JP6965025B2 - Membrane filtration device and membrane filtration method - Google Patents

Description

The present invention relates to a membrane filtration apparatus and a membrane filtration method in which a flocculant is added to water to be treated to perform membrane filtration treatment.

In membrane filtration, a flocculant may be added in order to reduce membrane clogging (fouling) in which substances to be filtered adhere to and accumulate on the surface or pores of the filtration membrane (see, for example, Patent Document 1).

In such an agglutinating membrane filtration method, membrane clogging occurs even if an agglutinating agent is added and the agglutination conditions are optimized. Normally, the coagulant is added and mixed by providing a mixing tank, but if the coagulant is added and mixed by providing a mixing tank, the installation area and cost of the membrane filtration device increase, and the cost is increased. Since the pressure is released in the mixing tank, it is not possible to perform membrane filtration that supplies the water to be treated to the filtration device using the difference in head.

Japanese Patent No. 4517165

An object of the present invention is a membrane filtration method in which a flocculant is added to water to be treated to perform membrane filtration treatment, in which the occurrence of membrane blockage is suppressed and treated water having good treated water quality can be obtained without providing a mixing tank. It is an object of the present invention to provide a membrane filtration apparatus and a membrane filtration method.

In the present invention, the coagulant-adding means for adding a coagulant to the water to be treated and the coagulant-added water to which the coagulant is added are subjected to membrane filtration treatment using at least one of a microfiltration membrane or an ultrafiltration membrane. A flow path provided between the membrane filtration means, the flocculant addition means and the membrane filtration means through which the flocculant-added water flows, and a stirring blade provided in the flow path and rotated by power are provided. The membrane is provided with a stirring device for stirring the coagulant-added water, the stirring device is an in-line mixer, and the stirring intensity G value in the stirring device is in the range of 500 to 1900 / s. It is a filtration device.

In the membrane filtration device, it is preferable that the stirring device further includes a rotation speed control device for controlling the rotation speed of the stirring blade.

In the membrane filtration apparatus, it is preferable to provide a coagulation aid adding means for adding an inorganic coagulation aid to the water to be treated in front of the coagulant adding means. In the membrane filtration apparatus, the power in the in-line mixer is preferably a motor. In the membrane filtration device, the stirring intensity G value is preferably expressed by the following formula.
G = [ρCΣ _i (a _i v _i ³ ) / 2 μV] ^1/2
ρ: Water density (kg / m ³ , 20 ° C)
C: Drag coefficient of stirring blade
a _i : Area perpendicular to the direction of movement of the stirring blade i (m ² )
v _i : Average speed of stirring blade i (m / s)
μ: Viscosity coefficient of water (kg / m · s, 20 ° C)
V: Capacity of stirrer (m ³ )

Further, in the present invention, the coagulant addition step of adding a coagulant to the water to be treated and the coagulant-added water to which the coagulant is added are membrane-filtered using at least one of a microfiltration membrane or an ultrafiltration membrane. A flow path through which the coagulant-added water flows and a flow path provided in the flow path between the coagulant addition step and the membrane filtration step, including a membrane filtration step to be treated, and rotated by power. A membrane filtration method in which the aggregating agent-added water is agitated by a agitator having a agitation blade, the agitator is an in-line mixer, and the agitation intensity G value in the agitator is in the range of 500 to 1900 / s. Is.

In the membrane filtration method, it is preferable that the stirring device further includes a rotation speed control device for controlling the rotation speed of the stirring blade.

In the membrane filtration method, it is preferable to include a coagulation aid addition step of adding an inorganic coagulation aid to the water to be treated before the coagulant addition step. In the membrane filtration method, the power in the in-line mixer is preferably a motor. In the membrane filtration method, the stirring intensity G value is preferably expressed by the following formula.
G = [ρCΣ _i (a _i v _i ³ ) / 2 μV] ^1/2
ρ: Water density (kg / m ³ , 20 ° C)
C: Drag coefficient of stirring blade
a _i : Area perpendicular to the direction of movement of the stirring blade i (m ² )
v _i : Average speed of stirring blade i (m / s)
μ: Viscosity coefficient of water (kg / m · s, 20 ° C)
V: Capacity of stirrer (m ³ )

In the present invention, in the membrane filtration method in which a flocculant is added to the water to be treated and the membrane filtration treatment is performed, the occurrence of membrane clogging can be suppressed and treated water having good treated water quality can be obtained without providing a mixing tank. Filtration equipment and membrane filtration methods can be provided.

