JP5597002B2 - 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 of biologically treating wastewater containing ammonia nitrogen, a treatment of oxidizing ammonia nitrogen to nitrate nitrogen and nitrite nitrogen by nitrifying bacteria is generally performed. Oxidation is required for the nitrification reaction, and examples of the treatment method include a floating sludge method, a fluid carrier method, a biofilm filtration method, etc., and all use air as an oxygen source (for example, Patent Documents). 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, You have to supply a lot of air. Furthermore, in order to efficiently promote nitrification along with organic oxidative decomposition treatment, it is necessary to maintain the dissolved oxygen concentration (DO) in the nitrification tank higher than in the case where only the organic oxidative decomposition treatment is intended. When air with a concentration of 21% is used, there is a limit to reducing the cost of power for facilities such as downsizing and air supply facilities. As a method for solving such problems, 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 used (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 this purpose, DO must be maintained high to increase the activity of nitrifying bacteria in the sludge, and the suspended sludge concentration (MLSS concentration) 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 in the case of 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. One of the methods for solving these problems is a method using a carrier on which microorganisms are fixed, and 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 can be carried out with compact equipment, and various device structures and methods have been studied (for example, Patent Document 2)

In the oxygen activated sludge method, 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 this problem, 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, and nitrification is performed by this method. There is an example (for example, nonpatent literature 1).
However, in the method of circulating and aeration using a blower, it is not necessary to supply the amount of oxygen necessary for the reaction, and the power for maintaining the fluidity of the support must be provided by aeration. Then, if air is diffused to cause the carrier to flow, power is applied as compared with the surface aeration method. As described above, since the oxygen dissolution efficiency is high, the maximum advantage of the oxygen activated sludge method, which requires less power for aeration, cannot be utilized.
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, the present invention provides a wastewater treatment apparatus for biologically oxidizing ammonia nitrogen and / or organic nitrogen in wastewater to nitrate nitrogen and / or nitrite nitrogen. , A sealable nitrification tank filled with a binding immobilization carrier having nitrifying bacteria attached to the surface, an oxygen supply line for supplying high-concentration oxygen gas to the gas phase part of the nitrification tank, and the above-mentioned without performing surface aeration It comprises a blower for introducing gas in the gas phase portion in the nitrification tank and aerating it into the liquid phase and an aeration device, and a stirring means for maintaining the fluidity of the carrier of the nitrification tank. Wastewater treatment equipment or wastewater treatment equipment that biologically oxidizes ammonia nitrogen and / or organic nitrogen to nitrate nitrogen and / or nitrite nitrogen and denitrifies it And binding immobilization with nitrifying bacteria attached to the surface Lead and closable nitrification tank filled with body, and the high concentration oxygen gas oxygen supplied supplied to the gas phase portion of the nitric of tank line, the gas phase of the gas in the nitrification tank without surface aeration An aeration means having a blower for aeration in the liquid phase and an air diffuser; and an agitation means for maintaining the fluidity of the carrier of the nitrification tank; and a denitrification tank is provided upstream of the nitrification tank, The waste water treatment apparatus is characterized in that a return line for returning the liquid phase and / or sludge of the nitrification tank is provided in the nitrogen tank.

The present invention also relates to a wastewater treatment method for biologically oxidizing ammonia nitrogen and / or organic nitrogen in waste water to nitrate nitrogen and / or nitrite nitrogen, wherein the waste water is oxidized. A high-concentration oxygen gas is supplied to the gas phase part of the sealable nitrification tank filled with the binding immobilization carrier with the nitrifying bacteria attached to the surface, and the gas in the gas phase part in the nitrification tank is subjected to surface aeration. A wastewater treatment method, wherein the liquid phase part is agitated in order to maintain the fluidity of the carrier in the nitrification tank while aerating the liquid phase part via a blower and a diffuser without performing the process, or A wastewater treatment method for biologically oxidizing ammonia nitrogen and / or organic nitrogen to nitrate nitrogen and / or nitrite nitrogen to denitrify the wastewater, and oxidizing the wastewater Packed with a binding immobilization carrier with the nitrifying bacteria to be treated attached to the surface The gas phase of the sealable nitrification tank were supplies the high concentration oxygen gas, the liquid phase through a blower and an air diffuser without gas surface aeration in the gas phase portion of the nitrification tank While aeration, in order to maintain the fluidity of the carrier in the nitrification tank, the liquid phase part is agitated, and the liquid phase and / or sludge of the nitrification tank is added to the denitrification tank provided in the previous stage of the nitrification tank. The wastewater treatment method is characterized in that it is returned and denitrified.
In the waste water treatment apparatus and the waste water treatment method, the stirring means can set the stirring conditions to 1 to 100 W / m ³ in terms of power density per tank capacity and / or a peripheral speed of the stirring blade of 1 to 4 m / sec. , based on the difference between the aeration amount for supplying aeration amount and the required amount of oxygen required to maintain the fluid carrier by the aeration means may comprise a control device for controlling the stirring means.

