JPH1076263A - Sewage treatment apparatus using immersion type membrane separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable operation under a small aeration strength, to suppress foaming in a tank to enhance the concn. of MLSS and to achieve cost reduction. SOLUTION: An immersion type membrane separator 14 wherein a circulating system consisting of ascending and descending passages 4, 5 is formed in an immersion tank 1 and an air diffuser 6 is arranged to the lower part of the ascending passage 4 and a plurality of tubular membrane elements 15 are arranged on the way of the ascending passage 4 along the ascending passage 4 in up and down direction is provided and a stirrer 13 generating descending streams is provided to the upper part of the descending passage 5. By this constitution, the passage resistance caused by the membrane elements are sufficiently reduced and the flow speed of the ascending streams required in the washing of the surfaces of the membranes of the membrane elements can be obtained under small aeration strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a leachate treatment apparatus,
The present invention relates to a sewage treatment apparatus using an immersion type membrane separation apparatus used for an organic sewage treatment apparatus, an apparatus for removing dioxins in wastewater, and the like.

[0002]

2. Description of the Related Art Conventionally, for example, as a method for removing nitrogen and phosphorus from domestic wastewater, there is an activated sludge treatment method in which raw water is biologically treated in an anaerobic tank and an aerobic tank. In this activated sludge treatment method, in an anaerobic tank, a coagulant is added to raw water flowing from outside the system, sludge is returned from an aerobic tank in a subsequent process, and the mixed liquid in the tank is stirred, In the tank, the mixed solution flowing from the anaerobic tank is aerated with air from a diffuser, the mixed solution is circulated in the tank, and the mixed solution is filtered by a membrane separator immersed in the tank. The treated water that has passed through is discharged to the treated water tank.

[0003] A membrane separation device arranged in an aerobic tank is located above a diffuser and exposes the membrane surface to an upward flow of a gas-liquid mixed phase generated by aerated air. The mixture is filtered under a cross-flow method (circulation method) flowing parallel to the surface, and the upward flow serves as a scavenging flow to wash the film surface, thereby suppressing the adhesion of solids to the film surface.

[0004]

In the case of organic sewage in which the nutritional balance of nitrogen, phosphorus, and BOD is lost, the MLSS concentration is increased because foaming increases during aeration due to its properties. However, there was a problem that the BOD removal efficiency became unstable. The appropriate value of the nutritional balance is BOD: N: P = 100: 5: 1, but in the case of landfill leachate, BOD: N: P = 5: 5: 0.1, The appropriate MLSS concentration is 10,000 to 12,000 mg / l, but in the case of organic wastewater as described above, the MLSS
The concentration is between 2,000 and 4,000 mg / l.

[0005] In order to upward flow arising by aeration fulfill cleaning function of the solids content of the sludge adhering to the membrane surface, aeration intensity required for this washing is the rate-limiting, 10~12m ³ / m ³ /
Aeration of about hr is performed, which is several times the amount of oxygen required by microorganisms in the tank. For this,
Not only is foaming easy to occur, but also large blower equipment is required, resulting in high costs and running costs such as electricity costs.

The present invention has been made to solve the above-mentioned problems, and enables operation with a small aeration intensity, suppresses foaming in a tank, increases the MLSS concentration, and reduces the cost. An object of the present invention is to provide a sewage treatment apparatus using a type membrane separation device.

[0007]

In order to solve the above-mentioned problems, a sewage treatment apparatus using the immersion type membrane separation device of the present invention comprises an upward flow path and a downward flow path in an immersion tank. An in-tank circulation system was formed, an air diffuser was arranged below the upward flow path, and a plurality of tubular membrane elements were vertically arranged along the upward flow path in the middle of the upward flow path. An immersion type membrane separation device is provided, and a forced circulation means in a tank for generating a downward flow is provided above the downward flow channel.

With this configuration, in the immersion tank, the upward flow of the gas-liquid mixed phase is generated in the upward flow path by the aerated air supplied from the diffuser, and the downward flow path is formed by the forced circulation means in the tank. A downward flow occurs. As a result, the mixed liquid in the tank staying at the bottom of the immersion tank moves to the top of the tank through the upward flow path, and the mixed liquid in the tank at the top of the tank moves to the bottom of the tank through the downward flow path. The internal mixture circulates and moves in the circulation system in the tank.

