Water treatment installation

Abstract

To provide a water treatment installation capable of reducing an amount of nitrous oxide (N2O) generated in a biological denitrification process.SOLUTION: A water treatment installation 2 includes a nitrification tank 4 in which ammonia oxidizing bacteria and perfect nitrifying bacteria exist to oxidize ammonia contained in organic wastewater to produce nitric acid in an aerobic environment, and a denitrification tank 3 in which denitrifying bacteria exist to reduce nitric acid in an anaerobic atmosphere to produce nitrogen gas. The hydrogen ion concentration index of the organic wastewater in the nitrification tank 4 is adjusted to a weakly acidic range. The amount of complete nitrifying bacteria present is equal to or greater than the amount of ammonia oxidizing bacteria present.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment facility for treating nitrogen-containing organic wastewater using a biological denitrification method. [Background technology]

[0002] A biological denitrification process is known as a variation of the activated sludge process. The biological denitrification process has a nitrification step and a denitrification step, and removes not only organic components but also nitrogen components from nitrogen-containing organic wastewater.

[0003] It is known that nitrous oxide (N2O) is generated in biological denitrification. The global warming potential of nitrous oxide is several hundred times that of carbon dioxide (CO2). In other words, nitrous oxide is a greenhouse gas that has a greenhouse effect several hundred times greater than that of carbon dioxide. Therefore, it is desirable to reduce the amount of nitrous oxide emitted into the atmosphere in biological denitrification. According to the knowledge obtained by the present inventor, nitrous oxide is generated via nitrite nitrogen (NO2-N). In other words, according to the knowledge obtained by the present inventor, nitrite nitrogen is a precursor of nitrous oxide.

[0004] Patent Document 1 discloses a method for suppressing nitrous oxide emissions, in which the oxidation-reduction potential of a nitrification tank is maintained and controlled at 50-200 mV (silver / silver chloride standard) and the aeration volume is increased or decreased until the nitrite nitrogen concentration in the nitrification tank reaches 0-2 mg / L. Patent Document 2 discloses a water treatment facility that controls the volume of aeration air diffused to an aeration section so that the dissolved oxygen concentration measured by a second dissolved oxygen concentration meter installed in an aerobic tank at the front stage is greater than the dissolved oxygen concentration measured by a first dissolved oxygen concentration meter installed in an aerobic tank at the rear stage. The techniques described in Patent Documents 1 and 2 can reduce the amount of nitrous oxide generated in biological denitrification methods.

[0005] However, the techniques described in Patent Documents 1 and 2 generate nitrite from ammonia contained in raw water, etc., and generate nitric acid from the nitrite. In other words, the techniques described in Patent Documents 1 and 2 are two-stage nitrification biological denitrification methods that generate nitric acid from ammonia via nitrite. Therefore, there is room for further improvement in terms of reducing the amount of nitrous oxide generated in the biological denitrification method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-94665 A [Patent Document 2] JP 2010-269254 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances, and has an object to provide a water treatment facility capable of reducing the amount of nitrous oxide (N2O) generated in a biological denitrification method. [Means for solving the problem]

[0008] One aspect of the present invention is a water treatment facility that treats nitrogen-containing organic wastewater using a biological denitrification method, comprising a nitrification tank in which ammonia oxidizing bacteria and complete nitrifying bacteria are present and which oxidizes ammonia contained in the organic wastewater to produce nitric acid in an aerobic environment, and a denitrification tank in which denitrifying bacteria are present and reduce the nitric acid to produce nitrogen gas in an anaerobic environment, wherein the hydrogen ion concentration index of the organic wastewater in the nitrification tank is adjusted to a weak acidic range, and the amount of complete nitrifying bacteria present is equal to or greater than the amount of ammonia oxidizing bacteria present. Effect of the Invention

[0009] According to the present invention, it is possible to provide a water treatment facility capable of reducing the amount of nitrous oxide (N2O) generated in a biological denitrification method. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram showing a water treatment facility according to an embodiment of the present invention. [Diagram 2] FIG. 11 is a block diagram showing a water treatment facility according to a modified example of the present embodiment. [Diagram 3] FIG. 1 is a block diagram showing the continuously operating apparatus used in this study. [Figure 4] 1 is a table illustrating analysis conditions for real-time PCR. [Diagram 5] 1 is a table showing the composition of inorganic synthetic wastewater used in this study. [Figure 6] 1 is a table showing the operating conditions of the continuously operating device in this study. [Figure 7] 1 is a graph showing an example of the results of confirming changes in water quality over time. [Figure 8] 1 is a graph showing an example of the results of real-time PCR of a bacterial lawn supported on a carrier. [Figure 9] 1 is a table showing the implementation schedule of this study and the samples used in this study. [Figure 10] 10 is a graph showing an example of the results of confirming the change over time in water quality of "RUN1" shown in FIG. 9. [Figure 11] 10 is a graph showing an example of the results of confirming the change over time in water quality of "RUN2" shown in FIG. 9. [Figure 12] FIG. 10 is a graph showing an example of the results of confirming the change over time in the amount of nitrite produced in “RUN1” and “RUN2” shown in FIG. [Figure 13] FIG. 10 is a graph showing an example of the results of confirming the change over time in the nitrite conversion rate of “RUN1” and “RUN2” shown in FIG. [Figure 14] 10 is a graph showing an example of the results of confirming changes over time in the quantitative analysis of functional microorganisms in "RUN1" shown in FIG. 9. [Figure 15]10 is a graph showing an example of the results of confirming changes over time in the quantitative analysis of functional microorganisms in "RUN2" shown in FIG. 9. [Figure 16] 10 is a graph showing an example of the results of bacterial flora analysis by next-generation sequencing for "RUN1" shown in FIG. 9. [Figure 17] 10 is a graph showing an example of the results of bacterial flora analysis by next-generation sequencing for "RUN2" shown in FIG. 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The embodiments described below are preferred specific examples of the present invention, and therefore various technically preferable limitations are applied to them, but the scope of the present invention is not limited to these aspects unless otherwise specified in the following description to the effect that the present invention is limited to these aspects. In addition, in each drawing, similar components are given the same reference numerals, and detailed descriptions thereof are omitted as appropriate.

