JP5883697B2 - Waste water treatment apparatus and waste water treatment method - Google Patents

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 settling 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 the oxygen activated sludge method, a surface aeration method is adopted as an aeration method for 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 in the nitrification tank via a circulation blower instead of the surface aeration method. There is 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. A gas having a higher oxygen concentration than air such as oxygen-enriched air or pure oxygen used in the oxygen activated sludge method (hereinafter referred to as high-concentration oxygen gas) is expensive to produce. In addition, the combined use of a blower that consumes a large amount of power further increases the running cost. To put into practical use a method of circulating air diffuser using a blower, an operating method that reduces the running cost as much as possible. It was necessary to consider.

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 biologically oxidizes nitrogen-containing wastewater that can reduce the total running cost of wastewater treatment in an oxygen activated sludge method that circulates and diffuses with a blower. It is an object of the present invention to provide a wastewater treatment apparatus and method for processing.

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 nitrification tank, and the nitrification tank include The gas phase part and the liquid phase part are in continuous communication through the partition wall, and the gas in the gas phase part in the nitrification tank is put into the liquid phase in the nitrification tank. Drainage for biologically oxidizing ammonia nitrogen and / or organic nitrogen in wastewater to nitrate nitrogen and / or nitrite nitrogen, equipped with aeration means having a blower for guiding and aeration and a diffuser A treatment apparatus, wherein the dissolved oxygen concentration is detected in the plurality of nitrification tanks, and the dissolved oxygen concentration is maintained at a set value based on a detection result by the dissolved oxygen detection device. Control the aeration air volume of the aeration means Together and means that, among the plurality of nitrification tank, at least, to the first tank flows into the first sewage most, and the oxygen concentration measuring means for measuring the oxygen concentration of the gas in the vapor phase, oxygen concentration Based on the measurement result by the measuring means, the oxygen gas supply amount of the oxygen gas supply line for supplying the high-concentration oxygen gas is controlled so that the measured oxygen concentration in the gas phase part of the nitrification tank is maintained within a predetermined range. A wastewater treatment apparatus 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 the nitrification tank, and the nitrification tank are partitioned by a partition wall, A blower comprising a plurality of tanks in which a gas phase part and a liquid phase part are sequentially communicated with each other through the partition wall; and a blower for introducing the gas in the gas phase part in the nitrification tank into the liquid phase and aerating the plurality of nitrification tanks; A denitrification tank is provided in front of the first tank of the plurality of nitrification tanks, and the liquid phase and / or sludge of the final tank of the nitrification tank is returned to the denitrification tank. A wastewater treatment apparatus which is provided with a return line and denitrifies by biologically oxidizing ammonia nitrogen and / or organic nitrogen in waste water to nitrate nitrogen and / or nitrite nitrogen, The dissolved acid for detecting the dissolved oxygen concentration in the liquid phase in the plurality of nitrification tanks Detection means, based on the detection result by the solution exist oxygen detecting means provided with a means for controlling the aeration amount of the aeration unit such that the dissolved oxygen concentration is maintained at the set value, the plurality of nitrification tank Of these, at least in the first tank into which sewage flows first, an oxygen concentration measuring means for measuring the oxygen concentration of the gas in the gas phase portion, and the measured nitrification based on the measurement result by the oxygen concentration measuring means as the oxygen concentration of the bath is maintained at a predetermined range, which has a waste water treatment apparatus, characterized in that it comprises a means for controlling the oxygen gas supply amount of the oxygen gas supply line for supplying the high-concentration oxygen gas is there.

  In the wastewater treatment apparatus, an arbitrary plurality of nitrification tanks of the plurality of nitrification tanks are provided with an oxygen concentration measurement means for measuring the oxygen concentration in the gas phase part in the nitrification tank, and the measurement result by the oxygen concentration measurement means On the basis of the above, for each nitrification tank equipped with the oxygen concentration measuring means, it can be provided with means for controlling the oxygen gas supply amount of the oxygen gas supply line so that the oxygen concentration in the gas phase is maintained within a predetermined range, The nitrification tank that does not have a means for controlling the oxygen gas supply amount is provided with oxygen concentration measurement means for measuring the oxygen concentration of the gas in the gas phase in the nitrification tank, Ventilation adjusting means for adjusting the amount of gas flow to the communicating portion communicating with the gas phase portion of the nitrification tank, and means for controlling the amount of gas flow by the ventilation adjusting means based on the measurement result by the oxygen concentration measuring means. be able to.

