on the organic wastewater, and a pH adjustment unit which neutralizes the acid-fermented solution produced in the acid production unit to a pH of 5.0 or more and 7.5 or less using a pH adjuster and supplies the neutralized solution to the anaerobic wastewater treatment unit.

[0017] When organic wastewater that has only been neutralized without undergoing acid fermentation is supplied to an anaerobic wastewater treatment plant, acid fermentation, which lowers the pH, and methane fermentation, which uses organic acids to raise the pH, occur simultaneously. This makes the pH unstable, making it difficult to achieve stable methane fermentation. According to the above-described characteristic configuration, the acid production unit performs acid fermentation on the organic wastewater to produce an acid-fermented solution by decomposing the organic matter contained in the organic wastewater into organic acids. The pH adjustment unit then adjusts the pH of the acid-fermented solution to a pH suitable for methane fermentation in the anaerobic wastewater treatment unit. Therefore, according to the above characteristic configuration, the pH of the methane fermentation treated water can be maintained, and stable and efficient operation is possible.

[0018] Further characteristic configurations of the organic wastewater treatment system according to the present invention include: The control means adjusts the amount of the methane fermentation treated water supplied by the methane fermentation treated water supply means so that the pH in the methanation section is 9.0 or less.

[0019] As methanation progresses, the amount of carbon dioxide in the methanation section decreases, the pH rises, and the activity of methane bacteria decreases, putting the system at risk of shutting down. According to the above-described characteristic configuration, when the methane concentration in the methanation unit increases as methanation progresses and the pH exceeds 9.0, the amount of methane fermentation-treated water supplied by the methane fermentation-treated water supply means is increased. Because the pH of methane fermentation-treated water is approximately 7.0 to 8.0, the pH in the methanation unit can be reduced to 9.0 or below more quickly than by simply reducing the flow rate of hydrogen supplied to the demethanizer / carbonate unit or methanation unit. This makes it easier to maintain the pH in the methanation unit below a certain value, preventing situations in which an increase in pH in the methanation unit reduces the activity of methanogens, reduces operating efficiency, and causes the system itself to malfunction. Therefore, according to the above characteristic configuration, the pH in the methanation unit can be kept lower than a certain value, enabling more stable and efficient operation than conventional methods.

[0020] Further characteristic configurations of the organic wastewater treatment system according to the present invention include: the methanation unit includes a methanation-treated water supply means for recovering methanation-treated water produced by the methanation and supplying the water to the pH adjustment unit; The control means adjusts the amount of the methanation-treated water supplied by the methanation-treated water supply means so that the neutralization solution in the pH adjustment unit has a pH of 5.0 or higher and 7.5 or lower and a COD of 2000 mg / L or higher.

[0021] Because the methanation-treated water discharged from the methanation unit has a high pH (approximately 7.5 to 9.0), returning it to the pH adjustment unit reduces the amount of pH adjuster used in the pH adjustment unit. However, depending on the organic matter concentration in the organic wastewater, increasing the supply of methanation-treated water may reduce the COD of the neutralization solution supplied to the anaerobic wastewater treatment tank, potentially reducing the efficiency of methane fermentation. To avoid this, the control unit can adjust the amount of methanation-treated water supplied and the amount of pH adjuster added so that the neutralization solution meets the pH standards of 5.0 to 7.5 and a COD of 2000 mg / L or more, thereby preventing excessive dilution of the neutralization solution. Furthermore, because the methanation-treated water has a temperature of approximately 55°C, the neutralization solution can be heated to a temperature suitable for anaerobic wastewater treatment. Therefore, according to the above characteristic configuration, a neutralized solution with appropriate conditions can be produced, enabling more stable and efficient operation than conventional methods.

[0022] Further characteristic configurations of the organic wastewater treatment system according to the present invention include: The control means controls the temperature in the methanation unit to be 50°C or higher and 60°C or lower.

[0023] Methane fermentation in the anaerobic wastewater treatment unit is generally carried out at medium temperatures (30°C to 40°C), but methanation in the methanation unit is carried out at high temperatures (50°C to 60°C), which further increases the efficiency of methane production. Therefore, according to the above characteristic configuration, methanation efficiency is improved, and more stable and efficient operation than conventional is possible.

