JP2007289847A - Raw tap water purification method and its apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a raw tap water purification method which can reduce the load of pollutants on membrane filtration, reduce the installation area of an apparatus and system and a construction cost, and reduce the volume of wastewater from the whole plant. <P>SOLUTION: After adding an inorganic coagulant D to raw tap water A containing organic matter, rapid agitation and slow agitation are carried out to form coagulated flocs. The raw tap water is introduced a single treatment tank 3 where a pressure floatation part is formed in the upper space, and an immersed filtration membrane module 13 is installed in the lower space. In the treatment tank 3, the coagulated flocs are subjected to a pressure floatation in the upward direction, and at the same time the raw tap water is subjected to suction filtration through the immersed filtration membrane module 13 to obtain purified water B. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water purification treatment method and a water purification treatment apparatus for purifying raw tap water containing organic matter such as turbidity, bacteria, pathogenic microorganisms, algae, iron, manganese, and humin to obtain sanitary tap water. .

In recent years, membrane filtration devices such as microfiltration (MF) or ultrafiltration (UF) that can remove almost completely turbidity, bacteria, pathogenic microorganisms, etc. contained in tap water are used in the field of water purification. Membrane filtration water treatment is rapidly spreading.
Filtration membranes (MF membranes, UF membranes) applied to this membrane filtration water purification treatment are organic membranes made of organic compounds such as cellulose compounds, polysulfone, polyethersulfone, polyacrylonitrile, polyethylene, polypropylene, polyolefin, polyimide, and the like. It is roughly classified into inorganic films made of ceramics obtained by firing high-purity alumina (for example, see Non-Patent Document 1).
Recently, a filtration membrane made of polyvinylidene fluoride, which has excellent chemical properties such as chemical resistance, has been developed and used for water purification treatment.

  In addition, the membranes used for membrane filtration water treatment include hollow fibers, spirals (winding), tubulars (winding), and flat membranes. It is practically used as a membrane module formed by housing or accumulating membranes in casings, cans, outer frames or the like.

  As a method of membrane filtration water purification treatment, a membrane module is integrated with a casing or accommodated as a number of elements in a casing, and water to be treated (raw water) is pressurized with a pump and subjected to membrane filtration. Body type or casing storage type / pump pressurization method) and a system (immersion type / pump suction method) in which a membrane module integrated with a framework is immersed in a treatment tank and suction filtered with a pump (See, for example, Non-Patent Document 2).

Membrane filtration is divided into microfiltration (MF) and ultrafiltration (UF) depending on the pore diameter or molecular weight cut off on the membrane surface.
The microfiltration (MF) membrane surface has pores with a diameter of approximately 0.05 to 0.5 μm, and the ultrafiltration (UF) membrane surface has pores that can fractionate those with a molecular weight of approximately 10,000 to 1 million daltons. It has been opened.
All of these are applied to water purification.
Then, by filtering the raw tap water, the turbidity, bacteria, pathogenic microorganisms, etc. contained in the raw tap water are removed by the sieving action of a large number of fine holes opened on the membrane surface. It is processed.

By the way, if the membrane filtration is continued, the removed substance accumulates on the surface of the membrane, the filtration resistance is increased, and when the control is performed so that the amount of filtered water is constant, the pressure difference across the membrane ( (Membrane differential pressure) increases.
In order to prevent this and maintain a constant filtration performance, the membrane filtrate is pumped approximately every 15 to 90 minutes, from the filtrate side (secondary side) in the direction opposite to that during filtration. By feeding water, an operation for removing dirt accumulated on the membrane surface is performed. This operation is called back pressure water washing (back washing). At this time, it is known to enhance the physical cleaning effect by injecting a sodium hypochlorite solution into the membrane filtrate used for cleaning.
In addition, a method of removing dirt on the membrane surface (air) by sending coarse bubbles from the lower side of the membrane module without backwashing, and using the shear force of the water flow generated when the bubbles rise along the membrane surface. Bubbling or air scrubbing) or a combination of this method and backwashing is also known as a physical cleaning method for membranes.

