JPH09299988A - Nitrification / denitrification method and device - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To provide a nitrification / denitrification method and apparatus capable of efficiently performing both a nitrification reaction requiring an aerobic condition and a denitrification reaction requiring an anaerobic condition in a single tank. provide. SOLUTION: A large number of carriers 32, in which at least nitrifying bacteria and denitrifying bacteria are coexistently immobilized and co-immobilized, are introduced into the nitrifying / denitrifying tank 14 into which wastewater flows, so that the dissolved oxygen level in the wastewater of the nitrifying / denitrifying tank 14 is Since the air aeration amount from the aeration pipe 16 is controlled by the controller 24 based on the measured value of the dissolved oxygen meter 22 so as to be 0.1 to 1.5 mg / l, the carrier 32
Both the nitrification treatment and the denitrification treatment can be carried out with the same carrier by utilizing the aerobic zone formed on the surface part of and the anaerobic zone formed inside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for removing nitrogen in waste water, and more particularly to a method and a device for removing nitrogen in biological waste water using an entrapping immobilization carrier.

[0002]

2. Description of the Related Art In recent years, the examination of measures for preventing water pollution on a global environmental scale has been demanded.
One of the development issues is to improve the efficiency of nitrogen removal from wastewater,
Various studies are being conducted. Conventionally, a modified activated sludge circulation method has been used as a biological nitrogen removal method. The nitrification / denitrification equipment to which this method is applied consists of two tanks, an anaerobic denitrification tank and an aerobic nitrification tank. In the nitrification tank, nitrifying bacteria nitrify the ammoniacal nitrogen in the wastewater into nitric acid. Then, the nitrification solution nitrified in the nitrification tank is circulated to the denitrification tank, so that the nitrogen component in the waste water is released to the atmosphere as nitrogen gas and removed. A part of this circulated liquid is withdrawn as treated water.

In this modified activated sludge circulation method, immobilization of nitrifying bacteria has been studied in order to increase the nitrification efficiency, and a process of introducing the immobilized nitrifying bacteria into a nitrifying tank is considered.

[0004]

However, the conventional nitrification / denitrification apparatus is composed of a nitrification tank that needs an aerobic condition to work nitrifying bacteria and a denitrification tank that needs an anaerobic condition to work denitrifying bacteria. However, there is a drawback that the apparatus becomes large because it requires two tanks. The present invention has been made in view of such circumstances, and it is possible to efficiently perform both a nitrification reaction that requires an aerobic state and a denitrification reaction that requires an anaerobic state in a single tank. It is an object of the present invention to provide a nitrification / denitrification method and device that can significantly reduce the size of the product.

[0005]

In order to achieve the above object, the present invention provides a nitrification / denitrification method for removing nitrogen components in wastewater, in which at least nitrifying bacteria and denitrifying bacteria are allowed to coexist with the wastewater. And the carrier immobilized comprehensively is contacted at a dissolved oxygen level in the wastewater of 0.1 to 1.5 mg / l to perform nitrification treatment of the ammonia nitrogen component in the wastewater on the surface of the carrier. It is characterized in that a nitrate nitrogen component is denitrified inside the carrier.

Further, in order to achieve the above object, the present invention provides:
In a nitrification / denitrification device that removes nitrogen components from wastewater,
Nitrification consisting of a single tank for contacting the wastewater with at least a carrier that has been entrapped and immobilized in the presence of nitrifying bacteria and denitrifying bacteria.
A denitrification tank, an aeration means for aerating the wastewater in the nitrification / denitrification tank with air, a measuring means for measuring dissolved oxygen in the wastewater in the nitrification / denitrification tank, and the aforesaid measurement value based on the measurement value of the measuring means. The aeration amount of air from the aeration means is controlled so that the dissolved oxygen level in the wastewater is maintained at 0.1 to 1.5 mg / l to form an aerobic zone on the surface part of the carrier and at the same time inside the carrier. It is characterized in that it comprises a control means for forming an anaerobic zone, and performs both nitrification treatment and denitrification treatment in the single nitrification / denitrification tank.

