JP5944468B2 - Sewage treatment system - Google Patents

Description

  The present invention relates to a sewage treatment system that nitrifies ammoniacal nitrogen contained in sewage to nitrite nitrogen or nitrate nitrogen by aerobic treatment.

  Ammonia nitrogen contained in sewage such as domestic and industrial wastewater is known to cause a decrease in dissolved oxygen and eutrophication in closed water areas such as lakes and inner bays where sewage is discharged. Yes. For this reason, aerobic treatment is performed in the sewage treatment facility. Aerobic treatment means nitrification of ammonia nitrogen into nitrite nitrogen or nitrate nitrogen by using aerobic microorganisms such as nitrifying bacteria that are introduced into the sewage in the reaction tank or originally exist in the sewage. Means processing.

In such aerobic treatment, it is known that nitrous oxide gas (N ₂ O) is generated as a reaction by-product due to changes in microbial activity, reaction tank operating conditions, and the like. Nitrous oxide gas is a greenhouse gas, and its greenhouse effect is as high as about 310 times that of carbon dioxide gas. Nitrous oxide gas is also regarded as a problem as an ozone depleting gas that destroys the stratospheric ozone layer, like chlorofluorocarbon gas. For this reason, it is an urgent task to suppress the release of nitrous oxide gas to the atmosphere from the viewpoint of protecting the global environment.

  Against this background, in recent years, several inventions for suppressing the release of nitrous oxide gas into the atmosphere have been proposed (see Patent Documents 1 to 3). The invention described in Patent Document 1 is to reduce the nitrous oxide gas to nitrogen gas by denitrifying bacteria in the oxygen-free tank by supplying an absorption liquid in which the nitrous oxide gas is dissolved to the oxygen-free tank. In the invention described in Patent Document 2, oxygen that inhibits the reaction of denitrifying bacteria is removed from the containing gas before the containing gas containing nitrous oxide gas is supplied into the anoxic tank. The invention described in Patent Document 3 reduces nitrous oxide gas to nitrogen gas by treating an absorbing solution in which nitrous oxide gas is dissolved under anaerobic conditions.

JP-A-10-128389 JP 2000-246055 A JP 2002-204926 A

  However, according to the inventions described in Patent Documents 1 and 3, it is necessary to prepare an additional device such as an absorption tank for storing the absorption liquid and a circulation pump for circulating the absorption liquid in the absorption tank. Further, according to the invention described in Patent Document 2, it is necessary to prepare an oxygen removing device for removing oxygen from the contained gas. For this reason, according to invention of patent documents 1-3, it was difficult to comprise the sewage treatment system which suppresses discharge | release of the nitrous oxide gas to air | atmosphere at low cost.

  This invention is made | formed in view of the said subject, The objective is to provide the sewage treatment system which can suppress discharge | release of nitrous oxide gas to air | atmosphere at low cost.

  In order to solve the above problems and achieve the object, a sewage treatment system according to one embodiment of the present invention activates organic substances contained in raw water under anaerobic conditions in which the raw water supplied from the raw water supply path flows. An anaerobic tank that takes in the sludge and releases phosphorus contained in the activated sludge to the raw water, and a nitrite nitrogen contained in the treated raw water under anoxic conditions into which the treated raw water flowing out of the anaerobic tank flows And an oxygen-free tank for reducing nitrate nitrogen to nitrogen gas, and treated raw water flowing out of the oxygen-free tank flows in. Ammonia nitrogen contained in the treated raw water under aerobic conditions is converted to nitrite nitrogen and nitric acid. A plurality of aerobic tanks arranged in the flow direction of the treated raw water, which are nitrified to oxidative nitrogen and take in phosphorus contained in the treated raw water into the activated sludge, and the treated raw water flowing out of the aerobic tank The treated raw water flowing in A sedimentation tank for precipitating the activated sludge contained therein, a sludge return path for returning the activated sludge accumulated in the sedimentation tank to the anaerobic tank, and a nitrification solution in the most downstream aerobic tank are circulated to the anoxic tank A nitrifying liquid circulation path, a concentration detection unit for detecting a concentration of nitrous oxide gas generated in the plurality of aerobic tanks, and a detection result of the concentration detection unit, in the plurality of aerobic tanks A gas supply path for supplying the nitrous oxide gas present to the oxygen-free tank, and a sub-flow detected by the concentration detector so that the amount of nitrous oxide gas generated in the aerobic tank is less than a predetermined value. A gas feed control device that controls a supply amount of the nitrous oxide gas in the aerobic tank to the anoxic tank based on a generation amount of the nitrogen oxide gas.

