JP2006263584A - Method for cleaning membrane filtration apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently backwashing a filtration membrane for membrane-filtering external circulating water from a biological treatment tank by water in a short time or a method for efficiently cleaning the filtration membrane by a liquid chemical in a short time. <P>SOLUTION: When the differential pressure of the membrane in a membrane filtration apparatus 2 for membrane-filtering the external circulating water withdrawn from the biological treatment tank 1 is increased, the membrane is cleaned by any one of the below-mentioned two methods. A first method for backwashing the membrane by water comprises a step of fluidizing a liquid on the primary side of the membrane by a gas to exfoliate/remove attachments on the surface of the membrane while making washing water flow from the secondary side of the membrane toward the primary side. A second method for cleaning the membrane by the liquid chemical comprises the steps of: immersing the whole surface of the membrane in the liquid chemical by making the liquid chemical flow from the secondary side of the membrane toward the primary side; and fluidizing the liquid on the primary side of the membrane by the gas to dissolve/remove adherent material on the surface of the membrane. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cleaning method for a membrane filtration device for membrane filtration of circulating water drawn out from a biological treatment tank.

  Conventionally, biological treatment has been widely used for wastewater treatment such as sewage, sewage return water, factory wastewater, waste leachate, human waste, agricultural wastewater, livestock wastewater, and aquaculture wastewater. As a typical biological treatment, there is an activated sludge method, and many other biological treatment methods such as a nitrification liquid circulation method, an AO method, an A2O method, and a nitrification + endogenous denitrification method are carried out.

  In general, the treated water treated in the biological treatment tank is guided to the final settling basin to separate the solid and liquid, and the solid content is discharged as sludge while the supernatant water is discharged (FIG. 3 of Patent Document 1). However, a large space and a long time are required for the final sedimentation basin in order to perform gravity sedimentation. For this reason, it replaces with a final sedimentation basin, and it exists in the tendency which aims at shortening of processing time while aiming at reduction of a space.

  As shown in Patent Document 2, this membrane filtration apparatus includes an immersion type installed inside the biological treatment tank and an apparatus installed outside the biological treatment tank. In the case of the immersion type, the water in the tank is directly filtered, and in the case of the external installation type, the external circulating water drawn from the biological treatment tank is cross-flow filtered. These membranes need to be washed to avoid clogging with sludge, and for immersion type membranes, as shown in Patent Document 2, there is known a method in which suspended solids are brought into contact with the membrane surface by bubbles and constantly washed. ing. On the other hand, the externally installed membrane is usually cleaned regularly like a normal filtration membrane.

  Such an externally installed membrane is cleaned by water backwashing or chemical cleaning. However, depending on the water quality of the water drawn from the biological treatment tank, the adhering material adhering to the primary side membrane surface may be completely peeled off even if the water is backwashed with washing water from the secondary side of the membrane. There are things that cannot be done.

In addition, cleaning with a chemical solution is performed by pouring cleaning water containing a chemical solution from the secondary side of the film so that the entire film is immersed in the chemical solution, and then leaving the film for a certain period of time to dissolve the deposits on the film surface. . The chemical solution rapidly consumed on the film surface to dissolve the deposit on the film surface is replenished by diffusion due to a concentration gradient from the primary side or the secondary side of the film. For this reason, the consumed chemical solution cannot be replenished quickly, and there is a problem that a long cleaning time is required or a high concentration chemical solution is required.
Japanese Patent No. 3394839 Japanese Patent Laid-Open No. 9-136021

  The present invention solves the above-mentioned conventional problems, and provides a method capable of efficiently performing water backwashing or chemical cleaning of a filtration membrane for membrane filtration of external circulating water in a biological treatment tank in a short time. It was made as a purpose.

  A first invention made to solve the above problems is a method of cleaning a membrane filtration device for membrane filtration of external circulating water drawn from a biological treatment tank, and is directed from the secondary side to the primary side of the membrane. The liquid on the primary side of the film is fluidized with gas while flowing the cleaning water, and the deposit on the film surface is peeled off and removed.

  The second invention is a cleaning method for a membrane filtration device for membrane filtration of external circulating water drawn from a biological treatment tank, wherein a chemical solution is flowed from the secondary side to the primary side of the membrane to remove the membrane surface from the chemical solution. In addition, the liquid on the primary side of the film is fluidized with gas to dissolve and remove deposits on the film surface. In any of the inventions, any of air, ozone, and nitrogen gas can be used as the gas for flowing the primary liquid. Further, the gas can be ejected intermittently or continuously.

