JP2005074357A - Membrane washing method in membrane separation activated sludge method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane washing method in a membrane separation activated sludge method for effectively scratching off depositions on the surface of a membrane used in the membrane separation activated sludge method and for preventing the reduction of a membrane separation rate. <P>SOLUTION: In the membrane washing method, membrane washing particles 4 in which each surface is hydrophilized, and has ruggedness of ≥100 μm are charged inside a bioreaction tank 1, are made to flow by the air lift effect of bubbles jetted from a diffuser 3, and are made to scratch off depositions on the surface of a separation membrane element 2. In the membrane washing method, membrane washing particles 4 of non-pores or independent pores are used. In the membrane washing method, the membrane washing particles 4 in which antibacterial components of copper, silver or the like are carried on each surface or inside are used. In the membrane washing method, the membrane washing particles 4 are periodically placed in an anaerobic condition, and microorganisms on the surfaces of the particles are peeled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a membrane cleaning method in a membrane separation activated sludge method used in wastewater treatment at a sewage treatment plant or the like.

  When organic wastewater is treated with activated sludge, a method in which a sedimentation separation tank is provided after the reaction tank and the sludge is separated by sedimentation is common. However, since this conventional method requires a large sedimentation separation tank, for example, in urban sewage treatment plants where there is not enough space on the site, a separation membrane element is installed inside the reaction tank to perform solid-liquid separation. A membrane separation activated sludge method for taking out the liquid as membrane filtered water has been studied. According to this method, a large sedimentation tank is not required.

  However, in the membrane separation activated sludge method, sludge and the like adhere to the surface of the separation membrane, and the membrane filtration rate may decrease in a short time. Therefore, as shown in Patent Document 1, an air ejection nozzle is installed below the separation membrane element, and floating solid is introduced into the biological reaction tank, and the floating solid is caused to flow by the lift action of bubbles from the air ejection nozzle, and separated. There has been proposed a method of scraping off deposits on the film surface with floating solids. In the invention described in Patent Document 1, a sponge-like foamed resin is used as a floating solid.

However, the conventional sponge-like floating solid gradually generates bubbles in the internal communication pores, and the bubbles are difficult to escape because the material of the floating solid is hydrophobic. Easy to break. Further, the surface of the sponge-like floating solid is gradually covered with microorganisms and its in vitro substances, and since these are too soft, the effect of scraping off deposits (scale layer) on the film surface cannot be obtained. Furthermore, when using the membrane cleaning particles with less irregularities on the surface of the floating solid, there is a problem that the deposit (scale layer) on the membrane surface is not effectively scraped off.
Japanese Patent Laid-Open No. 9-136021

  The present invention solves the above-mentioned conventional problems, can effectively scrape the deposits on the membrane surface used in the membrane separation activated sludge method, and in the membrane separation activated sludge method capable of preventing a decrease in membrane filtration rate. The present invention has been made to provide a film cleaning method.

  In order to solve the above problems, the membrane cleaning method in the membrane separation activated sludge method of the present invention is such that the separation membrane element is immersed in membrane cleaning particles whose surface is hydrophilized and whose surface irregularities are 100 μm or more. The membrane cleaning particles are made to flow by the air lift effect of bubbles injected into the biological reaction tank and ejected from the air diffuser, and the deposits on the surface of the separation membrane element are scraped off. Moreover, the film | membrane washing | cleaning particle | grains which consist of a material of a non-porous or an independent pore can be used.

  In addition, the film | membrane washing | cleaning particle | grains by which the antimicrobial component was carry | supported on the surface or inside can be used, and this antimicrobial component can be made into silver or copper. In addition, it is preferable to periodically place the membrane cleaning particles in an anaerobic state to peel off the microorganisms on the surface of the particles.

  According to the first aspect of the present invention, the membrane cleaning particles whose surface is hydrophilized and whose surface irregularities are 100 μm or more are caused to flow, and the deposits on the surface of the separation membrane element are scraped off. Even if bubbles are generated inside, the surface is hydrophilized so that the bubbles are quickly removed. Furthermore, since the unevenness of the surface of the membrane cleaning particles is 100 μm or more, the deposits on the surface of the separation membrane element can be efficiently scraped off. As a result, it is possible to prevent a decrease in the membrane filtration rate of the separation membrane element.

