KR101633827B1 - Method and apparatus for membrane cleaning with bio-gas purging - Google Patents

Abstract

The present invention relates to a separation membrane cleaning method and apparatus using biogas capable of simultaneously inducing a physical cleaning effect and a chemical cleaning effect by cleaning a separation membrane using biogas and preventing damage of the separation membrane, the membrane washing method using a gas is injected into the phase and the carbon dioxide (CO ₂₎ the biogas contain preparing a biogas containing carbon dioxide (CO ₂₎ generated in the anaerobic digestion process in the membrane the step of washing the separation membrane In the step of cleaning the separation membrane, physical cleaning by biasing of the biogas and chemical cleaning by carbon dioxide in the biogas proceeds.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for cleaning a membrane using biogas,

The present invention relates to a separation membrane cleaning method and apparatus using biogas. More particularly, the present invention relates to a separation membrane cleaning method and apparatus for separating membrane by biogas, And more particularly, to a method and apparatus for cleaning a membrane using a gas.

Separation membranes are widely used in various water treatment processes. As the permeation water and permeation time are increased, the pollution degree of the membrane is drastically increased due to the membrane pollutants such as scale, protein and microorganisms existing in the water system, Becomes inevitable. Accordingly, the membrane should be cleaned or replaced at regular intervals.

There are physical cleaning methods and chemical cleaning methods as cleaning methods of membranes which are mainly used at present. Physical cleaning methods include air purging, flushing, and reverse filtration. The air cleaning is a method of removing contaminants on the surface of the separation membrane by using the fluctuation generated when the air is injected, and the flushing is a method of removing contaminants using raw water, and the backwashing is performed in the opposite direction of the raw water supply, To remove contaminants.

On the other hand, the chemical cleaning method is a method of chemically decomposing and removing contaminants attached to the surface of a separation membrane by using a cleaning liquid containing an acid, a base, a surfactant, and a disinfectant. However, the cleaning liquid used in the chemical cleaning method is used only in a limited case due to the problem of causing damage to the separation membrane. Further, in the case of the chemical cleaning method, there is a problem that the cost of using the cleaning liquid increases and the operation of the separation membrane must be stopped during the cleaning process.

In addition, although a method of using a physical cleaning method and a chemical cleaning method in combination has been proposed (see Korean Patent No. 1010858), the problems of the chemical cleaning method can not be avoided because the respective methods are applied in a time-wise manner.

Korean Patent No. 1010858

Disclosure of the Invention The present invention has been devised to solve the problems as described above, and it is an object of the present invention to provide a biogas-based separation membrane cleaning method capable of simultaneously inducing a physical cleaning effect and a chemical cleaning effect, A method and an apparatus are provided.

Membrane cleaning method using a bio gas according to the present invention for achieving the above object is a bio includes the step and the carbon dioxide (CO ₂₎ to prepare a biogas containing carbon dioxide (CO ₂₎ generated in the anaerobic digestion process And cleaning the separation membrane by injecting gas into the separation membrane. In the step of cleaning the separation membrane, physical cleaning by biasing of the gas is performed and chemical cleaning by carbon dioxide in the biogas proceeds .

The content of carbon dioxide (CO ₂ ) in the biogas containing the carbon dioxide (CO ₂ ) is 20 vol% or more. Also, in the step of washing the separation membrane, the injection rate of the biogas is 0.2 to 1.5 m ³ biogas / m ² separation membrane · hr.

The step of: prior to the step of cleaning the separation membrane, the carbon dioxide intended for the biogas containing the (CO _2), using a gas separation membrane module to increase the amount of carbon dioxide in the biogas can be further included. Further, the carbon dioxide (CO ₂₎ the biogas that contains methane (CH ₄₎ and is configured to include a carbon dioxide (CO _2), the gas separation membrane module permeability difference between methane (CH ₄₎ and carbon dioxide (CO ₂₎ Can be used to increase the concentration of carbon dioxide (CO ₂ ).