[0012] FIG. 1 is a block diagram showing a water treatment facility according to an embodiment of the present invention. The water treatment plant 2 according to this embodiment treats nitrogen-containing organic wastewater using a biological denitrification method having a nitrification process and a denitrification process. As shown in FIG. 1, the water treatment plant 2 includes a denitrification tank 3, a nitrification tank 4, and a control unit 7.

[0013] 1 is a facility that treats nitrogen-containing organic wastewater using a nitrification liquid circulation type denitrification method, and includes an anaerobic denitrification tank 3 on the relatively upstream side and an aerobic nitrification tank 4 on the relatively downstream side. Note that the water treatment facility 2 according to this embodiment is not limited to a facility that uses a nitrification liquid circulation type denitrification method, and may be a facility that uses a nitrification denitrification method that includes an aerobic nitrification tank 4 on the relatively upstream side and an anaerobic denitrification tank 3 on the relatively downstream side.

[0014] As shown in FIG. 1, raw water flows into a denitrification tank 3. The raw water is organic wastewater containing nitrogen (e.g., ammonia nitrogen). Examples of the raw water include general urban sewage such as domestic wastewater and industrial wastewater. Note that the raw water is not limited to sewage, and may be drinking water. Ammonia nitrogen (NH4-N) is a nitrogen compound formed by the decomposition of nitrogen-containing organic matter such as protein.

[0015] The denitrification tank 3 is provided with an agitator 32. The agitator 32 operates by receiving power transmitted from the motor 31, and agitates the raw water in the denitrification tank 3. Specifically, the motor 31 transmits power to the agitator 32 based on a control signal sent from the control unit 7, and drives the agitator 32 to agitate the raw water in the denitrification tank 3. The denitrification tank 3 also contains denitrifying bacteria such as Pseudomonas. The denitrification tank 3 uses organic matter (BOD components) in the raw water as a hydrogen donor, and generates nitrogen gas by reducing nitrate in an anaerobic environment.

[0016] The nitrification tank 4 is provided with an aeration pipe 42. The aeration pipe 42 supplies air bubbles flowing from the lower part to the upper part of the nitrification tank 4 by air supplied from the aeration device 41. Specifically, the aeration device 41 supplies a predetermined amount of air (i.e., an amount of air diffused) to the aeration pipe 42 based on a control signal transmitted from the control unit 7, and supplies air bubbles to the nitrification tank 4 via the aeration pipe 42. The aeration pipe 42 may have a capability of supplying air bubbles. Examples of materials for the aeration pipe 42 include glass, stainless steel, sintered metal, and resin. The aeration device 41 may be a device capable of pumping air, such as a blower.

[0017] In the nitrification tank 4, ammonia oxidizing bacteria (AOB) and complete nitrifying bacteria are present. The ammonia oxidizing bacteria are bacteria that oxidize ammonia contained in organic wastewater containing nitrogen (e.g., ammonia nitrogen) to generate nitrite. An example of the ammonia oxidizing bacteria is Nitrosomonas. The complete nitrifying bacteria are bacteria that oxidize ammonia contained in organic wastewater containing nitrogen (e.g., ammonia nitrogen) to generate nitrite without going through nitrite. An example of the complete nitrifying bacteria is Comammox (Complete Ammonia Oxidation) bacteria. Comammox bacteria are bacteria belonging to the genus Nitrospira, and are bacteria that can directly generate nitrate from at least one of ammonia and urea contained in nitrogen-containing organic wastewater. Comammox bacteria generate nitrate without going through nitrite during the oxidation of ammonia in the nitrification process, so that the oxidation of ammonia in the nitrification process can be efficiently performed. The nitrification tank 4 oxidizes ammonia contained in nitrogen-containing organic wastewater in an aerobic environment to generate nitrate.

[0018] The nitrification tank 4 is further provided with a membrane device 43. The membrane device 43 is a device that performs a membrane filtration operation to perform filtration using a separation membrane and obtain treated water that has permeated the separation membrane. The separation membrane of the membrane device 43 is immersed and disposed in the nitrification tank 4 to filter the water to be treated. The separation membrane may be any membrane capable of separating solids and liquids, such as a hollow fiber membrane or a flat membrane. Examples of the separation membrane include a reverse osmosis (RO) membrane, a nanofiltration (NF) membrane, an ultrafiltration (UF) membrane, and a microfiltration (MF) membrane. However, the separation membrane of the membrane device 43 is not limited to these.

[0019] The first pump 44 operates based on a control signal sent from the control unit 7, and discharges a portion of the sludge in the nitrification tank 4 as extracted sludge or excess sludge from the nitrification tank 4. The second pump 45 operates based on a control signal sent from the control unit 7, and returns a portion of the organic wastewater in the nitrification tank 4 to the denitrification tank 3 as nitrification liquid (i.e., a liquid containing nitric acid generated from ammonia in the nitrification process). The nitrification liquid returned to the denitrification tank 3 is also called the "nitrification circulating liquid", etc.

[0020] Here, the nitrification process of a general biological denitrification method is based on a two-stage nitrification process that includes a stage in which ammonia is oxidized to nitrite by the action of ammonia oxidizing bacteria, and a stage in which nitrite is oxidized to nitrate by the action of nitrite oxidizing bacteria (NOB). The rate of the nitrification process of the two-stage nitrification is determined by the activity of the ammonia oxidizing bacteria. Therefore, the hydrogen ion concentration exponent (hereinafter, for convenience of explanation, referred to as "pH") in the nitrification process of a general biological denitrification method is adjusted to a neutral or weakly alkaline range where the activity of ammonia oxidizing bacteria is high.