Furthermore, in the present invention, the liquid phase of a sealable nitrification tank filled with a carrier to which a nitrifying bacterium composed of a plurality of tanks partitioned by a partition and sequentially communicating the liquid phase part and the gas phase part through the partition is filled. In the wastewater treatment method for biologically oxidizing ammonia nitrogen and organic nitrogen in waste water for aeration of high-concentration oxygen gas to nitrate nitrogen and nitrite nitrogen, the liquid phases of the plurality of nitrification tanks And the amount of aeration air to be aerated in the liquid phase of the detected nitrification tank is controlled so that the dissolved oxygen concentration is maintained at a set value based on the detection result. Among the nitrification tanks , at least the oxygen concentration of the gas in the gas phase part of the first tank in which sewage flows first is measured, and based on the measurement results, the oxygen concentration is maintained within a predetermined range. The gas phase part of the nitrification tank measured It is obtained by a waste water treatment method characterized by controlling the high concentration oxygen gas supply amount supplied.

Further, in the present invention, the liquid phase of a sealable nitrification tank filled with a carrier attached with nitrifying bacteria composed of a plurality of tanks partitioned by a partition and sequentially communicating a liquid phase part and a gas phase part through the partition. In addition to aeration of high-concentration oxygen gas, the liquid phase and / or sludge in the final tank of the nitrification tank is returned to the denitrification tank provided in the front stage of the first tank of the nitrification tank, and ammonia in the wastewater In a wastewater treatment method that biologically oxidizes natural nitrogen and organic nitrogen to nitrate nitrogen and nitrite nitrogen, and denitrifies, the concentration of dissolved oxygen in the liquid phase of the plurality of nitrification tanks is detected. And controlling the amount of aeration air to be aerated in the liquid phase of the detected nitrification tank so that the dissolved oxygen concentration is maintained at a set value based on the detection result, and at least of the plurality of nitrification tanks , sewage of the gas phase portion of the first tank to flow into the first best Measuring the oxygen concentration of the body, and controlling the amount of high-concentration oxygen gas supplied to the gas phase part of the measured nitrification tank so that the oxygen concentration is maintained within a predetermined range based on the measurement result This is a characteristic wastewater treatment method.

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 is 30 to 80% (volume) It is good to do.
In the wastewater treatment method, the predetermined range of the oxygen concentration in the gas phase of the nitrification tank that controls the oxygen gas supply amount is a pollutant that requires oxidation treatment contained in the inflow wastewater flowing into the first tank. The nitrification tank that does not control the oxygen gas supply amount can measure the oxygen concentration of the gas in the gas phase in the nitrification tank, and based on the measurement result, The amount of gas flow from the nitrification tank in the previous stage can be adjusted.

According to the waste water treatment apparatus and the waste water treatment method of the present invention, it is possible to reduce the total running cost for waste water treatment in the oxygen activated sludge method that circulates and diffuses with a blower.
In recent years, the production cost of high-concentration oxygen gas by a high-concentration oxygen gas generator (for example, the PSA method) has become low, which may be lower than the power cost of the diffuser blower. On the contrary, the running cost of the entire system can be reduced by using a large amount of high-concentration oxygen gas to increase the oxygen concentration in the gas phase of the nitrification tank and keeping the blower power low. According to the present invention capable of controlling the gas phase oxygen concentration in the first nitrification tank, the gas phase oxygen concentration in the first nitrification tank having a large amount of oxygen utilization can be controlled and maintained at a high level. Therefore, the blower power cost can be significantly reduced, and a remarkable effect can be obtained in the cost reduction of the entire system.

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 partial flow block diagram which shows the other example only of the control relationship of the nitrification tank part of the waste water treatment equipment of this invention. The partial block diagram which shows the other example only of the control relationship of the gaseous-phase part of the nitrification tank of the waste water treatment equipment of this invention. The partial block diagram which shows the other example only of the control relationship of the gaseous-phase part of the nitrification tank 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 of the waste water treatment equipment used for the comparative example 1.

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 experiments where only the aeration system was used with the gas circulation aeration method under the same conditions, it was found that good nitrification performance was obtained and that the processing performance was superior to the conventional surface aeration method. . However, since the power cost of the air diffuser used to perform the gas circulation aeration (for example, blower) is high and the running cost of the entire system is increased, the high-concentration oxygen gas cost and the power cost of the air diffuser are considered. As a result, it has been thought that it is essential to establish a processing apparatus and a processing method that can reduce the running cost of the entire system.

In the conventional oxygen activated sludge method, it has been understood that it is essential and important to operate with high oxygen utilization efficiency in order not to waste oxygen input for wastewater treatment. The present inventors also followed the idea at the beginning, and were also developing the oxygen activated sludge method combining the carrier nitrification method and the circulation aeration method with the aim of achieving high oxygen utilization efficiency.
However, while the present inventors are diligently pursuing research and development, achieving high oxygen utilization efficiency in the oxygen activated sludge method combining the carrier nitrification method and the circulation aeration method is not necessarily the running cost of the entire system. It has been found that it does not contribute to the decline of
In recent years, the production cost of high-concentration oxygen gas by a high-concentration oxygen gas generator (for example, PSA method) has become low, and may be lower than the power cost of the diffuser blower. This is because it is not necessary to achieve efficiency, and conversely, the running cost of the entire system can be reduced by increasing the oxygen concentration by using a high concentration of oxygen gas and keeping the blower power low. In particular, in the multistage nitrification tank, the amount of oxygen required is the largest in the first tank, so by increasing the gas phase oxygen concentration in the first tank, the blower power can be greatly reduced, As a result, the running cost of the entire system can be reduced.

