Scum generation suppressing system and scum generation suppressing method

Abstract

To provide a scum generation suppressing system and a scum generation suppressing method, efficiently suppressing scum generation in a sewage disposal plant.SOLUTION: The scum generation suppressing system according to an embodiment of the present invention, comprises a measuring instrument 12 measuring a nitrogen compound concentration in water to be treated present in a precipitation pond precipitating a precipitable substance to separate from the water to be treated in a sewage disposal plant, a culturing tank 14 culturing microalgae included in the water to be treated inflowing from the precipitation pond and comprising a pump P delivering a cell suspension liquid including the cultured microalgae to the precipitation pond, a dehydrator 13 dehydrating the water to be treated inflowing from the precipitation pond to extract the microalgae and to feed the extracted microalgae into the culturing tank, and a controller 11 acquiring the nitrogen compound concentration measured by the measuring instrument 12 and operating the dehydrator 13 and the pump P based on the acquired nitrogen compound concentration.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a scum generation suppression system and a scum generation suppression method. [Background technology]

[0002] In the sedimentation tanks of sewage treatment plants, the sponge-like layer of sludge that forms on the surface of the tank is called scum. Scum occurs when nitrogen generated in sewage is released into the air, causing the sludge that has accumulated at the bottom of the sedimentation tank to rise to the surface along with the nitrogen. For example, if scum forms in the final sedimentation tank, it will flow out with the supernatant when the treated water is released, leading to a deterioration in the quality of the treated water and causing problems such as foul odors. For this reason, in addition to methods for removing scum in sedimentation tanks, mechanisms to prevent scum from forming are being investigated. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-123392 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, when scum removal equipment is used in sewage treatment plants, costs are incurred for installing and operating the equipment. Furthermore, since the use of scum removal equipment does not solve the odor problem caused by scum generation, it has been desired to not only remove the generated scum but also suppress the generation of scum in the settling tank.

[0005] The embodiments of the present invention have been made in consideration of the above circumstances, and have an object to provide a scum generation suppression system and a scum generation suppression method that efficiently suppress the generation of scum in sewage treatment plants. [Means for solving the problem]

[0006] The scum generation prevention system of one embodiment includes a measuring instrument that measures the nitrogen compound concentration of the water to be treated in a sedimentation tank at a sewage treatment plant, which separates sedimentable substances from the water to be treated by settling them; a culture tank that cultures microalgae contained in the water to be treated flowing in from the sedimentation tank and is equipped with a pump that sends a cell suspension containing the cultured microalgae to the sedimentation tank; a dehydrator that dehydrates the water to be treated flowing in from the sedimentation tank to extract the microalgae and introduces the extracted microalgae into the culture tank; and a control device that acquires the nitrogen compound concentration measured by the measuring instrument and operates the dehydrator and the pump based on the acquired value of the nitrogen compound concentration. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing an example of a treatment flow of a sewage treatment plant in which a scum generation prevention system according to an embodiment is operated. [Figure 2] FIG. 2 is a diagram schematically illustrating an example of the configuration of a scum generation suppression system according to an embodiment. [Figure 3] FIG. 3 is a flowchart illustrating an example of the operation of the scum generation prevention system according to the embodiment. [Figure 4] FIG. 4 is a diagram for explaining the effect of the scum generation suppression system according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a treatment flow of a sewage treatment plant in which a scum generation prevention system according to an embodiment is operated.

[0009] A sewage treatment plant in which a scum generation prevention system according to an embodiment is operated purifies raw water such as sewage that flows in and discharges clear treated water to the outside. The sewage treatment plant according to an embodiment includes a final settling tank 1, a primary settling tank 2, and a reaction tank 3.

[0010] The primary sedimentation tank 2 is a facility for removing sedimentable materials such as sand and garbage contained in the water to be treated. The water to be treated is obtained by removing solids from raw water such as sewage flowing in from the outside using a screen or the like. In the primary sedimentation tank 2, sedimentable organic matter such as sand and garbage in the water to be treated settles and is separated from the water to be treated. The water to be treated that has been separated from the sedimentable organic matter in the primary sedimentation tank 2 flows out into the reaction tank 3.

