JP2010201394A - Nitrous acid type nitrification reaction sludge, method and apparatus for manufacturing the same, and method and apparatus of wastewater treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitrous acid type nitrification reaction sludge that has low energy cost and that facilitates stable wastewater treatment over a long period, to provide a method and apparatus for manufacturing the same, and to provide a method and apparatus of wastewater treatment. <P>SOLUTION: In order to control pH of an activated sludge 12 containing ammonia-oxidizing bacteria and nitrite-oxidizing bacteria into 6 or less, acid liquid is added to the activated sludge 12 from an acid liquid tank 18. As a result, nitrite-oxidizing bacteria in the activated sludge 12 is deactivated to make the ammonia-oxidizing bacteria accumulate with priority. Consequently, with nitrification reaction of ammonia nitrogen stopped in the stage of nitrous acid, the supply quantity of oxygen during the nitrification reaction and the supply quantity of a hydrogen donor during the reduction reaction are reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nitrite type nitrification reaction sludge, a production method and a production apparatus thereof, and a wastewater treatment method and a wastewater treatment apparatus. Here, the nitrite-type nitrification sludge is activated sludge in which ammonia-oxidizing bacteria that oxidize ammoniacal nitrogen to nitrous acid are preferentially accumulated.

  As a treatment method of wastewater containing ammonia nitrogen, nitrification and denitrification removes ammonia nitrogen by nitrifying (oxidizing) ammonia nitrogen to nitric acid by nitrifying bacteria and then reducing this nitric acid to nitrogen gas by denitrifying bacteria. Nitrogen methods are known.

However, in the above nitrification denitrification method, ammonia nitrogen (NH ₄ ) in waste water is nitrified to nitric acid (NO ₃ ) via nitrous acid (NO ₂ ), so that a large amount of oxygen is used during the nitrification reaction. It is necessary to supply. Further, it is necessary to supply a large amount of hydrogen donor (for example, methanol) in the denitrification reaction from nitric acid to nitrogen gas.

  Therefore, by stopping the nitrification reaction of ammonia nitrogen at the nitrous acid stage and denitrifying this nitrous acid into nitrogen gas, the supply amount of oxygen during the nitrification reaction and the supply of hydrogen donor during the denitrification reaction It is conceivable to reduce the amount.

  On the other hand, as a wastewater treatment method that replaces the conventional nitrification denitrification method, a wastewater treatment method involving denitrification treatment with anaerobic ammonia-oxidizing bacteria is attracting attention. In this method, ammonia nitrogen in wastewater is nitrified to nitrous acid, and then the nitrous acid and ammonia nitrogen in the waste water are simultaneously denitrified by anaerobic ammonia oxidizing bacteria. This is advantageous over the conventional nitrification denitrification method in that not only can the supply amount of hydrogen be reduced but also it is not necessary to supply a hydrogen donor during the denitrification reaction. However, in order to perform wastewater treatment using anaerobic ammonia oxidizing bacteria, it is necessary to stop the nitrification reaction of ammoniacal nitrogen in the wastewater at the nitrous acid stage.

  For this reason, several methods for producing a microbial carrier that provide a nitrite-type nitrification reaction in which ammonia nitrogen in wastewater is nitrified to nitrite have been proposed.

  For example, Patent Document 1 describes a method of stopping the nitrification reaction of ammoniacal nitrogen at the nitrite stage by accumulating only nitrifying bacteria suitable for the nitrite type nitrification reaction by heat treatment. In this method, heat treatment is applied to a carrier containing ammonia-oxidizing bacteria that oxidize ammonia nitrogen to nitrite and nitrite-oxidizing bacteria that nitrify nitrite to nitric acid, thereby inactivating the nitrite-oxidizing bacteria. Thus, ammonia-oxidizing bacteria are preferentially accumulated in the carrier. If this carrier is used, the nitrification reaction of ammoniacal nitrogen in wastewater can be stopped at the nitrous acid stage.

  However, in the method described in Patent Document 1, it is necessary to supply a large amount of heat energy during the heat treatment of the carrier. For this reason, from the viewpoint of reducing energy costs, a method that does not involve heat treatment of the carrier has been proposed.

  For example, Patent Document 2 discloses that a carrier in which ammonia-oxidizing bacteria are preferentially accumulated is produced by performing acid treatment on a carrier in which activated sludge containing ammonia-oxidizing bacteria and nitrite-oxidizing bacteria is immobilized. Discloses a method of performing wastewater treatment using the carrier.

Japanese Patent No. 3788601 JP 2008-272610 A

  However, in the method described in Patent Document 2, it is necessary to periodically acid-treat the carrier in order to inactivate nitrite-oxidizing bacteria brought in from the outside due to waste water or the like. Depending on the conditions of this acid treatment, The mechanical strength may gradually deteriorate, and nitrifying bacteria inside the carrier may flow out.

  Further, in order to periodically acid-treat the carrier, it is necessary to separate the waste water and the carrier in the nitrification reaction tank and collect only the carrier, which requires a complicated process for collecting the carrier.

  The present invention has been made in view of the above circumstances, and has a low energy cost and can easily perform stable wastewater treatment over a long period of time, a nitrite-type nitrification reaction sludge, a manufacturing method and a manufacturing apparatus thereof, and wastewater. An object is to provide a treatment method and a wastewater treatment apparatus.

  The method for producing a nitrite-type nitrifying sludge according to the present invention is a method for producing a nitrite-type nitrifying sludge in which ammonia-oxidizing bacteria are preferentially accumulated, and at least ammonia-oxidizing bacteria and nitrite-oxidizing bacteria It includes a step of subjecting the activated sludge to an acid treatment so that the pH of the contained activated sludge is 6 or less.

Here, “pH is 6 or less” includes not only the case where the pH is 0 or more and 6 or less, but also the case where the pH is less than 0, which is difficult to actually measure with a pH meter. In the present specification, “pH” means −log ₁₀ [H ⁺ ] at 25 ° C. and 1 atm (where [H ⁺ ] is a hydrogen ion concentration (mol / L)).

  As a result of intensive studies by the inventor of the present application, it has been clarified that ammonia oxidizing bacteria have high resistance to acids, while nitrite oxidizing bacteria have low resistance to acids. The above production method utilizes such a difference in acid resistance between ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, and by applying acid treatment to activated sludge, the nitrite-oxidizing bacteria are inactivated. Ammonia-oxidizing bacteria can preferentially accumulate.

  In addition, since the acid treatment can be performed at a lower cost than the heat treatment of the carrier, the energy cost can be reduced.

  Further, by accumulating ammonia oxidizing bacteria in activated sludge instead of the carrier, it is possible to prevent a decrease in the nitrification reaction rate due to the breakage of the carrier and to omit a complicated process for collecting the carrier.