Thus, the present inventors have found that it is preferable to be able to control the gas phase oxygen concentration in the first nitrification tank in order to reduce the running cost of the entire system.
In the present invention, an apparatus as shown in FIG. 1 can be used. This device consists of a closed nitrification tank into which a nitrification carrier with two nitrifying bacteria fixed on the surface is charged. The nitrification tank has an oxygen supply line connected to the first tank and an exhaust gas line connected to the second tank. Yes. Aeration in the nitrification tank is performed by a gas circulation system using a circulation blower and a diffusion device, and the amount of the aeration is controlled and supplied by each nitrification tank DO. The supply amount of the high concentration oxygen gas is controlled and supplied by the oxygen concentration in the gas phase portion of the nitrification tank of the first tank.

  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, so 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. 7), 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.

  Specifically, a method of changing the upper and lower limit set values of the dissolved oxygen concentration of the nitrification tank mixed solution in advance based on the fluctuation pattern of the ammonia nitrogen or organic nitrogen load with time can be employed. 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.

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.

As a method for controlling the supply amount of oxygen gas, there is a method of supply control based on a change in pressure in the gas phase part of the nitrification tank or a change in the flow rate of exhaust gas, which is often employed in the surface aeration method.
However, in the circulation aeration method, when these methods are applied, the gas movement and pressure change are more remarkable than the surface aeration method, and stable operation cannot be performed, so based on the measurement results of the oxygen concentration in the gas phase, Adopting a control method for supplying high-concentration oxygen gas is suitable.

In the method of the present invention, high concentration oxygen gas is controlled and supplied based on the measurement result of the oxygen concentration in the gas phase part of the first tank of the nitrification tank. 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, since the oxygen concentration in the gas phase can be set arbitrarily, it not only contributes to the operation of the blower and the stabilization of the nitrification tank DO, but also adjusts the oxygen utilization efficiency arbitrarily, so that stable and efficient operation is possible. Can do.
The oxygen concentration measurement location for controlling the supply of high-concentration oxygen gas is the running of the entire system taking into account the operation of the blower, stabilization of the nitrification tank DO, the power cost of the blower, and the generation cost of the high-concentration oxygen gas. Since it is easy to adjust cost efficiency, it is preferable to control by the oxygen concentration of the gas phase part of the nitrification tank of the first tank.

By setting the oxygen concentration in the gas phase part of the nitrification tank of the first tank, the overall cost of the target system can be reduced, but generally a high DO with a small amount of air diffused considering the blower power cost. In order to maintain the system, the oxygen concentration in the gas phase part of the nitrification tank of the first tank is controlled to about 30% to 80%, preferably about 50% to 75%, thereby advantageously operating the cost efficiency of the entire system. can do. This depends on the concentration of the high-concentration oxygen gas used, but if it is 30% or less, the high-concentration oxygen gas cannot be used to achieve the advantage of reducing the amount of diffused air. In addition, when it is 80% or more, the oxygen concentration of the exhaust gas becomes too high, the oxygen utilization efficiency is remarkably lowered, and the generation cost of the high concentration oxygen gas is excessively increased.
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 oxygen concentration of 90% or more obtained by a PSA (Pressure Swing Adsorption) type oxygen gas generator having a low production cost can be used. 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 efficiency of oxygen utilization can be increased by aeration to the liquid phase of the same nitrification tank or the liquid tank of the next nitrification tank repeatedly 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. The division of the tank may be in parallel or in series with the inflow of raw water, but in particular, in order to increase the utilization 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 a mist separator, gas filter, etc. for removing sludge mist, dust, and fine dust in the circulating gas 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. .
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 has a two-stage structure in series with the inflow of raw water by partitioning the nitrification tank with a partition wall, and the nitrification carrier 5 to which nitrifying bacteria are attached is stored. Second nitrification tanks 2-1 and 2-2, sedimentation tank 3, oxygen gas supply line 10, exhaust gas line 11, raw water supply line 1, and treated water outflow line 4 are provided. A flow rate control valve 17 is installed in the oxygen gas supply line 10, and an oxygen concentration meter 14 for measuring the oxygen concentration is installed in the gas phase section 12 of the first nitrification tank 2-1.
In the two nitrification tanks 2-1 and 2-2, a gas circulation line 15 for circulating and diffusing the nitrification tank gas phase gas 12 between the liquid level and the ceiling of the nitrification tank through the blower 9; The dissolved oxygen concentration meter 13 is provided.
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 measurement 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 2-1 through the line 1. The waste water introduced into the nitrification tank 2-1 is mixed with a carrier on which nitrifying bacteria in the nitrification tank 2-1 are fixed.
Next, high-concentration oxygen gas is supplied from the line 10 through the gas circulation line 15 into the nitrification tank 2-1, and by operating the blower 9, it is sent to the diffuser pipe 8 in the nitrification tank 2-1. It diffuses in the liquid mixture of 2-1.
In this way, oxygen supplied from the line 10 into the sealable nitrification tank 2-1 is more efficiently dissolved in the mixed liquid in the nitrification tank 2-1 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 a necessary amount of oxygen is always supplied, so that the oxygen concentration in the nitrification tank gas phase section 12 is stabilized. . 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.
The liquid in the liquid phase part and the gas in the gas phase part of the nitrification tank 2-1 flow into the nitrification tank 2-2 through the screen 24 and the gas phase communication part 25, and the gas is diffused through the blower as the exhaust gas 11. Exhausted.

