JP2011212670A - Wastewater treatment apparatus and wastewater treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wastewater treatment apparatus and a wastewater treatment method which can perform high load nitrification of wastewater containing nitrogen which enables miniaturization of equipment and reducing a total cost.SOLUTION: The wastewater treatment apparatus including a nitrification tank 2 filled up with a carrier 5 to which nitrifying bacteria is made to adhere and which can be sealed, a feed line 10 of high concentration oxygen gas in a gas phase part 12, a discharge line 11 discharging an exhaust gas from the gas phase part 12, and an aeration means 15 having a blower 9 aerating the gas of the gas phase part 12 in the nitrification tank 2 into a liquid phase and an air diffuser 8, which carries out oxidation treatment of NH-N and/or O-N in wastewater to NObiologically, includes a dissolved oxygen detecting means 13 in a liquid phase in the nitrification tank 2, a means 16 controlling the aeration air flow of the aeration means 15 so that the dissolved oxygen concentration is maintained to a set value by a result of the dissolved oxygen detecting means 13, and an oxygen detecting means 14 detecting the oxygen concentration of the gas phase part 12 in the nitrification tank 2, and a means 18 for controlling the amount of the high concentration gas supplied from the feed line 10 so that the oxygen concentration may be maintained to a prescribed range by the detected result of the oxygen detecting means 14.

Description

  The present invention relates to a waste water treatment apparatus and a waste water treatment method for biologically oxidizing waste water containing ammonia nitrogen and organic nitrogen.

As a method for biologically treating wastewater containing ammonia nitrogen, a treatment for oxidizing ammonia nitrogen to nitrate nitrogen and nitrite nitrogen by nitrifying bacteria is generally performed. The nitrification reaction requires oxygen, and air is used as an oxygen source (for example, Patent Document 1).
In the nitrification reaction of ammonia nitrogen and organic nitrogen, about 4.6 kg of oxygen is required to nitrify 1 kg of nitrogen. Therefore, in the conventional wastewater treatment method using air as an oxygen source, A large amount of air must be supplied. Furthermore, in order to promote nitrification efficiently, it is necessary to maintain the DO of the mixed solution higher than that of the oxidative decomposition treatment of organic matter. When air with an oxygen concentration of 21% is used, the equipment can be downsized. There has been a limit to reducing the power cost of air supply facilities. As a method for solving such a problem, an oxygen activated sludge method using oxygen-enriched air having an oxygen concentration higher than that of air as an oxygen source necessary for the nitrification reaction is employed (for example, Patent Document 2).

In order to perform nitrification under high load conditions, it is necessary to increase the supply capacity of oxygen and hold a large amount of nitrifying bacteria in the nitrification tank. For that purpose, DO must be maintained high to increase the activity of nitrifying bacteria in the sludge, and the sludge concentration (MLSS concentration) of the mixed solution must be increased. In the case of the oxygen activated sludge method, there is a merit that the DO can be set high, but if the MLSS concentration is increased unnecessarily, there is a problem that it becomes difficult to separate the sludge and the treated water in the sedimentation basin as with the standard activated sludge method. Arise. A membrane may be used for this solid-liquid separation, but an expensive membrane separation system is required, and there are many problems to be solved and improved such as clogging of the membrane. Furthermore, raising the MLSS concentration promotes the occurrence of scum in the aeration tank and the sedimentation basin, and there is a problem that operation management becomes complicated. In order to solve these problems, a method using a carrier on which microorganisms are fixed is widely used in nitrification treatment.
By combining the oxygen activated sludge method with excellent oxygen supply capability and the carrier nitrification method with excellent nitrification capability, nitrification treatment can proceed with compact equipment, and various device structures and methods have been studied (for example, Patent Document 2).

In oxygen activated sludge, the surface aeration method is adopted as the aeration method of the nitrification tank. However, as described in Patent Document 2, there has been a case where the nitrification carrier is worn or collapsed by aeration stirring.
In order to solve the problem of carrier wear, there is a method (gas circulation aeration method) in which high-concentration oxygen gas is circulated and scattered in the aeration tank via a circulation blower instead of the surface aeration method. There is also an example (for example, Non-Patent Document 1).
However, the method of circulating and aeration using a blower has fewer practical examples than the surface aeration method, and the implementation conditions for stabilizing the operation and operating efficiently have not been sufficiently studied. In particular, in the oxygen activated sludge method, a gas having a higher oxygen concentration than the air such as oxygen-enriched air or pure oxygen to be used (hereinafter referred to as high oxygen gas) is expensive to generate. Also, a small aeration tank, which is a feature of the oxygen activated sludge method, that is, a processing apparatus and a processing method for efficiently carrying out the nitrification reaction under conditions with a short hydraulic retention time (HRT) have been sufficiently established. Absent.

JP 2000-31898 A JP-A-8-173983

Sumiyama et al., 30th Sewerage Research Conference Lecture, p524 (1993)

  The present invention has been made in view of the above circumstances, and provides a wastewater treatment apparatus and method for biologically oxidizing nitrogen-containing wastewater capable of reducing the load and size of a nitrification tank and saving energy. This is the issue.

  In order to solve the above problems, in the present invention, a sealable nitrification tank filled with a carrier to which nitrifying bacteria are attached, an oxygen gas supply line for supplying high-concentration oxygen gas to the gas phase part of the nitrification tank, A discharge line for discharging exhaust gas from the gas phase part of the nitrification tank, a blower for introducing the gas in the gas phase part in the nitrification tank into the liquid phase and aeration, and an aeration means having an air diffuser. A waste water treatment apparatus for biologically oxidizing ammonia nitrogen and / or organic nitrogen in waste water to nitrate nitrogen and / or nitrite nitrogen, and dissolved oxygen in the liquid phase in the nitrification tank Dissolved oxygen detection means for detecting the concentration, and means for controlling the aeration air volume of the aeration means based on the detection result by the dissolved oxygen detection means so that the dissolved oxygen concentration is maintained at a set value; Gas in the gas phase part in the nitrification tank or front Oxygen detection means for detecting the oxygen concentration of the exhaust gas, and means for controlling the oxygen gas supply amount of the oxygen gas supply line so that the oxygen concentration is maintained within a predetermined range based on the detection result by the oxygen detection means The waste water treatment apparatus is characterized by comprising:

  Further, in the present invention, a sealable nitrification tank filled with a carrier to which nitrifying bacteria are attached, an oxygen gas supply line for supplying high-concentration oxygen gas to a gas phase part of the nitrification tank, and a gas phase of the nitrification tank A discharge line for discharging exhaust gas from the section, a blower for introducing the gas in the gas phase section in the nitrification tank into the liquid phase and aeration means having a diffuser, and a front stage of the nitrification tank Provided with a denitrification tank, and provided with a return line for returning the liquid phase and / or sludge of the nitrification tank to the denitrification tank, biologically nitrate nitrogen and / or organic nitrogen in the waste water. A wastewater treatment apparatus that oxidizes to nitrite nitrogen and denitrifies, and includes dissolved oxygen detection means that detects the dissolved oxygen concentration in the liquid phase in the nitrification tank, and the dissolved oxygen detection means Based on the detection result, the dissolved oxygen concentration becomes a set value. A means for controlling the amount of aeration air of the aeration means so as to be held, an oxygen detection means for detecting the oxygen concentration of the gas in the gas phase in the nitrification tank or the exhaust gas, and the oxygen detection means And a means for controlling an oxygen gas supply amount of the oxygen gas supply line so that the oxygen concentration is maintained within a predetermined range based on a detection result.

