JP2012148217A - Biological treatment method of wastewater, and wastewater treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and system capable of effectively suppressing discharge of NO to the atmosphere using an existing facility or the like as much as possible.SOLUTION: Raw water is denitrified by denitrifying bacteria in a denitrification tank 11 under a non-oxygen state. The water to be treated in the denitrification tank 11 is aerated in a nitrification tank 12 and nitrified by aerobic microorganisms under an aerobic state. The nitrification liquid which is nitrified in the nitrification tank 12 is solid-liquid separated into treated water and an activated sludge. Gases containing NO generated from the denitrification tank 11 and the nitrification tank 12 in these steps are collected by a gas collecting mechanism 21. The collected gases are oxidized in a biological oxidation treatment section 22 and NO is changed into NO.

Description

  Embodiments of the present invention relate to a biological treatment method and wastewater treatment apparatus for biologically treating raw water with a biological reaction apparatus.

In the wastewater treatment method and device that biologically treats nitrogen components in wastewater, after reducing treatment with denitrifying bacteria in an oxygen-free denitrification tank, biooxidation treatment is performed with nitrifying bacteria in an aerobic nitrification tank ing. In these treatment processes, it is known that N ₂ O (nitrous oxide) gas is generated as a reaction byproduct. N ₂ O gas is said to have a greenhouse effect 310 times that of carbon dioxide gas. The global warming problem has become an international problem, and the reduction of N ₂ O gas, which is a greenhouse gas, is important along with the reduction of carbon dioxide gas and methane gas. From such a background, studies for suppressing the generation of N ₂ O have been made.

For example, there is a type in which a microaerobic biological reaction tank is provided in front of the denitrification tank, N ₂ O-containing gas generated in the nitrification tank is directly introduced into the microaerobic tank, and N ₂ O is reduced (for example, Patent Document 1). In addition, there is a type in which N ₂ O-containing gas generated in a nitrification tank is sent to an oxygen removing device, and deoxygenated gas from which oxygen contained in the contained gas has been removed in advance is introduced into the wastewater of the denitrification tank for reduction treatment. (For example, refer to Patent Document 2). Further, the N ₂ O-containing gas generated in the nitrification tank is sent to the recovery tank, and diffused into the nitrification liquid fed into the recovery tank through the nitrification liquid circulation line, so that the N ₂ O gas is contained in the nitrification liquid. There is also a method in which N ₂ O dissolved in the nitrification solution is fed to a denitrification tank for reduction treatment (see, for example, Patent Document 3).

JP 2007-75821 A JP 2000-246055 A JP-A-10-128389

  However, in the method using a microaerobic tank, it is necessary to newly install this microaerobic tank, and it may be difficult to newly install a microaerobic tank in a sewage treatment plant with limited space. There is. Moreover, when using an oxygen removal apparatus, molecular sieve activated carbon and a gas separation membrane are recommended as an optimal oxygen removal apparatus. However, these apparatuses are expensive, and it is necessary to periodically replace the activated carbon or the separation membrane, which is troublesome.

For this reason, there has been a demand for a method and system that can utilize existing equipment as much as possible and effectively suppress the release of N ₂ O into the atmosphere.

In the biological treatment method of wastewater according to the embodiment of the present invention, raw water is reduced by denitrifying bacteria in an oxygen-free denitrification tank, and the treated water that has passed through this denitrification tank is in an aerobic nitrification tank. When performing a biooxidation treatment by an aerobic microorganism, a gas containing N ₂ O generated in the biological treatment process is collected by a gas collection mechanism, and the gas collected by the gas collection mechanism is subjected to a biooxidation treatment. It is characterized by changing N ₂ O to NO ₃ .

A wastewater treatment apparatus according to an embodiment of the present invention is a denitrification tank that reduces raw water by denitrifying bacteria in an oxygen-free state, and the treated water that has passed through this denitrifying tank is biologically treated by nitrifying bacteria in an aerobic state by aeration. It has a nitrification tank that performs oxidation treatment, and a solid-liquid separation device that separates the nitrified nitrification solution into treated water and activated sludge, and is generated in the biological treatment process in the denitrification tank and the nitrification tank. N collect gas containing _{2 O} were, a gas collection system for sending and the N 2 _O to the feed biological response to biological oxidation process, the gas collection mechanism gases collected by processing the biological oxidation, N 2 _O NO _And a bio-oxidation treatment part to be changed to ₃ .