In this state, the immersion type membrane separation apparatus filters the mixed solution in the tank flowing in the upward flow path, and the permeated liquid permeated through the membrane of the membrane element passes through the internal flow path of the membrane element and passes through the internal flow path of the membrane element. The water flows out of the tank through a treated water pipe communicating with the element. On the other hand, the upward flow flowing between the membrane elements becomes a scavenging flow to wash the membrane surface of each membrane element, thereby suppressing the adhesion of solids to the membrane surface.

At this time, since each of the membrane elements is arranged vertically along the upward flow path, the flow path resistance caused by the membrane element becomes sufficiently smaller than in the prior art, and the membrane surface of the membrane element is cleaned. Can be obtained under a small aeration intensity. In addition, since the upward flow flows along the axial direction of the membrane element, the sweeping action acts on the entire length of the membrane element, and the cleaning efficiency per unit power is improved.

By the way, if the amount of aerated air is adjusted in accordance with the required oxygen amount standard corresponding to the BOD concentration of the inflowing raw water, B
When the OD concentration is low, it becomes impossible to secure the circulation flow rate in the tank required for stirring and mixing or cross-flow filtration, but it depends on the amount of aerated air by generating a downward flow by forced circulation means in the tank. Thus, the circulation flow rate in the tank required for cross-flow filtration can be ensured, foaming can be suppressed, the MLSS concentration can be increased, and the BOD removal efficiency can be stabilized.

By using a stirrer as the forced circulation means in the tank, the circulating flow per unit power can be increased as compared with other equipment such as a pump, and equipment costs and power costs can be reduced.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3, the immersion tank 1 is
Raw water such as organic wastewater or leachate is led through the inflow pipe 2,
The immersion tank 1 forms a biological treatment tank for biological treatment with activated sludge. Inside the immersion tank 1, an in-tank circulation system including an upward flow path 4 and a downward flow path 5 partitioned by a partition wall 3. Are formed, and the upward flow path 4 is located radially around the downward flow path 5 located at the center of the tank. The forms of the upward flow path 4 and the downward flow path 5 are not limited to those described above, and the upward flow path 4 and the downward flow path 5 can be arranged in reverse. Various shapes such as a cylindrical shape, a fan shape, and a rectangular shape can be considered as the cross-sectional shape of the flow path.

An air diffuser 6 is disposed below the upward flow path 4, and the air diffuser 6 is connected to a blower 9 via an aerated air supply pipe 7 and a first valve 8. Also, blower 9
Is connected through a second valve 10 and a backwash air supply pipe 11 to a treated water pipe 12 described later. A stirrer 13 is disposed in the upper part of the downward flow path 5 as forced circulation means in the tank for generating a downward flow. It is also possible to use a device such as a pump as the forced circulation means in the tank.

In the middle of the upward flow path 4, the immersion type membrane separation device 1
4 are arranged. The immersion-type membrane separation device 14 is configured to arrange a plurality of tubular membrane elements 15 in the vertical direction along the upward flow path 4. 1
The internal flow path 6 communicates with each membrane element 15, and the membrane element 15 is connected and held by a connection plate 17 on the lower end side. The header 16 and the connecting plate 17 are formed with a water passage 18 through which the upward flow passes.

The header 16 has an internal flow path of the treated water pipe 12.
A third water supply pipe 21 communicates with a treated water pump 20 via a third valve 19, and a water supply pipe 21 connected to the treated water pump 20 communicates with a treated water tank 22. A backwash water system 23 is provided between the treated water tank 22 and the treated water pipe 12, and the backwash water system 23 has a backwash water pipe 24, a backwash pump 25, and a fourth valve 26. The surplus sludge discharge system 27 is connected to the bottom of the immersion tank 1, and the surplus sludge discharge system 27 has a fifth valve 28, a sludge extraction pipe 29, and a sludge pump 30.