  In the wastewater treatment apparatus, the nitrification tank is composed of a plurality of tanks partitioned by a partition wall, and a dissolved oxygen detection means for detecting a dissolved oxygen concentration in the liquid phase, a blower and a dispersion for each tank of the plurality of tanks. An aeration means having an air device, and means for controlling the aeration air volume of the aeration means so that the dissolved oxygen concentration is maintained at a set value for each tank, or the nitrification tank A plurality of tanks partitioned by a partition wall, and each of the tanks of the plurality of tanks includes dissolved oxygen detection means for detecting a dissolved oxygen concentration in the liquid phase, at least one of the aeration means and the aeration means. An aeration means having a flow control valve connected thereto, and having one inverter-controlled blower connected to the aeration means for each tank, and connected to the air volume of the blower and / or the aeration means The dissolved oxygen concentration depends on the opening of the flow control valve. So as to maintain the set value for each, it can be further comprising means for controlling the aeration amount of the aeration unit.

  Furthermore, in the present invention, a high-concentration oxygen gas is supplied into the gas phase of a sealable nitrification tank filled with a carrier to which nitrifying bacteria are attached, and exhaust gas is discharged from the gas phase of the nitrification tank, A gas in the gas phase in the nitrification tank is aerated in a liquid phase through a blower and a diffuser, and ammonia nitrogen and organic nitrogen in the waste water are biologically converted into nitrate nitrogen and nitrite nitrogen. In the wastewater treatment method for oxidation treatment, the dissolved oxygen concentration in the liquid phase in the nitrification tank is detected, and aeration is performed in the liquid phase so that the dissolved oxygen concentration is maintained at a set value based on the detection result. Controlling the amount of aeration air to be generated, detecting the gas concentration in the gas phase section in the nitrification tank or the oxygen concentration of the exhaust gas, and maintaining the oxygen concentration in a predetermined range based on the detection result Controls the oxygen gas supply amount supplied to the gas phase part of the tank It is obtained by a waste water treatment method characterized by Rukoto.

In the present invention, a high-concentration oxygen gas is supplied into the gas phase of a sealable nitrification tank filled with a carrier to which nitrifying bacteria are attached, and exhaust gas is discharged from the gas phase of the nitrification tank, The gas in the gas phase in the nitrification tank is aerated into the liquid phase via a blower and a diffuser, and the liquid phase and / or sludge in the nitrification tank is returned to the denitrification tank provided in the previous stage of the nitrification tank. In the wastewater treatment method of biologically oxidizing ammonia nitrogen and organic nitrogen to nitrate nitrogen and nitrite nitrogen and denitrifying, in the liquid phase in the nitrification tank The dissolved oxygen concentration is detected, and the amount of aeration air to be aerated in the liquid phase is controlled so that the dissolved oxygen concentration is maintained at a set value based on the detection result, and the gas phase portion in the nitrification tank is controlled. Detecting the oxygen concentration of the gas or the exhaust gas, and based on the detection result, As oxygen concentration is maintained at a predetermined range, in which the waste water treatment method characterized by controlling the oxygen gas supply amount supplied to the gas phase portion of the nitrification tank.
In the wastewater treatment apparatus and method, the set value of the dissolved oxygen concentration in the liquid phase is 2 to 12 mg / L, and the predetermined range of the oxygen concentration in the gas phase part or the exhaust gas is 30 to 70. % (Capacity) is recommended.

  According to the wastewater treatment apparatus and wastewater treatment method of the present invention, pure oxygen or oxygen-enriched gas can be used for wastewater treatment by nitrification reaction, so that wastewater treatment is efficient, that is, the nitrification tank is highly loaded or downsized. Is possible. In addition, since only the necessary amount of pure oxygen or oxygen-enriched gas is supplied, the running cost can be kept low, and the total cost can be reduced.

The flow block diagram which shows an example of the waste water treatment equipment of this invention. The flow block diagram which shows the other example of the waste water treatment equipment of this invention. The flow block diagram which shows the other example of the waste water treatment equipment of this invention. The flow block diagram which shows the other example of the waste water treatment equipment of this invention. The flowchart which shows an example of control operation | movement of this inventor. The graph which shows the relationship between DO and nitrification performance. The flow block diagram which shows an example of the conventional waste water treatment equipment.

Hereinafter, the present invention will be described in detail.
In the present invention, first, in order to clarify the problems of the conventional surface aeration method, a comparative experiment between the surface aeration method and the gas circulation aeration method was performed using a carrier having a shape and material that is difficult to wear. . As a result, in the surface aeration method, even when the carrier itself was not worn, it was found that the nitrification performance was estimated to be caused by the inhibition of nitrifying bacteria adhering to the carrier surface by aeration stirring. On the other hand, in an experiment conducted using only the aeration method under the same conditions as this and the gas circulation aeration method, good nitrification performance was obtained. Further, as shown in FIG. 5, the nitrification performance depends on DO of the nitrification tank mixture. It was also found out. Based on these findings, in order to advance the nitrification reaction efficiently under short conditions of HRT, it is essential to perform aeration with gas circulation aeration and adjust the DO value corresponding to the required nitrification rate. In addition, in order to put this method into practical use, it is indispensable to establish a processing apparatus and a processing method that can exhibit the utilization efficiency (oxygen utilization efficiency) of high-concentration oxygen gas equivalent to or higher than that of the conventional surface aeration method. I came up with the idea.

  As a method for adjusting the DO of the mixed liquid, attention was paid to a method for controlling the amount of air diffused by the DO value widely used in the standard activated sludge method, and it was considered to apply this method to the oxygen activated sludge method. However, simple controls such as the standard activated sludge method did not work. In other words, the amount of air diffused to stabilize DO changes only with the load fluctuation of the drainage and the water temperature when the air is diffused temporarily, whereas with the oxygen activated sludge method. The oxygen concentration of the gas diffused varies depending on the amount of high-concentration oxygen gas supplied. The required amount of diffused air changes greatly due to this concentration change, and the gas is repeatedly circulated, so it turns out that changes due to drainage load conditions and water quality conditions are incomparably large compared to transient diffusers. did. Furthermore, in the oxygen activated sludge method using a sealable nitrification tank, if the oxygen concentration in the gas phase part of the most downstream nitrification tank fluctuates or increases, the oxygen concentration in the exhaust gas is not stabilized and is not used. As a result, a large amount of oxygen was discharged out of the system, and the target oxygen utilization efficiency could not be obtained.

Therefore, it is considered essential to stabilize the oxygen concentration in the gas phase part of the nitrification tank and to stabilize the DO of the mixed solution. And found that it is preferable to control and supply high concentration oxygen gas.
In the present invention, an apparatus as shown in FIG. 1 can be used. This apparatus comprises a sealed nitrification tank into which a nitrification carrier having nitrifying bacteria fixed on the surface is charged, and an oxygen supply line and an exhaust gas line are connected to the nitrification tank. Aeration of the nitrification tank is performed by a gas circulation system using a circulation blower and an air diffuser, and the amount of air diffused is controlled and supplied by the nitrification tank DO. Further, the supply amount of the high concentration oxygen gas is controlled and supplied by the gas phase portion of the nitrification tank or the oxygen concentration of the exhaust gas.

  The nitrification performance of the carrier greatly depends on the DO of the nitrification tank, and 2 mg / L or more of DO was necessary to maintain high nitrification performance. On the other hand, the higher the DO, the higher the nitrification performance. Therefore, it is better to set the DO as high as possible. However, if the DO exceeds 12 mg / L, the nitrification performance reaches its peak (see FIG. 6), which is preferable. The DO condition of the liquid mixture in the nitrification tank liquid phase is 2 to 12 mg / L. Further, the high dependency of DO means that the nitrification performance can be arbitrarily adjusted by setting the optimal DO value according to the load condition and the required processing performance. In particular, when there is load fluctuation, the DO value is set low during the low load period, and conversely, the DO value is set high during the high load period. Performance can be demonstrated.

