JP2000312898A - Waste water treatment apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrifying soln. circulating type waste water treatment apparatus and method capable of performing nitrification and denitrification reaction efficiently and capable of also preventing the contamination of a membrane surface. SOLUTION: A waste water treatment apparatus is equipped with a denitrification tank 1 receiving waste water containing org. nitrogen to decompose nitrate nitrogen in waste water by denitrifying bacteria, a nitrification tank 2 oxidizing ammonia nitrogen in waste water to nitrate nitrogen by nitrifying bacteria, a pump 6 for returning the treated soln. in the nitrification tank to the denitrification tank to circulate the same, an immersion flat membrane device 3 filtering a clarified component from the treated soln. in the nitrification tank to discharge the same out of the tank, an air diffusion pipe 4 supplying air to the immersion flat membrane device 3, an aeration system consisting of a blower 7 and an air venting valve 8, a dissolved oxygen meter 5 for measuring the amt. of dissolved oxygen in the nitrification tank 2 and a control device 10 adjusting aeration air quantity so as to hold the amt. of dissolved oxygen in the nitrication tank to a predetermined range while ensuring air quantity necessary for washing the membrane surface of the immersion flat membrane device 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment apparatus and method for biologically treating wastewater containing organic nitrogen such as domestic wastewater and human waste, and more particularly to wastewater treatment using a nitrification liquid circulation denitrification system. Apparatus and method.

[0002]

2. Description of the Related Art As a method for treating wastewater containing organic nitrogen, there is known a treatment method in which organic nitrogen in wastewater is reduced to nitrogen gas using a biological nitrification and denitrification reaction. I have. As a processing facility for performing this type of processing method, a technique disclosed in Japanese Patent No. 25559513 is known.

According to this technique, a nitrification tank for performing a nitrification reaction is disposed downstream of a denitrification tank for performing a denitrification reaction, and a circulating means for returning a part of the activated sludge mixed liquid in the nitrification tank to the denitrification tank. An ultrafiltration membrane device that is installed in the tank and discharges treated water permeated from the mixed solution to the outside of the system, and is installed below the ultrafiltration membrane device, per 1 m ² of the membrane surface of the ultrafiltration membrane device 0.2Nm ³
/ H or more.

[0004] The denitrification reaction in the denitrification tank is carried out in an oxygen-free state in which the concentration of dissolved oxygen is almost zero, while the nitrification reaction in the nitrification tank is carried out under aerobic conditions in which the concentration of dissolved oxygen is at least a certain level. In this technology, the film surface is cleaned by the ascending flow formed by the aeration supplied by using the aeration of the mixed solution in the nitrification tank, so that it is not necessary to separately perform the film surface cleaning, and simple equipment can be used. It is described that efficient nitrification and denitrification can be performed.

[0005]

However, in this technique, since only the lower limit of the aeration amount is specified,
If the amount of aeration is insufficient, the nitrification reaction of ammonia nitrogen does not proceed as expected, and the quality of treated water deteriorates. Conversely, if the aeration amount is increased too much, a large amount of oxygen will dissolve into the mixture, and when a part of the mixture is transferred to the denitrification tank by the circulation means, the inside of the denitrification tank will not be in an oxygen-free state, and the denitrification reaction will not occur. There is a risk of stopping.

Accordingly, an object of the present invention is to provide a nitrification liquid circulating wastewater treatment apparatus and method capable of efficiently performing a nitrification / denitrification reaction and preventing contamination of a membrane surface.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, a wastewater treatment apparatus according to the present invention is a wastewater treatment apparatus for biologically treating wastewater containing organic nitrogen. And (2) a denitrification tank connected to a denitrification tank for decomposing nitrate nitrogen in wastewater by denitrifying bacteria, and oxidizing ammonia nitrogen in wastewater to nitrate nitrogen by nitrifying bacteria. A nitrification tank, and (3) a circulating means for returning the treatment liquid in the nitrification tank to the denitrification tank and circulating the treatment liquid;
(4) an immersion flat membrane device that is immersed and arranged in a nitrification tank, filters a clarified substance from the treatment liquid in the nitrification tank, and discharges the clarified substance out of the tank.
(5) An aeration device arranged below the immersion flat membrane device in the nitrification tank and supplying air toward the immersion flat membrane device, and (6) an aeration device arranged in the nitrification tank to measure the amount of dissolved oxygen in the treatment liquid. A dissolved oxygen meter, and (7) aeration by an aeration device so that the amount of dissolved oxygen in the nitrification tank measured by the dissolved oxygen meter is maintained within a predetermined range while securing the air volume necessary for cleaning the membrane surface of the immersion flat membrane device. And a control device for adjusting the air volume.