  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. Moreover, since only the necessary amount of pure oxygen or oxygen-enriched gas needs to be supplied, the running cost can be kept low, and the total cost can be reduced.

  Hereinafter, the present invention will be described in detail. First, in order to clarify the problems of the conventional surface aeration method, we conducted a comparative experiment between the surface aeration method and the gas circulation aeration method using a carrier with a shape and material that is difficult to wear. As a result, in the surface aeration method, even when there was no wear of the carrier itself, it was found that a nitrification performance failure estimated to be caused by the inhibition of attachment of nitrifying bacteria to the carrier surface by stirring for aeration occurred. On the other hand, in an experiment conducted using the gas circulation aeration method only under the same conditions as this, good nitrification performance was obtained, so that it was efficiently performed under a short hydraulic retention time (HRT). In order to advance the nitrification reaction, it was found that it is essential to perform aeration with gas circulation aeration. By maintaining the fluidity of the carrier using a stirring means, we succeeded in making use of the features of the oxygen activated sludge method that the amount of air diffused is small, and stable nitrification performance at extremely high loads and low running It was possible to realize at a cost.

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 a stirring means is provided to maintain the fluidity of the carrier.
The present invention promotes nitrification in wastewater with space saving and cost saving by combining an oxygen activated sludge method and a carrier nitrification method. In general, the aeration of the oxygen activated sludge method is widely adopted a surface aeration method using a stirring means because of its high energy efficiency, but if a nitrification carrier is used for the surface aeration method, the carrier by agitation of the surface aeration In addition to the problems of long-term use such as wear and breakage, it has been found that there is inhibition of nitrifying bacteria in the initial stage of use even if the carrier itself is not worn. On the other hand, in the circulation aeration type using a circulation blower and an air diffuser as shown in FIG. 1, the nitrifying bacteria adherence is not inhibited, and extremely high nitrification performance is exhibited under the high load condition of the oxygen activated sludge method.
When air is diffused by the oxygen activated sludge method, the nitrification tank is sealed and the once diffused gas is repeatedly supplied to the blower to circulate and diffuse, without escaping high-concentration oxygen gas outside the system. This is because the oxygen thus used is efficiently used for the reaction.

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 to remove 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.

In order to exhibit high nitrification performance, it is important to allow the carrier to flow sufficiently in the tank. In the air aeration method, since the oxygen concentration is low, in order to supply oxygen necessary for the reaction to the liquid phase, a large amount of air must be diffused, and at the same time, the fluidity of the carrier can be maintained sufficiently In contrast, in the oxygen activated sludge method, the oxygen concentration of the gas to be diffused is high, so the amount of aeration required to secure the required amount of oxygen is relatively low, and the reaction In many cases, the fluidity of the carrier cannot be maintained only by the amount of aeration required for this. Therefore, even if the amount of oxygen is sufficient, the fluidity of the carrier becomes insufficient. Since the present invention has found the merit of the combination of the aeration by the circulation blower and the stirring means, the application range is an aeration condition where it is difficult to maintain the fluidity of the carrier only by the aeration. A great effect was obtained when air was diffused under conditions of air diffuse strength per water tank flat area of 0.3 m ³ / (m ² · min) or less. It depends on the structure of the water phase, the type of the diffuser, and the installation position.Therefore, it is not limited to this condition. It was.

The stirring means used in the present invention is not limited as long as the nitrification carrier can be flowed without causing abrasion or damage of the nitrification carrier and inhibition of nitrifying bacteria adhesion. In addition to the vertical axis stirring means, a horizontal axis stirrer, an oblique axis stirrer, an underwater stirrer, an underwater pump, and the like can be used. The stirring blade can be of any shape as long as it can flow the nitrification carrier without causing wear or damage to the nitrification carrier or inhibition of nitrifying bacteria adhesion. The propeller, flat blade, angle A flat blade with a pitch, a flat blade with a pitch, a flat blade disk turbine, a curved blade, etc. may be used by selecting the number of blades at an arbitrary position as required.
In the present invention, agitation for surface aeration should not be performed due to poor nitrification performance presumed to be caused by inhibition of adhesion of nitrifying bacteria to the carrier surface by agitation for surface aeration. However, it can be used as the stirring means of the present invention by removing or submerging the stirring blade for surface aeration near the water surface.
In addition, there are cases where the anaerobic tank is agitated by aeration, and the definition of agitation means may include an aeration device for agitation, but the agitation means of the present invention is agitated by aeration. Excluded.

