JPH1043794A - Nitrogen removing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrogen removing device capable of holding a microorganism immobilizing carrier used in a fluid state in a tank and also easy in maintenance and administration. SOLUTION: A nitrifying bacterium immobilizing carrier 12 is charged in an aerobic tank 11, and an air diffuser 13 generating a circulating flow 17 in the tank is provided, and a screen 16 surrounding an outlet 14 of a nitrified water 19 is provided. The screen 16 is provided in parallel with a diagonal stream formed between each stream at a place at which the circulating flow 17 in the tank is converted from a horizontal stream to a downward stream. In this way, the carrier 12 is surely held in the tank, and also an accumulation.holding of the carrier 12 on the screen 16 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen removing apparatus for biologically treating wastewater such as sewage and industrial wastewater to remove organic substances such as BOD and nitrogen.

[0002]

2. Description of the Related Art Conventionally, sewage such as sewage and industrial wastewater is led to an anoxic tank for denitrification and subsequently to an aerobic tank for nitrification.
A portion of the nitrification-treated water flowing out of the aerobic tank is circulated and returned to the anoxic tank, and the remaining nitrification-treated water is treated by the flow sent to the final sedimentation basin.
Components and nitric acid or nitrite nitrogen are removed by a denitrification reaction, and in an aerobic tank, Kjeldahl nitrogen including ammonia nitrogen is nitrified to nitric acid or nitrite. This process is called a circulating nitrification and denitrification method, and it is a conventional general technique to use suspended activated sludge.

[0003] A multi-stage type in which the nitrogen removal rate is improved by using a plurality of combinations of an anoxic tank and an aerobic tank in the anaerobic / anoxic / aerobic method utilizing the above-mentioned principle or the above-mentioned circulating nitrification / denitrification method. Circulating nitrification and denitrification method.

[0004]

Generally, when nitrogen is removed from sewage or other sewage as part of the eutrophication prevention of public water bodies, the above-mentioned circulating nitrification and denitrification method using floating activated sludge is used. ing. However, since the total hydraulic residence time in the anoxic tank and the aerobic tank in this method requires as much as 12 to 16 hours on the basis of the amount of inflowed sewage, the standard activated sludge method is adopted, and the residence time in the aeration tank is reduced. 6-8
At existing sewage treatment plants in large and middle urban areas that are designed and operated as time, it is actually difficult to adopt a new circulating nitrification denitrification method because it is difficult to secure land. Similarly, it is difficult to adopt the anaerobic / anoxic / aerobic method and the multi-stage circulating nitrification / denitrification method.

For this reason, in order to increase the nitrification rate by maintaining a high concentration of nitrifying bacteria whose nitrification activity decreases at a low water temperature in a tank, the application of an immobilization technique for immobilizing the nitrifying bacteria on a carrier has been studied. Has been transformed. In such a method, since the carrier is generally used in a fluidized state, it is necessary to install a carrier separation device to keep the carrier from flowing out of the tank,
There is a need for a carrier separation device that exhibits a function stably without blocking.

As one of the means, in the biological nitrogen removing apparatus proposed by the inventors of the present application, a stationary zone for separating the carrier is provided in communication with the lower part of the nitrification tank,
The nitrification treatment water in the nitrification tank flows into the stationary zone from the lower part and flows out from the upper part of the stationary zone. In this apparatus, the cross-sectional area of the stationary zone is designed so that the rising speed of the nitrification treatment water in the stationary zone is smaller than the minimum value of the gravitational sedimentation speed of the carrier. It returns to the inside of the nitrification tank to prevent it from flowing out of the nitrification tank. However, the amount of sewage flowing into the sewage treatment plant fluctuates greatly over time. In the carrier separating means of the system, there is a possibility that the carrier may flow out when the inflow amount increases rapidly.