[0011] The reaction tank 3 is a facility for decomposing organic matter contained in the water to be treated, which causes pollution. The water to be treated, from which sand, garbage, etc. have been removed in the primary sedimentation tank 2, flows into the reaction tank 3. In the reaction tank 3, activated sludge is added to the water to be treated and air is blown in, so that the organic matter in the water to be treated comes into contact with the microorganisms in the activated sludge and is decomposed. The water to be treated, from which the organic matter has been decomposed in the reaction tank 3, flows out into the final sedimentation tank 1.

[0012] Final settling tank 1 is a facility for removing settleable substances such as activated sludge contained in the water to be treated. The water to be treated, which contains activated sludge and has been subjected to organic matter decomposition treatment in reaction tank 3, flows into final settling tank 1. In final settling tank 1, the activated sludge in the water to be treated settles and is separated from the water to be treated. Of the water to be treated that has been separated from the activated sludge in final settling tank 1, the supernatant water flows out through a treated water pipe as treated water, and after undergoing disinfection etc., is discharged into a river or other such location.

[0013] The sewage treatment plant in which the scum generation prevention system of the embodiment is operated may have other structures. For example, the sewage treatment plant may have a grit basin that removes large debris and sand upstream of the primary sedimentation basin 2, or an advanced treatment facility that improves the quality of treated water downstream of the final sedimentation basin 1. Also, in Fig. 1, equipment for injecting chemicals and air into the water to be treated during sewage treatment, equipment for extracting settled sludge, and the like are omitted.

[0014] Next, the configuration of the scum generation suppression system according to the embodiment will be described. FIG. 2 is a diagram schematically illustrating an example of the configuration of a scum generation suppression system according to an embodiment.

[0015] The scum generation suppression system of the embodiment suppresses the generation of scum in a settling tank. In the following description, the scum generation suppression system of the embodiment is assumed to be operated in the above-mentioned sewage treatment plant and to suppress the generation of scum in the final settling tank 1. The scum generation prevention system includes a control device 11, a measuring instrument 12, a dehydrator 13, and a culture tank 14.

[0016] Measuring instrument 12 measures the nitrogen compound concentration of the water to be treated in final sedimentation tank 1. For example, measuring instrument 12 measures the nitrogen content of the water to be treated (the total concentration of inorganic nitrogen and organic nitrogen corresponding to ammonium ions, nitrite ions, and nitrate ions in the water) as the nitrogen compound concentration. Alternatively, measuring instrument 12 measures the total concentration of nitrite ions and nitrate ions contained in the water to be treated as the nitrogen compound concentration. Alternatively, measuring instrument 12 measures the concentration of nitrite ions and the concentration of nitrate ions contained in the water to be treated individually as the nitrogen compound concentration. Measuring instrument 12 transmits the measured nitrogen compound concentration value to control device 11.

[0017] The dehydrator 13 is controlled by the control device 11, and extracts microalgae by dehydrating the water to be treated that flows in from the final settling tank 1, and then feeds the extracted microalgae into the culture tank 14. A portion of the water to be treated that flows out from the final settling tank 1 into the treated water pipe flows into the dehydrator 13. The inflowing water to be treated is dehydrated in the dehydrator 13, and the microalgae contained in the water to be treated are extracted. The microalgae extracted in the dehydrator 13 are fed into the culture tank 14. In the dehydrator 13, wastewater separated during the extraction of microalgae (the water to be treated after the microalgae have been extracted) is discharged into the treated water pipe and flows out to the outside as treated water together with the water to be treated that flows out from the final settling tank 1.

[0018] The culture tank 14 cultivates microalgae contained in the water to be treated that flows in from the final sedimentation tank 1. The culture tank 14 is configured to allow the water to be treated to flow in from the final sedimentation tank 1. The culture tank 14 receives the microalgae extracted in the dehydrator 13 and cultivates them in the water to be treated, thereby producing a highly concentrated cell suspension. The culture tank 14 cultivates the microalgae in the water to be treated that flows in from the final sedimentation tank 1 under specified liquid phase conditions. The liquid phase conditions only require exposure to sunlight, such as outdoors, and environmental conditions such as temperature and light are not limited. The culture tank 14 also includes a pump P that sends the cell suspension containing the cultivated microalgae to the final sedimentation tank 1.