  Thus, the upper and lower limit set values of the dissolved oxygen concentration of the nitrification tank mixture may be changed in advance based on the fluctuation pattern of the ammonia nitrogen or organic nitrogen load with time. Since the load is calculated by the product of wastewater inflow and wastewater concentration, (drainage inflow) x (drainage concentration), both wastewater inflow and wastewater concentration are used as indicators. Is small, the drainage concentration may be used as an index, and conversely, when the fluctuation of the drainage concentration is small, the drainage inflow amount may be used as an index. Here, the liquid phase as an index is not limited to waste water. That is, following the load fluctuation, the concentration of ammonia nitrogen in the liquid phase such as the mixed liquid in the nitrification tank, the water in the sedimentation basin, and the treated water also changes. The upper and lower limit set values of the dissolved oxygen concentration of the nitrification tank mixture may be changed in advance.

  The liquid phase used as an indicator is not limited as long as the change in ammoniacal nitrogen concentration can be grasped. However, in order to better follow the load fluctuation pattern, the wastewater to be treated and the nitrification reaction progress. A nitrification tank is preferred. Furthermore, based on the detection result of measuring ammonia nitrogen or organic nitrogen load or ammonia nitrogen concentration in the liquid phase, it had a function to change the upper and lower limit set values of dissolved oxygen concentration in the nitrification tank mixture You may control automatically using a control apparatus. Examples of these detectors include an ammonia concentration meter and a nitrogen concentration meter. As for load fluctuations, changes in the amount of water affect the concentration, so it is sufficient to use a water meter together with these concentration meters, or use a load meter that measures the concentration and water volume and calculates the load. May be. Of course, the detector is not limited to these detectors as long as it is a detection means capable of grasping and predicting ammonia nitrogen or organic nitrogen load or liquid ammonia ammonia concentration.

  When circulating aeration by the oxygen activated sludge method, there are mainly two methods for adjusting DO of the nitrification tank mixture. One is a method for controlling the amount of air diffused by the DO value of the liquid mixture, and the other is a method for controlling the amount of oxygen supplied to the gas phase part of the nitrification tank. The former adjusts and stabilizes DO by simply decreasing DO and increasing the amount of air diffusion, and conversely decreasing DO when the DO increases. The latter adjusts the nitrification tank DO by changing the gas phase of the nitrification tank, that is, the oxygen concentration of the gas to be diffused according to the supply amount of oxygen. With either method, it is possible to adjust the DO of the mixed solution to the target value, but the former requires a large amount of aeration when the oxygen concentration is lowered. Necessary and high power costs. In the latter, since the oxygen concentration of the aeration increases as the required oxygen amount increases, the oxygen concentration of the exhaust gas also increases accordingly, and the oxygen utilization efficiency decreases. Both have their own problems, and independent control increases the running cost due to an increase in blower power or a decrease in oxygen utilization efficiency. In order to solve all these problems, the method of stabilizing the oxygen concentration in the gas phase part of the nitrification tank and controlling the amount of air diffused by the DO value of the former mixed solution was devised, and the method of the present invention was achieved. .

There are no restrictions on the location of DO concentration measurement in the nitrification tank mixture to control the amount of air blower blower, as long as the operation of the blower and stabilization of the nitrification tank DO are possible. It is preferable that a DO meter and a blower are provided in each nitrification tank, and the blower is individually controlled by DO. This is because it is necessary to maintain an appropriate DO in all nitrification tanks in order to advance nitrification efficiently. The blower is controlled by increasing or decreasing the number of rotations of the blower with an inverter based on the detection result of the DO value, or by adjusting the opening of the air volume control valve.
The DO meter used in the present invention is not limited as long as it can be used for a long period of time without being affected by the measurement of the mixed liquid and wastewater components. Is preferred.

  The conventional method used to stabilize the oxygen concentration in the nitrification gas phase is to control the supply of high-concentration oxygen gas based on the pressure change in the nitrification gas phase and the flow rate of exhaust gas. It is a method to do. This is because oxygen supplied to the nitrification tank becomes nitrate nitrogen and nitrite nitrogen by microbial reaction or respiration and moves to the liquid phase, or becomes carbon dioxide that is more soluble in water than oxygen. Since the portion is absorbed by water, the volume of the discharged gas is reduced rather than the volume of the gas supplied by receiving the action of microorganisms. These methods are generally applied in the surface aeration apparatus, and there are cases where the operation is stable. However, the operation may become unstable due to other factors that affect the pressure change, such as fluctuations in water volume. . Furthermore, when this method is applied to the circulation aeration method, the gas movement and pressure change are more remarkable than the surface aeration method, so that stable operation cannot be performed.

Therefore, in the method of the present invention, the high concentration oxygen gas is controlled and supplied based on the measurement result of the oxygen concentration of the nitrification tank gas phase or the exhaust gas. Specifically, for example, when the oxygen concentration in the gas phase part falls below the lower limit value, the flow control valve (17 in FIG. 1) installed in the oxygen gas supply pipe (10 in FIG. 1) is opened, or the opening degree The amount of supplied oxygen can be increased by increasing. Conversely, when the oxygen concentration exceeds the upper limit, the amount of supplied oxygen can be reduced by closing the flow rate control valve installed in the oxygen gas supply pipe or reducing the opening. In this method, not only is not affected by the pressure fluctuation of the nitrification tank gas phase part, but also the oxygen concentration of the gas phase part can be arbitrarily set, not only contributes to the operation of the blower and the stabilization of the nitrification tank DO, Oxygen utilization efficiency can be arbitrarily adjusted to enable stable and efficient operation.
The oxygen concentration measurement location for controlling the high-concentration oxygen gas supply is not limited as long as the operation of the blower, stabilization of the nitrification tank DO, and adjustment of oxygen utilization efficiency are possible, but the oxygen utilization efficiency is adjusted. Therefore, it is preferable to control by the gas phase part of the most downstream nitrification tank or the oxygen concentration of the exhaust gas.

The target oxygen utilization efficiency can be easily obtained by setting the oxygen concentration in the gas phase gas or exhaust gas of the nitrification tank, but generally the oxygen utilization efficiency of about 80 to 90% is obtained in the oxygen activated sludge method. Since it is required, the oxygen utilization efficiency of 80% or more can be obtained by controlling the oxygen concentration of the gas phase gas or exhaust gas in the most downstream to about 30% to 70%, preferably about 40% to 60%. It was shown that This condition depends on the concentration of the high-concentration oxygen gas to be used, but if it is 30% or less, the advantage of the oxygen method of maintaining a high DO with a small amount of aeration cannot be exhibited. In the above case, the oxygen concentration of the exhaust gas became too high and the oxygen utilization efficiency was lowered.
The oxygen concentration meter used in the present invention is not limited as long as it can withstand long-term use without being affected by the measurement of the gas diffused and the components of the exhaust gas, but is included in the target gas at a high concentration. A zirconia oxygen concentration meter, a magnetic oxygen concentration meter, and an infrared oxygen concentration meter that are not easily affected by carbon dioxide are suitable.

