JP2014188453A - Water treatment system and water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment system capable of uniformly flowing the raw water of a gas-liquid mixed flow to a plurality of tubular membranes even at a low flow velocity while retaining a bubble charging ratio high in a membrane cleaning effect.SOLUTION: Provided is a water treatment system comprising: a membrane module having a plurality of tubular membranes and filtering raw water; a raw water feed part of feeding the raw water from a water source of the raw water to the membrane module; a gas feed part of feeding a gas to the raw water and making the raw water fed to the membrane module into a gas-liquid mixed flow; and a surface tension emollient feed part of adding the surface tension emollient to the raw water.

Description

The present invention relates to a water treatment system and a water treatment method.

  Various water treatment systems that perform raw water treatment using membrane modules are known. For example, a membrane module having a plurality of tubular membranes and performing solid-liquid separation by suction filtration of raw water through the membrane module is known. The treated water filtered by the tubular membrane of the membrane module is collected in a storage tank, and the raw water that has passed without being filtered by the membrane module is returned to the water source. For example, as shown in Patent Document 1, water is treated by mixing raw water with air and flowing the raw water in a gas-liquid mixed phase flow through a membrane module.

JP 2007-245058 A

  Here, the membrane module used in the water treatment system as described above is composed of tens to hundreds of tubular membranes. When a gas-liquid mixed phase flow in which air is mixed with raw water flows through such a membrane module, the raw water and air do not flow uniformly through a number of tubular membranes in the membrane module, and the tubular membrane is clogged with air. In some cases, raw water does not flow at all. Thus, when a tubular membrane in which raw water does not flow is generated, the filtration efficiency is lowered by reducing the number of tubular membranes that substantially contribute to filtration, and the solid adhered by the suction pressure is dried, There arises a problem that the lifetime of the tubular membrane is shortened.

  Such a problem is likely to occur when the flow rate of the raw water is reduced in order to reduce power while maintaining the bubble injection ratio with a high membrane cleaning effect. Therefore, it is conceivable to reduce the amount of air and operate at a flow rate equal to or higher than a predetermined speed so that bubbles are not clogged in the tubular membrane due to the momentum of the flow rate. However, even if this method is adopted, it may not be possible to uniformly flow through the plurality of tubular membranes. Further, this method has a problem that the film cleaning effect cannot be enhanced and high power is required.

  The present invention has been made in order to solve such a problem, and can uniformly feed raw water of a gas-liquid mixed phase flow to a plurality of tubular membranes with low power while maintaining high membrane cleaning efficiency. An object is to provide a water treatment system and a water treatment method.

  The inventors of the present invention have eagerly studied paying attention to the portion of the tubular membrane clogged with air, and have found the following knowledge. That is, the present inventors have found that when filtering raw water, by adding a surface tension relaxation agent to the raw water, the resistance to invasion of bubbles due to surface tension into the tubular membrane is reduced. As a result, the present inventors have found that the gas-liquid multiphase flow uniformly flows in the plurality of tubular membranes by the method.

  Therefore, the water treatment system according to the present invention has a plurality of tubular membranes, a membrane module that filters raw water, a raw water supply unit that supplies raw water from a raw water source to the membrane module, and supplies gas to the raw water, The gas supply part which makes the raw | natural water supplied to a membrane module a gas-liquid mixed phase flow, and the surface tension relaxation agent supply part which adds a surface tension relaxation agent to raw | natural water are provided.