  In the method for producing nitrite-type nitrification reaction sludge, in the step of performing the acid treatment, an acid solution is added to the activated sludge so that the pH of the activated sludge is 0.5 or more and 6.0 or less (more preferably It is preferable to hold in the range of 0.5 to 5.0.

  By adjusting the pH of the activated sludge to the above range, the nitrite oxidizing bacteria can be selectively deactivated without deactivating the ammonia oxidizing bacteria.

  In the method for producing a nitrite-type nitrification reaction sludge, the acid treatment is preferably performed under at least one of the following conditions (1) to (3).

    (1) Hold the pH of the activated sludge for 30 seconds or more in the range of less than 2.0.

    (2) Maintaining the pH of the activated sludge in the range of 2.0 or more and less than 4.0 for 3 minutes or more.

    (3) Maintaining the pH of the activated sludge in the range of 4.0 or more and 6.0 or less for 15 minutes or more.

  This makes it possible to produce activated sludge in which nitrite-oxidizing bacteria are reliably inactivated and ammonia-oxidizing bacteria are more selectively accumulated.

  The nitrite type nitrification reaction sludge according to the present invention can be manufactured by the above-described method for manufacturing a nitrite type nitrification reaction sludge.

  A nitrite-type nitrification reaction sludge production apparatus according to the present invention is a nitrite-type nitrification reaction sludge production apparatus in which ammonia-oxidizing bacteria are preferentially accumulated, and at least ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. It includes an acid treatment device that performs acid treatment on the activated sludge so that the pH of the activated sludge is 6 or less.

  By applying acid treatment at pH 6 or lower to the activated sludge with the acid treatment apparatus, the nitrite oxidizing bacteria in the activated sludge can be deactivated, and ammonia oxidizing bacteria can be preferentially accumulated.

  The wastewater treatment method according to the present invention is a wastewater treatment method for treating wastewater containing ammoniacal nitrogen, wherein the activated sludge containing at least ammonia oxidizing bacteria and nitrite oxidizing bacteria has a pH of 6 or less. A step of subjecting the activated sludge to acid treatment; a step of oxidizing the ammoniacal nitrogen contained in the wastewater into nitrous acid by the activated sludge subjected to the acid treatment; and denitrification of the nitrite. And a process of performing a process.

  According to the above wastewater treatment method, the ammonia-oxidizing bacteria are preferentially accumulated in the activated sludge by subjecting the activated sludge to an acid treatment at a pH of 6 or less, and the nitrification stage of ammonia nitrogen is performed in the nitrous acid stage. You can stop at. Thereby, the supply amount of oxygen during the nitrification reaction and the supply amount of hydrogen donor during the reduction reaction can be reduced.

  In the wastewater treatment method, in the step of performing the denitrification treatment, the subnitrogen generated in the step of oxidizing the ammoniacal nitrogen by anaerobic ammonia oxidizing bacteria using the ammoniacal nitrogen contained in the wastewater as a hydrogen donor. Nitric acid may be denitrified.

  In the wastewater treatment method, in the step of performing the denitrification treatment, the nitrous acid generated in the step of oxidizing the ammoniacal nitrogen may be denitrified by a denitrification bacterium.

  The wastewater treatment method may include a step of recovering the activated sludge used in the step of oxidizing the ammonia nitrogen to the nitrous acid and a step of performing the acid treatment on the recovered activated sludge. preferable.

  Thereby, even if nitrite-oxidizing bacteria are brought in from the outside, the nitrite-type nitrification performance can be maintained over a long period of time.

  The wastewater treatment method preferably includes a step of adjusting the pH of the activated sludge by adding an alkaline agent to the activated sludge subjected to the acid treatment.

  Thus, by adjusting the pH of the activated sludge after acid treatment by adding an alkali agent, it is possible to prevent the efficiency of wastewater treatment from being reduced.

  The wastewater treatment apparatus of the present invention is a wastewater treatment apparatus for treating wastewater containing ammonia nitrogen, wherein the activated sludge containing at least ammonia oxidizing bacteria and nitrite oxidizing bacteria has a pH of 6 or less. An acid treatment device that performs acid treatment on sludge, a nitrous acid generation tank that oxidizes the ammoniacal nitrogen contained in the wastewater to nitrous acid by the activated sludge that has been subjected to the acid treatment, and nitrous acid. And a denitrification tank that performs a denitrification process.

  In the wastewater treatment apparatus, the denitrification tank may denitrify the nitrous acid generated in the nitrous acid generation tank by anaerobic ammonia oxidizing bacteria using the ammoniacal nitrogen contained in the wastewater as a hydrogen donor. Good.

  In the wastewater treatment apparatus, the denitrification tank may denitrify the nitrous acid generated in the nitrous acid generation tank by denitrifying bacteria.

  In the wastewater treatment device, a recovery device that recovers the activated sludge from the nitrous acid production tank, and a regeneration device that regenerates the activated sludge by performing the acid treatment on the activated sludge recovered by the recovery device. Are preferably included.

  The wastewater treatment apparatus preferably includes a pH adjuster that adjusts the pH of the activated sludge by adding an alkaline agent to the activated sludge subjected to the acid treatment.

  According to the present invention, by subjecting activated sludge to an acid treatment at pH 6 or lower, nitrite-oxidizing bacteria can be inactivated and ammonia-oxidizing bacteria can be preferentially accumulated. Thereby, the nitrification reaction of ammonia nitrogen in the wastewater can be stopped at the nitrous acid stage, and the supply amount of oxygen during the nitrification reaction and the supply amount of hydrogen donor during the reduction reaction can be reduced.

  Since the acid treatment can be performed at a lower cost than the heat treatment of the carrier, the energy cost can be reduced.

  Further, by accumulating ammonia oxidizing bacteria in activated sludge instead of the carrier, it is possible to prevent a decrease in the nitrification reaction rate due to the breakage of the carrier and to omit a complicated process for collecting the carrier.