As the high-concentration oxygen gas used in the method of the present invention, a gas having an arbitrary oxygen concentration in which the oxygen concentration is higher than that of air can be used. Examples of such a gas include oxygen-enriched air in which the oxygen gas concentration is increased using an oxygen enricher, and pure oxygen gas whose oxygen concentration is close to 100%. Such a high-concentration oxygen gas can be directly supplied to the gas phase part of the nitrification tank or the circulation aeration pipe. When supplied to the circulating air diffuser piping, the oxygen concentration in the nitrification tank gas phase and the DO responsiveness of the mixed solution were slightly accelerated.
In the present invention, a gas having a high oxygen concentration is diffused into the mixed solution. However, the exhaust gas that has been diffused and has come out of the water surface has a higher oxygen concentration than the atmosphere, so this exhaust gas is not released into the atmosphere. The oxygen utilization efficiency could be increased by repeatedly aeration into the liquid phase through the blower. Therefore, the gas once diffused is not directly discharged to the outside of the tank, but can be sealed so that most of the gas other than the discharged gas can be supplied again to the blower and repeatedly diffused. There are no restrictions on the shape, number, arrangement, etc. of the tank. When the tank structure is simplified, a single tank may be used, or the tank may be divided into multiple tanks in consideration of the fluidity of the carrier. The division of the tank may be parallel or serial with respect to the inflow of raw water. However, in particular, in order to increase the use efficiency of oxygen, a multistage structure as shown in FIG. The high-concentration oxygen (10) is supplied to the gas phase part of the gas or the circulation aeration line (15), and the gas is sequentially flowed from the upstream tank to the downstream tank via the gas phase communication part. The most efficient method is to exhaust the exhaust gas (11) from the most downstream water tank.

The air diffuser used in the present invention does not cause nitrification carrier wear / breakage, nitrifying bacteria adherence inhibition, and the gas emitted from the water surface of the nitrification tank is repeatedly aerated to produce a sludge mist. Any porous tube, disk diffuser, sparger, etc. may be used as long as they are not easily clogged by dust or the like. In addition, by installing sludge mist in the circulating gas, mist separator for removing dust, fine dust, etc., gas filtration air, etc. on the suction side of the blower, a fine bubble diffuser with higher oxygen transfer efficiency An apparatus can also be used. Examples of such a diffuser include a diffuser plate and diffuser made of ceramic or synthetic resin, and a membrane diffuser.
The blower is not limited as long as it does not hinder hermeticity and continuous operation for a long time, but a Roots blower is preferable.

As the carrier used in the present invention, a binding-immobilized carrier that allows nitrifying bacteria to adhere to the surface of the carrier is suitable. Moreover, if the adherence of nitrifying bacteria is good and can hold a sufficient amount of nitrifying bacteria for treatment, and the flowability and durability are good, there is no limitation on the shape, material, and physical properties, but the shape is Since it has a large surface area and good wear resistance, it is preferably granular or spherical. The size is preferably a granule having a diameter of 1 to 10 mm, and the material preferably includes polyethylene glycol (PEG) or polyethylene glycol. The specific gravity is preferably in the range of 0.90 to 1.1 in terms of fluidity.
The binding immobilization carrier is suitable in that nitrifying bacteria adhere to the carrier spontaneously in the nitrification tank to form a biofilm. According to the study by the present inventors, the pH is 6 or less, and in some cases 5 This is because it has been found that even under extremely low conditions of about 5 or less, high nitrification performance can be exhibited by gradually adapting to the conditions. This makes it possible to proceed with nitrification only by adjusting the pH with a small amount of an alkaline agent without performing any neutralization treatment even in the oxygen activated sludge method in which the pH tends to decrease.

The target waste water of the present invention is not limited to sewage and industrial waste water, and may be water containing ammonia nitrogen and / or organic nitrogen, and the concentration of the waste water is not limited. For example, in the case of water lacking the alkalinity necessary for nitrification and other components such as phosphorus and iron necessary for the nitrification reaction, these may be added, and copper and hydrogen sulfide that inhibit the nitrification reaction About water that contains etc., it can be set as target drainage by performing abatement treatment.
The circulating air diffuser not only supplies DO but also has a role of causing the carrier to flow. If necessary, a stirrer may be used in combination to maintain the fluidity of the carrier. The stirrer to be used is not limited as long as it can flow the nitrification carrier without causing abrasion or damage of the nitrification carrier and inhibition of nitrifying bacteria adhesion.

  Furthermore, the detailed conditions for the nitrification reaction under the low pH conditions revealed by the present inventors are that the alkalinity is important, specifically, the pH of the nitrification tank is 5 to 6, and the alkalinity is The minimum amount required for nitrification, preferably the alkalinity of the nitrification tank was 10 mg / L or more, more preferably the alkalinity of the nitrification tank was 30 mg / L or more. If it can be set in such a range, it is not necessary to use a decarboxylation treatment or a pH adjuster, and if the pH is further lowered, or if the alkalinity is insufficient, an alkali agent sufficient to meet the shortage is injected, What is necessary is just to perform the decarboxylation process of a required amount. In addition, as shown in FIG. 2, a denitrification step may be provided in the front stage of the nitrification tank, and the increase in alkalinity due to the denitrification reaction may be utilized by returning the liquid phase and / or sludge of the nitrification tank.

  In our research, with various effluents such as sewage and other industrial wastewater, a denitrification tank is installed in the front stage of the nitrification tank, and even if circulation nitrification denitrification equivalent to the returned sludge is performed, without using chemicals, It was possible to keep the alkalinity of the nitrification tank in a sufficiently suitable range. Of course, a circulation line may be provided in the nitrification tank and the denitrification tank for circulation. The circulation rate including the amount of returned sludge is preferably 0.3 times or more of the raw water amount, and more preferably 0.5 or more. Thus, by incorporating the denitrification step, not only the purpose of nitrogen removal can be achieved, but also the stabilization of nitrification performance by keeping the alkalinity suitable can be realized without using chemicals. The installation of a denitrification tank in front of the nitrification tank itself is a general method as a nitrification denitrification system, but alkalinity is supplied for the conditions of the oxygen activated sludge method using the nitrification carrier of the present invention. By doing so, it has a big role of stabilizing the performance at a low cost.

The suspended sludge in the nitrification tank mixed solution may have the removal of BOD coexisting in the waste water and the nitrification performance, so it is advantageous to coexist in the nitrification tank together with the carrier. However, if the treatment can be satisfied only by nitrification with a carrier, it is not necessary to use floating sludge. In such a case, the return sludge line is not necessary, and naturally, if the circulation type nitrification denitrification operation is not performed, the circulation line is also unnecessary.
According to the method of the present invention, since high nitrification performance can be exhibited, the nitrification tank capacity can be made compact, and the treatment performance can be satisfied with an extremely short residence time of about HRT 1.4-2 hr. It was.
The screen for separating the carrier installed in the nitrification tank is not limited as long as the carrier can be separated and damaged and worn, but the oxygen activated sludge method has a maintenance structure because the nitrification tank has a sealed structure. Good specification is suitable. As a result of the study by the present inventors, it was found that a cylindrical mechanical screen that can be installed and rotated, in particular, has a most preferable specification.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a flow configuration diagram showing an example of a wastewater treatment apparatus of the present invention. As shown in FIG. 1, the waste water treatment apparatus includes a sealable nitrification tank 2 storing a nitrification carrier 5 to which nitrifying bacteria are attached, a sedimentation basin 3, an oxygen gas supply line 10, an exhaust gas line 11, and a raw water supply. Line 1 and treated water outflow line 4 are provided. The oxygen gas supply line 10 is provided with a flow rate control valve 17, and the exhaust gas line 11 is provided with an oxygen concentration meter 14.
The nitrification tank 2 includes a gas circulation line 15 for circulating and diffusing the nitrification tank gas phase gas 12 between the liquid surface and the ceiling of the nitrification tank through the blower 9 and a dissolved oxygen concentration meter 13. ing.
Furthermore, the waste water treatment apparatus of the present invention is provided with a control device. The control device 16 functions as a control unit that controls the amount of air diffused by the blower 9 based on the detection result of the dissolved oxygen concentration meter 13. The blower 9 is controlled by increasing or decreasing the number of rotations of the blower based on the detection result of the DO value, or by adjusting the opening of the air volume control valve. On the other hand, the control device 18 functions as a control means for adjusting the opening / closing operation or the opening degree of the flow control valve 17 of the high concentration oxygen gas based on the detection result of the oximeter 14.