However, if membrane filtration is continued in a cycle in which the physical cleaning method and membrane filtration are repeated, the effect of physical cleaning is observed in the short term, but the membrane differential pressure gradually increases in the long term.
This is because organic substances, iron, manganese, and the like that cannot be removed by physical cleaning adhere to the film surface or the inside of the film pores.
Depending on the type of membrane or membrane module and the membrane filtration device, the chemical solution is sent to the membrane module and the chemical solution and the membrane are brought into contact with each other for a certain period of time before reaching a predetermined upper limit membrane differential pressure. An operation for recovering the membrane filtration performance is carried out by eluting the soil components of the solution into the solution. This operation is called chemical cleaning, and the chemical used is for removing soil caused by metals, such as sodium hypochlorite solution or caustic soda solution, or a combination of these. It is known that an inorganic acid or organic acid solution is effective for use. This chemical cleaning needs to be performed after stopping the operation of the membrane filtration apparatus for about 1 to 2 days. At that time, waste liquid is generated due to the chemical cleaning, and it costs money for its treatment and disposal. Although it is desirable to have less water, it is also related to the quality of the raw water to be treated and the set value of the membrane filtration flow rate (membrane filtration flow rate), so the membrane filtration device design should be about once or twice a year. It is common to determine the operating factors.

In order to reduce the frequency of the above chemical cleaning when water raw water containing organic substances such as turbidity, bacteria, pathogenic microorganisms, algae, iron, manganese, humin, etc. is purified by membrane filtration, A method is known in which pretreatment is performed by coagulation sedimentation or in combination with rapid filtration that is provided after them to reduce the load of the contaminants on membrane filtration (see Non-Patent Document 3).
According to the method described in Non-Patent Document 3, by removing in advance the organic matter such as turbidity, bacteria, pathogenic microorganisms, algae, iron, manganese, humin, etc. in the tap water that clogs the membrane, By reducing the load of these substances on the membrane filtration, it is possible to stabilize the membrane filtration and reduce the frequency of chemical cleaning of the filtration membrane module. Along with the increase, the number of structures such as water tanks necessary for water purification facilities also increases, which causes a problem of increasing the installation area and the construction cost. Moreover, since the coagulation sedimentation installed as a pretreatment facility and the waste water from rapid filtration generate | occur | produce newly, there also exists a problem that the water recovery rate as the whole water purification treatment facility falls.
Supervised by National Emblem of Japan, “Introduction to Water Membrane Filtration Method”, Nihon Suido Shimbun, January 28, 2002, p. 32, 37 Membrane Separation Technology Promotion Association, Membrane Water Purification Committee, “Purified Water Membrane” Gihodo Publishing, June 10, 2003, p. 74-78 Membrane Separation Technology Promotion Association, Membrane Water Purification Committee, “Purified Water Membrane” Gihodo Publishing, June 10, 2003, p. 13

  In view of the problems of the above-described conventional method of purifying water by membrane filtration, the present invention reduces the load of pollutants on membrane filtration, and reduces the installation area and construction cost of the equipment and equipment, It aims at providing the membrane filtration water treatment method and apparatus which can also reduce the amount of drainage from the whole facility.

  In order to achieve the above object, the raw water purification method for tap water of the present invention adds an inorganic flocculant to tap water containing organic matter, and then performs rapid stirring and slow stirring to form an aggregate floc, The pressure levitation separation part is formed in a single treatment tank having an immersion filtration membrane module installed in the lower space, and the aggregated flocs are separated by pressure levitation in the treatment tank in the upward direction, and immersion filtration is performed. Purified water is obtained by suction filtration through a membrane module.

  In addition, the water purification apparatus for raw water of the present invention is a water purification apparatus for raw water containing organic matter, an inorganic flocculant adding means, means for performing rapid stirring and slow stirring to form a flocs floc, A treatment tank to which the formed raw water is introduced, a pressurized floating separation part is formed in the upper space of the treatment tank, an immersion filtration membrane module is installed in the lower space, and the treatment tank is agglomerated in the upward direction. The floc is floated and separated by pressure, and purified water is obtained by suction filtration means through an immersion filtration membrane module.

  According to the water purification method and apparatus for raw water of the present invention, membrane filtration water purification corresponding to a wide range of raw water containing organic matter such as turbidity, bacteria, pathogenic microorganisms, algae, iron, manganese, humin, etc. Even when such raw tap water is subjected to membrane filtration and purification treatment, coagulation, pressure flotation and membrane filtration as pretreatment can be performed in the same and single treatment tank, so it is safe and hygienic. Compared with the conventional method and apparatus for obtaining tap water, the installation area of the facility becomes compact, so that the construction cost can be reduced. In addition, wastewater generated by cohesive pressurization flotation should be discharged in a concentrated state (in addition, wastewater generated during backwashing of the membrane module can be returned to the inflow section of tap water through a drainage tank) Thus, the amount of waste water generated from the entire water purification treatment facility can be greatly reduced, and the discharged sludge can be obtained with a high concentration.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a water purification method and apparatus for raw water according to the present invention will be described with reference to the drawings.