[0021] According to the findings of the present inventors, the optimum pH in the nitrification process of a general biological denitrification method (i.e., the optimum pH of the organic wastewater in the nitrification tank) is 6.8 or more and 8.5 or less. In addition, the type of nitrification is easily affected by pH. For example, in the nitrification process, when pH=6.8 to 7.5, nitrate-type nitrification (i.e., nitrification in which the reaction proceeds from ammonia to nitrate) is likely to occur, and when pH=7.5 to 8.5, nitrite-type nitrification (i.e., nitrification in which the reaction stops at the stage from ammonia to nitrite) is likely to occur. As mentioned above, since the nitrification process of the two-stage nitrification is rate-determined by the activity of ammonia-oxidizing bacteria, the pH in the nitrification process is generally adjusted to a neutral or weakly alkaline range.

[0022] When nitric acid is produced from ammonia in the nitrification process, the pH in the nitrification process (i.e., the pH of the organic wastewater in the nitrification tank) may drop to 6.8 or more and less than 7.0. In this case, an alkaline liquid or the like may be added to the nitrification tank from the outside to adjust the pH of the organic wastewater in the nitrification tank to a weak alkaline range. On the other hand, even if the pH in the nitrification process drops, for example, for economic reasons, the pH of the organic wastewater in the nitrification tank may not be adjusted, and the water treatment equipment may be forced to continue operating with a pH of 6.8 or more and less than 7.0. In either case, it is not common to intentionally adjust the pH in the nitrification process to a weak acid range, but rather to intentionally adjust the pH in the nitrification process to a neutral range or a weak alkaline range.

[0023] However, this results in the generation of nitrous oxide (NO2) in the nitrification step of a typical biological denitrification method (i.e., the nitrification step of a two-stage nitrification method). According to the findings of the present inventor, nitrite nitrogen (NO2-N) is a precursor of nitrous oxide (N2O). That is, according to the findings of the present inventor, nitrous oxide (N2O) is generated via nitrite nitrogen (NO2-N). The global warming potential of nitrous oxide is several hundred times that of carbon dioxide (CO2). That is, nitrous oxide is a greenhouse gas that has a greenhouse effect several hundred times that of carbon dioxide. Therefore, it is desired to reduce the amount of nitrous oxide emitted into the atmosphere in the biological denitrification method.

[0024] In contrast, in the water treatment equipment 2 according to the present embodiment, the pH of the organic wastewater in the nitrification tank 4 is adjusted to a weak acidic range. For example, the pH of the organic wastewater in the nitrification tank 4 is adjusted to 5.0 or more and 6.0 or less. Alternatively, for example, the pH of the organic wastewater in the nitrification tank 4 is adjusted to 5.0 or more and 5.5 or less. The abundance of the complete nitrifying bacteria is equal to or greater than the abundance of the ammonia oxidizing bacteria. That is, as described above, the ammonia oxidizing bacteria have high activity and tend to grow in a neutral or weak alkaline range. The present inventor has focused on this point and intentionally adjusted the pH of the organic wastewater in the nitrification tank 4 to a weak acidic range to suppress the activity and growth of the ammonia oxidizing bacteria, thereby relatively increasing the activity of the complete nitrifying bacteria and creating an environment in which the complete nitrifying bacteria are relatively likely to grow. The present inventor has created an environment in which the abundance of the complete nitrifying bacteria is equal to or greater than the abundance of the ammonia oxidizing bacteria.

[0025] When the pH of the organic wastewater in the nitrification tank 4 is adjusted to a weakly acidic range, the ammonia oxidizing bacteria cannot become the dominant species in the nitrification tank 4, and hardly produce nitrite from the ammonia contained in the organic wastewater. On the other hand, even if the complete nitrifying bacteria cannot become the dominant species in the nitrification tank 4, if they are present in an amount equal to or greater than that of the ammonia oxidizing bacteria, they can directly produce nitrate from the ammonia contained in the organic wastewater without going through the production of nitrite. Furthermore, even if nitrite is present in the organic wastewater in the nitrification tank 4, the complete nitrifying bacteria can produce nitrate from the nitrite contained in the organic wastewater. In this way, the complete nitrifying bacteria can not only produce nitrate from ammonia, but also produce nitrate from nitrite.

[0026] As a result, the water treatment facility 2 according to this embodiment can reduce the generation of nitrous oxide in the nitrification process of the biological denitrification method, compared to a water treatment facility using a general biological denitrification method having a two-stage nitrification process. The water treatment facility 2 according to this embodiment can reduce nitrite as a precursor of nitrous oxide, and therefore can reduce the generation of nitrous oxide in the nitrification process of the biological denitrification method.

[0027] As shown in FIG. 1, the water treatment facility 2 according to the present embodiment may further include an acid storage tank 5, an alkali storage tank 6, a pH meter 46, an acid injection pump 51, and an alkali injection pump 61. The acid storage tank 5 is connected to the nitrification tank 4 via piping or the like, and stores an acidic liquid. Examples of the acidic liquid stored in the acid storage tank 5 include liquids containing sulfuric acid or hydrochloric acid. The alkali storage tank 6 is connected to the nitrification tank 4 via piping or the like, and stores an alkaline liquid. Examples of the alkaline liquid stored in the alkali storage tank 6 include liquids containing sodium hydroxide. The pH meter 46 measures the hydrogen ion concentration index (hereinafter, for convenience of explanation, referred to as "pH") of the organic wastewater in the nitrification tank 4, and transmits a signal related to the pH of the organic wastewater to the control unit 7 as a measurement result.

