JP2011194305A - Membrane-separation activated sludge treatment method and apparatus for sewage - Google Patents

Abstract

In a membrane separation activated sludge method and apparatus, the amount of air required for cleaning an immersion membrane unit installed in a membrane separation tank is reduced, thereby reducing costs and saving energy.
A biological reaction tank 1 and a membrane separation tank 2 in which a submerged membrane unit 3 is immersed are provided separately, sealed in a state where a gas phase is formed in an upper space 17 of the biological reaction tank 1, and an upper space 17 And the aeration pipe 4 for washing the immersion membrane unit installed below the immersion membrane unit 3 immersed in the membrane separation tank 2 are connected by a pipe 16, and the off-gas of the air blown into the biological reaction tank 1 is immersed in the immersion membrane unit. Used for cleaning.
[Selection] Figure 2

Description

  The present invention reduces the amount of air for cleaning the submerged membrane unit installed in a state where it is immersed in the membrane separation tank, which is installed separately from the biological reaction tank, thereby reducing costs and saving energy. The present invention relates to a method and an apparatus for treating activated sludge with membrane separation of sewage.

  As a wastewater treatment method that purifies industrial wastewater, domestic wastewater, sewage, and other sewage to obtain high-quality treated water and can reduce the size of the equipment, the "membrane separation activated sludge method" (hereinafter referred to as "MBR") ) And its devices have attracted attention in recent years.

On the other hand, the conventional activated sludge treatment method and apparatus is an aeration tank (hereinafter referred to as an aeration tank) for bringing sewage and activated sludge into mixed contact while blowing air and oxidatively degrading and purifying pollutants such as organic substances by biochemical reaction. And a sedimentation tank for separating the mixed liquid of activated sludge and treated water flowing out of this biological reaction tank into treated water and precipitated sludge by means of solid-liquid separation by natural sedimentation. It is composed of
By the way, in the conventional activated sludge treatment method, since there is a limit to the solid-liquid separation ability by precipitation, the activated sludge concentration (hereinafter referred to as “MLSS concentration”) that can be held in the biological reaction tank is naturally limited. In general, the MLSS concentration is generally operated in the range of 2,000 to 3,000 mg / L.

  On the other hand, in MBR, by performing suction filtration with a pump through a submerged membrane unit installed in a state of being immersed in a biological reaction tank, compared to solid-liquid separation by conventional precipitation, Since the MLSS concentration in the reaction vessel can be maintained at about 8,000 to 12,000 mg / L, the MLSS concentration in the biological reaction vessel can be kept constant if the organic load that can be taken with respect to the amount of activated sludge in the biological reaction vessel is constant. As a result, the entire apparatus including the biological reaction tank can be made extremely compact.

  In this MBR, it is known to use a hollow fiber-shaped or flat membrane-shaped microfiltration membrane (MF membrane) having a surface pore diameter in the range of about 0.1 to 0.4 μm for the separation of the activated sludge mixed liquid. It has become. A system in which these membranes are integrated to increase the area and unitized so that the immersed membrane unit is immersed in a biological reaction tank or membrane separation tank, and the membrane is continuously filtered by pump suction to obtain treated water. Is known. Such a method is called “tank immersion type MBR”.

When the activated sludge mixture is continuously membrane-filtered, finer activated sludge particles and polymer substances that are metabolites of activated sludge accumulate on the surface of the membrane, resulting in a filtration resistance layer called a gel layer. As a result, the filtration pressure rises rapidly.
In order to prevent the formation of this gel layer, as disclosed in Patent Literature 1 and Patent Literature 2, air from the blower is continuously installed below the immersion membrane unit from below the immersion membrane unit. The method of preventing by blowing through an apparatus is used as a known method. Such an operation is called air bubbling or air scrubbing and is a kind of physical cleaning method of the membrane.
The effect of this operation is that the relatively coarse bubbles rise along the membrane surface, thereby continuously peeling the gel layer formed on the membrane surface due to the shear effect of the bubble entrained upward flow formed. The main reason is that the film is shaken by the accompanying upward flow.

