JPH1094796A - Treatment of waste water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to be operated in either of an aerobic condition or an anaerobic condition by providing at least one intermediate reaction vessel between an aerobic vessel and an oxygen free vessel. SOLUTION: The intermediate vessel 4 is provided between the oxygen free vessel 3 and the aerobic vessel 6 in a circulation type nitrification denitrification method. The flow-in water is treated in the oxygen free vessel 3, the intermediate vessel 4 and the aerobic vessel 6. In the aerobic vessel 6, ammonia nitrogen and organic nitrogen are oxidized into NOx -N, a part thereof is circulated to the oxygen free vessel 3 through the circulation line 9 and denitrifacted. The intermediate vessel 4 is operated in the oxygen free condition or the aerobic condition in accordance with the temp. or the quality of the treating water. In the case of operating the intermediate vessel in the oxygen free condition, a stirrer 8 is used and in the case of operating in the aerobic condition, oxygen- containing gas is blown from the diffusion device 5. Since the operation condition of the intermediate vessel is appropriately switched in accordance with the quality of the flow-in water or the treating water, the treated water excellent in quality is stably secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biological treatment method for wastewater.

[0002]

2. Description of the Related Art Conventionally, as a method for biologically removing nitrogen components from wastewater, a circulating nitrification denitrification method has been used. In this method, a denitrification tank and a final sedimentation basin are provided, a part of the nitrification tank treatment water and return sludge from the sedimentation basin are introduced into the denitrification tank, and NO ₂ -N and / or NO ₃ -N (hereinafter, NO ₂ -N and NO ₃ -N are collectively referred to as N
The O _X referred to as -N) was reduced to nitrogen gas, subjected to removal of nitrogen components from the wastewater, ammonia nitrogen by the action of nitrifying bacteria under aerobic conditions in the nitrification reactor (NH ₄ -N) and organic nitrogen those oxidized to NO _X -N, some of nitrification tank processing solution is circulated in the aforementioned manner denitrification tank, the remaining nitrification tank treatment liquid is introduced into the settling tank, the treated water as a supernatant Is obtained,
Part of the settled sludge is returned to the denitrification tank as described above (returned sludge). Part of the returned sludge is extracted as excess sludge.

[0003] In this treatment process, since the BOD component is used as a reducing agent for denitrification in the denitrification tank, a part of the BOD component is also removed in the denitrification tank. The components are decomposed and removed under aerobic conditions in an aerobic tank.

Further, in the above-mentioned method, a technique has been developed in which nitrifying bacteria are held in a reaction tank at a high concentration by using a microorganism-immobilized carrier, and the reaction tank is reduced in size. Such a technique has already been described in Document 1, Japanese Patent Publication No. 5-46279, and Japanese Patent Application Laid-Open No. 63-97290. In these technologies, by introducing a carrier into the nitrification tank, nitrifying bacteria can be maintained at a high concentration inside the nitrification tank,
It is said that the nitrification tank can be significantly reduced in size.

Japanese Patent Application Laid-Open No. Hei 7-39899 describes an example in which an aerobic tank is provided between a denitrification tank and a nitrification tank using a microorganism-immobilized carrier, in which the microorganism-immobilized carrier is not charged. The role of the aerobic tank here is to decompose the organic matter and prevent excessive microorganisms, particularly filamentous bacteria, from adhering to the carrier.

As a method of supplying oxygen to the reaction tank and keeping the inside of the reaction tank in an aerobic state, a method using an aerator such as a jet aerator, a diffuser plate, a diffuser, and the like are installed in the reaction tank, and through these, A method of blowing an oxygen-containing gas into a reaction tank is a known fact.

Next, as a method of stirring the inside of the reaction tank under oxygen-free conditions, a method of installing a submersible stirrer inside the reaction tank,
There are a method of installing a pump for circulating the inside of the reaction tank, a method of installing a stirrer at the top of the reaction tank, and a method of repeatedly blowing gas existing in the upper space of the reaction tank into the reaction tank by making the upper space of the reaction tank a closed structure. .