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 2-1 and 2-2 in series with the raw water inflow, 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, but the liquid phase communicates via a carrier separation screen 24, while the gas phase also has a gas phase communication part 25. Each nitrification tank is provided with a gas circulation line, and the oxygen supply line 10 is connected to the nitrification tank 2-1.
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 waste water after denitrification is sent in the order of the nitrification tank 2-1 and the nitrification tank 2-2, mixed with the carrier to which the 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 part 12 of the nitrification tank 2-1, so that the gas phase part 12 is filled 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 diffuser pipe 8 in the nitrification tank 2-1 and dispersed in the waste water in the nitrification tank 2-1. I care.

Next, the remaining oxygen gas discharged from the nitrification tank 2-1 is supplied to the gas phase section 12 of the nitrification tank 2-2, and the gas phase section 12 is filled 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 diffuser pipe 8 in the nitrification tank 2-2 to be dispersed in the waste water in the nitrification tank 2-2. I care.
For the high-concentration oxygen gas, the control device 18 is operated, the flow control valve 17 is controlled based on the indicated value of the oxygen concentration meter 14 provided in the nitrification tank 2-1, and the necessary amount of oxygen is always supplied. The oxygen concentration in the nitrification tank gas phase section 12 is stabilized. 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. The concentration is stable.

In this way, the oxygen supplied from the line 10 into the sealable nitrification tank 2-1 dissolves in the liquid phase in the nitrification tank 2-1 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 high concentration oxygen gas is measured by measuring the oxygen concentration in the gas phase part of the nitrification tank 2-1, and supplied from the line 10 to the gas phase part 12 of the nitrification tank 2-1. This is because the oxygen concentration in the nitrification tank 2-1 is set high so that the operation can be efficiently performed because the oxygen concentration in the section is increased to reduce the amount of gas to circulate and keep the blower power low.

Next, the waste water treatment apparatus and waste water treatment method of the present invention will be described with reference to FIG.
FIG. 3 is a partial configuration diagram of only the nitrification tank portion of FIG. 2, and the configuration of the denitrification tank and the sedimentation basin is the same as FIG. 2, and the same or corresponding parts as in FIG. Details thereof are omitted.
In FIG. 3, the nitrification tank has a five-stage structure (2-1 to 2-5) in series with the raw water inflow partitioned by the partition walls, and each tank is partitioned by the partition walls in both the liquid phase and the gas phase. As in FIG. 2, each tank communicates the liquid phase via a carrier separation screen (omitted), and a gas phase communicating portion (omitted) is provided in the gas phase.
Of the nitrification tanks 2-1 to 2-5, the nitrification tanks 2-1 and 2-4 are provided with an oxygen concentration meter 14 for measuring the oxygen concentration in the gas phase, and the detection result of the oxygen concentration meter 14 On the basis of the above, the control device 18 adjusts the opening / closing device or the opening degree of the flow control valve 17 of the high-concentration oxygen gas to control the oxygen concentration in the gas phase portion of the nitrification tanks 2-1 and 2-4.

The dissolved oxygen concentration meter 13 is installed in all of the nitrification tanks 2-1 to 2-5, and the controller 16 is operated so that the amount of air diffused in the blower 9 is based on the indicated value of the dissolved oxygen concentration meter 13. Controlled, the required amount of aeration is always performed in all nitrification tanks, and the dissolved oxygen concentration in the liquid phase is stabilized.
In this way, when a large number of nitrification tanks are installed, the oxygen concentration in the gas phase part of the nitrification tank in the subsequent stage decreases, and the amount of air diffused to maintain the dissolved oxygen concentration in the liquid phase part increases. In order to prevent this, it is possible to reduce the amount of diffused air by injecting high-concentration oxygen gas into the nitrification tank of any subsequent stage (nitrification tank 2-4 in FIG. 3) in which the oxygen concentration in the gas phase has decreased. it can.
In addition, by subdividing the nitrification tank into multiple stages, the oxygen concentration in the tank with high pollution load can be kept higher, and the amount of air diffused can be reduced by injecting oxygen gas into the subsequent tank where the oxygen concentration decreases. it can.