[0007] On the other hand, a mechanical pump is generally used to circulate the nitrification-treated water to the oxygen-free tank. However, the mechanical pump is clogged with fibers or dust contained in sewage such as sewage. In order to facilitate the maintenance and to reduce the power cost associated with the operation of the pump, there is a demand for a circulating means that is easy to maintain and inexpensive to maintain.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a nitrogen removing apparatus which can hold a microorganism-immobilized carrier used in a fluidized state in a tank and which can be easily maintained. is there.

[0009]

In order to solve the above problems, a nitrogen removing apparatus according to claim 1 of the present invention is characterized in that a nitrifying bacteria-immobilized carrier is charged into an aerobic tank and air or an oxygen-containing gas is introduced. In the nitrogen removal device equipped with a diffuser that generates a circulating water flow in the tank consisting of an upward flow, a horizontal flow, and a downward flow by ejecting water, the outflow portion where the nitrification-treated water in the aerobic tank flows out Surrounding the carrier separation means, the carrier separation means, at a position near the water surface where the circulating water flow in the tank turns from a horizontal flow to a downward flow, a separation surface is formed between the horizontal flow and the downward flow It is provided so as to be substantially parallel to the oblique flow.

[0010] The nitrogen removing apparatus according to claim 2 is provided with an oxygen-free tank for circulating a part of the nitrification-treated water treated in the aerobic tank, and is connected to a permeate side of the carrier separating means in the aerobic tank. A downward flow path is provided, and an upward flow path is provided in which the lower end communicates with the downward flow path and the upper end communicates with the anoxic tank.At the bottom of the upward flow path, the nitrification-treated water in the upward flow path is air-lifted. It is provided with an air diffusing device that sends it out to the anoxic tank by the action.

According to the first aspect of the present invention, the carrier is securely held in the tank by the carrier separating means, and the carrier flows in the direction along the separation surface of the carrier separating means. A large amount of the carrier is not accumulated and retained, and the passage of the nitrification-treated water in the tank through the carrier separating means is not hindered. In an apparatus configured so that the nitrification-treated water overflows outside the tank, a carrier separating means may be provided around the overflow section, and such an apparatus can cope with a rapid increase in the inflow amount.

As the carrier separating means, any screen or punching plate may be used as long as it has a mesh width or a hole smaller than the carrier size.
It is desirable to install a screen having a small eye width so that the bar faces up and down.

The inclination angle of the separating surface of the carrier separating means is set as follows. In FIG. 6, the gravitational sedimentation velocity v (m / s) of the carrier and the separation surface
The effective area of the separation surface (simply submerged) A (m ² ), the angle θ between the separation surface and the vertical direction
(Degree), the amount of water passing through the separation surface Q (m ³ / s).

In this case, the amount of passing water per unit area of the separation surface, that is, the flow velocity of the passing water is Q / A (m /
s), and the flow velocity component in the direction perpendicular to the separation surface is (Q /
A) × cos θ (m / s). The gravitational sedimentation velocity component of the carrier in the direction perpendicular to the separation surface is v × sin θ (m
/ S).

Here, the condition for preventing the carrier from adhering to the separation surface or closing the separation surface is that the flow velocity component in the direction perpendicular to the separation surface ≦ the gravity sedimentation velocity component of the carrier in the direction perpendicular to the separation surface. It is true. That is, the following equation (1) holds true for the maximum value of Q / A.

(Q / A) × cos θ ≦ v × sin θ (1) For example, when the maximum value of Q / A is 0.0167 (m / s), the sample carrier is a 3 mm square polyvinyl folder. In the case of Marle carrier, since v = 0.029 (m / s),
From Expression (1), the minimum value of θ is determined to be 30 degrees.
When the test was actually performed at θ = 30 degrees, the carrier did not adhere to the separation surface and no clogging occurred. Even when the carrier was attached, the carrier was peeled off by the flow parallel to the separation surface. From these facts, it is understood that it is sufficient to provide the carrier separating means as described above.