A separation membrane cleaning apparatus using biogas according to the present invention comprises a separation membrane for membrane filtration of raw water to produce treated water, a biogas generating source for generating biogas containing carbon dioxide (CO ₂ ) through an anaerobic digestion process, And a biogas injection device for storing the biogas generated from the source and injecting the biogas into the separation membrane during the cleaning process of the separation membrane. When the biogas is injected into the separation membrane, Cleaning and chemical cleaning with carbon dioxide in the biogas.

The gas separation membrane module further includes a gas separation membrane module that receives the biogas from the biogas injection device and increases the carbon dioxide content in the biogas using the difference in permeability of methane (CH ₄ ) and carbon dioxide (CO ₂ ) .

The separation membrane cleaning method and apparatus using biogas according to the present invention have the following effects.

By using the biogas containing carbon dioxide (CO ₂ ), it is possible to physically wash the biogas by swinging the gas itself, and to obtain the chemical cleaning effect by the carbon dioxide contained in the biogas incidentally.

In addition, as the chemical cleaning without using the cleaning liquid proceeds, damage to the separation membrane can be prevented, cleaning cost can be reduced, and it is not necessary to stop the separation membrane operation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a separation membrane cleaning apparatus using biogas according to an embodiment of the present invention; FIG.

The present invention provides a technique for cleaning a separation membrane using biogas as a cleaning means. Bio-gas is generated in the anaerobic digestion process, and includes methane (CH ₄ ), carbon dioxide (CO ₂ ), etc., and physical cleaning by the gas fluctuation of the biogas itself and carbon dioxide Can be induced by chemical cleaning. Hereinafter, a method and an apparatus for separating membrane using biogas according to an embodiment of the present invention will be described in detail.

In a water treatment apparatus using a separation membrane, a filtration process by a separation membrane and a cleaning process for a separation membrane are usually performed. The filtration process with the separation membrane and the separation process with the separation membrane are alternately repeated and the separation process can be performed by a physical cleaning method and a chemical cleaning method as described in the Background of the Invention come.

The present invention provides a technique for additionally obtaining a chemical cleaning effect based on a physical cleaning method. Specifically, the biogas contains an injected into the separation membrane in the biogas with the removal of contaminants attached to the membrane surface through the gas motion in the biogas is physically carbon dioxide (CO ₂₎ is to be reacted with the pollutant Incidentally induces chemical cleaning. At the time of cleaning the separation membrane, the biogas is injected into the primary side (raw water side) or the secondary side (treated water side) of the separation membrane.

Biogas is produced from the anaerobic digestion process, methane (CH ₄₎ as a carbon dioxide (CO ₂₎ the main component and gas containing very small amount of nitrogen (N _2), hydrogen sulfide (H ₂ S), water vapor (H ₂ O) to be. Accordingly, the biogas can be supplied from a water treatment apparatus or an organic waste treatment apparatus (for example, an animal manure treatment apparatus) to which an anaerobic digester is applied. Further, in the case of the water treatment apparatus or the organic waste treatment apparatus to which the anaerobic digestion tank and the separation membrane are applied together, the biogas produced in the anaerobic digestion tank may be directly used for cleaning the separation membrane.

A method of increasing the concentration of carbon dioxide in the biogas may be applied to improve the chemical cleaning effect by the biogas. As the carbon dioxide contained in the biogas forms a local acidic condition on the surface of the separator to induce the decomposition of the pollutant, the larger the carbon dioxide content in the biogas is, the more the chemical cleaning effect is increased.

The composition of biogas depends on the application field of anaerobic digesters (water treatment or organic waste treatment), but mainly methane (CH ₄ ) and carbon dioxide (CO ₂ ) are the main components. Therefore, it is possible to separate methane (CH ₄ ) and carbon dioxide (CO ₂ ) by using a gas separation membrane module that separates the gas according to the permeability, thereby obtaining a biogas having a large amount of carbon dioxide, So that the chemical cleaning effect can be doubled.