[0028] The acid injection pump 51 operates based on a control signal sent from the control unit 7, and injects the acidic liquid stored in the acid storage tank 5 into the nitrification tank 4 via piping or the like. The alkali injection pump 61 operates based on a control signal sent from the control unit 7, and injects the alkaline liquid stored in the alkali storage tank 6 into the nitrification tank 4. For example, the control unit 7 controls at least one of the acid injection pump 51 and the alkali injection pump 61 based on the measurement result of the pH meter 46 to inject at least one of the acidic liquid and the alkaline liquid into the nitrification tank 4, thereby executing control to adjust the pH of the organic wastewater in the nitrification tank 4 to a weakly acidic range.

[0029] Specifically, when the measurement result of the signal transmitted from the pH meter 46 indicates that the pH of the organic wastewater in the nitrification tank 4 is higher than 6.0, the control unit 7 controls the acid injection pump 51 to inject an acidic liquid into the nitrification tank 4 and adjusts the pH of the organic wastewater in the nitrification tank 4 to 5.0 or higher and 6.0 or lower. Alternatively, when the measurement result of the signal transmitted from the pH meter 46 indicates that the pH of the organic wastewater in the nitrification tank 4 is higher than 5.5, the control unit 7 controls the acid injection pump 51 to inject an acidic liquid into the nitrification tank 4 and adjusts the pH of the organic wastewater in the nitrification tank 4 to 5.0 or higher and 5.5 or lower.

[0030] Furthermore, when the pH of the organic wastewater in the nitrification tank 4 is less than 5.0 as a measurement result of the signal transmitted from the pH meter 46, the control unit 7 executes control to control the alkali injection pump 61 to inject an alkaline liquid into the nitrification tank 4 and adjust the pH of the organic wastewater in the nitrification tank 4 to 5.0 or more and 6.0 or less. Alternatively, when the pH of the organic wastewater in the nitrification tank 4 is less than 5.0 as a measurement result of the signal transmitted from the pH meter 46, the control unit 7 executes control to control the alkali injection pump 61 to inject an alkaline liquid into the nitrification tank 4 and adjust the pH of the organic wastewater in the nitrification tank 4 to 5.0 or more and 5.5 or less.

[0031] In this way, when the control unit 7 controls at least one of the acid injection pump 51 and the alkali injection pump 61 based on the measurement result of the pH meter 46 to inject at least one of the acidic liquid and the alkaline liquid into the nitrification tank 4, the pH of the organic wastewater in the nitrification tank 4 can be automatically adjusted to a weakly acidic range with higher accuracy. As a result, the water treatment equipment 2 can reduce the generation of nitrous oxide in the nitrification step of the biological denitrification method with higher accuracy than a water treatment equipment using a general biological denitrification method having a two-stage nitrification nitrification step. The water treatment equipment 2 can reduce nitrous oxide as a precursor of nitrous oxide with higher accuracy, and therefore can reduce the generation of nitrous oxide in the nitrification step of the biological denitrification method with higher accuracy.

[0032] As shown in FIG. 1, the water treatment facility 2 according to this embodiment may further include a dissolved oxygen meter 47. The dissolved oxygen meter 47 measures the dissolved oxygen concentration (hereinafter, for convenience of explanation, referred to as "DO") of the organic wastewater in the nitrification tank 4, and transmits a signal related to the DO of the organic wastewater as a measurement result to the control unit 7. For example, based on the measurement result of the signal transmitted from the dissolved oxygen meter 47, the control unit 7 controls the air diffuser 41 to supply air bubbles to the nitrification tank 4 via the air diffuser tube 42, and executes control to adjust the dissolved oxygen concentration of the organic wastewater in the nitrification tank 4 to 2 mg / L or more and 3 mg / L or less. Details of the dissolved oxygen concentration of the organic wastewater in the nitrification tank 4 will be described later.

[0033] According to this, the activity and growth of ammonia oxidizing bacteria can be further suppressed, the activity of complete nitrifying bacteria can be relatively further increased, and an environment in which complete nitrifying bacteria can relatively easily grow can be created. Therefore, an environment in which the amount of complete nitrifying bacteria is equal to or greater than the amount of ammonia oxidizing bacteria can be more reliably created. As a result, the water treatment facility 2 can more reliably reduce the generation of nitrite in the nitrification process of the biological denitrification method compared to a water treatment facility using a general biological denitrification method having a nitrification process of two-stage nitrification. In addition, the water treatment facility 2 can more reliably reduce nitrite as a precursor of nitrous oxide, and therefore can more reliably reduce the generation of nitrous oxide in the nitrification process of the biological denitrification method.

[0034] Next, a modification of the embodiment of the present invention will be described. In addition, in cases where the components of a water treatment equipment 2A relating to a modified example of this embodiment are similar to the components of the water treatment equipment 2 relating to this embodiment described above with reference to Figure 1, duplicate explanations will be omitted as appropriate, and the following explanation will focus on the differences.

[0035] FIG. 2 is a block diagram showing a water treatment facility according to a modified example of this embodiment. The water treatment equipment 2A according to this modification includes a settling tank 8 instead of the membrane device 43. As in the water treatment equipment 2A according to this modification, the means for obtaining treated water from the nitrification tank 4 is not limited to the membrane device 43, but may be the settling tank 8. As shown in Fig. 2, the settling tank 8 is connected to the nitrification tank 4 via piping or the like.

[0036] The first pump 81 operates based on a control signal sent from the control unit 7, and discharges a portion of the sludge in the settling tank 8 from the settling tank 8 as extracted sludge or excess sludge. The second pump 82 operates based on a control signal sent from the control unit 7, and returns a portion of the sludge in the settling tank 8 to the denitrification tank 3 as returned sludge. The rest of the structure of the water treatment facility 2A is similar to the structure of the water treatment facility 2 described above with reference to FIG.