[0019] The control device 11 acquires the nitrogen compound concentration measured by the measuring device 12 and operates the dehydrator 13 and the pump P based on the acquired nitrogen compound concentration value. The control device 11 has at least one processor such as a CPU (Central Processing Unit) and a storage unit (memory or auxiliary storage device) storing a program executed by the processor, and executes the program. Note that all or part of the functions of the control device 11 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be stored in a computer-readable storage medium. Examples of the computer-readable storage medium include portable media such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and storage devices such as a hard disk built into a computer system. The program may be transmitted via a telecommunications line.

[0020] The storage unit of the control device 11 stores in advance the threshold value of the nitrogen compound concentration and the operation duration time required for the processing of the control device 11, which will be described later. The threshold value of the nitrogen compound concentration and the operation duration time are set and stored in advance by, for example, an administrator of the control device 11.

[0021] Next, the operation of the scum generation prevention system of the embodiment will be described. The scum generation prevention system performs the following operations by the control device 11 executing a program stored in advance. FIG. 3 is a flowchart illustrating an example of the operation of the scum generation prevention system according to the embodiment.

[0022] First, the control device 11 determines whether the nitrogen compound concentration of the water to be treated in the final sedimentation tank 1 exceeds a predetermined threshold (step S1). The control device 11 acquires the value of the nitrogen compound concentration of the water to be treated in the final sedimentation tank 1 measured by the measuring instrument 12. The control device 11 determines whether the acquired nitrogen compound concentration value exceeds the nitrogen compound concentration threshold value stored in the memory unit. The nitrogen compound concentration threshold value varies depending on the type of value measured by the measuring instrument 12 as the nitrogen compound concentration (nitrogen content, total concentration of nitrite ions and nitrate ions, individual concentrations of nitrite ions and nitrate ions, etc.), but may be a value determined with reference to wastewater standards set forth in the Water Pollution Control Act, etc. For example, when the measuring instrument 12 measures the nitrogen content as the nitrogen compound concentration, the nitrogen compound concentration threshold value is 60 mg / L.

[0023] When the control device 11 determines that the nitrogen compound concentration value acquired from the measuring device 12 does not exceed the threshold value (step S1: NO), the control device 11 performs the process of step S1 again. That is, the control device 11 repeats the operation of step S1 while the nitrogen compound concentration value of the water to be treated in the final sedimentation tank 1 is equal to or less than the threshold value.

[0024] On the other hand, when the control device 11 determines that the nitrogen compound concentration value acquired from the measuring device 12 exceeds the threshold value (step S1: YES), it operates the pump P and the dehydrator 13 (step S2). The control device 11 controls the pump P to feed the cell suspension containing a high concentration of microalgae in the culture tank 14 into the final sedimentation tank 1. The control device 11 feeds, for example, a predetermined amount of cell suspension into the final sedimentation tank 1. The control device 11 also controls the dehydrator 13 to dehydrate the water to be treated that has flowed from the final sedimentation tank 1 into the dehydrator 13, thereby extracting microalgae and feeding the extracted microalgae into the culture tank 14. The control device 11 operates the dehydrator 13 in accordance with the operation of the pump P and also appropriately flows the water to be treated from the final sedimentation tank 1 into the culture tank 14, thereby replenishing the amount of water in the cell suspension in the culture tank 14 and maintaining a high concentration of microalgae in the water.

[0025] The control device 11 stops the operation of the pump P (step S3). For example, the control device 11 stops the operation of the pump P when the amount of cell suspension fed from the culture tank 14 to the final settling tank 1 by controlling the pump P reaches a predetermined amount. Alternatively, the control device 11 stops the operation of the pump P when it determines that a predetermined time has elapsed since the operation of the pump P started. The control device 11 stops the operation of the pump P and starts a timer at the same time.

[0026] The control device 11 determines whether a predetermined time has elapsed since the pump P was stopped (step S4). The control device 11 determines whether the time elapsed since the pump P was stopped, measured by the timer, has exceeded the operation duration stored in the memory unit.

[0027] When the control device 11 determines that the time elapsed since the pump P was stopped does not exceed the operation duration (step S4: NO), the control device 11 performs the process of step S4 again. That is, the control device 11 repeats the process of step S4 until the time elapsed since the pump P was stopped exceeds the operation duration.