It is a block diagram which shows an example of the manufacturing apparatus (reactive sludge manufacturing apparatus) of the nitrite type nitrification reaction sludge which concerns on this invention. It is a block diagram which shows an example of the nitrification processing apparatus using a nitrite type nitrification reaction sludge. It is a table | surface which shows the quality of the synthetic wastewater used for the 1st wastewater treatment experiment. It is a graph which shows the nitrogen concentration in the treated water on the conditions of a 1st wastewater treatment experiment, (a)-(c) shows the nitrogen concentration at the time of using this invention sludge AC, respectively, (d) is a comparison The nitrogen concentration when sludge is used is shown. It is a table | surface which shows the quality of the synthetic wastewater used for the 2nd wastewater treatment experiment. (A) is a table | surface which shows the quality of the synthetic wastewater which contains 44 mg / L of nitrite nitrogen, (b) is a table | surface which shows the quality of the synthetic wastewater which contains 44 mg / L of ammonia nitrogen. It is a block diagram which shows the aerobic reaction tank used for the 2nd wastewater treatment experiment. (A) is a graph which shows the nitrate nitrogen density | concentration of the supernatant liquid obtained by carrying out the continuous aeration process of the synthetic waste water (refer FIG. 5 (a)) containing 44 mg / L of nitrite nitrogen for one month. (B) is a graph showing the concentration of nitrite nitrogen in the supernatant obtained by continuous aeration treatment of synthetic wastewater containing 44 mg / L of ammoniacal nitrogen (see FIG. 5B) for one month. It is a block diagram which shows an example of the nitrification processing apparatus which performs the acid treatment of reaction sludge regularly. It is a table | surface which shows the average water quality of the wastewater used for the 3rd wastewater treatment experiment. It is a graph which shows the nitrogen concentration in the treated water under the conditions of the third wastewater treatment experiment. (A) is a flowchart showing a wastewater treatment method involving denitrification treatment by denitrifying bacteria, and (b) is a flowchart showing a wastewater treatment method involving denitrification treatment by anaerobic ammonia oxidizing bacteria. It is a block diagram which shows an example of the waste water treatment apparatus for enforcing the waste water treatment method which concerns on this invention. It is a block diagram which shows the modification of the waste water treatment apparatus shown in FIG. It is a block diagram which shows the other modification of the waste water treatment apparatus shown in FIG. It is a block diagram which shows the other modification of the waste water treatment apparatus shown in FIG. It is a block diagram which shows the modification of the waste water treatment apparatus shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  The nitrite-type nitrification sludge according to the present invention is an activated sludge in which ammonia-oxidizing bacteria that oxidize ammoniacal nitrogen to nitrous acid are preferentially accumulated.

  FIG. 1 is a configuration diagram showing an example of a nitrite-type nitrifying reaction sludge production apparatus (reaction sludge production apparatus). As shown in the figure, the reaction sludge production apparatus 10 is based on an acid treatment tank 14 in which activated sludge 12 is stored, a pH measuring device 16 that measures the pH of the activated sludge 12, and a measurement result of the pH measuring device 16. And a pump P for supplying the acid solution stored in the acid solution tank 18 to the acid treatment tank 14.

  The activated sludge 12 is a complex microbial sludge containing at least ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. For example, activated sludge in a treatment plant that treats sewage and factory wastewater, lakes, rivers, sea bottom mud, surface Can be used.

  The pH of the activated sludge 12 is constantly measured by the pH measuring device 16, and the supply amount of the acid solution to the acid treatment tank 14 by the pump P is adjusted based on the measurement result of the pH measuring device 16. Thereby, the acid treatment of pH 6 or less is performed on the activated sludge 12. Here, “pH is 6 or less” includes not only the case where the pH is 0 or more and 6 or less, but also the case where the pH is less than 0, which is difficult to measure with a general pH meter. For example, even when the activated sludge 12 is charged into 2N sulfuric acid having a negative pH value in theory, the activated sludge 12 after neutralizing the acid-treated sludge 12 and leaving it for a certain period of time can be used. The ammonia oxidizing bacteria in 12 can be reactivated.

  As a result of intensive studies by the inventor of the present application, it has been clarified that ammonia oxidizing bacteria have high resistance to acids, while nitrite oxidizing bacteria have low resistance to acids. The reaction sludge production apparatus 10 having the above configuration utilizes the difference in acid resistance between such ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, and by subjecting the activated sludge 12 to an acid treatment of pH 6 or less, By reacting with nitrite-oxidizing bacteria, a reaction sludge in which ammonia-oxidizing bacteria preferentially accumulate can be produced.

  In the acid treatment of the activated sludge 12, the pH is preferably in the range of 0.5 to 6.0, and more preferably in the range of 0.5 to 5.0. Thereby, it is possible to quickly sterilize the nitrite oxidizing bacteria without inactivating the ammonia oxidizing bacteria.

  In addition, the acid treatment of the activated sludge 12 is preferably performed under at least one of the following conditions (1) to (3).

    (1) Hold the pH of the activated sludge for 30 seconds or more in the range of less than 2.0.

    (2) Maintaining the pH of the activated sludge in the range of 2.0 or more and less than 4.0 for 3 minutes or more.

    (3) Maintaining the pH of the activated sludge in the range of 4.0 or more and 6.0 or less for 15 minutes or more.

  Thereby, the nitrite oxidizing bacteria in the activated sludge 12 can be reliably deactivated, and the ammonia oxidizing bacteria can be more selectively accumulated.

  Moreover, it is preferable to adjust the pH of the activated sludge 12 by adding an alkali agent to the activated sludge 12 after the acid treatment. Thereby, it can prevent that the efficiency of wastewater treatment falls.

  Although FIG. 1 shows an example in which a predetermined amount of activated sludge 12 is subjected to acid treatment in a batch mode, the activated sludge 12 passing through the acid treatment tank 14 at a constant flow rate is acid-treated in a continuous manner. May be performed. When acid treatment is performed in a continuous manner, the acid treatment time (pH retention time) under the conditions (1) to (3) above can be read as the average residence time of the activated sludge 12 in the acid treatment tank 14 and applied. .

  Moreover, although FIG. 1 demonstrated the example in which the reaction sludge production apparatus 10 became independent, you may incorporate the reaction sludge production apparatus 10 in a wastewater treatment apparatus, and may be used as a part of wastewater treatment apparatus.

  Next, the configuration of a nitrification treatment apparatus that oxidizes (nitrifies) ammonia nitrogen in wastewater to nitrous acid using the nitrite type nitrification reaction sludge produced by the reaction sludge production apparatus 10 having the above configuration will be described.

  FIG. 2 is a configuration diagram showing an example of a nitrification processing apparatus using nitrite type nitrification reaction sludge. The nitrification apparatus 20 mainly includes a raw water tank 22 for storing wastewater raw water, an aerobic reaction tank (nitrite production tank) 24 in which nitrification of wastewater raw water flowing from the raw water tank 22 is performed, and nitrification treatment is performed. The waste water (treated water 30) and the reaction sludge (nitrite-type nitrification reaction sludge) 28 are separated from each other.

  Between the raw water tank 22 and the aerobic reaction tank 24, a pump P <b> 1 (raw water pump) that sends raw waste water to the aerobic reaction tank 24 is provided, and between the precipitation tank 26 and the aerobic reaction tank 24. Is provided with a pump P2 (return sludge pump) for returning the reaction sludge 28 to the aerobic reaction tank 24.

