JP2001212587A - Method and apparatus for diffusing air of membrane separation activated sludge method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply sufficient oxygen without damaging the membrane surface washing effect due to coarse air bubbles and accompanied by the diffusion of an excessive amount of air. SOLUTION: A predetermined amount of air is divided to be supplied to first and second air diffusers 8, 9 and a first aeration zone L3 is formed by fine air bubbles A diffused from the first air diffuser 8 arranged under an immersion type membrane separation apparatus 3 and a second aeration zone L2 is formed by coarse air bubbles B diffused from the second air diffuser 9 arranged above the first air diffuser 8 and finer air bubbles A diffused from the first air diffuser 8 and oxygen is supplied to the activated sludge mixed liquid in a tank with high dissolving efficiency by the independent aeration due to fine air bubbles A in the first aeration zone L3 and oxygen is supplied by the mixing aeration of coarse air bubbles B and fine air bubbles A in the second aeration zone L3 and the ascending streams of a gas-liquid mixed phase generated by the air lift action of coarse bubbles B and fine air bubbles A are allowed to act on the membrane surface of the immersion type membrane separation apparatus 3 as sweeping streams.

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 diffusing activated sludge by a membrane separation activated sludge method, and more particularly to a technique for treating an organic sludge using an immersion type membrane separation apparatus. It is related to.

[0002]

2. Description of the Related Art Conventionally, there is an activated sludge treatment as a method for treating organic wastewater, and there is a membrane separation activated sludge treatment for maintaining a high concentration of activated sludge in a tank by using a membrane separation device.

[0003] In a general membrane separation activated sludge method, an immersion type membrane separation device is installed in a reaction tank, an air diffuser is arranged below the immersion type membrane separation device, and air diffused from the air diffuser is provided. Activated sludge treatment is performed by supplying oxygen, and the upward flow generated by the air lift action of air is swept to the membrane surface of the immersion type membrane separation device to act, and the cake attached to the membrane surface is continuously washed. ing.

[0004] In the air diffuser, a porous tube having an air diffuser having a hole diameter of 6 to 13 mm is used in order to generate large bubbles having a high membrane surface cleaning effect.

[0005]

However, a perforated tube-type air diffuser which prioritizes the effect of cleaning the membrane surface may have a low oxygen dissolving efficiency and an insufficient oxygen supply capability. For this reason, in order to supply oxygen sufficiently, it is necessary to diffuse an excessive amount of air more than the air volume required for cleaning the film surface, which leads to an increase in aeration power.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and can supply a sufficient amount of oxygen without impairing the effect of cleaning the film surface by coarse bubbles and without causing excessive air volume. An object of the present invention is to provide an air diffusion method and an air diffusion device for the membrane separation activated sludge method.

[0007]

In order to solve the above-mentioned problems, according to the first aspect of the present invention, there is provided a method for diffusing air by a membrane separation activated sludge method, comprising the steps of: Is supplied separately to a first air diffuser and a second air diffuser, and a first aeration zone is formed by fine air bubbles diffused from the first air diffuser disposed below the immersion type membrane separation device. A second aeration zone is formed by coarse air bubbles diffused from the second air diffuser arranged above the first air diffuser and fine air bubbles diffused from the first air diffuser; Oxygen is supplied to the activated sludge mixed liquid in the tank with high dissolving efficiency by single aeration by air bubbles, and oxygen is supplied by mixed aeration of coarse and fine bubbles in the second aeration zone, and air lift action of coarse and fine bubbles The upward flow of gas-liquid mixed phase caused by It is intended to act on the membrane surface of the submerged membrane separator in.

According to a second aspect of the present invention, in the method of the present invention, the amount of air supplied as coarse bubbles and the amount of air supplied as fine bubbles when a predetermined amount of air is aerated in the reaction tank. Is adjusted according to the properties of the target sludge flowing into the reaction tank.