The stirring condition is not limited as long as it can maintain the fluidity of the carrier and does not impair the carrier, such as wear or breakage. The density is 1 to 100 W / m ³ and / or the peripheral speed of the stirring blade is 1 to 4 m / sec. If the stirring conditions are weaker than this, the fluidity of the carrier is not sufficient. On the other hand, if the conditions are strong, there is a concern that the carrier is worn or damaged, and that nitrifying bacteria are not fixed on the carrier.
Further, the filling rate of the carrier is preferably 10 to 50% in terms of the apparent volume per nitrification tank volume. If it is higher than this, the carrier will hardly flow in the range of the stirring conditions. Conversely, if it is lower than this, the treatment effect by the carrier is small. In the present invention, since it is only necessary to maintain the fluidity of the carrier in combination with aeration, it is preferable to stir the amount that is not sufficient with only the aeration. That is, the combination of the amount of aeration and stirring intensity is important, and weak agitation is sufficient under conditions where the amount of aeration is relatively large, and conversely, strong agitation is required under conditions where the amount of aeration is relatively small. As described above, the setting of the stirring intensity may be changed according to the amount of aeration, or the agitation intensity may be controlled based on the measured value of the amount of aeration and the fluidity of the carrier (for example, an indication value of carrier concentration). Moreover, stirring and aeration may be performed continuously while adjusting the amount and strength, or may be performed intermittently.

Next, a specific method and apparatus for making such an efficient setting will be described. First, the relationship between the amount of air diffused or the intensity of air diffused and the fluidity of the carrier is obtained by experiments or the like. The relationship diagram shown in FIG. 4 (a) shows the relationship between the aeration intensity and the carrier concentration when the nitrification tank is filled with 20% of the carrier. In this experiment, when the aeration intensity is 0.3 m ³ / (m ² · min) or more, the carrier concentration in the surface layer is about 20%, which is the aeration intensity necessary for maintaining the fluidity of the carrier. is there. On the other hand, under conditions where the aeration intensity is lower than 0.3 m ³ / (m ² · min), it is presumed that the carrier concentration is lower than 20% and most of the carrier has settled at the bottom. This region indicates “aeration amount for supplying the required oxygen amount” when the required oxygen amount is small.
Next, the rotation speed of the stirrer for maintaining the fluidity of the carrier is determined for each amount of diffused air. Usually, the lower the aeration intensity, the higher the number of rotations of the stirrer necessary for flowing the carrier (FIG. 4 (b)). The aeration intensity shown here and the rotation speed of the agitator are not limited to these values because they vary greatly depending on the structure of the water tank and the aeration apparatus, the properties of the carrier used, and the specifications of the agitator. Based on this relationship, efficient operation can be achieved by assigning and setting the required number of agitator revolutions for each amount of diffused air. Setting may be performed manually, but by using a control device capable of setting a program, it is possible to perform more precise low-cost operation. Further, more efficient operation can be realized by controlling the number of revolutions of the stirrer based on the detection result of the amount of air diffused or the intensity of air diffused by an air flow meter for measuring the state of air diffused.

In addition to measuring the carrier concentration, the above method sets the number of revolutions of the stirrer based on the difference in mixing and stirring speed obtained from the simple sedimentation speed of the carrier and the amount of air diffused to supply the required amount of oxygen. It can also be performed using a control device. In this case, the settling velocity of the carrier to be used is obtained by actual measurement or calculation from the Stokes equation. Then, the relationship between the amount of air diffused or the intensity of air diffused and the fluidity of the carrier is obtained by experiments or the like (FIG. 5 (A)). Furthermore, the number of rotations of the stirrer is also obtained by experiments or the like (FIG. 5 (B)). What is necessary is just to control the rotation speed of a stirrer so that the sum of the rising speed by rotation of a stirrer and the rising speed by aeration may become more than equivalent to the sedimentation speed of a support | carrier. For example, when the sedimentation rate of the carrier is 25 cm / sec and the amount of air diffused to supply the necessary oxygen amount is 0.1 m ³ / (m ² · min), the liquid phase rises due to the air diffused from FIG. Since the speed is about 10 cm, the rising speed of 10 cm / sec, which is insufficient, may be compensated with a stirrer. The rotational speed of the stirrer for producing this ascending speed is 80 rpm. Note that the settling speed, aeration intensity, and rotation speed of the stirrer shown here vary greatly depending on the structure of the water tank and the aeration apparatus, the properties of the support used, and the specifications of the stirrer, so these values are limited However, based on such a relationship, efficient operation can be achieved by assigning and setting the required number of agitator rotations. Although the setting may be performed manually, a more precise and low-cost operation can be performed by using a control device capable of setting a program. Further, more efficient operation can be realized by controlling the number of revolutions of the stirrer based on the detection result of the amount of air diffused or the intensity of air diffused by an air flow meter for measuring the state of air diffused.