Next, a wastewater treatment method using the wastewater treatment apparatus configured as described above will be described.
First, the waste water to be treated is introduced into the nitrification tank 2 via the line 1. The waste water introduced into the nitrification tank 2 is mixed with a carrier on which nitrifying bacteria in the nitrification tank 2 are fixed.
Next, high-concentration oxygen gas is supplied into the nitrification tank 2 through the line 10 to fill the gas phase part 12 with high-concentration oxygen. Then, by operating the blower 9, the gas in the gas phase portion 12 is once sucked, and this gas is sent to the diffusion tube 8 in the nitrification tank 2 and diffused into the mixed liquid in the nitrification tank 2.
In this way, oxygen supplied from the line 10 into the sealable nitrification tank 2 dissolves in the mixed liquid in the nitrification tank 2 more efficiently than air.
Next, the control device 18 is operated, the flow rate control valve 17 is controlled based on the indicated value of the oximeter 14, and the necessary amount of oxygen is always supplied, so that the oxygen concentration of the nitrification gas phase gas 12 is stable. To do. Further, the control device 16 is operated, and the amount of air diffused in the blower 9 is controlled based on the indicated value of the dissolved oxygen concentration meter 13, so that the necessary amount of air is always diffused and the dissolved oxygen concentration of the mixed liquid is stabilized.

Next, another example of the wastewater treatment apparatus and the wastewater treatment method of the present invention will be described based on the flow configuration diagram of FIG. 2, the same reference numerals are given to the same or corresponding parts as in FIG. 1, and detailed description thereof will be omitted.
In FIG. 2, the nitrification tank is partitioned by a partition wall to form a two-stage structure in series with the inflow of raw water, and a denitrification tank 20 is provided in the front stage of the nitrification tank. The nitrification tank is divided into a liquid phase and a gas phase by a partition wall, but the liquid phase communicates with the carrier separation screen 24, while the gas phase also has a gas communication portion 25. Each nitrification tank is provided with a gas circulation line, and the oxygen supply line 10 is connected to the first nitrification tank.
The denitrification tank 20 biologically treats the introduced wastewater to be treated using activated sludge mainly composed of denitrifying bacteria. For example, floating activated sludge is accommodated in the denitrification tank 20, A stirring device 21 for stirring the waste water is provided.

Next, a wastewater treatment method using the wastewater treatment apparatus of FIG. 2 will be described.
First, the wastewater to be treated is introduced into the denitrification tank 20 through the line 1. The wastewater introduced into the denitrification tank 20 is mixed with the activated sludge and stirred, so that the organic matter supplied from the raw water is used as a hydrogen donor, and nitrate nitrogen and nitrite nitrogen supplied from the return sludge 6 are used. Is decomposed into nitrogen gas.
The drained water after denitrification is sent in the order of the first nitrification tank 2 and the second nitrification tank 2 ′, and is mixed with the carrier to which nitrifying bacteria adhere, and nitrification proceeds.
The effluent after nitrification is sent to the sedimentation basin 3, and activated sludge is separated from the effluent after nitrification. The supernatant waste water from which the activated sludge has been separated is discharged as treated water 4. On the other hand, the separated and separated sludge is returned to the denitrification tank through the return sludge 6 line. Further, surplus separated sludge is discharged from the surplus sludge line 7 to the outside of the system.
The high-concentration oxygen gas is supplied from the line 10 to the gas phase portion 12 of the first nitrification tank 2 so that the gas phase portion 12 is filled with high-concentration oxygen. Then, by operating the blower 10, the gas in the gas phase portion 12 is once sucked, and this gas is sent to the diffuser pipe 8 in the nitrification tank 2 and aerated into the waste water in the nitrification tank 2.

Next, the remaining oxygen gas discharged from the first nitrification tank 2 is supplied to the gas phase section 12 ′ of the second nitrification tank 2 ′, and the gas phase section 12 ′ is filled with high-concentration oxygen. Then, by operating the blower 10 ′, the gas in the gas phase portion 12 ′ is once sucked, and this gas is sent to the diffuser tube 8 ′ in the nitrification tank 2 ′ and discharged into the nitrification tank 2 ′. Aerate.
Next, the control device 18 is operated, the flow rate control valve 17 is controlled based on the indicated value of the oximeter 14, and a necessary amount of oxygen is always supplied, and oxygen in the nitrification tank gas phase gas 12, 12 ′. The concentration is stable. Further, the control devices 16 and 16 ′ are operated, and the amount of air diffused in the blowers 10 and 10 ′ is controlled based on the indicated values of the dissolved oxygen concentration meters 13 and 13 ′, so that the necessary amount of air is always diffused. The dissolved oxygen concentration of the nitrification tank mixture is stabilized.

In this way, the oxygen supplied from the line 10 into the sealable nitrification tank 2, 2 ′ dissolves in the waste water in the nitrification tank 2, 2 ′ more efficiently than air. In addition, the nitrification tanks are multistage in series, and oxygen is supplied to the upstream tank, so that oxygen is efficiently used from the upstream side, and the oxygen concentration decreases toward the downstream side, and is discharged out of the system as exhaust gas. Therefore, the amount of oxygen to be used can be kept low and oxygen can be used efficiently.
The purpose of supplying the high concentration oxygen gas from the line 10 to the gas phase portion 12 of the first nitrification tank 2 is to use oxygen efficiently. The injection point and gas flow are not limited to the first nitrification tank 2. For example, if the gas phase part of the second nitrification tank 2 ′ is also injected near the boundary with the gas phase part of the first nitrification tank 2, a part of the high-concentration oxygen gas is first from the second nitrification tank 2 ′. It was also supplied to the nitrification tank 2 and efficient operation was possible.

Next, a wastewater treatment method using the wastewater treatment apparatus of FIG. 3 will be described. The flow of water is the same as described above with reference to FIG.
A different part from FIG. 2 is demonstrated below. In FIG. 3, by operating the blower 9 as a single unit, the gas in the gas phase part 12 ′ of the second nitrification tank is once sucked, and this gas is used as the first nitrification tank 2 and the second nitrification tank 2 ′. Aerated during drainage. Flow control valves 26 and 26 'are attached to the pipes leading to the air diffusers 8 and 8' of the first nitrification tank 2 and the second nitrification tank 2 ', respectively. A dissolved oxygen concentration meter 13 is installed in the first nitrification tank 2 and a dissolved oxygen concentration meter 13 'is installed in the second nitrification tank 2', which is controlled by the indicated values of the dissolved oxygen concentration meters 13 and 13 '. The apparatus 16 is operated, and the aeration amount of each nitrification tank is adjusted by adjusting the inverter frequency of the blower 9 and the opening degree of the flow rate control valves 26 and 26 ', so that a necessary amount of aeration is always performed and nitrification is performed. The dissolved oxygen concentration in the tank mixture is stabilized.
In this way, while performing the same control as the flow shown in FIG. 2, the number of devices is reduced by reducing the initial cost and maintenance cost by sharing the blower 9 with one blower 9 and sharing the blower with a plurality of tanks. Leads to.

Next, a wastewater treatment method using the wastewater treatment apparatus of FIG. 4 will be described. The flow of water is the same as described above with reference to FIGS.
A different part from FIG. 3 is demonstrated below. In FIG. 4, the air volume control valve 26 is installed in the pipe leading to the air diffuser 8 or 8 ′ in either the first nitrification tank or the second nitrification tank. That is, the amount of aeration air to one nitrification tank is controlled by adjusting the opening degree of the flow control valve 26, and the amount of aeration air to the other nitrification tank is controlled by adjusting the inverter frequency of the blower 9. I do. Each control is based on the indicated value of dissolved oxygen concentration meter 13 and 13 'installed in each tank.