Next, a separation membrane cleaning apparatus using biogas according to an embodiment of the present invention will be described.

Referring to FIG. 1, the apparatus for cleaning a membrane using biogas according to an embodiment of the present invention includes a biogas generating source 110 and a biogas injecting apparatus 120.

The biogas generating source 110 is a device for generating biogas through the anaerobic digestion process, and the anaerobic digester of the water treatment apparatus or the anaerobic digestion tank of the organic waste treatment apparatus may be a biogas generating source 110. The biogas produced through the anaerobic digestion process contains methane (CH ₄ ) and carbon dioxide (CO ₂ ) as main components and may contain a trace amount of nitrogen (N ₂ ), hydrogen sulfide (H ₂ S), and water vapor (H ₂ O) have.

The biogas injector 120 stores the biogas generated from the biogas generator 110 and controls the primary side (raw water side) or the secondary side (treated side) of the separation membrane 10 during the cleaning process of the separation membrane 10 Water side). The biogas injected into the separation membrane 10 removes contaminants on the surface of the separation membrane by physically cleaning the biogas by physical swinging of the biogas, and the carbon dioxide contained in the biogas induces local oxidation of the surface of the separation membrane, Decontaminate the pollutants chemically.

The separation membrane 10 to be cleaned by the biogas is an apparatus for producing treated water by filtrating raw water, and may be composed of a microfiltration membrane, an ultrafiltration membrane, a reverse osmosis membrane, or the like.

In addition, the gas separation membrane module 130 may be further provided in addition to the biogas generation source 110 and the biogas injection device 120. The gas separation membrane module 130 is a device for separating an injection gas into a permeable gas and a recovered gas by using the permeability of the gas. The gas separator module 130 is a device for separating carbon dioxide into a permeable gas and a recovered gas by using the difference between the permeability of methane and the permeability of carbon dioxide. It can be recovered by the recovery gas. That is, when biogas is injected into the gas separator module 130 through the injector, methane is permeated and discharged, and the high concentration of carbon dioxide can be recovered.

The high concentration of the carbon dioxide recovered through the gas separation membrane module 130 is injected into the separation membrane 10 during the washing process of the separation membrane 10 and the amount of carbon dioxide The cleaning effect can be doubled.

In order to induce the chemical cleaning effect by the biogas, the carbon dioxide content in the biogas should be 20 vol% or more. When the carbon dioxide content in the biogas is less than 20 vol%, the biogas in the biogas injector 120 is separated from the separation membrane 10, It is preferable that the carbon dioxide is injected into the separation membrane 10 through the gas separation membrane module 130 without increasing the amount of carbon dioxide. In addition, in order to improve the physical cleaning and chemical cleaning effect by the biogas, the injection rate of the biogas is preferably set to 0.2 to 1.5 m ³ biogas / m ² separation membrane · hr.

Next, an apparatus and method for separating membrane using biogas according to the present invention will be described in more detail with reference to experimental examples.

<Experimental Example>

Continuous permeation characteristics of the membranes were measured using a continuous membrane apparatus with a 20 L bench scale scale membrane. First, a commercial filtration membrane of polyvinylidene difluoride (PVDF) having a rectangular shape of 12 cm ² was prepared. Then, to obtain the specific resistance (R _m ) of the membrane, three membranes of a continuous membrane apparatus were permeated with 0.1 M of PBS (phosphate buffer solution) added with ultrapure water. Activated sludge collected at the sewage treatment plant was then passed through three separators of the continuous separation membrane apparatus to calculate the total resistance (R _t ) of each separation membrane. At this time, the concentration of the activated sludge used was measured to be about 2,000 mg / L, and the pH was measured to be 7.2. Next, air and biogas were injected into the permeate line of the separation membrane and the purging rate was maintained at 100 cc / min for cleaning the separation membrane.