Next, another example of the waste water treatment apparatus of the present invention will be described with reference to FIGS.
4 is a partial configuration diagram showing only the control relationship of the high-concentration oxygen gas in the gas phase portion of the nitrification tank of FIG. 1 or FIG. 2, and the control relationship of the dissolved oxygen concentration in the liquid phase portion is the same as that shown in FIG. It is the same, and the dissolved oxygen in the liquid phase part is controlled by a dissolved oxygen concentration meter, a control device and a blower for each nitrification tank.
In FIG. 4, a ventilation adjusting means 26 and a control device 27 are installed in the gas phase communication portion 25 that communicates the gas phase portions of the nitrification tanks 2-1 and 2-2. The nitrification tank 2-2 is provided with an oxygen concentration meter 14 for measuring the oxygen concentration in the gas phase portion, and the control device 27 is operated based on the measurement result of the oxygen concentration meter 14 so that the nitrification tank 2 -1 to the nitrification tank 2-2 are controlled by the ventilation adjusting means 26. As the air flow adjusting means 26, a flow rate adjusting valve, a dambar or the like can be used. Since the gas phase part is completely mixed, even if the oxygen concentration meter 14 installed in the gas phase part of the nitrification tank 2-2 is installed in the exhaust gas line 11, the same oxygen concentration can be obtained.
By controlling the amount of ventilation from the nitrification tank 2-1 to the nitrification tank 2-2, the oxygen concentration of the nitrification tank 2-1 having a large amount of oxidation of the pollutant is increased, and the oxygen concentration in the nitrification tank 2-2 is gas. By controlling the amount of movement, the oxygen concentration in the nitrification tank 2-2 can be increased, and the amount of diffused air can be reduced.

FIG. 5 is a partial configuration diagram showing only the control relationship of the high-concentration oxygen gas in the gas phase part of the nitrification tank of FIG. 3, and the dissolved oxygen concentration in the liquid phase part is the dissolved oxygen concentration in each nitrification tank as in FIG. It is controlled by a meter, a control device and a blower.
In FIG. 5, aeration adjustment is made in the gas phase communication section 25 that communicates the gas phase sections of the nitrification tanks 2-1 and 2-2, the nitrification tanks 2-2 and 2-3, and the nitrification tanks 2-4 and 2-5. The means 26 and the control device 27 are installed, and the nitrification tanks 2-2, 2-3 and 2-5 are provided with an oxygen concentration meter 14 for measuring the oxygen concentration in each gas phase portion. Based on the measurement result of the oximeter 14, the control device 27 is operated, and the ventilation amount from each nitrification tank is controlled by the ventilation adjustment means 26.
In this way, by controlling the amount of gas movement with the oxygen concentration of each tank, the oxygen concentration in the gas phase part of each tank can be kept higher, and oxygen gas flows into the subsequent tank where the oxygen concentration decreases. By doing so, the amount of diffused air can be reduced.

Next, referring to FIG. 6, 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. 6, first, automatic air flow adjustment operation is performed in step S <b> 1 by the inverter control of the circulation blower and / or the opening adjustment of the air flow control valve by the start of the automatic operation. 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. Next, the process proceeds to step S4, where if the gas phase gas O ₂ concentration is not appropriate, the process returns to S3, and the gas phase gas O ₂ concentration is made appropriate by opening / closing the oxygen gas inlet valve or adjusting the opening. . If the gas phase gas O ₂ concentration is appropriate, the process returns to S1. Thus, by repeating steps S1 to S4, it is possible to stably maintain the DO of the nitrification tank mixed solution and the O ₂ concentration of the gas phase gas.

Furthermore, the appropriate DO value that is the basis for the determination in step S2 is based on the relationship between DO and nitrification rate as shown in FIG. 7, 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 through experiments are shown in Table 2.
Example 1
Experimental apparatus of circulation aeration system 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 5 m ³ , return sludge volume 82.5 m ³ / day) The nitrification carrier is added to the sewage primary treated water (hereinafter, referred to as “ammonia nitrogen (NH ₄ -N) concentration 16-25 mg / L, organic nitrogen (Org-N) concentration 3-11 mg / L) shown in Table 1”. A treatment experiment was conducted on the raw water.
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 supplied high concentration oxygen gas: 80 to 90%
High-concentration gas supply amount: 72 to 151 L / min
Setting DO: 7.5 mg / L
Set exhaust gas O ₂ concentration: Result Setting control oxygen concentration Nitrification tank 2-1: 73%
Aeration amount: 30 to 55 m ³ / h