  In the aerobic reaction tank 24, a mixed liquid 32 of raw water wastewater sent from the raw water tank 22 by the pump P1 and reaction sludge 28 returned from the settling tank 26 by the pump P2 is accumulated. The aeration apparatus 34 provided in the aerobic reaction tank 24 is aerated and stirred. For example, the air diffuser 34 has a configuration in which air is ejected from a plurality of holes provided in a cylindrical pipe, and the liquid mixture 32 is uniformly stirred and oxygen necessary for nitrification is aerobically reacted. Supply to tank 24.

  The pH of the mixed solution 32 in the aerobic reaction tank 24 is constantly (or periodically) measured by the pH measuring device 16, and based on the measured value of the pH measuring device 16, the acid solution tank 18 is pumped by the pump P 3. To the aerobic reaction tank 24. Thereby, the pH of the liquid mixture 32 can be adjusted within a predetermined range.

  In the aerobic reaction tank 24 configured as described above, the ammoniacal nitrogen in the mixed solution 32 is oxidized (nitrified) into nitrous acid by ammonia oxidizing bacteria brought in by the reaction sludge 28.

  The liquid mixture 32 that has been subjected to nitrification in the aerobic reaction tank 24 is sent to a precipitation tank 26 and separated into reaction sludge 28 and treated water 30. Separation of the reaction sludge 28 and the treated water 30 in the settling tank 26 can be performed by any method. In FIG. 2, the example which isolate | separates using the specific gravity difference of the reaction sludge 28 and the treated water 30 is shown.

  The reaction sludge 28 that has been gravity-precipitated in the settling tank 26 is extracted from below the settling tank 26, and the treated water 30 that is a supernatant is discharged from the settling tank 26.

  Thereafter, the reaction sludge 28 is returned again to the aerobic reaction tank 24 by operating the pump P2 with the return sludge valve V1 opened. The total amount of the reaction sludge 28 in the nitrification apparatus 20 can be adjusted by opening and closing the sludge extraction valve V2.

  In order to confirm the nitrite type nitrification performance of the nitrite type nitrification reaction sludge produced by the reaction sludge production apparatus 10 using the nitrification treatment apparatus 20 having the above configuration, a first wastewater treatment experiment by the following method was performed. It was.

  As waste water to be subjected to nitrification treatment, synthetic waste water adjusted to have an ammoniacal nitrogen concentration of 40 mg / L was used. FIG. 3 is a table showing the quality of the synthetic wastewater that is the object of nitrification treatment.

  The reaction sludge 28 was subjected to an acid treatment and a neutralization treatment under the following conditions with respect to a return sludge collected at a sewage treatment plant (activated sludge suspended solids concentration (MLSS concentration: Mixed Liquor Suspended Solid) = 6,000 mg / L). Reaction sludge (the present invention sludge AC and comparative sludge) was used.

  The sludge A of the present invention was prepared by maintaining the pH of the returned sludge at 0.4 to 0.6 for 5 minutes, and then neutralizing to pH 7.5 by adding an alkaline agent.

  The sludge B of the present invention was prepared by maintaining the pH of the returned sludge at 1.9 to 2.1 for 15 minutes and then neutralizing to pH 7.5 by adding an alkaline agent.

  The sludge C of the present invention was prepared by maintaining the pH of the returned sludge at 3.9 to 4.1 for 60 minutes, and then adding an alkali agent to neutralize to pH 7.5.

  The comparative sludge was produced by maintaining the pH of the returned sludge at 7.4 to 7.6 for 60 minutes.

  For the acid treatment and neutralization treatment, 1 mol / L sulfuric acid and 2 mol / L sodium hydroxide were used.

  The reaction volume of the aerobic reaction tank 24 was 2 L, and the MLSS concentration in the aerobic reaction tank 24 was operated to be 2500 to 3,500 mg / L. Moreover, the water temperature in the aerobic reaction tank 24 was adjusted to 18-22 degreeC (average 20 degreeC). The hydraulic residence time of the wastewater in the aerobic reaction tank 24 was 3 hours.

  The dissolved oxygen (DO: Dissolved Oxygen) concentration in the aerobic reaction tank 24 is set to 4.0 mg / L or more so that the nitric acid type nitrification reaction is likely to occur in order to easily evaluate the nitrite type nitrification performance. The amount of air ejected from the air diffuser 34 was adjusted.

  The pH in the aerobic reaction tank 24 is 7.0 to 7.5 so that the nitric acid type nitrification reaction is likely to occur, so that the nitrite type nitrification performance can be easily evaluated. The amount added was adjusted.

  FIG. 4 is a graph showing the nitrogen concentration in the treated water 30 under the above-mentioned conditions. FIGS. 4 (a) to 4 (c) show the nitrogen concentration when the sludges A to C of the present invention are used, respectively. (D) shows the nitrogen concentration when comparative sludge is used. 4 (a) to (d), ◯ indicates the ammonia nitrogen concentration of the wastewater raw water, ● indicates the ammonia nitrogen concentration of the treated water 30, and ▲ indicates the nitrite nitrogen concentration of the treated water 30, (2) indicates the nitrate nitrogen concentration of the treated water 30.

  As shown in FIGS. 4 (a) to (c), in the wastewater treatment using the sludges A to C of the present invention, the ammonia oxidation activity increased from the first week from the start, and the nitrite production rate was 90% at the third week. The above nitrous acid production ability was confirmed. Thereafter, nitrification of synthetic wastewater was continued for 2 months or more, but the nitric acid production ability did not increase. Thus, it has been found that when the reaction sludge 28 produced by the production method of the present invention is used, a nitrite type nitrification reaction occurs in the aerobic reaction tank 24.

  On the other hand, as shown in FIG. 4 (d), in the wastewater treatment using the comparative sludge, only the ability to produce nitrous acid increased for 2 weeks immediately after the start of operation, but thereafter, the ability to produce nitric acid increased, and 3 weeks From the first time, the ability to produce nitric acid with a nitric acid production rate of 90% or more was confirmed. Thereafter, wastewater treatment was performed for 2 months or more, but suppression of nitric acid production ability was not confirmed.

  From the above, it is confirmed that the reaction sludge 28 having nitrite type nitrification performance can be produced by subjecting activated sludge containing at least ammonia oxidizing bacteria and nitrite oxidizing bacteria to acid treatment at pH 6 or lower. It was done.

  Next, in order to examine the relationship between the acid treatment conditions for producing the reaction sludge 28 and the nitrite-type nitrification performance of the reaction sludge 28, a second wastewater treatment experiment was performed by the following method.

  As the nitrite-type nitrification reaction sludge, as in the first wastewater treatment experiment, sludge having a MLSS concentration of 6,000 mg / L (collected at a sewage treatment plant) subjected to acid treatment and neutralization treatment was used. The acid treatment of sludge has a pH of 0, 0.5, 2, 3, 4, 5, 6 or 7, and a treatment time (minute) of 0.1, 0.5, 1, 3, 9, 15, The test was performed under 30 or 60 conditions. Thereafter, the sludge after acid treatment was immediately neutralized to pH 7.5 with an alkaline solution.