1 is an overall configuration diagram showing a first embodiment of a wastewater treatment apparatus according to the present invention. It is a partial block diagram which shows the modification which provided the baffle plate in the bio-oxidation process part in 1st Embodiment same as the above. It is a whole block diagram which shows the modification which provided the support | carrier in the biological oxidation process part in 1st Embodiment same as the above. It is a whole block diagram of 2nd Embodiment which divided the nitrification tank into several in the waste water treatment apparatus which concerns on this invention. It is a whole block diagram of the modification which changed the absorption part of the gas in 2nd Embodiment same as the above, and the return place of a gas component solution. It is the whole block diagram of the modification which made the absorption part of the gas in 2nd Embodiment same as the above, and the return place of a gas component solution applicable to each place. FIG. 5 is an overall configuration diagram of a modified example in which an N ₂ O measurement device is provided in the first embodiment of the present invention illustrated in FIG. 1 and control according to a measurement value is enabled. It is a whole block diagram which shows 3rd Embodiment using a biological reaction tank as a biological oxidation process part of the waste water treatment apparatus which concerns on this invention. It is the whole block diagram of the modification which changed the return place of the treated water of the biological reaction tank in 3rd Embodiment same as the above into the nitrification tank. It is a whole block diagram of the modification which changed the return place of the treated water of the biological reaction tank in 3rd Embodiment same as the above to the raw water tank. It is a whole block diagram of the modification which used the thing of the structure which has a support | carrier as a biological reaction tank in 3rd Embodiment same as the above.

  Embodiments of the present invention will be described below.

  FIG. 1 is a configuration diagram illustrating a first embodiment of a wastewater treatment apparatus according to the present invention. The wastewater treatment apparatus of this embodiment includes a denitrification tank 11, a nitrification tank 12, and a final sedimentation tank 13 as a solid-liquid separation device. Waste water such as sewage is introduced into the denitrification tank 11 as raw water, and the raw water is reduced by denitrifying bacteria in an oxygen-free state. Water to be treated that has passed through the denitrification tank 11 is introduced into the nitrification tank 12, and the air supplied from the blower 16 is aerated by an air diffuser 15 provided at the bottom of the nitrification tank 12 to keep it in an aerobic state. In this aerobic state, oxidation treatment is performed with nitrifying bacteria. The final sedimentation basin 13 is introduced with the nitrification liquid oxidized in the nitrification tank 12, and the nitrification liquid is solid-liquid separated into treated water and activated sludge. A part of the nitrification liquid is returned to the denitrification tank 11 by the pump 17. Moreover, a part of the activated sludge separated into solid and liquid in the final sedimentation tank 13 is returned to the denitrification tank 11 by the pump 18 to maintain the biomass in the denitrification tank 11. In addition, the remaining activated sludge is discharged | emitted out of the apparatus through a discharge pipe as surplus sludge.

For the denitrification tank 11 and the nitrification tank 12, a gas collection mechanism 21 and a biological oxidation treatment unit 22 are provided. The gas collection mechanism 21 collects a gas containing N ₂ O, which will be described in detail later, from the denitrification tank 11 and the nitrification tank 12. The biological oxidation treatment unit 22 performs a biological oxidation treatment on the gas collected by the gas collection mechanism 21 to change N ₂ O to NO ₃ .

In this embodiment, as the biological oxidation treatment unit 22, a unit having a watering device 23 for watering the gas collected by the gas collecting mechanism 21 and dissolving the gas component in water is used. Then, the water dissolved the gas components to oxidation treatment by returning to the nitrification tank 12, changing the N 2 _O into NO _3.