[0037] According to the water treatment facility 2A of this modification, even if the means for obtaining treated water from the nitrification tank 4 is the settling tank 8 instead of the membrane device 43, the same effects as those described above with reference to FIG. 1 can be obtained.

[0038] Next, an example of the study carried out by the present inventor will be described with reference to the drawings. FIG. 3 is a block diagram showing the continuously operating apparatus used in this study. FIG. 4 is a table illustrating analysis conditions for real-time PCR. In the following description, Comamox bacteria will be mentioned as an example of the "complete nitrifying bacteria" of the present invention.

[0039] First, the continuous operation apparatus 2B used in this study and the analysis conditions of the real-time PCR carried out in this study will be described. As shown in Fig. 3, the continuous operation apparatus 2B used in this study includes a water tank 9, an acid storage tank 5, an alkali storage tank 6, an acid injection pump 51, an alkali injection pump 61, a pH controller 46B, an aeration device 41, an aeration pipe 42, a thermocouple 91, and a heater 92. The acid storage tank 5, the alkali storage tank 6, the acid injection pump 51, the alkali injection pump 61, the aeration device 41, and the aeration pipe 42 are as described above with reference to Fig. 1.

[0040] Sewage from a sewage treatment plant (located in Gunma Prefecture) that uses a typical activated sludge method was used as the nitrogen-containing water containing nitrifying bacteria. The concentration of ammonia nitrogen contained in the nitrogen-containing water to be treated was approximately 48 mg / L. Return sludge from the sewage treatment plant in an amount equivalent to 90% of the volume of the water tank 9 and carrier 93 in an amount equivalent to 10% of the volume of the water tank 9 were placed in the water tank 9, and the nitrogen-containing water to be treated was passed through at a flow rate that would replace the nitrogen-containing water in an amount equivalent to 100% of the volume of the water tank 9 in one day. The effective volume of the water tank 9 was 1.1 liters (L).

[0041] The acid storage tank 5 stores 0.5N hydrochloric acid. The alkali storage tank 6 stores 5% (W / V) NaHCO3. The pH controller 46B controls the acid storage tank 5 and the alkali storage tank 6, and pours hydrochloric acid or NaHCO3 into the water tank 9 as necessary. A polyvinyl alcohol (PVA) sponge carrier (manufactured by AION, 4 mm square) was used as the carrier 93.

[0042] The primers used when the bacterial flora of carrier 93 was analyzed by real-time PCR are shown in FIG. 4. DNA extraction from carrier 93 was performed using DNeasy PowerBiofilm Kit (Qiagen). For real-time PCR, environmental samples were used, and the purified products of the target genes were used as standards. For the measurements, TB Green (registered trademark) Premix Ex Taq (trademark) II (Tli RNaseH Plus) (Takara Bio) was used. The real-time PCR device used was StepOnePlus (trademark) Real-time PCR (Applied Biosystems).

[0043] [First Consideration] FIG. 5 is a table showing the composition of the inorganic synthetic wastewater used in this study. FIG. 6 is a table showing the operating conditions of the continuously operating device in this study. FIG. 7 is a graph showing an example of the results of observing changes in water quality over time. FIG. 8 is a graph showing an example of the results of real-time PCR of the bacterial lawn supported on the carrier.

[0044] In this study, the appropriate culture conditions for complete nitrifying bacteria were examined. The apparatus used in this study is as described above with reference to FIG. 3. The composition of the inorganic synthetic wastewater used in this study is as shown in FIG. 5. The operating conditions of the continuous operation apparatus 2B are as shown in FIG. 6.

[0045] The carrier as the seed bacteria shown in FIG. 6 (Enohi et al. (2021), Journal of Water Treatment Biology, 57, 35-41) and a new sponge carrier were introduced into a continuous operation device 102 having inorganic synthetic wastewater shown in FIG. 5. The pH of the inorganic synthetic wastewater was adjusted to 6.0 by supplying air bubbles to the water tank 9 using the aeration device 41 and the aeration pipe 42. The day when the pH of the inorganic synthetic wastewater became 6.0 was set as the 0th day of operation, and the pH was maintained at 6.0 until the 149th day, during which the inorganic synthetic wastewater was acclimatized.

[0046] An example of the results of confirming the change over time in water quality of inorganic synthetic wastewater in an acidic environment is shown in Figure 7. "Raw water NH4-N" in Figure 7 refers to the ammonia nitrogen contained in the inorganic synthetic wastewater. "Raw water NO2-N" in Figure 7 refers to the nitrite nitrogen contained in the inorganic synthetic wastewater. "Raw water NO3-N" in Figure 7 refers to the nitrate nitrogen contained in the inorganic synthetic wastewater. "Treated water NH4-N" in Figure 7 refers to the ammonia nitrogen in the treated water (nitrification liquid). "Treated water NO2-N" in Figure 7 refers to the nitrite nitrogen in the treated water. "Treated water NO3-N" in Figure 7 refers to the nitrate nitrogen in the treated water. The concentration of "Raw water NH4-N" and other elements was measured using the Sewage Test Method (Japan Sewage Works Association, 2012 edition).

[0047] After that, the pH of the inorganic synthetic wastewater was changed to 5.5 and then to 5.0 at the time points shown in Figure 7, and the continuous operation device 2B was operated for about 60 days for each. During the operation period, the water temperature was maintained at 25°C and the dissolved oxygen was maintained at 7-8 mg / L, and the water quality was analyzed twice a week.

[0048] As shown in Figure 7, in the first stage of acclimation (up to 100 days), nitrite production and ammonia removal were observed, but the nitrification rate was about 54.19% (nitrification rate not shown). From 100th to 149th days (pH 6.0), the water quality was stable, and the nitrification rate reached 95.44%. At pH 5.5 (150th to 176th days), the nitrification rate reached 100%, and the abundance of comammox bacteria exceeded the abundance of ammonia-oxidizing bacteria, as described below. In operation at pH 5.0 (after 177 days), a small amount of nitrite was produced immediately after the conditions were changed, but in long-term operation (after 225 days), more stable water quality (average nitrification rate of 98.66%) was obtained.