According to the present invention, a carrier in which nitrifying bacteria and denitrifying bacteria are co-immobilized and co-immobilized has a dissolved oxygen level in the waste water of 0.1-
Under the condition of 1.5 mg / l, the surface of the carrier becomes an aerobic zone and the inside becomes an anaerobic zone, and nitrifying bacteria which are aerobic microorganisms are present in the aerobic zone and anaerobic zone. It was confirmed that the denitrifying bacteria, which are anaerobic microorganisms, can be naturally segregated, and that the nitrification process proceeds in the aerobic zone and the denitrification process proceeds in the anaerobic zone. It is a thing.

[0008] That is, according to the present invention, a carrier in which at least nitrifying bacteria and denitrifying bacteria are made to coexist and immobilize is introduced into a nitrifying / denitrifying tank into which wastewater flows, and the wastewater in the nitrifying / denitrifying tank is treated. Since the aeration control means controls the aeration amount of air from the aeration device based on the measured value of the dissolved oxygen meter so that the dissolved oxygen level becomes 0.1 to 1.5 mg / l, it is formed on the surface of the carrier. By utilizing the nitrifying bacteria zone and the anaerobic denitrifying bacteria zone formed inside the carrier, it is possible to perform both nitrification treatment and denitrification treatment with the same carrier.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a nitrification / denitrification method and apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a graph for explaining the theoretical basis of the nitrification / denitrification method according to the present invention.

Curve A shows ammonia nitrogen (NH ₄ −
It shows the relationship between the residual ratio of ammonia nitrogen and the dissolved oxygen in the waste water when the synthetic inorganic waste water containing N) is brought into contact with the carrier in which nitrifying bacteria and denitrifying bacteria are co-immobilized. is there. The curve B shows the residual ratio of nitrate nitrogen and the wastewater when the synthetic inorganic wastewater containing nitrate nitrogen (NO ₃ -N) and the carrier immobilized comprehensively in the presence of nitrifying bacteria and denitrifying bacteria are contacted. It shows the relationship of the dissolved oxygen in the inside.

From FIG. 1, the curve A shows that when the dissolved oxygen level in the synthetic inorganic wastewater containing ammonia nitrogen is gradually increased from zero, the nitrification reaction starts at about 0.01 mg / l of dissolved oxygen and the dissolved oxygen starts to dissolve. 100% when oxygen is 0.1 mg / l
It shows that ammonia nitrogen is removed at a similar removal rate. That is, it is shown that nitrifying bacteria that oxidize ammoniacal nitrogen to nitrate nitrogen can sufficiently perform nitrification reaction if the dissolved oxygen is 0.1 mg / l or more.

On the other hand, the curve B shows that when the dissolved oxygen level in the synthetic inorganic wastewater containing nitrate nitrogen is gradually increased from zero, nitric acid is removed at a removal rate close to 100% until the dissolved oxygen level is around 1.5 mg / l. Nitrogen is removed, but dissolved oxygen is 1.5
It shows that the action of denitrifying bacteria is rapidly decreased when the amount exceeds mg / l. That is, it has been shown that the denitrifying bacteria that reduce nitrate nitrogen to nitrogen gas can sufficiently perform the denitrification reaction if the dissolved oxygen is 1.5 mg / l or less.

FIG. 2 is a schematic view showing the inside of the carrier by cutting the carrier after maintaining the dissolved oxygen in the synthetic inorganic waste water at 0.1 to 1.5 mg / l. As can be seen from FIG. 2, a nitrifying bacterium zone that requires aerobicity is formed on the surface of the carrier, and a denitrifying bacterium zone that requires anaerobic is formed inside the carrier. From these facts, the present inventors have found that when a carrier in which at least nitrifying bacteria and denitrifying bacteria are co-immobilized is placed under conditions of a dissolved oxygen level of 0.1 to 1.5 mg / l, the surface of the carrier is favorable. Being an aerobic zone, the inside becomes an anaerobic zone, nitrifying bacteria that are aerobic microorganisms in the aerobic zone, and denitrifying bacteria that are anaerobic microorganisms are naturally distributed in the anaerobic zone. It was found that the nitrification process proceeds in the aerobic zone and the denitrification process proceeds in the anaerobic zone.