[0028] On the other hand, if the control device 11 determines that the time elapsed since the pump P was stopped exceeds the operation duration (step S4: YES), it stops the operation of the dehydrator 13 (step S5). The control device 11 executes the operations from step S3 to step S4 to operate the dehydrator 13 for a predetermined time (operation duration) after the pump P was stopped. In this way, the control device 11 can dehydrate the water to be treated that remained in the dehydrator 13 when the pump P was stopped, and extract the water without leaving any microalgae behind.

[0029] The control device 11 ends the operation after stopping the operation of the dehydrator 13. For example, the control device 11 waits for a certain time after completing the operations from step S1 to step S5, and then starts the operations from step S1 again. By performing the operations from step S1 to step S5, the control device 11 does not operate while the measured nitrogen compound concentration value does not exceed a predetermined threshold, and introduces microalgae into the final sedimentation tank 1 when the measured nitrogen compound concentration value exceeds the predetermined threshold.

[0030] Next, the effects of the scum generation suppression system according to the embodiment will be described. FIG. 4 is a diagram for explaining the effect of the scum generation suppression system according to the embodiment.

[0031] For example, in the reaction tank 3 or the final sedimentation tank 1 of a sewage treatment plant, ammonium ions (NH4 + ) is nitrified by the action of nitrifying bacteria, etc., and nitrite ions (NO2 - ) and nitrate ions (NO3 - The chemical reaction formula for the generation of nitrite ions and nitrate ions in the reaction tank 3 and final settling tank 1 is as follows:

[0032] [Formula 1] 2NH4 + + O2 → 2NO2 - + 2H2O + 4H + [Formula 2] 2NO2 - + O2 → 2NO3 -

[0033] The nitrite ions and nitrate ions generated by the above nitrification reaction are subjected to anaerobic conditions in the final settling tank 1, causing a denitrification reaction. As a result, nitrogen (N2) gas is generated in the treated water. The chemical reaction formula for nitrogen generation in the final settling tank 1 is as follows:

[0034] [Formula 3] 2NO2 - + 3(H2) → N2+ 2OH - + 2H2O [Formula 4] 2NO3 - + 5(H2) → N2+ OH - + 4H2O

[0035] During the denitrification reaction in the above formulas 3 and 4, the generated nitrogen rises to the surface along with the sludge that has accumulated at the bottom of the settling tank, causing scum to form on the surface of the water in the final settling tank. The scum generated in the final settling tank can cause problems such as a deterioration in the quality of the treated water and a foul odor.

[0036] The scum generation suppression system of this embodiment suppresses the denitrification reaction in the above formulas 3 and 4 by introducing microalgae cultured in a culture tank into the final sedimentation tank 1. Specifically, the microalgae introduced into the final sedimentation tank 1 absorb inorganic nitrogen (nitrite ions, nitrate ions, etc.) in the water to be treated as a nutrient source and metabolize it. As a result, the concentrations of nitrate ions and nitrite ions in the final sedimentation tank 1 decrease, and the denitrification reaction in formulas 3 and 4 is suppressed. When the denitrification reaction in the final sedimentation tank 1 is suppressed, the amount of nitrogen generated as a gas in the water to be treated decreases, making it possible to suppress the generation of scum in the final sedimentation tank 1.

[0037] As described above, according to this embodiment, it is possible to provide a scum generation suppression system and a scum generation suppression method that efficiently suppress the generation of scum in a sewage treatment plant.

[0038] That is, the scum generation suppression system in this embodiment includes a measuring device that measures the nitrogen compound concentration of the water to be treated in a settling tank, a culture tank that cultures microalgae contained in the water to be treated that flows in from the settling tank and is equipped with a pump that sends a cell suspension containing the cultured microalgae to the settling tank, a dehydrator that dehydrates the water to be treated that flows in from the settling tank to extract the microalgae and introduces the extracted microalgae into the culture tank, and a control device that acquires the nitrogen compound concentration measured by the measuring device and operates the dehydrator and the pump based on the acquired nitrogen compound concentration value. The scum generation suppression system can suppress the generation of nitrogen in the water to be treated and the generation of scum in the settling tank by introducing a cell suspension containing microalgae into the settling tank.