In order to continue the membrane filtration stably while favorably preventing the formation of the gel layer, an air amount of a certain amount or more is required. Non-Patent Document 1 discloses a hollow fiber MF immersion membrane unit. As an example of the required air amount in this case, it is shown that 0.2 m 3 / m 2 membrane area / hour or more is necessary.
The above required air amount is the same or more than the amount of air required for the decomposition of organic matter by activated sludge in the biological reaction tank and the nitrification of ammonia nitrogen, and a blower is separately provided for the biological reaction tank. This increases the energy consumption necessary for the operation of the blower, and this increases the installation cost and the operation cost of the MBR device, which is a factor that hinders the spread of MBR.

Japanese Patent Application Laid-Open No. 08-131783 JP-A-11-104670

Ishiyama, 2009 Symposium on Freshwater Technology, February 2009, p. 9

  An object of the present invention is to reduce the amount of air necessary for cleaning the submerged membrane unit, reduce the number of necessary blowers, and reduce the MBR device cost and the operating cost, thereby reducing the MBR and the wastewater treatment field of the device. The purpose is to further promote dissemination in the future.

  In order to solve the above-mentioned problems, in the present invention, a membrane separation tank installed in a state where a biological reaction tank and an immersion membrane unit are immersed is separated and installed (hereinafter referred to as “membrane separation tank separate type MBR”). The upper space of the biological reaction tank is sealed so as to form a gas phase, and the upper space of the biological reaction tank is connected to the air diffuser installed below the submerged membrane unit in the membrane separation tank by a pipe. The off-gas of air blown into the biological reaction tank was used for air cleaning of the submerged membrane unit.

  More specifically, the sewage membrane separation activated sludge treatment method of the present invention is a biological reaction in which sewage containing pollutants such as organic matter is brought into contact with activated sludge and reacted under aerobic conditions in which dissolved oxygen exists. A membrane separation activated sludge treatment method in which a tank and a membrane separation tank for separating activated sludge and treated water are installed separately, with a gas phase part formed in the upper space of the biological reaction tank The gas phase part is connected to the diffuser pipe installed below the submerged membrane unit in a state immersed in the membrane separation tank with a pipe, and the off-gas of the air blown into the biological reaction tank Is supplied to the diffuser pipe through the pipe and used for air cleaning of the submerged membrane unit.

  Further, the membrane separation activated sludge treatment apparatus of the present invention is a biological reaction tank in which sewage containing pollutants such as organic matter is brought into contact with activated sludge and reacted under aerobic conditions in which dissolved oxygen exists, A membrane separation activated sludge treatment device in which a sludge and a membrane separation tank for separating treated water are installed separately, sealed in a state where a gas phase portion is formed in the upper space of the biological reaction tank, The gas phase portion and a diffuser pipe installed below the submerged membrane unit installed in a state of being immersed in the membrane separation tank are connected by a pipe, and the off-gas of air blown into the biological reaction tank is connected to the pipe. It is characterized in that it is supplied to the diffusing tube through.

  In this case, the air pipe from the aeration blower to the biological reaction tank is branched and connected to the pipe connecting the gas phase part of the biological reaction tank and the diffuser pipe installed below the submerged membrane unit immersed in the membrane separation tank. The branched air branch pipe is provided with pressure adjusting means, and is connected to a pipe connecting the upper space of the biological reaction tank and the diffuser pipe installed below the submerged membrane unit immersed in the membrane separation tank. The air pipe from the aeration blower to the diffuser pipe of the biological reaction tank is provided with a check valve, and an air flow rate adjusting means controlled by a sensor installed in the liquid phase part of the biological reaction tank and a regulator based on the signal thereof Can be provided.

As an effect of the present invention, it is possible to reduce the number of required blowers in the membrane separation tank separate type MBR, and to reduce the apparatus cost.
Furthermore, since the energy required for the blower operation can be reduced, the operation cost can be reduced and the energy can be saved.

  In addition, by branching the air tube from the aeration blower to the biological reaction tank and supplying the air from the aeration blower to the aeration tube, it is possible to stabilize the membrane filtration while preventing the formation of the gel layer of the submerged membrane unit. Can continue.

It is a figure which shows the structure of the conventional membrane separation tank separate type | mold MBR apparatus. It is a figure which shows the 1st Example of this invention. It is a figure which shows the 2nd Example of this invention.

  Hereinafter, the content of the present invention will be described in more detail based on the drawings.