  The synthetic wastewater that is the target of nitrification treatment was synthetic wastewater containing 44 mg / L of nitrite nitrogen and synthetic wastewater containing 44 mg / L of ammoniacal nitrogen. FIG. 5A is a table showing the quality of synthetic wastewater containing 44 mg / L of nitrite nitrogen, and FIG. 5B is a table showing the quality of synthetic wastewater containing 44 mg / L of ammonia nitrogen. .

  These synthetic waste water 450mL and the above-mentioned nitrite type nitrification sludge 50mL are put into the aerobic reaction tank 24 shown in FIG. 6, respectively, and a continuous aeration process is performed under the conditions of a water temperature of 20 ° C. and an aeration air volume of 300 mL / min. went. In consideration of evaporation of the reaction solution in the aerobic reaction tank 24, aeration was stopped once a day to precipitate activated sludge, and semi-batch culture was performed in which 400 mL of the supernatant was replaced with each medium.

  FIG. 7 (a) is a graph showing the nitrate nitrogen concentration of the supernatant obtained by continuous aeration treatment of synthetic wastewater containing 44 mg / L of nitrite nitrogen (see FIG. 5 (a)) for one month. FIG. 7 (b) is a graph showing the concentration of nitrite nitrogen in the supernatant obtained by continuous aeration treatment of synthetic wastewater containing 44 mg / L of ammoniacal nitrogen (see FIG. 5 (b)) for one month. It is.

  From FIG. 7 (a) and (b), by performing the acid treatment of activated sludge under the following conditions (1) to (3), the production of nitrous acid is promoted while the production of nitric acid is suppressed. It was found that it is possible to produce reactive sludge that can be.

    (1) Hold the pH of the activated sludge for 30 seconds or more in the range of less than 2.0.

    (2) Maintaining the pH of the activated sludge in the range of 2.0 or more and less than 4.0 for 3 minutes or more.

    (3) Maintaining the pH of the activated sludge in the range of 4.0 or more and 6.0 or less for 15 minutes or more.

  Next, the configuration of a nitrification apparatus for stably maintaining the nitrite type nitrification performance of the nitrite type nitrification reaction sludge over a long period of time will be described.

  In the first wastewater treatment experiment and the second wastewater treatment experiment, since synthetic wastewater was used as a nitrification target, nitrite-oxidizing bacteria were not brought in from the outside. It is included. For this reason, if nitrification treatment is continued for a long period of time, nitrite-oxidizing bacteria that flow into the aerobic reaction tank along with the wastewater grow, and the nitrification reaction in the aerobic reaction tank shifts from nitrite-type nitrification to nitrate-type nitrification. There is a case.

  For this reason, from the viewpoint of maintaining the nitrite type nitrification performance over a long period of time, the pH of the reaction sludge (nitrite type nitrification reaction sludge) is regularly 6 or less (preferably pH 0.5 or more and 6.0 or less, more preferably Is preferably 0.5 to 5.0).

  In this case, it is preferable not to perform the acid treatment on all the reaction sludges at once, but to collect a part of the returned sludge returned from the sedimentation tank to the aerobic reaction tank and to periodically perform the acid treatment. . Thereby, while suppressing the nitrite oxidation activity in an aerobic reaction tank for a long term, the fall of the ammonia oxidation activity resulting from the lack of the ammonia oxidation bacteria in an aerobic reaction tank can be prevented. Moreover, the amount of acid solution added can be reduced by subjecting the returned sludge to acid treatment.

  FIG. 8 is a configuration diagram showing an example of a nitrification apparatus that periodically performs acid treatment of the reaction sludge. As shown in the figure, the nitrification apparatus 40 is mainly provided with a regeneration treatment tank 36 that performs acid treatment on a part of the reaction sludge 28 returned from the precipitation tank 26 to the aerobic reaction tank 24. It differs from the nitrification apparatus 20 shown in FIG. In addition, about the component which is common in the nitrification processing apparatus 20 among the components of the nitrification processing apparatus 40, a common code | symbol is attached | subjected and the description is abbreviate | omitted.

  The reaction sludge 28 separated in the sedimentation tank 26 of the nitrification apparatus 40 is returned to the aerobic reaction tank 24 by the power of the pump P2 with the return sludge valve V1 opened. At this time, a part of the reaction sludge 28 returned from the sedimentation tank 26 is sent to the regeneration treatment tank 36 by opening the recovered sludge valve V3.

  The opening and closing of the recovery sludge valve V3 is preferably adjusted so that the water level of the reaction sludge 28 in the regeneration treatment tank 36 is constant. For example, the water level of the reaction sludge 28 is detected by the water level sensor S attached to the regeneration treatment tank 36, and the opening / closing of the recovered sludge valve V3 is switched based on the detection result of the water level sensor S. The water level can be adjusted to a certain level.

  The pH of the reaction sludge 28 in the regeneration treatment tank 36 is constantly (or periodically) measured by the pH measuring device 16, and the pH of the reaction sludge 28 is adjusted based on the measured value of the pH measuring device 16. Specifically, based on the measurement result of the pH measuring device 16, the pump P3 adds the acid solution from the acid solution tank 18A to the regeneration treatment tank 36, or the pump P4 adds the alkali solution from the alkali solution tank 18B. Thus, the pH of the reaction sludge 28 can be adjusted to a desired range. In addition, at the time of pH adjustment of the reaction sludge 28, it is preferable to stir the reaction sludge 28 with the stirrer M attached to the reproduction | regeneration processing tank 36 from a viewpoint of performing pH adjustment correctly, for example.

  The recovered reaction sludge 28 is subjected to acid treatment (regeneration treatment) of pH 6 or less (preferably pH 0.5 or more and 6.0 or less, more preferably 0.5 or more and 5.0 or less) by the regeneration treatment tank 36 having the above configuration. As a result, the nitrite type nitrification performance of the reaction sludge 28 can be recovered.

  At this time, the acid treatment (regeneration treatment) of the recovered reaction sludge 28 is preferably performed under at least one of the following conditions (1) to (3).

    (1) Hold the pH of the activated sludge for 30 seconds or more in the range of less than 2.0.

    (2) Maintaining the pH of the activated sludge in the range of 2.0 or more and less than 4.0 for 3 minutes or more.

    (3) Maintaining the pH of the activated sludge in the range of 4.0 or more and 6.0 or less for 15 minutes or more.