FIG. 3 shows a first embodiment of the nitrification / denitrification apparatus of the present invention constructed on the basis of the above findings. As shown in FIG. 3, the nitrification / denitrification apparatus 10 mainly includes a wastewater inflow pipe 12 such as sewage, a nitrification / denitrification tank 14 formed of a single tank into which the wastewater flows, and a bottom of the nitrification / denitrification tank 14. The aeration pipe 16 provided in the aeration pipe 16 and the nitrification / denitrification tank 1 from the aeration pipe 16
The compressed air supplied to the air reservoir 18 at the bottom of 4 is nitrified.
A wire mesh diffusion plate 20 that diffuses throughout the denitrification tank 14, a dissolved oxygen meter 22 that measures dissolved oxygen in wastewater in the nitrification / denitrification tank, and an aeration pipe 1 based on the measured value of the dissolved oxygen meter 22.
6 and a control device 24 that controls the amount of air aeration. Control of the aeration pipe 16 by the control device 24 is performed by supplying compressed air from the blower 26 by controlling the opening degree of a valve 30 provided in the compressed air pipe 28.

In the nitrification / denitrification tank 14, a large number of carriers 32 in which activated sludge is entrapped and immobilized with a polymer gel are loaded. The polymer gel used for entrapping immobilization is not particularly limited, and various polymer substances such as polyacrylamide,
Polyethylene glycol, polyvinyl alcohol, agar, carrageenan, alginate and the like can be used.

As the shape of the carrier 32, in addition to a cubic shape, a spherical shape, a plate shape or a string shape can be used. The size of the carrier 32 depends on the type of polymer gel used, but the surface portion of the carrier 32 is an aerobic zone and the inside is an anaerobic zone, and the waste water can be in contact with the inside of the carrier from 2 to 50 mm. Is appropriate. According to the nitrification / denitrification apparatus 10 configured as described above, the wastewater and the carrier in which at least nitrifying bacteria and denitrifying bacteria are co-immobilized and immobilized, have a dissolved oxygen level in the wastewater of 0.1 to 1.5 mg / l.
Since the contact is made in the state of, the nitrifying bacteria zone formed on the surface of the carrier 32 and the denitrifying bacteria zone formed inside the carrier 32 are used to perform nitrification treatment and denitrification treatment on the same carrier 32. You can do both. Therefore, it is possible to perform nitrification and denitrification treatment efficiently in a single tank without the need for two tanks, an aerobic nitrification tank and an anaerobic denitrification tank as in the conventional case.

FIG. 4 shows a second embodiment of the nitrification / denitrification apparatus 10 of the present invention. In order for the denitrifying bacteria of the carrier 32 to perform the denitrification treatment, a carbon source as a nutrient source is necessary.
The wastewater contains a certain amount of organic matter, and this organic matter can be used as a carbon source. However, when the organic matter concentration (carbon source concentration) in the wastewater is low, or when the nitrogen concentration (nitrogen source concentration) is higher than the organic matter concentration in the wastewater, the action of the denitrifying bacteria on the carrier decreases and the wastewater Removal of the nitrogen component of the product becomes insufficient.

In the second embodiment, in consideration of such a situation, the ratio of the nitrogen source to the carbon source in the waste water is actively managed. As shown in FIG. 4, in the second embodiment, a nitrification / denitrification tank 14 is provided with a nitrogen concentration meter 34 for measuring the concentration of nitrogen source and a BOD meter 36 for measuring the concentration of organic substances as carbon source. These measured values are input to the controller 24. Further, above the nitrification / denitrification tank 14, a carbon source, for example, an addition device 38 for adding methanol is added.
The amount of carbon source added from the addition device 38 is controlled by the control device 24. Other devices are the same as those in the first embodiment.

According to the second embodiment thus constructed, the dissolved oxygen level in the wastewater in the nitrification / denitrification tank 14 is maintained at 0.1 to 1.5 mg / l, and the nitrogen source in the wastewater is maintained. Since the concentration of the carbon source is controlled so that the ratio of N and the carbon source C (C / N ratio) is 0.1 to 4, the denitrification treatment can be performed more reliably than in the first embodiment. . In addition, the nitrification / denitrification method of the present invention discharges the treated water of the nitrification / denitrification tank every time even in the continuous treatment in which the wastewater continuously flows into and is discharged from the nitrification / denitrification tank. A batch process for supplying wastewater can be applied to both. The flow of the liquid in the nitrification / denitrification tank may be an upward flow or a downward flow.