  In the above configuration, the raw water flows into the oxygen-free denitrification tank 11 and is decomposed and then sent to the aerobic nitrification tank 12. A part of the nitrification liquid treated in the nitrification tank 12 is returned to the denitrification tank 11 through the circulation path, and the rest is sent to the final sedimentation tank 13. In the nitrification tank 12, the air supplied from the blower 16 is diffused by the air diffuser 15, and ammonia nitrogen in the wastewater is converted into nitrite nitrogen or nitrous acid by nitrifying bacteria which are aerobic microorganisms in activated sludge under aerobic conditions. Oxidized to nitrate nitrogen. Moreover, the organic matter in the wastewater that could not be treated in the denitrification tank 11 is decomposed into water and carbon dioxide.

  Since the liquid is circulated from the nitrification tank 12 to the preceding denitrification tank 11 through a circulation path having a pump 17, in the denitrification tank 11, nitrite nitrogen and nitrate nitrogen are reduced by the denitrifying bacteria to be nitrogen. Reduce to gas.

In the process of such wastewater treatment, the aforementioned N ₂ O (nitrous oxide) is produced as a reaction byproduct of the oxidation treatment in the nitrification tank 12 and as an intermediate product of the reduction treatment in the denitrification tank 11. The N ₂ O gas, which is an intermediate product, is not always generated, but is incompletely denitrified in the denitrification tank 11 (caused by the incorporation of dissolved oxygen, the nitric acid load is too high, and the organic matter used by the denitrifying bacteria. Occurs when there is a shortage. It occurs when incomplete nitrification (oxygen shortage due to high ammonia / organic load) occurs in the nitrification tank 11. Although there is a possibility that N ₂ O is generated by other factors, in many cases, the above two are considered to be large factors.

The generated N ₂ O gas accumulates in the head space portion of the nitrification tank 12 and the denitrification tank 11 together with air or other generated gas. If this N ₂ O gas is released into the atmosphere as it is, problems arise as a countermeasure against global warming as described above. Therefore, in order to suppress this, the gas is collected by the gas collecting mechanism 21. The N ₂ O-containing gas collected from the denitrification tank 11 and the nitrification tank 12 by the gas collection mechanism 21 is sent to the biological oxidation treatment unit 22.

The biological oxidation treatment unit 22 is provided with a watering device 23 in the flow path of the N ₂ O-containing gas. The watering device 23 is supplied with a nitrification liquid discharged from the nitrification tank 12 by a pump 24 and is watered. ing. For this reason, the gas component of the collected N ₂ O-containing gas is dissolved in the nitrification liquid being sprinkled and returned to the nitrification tank 12. And it is biologically oxidized in this nitrification tank 12 and becomes NO ₃ .

As described above, the N ₂ O-containing gas generated in the denitrification tank 11 and the nitrification tank 12 is dissolved in the nitrification liquid sprinkled by the water sprinkler 23 constituting the biological oxidation treatment unit 22, and then in the nitrification tank 12. It is greatly reduced by being oxidized again by nitrifying bacteria. That is, N ₂ O in the gas can be treated in a nitrification / denitrification treatment system. Thereby, the gas collection mechanism 21, the biological oxidation treatment unit 22, and the watering device 23 are added to the existing equipment without requiring a special device for detoxifying the N ₂ O gas generated from the wastewater treatment device. With this simple configuration, it is possible to effectively reduce the release of N ₂ O gas to the atmosphere.

In addition, in order to increase these gas-liquid contact areas in the contact part of the water sprinkled from the water sprinkling device 23 of the biological oxidation process part 22 and the gas collected by the gas collection mechanism 21, for example, it shows in FIG. Such a baffle plate 25 may be provided. According to this structure, by the contact area of the gas-liquid is increased, it is possible to increase the dissolution efficiency of the nitrification liquid N 2 _O-containing gas. Moreover, the gas collection mechanism 21 may collect gas with a fan. Further, the liquid to be sprinkled is not limited to the nitrification liquid, but may be treated water separated from the nitrification liquid or normal tap water.

  FIG. 3 shows a modification of the first embodiment, in which the biological oxidation treatment unit 22 removes aerobic microorganisms in a path for returning water in which gas components are dissolved by watering from the watering device 23 to the nitrification tank 12. A carrier 26 to be attached is arranged. That is, as shown in the figure, a carrier 26 for attaching aerobic microorganisms is disposed at the lower part of the sprinkler 23. Any material may be used for the carrier 26, and for example, a material having air permeability to which aerobic microorganisms are effectively attached, such as an aggregate of plastic pieces whose surfaces are roughened, may be used.