  The water treatment system according to the present invention includes a surface tension relaxation agent supply unit that adds a surface tension relaxation agent to raw water. By adding a surface tension relaxation agent to the raw water, the surface tension of the raw water in the gas-liquid mixed phase flow is relaxed, and the resistance force due to the surface tension when bubbles in the raw water enter the tubular membrane in the membrane module is reduced. Thereby, it becomes easy for a bubble to penetrate | invade into a tubular film | membrane, and it becomes difficult to clog. Therefore, even when the membrane module has a plurality of tubular membranes, the raw water in the gas-liquid mixed phase flow can uniformly flow through each of the tubular membranes. Furthermore, even when the flow rate is reduced to reduce power, the raw water of the gas-liquid mixed phase flow can flow uniformly through each tubular membrane. As described above, the water treatment system can flow the gas-liquid mixed phase raw water uniformly to the plurality of tubular membranes with low power while maintaining high membrane cleaning efficiency.

  In the water treatment system according to the present invention, the surface tension relaxant is preferably a plant surfactant or a cereal-derived fatty acid sodium. This is because it does not adversely affect the microorganisms used in the raw water and in the subsequent treatment process, and is decomposed by the microorganisms, and therefore does not adversely affect the subsequent treatment process and the environment.

  In the water treatment system according to the present invention, the raw water supply unit is preferably a raw water pump, and the surface tension relaxation agent supply unit is preferably installed upstream of the raw water pump. As a result, the surface tension relaxation agent in the raw water is agitated in the raw water pump, so that the surface tension relaxation agent spreads uniformly in the raw water. Therefore, the raw water can be made to flow more reliably to the plurality of tubular membranes in the membrane module.

  The water treatment method of the present invention includes a step of adding a surface tension relaxation agent to raw water, a step of supplying a gas to the raw water to form a gas-liquid mixed phase flow, and a gas-liquid mixed phase to a membrane module having a plurality of tubular membranes. A step of supplying a flow, and a step of performing filtration by passing a gas-liquid mixed phase flow through a plurality of tubular membranes. By using this method, a surface tension relaxant can be added to the raw water, the surface tension of the raw water in the gas-liquid mixed phase flow is relaxed, and the surface tension when bubbles in the raw water enter the tubular membrane in the membrane module Resistance is reduced. Thereby, it becomes easy for a bubble to penetrate | invade into a tubular film | membrane, and it becomes difficult to clog. Therefore, with respect to the membrane module having a plurality of tubular membranes, the raw water in the gas-liquid mixed phase flow can be made to flow uniformly through each of the tubular membranes. Furthermore, even when the flow velocity is reduced to reduce power, the raw water of the gas-liquid mixed phase flow can flow uniformly through each tubular membrane. As described above, by adopting this water treatment method, the raw water of the gas-liquid mixed phase flow can be uniformly fed to the plurality of tubular membranes with low power while maintaining high membrane cleaning efficiency.

According to the present invention, a gas-liquid mixed phase flow can be made to flow uniformly through a plurality of tubular membranes with low power while maintaining a high membrane cleaning effect.

It is a schematic structure figure showing a water treatment system concerning an embodiment of the present invention. It is the schematic which shows a mode that raw | natural water flows into the several tubular membrane of a membrane module.

  Hereinafter, an embodiment of a water treatment system according to the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are examples for explaining the present invention, and the present invention is not limited to the following contents. The accompanying drawings show an example of the embodiment, and the form is not construed as being limited thereto. The present invention can be implemented with appropriate modifications within the scope of the gist thereof. Note that the positional relationships such as up, down, left and right in the drawings are based on the positional relationships shown in the drawings unless otherwise specified. The dimensions and ratios of the drawings are not limited to those shown in the drawings.

  Hereinafter, an embodiment of a water treatment system according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic configuration diagram showing a water treatment system 1 according to the present embodiment. As shown in FIG. 1, a water treatment system 1 includes a membrane module 2, a raw water tank (raw water source) 3, a raw water pump (raw water supply unit) 4, a flow meter 6, and an air blower (gas supply unit). 7, pressure gauges 8 and 9, a filtration water tank 11, a filtration pump 12, a backwash pump 13, a surface tension relaxation agent supply unit 14, and a control unit 16. On the upstream side of the membrane module 2, the raw water tank 3 and the membrane module 2 are connected by a line L1. On the downstream side of the membrane module 2, the raw water tank 3 and the membrane module 2 are connected by a line L2.