  The reaction sludge 28 is preferably neutralized by adding an alkaline solution from the alkaline solution tank 18B after acid treatment (regeneration treatment) is performed in the regeneration treatment tank 36. Thereafter, the reaction sludge 28 is returned to the aerobic reaction tank 24 by the power of the pump P5 (regenerated sludge return pump).

  FIG. 8 illustrates an example (batch method) in which a predetermined amount of the reaction sludge 28 is accumulated in the regeneration treatment tank 36 and then the reaction sludge 28 is subjected to an acid treatment (batch method). You may carry out by a continuous system. When acid treatment is performed in a continuous manner, the treatment time (holding time) under the conditions (1) to (3) above can be read as the average residence time of the reaction sludge 28 in the regeneration treatment tank 36 and applied.

  Next, a third wastewater treatment experiment conducted to confirm the long-term stability of the nitrite type nitrification performance by the nitrification apparatus 40 having the above-described configuration will be described.

  First, the water quality synthetic waste water shown in FIG. 3 was subjected to nitrification treatment with the sludge A of the present invention used in the first waste water treatment experiment until it reached a steady state.

Thereafter, the wastewater to be treated was switched to sewage-adjusted wastewater adjusted to have an ammoniacal nitrogen concentration of 40 mg / L by adding NH ₄ Cl to the sewage treated water. FIG. 9 is a table showing the average water quality of sewage adjustment wastewater that is the object of nitrification treatment.

  When the wastewater subject to nitrification is switched from synthetic wastewater to sewage adjustment wastewater, the nitrite-oxidizing bacteria that flow into the aerobic reaction tank 24 together with the sewage adjustment wastewater proliferate, and the nitrification reaction in the aerobic reaction tank 24 is converted to nitrite type nitrification. Shift to nitric acid type nitrification.

  In this wastewater treatment experiment, after the nitrification reaction in the aerobic reaction tank 24 was shifted from nitrite type nitrification to nitric acid type nitrification, a part of the returned sludge was switched to an operation in which acid treatment was performed periodically, and then regenerated. The effect of the acid treatment (regeneration treatment) of the reaction sludge 28 by the tank 36 was confirmed.

  As the acid treatment (regeneration treatment) conditions for the reaction sludge 28, 30 mL of the reaction sludge 28 is drawn into the regeneration treatment tank 36 once every 12 hours, and an acid solution is added while stirring, so that the pH is 0.4 to Maintained at 0.6 for 5 minutes. Thereafter, an alkaline solution was added to the acid-treated reaction sludge 28, stirred, neutralized to pH 7.5, and returned to the aerobic reaction tank 24. For the acid treatment and neutralization treatment, 1 mol / L sulfuric acid and 2 mol / L sodium hydroxide were used.

  The reaction volume of the aerobic reaction tank 24 was 2 L, and the MLSS concentration in the aerobic reaction tank 24 was operated to be 2500 to 3,500 mg / L. Moreover, the water temperature in the aerobic reaction tank 24 was adjusted to 18-22 degreeC (average 20 degreeC). The hydraulic residence time of the wastewater in the aerobic reaction tank 24 was 3 hours.

  The dissolved oxygen (DO: Dissolved Oxygen) concentration in the aerobic reaction tank 24 was adjusted to 4.0 mg / L or more. Moreover, the pH in the aerobic reaction tank 24 was adjusted within the range of 7.0 or more and 7.5 or less.

  FIG. 10 is a graph showing the nitrogen concentration in the treated water 30 under the above conditions. In FIG. 10, ○ indicates the ammoniacal nitrogen concentration of the wastewater raw water, ● indicates the ammoniacal nitrogen concentration of the treated water 30, ▲ indicates the nitrite nitrogen concentration of the treated water 30, and ■ indicates the nitric acid concentration of the treated water 30 The nitrogen concentration is shown. In addition, the horizontal axis of FIG. 10 indicates the number of days that have elapsed since the wastewater to be treated was switched from the synthetic wastewater to the sewage adjustment wastewater (the wastewater switching point).

  As can be seen from FIG. 10, the nitrite type nitrification reaction was maintained for about two weeks from the point of time when the wastewater was switched, but thereafter, the concentration of nitric acid in the treated water increased and the nitrite type nitrification reaction was shifted to. Periodic drawing acid treatment (regeneration treatment) was started on the 79th day from the time of switching to the wastewater, but no significant nitric acid production suppressing effect was confirmed until the 105th day. However, the concentration of nitric acid in the treated water began to decrease from around day 117. On day 175, the nitric acid concentration in the treated water fell below 5 mg / L, and thereafter a stable nitrite-type nitrification reaction continued for about 200 days or more. did.

  From the above, it was found that the nitrite-type nitrification performance of the reaction sludge 28 can be maintained by subjecting the recovered reaction sludge 28 to a periodic drawing acid treatment (regeneration treatment).

  Next, a wastewater treatment method for treating wastewater containing ammoniacal nitrogen according to the present invention will be described.

  In the wastewater treatment method according to the present invention, ammonia nitrogen in wastewater is oxidized (nitrified) to nitrous acid by nitrite-type nitrification reaction sludge, and then the produced nitrous acid is subjected to denitrification treatment to produce nitrogen gas. Decompose. As the denitrification treatment of nitrous acid, for example, a method using denitrifying bacteria or a method using anaerobic ammonia oxidizing bacteria can be used.

  FIG. 11A is a process diagram showing a wastewater treatment method involving denitrification treatment by denitrifying bacteria, and FIG. 11B is a process diagram showing a wastewater treatment method involving denitrification treatment by anaerobic ammonia oxidizing bacteria. .

  In a wastewater treatment method involving denitrification by denitrifying bacteria (see FIG. 11A), ammonia nitrogen in wastewater is oxidized to nitrous acid, and then the nitrous acid is decomposed into nitrogen gas by denitrifying bacteria. In contrast, in a wastewater treatment method involving denitrification treatment by anaerobic ammonia oxidizing bacteria (see FIG. 11B), ammonia nitrogen in wastewater is oxidized to nitrous acid, and then the nitrous acid is oxidized by anaerobic ammonia. Denitrify by bacteria. At this time, ammonia nitrogen in the wastewater is used as a hydrogen donor during the denitrification treatment.

  FIG. 12 is a block diagram showing an example of a wastewater treatment apparatus for carrying out the wastewater treatment method according to the present invention. As shown in FIG. 12, the wastewater treatment apparatus 50 mainly includes an anaerobic tank 42 for deaminating organic nitrogen contained in raw wastewater, an anaerobic tank 44 for denitrifying nitrous acid, and ammonia nitrogen. An aerobic reaction tank 24 that oxidizes to nitrous acid, a sedimentation tank 26 that separates the treated water 30 and the reaction sludge 28, and a regeneration treatment tank 36 that performs acid treatment on the reaction sludge 28.