  According to the sewage treatment system according to the present invention, release of nitrous oxide gas into the atmosphere can be suppressed at a low cost.

FIG. 1 is a block diagram showing a configuration of a sewage treatment system according to the first embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a sewage treatment system according to the second embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of a sewage treatment system according to the third embodiment of the present invention. FIG. 4 is a block diagram showing a configuration of a modified example of the sewage treatment system shown in FIG. FIG. 5 is a block diagram showing a configuration of a modified example of the sewage treatment system shown in FIG. FIG. 6 is a block diagram showing a configuration of a modified example of the sewage treatment system shown in FIG.

  Hereinafter, the configuration of a sewage treatment system according to the first to third embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
First, with reference to FIG. 1, the structure of the sewage treatment system which is the 1st Embodiment of this invention is demonstrated.

  Drawing 1 is a mimetic diagram showing composition of a sewage treatment system which is a 1st embodiment of the present invention. As shown in FIG. 1, the sewage treatment system 1 which is the 1st Embodiment of this invention is the anaerobic tank 11, the anoxic tank 12, several aerobic tanks 13a-13c, the sedimentation tank 14, and sludge. A return path 15 and a nitrating liquid circulation path 16 are provided.

  The raw water supplied from the raw water supply path 17 flows into the anaerobic tank 11. In the anaerobic tank 11, organic substances contained in the raw water are taken into the activated sludge under anaerobic conditions, and phosphorus contained in the activated sludge is released into the raw water.

  The treated raw water that has flowed out of the anaerobic tank 11 flows into the anaerobic tank 12. In the oxygen-free tank 12, nitrite nitrogen and nitrate nitrogen contained in the treated raw water are reduced to nitrogen gas under oxygen-free conditions.

  The plurality of aerobic tanks 13a to 13c are arranged in series along the flow direction of the treated raw water. The raw water treated from the anaerobic tank 12 flows into the plurality of aerobic tanks 13a to 13c by adjusting the weir height of each aerobic tank. Each aerobic tank is provided with an air diffuser (not shown) for performing air diffusion on the stored activated sludge. In the aerobic tanks 13a to 13c, ammonia nitrogen contained in the treated raw water is nitrified to nitrite nitrogen and nitrate nitrogen under aerobic conditions, and phosphorus contained in the treated raw water is contained in the activated sludge. It is captured.

  The processing raw water that has flowed out from the most downstream aerobic tank 13 c flows into the settling tank 14. In the settling tank 14, the treated raw water is separated into a separation liquid and activated sludge 18. A pipe (not shown) is connected to the side wall of the settling tank 14 so that the sterilized separation liquid can be discharged out of the system through the pipe (not shown). Further, a sludge return path 15 is connected to the bottom of the sedimentation tank 14 so that the activated sludge 18 deposited on the bottom of the sedimentation tank 14 can be returned to the anaerobic tank 11.

  The nitrification liquid circulation path 16 is a pipe connecting the anoxic tank 12 and the most downstream aerobic tank 13 c, and circulates the nitrating liquid in the aerobic tank 13 c to the anoxic tank 12.

  In the sewage treatment system 1 according to the first embodiment of the present invention, the load detectors 19a to 19d, the raw water step flow path 20, and the inflow nitrogen are used to suppress the release of nitrous oxide gas into the atmosphere. And a load control device 21.

  The load detection units 19a to 19d are provided in the anoxic tank 12 and the aerobic tanks 13a to 13c, respectively. The load detection units 19a to 19d are ammonia nitrogen loads in each tank (for example, ammonia oxidizing bacteria amount, nitrite oxidizing bacteria amount, ammonia nitrogen concentration, nitrite nitrogen concentration, nitrate nitrogen concentration, oxygen consumption rate, etc.) Is detected. The load detection units 19 a to 19 d input the detected ammonia nitrogen load value to the inflow nitrogen load control device 21.

  The raw water step flow path 20 is a pipe for supplying a part of the raw water supplied from the raw water supply path 17 to the anoxic tank 12 and the aerobic tanks 13a to 13c. The amount of raw water supplied from the raw water supply path 17 to each of the oxygen-free tank 12 and the aerobic tanks 13a to 13c is adjusted by controlling the openings of the valves 22a to 22d, respectively.