Next, with reference to FIG. 5, the control operation for adjusting the DO concentration of the nitrification tank mixture and the O ₂ concentration of the exhaust gas will be specifically described. In FIG. 5, the automatic air volume adjustment operation is first performed in step S1 by the start of the automatic operation and the inverter control of the circulation blower and / or the opening adjustment of the air volume control valve. Next, the process proceeds to step S2, where the nitrification tank DO value is returned to S1 if it is not proper, and the rotation speed of the circulation blower is increased or decreased by an inverter, or the air volume is increased or decreased by adjusting the opening of the air volume control valve. Make the tank DO value appropriate. If the nitrification tank DO value is appropriate, the process proceeds to step S3, where an automatic opening adjustment operation of the oxygen gas inflow valve is performed. Then proceeds to step S4, where the return to step S3 if not properly exhaust gas O ₂ concentration and the proper exhaust gas O ₂ concentration by the opening and closing operation or the opening adjustment of the oxygen gas inlet valve. Then, the exhaust gas _{O 2} concentration is returned to S1 if appropriate. Thus, by repeating steps S1 to S4, it is possible to stably maintain DO in the nitrification tank mixed solution and O ₂ concentration in the exhaust gas.

Furthermore, the appropriate DO value that is the basis of the determination in step S2 is based on the relationship between DO and nitrification rate as shown in FIG. 6, and the time of ammonia nitrogen or organic nitrogen load or liquid phase ammonia nitrogen concentration The DO program has been set in advance so that the nitrification rate corresponding to the fluctuation pattern with the course of the process can be obtained, the ammonia nitrogen or organic nitrogen load, or the liquid phase ammonia nitrogen concentration Based on the detection result of measuring, automatically control using a control device that has a function to change the upper and lower limits of the dissolved oxygen concentration of the nitrification tank mixture so that DO corresponding to the nitrification rate is obtained Thus, the power cost can be further reduced and the nitrification performance can be further stabilized.
As mentioned above, although preferred embodiment of this invention was described in detail, it cannot be overemphasized that this invention is not limited to the said embodiment.

Hereinafter, the present invention will be described in detail with reference to examples, and the results obtained by experiments are shown in Tables 2 and 3.
Example 1
The nitrification carrier is put into the experimental apparatus (circulation amount 165 m ³ / day, nitrification tank capacity 10 m ³ , HRT 1.5 hr, return sludge amount 82.5 m ³ / day) based on the flow shown in FIG. For the sewage primary treated water (hereinafter referred to as raw water) of ammonia nitrogen (NH ₄ -N) concentration 16 to 25 mg / L and organic nitrogen (Org-N) concentration 3 to 11 mg / L shown in Table 1, A treatment experiment was conducted.
The specifications of the experimental apparatus are as follows.
Oxygen gas generator: PSA (pressure swing adsorption) system DO meter: Fluorescent dissolved oxygen meter Oxygen meter: Zirconia oxygen concentration Blower: Roots blower diffuser: Porous tube Carrier: Spherical PEG carrier Carrier filling rate: 20 % (Apparent volume per nitrification tank volume)
The experimental conditions are as follows.
O ₂ concentration of the supplied high concentration oxygen gas: 80 to 90%
High concentration oxygen gas supply amount: 28 to 55 L / min
Setting DO: 7.5 mg / L
Set exhaust gas O ₂ concentration: 46%
Aeration amount: 41 to 86 m ³ / h

As a result, the nitrifying bacteria adhering to the carrier gradually became acclimatized, and the NH ₄ -N concentration of the treated water gradually decreased and became 0.2 to 0.9 mg / L on the 20th day from the start of the treatment. . Furthermore, since the supply amount of the high-concentration oxygen gas is controlled by the oxygen concentration of the exhaust gas, the oxygen concentration of the exhaust gas becomes constant at about 46% regardless of the water amount fluctuation, the load fluctuation, and the amount of diffused air, and as a result, it is as high as 85%. Oxygen utilization efficiency was achieved. The pH of the nitrification tank during this period was a low value of 5.0 to 5.2, but this is a closed type in which a small amount of high-concentration oxygen gas is injected, so the carbon dioxide partial pressure of the nitrification solution is low. This is because the alkalinity is high due to the high nitrification (the alkalinity of the nitrification tank is 10 to 25 mg / L). Moreover, DO of the nitrification tank was stable at 7.4 to 7.7 mg / L without being affected by fluctuations in water amount and load. This is because the aeration amount control based on the DO value was successfully performed. As described above, even in a low pH condition, good treatment performance could be exhibited by maintaining DO stably.

Example 2
Experimental apparatus of circulation aeration method based on the flow shown in FIG. 2 (throughput 165 m ³ / day, nitrification tank capacity 10 m ³ , HRT 1.5 hr, denitrification tank capacity 0.5 m ³ , return sludge volume 82.5 m ³ / The nitrification carrier was added to the sewage primary treated water of ammonia nitrogen (NH ₄ -N) concentration 16 to 25 mg / L and organic nitrogen (Org-N) concentration 3 to 11 mg / L shown in Table 1. Hereinafter, treatment experiments were conducted on raw water).
The specifications of the experimental apparatus are the same as those in Example 1, and the experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply: 25-50 L / min
Setting DO: 7.5 mg / L
Set exhaust gas O ₂ concentration: 46%
Aeration amount: 56-77 m ³ / h
The nitrifying bacteria adhering to the carrier gradually became acclimatized, and the NH ₄ -N concentration of the treated water gradually decreased, and was 0.2 to 0.4 mg / L on the 20th day from the start of the treatment. The nitrification performance was even better than that. This is because the alkalinity of the nitrification tank could always be maintained at 30 mg / L or more due to the increase in alkalinity due to the denitrification reaction. In this example, oxygen utilization efficiency as high as 85% was achieved.

Example 3
A treatment experiment under the same conditions as in Example 2 except that the load of ammonia nitrogen was calculated using a water meter and an ammonia concentration meter, and the DO setting value of the nitrification tank mixture was adjusted based on this value. Went.
The water meter uses an electromagnetic flow meter, the ammonia concentration meter uses an ion electrode type device, and other specifications are the same as those in the first embodiment. The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High-concentration gas supply amount: 17 to 50 L / min
Setting DO: Adjusting the setting DO with ammonia nitrogen load Setting exhaust gas O ₂ concentration: 46%
Aeration amount: 26 to 77 m ³ / h
In this example, the nitrification performance is further improved as compared with Example 2 by being maintained at high DO during the high load time period, and the NH ₄ —N concentration of the treated water is 0.1 to 0.2 mg / L. It was. On the other hand, in the low load time zone, the power of the aeration was suppressed by being maintained at low DO, and the power cost was reduced by about 10% compared to Example 2. In this example, the oxygen utilization efficiency was as high as 85%.

Example 4
A processing experiment based on the flow shown in FIG. 3 was performed. One blower was provided, and a flow rate control valve was provided at the inlet of the diffuser in each nitrification tank. The specifications of the experimental apparatus are the same as in Example 1, and the treatment experiment was performed under the same conditions as in Example 2. The specifications of the flow control valve are as follows.
Flow control valve: Pneumatically operated globe valve In this embodiment, even if the number of blowers is one, the nitrifying bacteria adhering to the carrier gradually acclimatize, and the NH _{4 of} the treated water is not inferior to the first and second embodiments. The -N concentration gradually decreased, and on the 20th day from the start of the treatment, it was 0.2 to 0.5 mg / L, indicating good nitrification performance. Also in this example, the set DO value of 7.5 mg / L could be stably maintained by controlling the opening degree of the flow control valve and the inverter of the blower, and the oxygen utilization efficiency was also 85%.
The power cost has been reduced by using one blower.