The operation of the above configuration will be described below.
Inside the immersion tank 1, the upward flow of the gas-liquid mixed phase is generated inside the upward flow path 4 by the aerated air supplied from the diffuser 6, and the downward flow is caused inside the downward flow path 5 by the stirrer 13. Since a flow is generated, the mixed liquid in the tank stagnating at the bottom of the immersion tank 1 passes through the upward flow path 4, passes through the connecting plate 17 and the water passage 18 of the header 16, moves to the upper part of the tank, and moves to the upper part of the tank. The mixture in the tank moves to the bottom of the tank through the downward flow path 5, and the mixture in the tank circulates and moves in the circulation system in the tank. During this time, the mixture in the tank is biologically activated sludge treated.

In this state, the immersion type membrane separation device 14
Receives the suction pressure of the treated water pump 20 and filters the mixture in the tank flowing through the upward flow path 4. The membrane permeated liquid that has passed through the membrane of the membrane element 15 flows through the internal flow path of the membrane element 15 into the internal flow path of the header 16 and then flows through the header 16.
Through the treated water pipe 12, the third valve 19, the treated water pump 20, and the water supply pipe 21 to the treated water tank.

On the other hand, the upward flow flowing through the flow path between the membrane elements 15 becomes a sweeping flow to wash the membrane surface of each membrane element 15 to suppress the adhesion of solids to the membrane surface. At this time, since each of the membrane elements 15 is arranged in the up-down direction along the upward flow path 4, the flow path resistance caused by the membrane element 15 becomes sufficiently smaller than in the past, and the membrane surface of the membrane element 15 is reduced. The upward flow velocity required for cleaning can be obtained under a small aeration intensity. In addition, since the upward flow flows along the axial direction of the membrane element 15, the sweeping action acts on the entire length of the membrane element 15, and the cleaning efficiency per unit power is improved.

When the BOD concentration of the inflowing raw water is low, the circulation flow in the tank required for stirring and mixing and cross-flow filtration cannot be ensured. It is possible to secure the circulation flow rate in the tank required for cross-flow filtration without depending on the amount of air, suppress foaming, and increase the MLSS concentration to increase the BOD.
The removal efficiency can be stabilized. Moreover, the stirrer 1
3 can increase the circulating flow rate per unit power as compared with other devices such as a pump, and can reduce equipment costs and power costs.

[0021]

As described above, according to the present invention, by arranging each of the membrane elements vertically along the upward flow path, the flow path resistance caused by the membrane element can be sufficiently reduced, The upward flow velocity required for cleaning the membrane surface of the membrane element can be obtained with a small aeration intensity, and the upward sweeping action acts over the entire length of the membrane element, thereby improving the cleaning efficiency per unit power. . Since a downward flow is generated by the forced circulation means in the tank, the required circulation flow rate in the tank can be secured without depending on the amount of aerated air, suppressing foaming and increasing the MLSS concentration to stabilize the BOD removal efficiency. Can be In addition, a large circulation flow rate per unit power can be obtained by the stirrer, and equipment costs and power costs can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a sewage treatment apparatus using a submerged membrane separation device according to an embodiment of the present invention.

FIG. 2 is a view as viewed in the direction of arrows AA in FIG. 1;

FIG. 3 is a cross-sectional view of the immersion type membrane separation device in the embodiment.

[Explanation of symbols]

 Reference Signs List 1 immersion tank 4 upward flow path 5 downward flow path 6 air diffuser 12 treated water pipeline 13 stirrer 14 immersion type membrane separation device 15 membrane element 16 header 18 water passage section

Claims (2)

[Claims] 1. An in-tank circulation system comprising an upward flow path and a downward flow path is formed in an immersion tank, and an air diffuser is disposed below the upward flow path. A immersion type membrane separation device in which a plurality of tubular membrane elements are arranged vertically along an upward flow path is provided, and an in-tank forced circulation means for generating a downward flow is provided above a downward flow path. A sewage treatment apparatus using a submerged membrane separation apparatus. 2. A sewage treatment apparatus using an immersion type membrane separation device according to claim 1, wherein the forced circulation in the tank comprises a stirrer having rotating blades.