First, FIG. 4 shows a flow chart of a conventional water purification treatment method in which raw water containing organic substances such as turbidity, bacteria, pathogenic microorganisms, algae, iron, manganese and humin is purified by membrane filtration.
In the conventional water purification treatment method, raw tap water A is continuously introduced into the rapid stirring step 34, and an oxidizing agent C such as sodium hypochlorite and inorganic such as polyaluminum chloride, ferric chloride, polysilica iron, and sulfate bands. After the flocculant D is injected and rapid stirring is performed to form fine flocs, in the slow stirring step 35, the flocs are grown by gradually stirring for a certain period of time to increase the diameter thereof. In the coagulation sedimentation step 37, the coagulation floc and the supernatant water are separated. Thereafter, in the membrane filtration step 36, the final purified water treatment is performed to obtain purified water B. In addition, the process illustrated in 37 may include rapid filtration in addition to coagulation sedimentation. Moreover, when iron and manganese contained in the tap water A are already oxidized, it is not necessary to inject an oxidizing agent C such as sodium hypochlorite.

On the other hand, FIG. 3 is a flow diagram of one embodiment of the water purification method of the present invention in which raw water containing organic matter such as turbidity, bacteria, pathogenic microorganisms, algae, iron, manganese, and humin is purified by membrane filtration. Indicates.
In the water purification method of the present invention, the raw water A is continuously introduced into the rapid stirring step 34, and an oxidizing agent C such as sodium hypochlorite and polyaluminum chloride, ferric chloride, polysilica iron, sulfuric acid band, etc. After injecting the inorganic flocculant D and performing rapid stirring to form fine flocs, in the slow stirring step 35, the flocs were grown by increasing the diameter by gently stirring for a certain period of time. After that, it is introduced into a single treatment tank, subjected to pressure levitation separation in the upper space of this treatment tank, and finally in a membrane filtration step 36 for suction filtration through a submerged filtration membrane module installed in the lower part of the treatment tank. To get clean water B. In the water purification method of the present invention, when iron and manganese contained in the raw water A are already oxidized, it is not necessary to inject an oxidizing agent C such as sodium hypochlorite. This is the same as the conventional water purification method.

Next, 1st Embodiment of the water purification apparatus which implements the water purification method of this invention in FIG. 1 is shown.
This water purification apparatus continuously introduces raw water tap water A into a rapid stirring tank 1 equipped with a quick stirring means 7 through an automatic valve 23 to remove oxides such as iron and manganese contained in the raw water tap water A. Fine flocs are prepared by injecting a sufficient amount of oxidizing agent C such as sodium hypochlorite and inorganic flocculant D such as polyaluminum chloride, ferric chloride, polysilica iron, sulfuric acid band, etc. To form.

  Next, in the slow agitation tank 2 provided with the slow agitation means 8 communicating with the rapid agitation tank 1, the agitation is gently performed for a certain period of time to grow a floc, and the pressure floatation that is a single processing tank It flows into the membrane separation tank 3.

  A vertical baffle 18 installed so that the lower end thereof is approximately 10 to 20 cm from the bottom surface of the tank and the lower end thereof are fixed to the bottom surface of the pressurized floating membrane separation tank 3, and the upper end and the pressurization are pressurized. An inclined baffle 19 so that the distance from the stationary water surface of the levitation membrane separation tank 3 is in the range of approximately 40 to 100 cm and the angle with the bottom surface is 45 to 75 °, preferably approximately 60 °; Is provided.

At the inflow portion formed by the vertical baffle 18 and the tank wall, the microbubble generator 16 connected via the pressurized water tank 6 and the automatic valve 28 and the pressurized water manifold 15 is approximately 10 to 20 cm from the tank bottom. It is installed to become.
The microbubble generator 16 pressurizes a part of the membrane filtrate stored in the membrane filtration water tank 4 with the pressurized water pump 10 and simultaneously sucks air E on the suction side of the pressurized water pump 10 to the pressurized water tank 6. This is a device that generates fine bubbles with a diameter of approximately several tens of microns by reducing the pressure water in which an amount of air corresponding to the pressure is dissolved to atmospheric pressure, and is similar to a needle valve or an orifice plate. It is effective.

Then, in the inflow part formed by the vertical baffle 18 and the tank wall, the apparent density of the floc-bubble aggregate in which the generated fine bubbles adhere to the aggregated floc formed in the slow stirring tank 2 is water. As a result, the floating sludge layer F is formed as a result of moving upward along the inclined baffle 19 together with the water flow and being separated to the water surface. This levitation sludge contains organic matter such as turbidity, bacteria, pathogenic microorganisms, algae, oxidized iron, oxidized manganese, and humic substances incorporated into the aggregated floc.
Therefore, these are removed to some extent under the floating sludge layer F to form a relatively clear pretreated water layer.