  The smaller the amount of aeration required for the reaction, the higher the effect of the stirring means. In particular, the effect of the present invention is exhibited when there is a load fluctuation of the drainage, and the amount of aeration in accordance with this load fluctuation. It is a case where it processes by adjusting. That is, in the present invention, since the fluidity of the carrier is maintained by the stirring means, the amount of air diffused may be set so as to supply only the necessary amount of oxygen in accordance with the load fluctuation. The setting method may be manually adjusted according to the load pattern, or may be set in advance so that the aeration amount automatically changes. Further, automatic control may be performed in conjunction with a measuring device for grasping the drainage load and the required amount of oxygen. Examples of the measuring device include a water meter, a nitrogen concentration meter, a BOD concentration meter, a nitrogen load meter, a BOD load meter, an oxygen concentration meter, and a dissolved oxygen concentration (DO) meter. Here, the load meter refers to a meter indicating the load calculated by measuring the concentration and the amount of water. These may be controlled individually or in combination. Among such controls, a method of controlling the amount of air diffused by the DO value of the nitrification tank is widely used. However, in the method of the present invention, particularly by controlling the amount of air diffused by this DO, particularly large cost merit Is demonstrated.

  In the present invention, DO of 2 mg / L or more is necessary to maintain high nitrification performance of the nitrification carrier. On the other hand, the higher the DO, the more pronounced the nitrification performance tends to increase. Therefore, it is better to set the DO as high as possible, but when the DO exceeds 12 mg / L, the nitrification performance reaches its peak ( FIG. 3). Therefore, the DO condition of the nitrification tank having a great effect of the present invention is 2 to 12 mg / L. The optimal DO value may be set according to the load conditions and required processing performance. When there is a load fluctuation, the DO value is not only fixed to a constant value, but also adjusted according to the fluctuation, If the fluctuation pattern is constant, the DO setting may be changed every time, or the necessary DO value may be automatically set in conjunction with a measuring device indicating an indicator of the required amount of load or oxygen.

The carrier used in the present invention is a bound and immobilized carrier that attaches nitrifying bacteria to the surface of the carrier. The binding immobilization carrier is a material in which nitrifying bacteria adhere to the carrier spontaneously in the nitrification tank to form a biofilm, so that the adherence of nitrifying bacteria is favorable, and a sufficient amount of nitrifying bacteria for treatment If the fluidity and durability are good, the shape, material and physical properties are not limited, but the shape has a large surface area and good wear resistance. A spherical shape is preferred. 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.
Such a binding immobilization carrier is difficult to exhibit high nitrification performance due to the inhibition of nitrifying bacteria adhesion by the surface aeration method, so as a method to reduce the inhibition of nitrifying bacteria adhesion by a stirrer, a depression is formed in the shape of the carrier. There is a method of using the inner surface as an attachment part, but it is not efficient because the entire surface of the carrier cannot be used. Further, by taking such a structure, the carrier It also leads to lowering the durability. In order to compensate for this, there is a method of using a material having excellent durability such as polyethylene or polypropylene, but there is a problem that adhesion of nitrifying bacteria is not so good.

As a carrier capable of holding a large amount of nitrifying bacteria, there is a entrapping immobilization carrier in addition to a binding immobilization carrier. This uses gel as the material and traps nitrifying bacteria in the gel during carrier production. It can fix nitrifying bacteria inside the carrier and does not require inoculum at the beginning of startup, and exhibits high performance in a short time. Has the advantage of. Further, it has been found that even if surface aeration is performed, the initial nitrification performance is not greatly affected. This is because the nitrifying bacteria are originally fixed inside the carrier, so that there is no concern about adhesion inhibition due to stirring, and it is difficult to detach.
By the way, when the nitrification reaction is advanced by the oxygen activated sludge process, the pH of the nitrification solution is 6 or less due to the consumption of alkalinity due to the nitrification reaction and the high carbon dioxide partial pressure. Decrease to about 5 or less. In general, the optimum pH for nitrification is a neutral or weakly alkaline condition of about 7-8, so that the activity of the immobilized nitrifying bacteria is significantly reduced under an acidic condition of about pH 5.5. The nitrifying bacteria that are preliminarily immobilized on the carrier cannot adapt to such low pH conditions, and in order to maintain the activity, a separate water tank is provided to perform decarboxylation treatment or a large amount of alkali It is necessary to adjust the pH to near neutral using an agent to at least about pH 6, and the equipment cost, power, and chemical cost become enormous.