  According to the invention of claim 2, since it is made of a material having no pores or independent pores, the membrane cleaning particles do not have pores communicating with the inside, so that bubbles are generated inside and float on the upper part of the biological reaction tank. The cleaning effect can be maintained. According to the third and fourth aspects of the invention, since the membrane cleaning particles carrying an antibacterial component such as silver or copper are used, microorganisms hardly adhere to the surface of the membrane cleaning particles. For this reason, it is possible to prevent a reduction in the scraping effect due to the formation of a soft microbial film on the surface of the film cleaning particles. Further, according to the invention of claim 5, since the membrane cleaning particles are periodically placed in an anaerobic state and microorganisms on the surface of the particles are peeled off, it is possible to prevent the scraping effect from being lowered. As a result, it is possible to prevent a decrease in the membrane filtration rate of the separation membrane element.

FIG. 1 shows a preferred embodiment of the present invention. 1 is a biological reaction tank in which biological treatment is performed using activated sludge, 2 is a separation membrane element that is immersed in the biological reaction tank 1 and takes out treated water. is there. This biological reaction tank 1 carries out activated sludge treatment of various effluents such as sewage, return water, factory effluent, waste leachate, manure, agricultural effluent, livestock effluent, aquaculture effluent, etc., and is clarified through a separation membrane element 2. The treated water can be taken out. In addition, as the biological reaction tank 1, methods such as an aerobic tank, an anaerobic tank, a nitrification liquid circulation method, an AO method, and an A ₂ O method can be used. Further, a membrane separation tank may be provided separately from the biological reaction tank 1.

  The membrane constituting the separation membrane element 2 may be a polymer membrane or a ceramic membrane, and the membrane shape is arbitrary such as a monolith type, a tubular type, a honeycomb type, and a flat membrane type. Further, the membrane may be either an external pressure type or an internal pressure type, and the cross-sectional shape may be round or polygonal. However, it is preferable to use a flat film type polymer film or ceramic film as shown in the drawing from the viewpoint of film area and detergency.

  An air diffuser 3 is installed below the separation membrane element 2 to supply air into the biological reaction tank 1. Due to the air lift effect of the air bubbles ejected from the air diffuser 3, an upward flow is generated near the surface of the separation membrane element 2 to remove the deposits on the membrane surface. Cleaning particles 4 are put into the biological reaction tank 1.

  The membrane cleaning particles 4 used in the present invention have a specific gravity of 0.9-2. Specifically, independent pores are also desirable when made of a polymer material such as polyethylene or polypropylene, or an inorganic material such as ceramic particles, and foamed for adjusting the specific gravity. Thereby, bubbles are not generated inside the membrane cleaning particles 4 and the membrane cleaning particles 4 do not float near the water surface.

  Further, the surface of the membrane cleaning particle 4 used in the present invention is made hydrophilic by attaching a hydrophilic group. Thereby, even if bubbles are generated inside the membrane cleaning particles 4, the bubbles easily escape into water. Therefore, unlike the conventional sponge-like film cleaning particles, the cleaning effect is not lost due to floating by internal bubbles. Furthermore, as shown in claim 2, if it is made of a material having no pores or independent pores, it does not have pores communicating from the surface to the inside, and bubbles do not form inside, so that they are floated by the inside bubbles. Therefore, the cleaning effect is not lost.

  The film cleaning particles 4 used in the present invention have a surface irregularity of 100 μm or more. The unevenness on the surface can be measured with a microscope. When sponge-like membrane cleaning particles are used, the hole diameter should be 100 μm or more. Thus, the film | membrane cleaning particle | grains 4 whose surface unevenness | corrugation is 100 micrometers or more are excellent in the cleaning effect at the time of contacting a film surface. However, the shape of the film cleaning particles 4 does not significantly affect the cleaning effect, and may be spherical or cubic. The size is preferably about 5 to 10 mm in the case of a polymer material and about 0.5 mm in the case of an inorganic material.