On the other hand, the wastewater treatment method according to the present invention
(1) The wastewater is introduced into a denitrification tank, and the nitric acid nitrogen in the wastewater is decomposed by denitrification bacteria. (2) After the denitrification step, the wastewater is led to a nitrification tank, and aeration is performed from an aeration device. A nitrification step of oxidizing ammonia nitrogen in wastewater to nitrate nitrogen by nitrifying bacteria, and (3) a circulation step of circulating the treatment liquid by returning the treatment liquid in the nitrification tank to the denitrification tank. (4) a filtration step of filtering a clarified component from the treatment liquid in the nitrification tank and discharging the filtered liquid out of the tank using an immersion flat membrane device immersed and arranged in the nitrification tank. While measuring the amount of dissolved oxygen in the nitrification tank with a dissolved oxygen meter while securing the amount of air necessary for cleaning the membrane surface of the immersion flat membrane device, the amount of aerated air by the aeration device so that the measured value is maintained within a predetermined range. Is adjusted.

In the wastewater treatment apparatus and method according to the present invention, since the aeration amount is adjusted so that the dissolved oxygen amount in the nitrification tank falls within a predetermined range, the nitrification does not occur due to overaeration or insufficient aeration. Both the nitrification reaction in the tank and the denitrification reaction in the denitrification tank can be performed efficiently. Since the aeration amount secures an air volume required for cleaning, efficient film surface cleaning can be performed. The aeration amount is not constant by the aeration amount adjustment, but fluctuates with time. However, the circulating flow formed in the nitrification tank also fluctuates due to the variation in the air volume, so that the cleaning of the membrane surface is further promoted, which is preferable.

This aeration apparatus has a blower capable of adjusting a supply air flow rate by controlling a rotation speed, and an opening provided on an air vent line connecting an aeration supply line from the blower to a nitrification tank and the atmosphere. An adjustable air vent valve is provided, and the control device preferably adjusts the amount of aeration air supplied to the nitrification tank by adjusting the rotation speed of the blower and the opening of the air vent valve.

In general, a blower has a limited discharge air volume range that can be adjusted by controlling the number of revolutions, and it is difficult to sufficiently reduce the minimum discharge air volume. By using it together with the air vent valve, it becomes possible to adjust the aeration air volume from 0 to the maximum air volume in a stepless manner.

[0012]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG.
BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the whole structure of the nitrification liquid circulation type wastewater treatment apparatus which concerns on this invention.

As shown in FIG. 1, this apparatus has a structure in which a denitrification tank 1 and a nitrification tank 2 each storing activated sludge are adjacent to each other with a barrier 1a interposed therebetween. In the nitrification tank 2, there is provided an immersion flat membrane device 3 in which immersion flat membranes are arranged with their membrane surfaces oriented vertically. A diffuser 4 is arranged below the immersion flat membrane device 3. In the liquid phase of the nitrification tank 2, a dissolved oxygen meter (DO sensor) 5 for measuring the amount of dissolved oxygen in the liquid phase is arranged.

A line L1 for supplying wastewater to be treated is connected to the denitrification tank 1, and a line L2 having a pump 6 for returning the wastewater from the nitrification tank 2 to the denitrification tank 1 between the nitrification tank 2 and the denitrification tank 1. Are provided to constitute the circulation means. The air diffuser 4 has a blower 7, an air release valve 8, and a flow meter 9.
Are connected to form an aeration system. The output of the DO sensor 5 and the flow meter 9 is sent, and a control device 10 for controlling the blower 7 and the opening valve 8 is provided. On the other hand, the immersion flat membrane device 3 is connected to a line L4 for discharging treated water that is filtered clear water.

Next, the operation of this embodiment, that is, the wastewater treatment method according to the present invention will be described in detail with reference to FIGS. FIG. 2 is a flowchart illustrating the operation of the aeration system.

The wastewater containing the organic nitrogen to be treated is first supplied to the denitrification tank 1 via the line L1.
Is mixed with the activated sludge inside. The denitrification tank 1 is maintained in a so-called anoxic state in which dissolved oxygen is insufficient. In this anoxic state, nitric nitrogen is reduced to nitrogen gas by denitrifying bacteria in activated sludge and released to the atmosphere. Is done. Part of the mixed solution in the denitrification tank 1 overflows over the barrier 1a and flows out to the nitrification tank 2.

In the nitrification tank 2, a line L3
Aeration is performed by sending air to the air diffuser 4 through the air. By this aeration, the amount of dissolved oxygen in the nitrification tank 2 is kept constant, and aerobic conditions are maintained.
The activated sludge attached to the membrane surface of the ultrafiltration membrane of the immersion flat membrane device 3 is washed by the circulating flow formed by the air lift of the aeration.