Further, a method has been developed in which a diffuser for generating bubbles having a large diameter is installed in a reaction tank, and the inside of the reaction tank is stirred by blowing air into the diffuser (Reference 2).

Reference 1: A report on the evaluation of a modified nitrification-promoting circulating method "Pegasus" using a comprehensive immobilized carrier, edited by the Technology Development Department, Japan Sewerage Corporation, June 1993 Reference 2: Konishi et al. Swirling stirrer for anaerobic tanks using the device, 33rd Sewer Research Conference Performance Collection, Japan Sewer Association (1995)

[0010]

In the prior art, the absolute value and the volume ratio of each reaction tank in the aeration tank are always constant after the plant has been constructed. It was not always possible to obtain an optimum tank configuration with respect to fluctuations, and the quality of treated water was sometimes deteriorated.

That is, the absolute value and the volume ratio of the volume of each reaction tank are determined based on the inflow water quality, the inflow water amount and the treated water quality, and the BOD removal rate, ammonia oxidation rate (hereinafter referred to as nitrification rate), and desorption rate. It is determined as an optimal solution using a reaction rate such as a nitrogen rate. Conversely, if conditions such as inflow water quality are different from the assumed values, this means that the tank configuration of the plant designed using the assumed values is not optimal.

[0012] However, the actual operation status of the wastewater treatment facility is such that the amount of inflow water and the quality of inflow water fluctuate during one day.
In general, the amount of influent water and the concentration of pollutants in the influent water vary within a range of about 50% to 150% with respect to the average value. In addition, seasonal fluctuations in inflow water quality and inflow volume are also observed. In winter, inflow is 10% to 20% compared to summer.
And the concentration of pollutants in the influent is 10% to 20%.
It is common to increase by about%. It is also known that the ratio of the BOD component and the nitrogen-based pollutant component in the influent varies with time and with season.

Next, the effect of fluctuations in the inflow water quality on the treated water quality will be considered, taking the system of the circulation type nitrification and denitrification method as an example (specific experimental results are described in the Examples section). The assumed conditions of the design are described below.

The BOD of the inflow water is BI (g / m ³ ), the total nitrogen concentration is NI (g / m ³ ) (all nitrogen is assumed to be nitrifying nitrogen), and the sludge concentration (MLSS) in the reaction tank is X
(G / m ³ ).

The target value of the total nitrogen of the treated water is NE (g / m
³ ). In the denitrification tank shall denitrification until all nitrogen gas NO _X -N flowing. The nitrification tank shall nitrification nitrification possible nitrogen components flowing until all NO _X -N.

It is assumed that the nitrogen component in the treated water exists only in the form of NO _x -N. The circulation ratio from the nitrification tank is r1,
The return ratio from the final sedimentation basin is r2, and R = r1 + r2.

The nitrification rate is defined as KN (gN / m ³ / d). The denitrification rate KD is expressed by the equation (1) as a function of the BOD-SS load (Ls) with respect to the amount of sludge in the combined denitrification tank and nitrification tank.

KD = k · Ls (gN / gMLSS / d) (1) where, k: denitrification rate constant (gN / gBOD), and Ls is represented by equation (2).

[0019] Ls = Q · BI / (VD + VN) / X (gBOD / gMLSS / d) (2) Here, VD: denitrification tank volume (m ³⁾ VN: nitrification tank volume (m ³⁾ Q: inflow water amount ( m ³ / d) Under the above assumed conditions, VN and VD can be obtained by equations (3) and (4), respectively.

VN = Q · NI / (KN / · X) (3) VD = Q · R · NE / (KD · X) (4) where NE: total nitrogen concentration of treated water (g / m ³⁾ ) By the way, the value of R required to make the total nitrogen of the treated water equal to or less than NE (g / m ³ ) is given by equation (5).

R = (NI−NE) / NE (5) Therefore, VN and VD can be calculated by calculating Expression (5) from Expression (1).