It is a schematic block diagram which shows an example of the membrane filtration apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows another example of the membrane filtration apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows the membrane filtration apparatus used in the comparative example. It is a figure which shows the relationship between the stirring intensity G value (/ s) and the differential pressure rise rate (kPa / d) between membranes in an Example and a comparative example. It is a figure which shows the relationship between the stirring intensity G value (/ s), the chromaticity (degree) of treated water, and TOC (mg / L) in an Example and a comparative example.

Embodiments of the present invention will be described below. The present embodiment is an example of carrying out the present invention, and the present invention is not limited to the present embodiment.

An outline of an example of the membrane filtration device according to the embodiment of the present invention is shown in FIG. 1, and its configuration will be described. The membrane filtration device 1 includes, as a stirring device, a flow path (mixing chamber) 34 through which the coagulant-added water flows, a motor 18 as a power source, and a stirring blade 20 provided in the flow path 34 and rotated by the motor 18. The in-line mixer 12 is provided, and as a membrane filtration means, a filtration device 14 having at least one microfiltration membrane or an ultrafiltration membrane is provided. The membrane filtration device 1 may include a water tank 10 to be treated.

In the membrane filtration device 1 of FIG. 1, a water pipe 22 to be treated is connected to the inlet of the water tank 10 to be treated, and the outlet of the water tank 10 to be treated and the inlet of the flow path 34 of the in-line mixer 12 are connected via a pump 16. It is connected by the water supply pipe 24 to be treated. The outlet of the flow path 34 of the in-line mixer 12 and the inlet of the filtration device 14 are connected by a coagulant-added water pipe 26. A treated water pipe 28 is connected to the outlet of the filtration device 14. A coagulant addition pipe 30 is connected as a coagulant addition means between the pump 16 in the water supply pipe 24 to be treated and the inlet of the flow path 34 of the in-line mixer 12. That is, a powered in-line mixer 12 is provided between the flocculant addition pipe 30 and the filtration device 14.

The membrane filtration method and the operation of the membrane filtration device 1 according to the present embodiment will be described.

The water to be treated is stored in the water tank 10 to be treated as needed through the water pipe 22 to be treated, and then sent to the in-line mixer 12 through the water supply pipe 24 to be treated by the pump 16. Here, the coagulant is added through the coagulant addition pipe 30 between the pump 16 in the water supply pipe 24 to be treated and the inlet of the flow path 34 of the in-line mixer 12 (coagulant addition step). The coagulant-added water is agitated and mixed by the stirring blade 20 rotationally driven by the powered motor 18 in the flow path 34 of the in-line mixer 12 to perform the coagulation treatment. A pH adjuster may be added together with the flocculant through a pH adjuster addition pipe (not shown) (pH adjuster addition step). After that, the coagulant-added water is sent to the filtration device 14 through the coagulant-added water pipe 26. The coagulant-added water is subjected to membrane filtration treatment using at least one of a microfiltration membrane or an ultrafiltration membrane in the filtration device 14 (membrane filtration step). The treated water that has been membrane-filtered is discharged through the treated water pipe 28.

The membrane filtration method according to the present embodiment is a membrane filtration method in which a flocculant is added to water to be treated to perform a membrane filtration treatment. This is a method in which a flocculant and water to be treated are mixed with an in-line mixer 12 to perform a membrane filtration treatment. As a result, in the membrane filtration method in which a flocculant is added to the water to be treated and the membrane filtration treatment is performed, the occurrence of membrane clogging is suppressed even if a mixing tank is not provided, and treated water having good treated water quality can be obtained. In addition, the installation area and cost of the membrane filtration device can be reduced.