With this configuration, by nitrification prepared by dissolving the N 2 _O-containing gas is brought into contact with the carrier 26, can process the N _{2 O} by aerobic microorganisms attached to the carrier, decomposition and removal rate of the N 2 _O Can be improved. In addition, as long as the water sprayed contacts the support | carrier 26, what kind of thing may be sufficient irrespective of the structure of illustration.

  4 and 5 show a second embodiment of the present invention. In this embodiment, the nitrification tank 12 is divided into a plurality of sections in the processing direction. In the example shown in the figure, the front part 12A and the rear part 12B are divided into two in the front and rear with respect to the processing direction. These front-stage part 12A and rear-stage part 12B are comprised so that to-be-processed water can distribute | circulate. Further, the air diffuser 15 is provided in common for the front stage part 12A and the rear stage part 12B.

  In FIG. 4, the gas collection mechanism 21 collects gas from the front part 12 </ b> A of the nitrification tank 12. The biological oxidation processing unit 22 is configured to sprinkle the collected gas with the watering device 23 and dissolve the gas component, and then return the water in which the gas component is dissolved to the rear stage 12B of the nitrification tank 12. ing. In FIG. 5, the gas collection mechanism 21 collects gas from the rear stage 12 </ b> B of the nitrification tank 12. The biological oxidation treatment unit 22 is configured to sprinkle the collected gas with the water sprinkling device 23 and dissolve the gas component, and then return the water in which the gas component is dissolved to the front part 12A of the nitrification tank 12. ing.

Here, as shown in FIG. 4, the gas is collected in the front stage 12A of the nitrification tank 12, and the water in which the gas is dissolved is returned to the rear stage 12B. The front stage 12A is more N ₂ O-containing than the rear stage 12B. This is a case where the amount of generation is large. That is, when an incomplete reaction occurs in the denitrification tank 11, N ₂ O is generated as described above. A part of this N ₂ O is dissolved in the water to be treated and flows into the front part 12 A of the nitrification tank 12. Then, in the front portion 12A, N _{2 O} that was dissolved in water, is released into a gas by bubbling by diffusing pipe 15, the N 2 _O-containing gas. For this reason, the amount of N ₂ O-containing gas generated from the front stage 12A close to the denitrification tank 11 increases. In such a case, the configuration as shown in FIG. 4 makes it possible to efficiently treat N ₂ O generated in the denitrification reaction process, and the amount of N ₂ O released can be effectively suppressed.

On the other hand, as shown in FIG. 5, the gas is collected in the rear stage 12B of the nitrification tank 12, and the water in which the gas is dissolved is returned to the front stage 12A. The rear stage 12B is more N ₂ O than the front stage 12A. This is a case where the amount of contained gas is large. That is, organic matter is oxidized in the nitrification tank 12, and the nitrification reaction progresses as it proceeds to the subsequent stage. It has been reported that N ₂ O-containing gas is generated as the nitrification reaction proceeds (for example, Patent Document 3). Therefore, in FIG. 5, N ₂ O gas generated in the rear stage portion 12B is collected and returned to the front stage portion 12A, thereby aiming at oxidation of N ₂ O. According to this method, it is possible to efficiently oxidize N ₂ O generated in the nitrification process.

Which of the configuration of FIG. 4 and the configuration of FIG. 5 described above is adopted may be determined according to individual characteristics as the wastewater treatment apparatus. In any case, it is possible to oxidize the re-dissolved N ₂ O to nitric acid by dissolving N ₂ O in the liquid and flowing it down to the nitrification tank 12.

In addition, as shown in the figure, a U-shaped portion is provided in the pipeline for dissolving N ₂ O in the liquid and allowing the nitrification liquid to flow down to the nitrification tank 12 to provide a water-filled structure so as to prevent backflow of gas from the downstream side. Yes.

  The rear stage part 12B in FIG. 4 and the front stage part 12A in FIG. 5 of the nitrification tank 12 are depicted in a sealed state in the respective drawings, but actually the air ejected from the air diffuser 15 is released to the outside. It is assumed that an escape portion is formed.