  The membrane module 2 is a module for solid-liquid separation by filtering raw water. The membrane module 2 has a plurality of tubular membranes (tubular membranes) 5. The membrane module 2 is configured by housing a plurality of tubular membranes 5 in a cylindrical case 10 in a bundled state. The tubular membrane 5 is a straw-like membrane having an inner diameter of about 3 to 20 mm and a length of about 50 to 300 cm. Examples of the material include PVDF and PE. One membrane module 2 has 50 to 1000 tubular membranes 5. However, these inner diameters, lengths, and numbers are examples, and are not limited to these numerical values, and may be smaller or larger than the range. The material is also an example and is not limited.

  The raw water tank 3 is a tank for storing raw water to be processed by the water treatment system 1. The raw water often contains various impurities and activated sludge. The source of raw water may be a sewage pump station or the like instead of the raw water tank 3. In this case, the line L1 sucks the raw water directly from the sewage pump station, and the line L2 discharges the raw water that has passed through the membrane module 2 to the sewage pump station. The raw water pump 4 is provided in the line L 1, sucks raw water from the raw water tank 3, and supplies it to the membrane module 2. The arrangement of the raw water pump 4 is not particularly limited, and is provided at any position on the lines L1 and L2. The flow meter 6 is provided on the line L <b> 1 and measures the flow rate of raw water pumped by the raw water pump 4.

  The air blower 7 supplies air to the raw water and uses the raw water supplied to the membrane module 2 as a gas-liquid mixed phase flow. The air blower 7 is provided on the line L <b> 1 and between the raw water pump 4 and the membrane module 2, but the position is not particularly limited as long as it is upstream of the membrane module 2. The pressure gauge 8 detects the pressure on the upstream side of the membrane module 2, specifically, the pressure immediately before the inlet of the membrane module 2. The pressure gauge 9 detects the pressure on the downstream side of the membrane module 2, specifically, the pressure immediately after the outlet of the membrane module 2. For example, the supply amount (supply speed) of air can be set to 0.05 to 0.5 m / s. However, since the merit of the present system is particularly large if the operation is performed within the range, the system is not limited to the range, and for example, supply of 1.0 m / s, 2.0 m / s or more is possible. You may drive by quantity.

  The flow of raw water flowing through the tubular membrane 5 of the membrane module 2 may be a bubble flow in which small bubbles rise, or a slag flow in which a long and bullet-like bubble is formed in a crushed state. Alternatively, it may be a churn flow in which bubbles of various sizes are mixed from the slag flow.

  The filtered water tank 11 is a tank for storing treated water that has been solid-liquid separated by the tubular membrane 5 of the membrane module 2. The filtration pump 12 is connected to the case 10 and is a pump for sucking raw water from the outside of the tubular membrane 5. As a result, the filtration pump 12 supplies the treated water that is solid-liquid separated by the tubular membrane 5 and flows out into the case 10 to the filtered water tank 11. The backwash pump 13 is connected to the case 10 and cleans the inside of the tubular membrane 5 by causing the filtered water stored in the filtered water tank 11 to flow back to the membrane module 2. Since the sludge in the raw water accumulates inside the tubular membrane 5 of the membrane module 2 by filtration, the tubular membrane 5 is washed by driving the backwash pump 13 after filtering for a certain period of time. be able to.

  The surface tension relaxation agent supply unit 14 is a part to which a drug (surface tension relaxation agent) that lowers the surface tension of raw water is added. By appropriately adding an appropriate amount of the surface tension relaxation agent to the raw water, it is possible to reduce the resistance against the invasion of bubbles into the tubular membrane 5 due to the surface tension at the inlet of the tubular membrane 5. Thereby, it is possible to prevent bubbles from being clogged at the entrance or inside of the tubular membrane.