According to the second aspect of the present invention, since the nitrified water is circulated by the air-lifting action of the air bubbles ejected from the air diffuser, the blockage occurs when a mechanical pump is used for circulation. The maintenance and management is easy, and the circulation flow rate can be easily controlled.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, an aerobic tank 11 for performing nitrification treatment is configured such that water to be treated such as an oxygen-free tank mixed liquid flows in the front side of the drawing and flows in a direction penetrating the drawing. The slopes facing each other are formed along the flow direction.

A nitrifying bacteria-immobilized carrier 12 having a specific gravity greater than that of water is charged into the tank, and a diffuser 13 is provided over the entire bottom surface.
And the outlet 14 is located at a position near the wall on the downstream side in the flow direction.
A screen 16 is provided so as to surround the outflow port 14 and to extend from above the water surface of the aerobic tank mixed liquid 15 to an appropriate position below the water surface along the flow direction of the water to be treated.

The screen 16 is composed of a plurality of bars arranged at an interval of about 1/2 of the carrier size.
A separation surface is formed between the horizontal flow and the downward flow at a position slightly closer to the wall than the position where the in-tank circulating water flow 17 formed by the air ejected from the horizontal direction changes from the horizontal flow to the downward flow. The bar is provided so as to be substantially parallel to the oblique flow, and each bar is oriented vertically.

According to the above-mentioned structure, the nitrifying bacteria-immobilized carrier 12 flows by the circulating water flow 17 in the tank, and the nitrifying bacteria immobilized on the carrier are efficiently mixed with the substance to be treated and the air supplied by the air diffuser 13. The substance to be treated is nitrified by good contact.

At this time, most of the nitrifying bacteria-immobilized carrier 12 flows near the screen 16 with the oblique flow parallel to the screen 16, so that a large amount of the nitrifying bacteria-immobilized carrier 12 accumulates on the screen 16.・ It will not be retained,
When it adheres to the screen 16, it is also peeled off by the oblique flow.

For this reason, the nitrifying bacteria-immobilized carrier 12 is securely held in the tank, so that nitrification is efficiently performed.
The nitrification-treated water 19 passes through the screen 16 without being hindered by the nitrifying bacteria-immobilized carrier 12, and flows out of the tank through the outlet 14.

The aerobic tank 11 shown in FIG. 2 has substantially the same configuration as the aerobic tank shown in FIG. 1, and a diffuser 13 is disposed over the entire bottom surface in the tank. However, the outlets 14 are provided at positions closer to both walls, respectively.
The screen 16 is installed along the flow direction of the water to be treated. The angle of inclination of each screen 16 and the direction of the bar are the same as those shown in FIG.

According to this configuration, similarly to the aerobic tank shown in FIG.
The two screens 16 and the two outlets 14 can surely hold the inside of the tank without being held, and can cope with a sudden increase in the inflow of the water to be treated.

The aerobic tank 11 shown in FIG. 3 has substantially the same structure as that of the aerobic tank shown in FIG. , So that the circulating water flow 1 in the tank as shown in the figure.
7 is formed. The inclination angle of the screen 16 and the direction of the bar are the same as those shown in FIG. According to this configuration, the same effect as in the aerobic tank shown in FIG. 1 can be obtained.

The aerobic tank 11 shown in FIG. 4 has substantially the same configuration as the aerobic tank shown in FIG. 1, but has an outlet 14 at the center in the width direction of the tank and surrounds the outlet 14. And two screens 16 are installed along the flow direction of the water to be treated.
Further, the air diffusers 13 are respectively arranged at positions near the two walls along the flow direction of the water to be treated, and the circulating water flow 17 in the tank as shown in the figure is formed. The angle of inclination of each screen 16 and the direction of the bar are the same as those shown in FIG. According to this configuration, the same effect as in the aerobic tank shown in FIG. 1 can be obtained.