  FIG. 6 shows a modification of the above-described second embodiment. Also in this example, the nitrification tank 12 is divided into a plurality of parts in the processing direction, and includes a front stage part 12A and a rear stage part 12B. In addition, the front-stage part 12A and the rear-stage part 12B thus divided are configured so that the water to be treated can flow.

  Gas collecting mechanisms 21A and 21B are provided for the front stage 12A and the rear stage 12B, respectively. These gas collecting mechanisms 21A and 21B are connected to the divided front stage part 12A and rear stage part 12B of the nitrification tank 12 via the corresponding on-off valves 31A and 31B, respectively, so that gas can be collected from either of them. is doing.

  The biological oxidation treatment unit 22 includes a watering device 23 that sprinkles water collected by the gas collecting mechanism 21A or 21B. The downstream side of the watering device 23 is connected to the rear stage part 12B and the front stage part 12B of the nitrification tank 12 through corresponding on-off valves 32A and 32B after passing through the full water part. That is, the water in which the gas component is dissolved can be returned to any of these. In addition, the opposite side of the biological oxidation treatment unit 22 that has passed through the water sprinkler 23 communicates with an external deodorization facility or the like via the corresponding exhaust valves 33A and 33B.

Furthermore, a measuring device 35 for measuring the N ₂ O concentration contained in the gas generated from the front stage 12A and the rear stage 12B of the nitrification tank 12 is provided. When the N ₂ O concentration contained in the gas from the front stage part 12A is higher than the gas from the rear stage part 12B, the measuring device 35 uses a controller (not shown) to open the on-off valve 31A of the gas collection mechanism 21A leading to the front stage part 12A. Open and collect gas from the front stage 12A. Moreover, the on-off valve 32A leading to the rear stage part 12B of the biological oxidation treatment part 22 is opened, and the water in which the gas component is dissolved is returned to the rear stage part 12B. Further, the corresponding exhaust valve 33A is opened, and the gas from which the gas component has been eluted is exhausted to the deodorizing device or the like through the watering device 23.

On the other hand, when the N ₂ O concentration contained in the gas from the rear stage part 12B is higher than the gas from the front stage part 12A, the measuring device 35 opens and closes the gas collection mechanism 21B leading to the rear stage part 12B by a controller (not shown). The valve 31B is opened, and the gas from the rear stage 12B is collected. Moreover, the on-off valve 32B leading to the front stage part 12A of the biological oxidation treatment part 22 is opened, and the water in which the gas component is dissolved is returned to the front stage part 12A. Further, the corresponding exhaust valve 33B is opened, and the gas from which the gas component has been eluted is exhausted to the deodorizing device or the like through the watering device 23.

That is, the N ₂ O concentration in the collected gas from the preceding nitrification tank 12A and the subsequent nitrification tank 12B is measured, and the generated gas is collected from the nitrification tank 12A or 12B having the higher measured value and dissolved in the liquid. The nitrification tank 12B or 12A having the lower measured value was allowed to flow down. Thereby, N ₂ O generated in the denitrification reaction process and the nitrification reaction process can be treated efficiently.

The N ₂ O concentration in the collected gas from the nitrification tank 12A at the front stage and the nitrification tank 12B at the rear stage is measured, and the collection destination of the gas and the return destination of the sprinkled water are either the front stage 12A or the rear stage 12B. As long as the configuration is determined, the configuration is not limited to the illustrated configuration, and any configuration may be used.

  In the said embodiment, although the case where the division | segmentation number of the nitrification tank 12 was two was illustrated, of course, you may divide into three or more. In this case, the preceding stage may be any section as long as it is a section close to the denitrification tank 11, and does not necessarily indicate a section adjacent to the denitrification tank 11. Similarly, the rear part may be any part as long as it is a rear part with respect to the front part, and does not necessarily indicate the discharge part of the nitrification tank 12.

  Although not shown in the second embodiment, the baffle plate 25 for increasing the gas-liquid area and the carrier 26 for aerobic microorganisms described as a modification in the first embodiment may be installed. Of course it is good.