[0024] Further characteristic configurations of the organic wastewater treatment system according to the present invention include: the acid production unit, the anaerobic wastewater treatment unit, and the methanation unit are each provided with a heat retention means for retaining hot water to prevent loss of internal heat, The present invention is characterized in that it includes a hot water resupply flow path that can supply the hot water supplied to the heat retention means of the methanation section to the heat retention means of the acid production section and the anaerobic wastewater treatment tank.

[0025] Methane fermentation in anaerobic wastewater treatment tanks is carried out at a medium temperature (30°C to 40°C). However, the temperature of organic wastewater is room temperature (about 15 to 25°C), and heating the large amount of organic wastewater discharged to a temperature suitable for methane fermentation requires a large amount of energy, making it uneconomical. The methanation reaction carried out by hydrogen-utilizing methanogens in the methanation unit is an exothermic reaction, and is carried out at a high temperature (50°C or higher and 60°C or lower). In the above-mentioned characteristic configuration, a hot water resupply flow path is provided that can supply the hot water used in the heat retention means of the methanation unit to the heat retention means of the acid production unit and the anaerobic wastewater treatment tank. The system is configured so that the heat (50°C or higher and 60°C or lower) used to keep the methanation tank warm can be used to heat the acid production unit and the anaerobic wastewater treatment tank. Therefore, according to the above characteristic configuration, it is possible to realize effective use of heat, and to achieve more stable and efficient operation than conventionally possible.

[0026] Further characteristic configurations of the organic wastewater treatment system according to the present invention include: The anaerobic wastewater treatment tank is of an upward flow type that treats the organic wastewater.

[0027] The use of an upward flow system for treating organic wastewater in an anaerobic treatment tank is suitable because it has a high methane conversion capacity relative to the amount of organic matter in the high-concentration organic wastewater and a fast reaction treatment speed.

[0028] The characteristic configuration of the organic wastewater treatment method according to the present invention is as follows: An organic wastewater treatment method comprising an anaerobic wastewater treatment step of methane fermenting organic wastewater, a demethanization / carbonation step, and a methanation step, A step of supplying methane and carbon dioxide generated by methane fermentation in the anaerobic wastewater treatment step to the methanation step; a step of supplying methane fermentation treated water generated by methane fermentation in the anaerobic wastewater treatment step to a demethanization / carbonation step and the methanation step; a step of supplying hydrogen gas to the demethanization / carbonation step to vaporize the methane and carbon dioxide dissolved in the methane fermentation treated water; and a step of supplying the methane, carbon dioxide and hydrogen vaporized in the demethanization / carbonation step to the methanation step, The feature is that methane is produced by methanation using the carbon dioxide and hydrogen supplied by the anaerobic wastewater treatment step and the demethanization and carbonation step.

[0029] Further characteristic features of the organic wastewater treatment method according to the present invention are: The amount of the methane fermentation treated water supplied to the methanation step is adjusted to a supply amount necessary for maintaining methane bacteria in the methanation step.

[0030] Further characteristic features of the organic wastewater treatment method according to the present invention are: The method comprises, before the anaerobic wastewater treatment process, an acid production process in which the organic wastewater is acid-fermented, and a pH adjustment process in which a pH adjuster is added to the acid-fermented solution produced in the acid production process to neutralize the pH to 5.0 or more and 7.5 or less, and the neutralized solution is supplied to the anaerobic wastewater treatment process.

[0031] Further characteristic features of the organic wastewater treatment method according to the present invention are: The point is to control the amount of the methane fermentation treated water supplied by the anaerobic wastewater treatment step so that the pH in the methanation step is 9.0 or less.

[0032] Further characteristic features of the organic wastewater treatment method according to the present invention are: The methanation-treated water produced by the methanation is supplied to the pH adjustment step, The amount of the methanation-treated water to be supplied is controlled so that the pH of the neutralization solution is 5.0 or more and 7.5 or less and the COD is 2000 mg / L or more.

[0033] Further characteristic features of the organic wastewater treatment method according to the present invention are: The methanation step is controlled to a temperature of 50°C or higher and 60°C or lower.

[0034] Further characteristic features of the organic wastewater treatment method according to the present invention are: The heat generated in the methanation step is reused as a heat source for keeping the temperature of the acid production step and the anaerobic wastewater treatment step.

[0035] Further characteristic features of the organic wastewater treatment method according to the present invention are: The methane fermentation is carried out by treating the organic wastewater in an upward flow manner. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a diagram showing a schematic configuration of an organic wastewater treatment system according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing a schematic configuration of an organic wastewater treatment system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0037] Hereinafter, organic wastewater treatment systems 1 and 10 according to embodiments of the present invention will be described with reference to the drawings.