  On the other hand, in the present invention, by using a binding immobilization carrier in a circulating air diffuser system, a habituation period is required until the bacterial cells adhere at the beginning of startup. High nitrification performance can be exhibited even under extremely low conditions of about 5.5 or less. The reason why high nitrification performance can be exhibited even under such conditions is that the nitrifying bacteria adapted to these conditions are gradually immobilized on the binding-immobilized carrier. Furthermore, the detailed conditions in the present invention, the alkalinity is important, specifically, the pH of the nitrification tank is 5-6, the alkalinity is at least the amount necessary for nitrification, preferably, The conditions are such that the alkalinity of the nitrification tank is 10 mg / L or more, more preferably the alkalinity of the nitrification tank is 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 the alkalinity is insufficient, an alkali agent corresponding to the shortage is injected or necessary. What is necessary is just to perform the decarboxylation process of a part. 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 the present invention, in various wastewaters such as sewage and other industrial effluents, a nitrification tank is provided in front of the nitrification tank, and only circulatory nitrification and denitrification equivalent to the return sludge is performed. The alkalinity of the tank can be kept in a 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. By incorporating the denitrification step in this way, not only the purpose of removing nitrogen can be achieved, but also the stabilization of nitrification performance by keeping the alkalinity suitable can be realized without using chemicals. Although the installation of the denitrification tank in front of the nitrification tank itself is a general method as a nitrification denitrification system, this method is low in comparison with the conditions of the oxygen activated sludge method using the nitrification carrier of the present invention. Great effect to stabilize performance at cost.

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 For water that contains water, etc., it can be made the target drainage by performing a separate detoxification treatment.
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 present invention, since high nitrification performance can be exhibited, the nitrification tank capacity can be made compact, and the processing performance can be satisfied with an extremely short residence time of about HRT 1.4 to 2 hr per nitrification tank. I was able to.

In the present invention, high-concentration oxygen gas is diffused in the liquid phase, but the exhaust gas that has been diffused and emerges from the water surface has a higher oxygen concentration than the atmosphere, so this exhaust gas is not released into the atmosphere, This is a method of increasing the utilization efficiency of oxygen by repeatedly aeration into the liquid phase through the blower. Therefore, instead of discharging the gas once diffused out of the tank as it is, it is sufficient if it has a sealable structure that can be repeatedly diffused by supplying the blower with the majority other than the amount discharged as exhaust gas, There are no restrictions on the shape, number, or arrangement of the tanks. 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 in series with the inflow of raw water, but in particular, in order to increase the utilization efficiency of oxygen, a multistage structure is used in series, and the gas phase part or circulation of the tank on the inflow side of the raw water is used. Supply high-concentration oxygen to the aeration line, arrange the gas to flow sequentially from the upstream tank to the downstream tank via the gas phase communication part, and exhaust the exhaust gas from the most downstream water tank out of the system Is the most efficient method.
The screen for separating the carrier installed in the nitrification tank is not limited as long as the carrier can be separated and the carrier is damaged or worn. However, in the oxygen activated sludge method, the nitrification tank has a sealed structure, so it is easy to maintain. Good specification is suitable. In the present invention, a cylindrical mechanical screen that can be rotated by installing a nozzle for cleaning is most preferable.

  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%. This high-concentration oxygen gas can be directly supplied to the gas phase part of the nitrification tank or the circulating air diffusion pipe. Since the supplied oxygen gas is consumed by nitrification reaction, oxidative decomposition reaction of organic matter, respiration of microorganisms, etc., the oxygen gas concentration in the system gradually decreases. If the concentration is too low, DO in the nitrification tank will drop, or excessive aeration will be required to maintain DO. On the other hand, if the oxygen concentration is too high, the amount discharged as exhaust gas increases and the oxygen utilization efficiency decreases. In order to properly maintain DO in the nitrification tank with low power and to maintain oxygen utilization efficiency properly, the oxygen concentration in the most downstream nitrification tank is about 30 to 70%, and further about 40% to 60%. It was preferable that the oxygen utilization efficiency of 80% or more was obtained with this setting. A high-concentration oxygen gas may be supplied in a fixed quantity so as to achieve such an oxygen concentration, and if there is a load fluctuation, control may be made so that oxygen is supplied efficiently. The control method is generally a method of controlling by atmospheric pressure utilizing the fact that the amount of gas in the gas phase decreases as the reaction proceeds, but it is controlled by using DO in the water tank, oxygen concentration in the gas phase, etc. as indicators. Also good.