  According to the first invention, the liquid on the primary side of the membrane is fluidized by the gas while flowing the washing water from the secondary side to the primary side of the membrane, so that it adheres to the surface on the primary side of the membrane. The deposits are subjected to a stirring effect due to the flow of the liquid as well as a peeling effect due to the washing water. Therefore, the film surface can be effectively cleaned in a shorter time than before.

  According to the second aspect of the invention, the concentration gradient layer of the chemical solution near the membrane surface is thinned by fluidizing the liquid on the primary side of the membrane with gas, and the diffusion rate of the chemical solution is remarkably increased. The drug solution is quickly replenished from the primary solution. For this reason, the film surface cleaning effect becomes higher than that of the conventional method, the chemical solution immersion time can be shortened, and the chemical solution concentration can be reduced.

Hereinafter, preferred embodiments of the present invention will be described.
FIG. 1 shows an embodiment of the first invention, wherein 1 is a biological treatment tank, and 2 is a membrane filtration device for membrane filtration of external circulating water drawn from the biological treatment tank 1. The biological treatment tank 1 can be various treatment tanks used for the activated sludge method, the nitrification liquid circulation method, the AO method, the A2O method, the nitrification + endogenous denitrification method, and the like.

  As the membrane filtration device 2, various materials and shapes can be used. That is, the material of the film may be a polymer film or a ceramic film, and various shapes such as a monolith film, a tubular film, and a honeycomb film can be adopted as the film shape. The type of membrane is preferably MF membrane or UF membrane. The filtration method may be external pressure type or internal pressure type, but the channel shape on the primary side should be round or polygonal more than quadrangle, and the cleaning effect by gas should be evenly distributed over the entire membrane surface Is preferred.

  Water in the tank (external circulation water) drawn from the biological treatment tank 1 is driven into the membrane filtration device 2 by the filtration pump 3, and membrane filtration by a cross flow method is performed. The membrane filtered water of the membrane filtration device 2 enters the treated water tank 4 and is discharged after performing necessary treatments. On the other hand, the water in the tank that has passed through the membrane filtration device 2 is returned to the biological treatment tank 1 by the pipe line 5. When membrane filtration is continued in this manner, deposits are gradually formed on the membrane surface, and the membrane differential pressure increases, so that the cleaning according to the present invention is performed.

  First, the filtration pump 3 is stopped, and the treated water in the treated water tank 4 is washed into the secondary side of the membrane filtration device 2 by the backwash pump 6 as washing water as before. At the same time, gas is supplied to the primary side of the membrane filtration device 2 by the gas supply means 7 to fluidize the liquid on the primary side. As the gas, any one of air, ozone, and nitrogen gas is preferably used. If ozone is used, an effect of decomposing organic matter in the deposit can be obtained. The gas ejection may be performed continuously or pulsed. Moreover, you may supply gas with respect to many membrane filtration apparatuses 2 in order. Instead of the backwash pump 6, a chemical solution using treated water may be stored in a pressurized water tank and driven into the secondary side of the separation membrane 2 as a pressure chemical solution.

  As a result, the adhering matter on the membrane surface passes through the inside of the membrane from the secondary side and is not only subjected to the peeling force from the membrane surface by the backwash water blown to the primary side, but also the stirring effect by the fluidized primary side liquid As a result, it becomes easier to peel off than the conventional method in which the liquid on the primary side is kept stationary. Therefore, the film surface can be effectively cleaned in a shorter time than before.

  FIG. 2 shows an embodiment of the first invention. Like FIG. 1, 1 is a biological treatment tank, 2 is a membrane filtration device for membrane filtration of external circulating water drawn from the biological treatment tank 1, and 3 is a filtration. A pump, 4 is a treated water tank, and 5 is a pipe line. In this embodiment, a chemical solution tank 7 is provided, and chemicals are added to the treated water from the treated water tank 4 to produce a chemical solution. Typical chemicals include sodium hypochlorite, hydrogen peroxide, citric acid, oxalic acid, hydrochloric acid, sulfuric acid and the like, but are not necessarily limited thereto.