The nitrifying bacteria adhering to the carrier gradually became acclimatized, and the NH ₄ -N concentration in the treated water gradually decreased, and was 0.2 to 0.5 mg / L on the 20th day from the start of the treatment. 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. Moreover, as a result of setting and controlling the oxygen concentration of the nitrification tank 2-1 to 73%, an oxygen utilization efficiency of 69% was shown. However, the amount of diffused air is as low as ³⁰ to 55 m ³ / h, and if the power cost of Comparative Example 1 for controlling the oxygen supply amount by the oxygen concentration of the exhaust gas is 1, the power cost of this embodiment is 0.4. The power cost of the entire system could be reduced.

Example 2
A processing experiment based on the flow shown in FIG. 3 was performed. The nitrification tanks were five tanks 2-1 to 2-5, and the control means for the gas phase oxygen concentration was provided in the nitrification tanks 2-1 and 2-4. Each nitrification tank was provided with a control means for controlling the dissolved oxygen concentration in the liquid phase part. The specifications of the experimental apparatus are the same as those in Example 1, and a treatment experiment was performed on the raw water shown in Table 1 of Example 1. The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High-concentration gas supply amount: 80 to 170 L / min
Setting DO: 7.5 mg / L
Setting control oxygen concentration Nitrification tank 2-1: 73%
Setting control oxygen concentration Nitrification tank 2-4: 65%
Aeration amount: 28 to 50 m ³ / h

The nitrifying bacteria adhering to the carrier are acclimatized, and the NH ₄ -N concentration of the treated water gradually decreases. On the 20th day from the start of the treatment, the concentration is 0.2 to 0.4 mg / L. there were. By subdividing the nitrification tank, the oxygen concentration in the tank with a high pollution load can be kept higher, and oxygen gas is injected into the subsequent tank where the oxygen concentration is reduced, thereby reducing the amount of diffused air. did. The oxygen utilization efficiency was 68%, but the amount of diffused air was reduced. If the power cost of Comparative Example 1 was 1, the power cost of this example was 0.37, and the cost of the entire system could be reduced. It was.

Example 3
A processing experiment based on the flow shown in the partial configuration diagram of FIG. 4 was performed. A treatment experiment under the same conditions as in Example 1 except that a gas flow rate communication unit from the nitrification tank 2-1 to 2-2 is provided with an aeration amount adjusting means based on the oxygen concentration in the gas phase part of the nitrification tank 2-2. Went.
The specifications of the experimental apparatus are the same as those in Example 1. The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High-concentration gas supply amount: 75 to 160 L / min
Setting DO: 7.5 mg / L
Setting control oxygen concentration Nitrification tank 2-1: 73%
Set exhaust gas O ₂ concentration: 62% (nitrification tank 2-2 gas phase part)
Aeration amount: 25 to 50 m ³ / h

In this example, the NH ₄ —N concentration of the treated water was 0.2 to 0.5 mg / L. The oxygen utilization efficiency was 67%. By controlling the amount of gas phase movement from the nitrification tank 2-1 by the oxygen concentration of the nitrification tank 2-2, the oxygen concentration of the nitrification tank 2-2 could be increased, and the amount of diffused air could be reduced. The power cost was 0.35, where Comparative Example 1 was 1.

Example 4
A processing experiment based on the flow shown in the partial configuration diagram of FIG. 5 was performed. As in Example 2, the nitrification tanks were five tanks 2-1 to 2-5, and control means for the gas phase oxygen concentration was provided in the nitrification tanks 2-1 and 2-4. The specifications of the experimental apparatus are the same as those of Example 1, and Example 3 and Example 2 are connected to the gas phase communication part between nitrification tanks 2-1 and 2-2, 2-2 and 2-3, 2-4 and 2-5. Similar air flow adjusting means was provided.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply amount: 85 to 175 L / min
Setting control oxygen concentration Nitrification tank 2-1: 73%
Setting control oxygen concentration Nitrification tank 2-4: 65%
Set exhaust gas O ₂ concentration: 63% (nitrification tank 2-5 gas phase part)
Aeration amount: 22 to 45 m ³ / h

In this example, the NH ₄ —N concentration of the treated water was 0.2 to 0.4 mg / L, and the oxygen utilization efficiency was 66%. By controlling the amount of gas movement with the oxygen concentration in each tank, the gas phase oxygen concentration was kept higher and the amount of diffused air was reduced. Assuming that Comparative Example 1 is 1, the power cost is 0.32, which can greatly reduce the power cost of the entire system.