Example 5
A processing experiment based on the flow shown in FIG. 4 was performed. As in Example 4, one blower and one flow control valve were used. The specification of the experimental apparatus is the same as that of the first embodiment, and the specification of the flow rate control valve is the same as that of the fourth embodiment.
In this embodiment, one blower and one flow control valve are used. However, stable control is possible without any difference from the other embodiments, and the concentration of NH ₄ -N in the treated water is gradually reduced. On the 20th day from the start, it was 0.2 to 0.4 mg / L, which was a good nitrification performance. Also in this example, the set DO value of 7.5 mg / L could be stably maintained by controlling the opening degree of the flow control valve and the inverter of the blower, and the oxygen utilization efficiency was also 85%.
The power cost has been reduced by the amount of blower and the amount of air flow control valve.

Comparative Example 1
The treatment experiment was performed under the same conditions as in Example 2 except that the supply amount of the high-concentration oxygen gas was controlled by the pressure change in the gas phase section of the nitrification tank.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply amount: 22 to 66 L / min
Setting DO: 7.5 mg / L
Set exhaust gas O ₂ concentration: Resulting aeration amount: 28-120 m ³ / h
In this comparative example, the supply amount of high-concentration oxygen gas is controlled by utilizing the fact that oxygen is used in the reaction and the pressure in the gas phase part of the nitrification tank is reduced. The control did not work well due to the influence of the pressure change in the phase part, the exhaust gas oxygen concentration was not stabilized at 42 to 60%, and the oxygen utilization efficiency was as low as 67 to 76%. Here, there were cases where the oxygen utilization efficiency was an apparently high value of 99% or more, but this corresponds to a time zone in which the amount of oxygen necessary for the reaction was not supplied, and the control did not function well. It is shown. Further, although the amount of air diffused was controlled by DO of the nitrification solution, it was not possible to control because the oxygen concentration in the gas phase was unstable, and the DO of the nitrification tank could not be stabilized. As a result, NH ₄ —N remained in the treated water at 0.2 to 7 mg / L, and the treatment performance was insufficient.

Comparative Example 2
The experiment was performed under the same conditions as in Example 2 except that the amount of air diffused by the nitrification solution DO was not controlled, and the supply amount of the high-concentration oxygen gas was controlled by the DO of the mixture solution in the nitrification tank.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High-concentration gas supply amount: 44 to 83 L / min
Setting DO: 7.5 mg / L
Set exhaust gas O ₂ concentration: Resulting aeration amount: 53 m ³ / h
In this comparative example, DO was maintained between 7.0 and 8.1 mg / L with respect to the set value of 7.5 mg / L regardless of water amount fluctuation and load fluctuation, and thus the nitrification performance was also maintained high. Treated water NH ₄ —N was about 0.2 to 0.4 mg / L as in Example 2. However, instead of stabilizing DO, the oxygen concentration in the gas phase and the oxygen concentration in the exhaust gas were not stable at 56 to 65%, and the oxygen utilization efficiency was as low as 57 to 71% and was unstable.

Comparative Example 3
The nitrification carrier is introduced into the experimental apparatus (surface treatment 165 m ³ / day, nitrification tank capacity 10 m ³ , HRT 1.5 hr, return sludge volume 82.5 m ³ / day) based on the flow shown in FIG. A treatment experiment was conducted on the raw water having the properties shown in Table 1. The difference from Example 2 is that the aeration is performed by the surface aeration method, and the supply amount of the high-concentration oxygen gas is controlled by the pressure of the nitrification tank gas phase.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply: 15 to 21 L / min
Setting DO: Result Setting exhaust gas O ₂ concentration: Resulting Although the control method of this comparative example was also adopted in Comparative Example 2 with a different aeration method, the control was more stable in this Comparative Example. This is presumably because the surface aeration method has a smaller pressure change in the gas phase part of the nitrification tank. However, even in the surface aeration method, the influence of the pressure change due to the fluctuation of the water amount is unavoidable, and the oxygen concentration of the exhaust gas is somewhat unstable at 43 to 52%. As a result, the oxygen utilization efficiency was slightly low and unstable at 75 to 82%. Moreover, since DO of the nitrification tank fluctuated greatly from 1.2 to 8.3 mg / L, NH ₄ -N remained in the treated water by about 6 to 13 mg / L, and the treatment performance was insufficient.

Comparative Example 4
A treatment experiment was performed under the same conditions as in Comparative Example 3 except that the supply amount of the high-concentration oxygen gas was controlled by DO of the nitrification tank mixture.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply rate: 15 to 38 L / min
Setting DO: 7.5 mg / L
Set exhaust gas O ₂ concentration: consequence In this comparative example, the oxygen concentration in the gas phase portion and the oxygen concentration in the exhaust gas were 43 to 57%, and the oxygen utilization efficiency was slightly low and unstable, 69 to 82%. Furthermore, although the DO in the nitrification tank was maintained at about 7.2 to 7.8 mg / L, which was advantageous for nitrification, the aeration of surface aeration hindered the attachment of nitrifying bacteria to the carrier, and the treated water As a result, NH ₄ —N remained at about 2 to 4 mg / L. In addition, it was guessed that the poor adhesion of Comparative Example 3 was also influenced by such adhesion inhibition.

Comparative Example 5
The treatment experiment was performed under the same conditions as in Example 2 except that the DO of the nitrification tank mixture was set to a low value of 1.5 mg / L.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply: 10 to 19 L / min
Setting DO: 1.5 mg / L
Set exhaust gas O ₂ concentration: 46%
Aeration amount: 26 to 41 m ³ / h
In this comparative example, the actual DO was 1.3 to 1.8 mg / L, and NH ₄ -N remained in the treated water due to the influence of DO shortage, and the treatment performance was insufficient. .

Comparative Example 6
The treatment experiment was performed under the same conditions as in Example 2 except that the DO setting of the nitrification tank mixture was set as high as 13 mg / L.
The experimental conditions are as follows.
O ₂ concentration of the supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply amount: 19 to 40 L / min
Setting DO: 13 mg / L
Set exhaust gas O ₂ concentration: 46%
Aeration amount: 110 to 215 m ³ / h
In this comparative example, the actual DO was 13 mg / L, the NH ₄ —N of the treated water was 0.2 to 0.4 mg / L, and the treatment performance was good, but to maintain the DO high. The power of the blower was applied, and the power cost was twice that of Example 2.

Comparative Example 7
A treatment experiment was performed under the same conditions as in Example 2 except that the exhaust gas oxygen concentration was set to a low 25%.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High-concentration gas supply amount: 12 to 19 L / min
Setting DO: 7.5 mg / L
Set exhaust gas O ₂ concentration: 25%
Aeration amount: 250 m ³ / h
In this comparative example, the oxygen utilization efficiency was as high as 93% or more. However, since the exhaust gas oxygen concentration was set as low as 25%, the oxygen concentration in the gas phase part of the nitrification tank was also low, and it was necessary to aerate with a large air volume in order to maintain an appropriate DO value. The maximum air flow of the blower was 250 m ³ / h, and the DO of the nitrification tank mixture could not be maintained at 7.5 mg / L. As a result, 12 to 19 mg / L of NH ₄ —N remained in the treated water, and the treatment performance was insufficient. In addition, since a large amount of aeration was performed, a large amount of scum was generated in the nitrification tank, and this was sucked into the circulation blower, resulting in frequent troubles that the blower stopped.