  In the embodiment shown in FIG. 1, the surface tension relaxation agent supply unit 14 is provided to add the surface tension relaxation agent to the raw water in the raw water tank 1. However, the installation place of the surface tension relaxation agent supply part 14 is not limited as shown in FIG. In the embodiment shown in FIG. 1, the raw water filtered by the membrane module 2 is circulated to the raw water tank 3 through the line L2, so that the surface tension relaxation agent supply unit 14 is connected to a part of the line L2. It may be provided. However, when the source of raw water is a river or the like, the raw water after filtration is drained into the river or the like, so it is necessary to connect it to the upstream side of the membrane module 2, for example, a part of the line L1. Moreover, the surface tension relaxation agent supply unit 14 is not limited to one, and a plurality of surface tension relaxation agent supply units 14 may be provided. In addition, it is preferable to install on the upstream side of the raw water pump 4 because the surface tension relaxation agent in the raw water is stirred in the raw water pump 4 and the surface tension relaxation agent spreads uniformly in the raw water.

  Examples of the method in which the surface tension relaxation agent supply unit 14 adds the surface tension relaxation agent to the raw water include liquid feeding using a pump and dropping by gravity. However, other methods may be used without being limited thereto. Further, a surface tension relaxant may be manually added to the raw water. In this case, the surface tension relaxant supply unit 14 is not necessarily provided. For example, the worker may carry the surface tension relaxation agent and add it to the raw water by putting it in the raw water tank 3 or the like. In the embodiment shown in FIG. 1, the surface tension relaxation agent supply unit 14 is controlled by a control unit 16 described later. However, the present invention is not limited to this, and the surface tension relaxation agent supply unit 14 may be controlled independently of the control unit 16.

  The component of the surface tension relaxation agent to be added preferably contains a substance having a hydrophilic group and a hydrophobic group such as a surfactant. Specifically, it is preferable to use plant surfactants derived from palm oil, cereal-derived fatty acid sodium, and the like. Particularly in the membrane separation activated sludge method, the main component of the raw water is activated sludge, which does not adversely affect microorganisms in the activated sludge. Furthermore, plant surfactants and cereal-derived fatty acid sodium are preferable because they are decomposed by microorganisms and do not adversely affect the treatment process and the environment.

  The control unit 16 performs operation control of the entire water treatment system 1. The control unit 16 is electrically connected to the raw water pump 4, the flow meter 6, the air blower 7, the pressure gauges 8 and 9, the filtration pump 12, the backwash pump 13, and the surface tension relaxation agent supply unit 14. When the membrane module 2 performs filtration, the control unit 16 can also control the raw water pump 4, the air blower 7, and the filtration pump 12 based on the detected values of the pressure gauges 8 and 9. The controller 16 controls the backwash pump 13 when backwashing the membrane module.

  Next, an example of an operation procedure when the water treatment system 1 performs water treatment of raw water will be described.

  First, the control unit 16 activates the raw water pump 4 and the air blower 7. The raw water pump 4 sucks raw water from the raw water tank 3 and supplies the raw water to the membrane module 2 through the line L1. The air blower 7 turns the raw water into a gas-liquid mixed phase flow by supplying air to the raw water. At this time, the raw water circulation speed can be set to a low speed of about 0.1 to 0.5 m / s. Moreover, the bubble injection | throwing-in ratio by the air blower 7 can be made high, and it can set to about 0.1-0.2, More preferably, about 0.3-0.5. Further, the control unit 16 activates the filtration pump 12. The flux of the filtration pump 12 is set to about 0.5 to 3.0 m / s. However, the raw water circulation speed, the bubble charging ratio, and the flux are not limited to the above numerical range, and may be smaller or larger than the numerical range.