FIG. 1 is a diagram showing the configuration of a conventional membrane separation tank separate MBR apparatus.
This apparatus is composed of a biological reaction tank 1 and a membrane separation tank 2, and a diffuser 5 for injecting air into the biological reaction tank 1 for dissolving / supplying oxygen necessary for the biological reaction is installed. ing.
The air diffuser 5 is connected to a biological reaction tank aeration blower 6 by piping.
An immersion membrane unit 3 is immersed in the membrane separation tank 2, and the biological reaction tank mixed liquid transferred from the biological reaction tank 1 is subjected to suction membrane filtration with a membrane filtration pump 9 to obtain membrane filtration treated water. It is configured.
The activated sludge mixed liquid concentrated in the membrane separation tank 2 is returned to the biological reaction tank 1 by the return sludge pump 8.
Below the immersion membrane unit 3, a diffuser tube 4 is installed as a diffuser for cleaning the immersion membrane unit, and is connected to a blower 7 for cleaning the immersion membrane unit by piping.
In addition, although not shown in FIG. 1, the means for discharging | emitting the excess activated sludge which increases with decomposing | disassembling organic substance etc. out of an apparatus is provided separately.

FIG. 2 is a diagram showing a first embodiment of the present invention.
In the present embodiment, the diffuser as a diffuser for cleaning the submerged membrane unit, which is hermetically sealed so as to form a gas phase portion in the upper space 17 of the biological reaction tank 1 and installed in the upper space 17 and the membrane separation tank 2. The trachea 4 is connected by a pipe 16, and the submerged membrane unit 3 is air-washed by an off-gas of air blown into the biological reaction tank 1.

  In the present embodiment, the blower 7 for cleaning the submerged membrane unit, which is essential for the conventional membrane separation tank separate MBR apparatus shown in FIG. 1, is not required.

In this embodiment, only about 20% of the oxygen in the air blown into the biological reaction tank 1 is consumed, so oxygen is contained in the off-gas that stays in the gas phase part of the upper space 17 of the biological reaction tank 1. Even when this off-gas is introduced into the membrane separation tank 2 for cleaning the submerged membrane unit 3, the liquid phase part in the membrane separation tank 2 is in an oxygen-deficient state. There is no.
Further, since the solubility of air mainly composed of nitrogen and oxygen is low, the amount of air reduced in the biological reaction tank 1 is extremely small. Therefore, the amount of off-gas generated in the biological reaction tank 1 may be considered to be substantially the same as the amount of air blown into the biological reaction tank 1.

Here, the amount of air discharged from the blower 6 in this embodiment is determined as follows.
When the amount of air necessary for the biological reaction is larger than the amount of air necessary for cleaning the submerged membrane unit 3, the amount is determined based on the amount of air necessary for the biological reaction.
Conversely, if the amount of air required for cleaning the submerged membrane unit 3 is greater than the amount of air required for biological reaction, it will exceed the respective amount based on the amount of air required for cleaning the submerged membrane unit 3. To decide.

  The discharge pressure of the blower 6 in the present embodiment is such that the water level of the diffuser 5 for the biological reaction tank, the water level of the diffuser pipe 4 as the diffuser for cleaning the submerged membrane unit in the membrane separation tank 2, and the respective diffusers It shall be greater than the sum of pressure loss and pressure loss in the air piping. The discharge pressure of the blower 6 is preferably 70 kPa or more.

  In this embodiment, a biological reaction tank mixed liquid transfer flow rate adjusting mechanism for controlling the transfer flow rate of the biological reaction tank mixed liquid almost constant in the middle of the piping from the biological reaction tank 1 to the membrane separation tank 2. 18 is provided.

FIG. 3 is a diagram showing a second embodiment of the present invention.
In this embodiment, an air flow rate adjusting valve 12 is provided in the middle of an air pipe between the blower 6 for aeration of the biological reaction tank and the diffuser 5 for the biological reaction tank.
The air flow rate control valve 12 is opened and closed via a controller 11 in response to a signal from a sensor 10 installed in the biological reaction tank 1. The sensor 10 is a dissolved oxygen concentration (DO) sensor or an oxidation-reduction potential (ORP) sensor, and a biological reaction is performed via the air flow rate control valve 12 in accordance with the concentration of organic matter in the raw water so that these values are constant. The air flow rate to the tank 1 is controlled.

  Excess air is branched from the air pipe between the blower 6 for aeration of the biological reaction tank and the diffusion device 5 for the biological reaction tank, and the diffusion space for cleaning the upper space 17 of the biological reaction tank 1 and the submerged membrane unit. It is used as air for washing the immersion membrane unit through the air branch pipe 15 connected to the pipe 16 connecting the air diffusion pipe 4 as the above, while favorably preventing the formation of the gel layer of the immersion membrane unit 3, Membrane filtration can be continued stably.