Next, a capacity calculation will be performed on the assumption of the following numerical conditions. (Value used for capacity calculation: Case 1) Q = 10000 (m ³ / d), NI = 40 (g / m
³ ), NE = 10 (g / m ³ ), BI = 150 (g / m ³ )
³ ), X = 2000 (g / m ³ ), k = 0.48 (gN
/ GBOD), KN = 0.048 (gN / gMLSS / d) By using the above values, VN = 4170 (m
³ ), VD = 2980 (m ³ ) is obtained, and the total volume of the reaction tank is 7150 (m ³ ).

On the other hand, assuming a case where the amount of inflow water changes and the NI drops to 35 (g / m ³ ) and the BI drops to 110 (g / m ³ ) (case 2), the other values are Using the value used in the above capacity calculation, VN '= 3650 (m
^{3), VD '= 3280 (} m 3), the reaction vessel total volume 6
A value of 930 (m ³ ) is obtained.

In this calculation example, since VN '<VN, 100% nitrification is performed, but VD'> VD, and the volume of the denitrification tank is assumed to be VD on the assumption of the inflow water quality assumed in Case 1.
When the inflow water of the water quality assumed in Case 2 flows into the treatment facility designed as the above, the capacity of the denitrification tank is insufficient, indicating that NO _X -N remains in the treated water and the treated water quality deteriorates. Have been.

Here, the characteristic point is that in case 2, B
Although it is shown that the total nitrogen concentration of the treated water is higher in Case 2 even though both I and NI are assumed to be smaller than Case 1, the conventional BOD component removal was performed. In biological water treatment technology, which is the center, a decrease in the concentration of pollutants in influent water has generally led to an improvement in the quality of treated water.
It is shown that in the case of the anoxic-aerobic method, it does not necessarily lead to an increase in the total nitrogen concentration of the treated water.

As described above, even if the concentration of pollutants in the influent water decreases, the cause of the deterioration of the total nitrogen concentration of the treated water is as follows (1).
As can be seen from the equation and the equation (2), this is because the denitrification rate is proportional to the BI, and the fluctuation of the BI concentration greatly affects the quality of the treated water.

Next, in the processing flow of the processing method called the nitrification-endogenous denitrification method, the configuration of the reaction tank is an aerobic tank, a non-oxidizing tank, and a re-aeration tank. Nitrification - The endogenous denitrification, after nitrification possible nitrogen components such as ammonia nitrogen and organic nitrogen in aerobic tank and nitrification in NO _X -N, nitrogen system and denitrification in the denitrification tank (anoxic tank) It is for treating pollutants.

This method is different from the above-mentioned circulation method, and is theoretically a method capable of denitrification of 100%. However, the BOD component which is a reducing agent for the denitrification reaction is preferably used in the preceding aerobic tank. Since it is decomposed by gas, the denitrification rate is reduced, and thus a large-sized reaction tank is required. As a method of increasing the denitrification rate and reducing the capacity of the denitrification tank, there is also a method of introducing a reducing agent such as methanol into the denitrification tank, but in this case, there is a problem that the processing cost increases.

As a method of stirring the reaction tank under oxygen-free conditions, there is a method of installing a diffuser for generating coarse bubbles in the reaction tank. However, there are problems such as reduction of the amount of diffused air and improvement of stirring energy. is there.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to ensure a stable and good quality of treated water according to the quality of inflow water, treated water and the amount of treated water. It is another object of the present invention to provide a method for treating wastewater that can reduce the amount of input reducing substances even when the denitrifying reducing agent is insufficient.

[0031]

SUMMARY OF THE INVENTION The wastewater treatment method of the present invention comprises biologically oxidizing in an aerobic tank under aerobic conditions and biologically denitrifying in an anoxic tank under anoxic conditions. In a wastewater treatment method for removing nitrogen-based pollutants in wastewater by combining the above, at least one intermediate reaction tank is provided between the aerobic tank and the anoxic tank, and any of the aerobic condition and the anoxic condition is provided. It can be operated even under the following conditions.