[0038] [Configuration of the organic wastewater treatment system according to the first embodiment] First, the configuration of an organic wastewater treatment system 1 according to the first embodiment will be described. Fig. 1 is a diagram showing a schematic configuration of the organic wastewater treatment system 1 according to the first embodiment. As shown in Fig. 1, the organic wastewater treatment system 1 includes a raw water tank 21, an acid production section 3, a pH adjustment section 4, an anaerobic wastewater treatment section 5, a demethanization / carbonation section 6, a hydrogen supply section 7 (an example of hydrogen supply means), and a methanation section 8. The operation of each section can be controlled by a control device A (an example of control means).

[0039] The raw water tank 21 is equipped with an organic wastewater supply section 22 that receives organic wastewater as raw water, and a raw water discharge section 23 that discharges raw water. Even if the flow rate of the organic wastewater discharged from the source fluctuates, it is configured so that it can be supplied to the acid generator 3 at a constant flow rate by being retained in the raw water tank 21.

[0040] [Acid generating part] The acid production section 3 is equipped with an acid production tank 31 that performs acid fermentation on raw water supplied from the raw water tank 21, and is configured so that the acid production tank 31 is equipped with a raw water supply section 32 that receives raw water and an acid fermentation liquid discharge section 33 that discharges acid fermented acid fermentation liquid. The acid production tank 31 contains sludge mainly composed of facultative anaerobic bacteria inside, and is configured so that an acid production step can be performed in which raw water supplied to the acid production tank 31 is acid fermented to produce organic acids such as acetic acid. The entire outer periphery of the acid generating tank 31 is provided with a jacket 34 (an example of a heat retention means) filled with hot water to prevent internal heat loss. The bottom of the jacket 34 is provided with a hot water supply section 34a for supplying hot water, a hot water supply path 34b, and a hot water discharge section 34c for discharging the hot water. Hot water is injected into the jacket 34 from a hot water tank (not shown). The supply and discharge of this hot water may be a circulating system.

[0041] [pH adjustment section] The pH adjustment unit 4 includes a pH adjustment tank 41 for neutralizing the acid-fermented solution. The pH adjustment tank 41 includes an acid-fermented solution supply unit 42 for receiving the acid-fermented solution, and a pH adjuster supply unit 44 for supplying a pH adjuster 4a, such as sodium hydroxide. The pH adjustment tank 41 is configured to mix the acid-fermented solution from the acid production unit 3 with the pH adjuster 4a to perform the pH adjustment process. The pH adjustment tank 41 is also equipped with a pH meter 91 and a COD meter 92, which measure the pH and COD of the neutralized solution in the pH adjustment tank 41. The control device A determines whether the pH and COD of the neutralized solution are within a predetermined range (e.g., pH 5.0 to 7.5 and COD 2000 mg / L or greater). If the pH and COD are within the predetermined range, the neutralized solution is sent from the neutralized solution discharge unit 43 to the anaerobic wastewater treatment tank 51. If the pH and COD are not within the predetermined range, the control device A is configured to perform the pH adjustment process again.

[0042] In this embodiment, the operation of a pump (not shown) provided in the neutralizing solution discharge section 43 can be controlled by the control device A. Therefore, the neutralizing solution can be supplied to the anaerobic wastewater treatment tank 51 in any amount and at any timing.

[0043] In addition to the pH adjuster input section 44, the pH adjustment section 4 is equipped with a methanation-treated water supply section 45, and is configured so that the acid-fermented solution can be neutralized by substituting methanation-treated water for part or all of the pH adjuster 4a to be supplied from the pH adjuster input section 44. Based on the pH and COD measurement results, the control device A can also control the supply amounts of pH adjuster 4a and methanation-treated water so that the pH and COD of the neutralized solution fall within the above-mentioned ranges. Furthermore, the pH adjuster 4a is not limited to sodium hydroxide, and an aqueous solution of an alkaline reagent such as potassium hydroxide or calcium hydroxide can also be used.