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.
In the nitrification tank 2, a gas circulation line 14 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 the air diffusion pipe 8, and stirring means 13 It has.

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, oxygen gas is supplied into the nitrification tank 2 through the line 10, and the gas phase portion 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 aeration pipe 8 in the nitrification tank 2 and diffused into the waste water in the nitrification tank 2.
In this way, oxygen supplied from the line 10 into the sealable nitrification tank 2 dissolves in the wastewater in the nitrification tank 2 more efficiently than air.
Next, the stirring means 13 is operated to bring the nitrification carrier 5 into a fluid state. Since the fluidity of the nitrification carrier is maintained by this stirring, it is sufficient to perform aeration only in an amount necessary for the reaction, and an increase in running cost can be prevented.

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 15 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 17, while the gas phase has a gas communication portion 18. 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 15 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 15 and the wastewater in the tank 15 is discharged. A stirrer 16 is provided for stirring.

Next, a wastewater treatment method using the wastewater treatment apparatus configured as described above will be described.
First, the wastewater to be treated is introduced into the denitrification tank 15 through the line 1. The wastewater introduced into the denitrification tank 15 is mixed with activated sludge and stirred to decompose the nitrate nitrogen supplied from the return sludge 6 into nitrogen gas using the organic matter supplied from the raw water as a hydrogen donor. To do. Moreover, alkalinity rises by progress of denitrification reaction here, and it contributes as the alkalinity replenishment process to a nitrification tank of a back | latter stage.
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 by the return sludge line 6. Further, surplus separated sludge is discharged from the surplus sludge line 7 to the outside of the system.

Oxygen gas is supplied from the line 10 to the gas phase part 12 of the first nitrification tank 2 to make the gas phase part 12 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 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 9 ′, the gas in the gas phase section 12 ′ is once sucked, and this gas is sent to the diffuser pipe 8 ′ in the nitrification tank 2 ′ to be discharged into the waste water in the nitrification tank 2 ′. Aerate.

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 oxygen gas from the line 10 to the gas phase section 12 of the first nitrification tank 2 is to efficiently use oxygen. If this purpose can be achieved, an injection point of high-concentration oxygen gas can be achieved. The gas flow is 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.
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
A fixed method of coupling to the circulating air diffuser based on the flow shown in FIG. 1 (throughput 13750m ³ / day, nitrification tank capacity 810m ³ , water depth 5m, HRT 1.5hr, return sludge amount 6880m ³ / day) Of sewage primary treated water (hereinafter, referred to as “ammonia nitrogen (NH ₄ -N) concentration 16 to 25 mg / L, organic nitrogen (Org-N) concentration 3 to 11 mg / L)” shown in Table 1. A treatment experiment was conducted on the raw water.
The specifications of the device are as follows.
Oxygen gas generator: PSA (Pressure Swing Adsorption)
Equipment of system Aeration system: Circulating aeration Blower: Roots blower Stirrer: Vertical axis stirrer Stirring blade: Flat blade with angle (4 blades, blade diameter 1.2m)
Carrier: Bound immobilization carrier (spherical PEG carrier)
Carrier filling rate: 20% (apparent volume per nitrification tank volume)
DO meter: Fluorescent dissolved oxygen meter

The experimental conditions are as follows.
O ₂ concentration of the supplied high concentration oxygen gas: 80 to 90%
High-concentration gas supply amount: 22 to 46 m ³ / min
Aeration amount: 870 to 2000 m ³ / h
Aeration intensity: 0.15 to 0.30 m ³ / (m ² · min)
Stirrer rotation speed: 34 rpm
Stirring blade peripheral speed: 2.1 m / sec
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. . Moreover, there was almost no wear and wear of the support | carrier after one year progress, and it was set to the blower 0.65 and the stirrer 0.35 when the sum of the power cost of a blower and a stirrer is set to 1. 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 high, And it is because alkalinity was consumed by progress of nitrification (the alkalinity of a nitrification tank is 10-25 mg / L).