Thus, the intermediate reaction tank installed between the anoxic tank and the aerobic tank is maintained in an aerobic state or an anoxic (anaerobic) state depending on the quality of the inflow water, the quality of the treated water, and the amount of treated water. By increasing the capacity of the aerobic tank or the oxygen-free tank as necessary, it is possible to stably obtain good treated water quality, and even when using a reducing agent such as methanol, it is possible to reduce the amount of the reducing agent used. The effect is obtained.

The wastewater treatment apparatus according to the present invention
An aerobic tank that oxidizes biologically under aerobic conditions, and an anoxic tank that biologically denitrifies under anoxic conditions, and wastewater that removes nitrogen-based pollutants in the wastewater In the processing device,
In the middle of the aerobic tank and the anoxic tank, at least one intermediate reaction tank operable under any of aerobic conditions performed by a diffuser or anoxic conditions performed by a stirrer is provided. Have been.

In this wastewater treatment apparatus, the aerobic tank has a microorganism-immobilized carrier. Thereby, the size of the aerobic tank can be significantly reduced. In addition, when the intermediate reaction tank is operated under aerobic conditions, nitrifying bacteria adhere to the microorganism-immobilized carrier as a preferential species, so that the effect of increasing the speed and stabilizing the nitrification treatment can be obtained.

Further, the stirring device provided in the intermediate reaction tank is a diffuser for generating coarse bubbles. By blowing air into the air diffuser, the intermediate reaction tank is stirred under oxygen-free conditions. Thereby, the intermediate tank can be stirred while limiting the dissolution of oxygen in water.

In the intermediate reaction tank provided with a diffuser for generating coarse bubbles, a draft tube, a baffle plate, and the like are provided for dividing the liquid in the tank into a rising part and a falling part. .

As a result, the bubbles rise along with the upward flow of the liquid, and the bubbles have an upward slip speed with respect to the liquid flow velocity, so that the residence time of the bubbles in the liquid (gas-liquid contact time) , The amount of dissolved oxygen can be further reduced, and the stirring energy in the tank increases, so that a better stirring state can be obtained.

Further, at least a part of the bottom of the intermediate reaction tank provided with an air diffuser for generating coarse bubbles has a concave shape. Thereby, the sludge settles and accumulates in the concave portion, and is again transferred to the upper portion of the intermediate tank by the air lift effect. Therefore, it is possible to obtain a good stirring state in the tank while preventing sludge from accumulating on the bottom portion.

A diffuser for generating coarse bubbles in the intermediate reaction tank is operated intermittently.
As a result, an operation in which the amount of dissolved oxygen in the intermediate tank is reduced becomes possible, and good nitrogen removal is achieved.

The upper space of the intermediate reaction tank has a closed structure, and a device for repeatedly blowing gas existing in the upper space of the tank into the tank is provided. With this configuration, the gas present in the upper space is repeatedly blown into the tank, whereby the oxygen concentration in the blown gas gradually decreases, and the operation in which the amount of dissolved oxygen in the intermediate tank is greatly reduced becomes possible. , Good nitrogen removal is achieved.

[0041]

FIG. 1 is an overall configuration diagram showing an example of an embodiment of the present invention. This is provided with an intermediate tank between the anoxic tank of the circulating type nitrification and denitrification method and the nitrification layer, and the inflow water 1 is treated in the anoxic tank 3, the intermediate tank 4, and the aerobic layer 6.

In the aerobic layer 6, ammonia nitrogen, organic nitrogen and the like in the influent 1 are oxidized to NO _x -N, and a part thereof is circulated to the anoxic tank 3 through the circulation line 9. Denitrification treatment is performed.

The intermediate tank 4 is operated under anoxic condition or aerobic condition depending on the quality of inflow water, water temperature, treated water quality, and the like.
The stirrer 8 is used when the intermediate tank 4 is operated in an oxygen-free condition, and the diffuser 5 is used when the intermediate tank 4 is operated in an aerobic condition.
, An oxygen-containing gas is blown.

FIG. 2 shows an intermediate tank provided between an aerobic tank (nitrification tank) and an anoxic tank (denitrification tank) in the nitrification-endogenous denitrification method. Intermediate tank 12, oxygen-free tank 1
3 and the re-aeration tank 14 in this order.