  In addition, as shown in Claim 3, the film | membrane washing | cleaning particle | grains 4 by which the antimicrobial component was carry | supported on the surface or inside can be used. Many antibacterial components are known to have the ability to prevent the growth of microorganisms, but organic chemicals can easily be washed away and can have an adverse effect on activated sludge. Is preferably used. By using the membrane cleaning particles 4 having the antibacterial component supported on the surface or inside as described above, a soft microbial film is not formed on the surface of the membrane cleaning particles, and a reduction in the scraping effect can be prevented. .

  The membrane cleaning particles 4 as described above are preferably added so that the volume ratio is about 0.1 to 5% with respect to the tank volume of the biological reaction tank 1. If it is less than this range, the cleaning effect will decrease, and even if it exceeds this range, the cleaning effect will not be improved. As a result, it is possible to prevent a decrease in the membrane filtration rate of the separation membrane element used in the membrane separation activated sludge method.

  As described above, in the inventions of claims 3 and 4, the use of the membrane cleaning particles 4 having antibacterial components such as silver or copper supported on the surface or inside thereof prevents adhesion of the microbial membrane. Then, by periodically placing the membrane cleaning particles 4 in an anaerobic state, microorganisms on the surface of the particles are peeled off. As a method of placing the membrane cleaning particles 4 in an anaerobic state, a method of taking the membrane cleaning particles 4 from the biological reaction tank 1 into the anaerobic tank, or a period in which the biological reaction tank 1 itself or a part of the biological reaction tank 1 is in an anaerobic state. You can take a method. Since the microorganism film formed on the surface of the membrane cleaning particle 4 in the aerobic state is easily separated by placing it in the anaerobic state, it is possible to prevent the scraping effect of the membrane cleaning particle 4 from being lowered.

In order to examine the effect of the membrane cleaning particles, a comparative experiment was performed using two types of particles (hydrophilic polyurethane sponge and hydrophobic polyurethane sponge). The biological reaction tank used was a nitrating liquid circulation type apparatus consisting of a denitrification tank and a nitrification tank. As a membrane, six polymer flat membranes having an effective area of 0.4 m ² were immersed in a nitrification tank to obtain treated water. The wastewater to be treated was waste leachate. The membrane cleaning particles were introduced into the nitrification tank by 0.7% by volume. The MLSS (floating solid concentration) in the biological treatment tank was operated at 5000 mg / L. The membrane filtration flux was started at 0.6 m / d at the beginning of the experiment, and the membrane filtration flux after 4 weeks was measured. Table 1 shows the comparison results of the membrane filtration flux.

表１に示すように、親水化ポリウレタンスポンジを用いた場合には、４週間経過後にも膜ろ過流束の低下がない。

As shown in Table 1, when a hydrophilic polyurethane sponge is used, there is no decrease in membrane filtration flux even after 4 weeks.

It is sectional drawing which shows embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Biological reaction tank 2 Separation membrane element 3 Air diffuser 4 Membrane cleaning particle

Claims (5)

  Membrane cleaning particles whose surface is hydrophilized and whose surface irregularities are 100 μm or more are introduced into a biological reaction tank in which a separation membrane element is immersed, and the membrane cleaning particles are produced by the air lift effect of bubbles ejected from the diffuser The membrane cleaning method in the membrane separation activated sludge method is characterized in that the deposits on the surface of the separation membrane element are scraped off.   The membrane cleaning method in the membrane separation activated sludge method according to claim 1, wherein membrane cleaning particles made of a material having no pores or independent pores are used.   The membrane cleaning method in the membrane separation activated sludge method according to claim 1, wherein membrane cleaning particles carrying an antibacterial component are used.   The membrane cleaning method in the membrane separation activated sludge method according to claim 3, wherein the antibacterial component is silver or copper.   The membrane cleaning method in the membrane separation activated sludge method according to claim 1, wherein the membrane cleaning particles are periodically placed in an anaerobic state to remove microorganisms on the surface of the particles.

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