Example 2
The apparatus of circulation diffuser method based on the flow shown in FIG. 2 (processing amount 13750m ³ / day, nitrification tank capacity 810m ^3, depth 5 m, HRT 1.5hr, denitrification tank capacity 405m ^3, return sludge volume 6880m ³ / day) The nitrification carrier of the binding immobilization method was added to the sewage primary 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 on treated water (hereinafter, raw water).
The specifications of the other devices are the same as in Example 1, and the main experimental conditions are as follows.
O ₂ concentration of the supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply amount: 20 to 40 m ³ / min
Aeration amount: 740 to 1800 m ³ / h
Aeration intensity: 0.15 to 0.27 m ³ / (m ² · min)
Stirrer rotation speed: 27rpm
Stirring blade peripheral speed: 1.7m / sec
Also in this example, the nitrifying bacteria adhering to the carrier gradually became acclimatized, and the NH ₄ -N concentration of the treated water gradually decreased, and on the 20th day from the start of the treatment, it was 0.2 to 0.4 mg / L. The nitrification performance was even better than that of Example 1. 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. The total power cost of the blower and the stirrer was equivalent to that in Example 1.

Example 3
The experiment was performed 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 set value of dissolved oxygen was set stepwise based on this ammonia load 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 the supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply amount: 14 to 40 m ³ / min
Aeration amount: 330 to 1800 m ³ / h
Aeration intensity: 0.066 to 0.27 m ³ / (m ² · min)
Stirrer rotation speed: 5-27 rpm
Stirring blade peripheral speed: 0.3 to 1.7 m / sec
In this example, since the amount of air diffused was increased and the DO setting was increased during the high ammonia load time period, the nitrification performance was further stabilized, and the NH ₄ -N concentration of the initial treatment water was 0.1 to 0.2 mg / L. On the other hand, in the time zone when the ammonia load was low, the amount of aeration was reduced and the DO setting was lowered. Furthermore, in order to maintain the fluidity of the carrier in accordance with the amount of diffused air, the rotation speed of the required stirrer is set, so that no unnecessary aeration power is applied and about 10% of the power than in Example 2 is applied. Cost reduction was possible.

Comparative Example 1
The treatment experiment was performed under the same conditions as in Example 2 except that the treatment apparatus based on the flow shown in FIG.
The experimental conditions are as follows.
O ₂ concentration of the supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply amount: 20 to 40 m ³ / min
Aeration amount: 2200 m ³ / h
Aeration intensity: 0.33 m ³ / (m ² · min)
Under these conditions, as in Example 2, the concentration of treated water NH ₄ -N after the 20th day from the start of treatment was 0.2 to 0.4 mg / L, indicating good nitrification performance. However, in order to cause the carrier to flow, aeration of 2200 m ³ / h had to be always performed regardless of the amount of oxygen necessary for nitrification, and the power cost was 1.3 times that of Example 2. Although the treatment performance was not inferior, it was not possible to take advantage of the oxygen activated sludge method, which required only a small amount of aeration.

Comparative Example 2
A processing apparatus based on the flow shown in FIG. 8 was used, and a processing experiment was performed using only a stirrer without performing aeration. The experimental conditions are as follows.
O ₂ concentration of the supplied high concentration oxygen gas: 80 to 90%
High concentration gas supply amount: 20 to 40 m ³ / min
Aeration amount: 0 m ³ / h
Stirrer rotation speed: 27rpm
Stirring blade peripheral speed: 0.3 to 1.7 m / sec
Under this condition, since no aeration was performed, the DO of the mixed solution was always less than 1 mg / L, so the nitrification reaction did not proceed and the treatment was impossible.
Here, Example 1, Example 2 and Example 3 of the present invention have a device configuration in which Comparative Example 1 in which only circulation aeration is performed and Comparative Example 2 in which only stirring is performed are combined. From the viewpoint of the quality of treated water in Example 2 and from the viewpoint of power cost, it was obvious that a special performance was exhibited by combining the devices.

The results of these experiments are summarized in Table 2.

The flow block diagram which shows an example of the waste water treatment equipment of this invention. The flow block diagram which shows another example of the waste water treatment equipment of this invention. The graph which shows the relationship between DO and nitrification performance. (B) A graph showing the relationship between the aeration intensity and the carrier concentration, and (b) the relationship between the aeration intensity and the number of rotations of the stirrer necessary for flowing the carrier. (B) A graph showing the relationship between the aeration intensity and the rising velocity of the liquid phase, and (b) the relationship between the rotational speed of the stirrer and the rising velocity of the liquid phase. The flow block diagram which shows an example of the conventional waste water treatment equipment. The flow block diagram which shows another example of the waste water treatment equipment of a prior art example. The flow block diagram which shows an example of the waste water treatment equipment used in the comparative example 2.