Here, the control operation of the aeration amount will be specifically described with reference to FIG. The control device 10 measures the dissolved oxygen amount (DO value) measured by the DO sensor 5, and determines in step S1 whether the value has changed to a predetermined value or more. If the fluctuation is within the predetermined value, the DO value is kept constant and the control operation of the aeration system is not performed.

If the DO value has increased to a predetermined value or more, it is determined that an over-aeration state has occurred, and the process proceeds to step S2. Here, the rotation speed of the blower 7 is compared with its control minimum value. If the current rotational speed of the blower 7 exceeds the control minimum value, the process proceeds to step S3, and the amount of air discharged from the blower 7 is suppressed by reducing the rotational speed of the blower 7. On the other hand, when the current rotation speed of the blower 7 is the control minimum value, it is determined that suppression of the discharge air volume by operating the rotation speed of the blower 7 is impossible, and the process proceeds to step S4, where the air release valve 8 is operated. By opening the valve a little, part of the air discharged from the blower 7 escapes to the atmosphere,
The amount of air sent to the air diffuser 4, that is, the amount of aeration is reduced.

When the adjustment of the aeration amount is completed, step S5
, The aeration amount measured by the flow meter 9 and the immersion flat membrane device 3
Is compared with the required amount of aeration, which is the amount of aeration required for cleaning.
The required washing amount is, for example, 0.1 mm per unit area of the flat membrane.
9 m ³ / m ² h. If the amount of aeration is equal to or greater than the required amount of cleaning, the adjustment process is terminated. If the amount of aeration does not reach the required amount of cleaning, the blower 7 is adjusted so that the required amount of cleaning becomes the amount of aeration.
And the opening degree of the air vent valve 8 are adjusted.

On the other hand, if the DO value has decreased to a predetermined value or less in step S1, the control device 10 determines that the aeration is insufficient and shifts to step S7. In step S7, it is checked whether or not the opening of the air release valve 8 is fully closed. And when it is fully closed, the blower 7
It is determined that the aeration amount adjustment by the rotation speed adjustment is necessary, and the process proceeds to step S8 to increase the rotation speed of the blower 7 and thereby increase the aeration amount from the air diffuser 4. On the other hand, if the air release valve 8 is not fully closed, it is determined that the adjustment of the aeration amount by operating the air release valve 8 should precede the adjustment of the rotation speed of the blower 7, and the process proceeds to step S9 to close the air release valve 8 slightly. This reduces the amount of air leaking from the air vent valve 8 and increases the amount of aeration from the air diffuser 4.

By repeating steps S1 to S9, the amount of aeration required for cleaning the membrane surface of the immersion flat membrane apparatus 3 can be secured while the DO value in the nitrification tank 2 is kept constant in principle. is there.

In the nitrification tank 2 in which the DO value is maintained in a constant state and kept in an aerobic state, the nitrifying bacteria in the activated sludge oxidize the ammonia nitrogen in the waste water to nitrate nitrogen. Decomposed. Since the DO value is kept constant, the nitrification reaction can be performed efficiently. A part of the waste water containing the decomposed nitrate nitrogen is returned by the pump 6 to the denitrification tank 1 via the line L2. As described above, in the denitrification tank 1, nitrate nitrogen is reduced and removed, so that ammonia nitrogen contained in the wastewater is also removed by the nitrification and denitrification reaction. At this time, since the amount of aeration is adjusted so that the inside of the nitrification tank 2 does not become over-aerated, it is possible to suppress the amount of oxygen brought into the denitrification tank 1 and maintain the oxygen-free state in the denitrification tank 1. Thus, the denitrification reaction in the denitrification tank 1 can be efficiently performed.

The clarified water separated from the mixed waste water and activated sludge in the nitrification tank 2 by the ultrafiltration membrane of the immersion flat membrane device 3 installed in the nitrification tank 2 is substantially free of organic nitrogen. It is discharged out of the system via the line L4. Here, since the amount of aeration air required for cleaning the membrane surface is always secured, the activated sludge does not adhere to the membrane surface, and the filtration treatment is suitably performed. Furthermore, since the circulation flow itself formed in the nitrification tank 2 also fluctuates due to the fluctuation of the aeration air flow by the aeration air flow control, more effective membrane surface cleaning can be performed, and oxygen can be efficiently supplied to the entire nitrification tank 2. It can be supplied, it is easy to keep the dissolved oxygen amount distribution in the nitrification tank 2 uniform, and the nitrification reaction can be performed more efficiently.