Ammonia nitrogen, organic nitrogen and the like in the influent 1 are oxidized to NO _x -N in the aerobic layer 11. The intermediate tank 12 is operated under anoxic condition when nitrification is achieved to almost 100% in the aerobic tank 11, and is operated under aerobic condition when nitrification in the aerobic tank 11 is insufficient. You. Intermediate tank 12
Is operated under oxygen-free conditions, the coarse bubble generator 1
By aeration from step 5, the intermediate tank 12 is stirred.
On the other hand, when the intermediate tank 12 is operated under aerobic conditions, an oxygen-containing gas is blown from the air diffuser 5.

The denitrification of NO _X -N in the anoxic tank 13 is performed. In order to increase the denitrification rate, a reducing agent such as methanol can be introduced into the anoxic tank 13.
A reducing agent such as methanol is charged into the intermediate tank 12 when the intermediate tank 12 is operated under oxygen-free conditions, and is charged into the oxygen-free tank 13 when the intermediate tank 12 is operated under aerobic conditions.

The re-aeration tank 14 aims to decompose unused methanol and to separate nitrogen gas generated in the oxygen-free tank 13 from sludge to improve the separation of sludge in the final sedimentation tank 7. However, the re-aeration tank 14 may not be required depending on the required quality of treated water.

Incidentally, the aerobic tank in the nitrification-endogenous denitrification method is generally designed on the basis of winter conditions in which the concentration of nitrogen-based pollutants is high and the nitrification rate is low and the water temperature is low. When the water temperature is high, or when the concentration of the nitrogen-based sludge substance in the inflow water is low, the processing apparatus is more than necessary.

When the nitrogen sludge substance at such a high water temperature or inflow water has a low concentration, in the present invention provided with an intermediate reaction tank, 100% nitrification can be achieved even in a small aerobic tank. Therefore, the intermediate tank can be used as an oxygen-free tank, and the total tank volume of the oxygen-free tank increases, so that denitrification is sufficiently performed.
BO containing influent BOD component or sludge
Since the D component is effectively used as a reducing agent, there is an advantage that the amount of the reducing agent can be reduced even when a reducing agent such as methanol is introduced.

In the nitrification-endogenous denitrification method, it is known that the rate of endogenous denitrification decreases as the treatment under aerobic conditions progresses. Because the volume is small, the rate of endogenous denitrification is high, and the volume of the oxygen-free tank is increased by the volume of the intermediate tank, so that the amount of methanol can be significantly reduced, and methanol is not added. Even in such cases, treated water quality is greatly improved.

FIGS. 1 and 2 show an example of the present invention. The effect of the present invention is that an intermediate reaction tank installed between an oxygen-free tank and an aerobic tank is used for controlling inflow water quality and treatment Since it is obtained by maintaining the aerobic state or the anaerobic state flexibly according to the water quality and the amount of inflow water, FIG.
In addition to FIG. 2 and the anaerobic-anoxic-aerobic method, the UCT method and the anaerobic-anoxic-aerobic-second denitrification-re-aeration method, an aerobic tank and an aerobic tank or an aerobic tank and anoxic The effect is obtained in all systems where tanks are connected.

In the present invention, as a method of operating the intermediate tank under aerobic conditions, an oxygen supply device is installed in the reaction tank. Examples of the oxygen supply method include a method using an aerator such as a jet aerator, a method in which a diffuser plate, a diffuser, and the like are installed in a reaction tank, and an oxygen-containing gas is blown into the reaction tank through these.

Next, as a method of stirring the inside of the reaction tank under oxygen-free conditions, a method of installing a submersible stirrer 8 inside the reaction tank, a method of installing a stirrer above the reaction tank, a pump for circulating the inside of the reaction tank, There is a method of installing, a method of making the upper space of the reaction tank a closed structure, and repeatedly blowing gas existing in the upper space of the reaction tank into the reaction tank.