1: raw water supply line, 2, 2 ': nitrification tank, 3 ... sedimentation basin, 4 ... treated water outflow line, 5 ... nitrification carrier, 6 ... return sludge line, 7 ... surplus sludge line, 8, 8': diffuser pipe 9, 9 ': blower, 10 ... oxygen gas supply line, 11 ... exhaust gas line, 12, 12' ... gas phase gas in nitrification tank, 13 ... stirring means, 14 ... gas circulation line, 15 ... denitrification tank, 16 ... Denitrification tank stirrer, 17, 17 ': Screen, 18: Gas phase communication part

Claims (8)

A wastewater treatment device that biologically oxidizes ammonia nitrogen and / or organic nitrogen in wastewater to nitrate nitrogen and / or nitrite nitrogen, and is bound and immobilized with nitrifying bacteria attached to the surface A sealable nitrification tank filled with a carrier, an oxygen supply line for supplying high-concentration oxygen gas to the gas phase part of the nitrification tank, and a gas in the gas phase part in the nitrification tank without conducting surface aeration A wastewater treatment apparatus comprising: an aeration means having a blower for aeration in a liquid phase and an aeration device; and an agitation means for maintaining fluidity of the carrier of the nitrification tank. A wastewater treatment apparatus that biologically oxidizes ammonia nitrogen and / or organic nitrogen to nitrate nitrogen and / or nitrite nitrogen, and denitrifies the nitrifying bacteria on the surface. A sealable nitrification tank filled with an attached bonded immobilization carrier, an oxygen supply line for supplying high-concentration oxygen gas to the gas phase part of the nitrification tank, and a gas phase in the nitrification tank without surface aeration An aeration means having a blower and an air diffuser for introducing the gas in the liquid portion into the liquid phase, and an agitation means for maintaining the fluidity of the carrier of the nitrification tank. A waste water treatment apparatus comprising a nitriding tank and a return line for returning the liquid phase and / or sludge of the nitrification tank to the denitrification tank. The stirring means has a stirring condition of 1 to 100 W / m in power density per tank capacity. ³ The wastewater treatment apparatus according to claim 1 or 2, wherein the peripheral speed of the stirring blade is 1 to 4 m / sec.   The agitation means includes a control device that controls the agitation means based on the difference between the aeration amount necessary for maintaining the fluidity of the carrier by the aeration means and the aeration amount for supplying the necessary oxygen amount. The wastewater treatment apparatus according to claim 1, 2, or 3. A waste water treatment method for biologically oxidizing ammonia nitrogen and / or organic nitrogen in waste water to nitrate nitrogen and / or nitrite nitrogen, the nitrifying bacteria for oxidizing the waste water on the surface A high-concentration oxygen gas is supplied to the gas phase part of the sealable nitrification tank filled with the bonded immobilization carrier, and the gas in the gas phase part in the nitrification tank is dispersed with the blower without performing surface aeration. A wastewater treatment method, wherein the liquid phase part is agitated in order to maintain the fluidity of the carrier in the nitrification tank while aerated to the liquid phase part via a gas device. A wastewater treatment method for biologically oxidizing ammonia nitrogen and / or organic nitrogen to nitrate nitrogen and / or nitrite nitrogen to denitrify the wastewater, and oxidizing the wastewater A high-concentration oxygen gas is supplied to the gas phase part of the sealable nitrification tank filled with the binding immobilization carrier with the nitrifying bacteria attached to the surface, and the gas in the gas phase part in the nitrification tank is subjected to surface aeration. The liquid phase part was agitated in order to maintain the fluidity of the carrier in the nitrification tank while aeration was carried out to the liquid phase part via a blower and a diffuser without being performed, and provided in the front stage of the nitrification tank. A wastewater treatment method, wherein the liquid phase and / or sludge in the nitrification tank is returned to the denitrification tank for denitrification treatment. In the stirring, stirring conditions are 1 to 100 W / m in terms of power density per tank capacity. ³ The wastewater treatment method according to claim 5 or 6, wherein the peripheral speed of the stirring blade is 1 to 4 m / sec.   The agitation means used for performing nitrification with the minimum power based on the difference between the aeration amount necessary for maintaining the fluidity of the carrier by aeration and the aeration amount for supplying the necessary oxygen amount. The effluent treatment method according to claim 5, 6 or 7, wherein the motive power is controlled.