[0044] [Anaerobic wastewater treatment unit] The anaerobic wastewater treatment unit 5 includes an anaerobic wastewater treatment tank 51. The anaerobic wastewater treatment tank 51 includes a sludge bed 54 at its bottom, which is filled with granules (aggregates) composed primarily of anaerobic bacteria, such as hydrogen-utilizing methanogens and acetogenic methanogens. The granules are black granular materials that utilize the self-granulating function of anaerobic microorganisms. The granules can retain a high density and high activity of methanogens without using a carrier for immobilizing the microorganisms. The anaerobic wastewater treatment tank 51 also includes a neutralizing solution supply unit 52 at its bottom, which supplies the neutralizing solution from the pH adjustment unit 4. This creates an upward flow of the introduced neutralizing solution and promotes circulation of the neutralizing solution inside, enabling the methane fermentation process (anaerobic wastewater treatment process) in which organic matter is fermented into methane by the flowing granules. The anaerobic wastewater treatment tank 51 may be any reaction tank capable of anaerobically treating organic wastewater containing organic matter in an upward flow, and may be a fixed-bed or fluidized-bed reaction tank using a carrier, or an upward-flow sludge-bed reaction tank using granules such as a UASB or EGSB system.

[0045] A separator plate 55 is provided above the sludge bed 54 to prevent the loss of granules and to transfer the treated supernatant liquid and generated methane gas upward. The treated methane fermentation solution transferred above the separator plate 55 is removed from the anaerobic wastewater treatment tank 51 via an overflow section 53 (an example of a means for supplying methane fermentation-treated water) and supplied to the demethanization / carbonation section 6 and the methanation section 8. The generated biogas is removed from the anaerobic wastewater treatment tank 51 via a gas recovery section 56 (an example of a means for supplying biogas) and supplied to the methanation section 8. A linear velocity of about 1 to 2 m / h is preferred within the tower because too high a velocity can result in the granules being worn or flowing out, while too low a velocity can slow the decomposition rate and allow suspended solids other than granules to accumulate.

[0046] In this embodiment, the operation of a pump (not shown) provided in the overflow section 53 can be controlled by the control device A. Therefore, the methane fermentation solution can be supplied to the demethanization / carbonation tank 61 and the methanation tank 81 in any amount and at any timing.

[0047] A booster blower (not shown) is connected to the gas recovery unit 56. The gas recovery unit 56 is also provided with an on-off valve and a flow rate adjustment valve whose operation can be controlled by the control device A. Therefore, the gas recovery unit 56 can recover biogas in any desired amount and at any desired timing. Note that approximately 60 to 80% of the biogas recovered by the gas recovery unit 56 is methane, with the remaining 20 to 40% containing carbon dioxide and the like. The gas recovery unit 56 is not particularly limited as long as it has a configuration that allows it to recover biogas.

[0048] The entire outer periphery of the anaerobic wastewater treatment tank 51 is provided with a jacket 57 (an example of a heat retention means) filled with hot water to prevent internal heat loss. The bottom of the jacket 57 is provided with a hot water supply section 57a ​​for supplying hot water, a hot water supply channel 57b, and a hot water discharge section 57c for discharging the hot water. Hot water is injected into the jacket 57 from a hot water tank (not shown). This hot water may be supplied and discharged using a circulating system. The anaerobic wastewater treatment tank 51 is maintained at a temperature suitable for efficient methane fermentation (for example, between 30°C and 40°C).

[0049] [Demethanization and carbonation section] The demethanizer / carbonator 6 is equipped with a bubble column-type demethanizer / carbonator 61, and is provided at the bottom of the demethanizer / carbonator 61 with a methane fermentation treated water supply unit 62 for receiving methane fermentation treated water and a hydrogen supply unit 7 (an example of a hydrogen supply means) for supplying hydrogen. A perforated pipe 65 for blowing hydrogen gas is provided at the bottom of the tank. A demethanizer / carbonator treated water discharge unit 63 for discharging treated water that has been demethanized and carbonated is provided at the top of the tank. A demethanizer / carbonator recovery unit 64 (an example of a demethanizer / carbonator supply means) is provided at the top of the tank for extracting vaporized carbon dioxide, methane, and hydrogen and supplying them to the methanation tank 81. The demethanizer / carbonator 6 having the above-described configuration retains methane fermentation treated water in the demethanizer / carbonator tank 61, blows hydrogen gas into the bottom of the tank to expel dissolved methane and carbon dioxide, and recovers vaporized methane, carbon dioxide, and hydrogen from the top of the tank, which can be supplied to the methanation unit 8.