Example 5
A processing experiment based on the flow shown in FIG. 2 was performed. The specifications of the experimental apparatus and the target raw water were the same as in Example 1, and the set value of the oxygen concentration in the gas phase part of the first nitrification tank was changed according to the load fluctuation of the pollutant in the target raw water.
The experimental conditions are as follows.
O ₂ concentration of supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply amount: 82 to 169 L / min
Setting DO: 7.5 mg / L
Control oxygen concentration: 73% (normal)
76% (high load)
Aeration amount: 24-48 m ³ / h
In this example, the NH ₄ —N concentration of the treated water was 0.2 to 0.4 mg / L, and the oxygen utilization efficiency was 67%. Since the gas phase oxygen concentration was increased during the high load time period, the oxygen gas supply amount increased compared to Example 1, the exhaust gas oxygen concentration also increased, and the oxygen utilization efficiency decreased. However, since the amount of diffused air could be reduced, the overall power cost could be reduced.

Comparative Example 1
The high-concentration oxygen gas supplied to the nitrification tank 2-1 was performed by the circulation aeration method based on the flow shown in FIG. 8, and the measurement result of the exhaust gas in the nitrification tank 2-2 was used. A treatment experiment was conducted under the same conditions.
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 in the treated water gradually decreased, and was 0.2 to 0.4 mg / L on the 20th day after the treatment was started. 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 comparative example, since the oxygen supply amount was controlled using the measurement result of the exhaust gas oxygen concentration, the exhaust gas oxygen concentration was stable and a high oxygen utilization efficiency of 85% could be achieved. However, since the gas phase oxygen concentration in the nitrification tank 2-1 was not controlled, the gas phase oxygen concentration in the nitrification tank 2-1 was not stable at 50 to 65%. As a result, the power cost of the aeration blower in the nitrification tank 2-1 increased. As a result, the power cost was 1.

Comparative Example 2
A treatment experiment was performed under the same conditions as in Comparative Example 1 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: 11 to 33 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, in order to keep the gas phase oxygen concentration in the nitrification tank 2-1 high, the exhaust gas oxygen concentration was set as high as 78%. As a result, the gas phase oxygen concentration in the nitrification tank 2-1 was kept at 80 to 85%. The amount of air needed to maintain an appropriate DO value was small. Therefore, the power cost was about 60% of Comparative Example 1. However, since the oxygen concentration of the exhaust gas was set extremely high, the oxygen utilization efficiency was a very low value of 23%. As a result, although the oxygen gas production cost increased excessively and the blower power cost could be reduced, the power cost of the entire system became higher than that of Example 1.
These results are summarized in Table 2.

  1: drainage, 2-1 to 2-5: nitrification tank, 3: sedimentation pond, 4: treated water, 5: nitrification carrier, 6: return sludge, 7: surplus sludge, 8: air diffuser, 9: blower, 10 : High-concentration oxygen gas, 11: Exhaust gas, 12: Nitrogen tank gas phase gas, 13: Dissolved oxygen concentration meter, 14: Oxygen concentration meter, 15: Gas circulation line, 16: Control device, 17: Flow control valve, 18 : Control device, 19: Stirrer, 20: Denitrification tank, 21: Stirrer, 24: Screen, 25: Gas phase communication part, 26: Aeration adjusting means, 27: Control device

Claims (8)