An immersion filtration membrane module 13 having one end connected to a membrane filtration suction pump 9 is installed in the lower part of the pressurized flotation membrane separation tank 3, and an automatic valve 24 is provided via the immersion filtration membrane of the immersion filtration membrane module 13. The water purification treatment is performed by suction filtration through the passage of the membrane filtration suction pump 9, the automatic valve 26 and the membrane filtration treatment water tank 4.
Although it does not specifically limit for this immersion filtration membrane module 13, The thing formed by integrating | stacking the external pressure hollow fiber filtration membrane made from a polyvinylidene fluoride in the vertical direction can be used suitably.

  A physical cleaning air diffuser 14 is installed below the submerged filtration membrane module 13, and air is continuously or intermittently or periodically sent from the physical cleaning blower 12 to the surface of the filtration membrane. The adhered clogging substance is peeled off by the physical action of the water flow generated by the rising of the bubbles.

  A flow meter 22 with a transmitter is installed in the pipe line from the membrane filtration suction pump 9 to the membrane filtration treatment water tank 4, and membrane filtration is performed via the inverter 17 based on this signal and a preset value of the membrane filtration flow rate. By controlling the number of rotations of the suction pump 9, a predetermined amount, for example, a constant amount of membrane filtered water can be always obtained.

By continuing the membrane filtration for a certain period of time, clogging of the membrane proceeds, and the membrane differential pressure for obtaining a certain amount of membrane filtrate is increased. The membrane module is physically cleaned when the preset membrane differential pressure is reached or after a preset membrane filtration duration.
This physical cleaning is performed according to the following procedure.
First, the membrane filtration suction pump 9 is stopped, the automatic valve 24 and the automatic valve 26 are closed, and membrane filtration is stopped.
Since the to-be-treated water containing the coagulated floc still flows from the slow stirring tank 2 into the pressurized floating membrane separation tank 3, the water level in the pressurized floating membrane separation tank 3 rises and the floating sludge is discharged. It overflows from the trough 20 with the floating sludge layer F. Although not shown in the figure, the levitation sludge layer F is discharged out of the system together with the overflow water. After a sufficient time has passed for the floating sludge layer F to be discharged, the automatic valve 23 and the automatic valve 28 are closed, and the pressurized water pump 10, the rapid stirring means 7, the slow stirring means 8 and the oxidant C are injected. Stop the injection of inorganic flocculant D.
Thereafter, by opening the automatic valve 29, the water level of the pressurized floating membrane separation tank 3 is lowered to the top end of the physical cleaning drainage trough 21.
The physical cleaning blower 12 is operated, relatively coarse bubbles are sent from below the submerged filtration membrane module 13 by the physical cleaning air diffuser 14, and the membrane surface is caused by the rising bubbles and the shearing action of the generated water flow. Remove the clogging material that has adhered. At the same time, the automatic valve 25 and the automatic valve 27 are opened, the membrane filtration suction pump 9 is operated, and the membrane filtrate stored in the membrane filtration water tank 4 is removed from the automatic valve 25, the membrane filtration suction pump 9 and the automatic. Water is fed to the immersion filtration membrane module 13 through the path of the valve 27 for approximately 1 minute in the direction opposite to that during membrane filtration. At this time, although not shown in the figure, when sodium hypochlorite is injected into the membrane filtrate used for backwashing so that the effective chlorine concentration is 1 to 5 mg / L, backwashing is performed more effectively. Can do.
The backwash drainage containing the clogged substances that have been peeled off is sent from the physical wash drainage trough 21 to the drainage tank 5. The physical washing wastewater is returned to the apparatus inflow portion by a fixed amount by the wastewater return pump 11 and mixed with the raw water A to be purified.
When the series of physical cleaning operations is completed, the automatic valve 27 and the automatic valve 25 are closed, the automatic valve 24, the automatic valve 26, the automatic valve 23, and the automatic valve 28 are opened, and the physical cleaning blower 12 is stopped. Then, the pressurized water pump 10, the rapid stirring means 7 and the rapid stirring means 8 are operated to restart the water purification process.