  The inflow nitrogen load control device 21 is configured by an information processing device such as a workstation or a personal computer. Inflow nitrogen load control device 21 is based on the value of ammonia nitrogen load in each tank of anaerobic tank 12 and aerobic tanks 13a-13c inputted from load detection parts 19a-19d, and ammonia nitrogen load in each tank The raw water is supplied to each tank by controlling the opening degree of the valves 22a to 22d so that becomes less than a predetermined value. For example, when the value of the ammonia nitrogen load detected by the load detector 19d is greater than or equal to a predetermined value, the inflow nitrogen load control device 21 supplies raw water into the aerobic tank 13c by opening the valve 22d. The amount of nitrous oxide gas generated in the aerobic tanks 13a to 13c increases as the ammoniacal nitrogen load increases. Therefore, by supplying raw water to the aerobic tanks 13a to 13c according to the value of the ammonia nitrogen load in this way, the value of the ammonia nitrogen load in the aerobic tanks 13a to 13c is kept below a predetermined value, and the atmosphere Release of nitrous oxide gas into the inside can be suppressed.

[Second Embodiment]
Next, with reference to FIG. 2, the structure of the sewage treatment system which is the 2nd Embodiment of this invention is demonstrated.

  FIG. 2 is a schematic diagram showing a configuration of a sewage treatment system according to a second embodiment of the present invention. As shown in FIG. 2, the sewage treatment system 2 which is the 2nd Embodiment of this invention is the anaerobic tank 11, the anoxic tank 12, several aerobic tanks 13a-13c, the sedimentation tank 14, and sludge. A return path 15 and a nitrating liquid circulation path 16 are provided. In addition, since these components are the same as the components in the sewage treatment system 1 which is 1st Embodiment, the description is abbreviate | omitted below.

  The sewage treatment system 2 according to the second embodiment of the present invention is provided with a residence time control device 31 in order to suppress the release of nitrous oxide gas into the atmosphere. The residence time control device 31 is configured by an information processing device such as a workstation or a personal computer. The residence time control device 31 controls the residence time of the activated sludge 18 in the sedimentation tank 14 by controlling, for example, the number of withdrawals and the withdrawal amount of the activated sludge 18 from the sedimentation tank 14 to the sludge return path 15. The nitrous oxide gas contained in the activated sludge 18 is decomposed in the activated sludge 18 while staying in the settling tank 14. Therefore, the activated sludge 18 is not pulled out to the sludge return path 15 immediately, but the residence time of the activated sludge 18 is controlled so as to stay for a predetermined time or more, thereby suppressing the release of nitrous oxide gas into the atmosphere. can do.

[Third Embodiment]
Finally, with reference to FIG. 3, the structure of the sewage treatment system which is the 3rd Embodiment of this invention is demonstrated.

  FIG. 3 is a schematic diagram showing a configuration of a sewage treatment system according to the third embodiment of the present invention. As shown in FIG. 3, the sewage treatment system 3 which is the 3rd Embodiment of this invention is the anaerobic tank 11, the anaerobic tank 12, several aerobic tanks 13a-13c, the sedimentation tank 14, and sludge. A return path 15 and a nitrating liquid circulation path 16 are provided. In addition, since these components are the same as the components in the sewage treatment systems 1 and 2 which are 1st and 2nd embodiment, the description is abbreviate | omitted below.

  In the sewage treatment system 3 according to the third embodiment of the present invention, in order to suppress the release of nitrous oxide gas into the atmosphere, gas detectors 41a to 41c, a gas supply path 42, and a gas feed control And a device 43.

The gas detection parts 41a-41c are provided in the aerobic tanks 13a-13c, respectively. The gas detection parts 41a-41c are comprised by the nitrous oxide gas sensor, and detect the density | concentration of the nitrous oxide gas in each aerobic tank. The gas detectors 41 a to 41 c input the detected nitrous oxide gas concentration value to the gas feed controller 43.

  The gas supply path 42 is a pipe for supplying nitrous oxide gas generated in the aerobic tanks 13 a to 13 c to the anoxic tank 12. The amount of nitrous oxide gas supplied from each aerobic tank to the oxygen-free tank 12 is adjusted by controlling the opening degree of the valves 44a to 44c.

The gas feed control device 43 is configured by an information processing device such as a workstation or a personal computer. Based on the value of the concentration of nitrous oxide gas in the aerobic tanks 13a to 13c input from the gas detectors 41a to 41c, the gas feed control device 43 determines the amount of nitrous oxide gas in the aerobic tanks 13a to 13c. The nitrous oxide gas in the aerobic tanks 13a to 13c is supplied to the anaerobic tank 12 by controlling the opening degree of the valves 44a to 44c so that the concentration value becomes less than a predetermined value. For example, when the concentration value of the nitrous oxide gas detected by the gas detection unit 41c is equal to or greater than a predetermined value, the gas feed control device 43 opens the valve 44c to remove the nitrous oxide gas in the aerobic tank 13c. Supply to the anoxic tank 12. The nitrous oxide gas supplied to the oxygen-free tank 12 is decomposed in the oxygen-free tank 12 by denitrification. Accordingly, by supplying the nitrous oxide gas in the aerobic tanks 13a to 13c to the anoxic tank 12 according to the concentration of the nitrous oxide gas in this way, the release of the nitrous oxide gas into the atmosphere is suppressed. be able to.