[0050] A booster blower (not shown) is connected to the demethanizer / carbon dioxide recovery section 64. The gas recovery section 56 is also provided with an on-off valve and a flow rate adjustment valve whose operation can be controlled by the control device A. Therefore, the demethanizer / carbon dioxide recovery section 64 can recover vaporized methane and carbon dioxide in any desired amount and at any desired timing together with the hydrogen gas supplied to the demethanizer / carbon dioxide tank 61. The demethanizer / carbon dioxide recovery section 64 is not particularly limited as long as it has a configuration that allows it to recover methane, carbon dioxide, and hydrogen.

[0051] The method of contacting the hydrogen gas with the demethanizer / carbonate tank 61 is not limited as long as it maintains a certain amount of liquid in the tank and is capable of sufficient vaporization (stripping). For example, a trickling filter system in which a carrier is filled in the tank and gas is absorbed at the interface between the water flowing through the carrier and the gas filling the tank, or a membrane system in which gas with small bubble diameters is introduced while pressurizing a membrane with micropores to increase the efficiency of gas dissolution into the water in the tank, may be employed. In addition, in this embodiment, a so-called standard bubble column is used, in which structures such as an agitator or baffles are not provided inside the tank, but the structure inside the tank is not limited to this. For example, an external circulation airlift bubble column in which the inside of the tank is divided by a flow guide wall or the like, or a bubble column with an agitator provided inside the tank, can be used.

[0052] [Hydrogen supply unit] The hydrogen supply unit 7 is composed of a hydrogen supply port 77 for supplying hydrogen gas to the bottom of the demethanizer-carbonate tank 61, a hydrogen supply port 87 for supplying hydrogen gas to the bottom of the methanation tank 81, and a hydrogen cylinder 72 in which hydrogen is stored. Hydrogen in the hydrogen cylinder 72 is supplied to the demethanizer-carbonate tank 61 or the methanation tank 81 via the hydrogen supply port 77. In this embodiment, the operation of an on-off valve (not shown) provided on the hydrogen cylinder 72 can be controlled by the control device A. Therefore, hydrogen gas can be supplied to the demethanizer-carbonate tank 61 in any amount and at any timing. The hydrogen cylinder 72 is not particularly limited as long as it is configured to be able to supply hydrogen gas to the demethanizer-carbonate tank 61. For example, a hydrogen production device may be used instead of the hydrogen cylinder 72.

[0053] [Methanation Department] The methanation unit 8 includes a methanation tank 81, which is equipped with a methane fermentation-treated water supply unit 82 that receives methane fermentation-treated water, a biogas supply unit 89 that receives biogas supplied from the anaerobic wastewater treatment tank 51, and a methanation-treated water discharge unit 83 that discharges methanation-treated water. This allows hydrogen-utilizing methanogens to methanate the carbon dioxide and hydrogen supplied to the methanation tank 81 (the methanation process). The resulting gas, primarily composed of methane, is extracted from the methanation tank 81 via a biogas recovery unit 86. The methanation-treated water is discharged from the methanation tank 81 via the methanation-treated water discharge unit 83, and a methanation-treated water supply flow path 85 (an example of a methanation-treated water supply means) is provided to supply a portion of the methanation-treated water to the pH adjustment tank 41. This reduces the amount of pH adjuster 4a used.

[0054] The entire outer periphery of the methanation tank 81 is provided with a jacket 84 (an example of a heat insulation means) filled with hot water to prevent internal heat loss. The bottom of the jacket 84 is provided with a hot water supply section 84a for supplying hot water and a hot water discharge section 84c for discharging the hot water. Hot water is injected into the jacket 84 from a hot water tank (not shown). This hot water may be supplied and discharged using a circulating system. The temperature is maintained at a suitable temperature for methanation (for example, 30°C to 40°C).

[0055] A booster blower (not shown) is connected to the biogas recovery unit 86. The biogas recovery unit 86 is also provided with an on-off valve and a flow rate adjustment valve whose operation can be controlled by the control device A. Therefore, the biogas recovery unit 86 can recover biogas in any desired amount and at any desired timing. Note that approximately 80 to 95% of the biogas recovered by the biogas recovery unit 86 is methane, with the remaining 5 to 20% containing carbon dioxide and the like. The biogas recovery unit 86 is not particularly limited as long as it has a configuration that allows it to recover biogas.