[0049] An example of the results of real-time PCR of bacterial flora supported on a carrier in inorganic synthetic wastewater with pH adjusted to 6.0, 5.5, and 5.0 is shown in FIG. 8. The horizontal axis of the graph shown in FIG. 8 indicates the number of days since the start of operation. The vertical axis of the graph shown in FIG. 8 indicates the amount of genes present per gram of carrier. In addition, "beta-AOB" shown in FIG. 8 refers to general ammonia oxidizing bacteria. "Comammox" shown in FIG. 8 refers to Comammox bacteria.

[0050] For the comammox bacteria and ammonia-oxidizing bacteria in the carriers, the amoA genes were quantified by real-time PCR using specific primers. The specific primers were the same as those shown in "Beta-AOB" and "comammox" in Figure 4. DNA was extracted from the carriers collected on the days shown on the horizontal axis of the graph in Figure 8 using a DNeasy PowerBiofilm Kit (Qiagen). The real-time PCR was as described above with reference to Figures 3 and 4.

[0051] As shown in Figure 8, the accumulation of Comammox bacteria was weak until around the 80th day after the start of operation. However, it was confirmed that Comammox bacteria became the dominant species after the 150th day after the start of operation when the pH was adjusted to 5.5. From the results shown in Figures 7 and 8, it is believed that under the condition of pH 6.0, the accumulation of Comammox bacteria gradually progressed, and by the 120th day after the start of operation, Comammox bacteria had become the dominant species. Furthermore, at pH 5.0, greater proliferation of Comammox bacteria was confirmed than at pH 5.5.

[0052] These results indicate that good treated water quality can be achieved even under acidic conditions by using nitrifying bacteria enriched by the complete nitrifying bacteria culture method. It also suggests that an acidic environment is favorable for the growth of Comamox bacteria in the carrier.

[0053] As described above, according to the first study, it was found that when the pH of the organic wastewater in nitrification tank 4 is adjusted to 5.0 or more and 6.0 or less, the comammox bacteria can be present in an amount equal to or greater than the amount of ammonia oxidizing bacteria, even if they cannot become the dominant species in nitrification tank 4. It was also found that when the pH of the organic wastewater in nitrification tank 4 is adjusted to 5.0 or more and 5.5 or less, the comammox bacteria can become the dominant species in nitrification tank 4, and can be present in an amount greater than the amount of ammonia oxidizing bacteria.

[0054] [Second Review] FIG. 9 is a table showing the implementation schedule of this study and the samples used in this study. In this study, we investigated the effect of DO conditions on the microflora and the contribution of enrichment cultures of the comammox bacteria to the suppression of emissions of nitrous oxide (N2O), a greenhouse gas.

[0055] The composition of the stock solution of the test material used in this study is as shown in Figure 5. That is, in this study, the inorganic synthetic wastewater described above with reference to Figure 5 is used as the stock solution of the test material. "RUN1" shown in Figure 9 is a sample of the Comamox system, and the seed bacteria is the return sludge from the Itakura Town Purification Center. "RUN2" shown in Figure 9 is a comparative sample other than the complete nitrifying bacteria, and the seed bacteria is the activated sludge provided by the company to which the present inventor belongs.

[0056] The continuous operation device 2B used in this study is as described above with reference to FIG. 3. The effective volume of the water tank 9 is 1.1 L. The concentration of ammonia nitrogen (NH4-N) in the raw water is 40 mg / L. The retention time of the raw water is 6 hours or more and 24 hours or less. A polyvinyl alcohol (PVA) sponge carrier (manufactured by AION Co., Ltd., 4 mm square) is used as the carrier 93. The filling rate of the PVA sponge carrier is 10%. The aeration rate (aeration rate) is 1 L / min. The pH controller 46B controls the acid storage tank 5 and the alkali storage tank 6, and adds hydrochloric acid or NaHCO3 to the water tank 9 as necessary to adjust the pH of the nitrogen-containing water in the water tank 9 to 5.5, and adjusts the temperature of the nitrogen-containing water in the water tank 9 to 25°C.

[0057] As a method of acclimation, first, 100 mL of carrier (carrier filling rate 10%) and 100 mL of seed sludge (MLSS 2400 mg / L) are put into the continuous operation device 2B. Next, a batch operation (preliminary experiment in FIG. 9) is performed with the inorganic synthetic wastewater described above with reference to FIG. 5, and then the operation is switched to a continuous treatment operation (main experiment in FIG. 9) and is performed for one month. In this specification, the term "batch operation" refers to an operation performed in a closed system (i.e., a state in which new inorganic synthetic wastewater is not added to the water tank), in other words, an operation performed only with the inorganic synthetic wastewater that was initially put in. In addition, in this specification, the terms "continuous treatment operation" and "continuous operation" refer to an operation performed in a state in which inorganic synthetic wastewater is added to the water tank and treated water is discharged from the water tank, resulting in replacement of the liquid in the water tank.

[0058] For the microbial analysis, for "RUN1" and "RUN2" shown in Figure 9, a portion of the carriers was collected on the 7th, 14th, 21st, and 28th days after the start of operation for each DO condition in the main experiment at the end of the preliminary experiment, and functional microorganisms (total bacteria, ammonia oxidizing bacteria, and comammox bacteria) were quantified using real-time PCR (i.e., quantitative PCR). The carriers on the 28th day after the start of operation were used for next-generation analysis (16S V4 region and amoA). In addition, to confirm the closeness of the accumulated nitrospira sequence to the known comammox sequence, amplicon analysis of the amoA gene was added.