FIG. 7 is a modification of the embodiment of FIG. 1 described above, and is provided with a measuring device 37 that measures the N ₂ O concentration of the gas collected by the gas collecting mechanism 21. The N ₂ O concentration measured by the measuring device 37 is input to a controller (control unit) 38 and compared with a preset value (N ₂ O concentration target value). When the measured value of the N ₂ O concentration is equal to or greater than a preset value, the controller 38 controls the activation of the pump 24 so as to execute watering by the watering device 23. That is, the N ₂ O concentration in the collected gas is measured, and only when the measured value is higher than the set target value, the watering pump 24 is operated to redissolve the N ₂ O gas. Thereby, the running cost of the pump 24 for watering can be reduced.

Further, the controller 38 may calculate the watering amount according to the deviation between the measured value of N ₂ O and the target value, and control the watering pump 24 to adjust the watering amount. Further, the blower 16 may be controlled in accordance with the measured N ₂ O concentration to adjust the amount of aeration with respect to the nitrification tank 12.

These perform control according to the measured value of N ₂ O contained in the collected gas, and can prevent wasteful operation and enable efficient operation.

  FIG. 8 shows a third embodiment. In addition, the same code | symbol is attached | subjected and demonstrated to the same apparatus and member as each embodiment mentioned above.

  The denitrification tank 11, the nitrification tank 12, the final sedimentation basin 13 as a solid-liquid separation device, and the circulation path from the nitrification tank 12 to the denitrification tank 11 are the same as those of the above-described embodiments, and the same devices and members as these. Are given the same reference numerals.

  In this embodiment, a biological reaction tank 22 </ b> A for biologically treating the water to be treated is used as the biological oxidation treatment unit 22. The water to be treated in the biological reaction tank 22A is aerated by the air diffuser 45 provided at the bottom of the tank.

  The gas generated from the denitrification tank 11 and the nitrification tank 12 is collected by the gas collection mechanism 21 and blown into the treated water in the biological reaction tank 22A by the fan 48. The treated water in the biological reaction tank 22A is treated water prepared separately, treated water in the denitrification tank 11 as shown in FIG. 8, or in the nitrification tank 12 as shown in FIG. The liquid to be treated may be introduced in a batch manner.

As described above, the N ₂ O gas and the odor gas generated as intermediate substances of the nitrification reaction in the nitrification tank 12 and the denitrification reaction in the denitrification tank 11 are converted into the biological reaction tank 22A through the gas path of the gas collection mechanism 21. Was introduced directly. Further, the treated water by the biological reaction in the biological reaction tank 22A was configured to be returned to the denitrification tank 11 or the nitrification tank 12 in a batch type.

According to the above configuration, the biological reaction tank 22A can oxidize N ₂ O and oxidize and deodorize the generated odor gas such as hydrogen sulfide gas and ammonia gas. Thus, it is possible to perform deodorization treatment of N 2 _O in the process and the odorous gas simultaneously. Since the organic substance load and nitrogen load of the biological reaction tank 22A are lower than those of the nitrification tank 12, incomplete oxidation hardly occurs, and more complete oxidation treatment of N ₂ O can be expected. The place where the treated water is returned may be a raw water tank (not shown) as shown in FIG.

  FIG. 11 shows a modification of the above-described third embodiment. A biological reaction tank 22B as a biological oxidation treatment unit 22 is a carrier 51 in which aerobic microorganisms are attached to an intermediate part in the height direction in the tank. The watering device 52 is provided in the upper part. This watering device 52 sprinkles the treated water separated from the nitrification liquid in the final sedimentation basin 13. The gas generated from the denitrification tank 11 and the nitrification tank 12 is collected by the gas collecting mechanism 21, supplied to the lower space of the carrier 51 by the fan 48, and passes through the arrangement portion of the carrier 51 in an upward flow.

Here, as described above, the carrier 51 is made by adhering aerobic microorganisms such as nitrifying bacteria, and the collected N ₂ O-containing gas is vented upward in the reaction tank 22B. In addition, N ₂ O can be efficiently oxidized by the aerobic microorganism attached to the carrier 51. In this case, since the gas collected by the gas collecting mechanism 21 is blown into the lower space of the carrier 51, the capacity of the fan 48 can be reduced compared with the case of blowing into the liquid, and a reduction in operating cost can be expected.