  In the middle of the air branch pipe 15 branched from the air pipe between the bioreactor aeration blower 6 and the bioreactor diffuser 5, a pressure regulating valve 13 is connected to the upper space 17 of the bioreactor 1. A check valve 14 is provided in the middle of the pipe 16 connecting the diffuser pipe 4 as the diffuser for cleaning the submerged membrane unit, and air from the air branch pipe 15 to the pipe 16 due to pressure imbalance is provided. I try to prevent backflow.

  In the present embodiment, the biological reaction tank mixed liquid transfer flow rate adjusting mechanism 18 for controlling the transfer flow rate of the biological reaction tank mixed liquid almost constant in the middle of the piping from the biological reaction tank 1 to the membrane separation tank 2. Is the same as in the first embodiment.

  The examples shown in FIGS. 2 and 3 show a part of the embodiments of the present invention, and the embodiments of the present invention are not necessarily limited to these embodiments without departing from the gist of the present invention.

  The membrane separation activated sludge method and apparatus of the present invention are newly installed because a simple mechanism can reduce the amount of air required for cleaning the submerged membrane unit installed in the membrane separation tank, thereby reducing costs and saving energy. The present invention can be widely applied to the existing MBR apparatus with separate membrane separation tanks as well as the existing MBR apparatus with separate membrane separation tanks.

DESCRIPTION OF SYMBOLS 1 Biological reaction tank 2 Membrane separation tank 3 Immersion membrane unit 4 Air diffuser (Aeration device for washing immersion membrane unit)
5 Aeration device for biological reaction tank 6 Blower for aeration of biological reaction tank 7 Blower for washing submerged membrane unit 8 Return sludge pump 9 Membrane filtration pump 10 Sensor installed in biological reaction tank 11 Controller 12 Air flow control valve 13 Pressure control valve 14 Check valve 15 Air branch pipe from the blower for aeration of the biological reaction tank 16 Pipe connecting the upper space of the biological reaction tank and the diffuser for cleaning the submerged membrane unit 17 Upper space of the biological reaction tank 18 Biological reaction Tank mixture liquid flow rate adjustment mechanism

Claims (3)

  Separately install a bioreactor that reacts sewage containing organic matter and other contaminants with activated sludge under aerobic conditions where dissolved oxygen is present, and a membrane separation tank that separates activated sludge and treated water It is a membrane separation activated sludge treatment method designed to be installed in a state where a gas phase portion is formed in the upper space of the biological reaction tank and sealed, and immersed in the gas phase portion and the membrane separation tank. Connect the diffuser pipe installed below the installed immersion membrane unit with a pipe, and supply the offgas of the air blown into the biological reaction tank to the diffuser pipe through the pipe for air cleaning of the immersion membrane unit. A membrane separation activated sludge treatment method of sewage characterized by being used.   Separately install a bioreactor that reacts sewage containing organic matter and other contaminants with activated sludge under aerobic conditions where dissolved oxygen is present, and a membrane separation tank that separates activated sludge and treated water It is a membrane separation activated sludge treatment device designed to be installed, sealed in a state where a gas phase part is formed in the upper space of the biological reaction tank, and immersed in the gas phase part and the membrane separation tank A diffuser pipe installed below the installed immersion membrane unit is connected by a pipe, and the off-gas of the air blown into the biological reaction tank is supplied to the diffuser pipe through the pipe. Membrane separation activated sludge treatment equipment for sewage.   The air pipe from the aeration blower to the biological reaction tank is branched and connected to the pipe connecting the gas phase part of the biological reaction tank and the diffuser pipe installed below the submerged membrane unit immersed in the membrane separation tank. The branched air branch pipe is provided with pressure adjusting means, and a check valve is provided in a pipe connecting the upper space of the biological reaction tank and the diffuser pipe installed below the submerged membrane unit immersed in the membrane separation tank. The air piping from the aeration blower to the diffuser pipe of the biological reaction tank is provided with air flow rate adjusting means controlled by a sensor installed in the liquid phase part of the biological reaction tank and a regulator based on the signal. The membrane separation activated sludge treatment apparatus of sewage according to claim 2 characterized by things.

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