FIG. 5 shows a nitrogen removing apparatus for performing a circulating nitrification denitrification method provided with an oxygen-free tank for circulating a part of the nitrification treatment water treated in the aerobic tank. An anoxic tank 21 and an aerobic tank 22 are provided separately from each other by a partition wall 23.
Is mixed with an oxygen-free tank mixture 25 containing activated sludge mainly containing denitrifying bacteria in a tank by introducing raw water 24,
Is introduced from the anoxic tank 21 to mix the anoxic tank mixed liquid 25 with the floating activated sludge mainly composed of nitrifying bacteria in the tank and the aerobic tank mixed liquid 27 containing the nitrifying bacteria immobilizing carrier 26.

An overflow section 23a and an overflow section 23b are formed at the upper edge of the partition wall 23, and the oxygen-free tank mixed liquid 25 in the oxygen-free tank 21 is surrounded by the overflow section 23a. A tubular mixed solution inflow passage 28 is provided to the bottom of the inside 22, and a nitrification treatment water circulation passage 30 which circulates the nitrification treatment water 29 treated in the aerobic tank 22 into the anoxic tank 21, surrounding the overflow 23 b. Is provided.

The anoxic tank 21 is provided at its bottom with a stirrer 31 for stirring the anoxic tank mixture 25. The aerobic tank 22 is provided with an air diffuser 32 substantially at the center of the bottom surface, and a screen 33 at the edge facing the mixed liquid inflow passage 28 from the upstream end to the downstream end. The screen 33 has a diagonal flow formed between the horizontal flow and the downward flow at a position closer to the wall than the position where the in-tank circulating water flow 34 formed by the air diffuser 32 turns from the horizontal flow to the downward flow. It is provided from an upper part of the water surface to an appropriate position below the water surface so as to be substantially parallel to.

A downward flow path 35 communicating with the permeation side of the screen 33 to circulate a part of the nitrified water 29 permeated through the screen 33 to the anoxic tank 21, and the remaining nitrified water 29 And a treated water flow path 36 through which the water flows out of the apparatus. An upward flow path 37 having a lower end communicating with the downward flow path 35 and an upper end connected to the overflow section 23b is provided. The nitrification treatment water 29 in the flow path is provided at the bottom of the upward flow path 37. Is provided to the nitrification-treated water circulation path 30 by an air lift function.

The operation of the above configuration will be described below.
The raw water 24 flows into the anoxic tank 21 and is mixed with the anoxic tank mixture 25 in the tank. The anoxic tank mixed liquid 25 is biologically agitated by the agitator 31 by denitrifying bacteria and the like in the floating activated sludge. Is processed. Anoxic tank mixture 25
Flows into the aerobic tank 22 through the mixed liquid inflow path 28 and is mixed with the aerobic tank mixed liquid 27.
And biologically treated with nitrifying bacteria immobilized in the floating activated sludge or on the carrier 26.

At this time, as described above, the circulating water flow
The screen 33 is placed at a position closer to the wall than the position at which the horizontal flow changes from the horizontal flow to the downward flow, so that the screen 33 is substantially parallel to the oblique flow formed between the horizontal flow and the downward flow. The nitrifying bacteria-immobilized carrier 26 is surely held in the tank without being accumulated and held on the screen 33. Therefore, the nitrifying bacteria concentration in the tank is kept high, and nitrification is performed effectively.

A portion of the nitrified water 29 that has passed through the screen 33 without being hindered by the nitrifying bacteria-immobilized carrier 26 flows into the downward flow path 35, and the remaining nitrified water 29
Flows out from the treated water flow path 36 as treated water 39 to a final sedimentation basin or the like outside the apparatus.

The nitrified water 29 flowing into the downward flow passage 35
Flows from the lower part into the upward flow path 37, but due to the air lift effect of the air ejected from the air diffuser 38 provided at the bottom of the partial flow path of the nitrification water 29 in the upward flow path 37. Ascending and flowing into the nitrification-treated water circulation path 30, the nitrification-treated water 29 in the downward flow path 35 is operated by the pump function at that time.
Descends.