  When cleaning the membrane, the filtration pump 3 is stopped, and a chemical solution is driven into the membrane filtration device 2 from the secondary side by the chemical solution injection pump 8 and is passed through the primary side to immerse the membrane surface in the chemical solution. This state is shown in FIG. Since the chemical solution is consumed by reacting with the deposit on the film surface, the concentration of the chemical solution is lowered on the film surface, but a concentration gradient layer is formed on both sides thereof. That is, a concentration gradient layer is formed inside the film, and a concentration gradient layer is also formed in the liquid on the primary side. Since the chemical solution reaches the film surface by diffusion through these concentration gradient layers, in this state, it takes time for cleaning as in the prior art.

  However, in the present invention, gas is supplied into the liquid on the primary side of the membrane filtration device 2 by the gas supply means 7, and the liquid on the primary side of the membrane is fluidized with the gas. Then, as shown in FIG. 4, the concentration gradient layer in the primary liquid near the film surface becomes thin and the diffusion rate increases remarkably, so that the chemical solution consumed by reacting with the adhering substance is quickly absorbed into the primary liquid. It is replenished from inside, and the speed of dissolving and removing the deposits increases. As a result, the chemical solution immersion time can be significantly shortened compared to the conventional case, and the chemical solution concentration can be reduced.

  An experiment was conducted to filter the external circulating water drawn from the activated sludge treatment tank of sewage with a ceramic membrane. The filtration membrane used is a monolith membrane manufactured by the applicant company, the membrane pore diameter is 0.1 μm, and the flow path diameter on the primary side is 4 mm. The MLSS of the external circulating water was 5000 mg / L, and when the membrane differential pressure reached 50 kPa, washing was performed by the following four methods.

The first was a conventional water backwashing method, in which 1.5 L of backwashing water per 1 m ^{2 of} membrane area was passed from the secondary side to the primary side at a pressure of 500 kPa.
The second is the method of the first invention of the present application, and 0.05 m / s air was blown into the liquid on the primary side when backwashing by the first method was performed. The washing time is 2 minutes.

The third is a conventional chemical cleaning method, in which hypochlorous acid water having a concentration of 100 mg / L is flowed from the secondary side of the membrane, the whole membrane is immersed in hypochlorous acid water for 5 minutes, and the membrane area is 1 m. 1.5 L of backwash water per ² was passed from the secondary side to the primary side at a pressure of 500 kPa.
The fourth is the method of the second invention of the present application, in which hypochlorous acid water having a concentration of 100 mg / L is allowed to flow from the secondary side of the membrane and the entire membrane is immersed in hypochlorous acid water for 5 minutes. While air of 0.05 m / s was blown into the liquid on the primary side, 1.5 L of backwash water per 1 m ^{2 of} membrane area was passed from the secondary side to the primary side at a pressure of 500 kPa.

  The cleaning results are shown in Table 1. According to the method of the present invention, when the cleaning time is the same, an excellent cleaning effect can be obtained as compared with the conventional method. Therefore, the cleaning time required to obtain the same cleaning effect can be greatly shortened.

It is explanatory drawing which shows embodiment of 1st invention. It is explanatory drawing which shows embodiment of 2nd invention. It is a graph which shows the chemical | medical solution concentration gradient in a chemical | medical solution immersion state. It is a graph which shows the chemical | medical solution concentration gradient in the state which fluidized the primary side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Biological treatment tank 2 Membrane filtration apparatus 3 Filtration pump 4 Treated water tank 5 Pipe line 6 Backwash pump 7 Gas supply means 8 Chemical liquid tank 9 Chemical liquid injection pump

Claims (4)

  A membrane filtration device cleaning method for membrane filtration of external circulating water drawn from a biological treatment tank, wherein the cleaning solution is flowed from the secondary side to the primary side of the membrane while the liquid on the primary side of the membrane is gasified A cleaning method for a membrane filtration device, characterized by fluidizing and peeling / removing deposits on the membrane surface.   A membrane filtration apparatus cleaning method for membrane filtration of external circulating water drawn from a biological treatment tank, wherein a chemical solution is flowed from the secondary side of the membrane toward the primary side so that the membrane surface is immersed in the chemical solution, A cleaning method for a membrane filtration device, wherein the liquid on the primary side is fluidized by gas to dissolve and remove deposits on the membrane surface.   The method for cleaning a membrane filtration device according to claim 1 or 2, wherein any one of air, ozone, and nitrogen gas is used as the gas.   The method for cleaning a membrane filtration device according to claim 1 or 2, wherein the gas is ejected intermittently or continuously.

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