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 nitrification tank, and the nitrification tank are partitioned by a partition, and a gas phase portion is passed through the partition And a plurality of tanks in which the liquid phase part is sequentially communicated, and the plurality of nitrification tanks have a blower and an air diffuser for introducing the gas in the gas phase part in the nitrification tank into the liquid phase for aeration A wastewater treatment apparatus that biologically oxidizes ammonia nitrogen and / or organic nitrogen in waste water to nitrate nitrogen and / or nitrite nitrogen, comprising aeration means, wherein the plurality of nitrification tanks And a dissolved oxygen detection means for detecting the dissolved oxygen concentration in the liquid phase, and the aeration air volume of the aeration means is controlled based on a detection result by the dissolved oxygen detection means so that the dissolved oxygen concentration is maintained at a set value. And a plurality of glasses. Of bath, at least, to the first tank flows into the first sewage most, and the oxygen concentration measuring means for measuring the oxygen concentration of the gas in the vapor phase, based on the measurement result by the oxygen concentration measuring means, the measuring as the oxygen concentration in the gas phase portion of the nitrification tank is maintained at a predetermined range, waste water, characterized in that it comprises means for controlling the oxygen gas supply amount of the oxygen gas supply line for supplying the high-concentration oxygen gas Processing equipment. 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 nitrification tank, and the nitrification tank are partitioned by a partition, and a gas phase portion is passed through the partition And a plurality of tanks in which the liquid phase part is sequentially communicated, and the plurality of nitrification tanks have a blower and a diffuser for introducing the gas in the gas phase part in the nitrification tank into the liquid phase and aeration In addition to providing aeration means, a denitrification tank is provided in front of the first tank of the plurality of nitrification tanks, and a return line for returning the liquid phase and / or sludge of the final tank of the nitrification tank is provided in the denitrification tank. A wastewater treatment apparatus that biologically oxidizes ammonia nitrogen and / or organic nitrogen to nitrate nitrogen and / or nitrite nitrogen, and denitrifies the wastewater treatment apparatus. A dissolved oxygen detecting means for detecting a dissolved oxygen concentration in the liquid phase; Based on the detection result by the oxygen detecting means provided with a means for controlling the aeration amount of the aeration unit such that the dissolved oxygen concentration is maintained at the set value, among the plurality of nitrification tank, at least, sewage The oxygen concentration measuring means for measuring the oxygen concentration of the gas in the gas phase part is measured in the first tank that flows into the first tank, and the measured oxygen concentration in the nitrification tank is determined based on the measurement result by the oxygen concentration measuring means. as will be maintained in the range, waste water treatment apparatus, characterized in that it comprises a means for controlling the oxygen gas supply amount of the oxygen gas supply line for supplying the high-concentration oxygen gas.   An arbitrary plurality of nitrification tanks of the plurality of nitrification tanks are provided with oxygen concentration measurement means for detecting the oxygen concentration in the gas phase portion in the nitrification tank, and based on the measurement result by the oxygen concentration measurement means, the oxygen concentration The wastewater treatment apparatus according to claim 1 or 2, further comprising means for controlling the oxygen concentration in the gas phase portion to be maintained within a predetermined range for each nitrification tank provided with the concentration measuring means.   The nitrification tank without means for controlling the oxygen gas supply amount is provided with oxygen concentration measurement means for measuring the oxygen concentration of the gas in the gas phase in the nitrification tank, and the gas phase part of the nitrification tank in the preceding stage and the nitrification tank A communication adjusting means for adjusting a gas communication amount to a communication port that communicates with the gas phase portion of the gas, and a means for controlling an adjustment amount by the communication adjusting means based on a measurement result by the oxygen concentration measuring means. The wastewater treatment apparatus according to claim 1, 2, or 3. In the liquid phase of a sealable nitrification tank filled with a nitrifying bacterium composed of a plurality of tanks that are partitioned by a partition wall and in which the liquid phase part and the gas phase part are in continuous communication through the partition wall, high concentration oxygen In a wastewater treatment method for biologically oxidizing ammonia nitrogen and organic nitrogen in wastewater for aeration of gas to nitrate nitrogen and nitrite nitrogen, the dissolved oxygen concentration in the liquid phase of the plurality of nitrification tanks is determined. Detecting and controlling the amount of aeration air to be aerated in the liquid phase of the detected nitrification tank so that the dissolved oxygen concentration is maintained at a set value based on the detection result, and among the plurality of nitrification tanks , At least the oxygen concentration of the gas in the gas phase portion of the first tank into which sewage flows first is measured, and the measured nitrification tank is maintained so that the oxygen concentration is maintained within a predetermined range based on the measurement result Concentrated oxygen supplied to the gas phase part Waste water treatment method characterized by controlling the scan feed amount. In the liquid phase of a sealable nitrification tank filled with a nitrifying bacterium composed of a plurality of tanks that are partitioned by a partition wall and in which the liquid phase part and the gas phase part are in continuous communication through the partition wall, high concentration oxygen A gas is aerated and the liquid phase and / or sludge of the final tank of the nitrification tank is returned to the denitrification tank provided in the front stage of the first tank of the nitrification tank, and ammonia nitrogen and organic nitrogen in the waste water are returned. In a wastewater treatment method for biologically oxidizing to nitrate nitrogen and nitrite nitrogen and denitrifying, the dissolved oxygen concentration in the liquid phase of the plurality of nitrification tanks is detected, and based on the detection result In order to maintain the dissolved oxygen concentration at a set value, the amount of aeration air to be aerated in the liquid phase of the detected nitrification tank is controlled , and at least sewage is first among the plurality of nitrification tanks. measuring the oxygen concentration in the gas phase of the gas in the first tank to flow And controlling the amount of high-concentration oxygen gas supplied to the gas phase part of the nitrification tank so that the oxygen concentration is maintained within a predetermined range based on the measurement result. . The predetermined range of the oxygen concentration in the gas phase of the nitrification tank of the first tank is changed in accordance with the fluctuation of the amount of pollutant that needs to be oxidized in the inflow wastewater flowing into the first tank. The wastewater treatment method according to claim 5 or 6 , characterized in that The nitrification tank that does not control the oxygen gas supply amount measures the oxygen concentration of the gas in the gas phase in the nitrification tank, and adjusts the gas flow rate from the preceding nitrification tank based on the measurement result. The wastewater treatment method according to claim 5, 6 or 7 .