[0059] As for the nitrous oxide generation characteristics, after the aforementioned one-month operation is completed, the nitrous oxide generation characteristics are confirmed using the carriers "RUN1" and "RUN2" shown in FIG.

[0060] FIG. 10 is a graph showing an example of the results of confirming the change over time in water quality of "RUN1" shown in FIG. FIG. 11 is a graph showing an example of the results of confirming the change over time in water quality of "RUN2" shown in FIG.

[0061] As shown in Figure 10, in the change over time of water quality in "RUN1," the average nitrification rates for each period were 100% (DO = 7-8 mg / L), 87.76% (DO = 3 mg / L), 93.53% (DO = 2 mg / L), and 56.41% (DO = 1 mg / L), respectively. Good treated water quality was obtained during the operation period when DO was 2 mg / L or higher, but ammonia was not sufficiently treated during operation at DO = 1 mg / L. In addition, no generation of nitrite (treated water NO2-N) was confirmed during the entire period, and the type of nitrification was nitrate type.

[0062] As shown in Figure 11, in the change over time of water quality in "RUN2," the average nitrification rates for each period were 92.81% (DO = 7-8 mg / L), 93.22% (DO = 3 mg / L), 93.63% (DO = 2 mg / L), and 76.63% (DO = 1 mg / L), respectively. As with RUN1, it was found that when DO was lowered to 1 mg / L, ammonia was not sufficiently treated. In addition, a large amount of nitrite (treated water NO2-N) was detected in the treated water, and the type of nitrification was nitrite.

[0063] FIG. 12 is a graph showing an example of the results of confirming the change over time in the amount of nitrite produced in "RUN1" and "RUN2" shown in FIG. FIG. 13 is a graph showing an example of the results of confirming the change over time in the nitrite conversion rate of "RUN1" and "RUN2" shown in FIG. The nitrite conversion rate was determined from the amount of nitrite produced in the continuous operation apparatus 2B.

[0064] As shown in Figure 13, for "RUN1", the average values ​​of the N2O conversion rates under each DO condition were 1.36% (DO = 7-8 mg / L), 1.93% (DO = 3 mg / L), 1.78% (DO = 2 mg / L), and 1.93% (DO = 1 mg / L). For "RUN2", in the middle period (from the start of operation to the 42nd day) when the plant was maintained at DO = 7-8 mg / L and DO = 3 mg / L, the amount of N2O generated was low, and the N2O conversion rate was 0.80-1.65%. On the other hand, for "RUN2", in the later period (from the start of operation to the 98th day) when the plant was maintained at DO = 3 mg / L, DO = 2 mg / L, and DO = 1 mg / L, the amount of N2O generated increased, and the N2O conversion rate was 1.15-6.68%.

[0065] Comparing the results of "RUN1" and "RUN2", the N2O conversion rate of "RUN1" was slightly higher than that of "RUN2" in the middle period (from the start of operation to the 42nd day) of the period of maintenance operation at DO = 7-8 mg / L and DO = 3 mg / L. On the other hand, it was found that the N2O conversion rate of "RUN2" was higher than that of "RUN1" in the subsequent period. Thus, the remarkable dominance of ammonia-oxidizing bacteria was confirmed in the later period of the period of maintenance operation at DO = 3 mg / L, DO = 2 mg / L, and DO = 1 mg / L (from the start of operation to the 98th day), suggesting that the abundance ratio of ammonia-oxidizing bacteria in the carriers contributes greatly to N2O release.

[0066] FIG. 14 is a graph showing an example of the results of confirming the time course of the quantitative analysis of functional microorganisms in "RUN1" shown in FIG. FIG. 15 is a graph showing an example of the results of confirming the time course of the quantitative analysis of functional microorganisms in "RUN2" shown in FIG. Quantitative analysis of functional microorganisms was performed using real-time PCR.

[0067] The daily changes in the abundance of each functional gene in "RUN1" during the operation period are shown in Figure 14. In "RUN1", the abundance of Comammox was 1.1 x 10 10 (copies / g carrier), and ammonia-oxidizing bacteria (AOB) were detected at 5.38 × 10 10 The copy number was detected at about 1000 copies / g carrier. The copy number was about the same during the maintenance operation at DO = 7-8 mg / L, and an increase in Comammox was confirmed during the maintenance operation at DO = 3 mg / L. In addition, ammonia oxidizing bacteria (AOB) temporarily increased during the maintenance operation at DO = 2 mg / L, but the copy number of AOB returned to the same level as that of Comammox. During the maintenance operation at DO = 1 mg / L, the copy number of Comammox was stable, but the copy number of AOB was unstable.

[0068] FIG. 16 is a graph showing an example of the results of bacterial flora analysis by next-generation sequencing for "RUN1" shown in FIG. FIG. 17 is a graph showing an example of the results of the bacterial flora analysis by next-generation sequencing for "RUN2" shown in FIG.

[0069] The results of the bacterial flora analysis of "RUN1" are shown in Figure 16. The abundance ratio of Nitrospira, to which the known comammox bacteria belong, tended to increase as DO decreased. In contrast, the abundance ratio of Nitrosomonadaceae, an ammonia-oxidizing bacteria (AOB), fluctuated throughout the period.

[0070] The results of the bacterial flora analysis of "RUN2" are shown in Figure 17. Nitrosomonadaceae, an ammonia oxidizing bacteria (AOB), was the most dominant species during the operation period when DO was 1 to 3 mg / L. In addition, the abundance ratio of Nitrosomonadaceae, an ammonia oxidizing bacteria (AOB), tended to increase as DO decreased. On the other hand, the abundance ratio of Nitrospira, to which the known comammox bacteria belongs, was extremely small.

[0071] As shown in Figures 14 to 17, in the microbial composition in "RUN1," comammox bacteria and ammonia oxidizing bacteria (AOB) were present at the same level. Depending on the period, the abundance of comammox bacteria exceeded the abundance of ammonia oxidizing bacteria (AOB). However, even when the abundance of comammox bacteria exceeded the abundance of ammonia oxidizing bacteria (AOB), comammox bacteria were not completely dominant.