Further, a diffuser 5 for generating bubbles having a large diameter may be provided in the reaction tank, and the inside of the reaction tank may be stirred by blowing air into the diffuser. In this method, although the dissolution of oxygen in the blown air poses a problem, the diameter of bubbles to be diffused should be increased by increasing the pore diameter of the bubble diffusion portion of the diffuser, or (and) the depth of the diffused water. It is also possible to reduce the amount of oxygen dissolved by reducing the depth of the reaction vessel and keep the inside of the reaction tank under conditions that cause a denitrification reaction.

In the method of blowing air from a large-diameter diffuser, the amount of dissolved oxygen can be reduced by reducing the amount of blown air. In this case, the power for stirring inside the reaction tank is also reduced. There is a problem.

However, as shown in FIG. 3, by diffusing air from only one side or the center of the reaction tank, the inside of the reaction tank is divided into a rising part and a falling part. By generating a swirling flow in the reaction vessel, a sufficient stirring flow rate can be obtained inside the reaction vessel while reducing the amount of dissolved oxygen.

This is because when the swirling flow is generated, the bubbles rise in the form accompanied by the rising flow of the liquid, and the bubbles themselves have a further upward slip speed with respect to the flow of the liquid. This is because the residence time in the liquid (gas-liquid contact time) is reduced and the oxygen dissolving efficiency is reduced, and the swirling flow method has a higher stirring power than the full air diffusion method.

Further, as shown in FIG. 4, a draft tube or a partition plate 16 is installed inside the reaction tank, and air is blown into the reaction tank so that the liquid rises and falls in the reaction tank due to the air lift effect. A similar effect can be obtained by clear separation.

Further, as shown in FIGS. 5 and 6, a concave portion 17 is provided at the bottom of the reaction tank, and the settled sludge is collected in the concave portion. By transferring to the upper part of the tank, it is possible to stir the inside of the reaction tank without depositing sludge on the bottom part.

In installing the draft tubes and the partition plates in the reaction tank, it is possible to finely divide the inside of the reaction tank by installing a plurality of draft tubes and partition plates in the reaction tank.

Furthermore, in the method of blowing air from the diffuser 15 having a large diameter, intermittent aeration is also effective. This is because the amount of oxygen dissolved in the reaction tank can be further reduced by intermittent aeration, and sufficient stirring in the reaction tank is possible even in the intermittent aeration method.

The setting of the intermittent aeration cycle is determined by the anaerobic degree and the stirring state of the reaction tank, and it is possible to determine the cycle from empirical values.
Automatic control can also be performed using an oxidation-reduction potential (ORP) meter, a sludge concentration meter, a sludge interface meter, or the like.

Incidentally, as a matter common to all of the above-mentioned agitation methods using aeration, it is possible to reduce the amount of dissolved oxygen by making the water depth of the aeration device shallow. In addition, as a matter common to all the above-described agitation methods using aeration, it is known that the biological denitrification reaction proceeds even if there is some dissolved oxygen on the liquid side. It is not necessary to make the inside of the reaction tank completely oxygen-free in order to advance the reaction. As a guide, the dissolved oxygen concentration (DO) in the reaction tank may be set to about 0.5 (g / m ³ ) or less.

The oxygen-free agitation can also be achieved by making the upper space of the intermediate tank a closed structure and repeatedly blowing gas present in the upper space into the reaction tank. In this case, even if oxygen gas is present in the upper part of the reaction tank in the initial stage, the oxygen gas dissolves in the liquid side, and the oxygen concentration in the gas gradually decreases, so that the oxygen-free condition is ensured. In addition, the upper space may be supplemented with a volume of air corresponding to the dissolved amount. As described above, the denitrification reaction proceeds even if a small amount of DO is present, so that the airtightness of the upper space does not need to be perfect.

The intermediate reaction tank provided between the oxygen-free tank and the nitrification tank provided in the present invention is operated under aerobic conditions or under oxygen-free conditions depending on the quality of the inflow water and the treated water. You can monitor and decide.

In general, when ammonia nitrogen remains in the nitrification tank effluent, the intermediate reaction tank is operated under aerobic conditions, and when NO _X -N remains in the oxygen-free tank effluent, Operate under anoxic conditions. In addition, ammonia nitrogen or NO
It is also possible to perform automatic control using an _X- N measuring device, DO meter, ORP meter and the like.