  The surface tension relaxation agent supply unit 14 adds a suitable amount of a surface tension relaxation agent to the raw water. The surface tension relaxation agent supply unit 14 may be added according to the operation of the control unit 16. Moreover, you may add based on the drive time of the water treatment system 1 independently of the control part 16, and an operator may add suitably by manual labor. In this case, the surface tension relaxation agent supply unit 14 is not necessarily provided. When adding a surface tension relaxation agent to raw | natural water, when a water treatment system is a circulation type shown in FIG. 1, it will not specifically limit, For example, you may add to the raw | natural water in the line L2. On the other hand, when the raw water source is a river or the like and the water treatment system is not a circulation type, it is necessary to provide upstream of the membrane module 2. For example, you may add to the raw | natural water in the line L1. In this case, the surface tension relaxation agent may be added to the raw water before the raw water is sucked by the raw water pump 4 or after the air is supplied to the raw water. In addition, it is preferable to install on the upstream side of the raw water pump 4 because the surface tension relaxation agent in the raw water is stirred in the raw water pump 4 and the surface tension relaxation agent spreads uniformly in the raw water.

  The control unit 16 acquires the detection value of the pressure gauge 8 on the inlet side of the membrane module 2 and the detection value of the pressure gauge 9 on the outlet side. The control unit 16 may control the raw water pump 4, the air blower 7, and the filtration pump 12 based on these detection results.

  Next, the operation and effect of the water treatment system 1 according to the present embodiment will be described.

  First, a conventional water treatment system will be described. The conventional water treatment system has a configuration in which the surface tension relaxation agent supply unit 14 is removed from the water treatment system 1 shown in FIG.

  As described above, the membrane module 2 is composed of several tens to several hundreds of tubular membranes. In a conventional water treatment system, when a gas-liquid mixed phase flow in which air is mixed with raw water flows through such a membrane module 2, as shown in FIG. The raw water and air do not flow uniformly in the membrane 5, and some of the raw water does not flow at all due to clogging of the tubular membrane 5. As described above, when the tubular membrane 5 in which raw water does not flow is generated, the number of the tubular membranes 5 that substantially contribute to the filtration is reduced, so that the filtration efficiency is lowered, and the solid adhered by the suction pressure is dried. This causes a problem that the lifetime of the tubular film 5 is shortened.

  Such a problem is likely to occur when the flow rate of the raw water is reduced in order to reduce power while maintaining the bubble injection ratio with a high membrane cleaning effect. Therefore, it is conceivable to reduce the amount of air and operate at a flow rate equal to or higher than a predetermined speed so that bubbles are not clogged in the tubular membrane 5 due to the momentum of the flow velocity. However, even if this method is adopted, it may not be possible to flow uniformly through the plurality of tubular films 5. Moreover, in this method, since the amount of air is small, the membrane cleaning effect cannot be enhanced, and high power is required. Therefore, there is a problem that the raw water pump 4 must be enlarged.

  Here, the present inventors came to find the following knowledge by paying attention to the part of the tubular membrane 5 clogged with air. That is, the present inventors have found that, when filtering raw water, by adding a surface tension relaxation agent to the raw water, the resistance to invasion of bubbles due to surface tension into the tubular membrane 5 is reduced. . As a result, the present inventors confirmed that the gas-liquid mixed phase flow uniformly flows through the plurality of tubular membranes 5 without increasing the circulation rate of the raw water and reducing the amount of air. I found it.

Therefore, the water treatment system 1 according to the present embodiment newly adds a surface tension relaxant supply unit 14 to add a surface tension relaxant to at least raw water filtered by the membrane module 2, so that the tubular The resistance force (repulsive force) against the penetration of bubbles into the tubular membrane 5 due to the surface tension at the entrance of the membrane 5 can be reduced. Further, even in the tubular membrane 5, since the resistance of the bubbles to the tubular membrane 5 can be reduced, it is possible to prevent the bubbles from being clogged. Furthermore, by adding the surface tension relaxation agent to the raw water, the bubbles in the gas-liquid mixed phase flow are reduced, so that the bubbles are less likely to clog the tubular membrane 5. Therefore, as shown in FIG. 2 (b), even when the membrane module 2 has a large number of tubular membranes 5, the raw water of the gas-liquid mixed phase flow flows through each tubular membrane 5 uniformly. Can do. Thereby, the number of the tubular membranes 5 which are actually filtered in the membrane module 2 is reduced, and the efficiency of the membrane filtration rate can be prevented from being lowered. Further, the solid adhered to the tubular membrane 5 by filtration is not dried and the lifetime of the tubular membrane 5 is not shortened.