After the membrane filtration step has been performed for a predetermined time, the filtration membrane may be backwashed or air-cleaned using treated water or separately backwashed water. As a result, the occurrence of membrane obstruction is suppressed, the differential pressure between membranes is restored, and it contributes to stable operation of the membrane.

In the membrane filtration device 1, the water to be treated may be sent from the water tank 10 to be treated to the in-line mixer 12 by utilizing the head difference. As a result, it is not necessary to provide the pump 16, and the power of the pump can be reduced.

The coagulant and, if necessary, the pH adjuster may be added in the water supply pipe 24 in front of the in-line mixer 12 or in the flow path 34 of the in-line mixer 12.

The in-line mixer 12 has, for example, a tubular flow path (mixing chamber) 34 through which the coagulant-added water flows, is installed in the motor 18 as power and in the flow path (mixing chamber) 34 as stirring means. The stirring blade 20 is rotationally driven by the motor 18.

The power provided by the in-line mixer 12 may be any as long as it drives the stirring means, and is not particularly limited, but is, for example, a motor.

Stirring intensity (G value) is one of the indexes of stirring conditions in flock formation. The G value is generally expressed by the following formula. In the formation of flocs by a flocculant in a mixing tank, if the stirring strength (G value) is too small, the growth of flocs slows down, and if it is too large, the flocs are destroyed by shearing force. To about 100 to 300 / s. However, the present inventors have found that the rate of increase in differential pressure of the membrane filtration apparatus can be suppressed by increasing the stirring intensity using an in-line mixer. It was also found that the differential pressure increase rate of the membrane filtration device can be suppressed even when the stirring intensity by the in-line mixer is equal to or less than the stirring speed in the mixing tank. The stirring intensity of the in-line mixer 12 is preferably in the range of 0 to 2300 / s, more preferably in the range of 160 to 2300 / s, further preferably in the range of 500 to 1900 / s, and further preferably in the range of 500 to 1900 / s. The range of 1300 / s is particularly preferable. By setting the stirring intensity in the in-line mixer 12 to these ranges, the occurrence of membrane blockage is further suppressed, and treated water having better treated water quality can be obtained.
G = [ρCΣ _i (a _i v _i ³ ) / 2 μV] ^1/2
ρ: Water density (eg 1.0 × 10 ³ kg / m ³ , 20 ° C)
C: Drag coefficient of stirring blade (= 1.5)
a _i : Area perpendicular to the direction of movement of the stirring blade i (m ² )
v _i : Average speed of stirring blade i (m / s)
μ: Viscosity coefficient of water (for example, 1.0 × 10 ^-3 kg / m · s, 20 ° C.)
V: Mixer capacity (m ³ )
In the above equation, it is assumed that the water flow does not cause a co-rotational motion.

Examples of the flocculant include inorganic flocculants such as polyaluminum chloride (PAC), ferric chloride and polysilica iron (PSI), and organic flocculants such as polyacrylamide. Inorganic flocculants containing at least one of aluminum, ferric chloride and polysilica iron are preferred.

Examples of the pH adjuster include acids such as hydrochloric acid and sulfuric acid, and alkalis such as sodium hydroxide.

The pH of the agglutinating agent-added water in the agglutination treatment is preferably in the range of the pH at which the metal ions of the agglutinating agent form a hydroxide. For example, when the flocculant is polyaluminum chloride, it is preferably in the range of 5 to 8, and when it is ferric chloride, it is preferably in the range of 3 to 11. If the pH of the coagulant-added water deviates from the pH range, aluminum or iron contained in the coagulant may leak into the treated water of the filtration membrane.

The filtration membrane is at least one of an ultrafiltration (UF) membrane and a microfiltration (MF) membrane. The filtration membrane may be an inorganic membrane such as a ceramic membrane or an organic membrane such as PVDF (polyvinylidene fluoride), PES (polyethersulfone), PS (polysulfone), or PTFE (polytetrafluoroethylene). Further, the filtration membrane may be either an external pressure type or an internal pressure type. An external pressure type organic membrane capable of purifying air is preferable.