  The anaerobic tank 42 deaminates organic nitrogen contained in the wastewater raw water to generate ammoniacal nitrogen. The ammoniacal nitrogen produced in the anaerobic tank 42 passes through the anoxic tank 44 immediately after it and is nitrified to nitrous acid in the aerobic reaction tank 24.

  Thereafter, waste water that has been subjected to nitrification in the aerobic reaction tank 24 is returned to the anaerobic tank 44 by a waste water return pipe 52 provided between the aerobic reaction tank 24 and the anaerobic tank 44. Thereby, the nitrous acid in the wastewater returned to the oxygen-free tank 44 is denitrified in the oxygen-free tank 44 and decomposed into nitrogen gas.

  Moreover, since the dissolved oxygen in raw | natural water wastewater is consumed in the anaerobic tank 42, the deoxygenation process in the anaerobic tank 44 can be performed efficiently, maintaining the amount of dissolved oxygen of the anoxic tank 44 low.

  A part of the reaction sludge 28 separated in the settling tank 26 is subjected to an acid treatment (regeneration process) in the regeneration treatment tank 36, and then returned to the front stage from the aerobic reaction tank 24. For example, the reaction sludge 28 after acid treatment may be returned immediately before the aerobic reaction tank 24 or may be returned immediately before the anaerobic tank 42 or the anaerobic tank 44. In FIG. 12, the return destination of the reaction sludge 28 after the acid treatment is set immediately before the anaerobic tank 42, immediately before the anaerobic tank 44 and immediately before the aerobic reaction tank 24 by opening and closing the return sludge valves V3, V4 and V5. The example which can choose to either was shown.

  FIG. 13 is a configuration diagram showing a modification of the wastewater treatment apparatus 50 shown in FIG. As shown in FIG. 13, the wastewater treatment device 60 adds a part of the reaction sludge 28 to the regeneration treatment (acid treatment) tank 36 </ b> A that acid-treats a part of the reaction sludge 28 separated in the sedimentation tank 26. 12 is different from the wastewater treatment apparatus 50 shown in FIG. 12 in that it includes a regeneration treatment (alkali treatment) tank 36B.

  The regeneration treatment (alkaline treatment) tank 36B utilizes the difference in bacterial alkali resistance that ammonia oxidizing bacteria have high resistance to alkali while nitrite oxidizing bacteria have low resistance to alkali. By subjecting the reaction sludge 28 to alkali treatment, the nitrite type nitrification performance can be recovered. Moreover, since the reaction sludge 28 regenerated by the acid treatment in the regeneration treatment tank 36A and the reaction sludge 28 regenerated by the alkali treatment in the regeneration treatment tank 36B are in a mutually neutralizing relationship, neutralization after the regeneration treatment is performed. It is possible to reduce the amount of drug required for the drug (or eliminate the need for the drug).

  In the alkali treatment in the regeneration treatment tank 36B, the pH is preferably in the range of 10 to 14, more preferably in the range of 11 to 14. Thereby, it is possible to quickly sterilize the nitrite oxidizing bacteria without inactivating the ammonia oxidizing bacteria.

  The alkali treatment in the regeneration treatment tank 36B is preferably performed under at least one of the following conditions (1) to (3).

    (1) Hold the pH of the reaction sludge 28 in the range of 13 or more for 5 minutes or more.

    (2) The reaction sludge 28 is kept at a pH of 12 or more and less than 13 for 10 minutes or more.

    (3) The reaction sludge 28 is kept at a pH of 10 or more and less than 12 for 60 minutes or more.

  Thereby, the nitrite oxidizing bacteria in the reaction sludge 28 can be reliably deactivated, and the ammonia oxidizing bacteria can be more selectively accumulated.

  Furthermore, the flow rate V1 (L / h) of the reaction sludge 28 after acid treatment returned from the regeneration treatment tank 36A, and the flow rate V2 (L / h) of the reaction sludge 28 after alkali treatment returned from the regeneration treatment tank 36B. Preferably satisfies the following relationship.

V1 × X1 = V2 × X2
(However, X1 is the hydrogen ion concentration [H ⁺ ] (mol / L) in the regeneration treatment tank 36A, and X2 is the hydroxide ion concentration [OH ⁻ ] (mol / L) in the regeneration treatment tank 36B).

  Thereby, since it is not necessary to neutralize the reaction sludge 28 after the regeneration treatment in the regeneration treatment tank 36A and the regeneration treatment tank 36B, the running cost can be reduced.

  FIG. 14 is a configuration diagram showing another modification of the wastewater treatment apparatus 50 shown in FIG. As shown in FIG. 14, the wastewater treatment apparatus 70 is filled with a carrier 54 in which ammonia-oxidizing bacteria are preferentially accumulated in the aerobic reaction tank 24, and carrier regeneration for performing a regeneration treatment on the carrier 54. It differs from the wastewater treatment apparatus 50 shown in FIG. 12 in that a treatment tank 56 is provided.

  The carrier 54 of the wastewater treatment apparatus 70 can be produced, for example, by subjecting a complex microbial sludge containing ammonia oxidizing bacteria and nitrite oxidizing bacteria to heat treatment, acid treatment, or acid treatment. Specifically, heat treatment at 40 ° C. or more and 100 ° C. or less, acid treatment at pH 10 or more (preferably pH 10 or more and 14 or less, more preferably pH 11 or more and 14 or less), or pH 6 or less with respect to the complex microbial sludge. The carrier 54 can be produced by performing an acid treatment (preferably an acid treatment with a pH of 0.5 or more and 5 or less).

  Further, since the nitrite type nitrification performance of the carrier 54 is deteriorated by long-term use, it is preferable to periodically perform a regeneration treatment (acid treatment or alkali treatment) by the carrier regeneration treatment tank 56.

  The carrier regeneration treatment tank 56 periodically regenerates the carrier 54 by extracting the carrier 54 in the aerobic reaction tank 24 with the pump P8. The regeneration treatment of the carrier 54 can be performed by adding an acid solution from the acid solution tank 18 </ b> A to the carrier regeneration treatment tank 56 based on the measurement result of the pH measuring device 16. As the acid treatment conditions, the same conditions as the acid treatment of the reaction sludge 28 in the regeneration treatment tank 36 already described can be used. The regeneration treatment of the carrier 54 is not limited to the acid treatment, and may be performed by adding an alkaline liquid from the alkaline liquid tank 18B to the carrier regeneration treatment tank 56 based on the measurement result of the pH measuring device 16.

  In the wastewater treatment apparatus 70 having the above-described configuration, the reaction sludge 28 and the carrier 54 are used in combination to perform nitrification in the aerobic reaction tank 24. Therefore, ammonia nitrogen in the wastewater is efficiently oxidized (nitrification) into nitrous acid. can do.