Furthermore, the present invention is also effective in a system in which a microorganism-immobilized carrier is charged into a nitrification tank. When the intermediate reaction tank is operated under aerobic conditions, the BOD component is suspended in the intermediate reaction tank. Due to the removal, the nitrification reaction mainly occurs on the surface of the microorganism-immobilized carrier, a biofilm mainly formed of nitrifying bacteria is formed on the microorganism-immobilized carrier,
There is an advantage that nitrification can be speeded up and stabilized.

Further, by providing a plurality of intermediate tanks, finer control can be performed, and a greater improvement in treated water quality can be achieved. The water depth of the reaction tank is generally about 5 m. However, the same effect can be obtained in an aeration tank having a water depth of about 10 m to about 20 m, which is called a deep aeration method.

As described above, compared to the conventional method, the present method achieves a high nitrogen removal rate that is easier with respect to fluctuations in the amount and quality of the influent water. The amount of methanol added can be significantly reduced.

[0070]

An embodiment of the present invention will be described below. In Example 1, the treatment system of the circulating nitrification and denitrification method to which the present method shown in FIG. 1 is applied and the treatment system of the circulating nitrification and denitrification method which is a conventional method (the flow chart of FIG. 1 from which the intermediate reaction tank is removed) ) Were performed, and the experimental conditions and experimental results are as shown in Table 1.

[0071]

[Table 1]

As shown in Table 1, the total volume of the reaction tanks is equal to each other. In this method, in RUN1, the intermediate reaction tank is placed under aerobic conditions, and RUN2 and RUN3 are run.
, The intermediate reaction tank is maintained in an oxygen-free condition.

Looking at the experimental results, it was found that BOD was used for RUN1.
When the concentration of the components is high, a high denitrification rate can be obtained, so that there is no significant difference in the treated water quality between the present method and the conventional method. On the other hand, in RUN2 and RUN3 in which the BOD concentration and the TN concentration of the influent water decreased due to the rise in water temperature, a sufficient nitrification reaction proceeded even if the aerobic tank was set to 0.9 (m ³ ). I was

In RUN2 and RUN3, the denitrification rate decreased due to the decrease in the BOD concentration of the inflow water.
In this method, since the intermediate tank is operated under anoxic condition, the TN of the treated water is about 3 (g / m ³ ) smaller than that of the conventional method. The improvement effect was remarkable.

As a method for keeping the intermediate tank in an oxygen-free condition, an underwater stirrer was used for RUN2, and a coarse bubble aerator was used for RUN3.
1 (g / m ³ ) or less, and the intermediate tank was used as a denitrification tank.

Example 2 is a side-by-side comparison of a nitrification-endogenous denitrification treatment system to which the present method shown in FIG. 2 is applied and a conventional treatment system (with the intermediate reaction tank of FIG. 2 removed). The experiment was performed, and the experimental conditions and results are as shown in Table 2.

[0077]

[Table 2]

As shown in Table 2, the total volume of the reaction tanks is equal to each other. In the present method, in RUN4, the intermediate reaction tank is placed under aerobic conditions, and RUN5 and RUN6
, The intermediate reaction tank is maintained in an oxygen-free condition.

According to the experimental results, since the inflow water concentration was relatively high in RUN4, an aerobic tank volume of 1.5 (m ³ ) was required to perform 100% nitrification even in this method. Since the intermediate tank is operated under aerobic conditions, and the total tank volume of the reaction tank under the aerobic conditions of the present method and the conventional method is equal,
There was no significant difference in the treated water quality between this method and the conventional method.

On the other hand, the RUN in which the quality of
In No. 5 and RUN 6, 100% nitrification was achieved even when the volume of the aerobic tank was 1.0 (m ³ ), and the intermediate tank was used as an oxygen-free tank.