Specific resistance (R _m) and the total resistance (R _t) of the separation membrane of the separation membrane, respectively were calculated through "Resistance in-series model (see following Expression 1), the mathematical model membrane permeable, the membrane resistivity (R _m) And the total resistance (R _t ) of the membrane, the contamination resistance (R _f ) of the membrane was calculated (see Equation 3).

The reason for calculating the contamination resistance (R _f ) of the separation membrane is to verify the effect of reducing the contamination of the separation membrane during cleaning by air or biogas by quantifying the separation membrane contamination caused by the contaminants attached to the surface of the separation membrane.

<Formula 1>

J =? P / (占 R)

(J is the permeation rate, P is the membrane pressure, μ is the viscosity, R is the membrane resistance, and the permeation rate (J)

<Formula 2>

Permeation rate (J) = permeation volume / (membrane area x permeable area)

<Formula 3>

R _t (total resistance of membrane) = R _m (specific resistance of membrane) + R _f (contamination resistance of membrane)

First, experiments were conducted to compare the biodegradation efficiency of the anaerobic digestion tank with the efficiency of separation by air injection. At this time, as a result of analyzing the composition of the biogas, the methane (CH ₄ ) content was 60 vol% and the carbon dioxide content was 40 vol%. And the cycle of washing for 20 minutes after the filtration operation for 60 minutes was carried out four times in total, and the change of the contamination degree of the separation membrane was measured.

The results of the experiments conducted as described above will be described below. Table 1 below shows the membrane fouling resistance (R _f ) of each of the untreated membrane, air-washed membrane, and biogas-washed membrane.

Operating condition
(Continuous filtration for 60 minutes, washing for 20 minutes) Membrane Pollution Resistance
(R _f , 10 ¹⁰ m ^-1 ) Control (not clean)
- 1 ^st cycle
- 2 ^nd cycle
- 3 ^rd cycle
- 4 ^th cycle

136.9
149.2
164.7
187.2 Air injection cleaning
- 1 ^st cycle
- 2 ^nd cycle
- 3 ^rd cycle
- 4 ^th cycle

113.5
118.2
130.3
143.6 Biogas injection cleaning
- 1 ^st cycle
- 2 ^nd cycle
- 3 ^rd cycle
- 4 ^th cycle

99.4
104.8
119.4
128.4

As shown in Table 1, in the case of the separator washed by injecting the biogas, the pollution degree was reduced by 27.4 to 31.4% in comparison with the unsealed membrane, and the pollution degree was 8.4 ~ And 12.4%, respectively. Particularly, as a result of calculation of the total contamination resistance value of the membrane increased during 4 cycles, it was 90.9 x 10 ¹⁰ m ^-1 in the case of control (non-cleaning), 40.7 x 10 ¹⁰ m in case of separator washed with air and biogas ^-1 and 34.1 × 10 ¹⁰ m ^-1 , respectively, and the air pollution resistance of the membrane was 38% higher than that of the cleaning gas using biogas.

Next, an experiment was conducted in which the biogas produced in the anaerobic digestion tank was injected into the gas separation membrane module to increase the content of carbon dioxide, and the biogas having an increased amount of carbon dioxide was injected into the separation membrane. At this time, the carbon dioxide content of the biogas is about 90 vol%. In addition, pH of the membrane near the surface of the membrane was found to be in the range of about 5 to 5.5 at the time of injecting biogas with an increased amount of carbon dioxide. A cycle of filtering for 60 minutes, and a cycle of washing for 5 minutes were carried out four times in total, and the change in the degree of contamination of the membrane was measured.

Table 2 below shows the membrane fouling resistance (R _f ) of the separation membrane without cleaning, the separation membrane with air cleaning, and the separation membrane subjected to high concentration carbon dioxide cleaning.