In this way, the amount of circulating nitrified water 29 is independently controlled by the air diffuser 38, and since there is no narrow flow path, the circulating pump is used to circulate the nitrified water. There is no blockage and maintenance is easy.

In addition, in addition to the above-described nitrogen removing device having an oxygen-free tank and an aerobic tank, a combination of an oxygen-free tank and an aerobic tank is provided in multiple stages to perform a circulating nitrification denitrification. The same effect as described above can be obtained by installing a screen in the same manner as described above in an apparatus or a nitrogen removing apparatus having an anaerobic tank for removing phosphorus in a stage preceding the oxygen-free and aerobic tank. can get. In this case, as described with reference to FIGS. 1 to 4, the screen may be installed at an appropriate position according to the specific gravity of the nitrifying bacteria-immobilized carrier, the position of the outflow portion, the position of the air diffuser, and the like.

[0038]

As described above, according to the present invention, the carrier for immobilizing nitrifying bacteria is placed in the tank by providing a carrier separating means at an appropriate position in the aerobic tank so as to be substantially parallel to the circulating water flow in the tank. In addition to being able to securely hold the nitrifying bacteria-immobilized carrier on the separation surface of the carrier separating means, the nitrifying bacteria-immobilized carrier can be prevented from being accumulated and retained, and the nitrification-treated water can pass through the carrier separating means smoothly.

By performing the circulation of the nitrification water by the pump function of the air diffuser, the blockage of the pump as in the case of performing the circulation of the nitrification water using a mechanical pump is eliminated, and the maintenance and management is facilitated. The circulation flow rate of the nitrification water can be easily controlled.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic overall configuration of an aerobic tank according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic overall configuration of an aerobic tank according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing a schematic overall configuration of an aerobic tank according to a third embodiment of the present invention.

FIG. 4 is a sectional view showing a schematic overall configuration of an aerobic tank according to a fourth embodiment of the present invention.

FIG. 5 is a perspective view showing an overall configuration of a nitrogen removing device including an anoxic tank and an aerobic tank according to a fifth embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating setting of an inclination angle of a carrier separating means provided in an aerobic tank.

[Explanation of symbols]

 11 Aerobic tank 12 Carrier for immobilizing nitrifying bacteria 13 Air diffuser 14 Outlet 16 Screen 17 Circulating water flow in tank 21 Oxygen tank 22 Aerobic tank 26 Carrier for immobilizing nitrifying bacteria 29 Nitrified water 32 Air diffuser 33 Screen 34 tank Internal circulating water flow 35 Downflow channel 37 Upflow channel 38 Air diffuser

Claims (2)

[Claims] 1. A nitrifying bacteria-immobilized carrier is charged into an aerobic tank, and air or oxygen-containing gas is ejected to generate a circulating water flow in the tank consisting of an upward flow, a horizontal flow, and a downward flow. In the nitrogen removing device provided with an aeration device, a carrier separating means is provided around the outflow portion of the aerobic tank through which the nitrification-treated water flows out, and the carrier separating means reduces the circulating water flow in the tank from a horizontal flow. A nitrogen removal device, wherein a separation surface is provided at a position near a water surface that turns into a countercurrent so as to be substantially parallel to an oblique flow formed between a horizontal flow and a downward flow. 2. An oxygen-free tank for circulating a part of the nitrification treatment water treated in the aerobic tank, and a downward flow path communicating with the permeate side of the carrier separating means in the aerobic tank is provided. An upward flow path is provided in which the lower end side communicates with the flow path and the upper end side communicates with the oxygen-free tank. At the bottom of the upward flow path, the nitrification treatment water in the upward flow path is directed toward the oxygen-free tank by an air lift action. The nitrogen removing device according to claim 1, further comprising an air diffuser for sending out.