In the above description, the denitrification tank 1 and the nitrification tank 2 are adjacent to each other, and the apparatus configuration for guiding the mixed solution overflowing in the denitrification tank 1 to the nitrification tank 2 has been described. A configuration may be adopted in which the mixed liquid is guided from the denitrification tank to the nitrification tank by piping or the like.

The control flow for the DO control is merely an example, and a method of finely adjusting the flow rate using a correspondence map between the blower rotation speed, the valve opening, and the aeration flow rate may be adopted. Various air supply systems other than the combination of the blower and the valve can be used.

[0027]

As described above, according to the present invention, in a wastewater treatment apparatus and method for treating organic nitrogen of a nitrification liquid circulation type, the present invention is applicable to cleaning of the surface of an immersion flat membrane apparatus installed in a nitrification tank. Since the required amount of aeration is controlled so that the amount of dissolved oxygen in the nitrification tank is maintained within a predetermined range, the nitrification reaction in the nitrification tank is efficiently performed, and the denitrification tank is The denitrification reaction can be performed efficiently by suppressing the amount of oxygen brought into the tank and maintaining the oxygen-free state of the denitrification tank. In addition, the cleaning of the flat film surface can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the entire configuration of a wastewater treatment device according to the present invention.

FIG. 2 is a flowchart showing a control operation of an aeration system in the apparatus of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Denitrification tank, 2 ... Nitrification tank, 3 ... Immersion flat membrane device, 4 ... Air diffuser, 5 ... DO sensor, 6 ... Pump, 7 ... Blower, 8 ... Air vent valve, 9 ... Air flow meter, 10 ... Control device.

Claims (4)

[Claims] 1. A wastewater treatment device for biologically treating wastewater containing organic nitrogen, wherein the wastewater is introduced, and a denitrification tank for decomposing nitrate nitrogen in the wastewater with denitrifying bacteria; A nitrification tank connected to the denitrification tank and oxidizing ammonia nitrogen in the wastewater to nitrate nitrogen by nitrifying bacteria; and returning the treatment liquid in the nitrification tank to the denitrification tank and circulating the treatment liquid. A circulating means to be immersed in the nitrification tank; an immersion flat membrane device for filtering clarified matter from the treatment liquid in the nitrification tank and discharging the filtered effluent to the outside of the tank; An aeration device arranged to supply air toward the immersion flat membrane device; a dissolved oxygen meter arranged in the nitrification tank to measure the amount of dissolved oxygen in the processing solution; and a membrane surface of the immersion flat membrane device While ensuring the air volume required for cleaning, the dissolved oxygen meter Waste water treatment apparatus, wherein a dissolved oxygen content of the measured nitrification tank is provided with a control device for adjusting the aeration amount by the aeration device to be maintained within a predetermined range. 2. The aeration apparatus is provided on a blower capable of adjusting a supply air flow rate by controlling a rotation speed, and on an air vent line connecting an aeration supply line from the blower to the nitrification tank and the atmosphere. The control device adjusts the amount of aeration air supplied to the nitrification tank by adjusting the number of rotations of the blower and the opening of the air release valve. The wastewater treatment device according to claim 1, wherein: 3. A wastewater treatment method for biologically treating wastewater containing organic nitrogen, comprising introducing the wastewater into a denitrification tank and decomposing nitrate nitrogen in the wastewater with denitrifying bacteria. A nitrification step; after the denitrification step, the wastewater is guided to a nitrification tank, and a nitrification step of oxidizing ammonia nitrogen in the wastewater to nitrate nitrogen by nitrifying bacteria while performing aeration from an aerator. A circulating step of returning the treatment liquid in the tank to the denitrification tank and circulating the treatment liquid, and filtering a clarified component from the treatment liquid in the nitrification tank by an immersion flat membrane device immersed in the nitrification tank. And a filtration step of discharging the outside of the tank.The aeration by the aeration apparatus is performed by reducing the amount of dissolved oxygen in the nitrification tank while securing an air flow required for cleaning the membrane surface of the immersion flat membrane apparatus. Measure with a dissolved oxygen meter and keep the measured value within a predetermined range. Waste water treatment method characterized by aeration air volume is adjusted by the aerator to be. 4. The aeration apparatus is provided on a blower capable of adjusting a supply air volume by controlling a rotation speed, and on an air vent line connecting an aeration supply line from the blower to the nitrification tank and the atmosphere. Air vent valve with adjustable opening,
4. The wastewater treatment method according to claim 3, wherein the adjustment of the aeration air amount is performed by adjusting a rotation speed of the blower and an opening of the air vent valve. 5.