[0056] In the organic wastewater treatment system 1 having the above configuration, hydrogen gas is supplied to the demethanizer / carbonator 61, so it does not affect the granules in the anaerobic wastewater treatment tank 51. Furthermore, the methane and carbon dioxide dissolved in the methane fermentation treated water can be vaporized in the demethanizer / carbonator 61, and the vaporized carbon dioxide can be methanated in the subsequent methanation tank 81, enabling stable and efficient control of methane production. Therefore, the organic wastewater treatment system 1 can be operated stably and efficiently.

[0057] [Configuration of organic wastewater treatment system according to the second embodiment] Next, the configuration of an organic wastewater treatment system 10 according to a second embodiment will be described. FIG. 2 is a diagram showing a schematic configuration of the organic wastewater treatment system 10 according to the second embodiment. As shown in FIG. 2, the organic wastewater treatment system 10 according to the second embodiment differs from the first embodiment in that the methanation tank 81 is maintained at a high temperature (50°C or higher and 60°C or lower) to further increase methanation efficiency, and the system is provided with a hot water resupply flow path 88 that can supply hot water used in the jacket 84 of the methanation tank 81 to the jacket 34 of the acid generation tank 31 and the jacket 57 of the anaerobic wastewater treatment tank 51. The organic wastewater treatment system 10 according to the second embodiment will be described below, but a description of the same configuration as that of the organic wastewater treatment system 1 according to the first embodiment will be omitted.

[0058] As shown in Fig. 2, the organic wastewater treatment system 10 according to the second embodiment is provided with a hot water re-supply passage 88 for supplying the hot water used in the jacket 84 of the methanation tank 81 to the acid generation tank 31 and the anaerobic wastewater treatment tank 51. One end of the hot water re-supply passage 88 is connected to a hot water discharge portion 84c, and is connected to a hot water supply passage 34b provided in the acid generation tank 31 and a hot water supply passage 57b provided in the anaerobic wastewater treatment tank 51 so that they can merge. In the jacket 34, the hot water discharged from the hot water discharge portion 84c and the hot water flowing through the hot water supply passage 34b merge, and the hot water is supplied to the jacket 34 via the hot water supply portion 34a. In the jacket 57, the hot water discharged from the hot water discharge portion 84c and the hot water flowing through the hot water supply passage 57b merge, and the hot water is supplied to the jacket 84 via the hot water supply portion 57a.

[0059] The methanation reaction carried out by hydrogen-utilizing methanogens in the methanation tank 81 is an exothermic reaction, and methanation is carried out while the methanation tank 81 is maintained at a high temperature (50°C or higher and 60°C or lower). According to the above embodiment, the hot water used to maintain the temperature is supplied to the jacket 34 of the acid generation tank 31 and the jacket 57 of the anaerobic wastewater treatment tank 51 via the hot water resupply passage 88, thereby making effective use of heat. It should be noted that a heat insulating material is provided in the hot water re-supply passage 88 to prevent heat loss. Also, the operation of a pump (not shown) provided in the hot water re-supply passage 88 can be controlled by the control device A. Therefore, hot water can be supplied to the jacket 34 or the jacket 57 in any supply amount and at any timing.

[0060] [Example of study of the effect on granules in anaerobic wastewater treatment tank 51] The linear velocity (Lv) of the anaerobic wastewater treatment tank 51 was simulated when the hydrogen supply unit 7 was provided in the anaerobic wastewater treatment tank 51 or when it was provided in the demethanization / carbonation tank 61. [Prerequisites] ·Organic wastewater Concentration: 5,000mg-COD / L Displacement: 1,000m 3 / day (≒41.7m 3 / h) COD load: 5,000kg-COD / day Anaerobic wastewater treatment tank 51 Tank diameter: 5m Tank cross-sectional area: 19.6m 2 Gas produced by methane fermentation Only methane and carbon dioxide.

[0061] [Wastewater treatment (methane fermentation) in anaerobic wastewater treatment tank 51] Assuming a decomposition rate of 90%, and that the biogas produced by methane fermentation from the carbon in the organic matter contained in the organic wastewater is 60% methane and 40% carbon dioxide, the amount of methane produced from the COD load of the wastewater is 1,575 m 3 / day, carbon dioxide production is 1,050m 3 / day.

[0062] [Amount of hydrogen required for methanation] The amount of hydrogen required for methanation is four times the amount of carbon dioxide. Therefore, 1,050m 3 / day×4=4,200m 3 / day(=175m3 / h).