  The treated water generated in the biological reaction tank 22B was configured to be returned to the denitrification tank 11. In addition, a nitrification tank or a raw water tank may be used as the place where the treated water is returned.

  In each of the above-described embodiments, the nitrification solution oxidized by nitrifying bacteria in the nitrification tank 12 is solid-liquid separated into treated water and activated sludge by the final sedimentation basin 13, but the final sedimentation basin 13 is not used. Alternatively, a membrane separation activated sludge method for solid-liquid separation may be used.

  In this membrane separation activated sludge method, a membrane filtration device is provided in the downstream portion in the nitrification tank 12, and solid-liquid separation is performed in the nitrification tank 12 by this membrane filtration device, and the separated treatment liquid is taken out. In this case, a part of the nitrification liquid is returned from the nitrification tank 12 to the denitrification tank 11 as in the above-described embodiments. Moreover, since the activated sludge solid-liquid separated by the membrane filtration device is accumulated in the nitrification tank 12, the accumulated activated sludge is extracted from the nitrification tank 12. A part of the extracted activated sludge is returned to the denitrification tank 11 and the rest is discharged out of the apparatus as excess sludge, as in the above-described embodiments.

As described above, in each embodiment of the present invention, raw water is reduced by denitrifying bacteria in an oxygen-free denitrification tank, and the treated water that has passed through the denitrification tank is aerated and nitrified in an aerobic nitrification tank. In performing oxidation treatment with bacteria, a gas containing N ₂ O generated in the biological treatment process is collected by a gas collecting mechanism, and the gas collected by this gas collecting mechanism is oxidized to convert N ₂ O into NO. since changing the _3, it is possible to effectively suppress the release into the atmosphere of N _{2 O} by use of existing facilities.

  Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Denitrification tank 12 ... Nitrification tank 21 ... Gas collection mechanism 22 ... Biological oxidation process part 22A, 22B ... Biological reaction tank 23 ... Sprinkler 25 ... Baffle plate 26 ... Carrier

Claims (18)