  FIG. 15 is a configuration diagram illustrating another modified example of the wastewater treatment apparatus 50 illustrated in FIG. 12. As shown in FIG. 14, the wastewater treatment apparatus 80 employs a multistage treatment method in which a plurality of anaerobic tanks 42 and aerobic reaction tanks 24 are arranged in series, and acid treatment is performed by the regeneration treatment tank 36. 12 differs from the wastewater treatment apparatus 50 shown in FIG. 12 in that a distributor 58 for distributing the reaction sludge 28 that has been subjected to (regeneration processing) and returning it immediately before each tank is provided.

  In the wastewater treatment apparatus 80, the overall size of the wastewater treatment apparatus can be reduced by arranging the plurality of anaerobic tanks 42 and the aerobic reaction tank 24.

  In the wastewater treatment apparatus 80, from the viewpoint of efficiently performing nitrite oxidation (nitrification) in the aerobic reaction tank 24, the carrier 54 in which ammonia-oxidizing bacteria are preferentially accumulated is packed in the aerobic reaction tank 24. ing.

  The wastewater treatment apparatus 80 does not perform the acid treatment (regeneration treatment) of the carrier 54. However, as shown in FIG. 16, the carrier 54 is acid-treated (regeneration treatment) periodically by the carrier regeneration treatment tank 56 described above. It may be done automatically.

  As mentioned above, although the wastewater treatment method concerning one embodiment of the present invention was explained, the present invention is not limited to this, and of course, various improvements and modifications may be made without departing from the gist of the present invention. It is. For example, wastewater treatment may be performed using a wastewater treatment device in which the components of each wastewater treatment device shown in FIGS.

DESCRIPTION OF SYMBOLS 10 ... Reaction sludge manufacturing apparatus, 12 ... Activated sludge, 14 ... Acid treatment tank, 16 ... pH measuring machine, 18 ... Acid solution tank, 20 ... Nitrification apparatus, 22 ... Raw water tank, 24 ... Aerobic reaction tank, 26 ... Precipitation tank, 28 ... reactive sludge, 30 ... treated water, 32 ... mixed solution, 34 ... aeration device, 36 ... regeneration treatment tank, 40 ... nitrification treatment device, 42 ... anaerobic tank, 44 ... anoxic tank, 50 ... waste water Treatment device 52 ... Waste water return pipe 54 ... Carrier 56 ... Carrier regeneration treatment tank 58 ... Distributor 60 ... Waste water treatment device 80 ... Waste water treatment device 90 ... Waste water treatment device

Claims (15)

A method for producing nitrite-type nitrification sludge in which ammonia-oxidizing bacteria are preferentially accumulated,
Production of nitrite-type nitrification reaction sludge characterized by comprising a step of subjecting said activated sludge to acid treatment so that the pH of activated sludge containing at least ammonia oxidizing bacteria and nitrite oxidizing bacteria is 6 or less Method.   2. The step of performing the acid treatment, wherein the pH of the activated sludge is maintained in a range of 0.5 or more and 6.0 or less by adding an acid solution to the activated sludge. A method for producing nitrite-type nitrifying sludge. The method for producing nitrite-type nitrification reaction sludge according to claim 1 or 2, wherein the acid treatment is performed under at least one of the following conditions (1) to (3).
(1) Hold the pH of the activated sludge for 30 seconds or more in the range of less than 2.0.
(2) Maintaining the pH of the activated sludge within a range of 2.0 or more and less than 4.0 for 3 minutes or more.
(3) The pH of the activated sludge is maintained for 15 minutes or more in the range of 4.0 or more and 6.0 or less.   A nitrite-type nitrification sludge produced by the production method according to any one of claims 1 to 3. An apparatus for producing nitrite-type nitrifying sludge that preferentially accumulates ammonia-oxidizing bacteria,
A nitrite-type nitrification sludge characterized by comprising an acid treatment device that performs acid treatment on the activated sludge so that the pH of the activated sludge containing at least ammonia-oxidizing bacteria and nitrite-oxidizing bacteria is 6 or less. Manufacturing equipment. A wastewater treatment method for treating wastewater containing ammonia nitrogen,
A step of subjecting the activated sludge to acid treatment so that the pH of the activated sludge containing at least ammonia oxidizing bacteria and nitrite oxidizing bacteria is 6 or less;
Oxidizing the ammonia nitrogen contained in the wastewater into nitrous acid by the activated sludge subjected to the acid treatment;
And a step of denitrifying the nitrous acid.   In the step of performing the denitrification treatment, anaerobic ammonia oxidizing bacteria denitrify the nitrous acid generated in the step of oxidizing the ammoniacal nitrogen using the ammoniacal nitrogen contained in the wastewater as a hydrogen donor. The wastewater treatment method according to claim 6.   The wastewater treatment method according to claim 6, wherein in the step of performing the denitrification treatment, the nitrous acid generated in the step of oxidizing the ammoniacal nitrogen is denitrified by a denitrification bacterium. Recovering the activated sludge used in the step of oxidizing the ammoniacal nitrogen to the nitrous acid;
The wastewater treatment method according to any one of claims 6 to 8, further comprising a step of performing the acid treatment on the recovered activated sludge.   The wastewater treatment method according to any one of claims 6 to 9, further comprising a step of adjusting the pH of the activated sludge by adding an alkaline agent to the activated sludge subjected to the acid treatment. . A wastewater treatment apparatus for treating wastewater containing ammonia nitrogen,
An acid treatment device that performs acid treatment on the activated sludge so that the pH of the activated sludge containing at least ammonia oxidizing bacteria and nitrite oxidizing bacteria is 6 or less;
A nitrous acid production tank that oxidizes the ammoniacal nitrogen contained in the wastewater into nitrous acid by the activated sludge subjected to the acid treatment;
A wastewater treatment apparatus comprising: a denitrification tank that performs a denitrification process on the nitrous acid.   The denitrification tank uses anaerobic ammonia oxidizing bacteria to denitrify the nitrous acid generated in the nitrous acid generation tank using the ammoniacal nitrogen contained in the wastewater as a hydrogen donor. The wastewater treatment apparatus described in 1.   The waste water treatment apparatus according to claim 11, wherein the denitrification tank denitrifies the nitrous acid generated in the nitrous acid generation tank by denitrifying bacteria. A recovery device for recovering the activated sludge from the nitrous acid production tank;
The wastewater according to any one of claims 11 to 13, further comprising a regeneration device that performs the acid treatment on the activated sludge collected by the collecting device to regenerate the activated sludge. Processing equipment.   The wastewater according to any one of claims 11 to 14, further comprising a pH adjusting device that adjusts the pH of the activated sludge by adding an alkaline agent to the activated sludge subjected to the acid treatment. Processing equipment.

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