Furthermore, even if the ratio of air in the gas-liquid multiphase flow is increased to increase the membrane cleaning efficiency and the flow rate is reduced to reduce power, the raw water of the gas-liquid multiphase flow is It can flow uniformly in the tubular membrane 5. Focusing on the flow rate, in the conventional water treatment system, when the raw water circulation rate is less than about 0.5 m / s, the probability that bubbles are clogged in the tubular membrane 5 as shown in FIG. It has been confirmed that On the other hand, when a surface tension relaxation agent is added, even if the raw water circulation speed is about 1/5 (about 0.1 m / s), the gas-liquid mixed phase flow is not the membrane module 2 as shown in FIG. It was confirmed that the gas flowed uniformly in the plurality of tubular membranes 5 inside. Therefore, by adding the surface tension relaxation agent, the raw water of the gas-liquid mixed phase flow can be made to flow uniformly to the plurality of tubular membranes with low power.

As the component of the surface tension relieving agent to be added, a substance having a hydrophilic group and a hydrophobic group such as a surfactant can be used. Specifically, a plant surfactant derived from palm oil or a grain derived fatty acid is used. Sodium or the like is preferably used. In particular, when activated sludge is contained in raw water, there is no adverse effect on microorganisms in the activated sludge. Furthermore, since the above materials are decomposed by microorganisms, there is an effect that the treatment process and the environment are not adversely affected. In addition, when the above components are used, the solid adhering to the tubular membrane 5 can be removed, so that the membrane cleaning power is improved.

The surface tension relaxation agent used in the water treatment system 1 according to the embodiment of the present invention is very small compared to the amount of raw water to be filtered. Therefore, since the surface tension relaxation agent supply unit 14 may be small compared with other configurations, it can be easily incorporated into a conventional water treatment system.

  The present invention is not limited to the embodiment described above. For example, FIG. 1 is only an example of the system configuration of the water treatment system 1, and a different system configuration may be adopted.

  DESCRIPTION OF SYMBOLS 1 ... Water treatment system, 2 ... Membrane module, 4 ... Raw water pump (raw water supply part), 5 ... Tubular membrane (tubular membrane), 7 ... Air blower (air supply part), 8, 9 ... Pressure gauge, 14 ... Surface tension relaxation agent supply unit, 16... Control unit.

Claims (4)

A membrane module having a plurality of tubular membranes and filtering raw water;
A raw water supply unit for supplying the raw water from the raw water source to the membrane module;
A gas supply unit configured to supply a gas to the raw water and use the raw water supplied to the membrane module as a gas-liquid mixed phase flow;
A water treatment system comprising: a surface tension relaxant supply unit that adds a surface tension relaxant to the raw water.   The water treatment system according to claim 1, wherein the surface tension relaxation agent is a plant surfactant or a cereal-derived fatty acid sodium. The raw water supply unit is a raw water pump,
The water treatment system according to claim 1 or 2, wherein the surface tension relaxation agent supply unit is installed on the upstream side of the raw water pump. Adding a surface tension relaxant to the raw water;
A gas-liquid mixed phase flow by supplying gas to the raw water;
Supplying the gas-liquid mixed phase flow to a membrane module having a plurality of tubular membranes;
And a step of performing filtration by passing the gas-liquid mixed phase flow through the plurality of tubular membranes.

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