[0063] [Linear velocity (Lv)] The linear velocity (Lv) can be calculated using the following formula: Lv(m / h)=Flow rate(m 3 / h) / cross-sectional area(m 2 ) When hydrogen gas is supplied to the demethanization and carbon dioxide tank 61 instead of the anaerobic wastewater treatment tank 51 The linear velocity (Lv) in the anaerobic wastewater treatment tank 51 is the linear velocity (Lv) of only the organic wastewater. Therefore, the linear velocity (Lv) in the anaerobic wastewater treatment tank 51 is 41.7m 3 / h÷19.6m 2 =2.1m / h. When hydrogen is supplied to the anaerobic wastewater treatment tank 51 The linear velocity (Lv) in the anaerobic wastewater treatment tank 51 is the sum of the linear velocity (Lv) of the organic wastewater and the linear velocity (Lv) of the hydrogen gas. The linear velocity (Lv) of hydrogen gas is 175 m 3 / h÷19.6m 2 =8.9m / h. Therefore, the linear velocity (Lv) in the anaerobic wastewater treatment tank 51 is 2.1m / h + 8.9m / h = 11.0m / h. The linear velocity (Lv) of the wastewater supplied into the tank to retain the granules in the lower part of the tank is generally about 1 to 2 m / h. Therefore, if hydrogen gas is supplied to the anaerobic wastewater treatment tank 51, the linear velocity (Lv) increases significantly, and it may not be possible to retain the granules in the lower part of the tank. According to this embodiment, the linear velocity (Lv) in the anaerobic wastewater treatment tank 51 is suppressed, thereby enabling stable and efficient operation without affecting the retention of the granules.

[0064] <Another embodiment>

[0065] In the above embodiment, a jacket covering the entire outer periphery of the tank is used as an example of the heat-retaining means, but the heat-retaining means is not limited to this. For example, a heat exchanger may be provided inside the tank to maintain the temperature inside the tank at a predetermined temperature.

[0066] Furthermore, the configurations disclosed in the above embodiments can be applied in combination with configurations disclosed in other embodiments as long as no contradictions arise, and the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0067] The present invention can be used in an organic wastewater treatment system for treating organic wastewater. [Explanation of symbols]

[0068] 1, 10: Organic wastewater treatment system 3: Acid generating part 4:pH adjustment section 4a: pH adjuster 5: Anaerobic wastewater treatment unit 6: Demethanation and carbonation section 7: Hydrogen supply unit (hydrogen supply means) 8: Methanation section 10: Organic wastewater treatment system 34: Jacket (insulation) 51: Anaerobic wastewater treatment tank 53: Overflow section (methane fermentation treated water supply means) 56: Gas recovery section (biogas supply means) 57: Jacket (insulation) 64: Demethanizer / carbonate recovery section (demethanizer / carbonate supply means) 84: Jacket (insulation) 88: Hot water resupply flow path A: Control device (control means)

Claims

1. An organic wastewater treatment system comprising: an anaerobic wastewater treatment unit having an anaerobic wastewater treatment tank in which an aggregate containing methanogens is provided in a lower portion and which performs methane fermentation of organic wastewater; a demethanization / carbonation unit; a methanation unit; and a control means for controlling operation, a biogas supply means for supplying methane and carbon dioxide generated by methane fermentation in the anaerobic wastewater treatment tank to the methanation unit; a methane fermentation treated water supply means for supplying the methane fermentation treated water generated by the methane fermentation in the anaerobic wastewater treatment tank to the demethanizer / carbonator and the methanation unit; a hydrogen supply means for supplying hydrogen gas to the demethanizer / carbonator to vaporize the methane and carbon dioxide dissolved in the methane fermentation treated water; a demethanizer / carbonator supply means for supplying the methane, carbon dioxide, and hydrogen vaporized in the demethanizer / carbonator to the methanation section, An organic wastewater treatment system configured to be able to perform methanation using carbon dioxide supplied by the biogas supply means and carbon dioxide and hydrogen supplied by the demethanizer / carbonate supply means.

2. 2. The organic wastewater treatment system according to claim 1, wherein the control means controls the hydrogen supply means so that a portion of the hydrogen gas supplied by the hydrogen supply means can be supplied to the methanation section.