[0020]

EXAMPLE Next, an example of using the nitrification / denitrification apparatus 10 of the present invention shown in FIG. 3 will be described. As the carrier 32 in which nitrifying bacteria and denitrifying bacteria are made to coexist and immobilize,
Standard activated sludge from a sewage treatment plant was used as an inoculum for immobilization. For entrapping immobilization, 2% by weight of activated sludge, 15% of polyethylene glycol prepolymer, 0.5% by weight of N, N, N ', N'-tetramethylethylenediamine and 0.25% by weight of potassium persulfate are mixed in water to cause gelation. I went by. The resulting gel is a 3 mm square pellet (carrier)
Cut to 32.

Then, the obtained pellet was cultivated in wastewater having an ammoniacal nitrogen concentration of 250 mg / l. Culture conditions are pellet filling rate 10%, dissolved oxygen level in wastewater
Performed at 4.5-6 mg / l. The number of nitrifying bacteria in the pellet on the 90th day of culture was 2.0 × 10 ¹⁰ cells per pellet.
/ Cm ³ , and the number of denitrifying bacteria is 4.57 × per pellet
It became 10 ⁹ cells / cm ³ .

In this example, the pellets cultured as described above were used.
Put the soot into the nitrification / denitrification tank so that the filling rate becomes 10%.
Waste containing carrier and ammonia nitrogen 20 mg / l
Contact with water and reduce the dissolved oxygen level in the wastewater to 0.
Residence time is 2 hours while controlling between 1 and 1.5 mg / l
Processed in. And at this time, ammonia nitrogen (NH
_Four-N) removal rate and total nitrogen (TN) removal rate
Was. Dissolved oxygen is controlled at the center of the nitrification / denitrification tank.
Dissolved oxygen meter was used to measure the dissolved oxygen in the wastewater.
Dissolved oxygen level in wastewater is 0.1-1.5 m based on the fixed value
Set the amount of air aeration from the aeration pipe so that it enters between g / l.
It was controlled by the controller.

Further, as Comparative Example 1, the case where the dissolved oxygen level in the waste water was controlled at 0 to 0.1 mg / l, and as Comparative Example 2 the case where the dissolved oxygen level in the waste water was controlled at 1.5 to 3 mg / l went. In Comparative Example 1 or 2, the conditions other than dissolved oxygen are the same as in this example. The results are shown in FIGS.

As can be seen from FIGS. 5 and 6, the dissolved oxygen level in the wastewater was 0.1 to 1.5 mg / l as in this example.
When controlled between, the removal rate of ammonia nitrogen is 95%
As described above, the removal rate of total nitrogen was 80 to 90%, and both nitrifying bacteria and denitrifying bacteria worked sufficiently. On the other hand, when the dissolved oxygen level was controlled at 0 to 0.1 mg / l, the removal rate of ammonia nitrogen was about 5%, and nitrifying bacteria were hardly working. The wastewater was anaerobic and satisfied the conditions for denitrifying bacteria. However, since nitrifying bacteria did not work and ammonia nitrogen did not become nitrate nitrogen, the total nitrogen removal rate was 5% or less.

The dissolved oxygen level is 1.5 to 3 mg / l.
When controlled by, the removal rate of ammonia nitrogen is 95
%, The total nitrogen removal rate was about 50 to 10%, and denitrifying bacteria were not working sufficiently. In this way, the carrier in which at least nitrifying bacteria and denitrifying bacteria are co-immobilized and immobilized, and the dissolved oxygen level in the wastewater is 0.1 to 1.5 mg.
Under the condition of 1 / l, the surface of the carrier becomes an aerobic zone and the inside becomes an anaerobic zone, and nitrifying bacteria that are aerobic microorganisms are in the aerobic zone and anaerobic in the anaerobic zone. It was demonstrated that the denitrifying bacteria, which are microorganisms, can be naturally distributed.