In front of the coagulant-adding pipe 30, for example, a coagulation aid-adding pipe or a coagulation aid-adding tank is provided as a coagulation aid-adding means for adding an inorganic coagulation aid to the water to be treated, and the coagulant is added. An inorganic coagulation aid may be added prior (step of adding the coagulation aid). By adding an inorganic coagulation aid before the coagulant is added, the occurrence of membrane blockage is suppressed, which contributes to stable operation of the membrane. Usually, the coagulation aid is used to make fine flocs generated by the flocculant into large flocs by adsorption and cross-linking action to promote sedimentation separation, and membrane filtration is performed by adding the flocculant to the water to be treated. In the method, a polymer flocculant is generally used. Since the inorganic coagulation aid causes filtration resistance, normally, the inorganic coagulation aid was not added, but the present inventor made it before the coagulant was added to the water to be treated. It was found that the occurrence of membrane occlusion was unexpectedly suppressed by adding an inorganic coagulation aid to the water. It is considered that this is because suspended solids, TOC components, metal ions of the flocculant, etc., which are the main causes of membrane blockage, are adsorbed by the flocculation aid and are less likely to adhere to the filtration membrane in a charged manner. In addition, since the flocs are increased by the coagulation aid, the resistance of the flocs adhering to the filtration membrane surface during backwashing or air cleaning is increased from the cleaning water or the cleaning air, and the flocs are easily peeled off from the filtration membrane surface. It is thought that it was a result.

Examples of the inorganic agglutinating aid include inorganic mineral agglutinating aids such as bentonite, kaolin, activated silicic acid, and activated carbon, and those containing at least one of bentonite, kaolin, activated silicic acid, and activated carbon. Is preferable. As the aggregating aid, a polymer polymer type may be considered, but the polymer polymer type hardly exerts the above-mentioned effect of suppressing the occurrence of membrane occlusion.

The volume average particle size of the aggregating aid is preferably in the range of 1 to 50 μm, and preferably in the range of 5 to 20 μm. If the volume average particle size of the agglutination aid is less than 1 μm, the agglutination aid may cause membrane blockage, and if it exceeds 50 μm, the effect of improving poor aggregation may be reduced. The volume average particle size of the aggregating aid can be measured by a laser diffraction type particle size distribution measuring method, and can be measured, for example, by using SALD-200VER manufactured by Shimadzu Science.

The amount of the aggregating aid added may be appropriately determined and adjusted by beaker test, data collection during test run of equipment, actual operation, etc., but is preferably in the range of 5 to 50 mg / L. It is preferable to add the mixture so that the sum with the amount of suspended solids in water is in the range of 20 to 100 mg / L. If the amount of the aggregating aid added is less than 5 mg / L, the effect of suppressing the occurrence of membrane occlusion may be reduced, and if it exceeds 50 mg / L, the aggregating aid may cause filtration resistance and hinder stable operation. There is.

The addition of the coagulation aid may be performed based on the intermembrane differential pressure of the filtration membrane in the filtration device 14. For example, while monitoring the intermembrane differential pressure of the filtration membrane, when the upper limit value of the predetermined intermembrane differential pressure is reached, a coagulation aid is added and the pressure is lowered to the lower limit value of the predetermined intermembrane differential pressure. Occasionally, the addition of the coagulation aid may be stopped. Further, the coagulation aid may be added at a predetermined time interval for a predetermined time. For example, the addition of the coagulation aid is preferably performed once every 10 hours or less for 5 hours or more each time. In addition to these, it can be appropriately determined and adjusted by beaker test, data collection during test run of equipment, actual operation, and the like.