According to a third aspect of the present invention, there is provided a membrane separation activated sludge method according to the present invention, in which air supplied as fine bubbles is quantitatively supplied to secure a minimum dissolved oxygen concentration required for activated sludge treatment. The amount of air supplied as air bubbles is adjusted according to the properties of the target sludge flowing into the reaction tank.

According to a fourth aspect of the present invention, in the method of the present invention, air supplied as coarse bubbles is quantitatively supplied to secure a minimum amount of air necessary for cleaning the membrane surface. Is adjusted according to the dissolved oxygen concentration.

According to a fifth aspect of the present invention, there is provided a diffuser for a membrane separation activated sludge method according to the present invention, wherein a submerged membrane separator is disposed in a reaction tank, and fine bubbles are diffused below the submerged membrane separator. An air diffuser and a second air diffuser that diffuses coarse bubbles are arranged, and a predetermined amount of air that diffuses into the reaction tank is separately supplied to the first air diffuser and the second air diffuser. Means are provided.

According to a sixth aspect of the present invention, in the diffuser of the membrane separation activated sludge method according to the present invention, an upper second diffuser is disposed at a predetermined distance above the first diffuser disposed below. It was done. In the diffuser of the membrane separation activated sludge method of the present invention according to claim 7, the first diffuser has small diffuser holes having a predetermined diameter, and fine bubbles ejected from the small diffuser holes have a predetermined oxygen dissolving efficiency. The second air diffuser has a large air diffusion hole having a predetermined diameter larger than the small air diffusion hole, and coarse air bubbles ejected from the large air diffusion hole have a bubble diameter satisfying a predetermined membrane surface cleaning effect. .

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a sewage supply system 2 for supplying organic sewage is connected to a reaction tank 1, and the immersion type membrane separation device 3 is placed in the reaction tank 1 under a predetermined water depth (500 to 150).
0 mm) L1.

In the immersion type membrane separation device 3, a plurality of flat membrane cartridges 4 are arranged in a case 5 along a vertical direction, and the flat membrane cartridges 4 are arranged in parallel with a predetermined gap therebetween. It is arranged between the adjacent flat membrane cartridges 4 and forms a flow passage through which the activated sludge mixed liquid in the tank flows in a cross flow.

The case 5 is divided into an upper membrane case 6 for accommodating the flat membrane cartridge 4 and a lower air diffusion case 7. The air diffusion case 7 has a first air diffusion device 8 and a second air diffusion device 8 therein. The air diffusers 9 are arranged in two stages, upper and lower, so that the entire amount of air ejected from the first air diffuser 8 and the second air diffuser 9 enters the membrane case 6. The membrane cartridge 4 is AB
Filtration membranes are arranged on both surfaces of a filter plate made of S resin, and a permeate flow path formed in the filter plate is communicated with a permeate outlet pipe 10.

The lower first diffuser 8 is disposed at a predetermined distance (0 to 300 mm) L4 from the bottom of the reaction tank 1, and the upper second diffuser 9 is disposed at a predetermined distance from the first diffuser 8. (3
00-800 mm) is located above L3 and is a predetermined distance (500-800 mm) below the immersion type membrane separation device 3.
The first diffuser 8 diffuses fine bubbles, and the second diffuser 9 diffuses coarse bubbles. Blowers 11 and 12 are individually connected to the air diffusers 8 and 9, and each of the blowers 11 and 12 controls a predetermined amount of air blown into the reaction tank 1 by controlling the driving thereof to adjust the amount of air. Is supplied separately to the first air diffuser 8 and the second air diffuser 9.

The predetermined amount of air is determined by the amount of air necessary for cleaning the membrane surface of the membrane cartridge 4 of the immersion type membrane separation device 3.
It can satisfy both the amount of air required to supply the amount of oxygen required for the activated sludge treatment in the tank, and differs depending on the properties of the inflowing target wastewater.