[0039] The scum generation suppression system of the embodiment utilizes microalgae that naturally occur in the settling tank, eliminating the need for additional chemicals or microorganisms. Furthermore, because the microalgae are cultured in a culture tank and a highly concentrated cell suspension is introduced into the settling tank, the culture tank, pump, and dehydrator in the scum generation suppression system of the embodiment can be small in capacity. Furthermore, since the microalgae that occur in the final settling tank in particular can be released directly into rivers and other streams without causing any problems, no additional processing is required after the microalgae are introduced into the final settling tank.

[0040] The scum generation suppression system of the embodiment operates a pump and a dehydrator when the acquired nitrogen compound concentration value exceeds a pre-stored threshold value. The scum generation suppression system operates the dehydrator in synchronization with the operation of the pump to feed the microalgae in the treatment water into the culture tank, thereby maintaining a high concentration of microalgae in the culture tank.

[0041] In an embodiment of the scum generation suppression system, when the amount of cell suspension sent from the culture tank to the settling tank reaches a predetermined amount, the pump is stopped, and the dehydrator is stopped a predetermined time after the pump is stopped. By operating the dehydrator for a predetermined time after the pump is stopped, the scum generation suppression system dehydrates the water to be treated that remains in the dehydrator when the pump is stopped, and can extract all of the microalgae without leaving any residue.

[0042] In the above embodiment, the scum generation prevention system has been described as being operated in a final settling tank of a sewage treatment plant, but the scum generation prevention system can also be operated in a primary settling tank of a sewage treatment plant. The components of the water to be treated in the settling tanks of the primary settling tank and the final settling tank are different, and the types of microalgae growing in the water are also different. Therefore, when the scum generation prevention system is operated in a primary settling tank, the scum generation prevention system suppresses scum generation in the primary settling tank by culturing microalgae collected from the primary settling tank in a culture tank different from that used in the final settling tank and then introducing the culture tank into the primary settling tank.

[0043] The program according to this embodiment may be transferred in a state where it is stored in an electronic device, or in a state where it is not stored in an electronic device. In the latter case, the program may be transferred via a network, or in a state where it is stored in a storage medium. The storage medium is a non-transitory tangible medium. The storage medium is a computer-readable medium. The storage medium may be in any form, such as a CD-ROM or a memory card, as long as it is capable of storing the program and is computer-readable.

[0044] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0045] 1...Final settling tank, 2...Primary settling tank, 3...Reaction tank, 11...Control device, 12...Measuring instrument, 13...Dehydrator, 14...Cultivator, P...Pump

Claims

1. a measuring instrument for measuring the nitrogen compound concentration of the water to be treated in a sedimentation tank in a sewage treatment plant, which separates sedimentable substances from the water to be treated by settling them; A culture tank for culturing microalgae contained in the water to be treated flowing in from the sedimentation tank and having a pump for sending a cell suspension containing the cultured microalgae to the sedimentation tank; A dehydrator that extracts the microalgae by dehydrating the water to be treated flowing in from the sedimentation tank and introduces the extracted microalgae into the culture tank; a control device that acquires the nitrogen compound concentration measured by the measuring instrument and operates the dehydrator and the pump based on the acquired nitrogen compound concentration value.

2. 2. The scum generation suppression system according to claim 1, wherein the control device operates the pump and the dehydrator when the acquired value of the nitrogen compound concentration exceeds a pre-stored threshold value.

3. 3. The scum generation suppression system according to claim 2, wherein the control device stops operation of the pump when the amount of the cell suspension sent from the culture tank to the settling tank reaches a predetermined amount, and stops operation of the dehydrator after a predetermined time has elapsed since operation of the pump was stopped.

4. measuring the nitrogen compound concentration of the water to be treated in a sedimentation tank in a sewage treatment plant, which separates sedimentable substances from the water to be treated by settling them; The microalgae contained in the water to be treated flowing in from the sedimentation tank are cultured in a culture tank, A method for suppressing scum generation, which comprises sending a cell suspension containing the cultured microalgae to the sedimentation tank based on the measured nitrogen compound concentration value, extracting the microalgae by dehydrating the treated water flowing in from the sedimentation tank, and introducing the extracted microalgae into the culture tank.

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