  Although the embodiment to which the invention made by the present inventor is applied has been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to this embodiment. For example, a sewage treatment system may be constructed by combining two or more of the sewage treatment systems according to the first to third embodiments. Moreover, although this embodiment applies this invention to the sewage treatment system using an A2O method, this invention is applicable also to the sewage treatment system using the standard method which performs only an aerobic treatment. .

  That is, as shown in FIG. 4, in the sewage treatment system including a plurality of aerobic tanks 13a to 13e arranged in series along the flow direction of the treated raw water, the aerobic tanks 13b to 13e after the second stage are used. Load detectors 19a to 19d and valves 22a to 22d are provided, and the inflow nitrogen load control device 21 is based on the value of ammonia nitrogen load in each of the aerobic tanks 13b to 13e input from the load detectors 19a to 19d. In addition, the opening of the valves 22a to 22d may be controlled so that the ammonia nitrogen load in each tank is less than a predetermined value, and raw water may be supplied to each tank.

  Further, in the sewage treatment system including a plurality of aerobic tanks 13a to 13e arranged in series along the flow direction of the treated raw water as shown in FIG. 5, the residence time control device 31 returns sludge from the settling tank 14, for example. You may make it control the residence time of the activated sludge 18 in the sedimentation tank 14 by controlling the frequency | count of extraction and the amount of extraction of the activated sludge 18 to the path 15. FIG.

Moreover, in the sewage treatment system provided with the several aerobic tanks 13a-13e arranged in series along the flow direction of process raw | natural water as shown in FIG. 6, with respect to the aerobic tanks 13b-13e after the 2nd step | paragraph. Gas detectors 41a to 41d and valves 44a to 44d are provided, and the gas feed control device 43 is based on the concentration value of nitrous oxide gas in the aerobic tanks 13b to 13e input from the gas detectors 41a to 41d. The nitrous oxide gas in the aerobic tanks 13b to 13e is favored by controlling the openings of the valves 44a to 44d so that the concentration of the nitrous oxide gas in the aerobic tanks 13b to 13e is less than a predetermined value. You may make it supply to the air tank 13a.

  As described above, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

1, 2, 3 Sewage treatment system 11 Anaerobic tank 12 Anoxic tank 13a-13c Aerobic tank 14 Sedimentation tank 15 Sludge return path 16 Nitrification liquid circulation path 17 Raw water supply path 18 Activated sludge 19a-19d Load detection part 20 Raw water step flow Path 21 Inflow nitrogen load control device 22a-22d, 44a-44c Valve 31 Residence time control device 41a-41c Gas detection part 42 Gas supply path 43 Gas feed control device

Claims (1)

An anaerobic tank into which raw water supplied from the raw water supply channel flows, takes in organic matter contained in the raw water under anaerobic conditions into the activated sludge, and releases phosphorus contained in the activated sludge to the raw water;
An anaerobic tank for reducing the nitrite nitrogen and nitrate nitrogen contained in the treated raw water to an oxygen gas under anaerobic conditions into which the treated raw water flowing out of the anaerobic tank flows;
Nitrogenous nitrogen contained in the treated raw water is nitrified to nitrite nitrogen and nitrate nitrogen under aerobic conditions into which the treated raw water that has flowed out of the oxygen-free tank flows, and phosphorus contained in the treated raw water. A plurality of aerobic tanks arranged along the flow direction of the treated raw water to be taken into the activated sludge;
A settling tank for precipitating activated sludge contained in the treated raw water into which the treated raw water flowing out of the aerobic tank flows;
A sludge return path for returning activated sludge accumulated in the settling tank to the anaerobic tank;
A nitrification liquid circulation path for circulating the nitrification liquid in the aerobic tank at the most downstream to the anoxic tank;
A concentration detector for detecting the concentration of nitrous oxide gas generated in the plurality of aerobic tanks;
Based on the detection result of the concentration detector, a gas supply path for supplying the nitrous oxide gas present in the plurality of aerobic tanks to the anoxic tank,
Based on the concentration of the nitrous oxide gas detected by the concentration detector so that the concentration of the nitrous oxide gas in the aerobic tank is less than a predetermined value, the nitrous oxide gas in the aerobic tank is A sewage treatment system comprising: a gas feed control device that controls a supply amount to the anoxic tank.

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