The first air diffuser 8 has small air holes having a predetermined diameter, and the fine bubbles A ejected from the small air holes have a bubble diameter satisfying a predetermined oxygen dissolving efficiency (for example, 0.5 to 2 m at the ejection port).
m), the second diffuser 9 has large diffuser holes having a predetermined diameter larger than the small diffuser holes, and the coarse and large bubbles B ejected from the large diffuser holes have a bubble diameter satisfying a predetermined membrane surface cleaning effect (for example, a discharge port). 0.8 to 20 mm).

The operation of the above configuration will be described. By driving the blowers 11 and 12, a predetermined amount of air (25 to 40 times the amount of treated water) is supplied to the first diffuser 8 and the second diffuser 9.
And supplied to the lower region of the immersion type membrane separation device 3,
A first aeration zone L3 is formed by the fine bubbles A diffused from the first diffuser 8, and the coarse bubbles B diffused from the second diffuser 9 and the fine bubbles A of the first diffuser 8 form the first aeration zone L3. 2
An aeration zone L2 is formed.

In the first aeration zone L3, the gas-liquid contact area per unit air to be diffused is increased by solely aeration with the fine bubbles A, so that the activated sludge mixed liquid in the tank has a high dissolving efficiency. To supply oxygen.

In the second aeration zone L2, the coarse bubbles B and the fine bubbles A are mixed and aerated, and oxygen is supplied to the activated sludge mixture in the tank while the large bubbles B and the fine bubbles A repeatedly merge and re-separate. The upward flow of the gas-liquid mixed phase generated by the air-lifting action of the coarse bubbles B and the fine bubbles A flows into the flow path between the adjacent plate-shaped membrane cartridges 4, and the activated sludge mixed solution is subjected to cross-flow immersion type membrane separation. The liquid is supplied to the apparatus 3 and is subjected to solid-liquid separation. The upward flow acts on the membrane surface of the immersion type membrane separation apparatus 3 as a scavenging flow.

At this time, both the coarse bubbles B and the fine bubbles A contribute to the cleaning, but the coarse bubbles B are particularly effective against the film surface contaminants (cake layer) when ascending the flow path between the film surfaces. High resistance, causing turbulence on the film surface to enhance the cleaning effect.

Further, when the entire amount of the coarse bubbles B and the fine bubbles A enters the membrane case 6, an upward flow generated inside the immersion type membrane separation device 3 and a downward flow generated around the immersion type membrane separation device 3. And the reaction tank 1
A circulating flow occurs without any trouble inside the tank, and the stirring in the tank can be performed smoothly.

Incidentally, the amount of oxygen necessary for treating the target sludge with activated sludge varies depending on the season or the water temperature. Therefore, when a predetermined amount (total aeration air amount) of air is aerated in the reaction tank 1, the supply ratio of the amount of air supplied as the coarse bubbles B and the amount of air supplied as the fine bubbles A is set to the target sludge flowing into the reaction tank 1. Adjust according to the properties of

For example, at a high water temperature at which the oxygen consumption increases, the air amount of the fine bubbles A is increased and the air amount of the coarse bubbles B is reduced. Conversely, when the oxygen consumption is low and the water temperature is low, the amount of air in the coarse bubbles B is increased, and the amount of air in the fine bubbles A is reduced.

As a result, the total amount of aerated air can always be minimized, and the aeration power of the blowers 11 and 12 can be reduced. Further, in a state where the air supplied as the fine bubbles A is supplied in a fixed amount to secure the minimum dissolved oxygen concentration necessary for the activated sludge treatment, the amount of air supplied as the coarse bubbles B is adjusted for the target sludge flowing into the reaction tank 1. It can be adjusted according to the properties.

In addition, the air supplied as the coarse bubbles B is supplied in a fixed amount to secure the minimum amount of air necessary for cleaning the film surface.
It is also possible to adjust the amount of air supplied as the fine bubbles A according to the concentration of dissolved oxygen.