For this reason, in the present method, the capacity of the anoxic tank is increased by about 17% compared to the conventional method, and in RUN5 with the same amount of methanol added, the TN of the treated water of the present method is higher than that of the conventional method. It was improved by about 1.1 (g / m ³ ).

Further, in RUN 6 in which the amount of methanol added in the present method was one third of the same amount in the conventional method, the TN values of the treated water of the present method and the conventional method were equivalent, and the treated water quality was equivalent. It was also experimentally confirmed that under the conditions described above, the effect of reducing the amount of methanol used, in other words, the effect of reducing the processing cost, was obtained.

In this experiment, the volumes of the aerobic tank and the anoxic tank were set at the values shown in Tables 1 and 2. However, the volume of the reaction tank in the actual installation was determined by the quality of the inflow water and the required treatment. Water quality,
It is determined in consideration of the facility area limit.

[0084]

As described above, according to the present invention, it is possible to set any of the aerobic condition and the anaerobic condition between the anaerobic tank and the aerobic tank or between the aerobic tank and the anaerobic tank. Since an intermediate tank is provided so that the operating conditions of the intermediate tank can be appropriately switched according to the quality of the inflow water and the quality of the treated water, the effect of stably ensuring good treated water quality can be obtained.

Also, in the case where a reducing agent for denitrification is insufficient and a reducing substance such as methanol is charged, the capacity of the denitrification tank can be increased in the present invention. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic flow chart showing an example of an embodiment of the present invention.

FIG. 2 is a schematic diagram of a wastewater treatment flow using the present invention.

FIG. 3 shows an example of a reaction tank structure in a coarse bubble blowing system.

FIG. 4 shows an example of a reaction tank structure in a coarse bubble blowing system.

FIG. 5 shows an example of a reaction tank structure in a coarse bubble blowing system.

FIG. 6 shows an example of a reaction tank structure in a coarse bubble blowing system.

[Explanation of symbols]

1 ... inflow water, 2 ... treated water, 3 ... oxygen-free tank, 4 ... intermediate tank,
5: diffuser, 6: aerobic tank, 8: stirrer, 15: coarse bubble generator, 16: baffle plate or draft tube, 17: recess.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toyoshi Sawada 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd.

Claims (8)

[Claims] 1. A combination of biologically oxidizing in an aerobic tank under aerobic conditions and biologically denitrifying in an anaerobic tank under anoxic conditions to reduce nitrogen-based pollutants in wastewater. In the method for treating wastewater to be removed, at least one intermediate reaction tank is provided between the aerobic tank and the anoxic tank, and can be operated under any of aerobic conditions and anoxic conditions. Wastewater treatment method. 2. An aerobic tank for biologically oxidizing under aerobic conditions and an anoxic tank for biologically denitrifying under anoxic conditions to remove nitrogen-based pollutants in wastewater. In the wastewater treatment apparatus for removal, at least in the middle of the aerobic tank and the anoxic tank, at least operable under any of aerobic conditions performed by a diffuser or anoxic conditions performed by a stirrer or the like. A wastewater treatment device comprising one intermediate reaction tank. 3. An apparatus for treating wastewater according to claim 2, wherein said aerobic tank has a microorganism-immobilized carrier. 4. The wastewater treatment apparatus according to claim 2, wherein the stirring device provided in the intermediate reaction tank is a diffuser for generating coarse bubbles. Processing equipment. 5. The wastewater treatment apparatus according to claim 4, wherein a draft tube, a baffle plate, and the like are provided in the intermediate reaction tank to divide the liquid in the tank into a rising part and a falling part. Waste water treatment apparatus characterized by the above-mentioned. 6. The wastewater treatment apparatus according to claim 4, wherein at least a part of a bottom of the intermediate reaction tank is concave. 7. The wastewater treatment apparatus according to claim 4, wherein the diffuser for generating coarse bubbles in the intermediate reaction tank is intermittently performed. Processing method. 8. The wastewater treatment apparatus according to claim 2, wherein an upper space of the intermediate reaction tank has a closed structure, and a gas existing in the upper space of the tank is repeatedly discharged. An apparatus for treating wastewater, comprising a device for blowing air into the inside.