Operating condition
(Continuous operation for 60 minutes, washing for 5 minutes) Membrane Pollution Resistance
(R _f , 10 ¹⁰ m ^-1 ) Control (not clean)
- 4 ^th cycle
188.4 Air injection cleaning
- 4 ^th cycle
139.5 Carbon dioxide injection cleaning
- 4 ^th cycle
110.1

As shown in Table 2, in the case of the separator washed with high concentration of carbon dioxide, the pollution degree was reduced by 41.5% as compared with the unseparated separator. When compared with the separator washed with air, the pollution degree was 21.1% Respectively.

Particularly, in the case of the separator membrane which was cleaned by injecting high-concentration carbon dioxide for 5 minutes in comparison with the experimental results at 20 minutes after the continuous operation of the separator membrane for 60 minutes in Table 1 above, The results showed that the higher the carbon dioxide (CO ₂ ) content, the more effective it was. It has been confirmed that the carbon dioxide contained in the biogas induces local acidic conditions on the surface of the separation membrane during the cleaning, thereby chemically decomposing the contaminants attached to the separation membrane surface simultaneously to induce high cleaning efficiency.

10: Membrane 110: Biogas source
120: Biogas injection device 130: Gas separation membrane module

Claims (10)

Preparing biogas containing carbon dioxide (CO ₂ ) produced in the anaerobic digestion process; And
And injecting the biogas containing the carbon dioxide (CO ₂ ) into the separation membrane to clean the separation membrane,
In the step of cleaning the separation membrane, the physical cleaning by biasing of the biogas and the chemical cleaning by the carbon dioxide in the biogas proceed,
Before the step of cleaning the separation membrane,
Further comprising the step of increasing the content of carbon dioxide in the biogas by using the gas separation membrane module for the biogas containing the carbon dioxide (CO ₂ ).
According to claim 1, wherein said carbon dioxide separation membrane cleaning method using the bio-gas, characterized in that at least (CO ₂₎ 20vol% the amount of carbon dioxide (CO ₂₎ from a biogas containing the.
^{2. The} separation membrane cleaning method using biogas according to claim 1, wherein, in the step of cleaning the separation membrane, an injection rate of the biogas is 0.2 to 1.5 m ³ biogas / m ² separation membrane · hr.
delete The method according to claim 1, wherein the biogas containing carbon dioxide (CO ₂ ) comprises methane (CH ₄ ) and carbon dioxide (CO ₂ )
The gas separation membrane module separation membrane cleaning method using the bio-gas, comprising a step of increasing the carbon dioxide (CO ₂₎ concentration rate using the transmission rate difference between the methane (CH ₄₎ and carbon dioxide (CO _2).
A separator membrane for filtering the raw water to produce treated water;
A biogas generating source for generating biogas containing carbon dioxide (CO ₂ ) through an anaerobic digestion process; And
And a biogas injection device for storing the biogas generated from the biogas source and injecting the biogas into the separation membrane during the cleaning process of the separation membrane,
When the biogas is injected into the separation membrane, physical cleaning by biasing of the biogas and chemical cleaning by the carbon dioxide in the biogas proceed,
A gas separation membrane module is further provided,
Wherein the gas separation membrane module serves to increase the carbon dioxide content in the biogas by receiving the biogas from the biogas injection device and utilizing the difference in permeability of methane (CH ₄ ) and carbon dioxide (CO ₂ ) .
delete The biogas separation membrane cleaning apparatus according to claim 6, wherein the biogas generating source is an anaerobic digestion tank of the water treatment apparatus or an anaerobic digestion tank of the organic waste treatment apparatus.
The biogas separation membrane cleaning apparatus according to claim 6, wherein the biogas to be injected into the separation membrane during the cleaning process of the separation membrane has a content of carbon dioxide (CO ₂ ) of 20 vol% or more.
The separation membrane cleaning apparatus using biogas according to claim 6, wherein the biogas injection rate is 0.2 to 1.5 m ³ biogas / m ² separation membrane · hr in the washing process of the separation membrane.

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