[0028]

As described above, according to the present invention, oxygen is supplied under high dissolving efficiency in the first aeration zone in which single aeration using fine bubbles is performed, and mixed aeration of coarse bubbles and fine bubbles is performed. (2) While supplying oxygen in the aeration zone, the entire upward flow of the gas-liquid mixed phase generated by the air-lifting action of the coarse bubbles and the fine bubbles is made to act on the membrane surface of the immersion type membrane separation device as a scavenging stream, so that Sufficient oxygen can be supplied into the reaction tank without impairing the membrane surface cleaning effect and without excessive air volume.
Also, when a predetermined amount (total aeration air volume) of air is aerated in the reaction tank, the supply ratio of the amount of air supplied as coarse bubbles to the amount of air supplied as fine bubbles depends on the properties of the target sludge flowing into the reaction tank. By making the adjustment, the total amount of the aerated air can always be minimized, and the aeration power can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a wastewater treatment apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reaction tank 2 sewage supply system 3 immersion type membrane separation device 4 flat membrane cartridge 5 case 6 membrane case 7 air diffusion case 8 first air diffusion device 9 second air diffusion device 10 permeated liquid outlet pipes 11, 12 blowers

Claims (7)

[Claims] In a reaction tank provided with an immersion type membrane separation device, a predetermined amount of air is separately supplied to a first air diffusion device and a second air diffusion device, and disposed below the immersion type membrane separation device. First
A first aeration zone is formed by fine bubbles diffused from the diffuser, and coarse bubbles diffused from the second diffuser and fine particles diffused from the first diffuser disposed above the first diffuser. The second aeration zone is formed by air bubbles, oxygen is supplied to the activated sludge mixture in the tank with high dissolution efficiency by single aeration using fine air bubbles in the first aeration zone, and coarse air bubbles and fine air bubbles are generated in the second aeration zone. Membrane separation activity characterized in that oxygen is supplied by mixing and aeration, and the upward flow of a gas-liquid mixed phase generated by the air-lift action of coarse and fine bubbles acts as a sweep on the membrane surface of the immersion type membrane separation device. Aeration method of the sludge method. 2. When a predetermined amount of air is aerated in the reaction tank, the supply ratio of the amount of air supplied as coarse bubbles to the amount of air supplied as fine bubbles is adjusted according to the properties of the target sludge flowing into the reaction tank. The method according to claim 1, wherein the activated sludge is aerated. 3. A fixed amount of air required for activated sludge treatment is ensured by quantitatively supplying air supplied as fine bubbles, and the amount of air supplied as coarse bubbles is determined according to the properties of the target sludge flowing into the reaction tank. The air diffusion method of the membrane separation activated sludge method according to claim 1, wherein the method is adjusted in accordance with the method. 4. The method according to claim 1, wherein a minimum amount of air necessary for membrane surface cleaning is secured by supplying a constant amount of air supplied as coarse bubbles, and the amount of air supplied as fine bubbles is adjusted according to the concentration of dissolved oxygen. The aeration method of the membrane separation activated sludge method according to claim 1. 5. A immersion type membrane separator in a reaction tank, wherein a first air diffuser for diffusing fine bubbles below the immersion type membrane separator and a second air diffuser for diffusing coarse bubbles. And a means for separately supplying a predetermined amount of air diffused into the reaction tank to the first diffuser and the second diffuser, wherein the diffuser of the membrane separation activated sludge method is provided. apparatus. 6. The activated activated sludge method according to claim 5, wherein an upper second diffuser is disposed at a predetermined distance above the first diffuser disposed at a lower position. Diffuser. 7. The first air diffuser has small air diffusers having a predetermined diameter, and the fine bubbles ejected from the small air diffusers have a bubble diameter satisfying a predetermined oxygen dissolving efficiency, and the second air diffuser has a small air diffuser. The membrane separation activated sludge according to claim 5 or 6, having a large diffuser hole having a larger predetermined diameter, and wherein coarse bubbles ejected from the large diffuser hole have a bubble diameter satisfying a predetermined membrane surface cleaning effect. Law diffuser.