3. 2. The organic wastewater treatment system according to claim 1, wherein the control means adjusts the amount of the methane fermentation treated water supplied to the methanation section by the methane fermentation treated water supply means to a supply amount necessary for maintaining methane bacteria in the methanation section.

4. 2. The organic wastewater treatment system according to claim 1, further comprising: an acid production unit that performs acid fermentation of the organic wastewater, and a pH adjustment unit that neutralizes the acid-fermented solution produced in the acid production unit to a pH of 5.0 or more and 7.5 or less using a pH adjuster, and supplies the neutralized solution to the anaerobic wastewater treatment unit, located upstream of the anaerobic wastewater treatment unit.

5. 2. The organic wastewater treatment system according to claim 1, wherein the control means adjusts the amount of the methane fermentation treated water supplied by the methane fermentation treated water supply means so that the pH in the methanation section is 9.0 or less.

6. the methanation unit includes a methanation-treated water supply means that recovers methanation-treated water generated by the methanation and supplies the water to the pH adjustment unit; 5. The organic wastewater treatment system according to claim 4, wherein the control means adjusts the supply amount of the methanation-treated water supplied by the methanation-treated water supply means so that the neutralization solution in the pH adjustment unit has a pH of 5.0 or more and 7.5 or less and a COD of 2000 mg / L or more.

7. 2. The organic wastewater treatment system according to claim 1, wherein the control means controls the temperature in the methanation unit to be 50°C or higher and 60°C or lower.

8. the acid production unit, the anaerobic wastewater treatment unit, and the methanation unit are each provided with a heat retention means for retaining hot water to prevent loss of internal heat; 8. The organic wastewater treatment system according to claim 7, further comprising a hot water resupply flow path capable of supplying the hot water supplied to the heat insulation means of the methanation section to the acid production section and the heat insulation means of the anaerobic wastewater treatment tank.

9. The organic wastewater treatment system according to any one of claims 1 to 8, wherein the anaerobic wastewater treatment tank is an upward flow type that treats the organic wastewater.

10. An organic wastewater treatment method comprising an anaerobic wastewater treatment process for methane fermentation of organic wastewater, a demethanization / carbonation process, and a methanation process, a step of supplying methane and carbon dioxide generated by methane fermentation in the anaerobic wastewater treatment step to the methanation step; a step of supplying methane fermentation-treated water generated by methane fermentation in the anaerobic wastewater treatment step to a demethanization / carbonation step and the methanation step; a step of supplying hydrogen gas to the demethanization / carbonation step to vaporize methane and carbon dioxide dissolved in the methane fermentation treated water; and a step of supplying the methane, carbon dioxide, and hydrogen vaporized in the demethanization / carbonation step to the methanation step, The organic wastewater treatment method includes producing methane by methanation using the carbon dioxide and hydrogen supplied by the anaerobic wastewater treatment step and the demethanization / carbonation step.

11. 11. The organic wastewater treatment method according to claim 10, wherein the amount of the methane fermentation treated water supplied to the methanation step is adjusted to a supply amount necessary for maintaining methanogens in the methanation step.

12. 11. The organic wastewater treatment method according to claim 10, further comprising: an acid production step of acid-fermenting the organic wastewater, which is performed prior to the anaerobic wastewater treatment step; and a pH adjustment step of adding a pH adjuster to the acid-fermented solution produced in the acid production step to neutralize the pH to 5.0 or more and 7.5 or less, and supplying the neutralized solution to the anaerobic wastewater treatment step.

13. The organic wastewater treatment method according to claim 10, wherein the amount of the methane fermentation-treated water supplied by the anaerobic wastewater treatment step is controlled so that the pH in the methanation step is 9.0 or less.

14. supplying methanation-treated water produced by the methanation to the pH adjustment step; The organic wastewater treatment method according to claim 12, wherein the supply amount of the methanation-treated water is controlled so that the neutralization solution has a pH of 5.0 to 7.5 and a COD of 2000 mg / L or more.

15. The organic wastewater treatment method according to claim 10, wherein the methanation step is controlled to a temperature of 50°C or higher and 60°C or lower.

16. 16. The organic wastewater treatment method according to claim 15, wherein heat generated in the methanation step is reused as a heat source for keeping the temperatures of the acid production step and the anaerobic wastewater treatment step constant.

17. The organic wastewater treatment method according to any one of claims 10 to 16, wherein the methane fermentation is carried out by treating the organic wastewater in an upward flow manner.

Images