[0072] As described above, according to the second study, it was found that when the dissolved oxygen concentration of the organic wastewater in the nitrification tank 4 is adjusted to 2 mg / L or more and 3 mg / L or less, even if the comammox bacteria cannot become the dominant species in the nitrification tank 4, they can be present in an amount equal to or greater than that of ammonia oxidizing bacteria.

[0073] Furthermore, compared to the control system (RUN2), in the condition where many Comammox bacteria were present (RUN1), no generation of NO2, which is a precursor of N2O, was observed. Furthermore, no generation of NO2 was observed even when the dissolved oxygen concentration (DO) was lowered during treatment. As a result, compared to the control system (RUN2), in the condition where many Comammox bacteria were present (RUN1), the amount of N2O generated was significantly reduced.

[0074] Ammonia oxidizing bacteria (AOB) may be present, and even in an environment where AOB are present at the same level as comammox, the nitrification ability of comammox can suppress the generation of NO2 and N2O. In other words, it is not necessary to eradicate AOB, and when applied to sewage treatment plants, it is sufficient to add comammox to maintain a certain number in the conventional state or to induce an increase in comammox through the treatment environment.

[0075] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims. The configurations of the above embodiments can be partially omitted or arbitrarily combined in a manner different from the above. [Explanation of symbols]

[0076] 2: Water treatment equipment, 2A: Water treatment equipment, 2B: Continuous operation device, 3: Denitrification tank, 4: Nitrification tank, 5: Acid storage tank, 6: Alkaline storage tank, 7: Control unit, 8: Sedimentation tank, 9: Water tank, 31: Motor, 32: Agitator, 41: Aeration device, 42: Aeration pipe, 43: Membrane device, 44: First pump, 45: Second pump, 46: pH meter, 46B: pH controller, 47: Dissolved oxygen meter, 51: Acid injection pump, 61: Alkaline injection pump, 81: First pump, 82: Second pump, 91: Thermocouple, 92: Heater, 93: Carrier, 102: Continuous operation device

Claims

1. A water treatment facility for treating nitrogen-containing organic wastewater using a biological denitrification method, a nitrification tank in which ammonia oxidizing bacteria and complete nitrifying bacteria are present and which oxidizes ammonia contained in the organic wastewater to produce nitric acid in an aerobic environment; a denitrification tank in which denitrifying bacteria are present and the nitrate is reduced to produce nitrogen gas in an anaerobic environment; Equipped with The hydrogen ion concentration index of the organic wastewater in the nitrification tank is adjusted to a weak acidic range, A water treatment facility characterized in that the amount of complete nitrifying bacteria present is equal to or greater than the amount of ammonia oxidizing bacteria present.

2. 2. The water treatment facility according to claim 1, wherein the hydrogen ion concentration index is adjusted to be 5.0 or more and 6.0 or less.

3. 2. The water treatment facility according to claim 1, wherein the hydrogen ion concentration index is adjusted to be 5.0 or more and 5.5 or less.

4. A pH meter for measuring the hydrogen ion concentration exponent; an acid storage tank connected to the nitrification tank and configured to store an acidic liquid; an acid injection pump that sends the acidic liquid stored in the acid storage tank to the nitrification tank; an alkaline storage tank connected to the nitrification tank and configured to store an alkaline liquid; an alkali injection pump that sends the alkaline liquid stored in the alkali storage tank to the nitrification tank; a control unit that controls at least one of the acid injection pump and the alkali injection pump based on the measurement result of the pH meter to inject at least one of the acidic liquid and the alkaline liquid into the nitrification tank, thereby executing control to adjust the hydrogen ion concentration index to the weak acidity range; The water treatment facility according to claim 1, further comprising:

5. 5. The water treatment facility according to claim 4, wherein, when the measurement result shows that the hydrogen ion concentration index is higher than 6.0, the control unit controls the acid injection pump to inject the acidic liquid into the nitrification tank, thereby executing control to adjust the hydrogen ion concentration index to be 5.0 or more and 6.0 or less.

6. 5. The water treatment facility according to claim 4, wherein, when the measurement result shows that the hydrogen ion concentration index is higher than 5.5, the control unit controls the acid injection pump to inject the acidic liquid into the nitrification tank, thereby executing control to adjust the hydrogen ion concentration index to be 5.0 or more and 5.5 or less.

7. 5. The water treatment facility according to claim 4, wherein, when the measurement result indicates that the hydrogen ion concentration index is less than 5.0, the control unit controls the alkali injection pump to inject the alkaline liquid into the nitrification tank, thereby executing control to adjust the hydrogen ion concentration index to be 5.0 or more and 6.0 or less.

8. 5. The water treatment facility according to claim 4, wherein, when the measurement result indicates that the hydrogen ion concentration index is less than 5.0, the control unit controls the alkali injection pump to inject the alkaline liquid into the nitrification tank, thereby executing control to adjust the hydrogen ion concentration index to be 5.0 or more and 5.5 or less.

9. an air diffuser for supplying air to the nitrification tank; an aeration pipe installed in the nitrification tank and adapted to supply air bubbles to the nitrification tank using the air supplied from the aeration device; a dissolved oxygen meter for measuring a dissolved oxygen concentration of the organic wastewater in the nitrification tank; a control unit that controls the aeration device based on the measurement result of the dissolved oxygen meter to supply the air bubbles to the nitrification tank through the aeration pipe and adjusts the dissolved oxygen concentration to 2 mg / L or more and 3 mg / L or less; The water treatment facility according to claim 1, further comprising:

10. 10. The water treatment facility according to claim 1, wherein the complete nitrifying bacteria is a comammox bacterium.

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