In addition, even if this physical cleaning operation is performed periodically, if the membrane differential pressure does not recover and it becomes difficult to continue the membrane filtration, chemical cleaning is performed.
Although this chemical cleaning is not shown in any of the drawings, the physical cleaning blower is operated with the operation of the processing apparatus stopped and the submerged filtration membrane module 13 left installed in the pressurized floating membrane separation tank 3. 12, the sodium hypochlorite solution and / or the caustic soda solution prepared in advance in another storage tank while sending coarse bubbles from below the submerged filtration membrane module 13, by natural flow due to water level difference, or By pumping, it is sent to the submerged membrane filter module 13 in the direction opposite to the membrane filtration direction, and left in that state for a certain period of time.
In this chemical cleaning, the operation of the processing apparatus was stopped, and the submerged filtration membrane module 13 was taken out from the pressurized flotation membrane separation tank 3 by a separately provided lifting and moving means, and adjusted to an appropriate concentration in advance. According to the method of immersing in another water tank filled with a sodium hypochlorite solution and / or a caustic soda solution, it can be carried out more effectively.

  By controlling devices such as automatic valves, pumps, and blowers in the figure with a control device incorporating a sequencer, this water purification apparatus can be operated fully automatically.

  Moreover, when iron and manganese contained in the tap water A are already oxidized, it is not necessary to inject an oxidizing agent C such as sodium hypochlorite.

Next, 2nd Embodiment of the water purification apparatus which enforces the water purification method of this invention in FIG. 2 is shown. 6 illustrates a variation of one embodiment.
This water purification apparatus is configured by installing a plurality of perforated plates 30 so as to be perpendicular to the water flow as slow stirring means.
In addition, a filler layer 33 is provided in the pressurized water tank 6 as a means for adjusting the pressurized water for generating fine bubbles necessary for levitation separation, and the air from the compressor 32 and the pressurized water are brought into countercurrent contact in the filler layer 33. By doing so, the dissolution efficiency of air is increased.
Furthermore, the pressurized water tank 6 includes a water level meter 31 with a transmitter for detecting the water level in the tank, and a means for controlling the amount of pressurized water from the pressurized water pump 10 based on the signal.
In addition, the other structure and effect | action of this water purifier are the same as the water purifier of the said 1st Embodiment.

  As mentioned above, although the water purification method and the apparatus of the raw water of this invention were demonstrated based on several embodiment, this invention is not limited to the structure described in the said embodiment, and does not deviate from the meaning. The configuration can be changed as appropriate within the range.

  The water purification method of raw water of the present invention and the apparatus reduce the load of contaminants on membrane filtration, reduce the installation area and construction cost of the apparatus and equipment, and reduce the amount of waste water from the entire facility. Therefore, it can be used suitably for the use for obtaining safe and sanitary tap water at low cost.

It is explanatory drawing which shows 1st Embodiment of the water purification apparatus by this invention. It is explanatory drawing which shows 2nd Embodiment of the water purification apparatus by this invention. It is a flowchart which shows one embodiment of the water purification method of this invention. It is a flowchart which shows the conventional water purification method.

Explanation of symbols

1 Rapid stirring tank 2 Slow stirring tank 3 Pressurized floating membrane separation tank (single treatment tank)
DESCRIPTION OF SYMBOLS 4 Membrane filtration water tank 5 Drainage tank 6 Pressurized water tank 7 Rapid stirring device 8 Slow stirring device 9 Membrane filtration suction pump 10 Pressurized water pump 11 Drainage return pump 12 Blower for physical washing 13 Immersion filtration membrane module 14 Physical cleaning aeration device 15 Pressurized water Manifold 16 Fine bubble generator 17 Inverter 18 Vertical baffle 19 Inclined baffle 20 Floating sludge discharge trough 21 Physical wash drain trough 22 Flow meter with transmitter 23-29 Automatic valve 30 Perforated plate 31 Water level meter with transmitter 32 Compressor 33 Filler layer 34 Rapid stirring process 35 Slow stirring process 36 Membrane filtration process 37 Coagulation sedimentation process and / or rapid filtration process A Tap water B Clean water C Oxidant D Inorganic flocculant E Air F Floating sludge layer

Claims (2)

  After adding an inorganic flocculant to tap water containing organic matter, rapid stirring and slow stirring are performed to form an agglomeration floc, a pressure floating separation part is formed in the upper space, and an immersion filtration membrane module is formed in the lower space. Raw tap water characterized in that it is introduced into a single treatment tank installed, and the aggregated floc is lifted and separated in the upward direction in the treatment tank, and purified water is obtained by suction filtration through an immersion filtration membrane module. Water purification method.   In a water purification system for raw water containing organic matter, an inorganic flocculant addition means, means for rapid and slow agitation to form coagulated flocs, and a treatment tank to which floc-formed tap raw water is introduced And forming a pressure floating separator in the upper space of the treatment tank, installing an immersion filtration membrane module in the lower space, separating the aggregated floc by pressure floating in the treatment tank in the upward direction, and immersion filtration Purified water treatment apparatus for raw water supply, wherein purified water is obtained by suction filtration means through a membrane module.

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