[0026]

As described above, according to the nitrification / denitrification method and apparatus of the present invention, the waste water and the carrier in which at least nitrifying bacteria and denitrifying bacteria are co-immobilized and immobilized are dissolved oxygen in the waste water. Since the contact was made at a level of 0.1 to 1.5 mg / l, the nitrifying bacteria zone was formed on the surface of the carrier and the denitrifying bacteria zone was formed inside the carrier. As a result, it is possible to perform both nitrification treatment and denitrification treatment using the same carrier by utilizing this nitrifying bacteria zone and denitrifying bacteria zone.

Therefore, since it is possible to perform nitrification / denitrification treatment efficiently in a single tank without the need for two tanks of aerobic nitrification tank and anaerobic denitrification tank as in the conventional case, the apparatus is significantly compact. Can be converted. Moreover, since complete nitrification can be performed for nitrification and denitrification with the same carrier, part of the circulating liquid is drawn as treated water while circulating the liquid between the nitrification tank and the denitrification tank as in the past. The quality of the treated water is better than when removing it.

[Brief description of drawings]

FIG. 1 is a graph illustrating a nitrification / denitrification method according to the present invention.

FIG. 2 is a cross-sectional view of the entrapping carrier in the nitrification / denitrification method according to the present invention.

FIG. 3 is a configuration diagram illustrating a nitrification / denitrification apparatus according to a first embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating a second embodiment of a nitrification / denitrification apparatus according to the present invention.

FIG. 5 is a graph showing the relationship between the removal rate of ammonia nitrogen and dissolved oxygen in an example of the nitrification / denitrification method of the present invention.

FIG. 6 is a graph showing the relationship between the total nitrogen removal rate and dissolved oxygen in an example of the nitrification / denitrification method of the present invention.

[Explanation of symbols]

 10 ... Nitrification / denitrification device 12 ... Inflow pipe 14 ... Nitrification / denitrification tank 16 ... Aeration pipe 18 ... Air reservoir 20 ... Diffusion plate 22 ... Dissolved oxygen meter 24 ... Control device 26 ... Blower 30 ... Valve 32 ... Carrier 34 ... Nitrogen Concentration meter 36 ... BOD meter 38 ... Addition device

Claims (4)

[Claims] 1. A nitrification / denitrification method for removing nitrogen components in wastewater, comprising dissolving the wastewater and a carrier in which at least nitrifying bacteria and denitrifying bacteria are co-immobilized and immobilized in the wastewater. Level is
Performing nitrification treatment of the ammonia nitrogen component in the waste water on the surface of the carrier by contacting in the state of 0.1 to 1.5 mg / l and performing denitrification treatment of the nitrate nitrogen component inside the carrier. Characterizing nitrification and denitrification method. 2. A ratio (C) of a nitrogen source N and a carbon source C in the wastewater.
/ N ratio) is set to 0.1 to 4, wherein the nitrification and denitrification method according to claim 1 is characterized. 3. A nitrification / denitrification device for removing nitrogen components in wastewater, comprising a single tank for contacting the wastewater with a carrier on which at least nitrifying bacteria and denitrifying bacteria are co-immobilized and immobilized. Nitrification
Denitrification tank, aeration means for aerating air to the wastewater in the nitrification / denitrification tank, measurement means for measuring dissolved oxygen in the wastewater in the nitrification / denitrification tank, and the aforesaid measurement value based on the measurement value of the measurement means The aeration amount of air from the aeration means is controlled so that the dissolved oxygen level in the wastewater is maintained at 0.1 to 1.5 mg / l to form an aerobic zone on the surface part of the carrier and at the same time inside the carrier. A nitrification / denitrification apparatus comprising: a control means for forming an anaerobic zone, and performing both nitrification treatment and denitrification treatment in the single nitrification / denitrification tank. 4. The nitrification / denitrification tank is provided with a nitrogen concentration meter for measuring nitrogen concentration in wastewater and a BOD meter for measuring organic matter concentration, and the nitrification / denitrification tank is based on the measured values of the nitrogen concentration meter and BOD meter. Ratio of nitrogen source N and carbon source C in the wastewater in the
The nitrification / denitrification apparatus according to claim 3, wherein the addition amount of the carbon source is controlled so that the ratio) becomes 0.1 to 4.