Comparative Example 8
A treatment experiment was performed under the same conditions as in Example 2 except that the exhaust gas oxygen concentration was set as high as 78%.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High-concentration gas supply amount: 97 to 212 L / min
Setting DO: 7.5 mg / L
Set exhaust gas O ₂ concentration: 78%
Aeration amount: 21 to 43 m ³ / h
In this comparative example, the DO of the nitrification tank mixture was properly maintained at 7.4 to 7.7 mg / L, so that the NH ₄ —N of the treated water was 0.2 to 0.4 mg / L and the treatment performance Was also good. Further, since the exhaust gas oxygen concentration was set as high as 78%, the oxygen concentration in the gas phase part of the nitrification tank was also high, and the amount of air needed to maintain an appropriate DO value was small, and the power cost was about 60% of that in Example 2. Met. However, since the oxygen concentration of the exhaust gas is high, the oxygen utilization efficiency was a very low value of 23%. The high-concentration oxygen gas used in the treatment test was the gas generated by the PSA system. However, the oxygen utilization efficiency of Comparative Example 8 was low, so the amount of gas supplied was insufficient, and the test equipment operating in parallel was stopped. I had to do it.
These results are summarized in Tables 2 and 3.

  1: drainage, 2, 2 ′: nitrification tank, 3: sedimentation pond, 4: treated water, 5: nitrification carrier, 6: return sludge, 7: surplus sludge, 8, 8 ′: air diffuser, 9, 9 ′: Blower, 10: High concentration oxygen gas, 11: Exhaust gas, 12, 12 ′: Nitrogen tank gas phase gas, 13, 13 ′: Dissolved oxygen concentration meter, 14: Oxygen concentration meter, 15, 15 ′: Gas circulation line, 16, 16 ': Control device, 17: Flow control valve, 18: Control device, 19: Stirrer, 20: Denitrification tank, 22: Surface aeration machine, 23: Pressure gauge, 24, 24': Screen, 25: Gas phase connection Passage, 26: Flow control valve

Claims (8)

  A sealable nitrification tank filled with a carrier with nitrifying bacteria attached thereto, an oxygen gas supply line for supplying high-concentration oxygen gas to the gas phase part of the nitrification tank, and an exhaust gas from the gas phase part of the nitrification tank Ammonia nitrogen and / or organic in the wastewater, comprising a discharge line for discharging, a blower for introducing the gas in the gas phase portion in the nitrification tank into the liquid phase and aeration means having a diffuser A wastewater treatment apparatus that biologically oxidizes nitrogen to nitrate nitrogen and / or nitrite nitrogen, the dissolved oxygen detection means for detecting the dissolved oxygen concentration in the liquid phase in the nitrification tank, and the dissolved oxygen And a means for controlling the amount of aeration air in the aeration means so that the dissolved oxygen concentration is maintained at a set value based on the detection result by the oxygen detection means, and the gas in the gas phase section in the nitrification tank or the Oxygen detection to detect oxygen concentration in exhaust gas And a means for controlling an oxygen gas supply amount of the oxygen gas supply line so that the oxygen concentration is maintained within a predetermined range based on a detection result by the oxygen detection means. apparatus.   A sealable nitrification tank filled with a carrier with nitrifying bacteria attached thereto, an oxygen gas supply line for supplying high-concentration oxygen gas to the gas phase part of the nitrification tank, and an exhaust gas from the gas phase part of the nitrification tank A discharge line for discharging, a blower for introducing the gas in the gas phase portion in the nitrification tank into the liquid phase and aeration means having an air diffuser, and a denitrification tank in the previous stage of the nitrification tank, The denitrification tank is provided with a return line for returning the liquid phase and / or sludge of the nitrification tank, and ammonia nitrogen and / or organic nitrogen in the wastewater is biologically nitrate nitrogen and / or nitrite nitrogen. Is a wastewater treatment device that performs a denitrification treatment on the basis of the dissolved oxygen detection means for detecting the dissolved oxygen concentration in the liquid phase in the nitrification tank, and the detection result by the dissolved oxygen detection means, Before the dissolved oxygen concentration is maintained at the set value A means for controlling the amount of aeration air of the aeration means, oxygen detection means for detecting the oxygen concentration of the gas in the gas phase part or the exhaust gas in the nitrification tank, and based on the detection result by the oxygen detection means, And a means for controlling an oxygen gas supply amount of the oxygen gas supply line so that the oxygen concentration is maintained within a predetermined range.   The nitrification tank is composed of a plurality of tanks partitioned by a partition wall, and for each tank of the plurality of tanks, dissolved oxygen detection means for detecting the dissolved oxygen concentration in the liquid phase, aeration means having a blower and a diffuser And a means for controlling the amount of aeration air of the aeration means so that the dissolved oxygen concentration is maintained at a set value for each tank.   The nitrification tank is composed of a plurality of tanks partitioned by a partition wall, and for each tank of the plurality of tanks, dissolved oxygen detection means for detecting the dissolved oxygen concentration in the liquid phase, aeration means, and aeration means Aeration means having a flow control valve connected to at least one, and has one inverter controlled blower connected to the aeration means for each tank, and the air volume and / or the dispersion of the blower 2. The apparatus according to claim 1, further comprising means for controlling the amount of aeration air of the aeration means so that the dissolved oxygen concentration is maintained at a set value for each tank by an opening degree of a flow control valve connected to the air means. Or the waste water treatment apparatus of 2.   The set value of the dissolved oxygen concentration in the liquid phase is 2 to 12 mg / L, and the predetermined range of the oxygen concentration of the gas phase part or the exhaust gas is 30 to 70% (volume). The wastewater treatment apparatus according to any one of claims 1 to 4.   A high-concentration oxygen gas is supplied into the gas phase of a sealable nitrification tank filled with a carrier to which nitrifying bacteria are attached, exhaust gas is discharged from the gas phase of the nitrification tank, and the gas in the nitrification tank is discharged. A wastewater treatment method in which ammonia nitrogen and organic nitrogen in wastewater are biologically oxidized to nitrate nitrogen and nitrite nitrogen by aeration of the gas in the phase into the liquid phase through a blower and a diffuser , The dissolved oxygen concentration in the liquid phase in the nitrification tank is detected, and the amount of aeration air to be aerated in the liquid phase is controlled so that the dissolved oxygen concentration is maintained at a set value based on the detection result In addition, the gas concentration in the nitrification tank is detected in the gas phase portion of the nitrification tank, or the oxygen concentration of the exhaust gas is detected, and the oxygen concentration is maintained within a predetermined range based on the detection result. Controlling the amount of oxygen gas supplied Water treatment process.   A high-concentration oxygen gas is supplied into the gas phase of a sealable nitrification tank filled with a carrier to which nitrifying bacteria are attached, and exhaust gas is exhausted from the gas phase of the nitrification tank. The gas inside is aerated in the liquid phase via a blower and a diffuser, and the liquid phase and / or sludge in the nitrification tank is returned to the denitrification tank provided in the previous stage of the nitrification tank, In a wastewater treatment method in which ammonia nitrogen and organic nitrogen are biologically oxidized to nitrate nitrogen and nitrite nitrogen and denitrified, the concentration of dissolved oxygen in the liquid phase in the nitrification tank is detected. The amount of aeration air to be aerated in the liquid phase is controlled so that the dissolved oxygen concentration is maintained at a set value based on the detection result, and the gas in the gas phase portion in the nitrification tank or the exhaust gas An oxygen concentration is detected, and the oxygen concentration is within a predetermined range based on the detection result. As will be maintained, the waste water treatment method characterized by controlling the oxygen gas supply amount supplied to the gas phase portion of the nitrification tank.   The set value of the dissolved oxygen concentration in the liquid phase is 2 to 12 mg / L, and the predetermined range of the oxygen concentration in the gas phase part or the exhaust gas is 30 to 70% (volume). The wastewater treatment method according to claim 6 or 7, characterized in that