This is a biological treatment method for wastewater in which raw water is reduced by denitrifying bacteria in an anaerobic denitrification tank, and the treated water passed through this denitrification tank is oxidized by nitrifying bacteria in an aerobic nitrification tank. And
A gas containing N ₂ O generated in the biological treatment process is collected by a gas collecting mechanism, and the gas collected by the gas collecting mechanism is dissolved in a liquid and oxidized to convert N ₂ O into NO ₃ . Biological treatment method of wastewater characterized by changing. A denitrification tank that performs reduction treatment of raw water with denitrifying bacteria in the absence of oxygen, a nitrification tank that oxidizes the treated water that has passed through this denitrification tank with nitrifying bacteria in an aerobic state by aeration, and an oxidized nitrification A wastewater treatment device having a solid-liquid separation device for solid-liquid separation of the liquid into treated water and activated sludge,
A gas collection mechanism for collecting a gas containing N ₂ O generated in the biological treatment process in the denitrification tank and the nitrification tank;
A bio-oxidation unit that dissolves the gas collected by the gas collection mechanism in a liquid and oxidizes the gas to change N ₂ O to NO ₃ ;
A wastewater treatment apparatus characterized by comprising:   The biological oxidation treatment unit has a watering device that sprinkles the gas collected by the gas collecting mechanism and dissolves the gas component in water, and returns the water in which the gas component is dissolved to the nitrification tank. The wastewater treatment apparatus according to claim 2, wherein the wastewater treatment apparatus is configured to be oxidized. The nitrification tank is divided into a plurality of treatment directions, and the front and rear stages with respect to the divided treatment directions are configured to allow the water to be treated to flow,
The gas collecting mechanism collects gas from the front part of the nitrification tank, and the biological oxidation treatment part returns the water in which the gas component is dissolved to the rear part of the nitrification tank and oxidizes it in the nitrification tank. The wastewater treatment apparatus according to claim 3. The nitrification tank is divided into a plurality of treatment directions, and the front and rear stages with respect to the divided treatment directions are configured to allow the water to be treated to flow,
The gas collecting mechanism collects gas from the rear stage part of the nitrification tank, and the biological oxidation treatment part returns the water in which the gas component is dissolved to the front stage part of the nitrification tank, and oxidizes in the nitrification tank. The wastewater treatment apparatus according to claim 3. The nitrification tank is divided into a plurality of treatment directions, and the front and rear stages with respect to the divided treatment directions are configured to allow the water to be treated to flow,
The gas collecting mechanisms are respectively connected to the front and rear stages of the nitrification tank via on-off valves, respectively, and can collect gas from either of them, and the biological oxidation treatment parts are respectively connected to the on-off valves. Connected to the rear stage and the front stage of the nitrification tank, respectively, and the structure that can return the water in which the gas component is dissolved to any of these, is oxidized in the nitrification tank.
The wastewater treatment apparatus according to claim 3. The measuring device has a measuring device for measuring the N ₂ O concentration of the gas generated from the front part and the rear part of the nitrification tank,
When the N ₂ O concentration of the gas from the front stage part of the nitrification tank is higher than the gas from the rear stage part, the gas collecting mechanism opening / closing valve leading to the front stage part is opened to collect the gas from the front stage part And the biological oxidation treatment unit opens an on-off valve leading to the rear stage part to return water in which the gas component is dissolved to the rear stage part,
When the N ₂ O concentration of the gas from the rear stage of the nitrification tank is higher than the gas from the front stage, the gas collection mechanism leading to the rear stage is opened to collect the gas from the rear stage The waste water treatment apparatus according to claim 6, wherein the biological oxidation treatment unit opens an on-off valve that communicates with the front stage and returns water in which the gas component is dissolved to the front stage.   4. The biological oxidation treatment unit has a baffle plate for improving a gas-liquid contact area at a contact portion between water sprayed and gas collected by the gas collecting mechanism. The wastewater treatment apparatus according to any one of claims 7 to 7.   8. The biological oxidation treatment unit according to any one of claims 3 to 7, wherein a carrier for attaching aerobic microorganisms is disposed in a path for returning water in which gas components are dissolved to the nitrification tank. Waste water treatment equipment.   The wastewater treatment device according to any one of claims 3 to 9, wherein water sprayed by the watering device is a nitrification liquid taken out from the nitrification tank.   The wastewater treatment apparatus according to any one of claims 3 to 9, wherein the water sprinkled by the watering apparatus is treated water that is solid-liquid separated from the nitrification liquid. The gas collecting mechanism has a measuring device that measures the N ₂ O concentration of the gas collected, and has a control unit that executes watering by the watering device when the measured N ₂ O concentration is equal to or higher than a preset value. The wastewater treatment apparatus according to any one of claims 3 to 11, wherein It has a measuring device which measures N ₂ O concentration of the gas which the gas collecting mechanism collects, and has a control part which adjusts the amount of watering by the watering device according to the measured N ₂ O concentration. The wastewater treatment apparatus according to any one of claims 3 to 11. It has a measuring device which measures the N ₂ O concentration of the gas body which the gas collection mechanism collects, and has a control part which adjusts the amount of aeration to the nitrification tank according to the measured N ₂ O concentration The wastewater treatment apparatus according to any one of claims 3 to 13.   As the biological oxidation treatment unit, a biological reaction tank that performs biological treatment by aeration of water to be treated is used, and the gas collected by the gas collecting mechanism is blown into the water to be treated in the biological reaction tank. The wastewater treatment apparatus according to claim 2.   The wastewater treatment apparatus according to claim 15, wherein a liquid in the denitrification tank is used as water to be treated in a biological reaction tank used as the biological oxidation treatment unit.   The wastewater treatment apparatus according to claim 15, wherein a liquid in the nitrification tank is used as water to be treated in a biological reaction tank used as the biological oxidation treatment unit.   A biological reaction provided with a watering device that disperses the treated water separated from the nitrification liquid from above by arranging a carrier having aerobic microorganisms attached to the intermediate portion in the height direction in the tank as the biological oxidation treatment unit. The gas collected by the gas collecting mechanism using a tank is supplied to a lower space of the carrier in the biological reaction tank, and the carrier arrangement portion is passed upwardly. The waste water treatment apparatus according to 2.

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