The TOC concentration of the water to be treated is preferably in the range of 0.5 to 10 mg / L. The suspended solids (SS) concentration in the water to be treated is preferably in the range of 1 to 100 mg / L. The water to be treated preferably has a TOC concentration in the range of 0.5 to 10 mg / L and a suspended solids (SS) concentration in the range of 1 to 20 mg / L. When the TOC concentration of the water to be treated is lower than 0.5 mg / L, membrane occlusion is unlikely to occur, so that the advantage of applying the membrane filtration method according to the present embodiment may be diminished. When the TOC concentration of the water to be treated is higher than 10 mg / L, membrane occlusion is likely to occur even if the membrane filtration method according to the present embodiment is applied. The lower the SS concentration of the water to be treated, the more difficult the agglutination treatment may be because there is no SS that is the core of the agglutination. When poor coagulation occurs, organic substances may not be sufficiently removed, or the coagulant itself may cause membrane blockage. Therefore, the membrane filtration method according to the present embodiment is particularly effective when the SS concentration is in the range of 1 to 20 mg / L.

Examples of the water to be treated include river water, factory effluent and the like.

When the water to be treated is river water or the like, the TOC and SS in the water to be treated may fluctuate. In this case, it is preferable that the membrane filtration device further includes a rotation speed control device that controls the rotation speed of the motor 18 or the like of the in-line mixer 12.

For example, the membrane filtration device 3 shown in FIG. 2 includes a rotation speed control device 32 in addition to the configuration of the membrane filtration device 1 shown in FIG. In the membrane filtration device 3, the rotation speed control device 32 is connected to the motor 18 powered by the in-line mixer 12 by an electrical connection or the like. By providing the rotation speed control device 32, the agglutination process can be performed more efficiently.

The rotation speed control device 32 preferably controls the stirring intensity of the in-line mixer 12 to be 0 to 2300 / s, more preferably 160 to 2300 / s, and more preferably 500 to 1900 / s. It is more preferable to control so as to be 500 to 1300 / s, and it is particularly preferable to control so as to be 500 to 1300 / s. By controlling the stirring intensity in the in-line mixer 12 to these ranges, the occurrence of membrane blockage is further suppressed, and treated water having better treated water quality can be obtained.

The rotation speed control device 32 may be any one capable of controlling the rotation speed of the power of the motor 18 of the in-line mixer 12, and is not particularly limited, but is, for example, an inverter.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Example 1, Comparative Example 1>
As the first embodiment, as shown in FIG. 2, a flow path (mixing chamber) 34 through which the coagulant-added water flows, a motor 18 as a power source, and a stirring blade provided in the flow path 34 and rotated by the motor 18. A mixing tank 52 having a membrane filtration device 3 (hereinafter, in-line system) using the in-line mixer 12 having 20 and a stirring device 60 instead of the in-line mixer 12 of the membrane filtration device 3 shown in FIG. 3 as Comparative Example 1. A comparative test was conducted with a membrane filtration device 5 (hereinafter referred to as a coagulation-mixed system) provided with the above. In the membrane filtration device 5 of FIG. 3, a water treatment pipe 62 is connected to the inlet of the water tank 50 to be treated, and the outlet of the water tank 50 to be treated and the inlet of the mixing tank 52 are supplied with water to be treated via a pump 56. It is connected by a pipe 64. The outlet of the mixing tank 52 and the inlet of the filtration device 54 are connected by a coagulant-added water pipe 66 via a pump 58. A treated water pipe 68 is connected to the outlet of the filtration device 54. A coagulant addition pipe 70 is connected to the mixing tank 52.

The conditions of Example 1 and Comparative Example 1 were the same except for the stirring method, and the operation was performed with a flux of 1.5 m / d, a recovery rate of the filtration device of 95%, and a flocculant (PAC) injection rate of 25 mg / L. In the first embodiment, the in-line mixer 12 is provided with an inverter as the rotation speed control device 32, and the rotation speed is changed (Example 1: stirring intensity G value (/ s) = 0,160,500,1300,1900,2300). , Comparative Example 1: Stirring strength G value (/ s) = 160) Water was passed. A multi-line mixer (manufactured by Satake Chemical Machinery Co., Ltd.) was used as the in-line mixer. The relationship between the stirring intensity G value (/ s) and the differential pressure increase rate between the membranes (kPa / d) is shown in FIG.

Example 1 remained at a lower intermembrane differential pressure as compared with Comparative Example 1 which was a conventional coagulation and miscibility system. Even if the stirring device was not rotated, turbulence was generated by the stirring blade of the stirring device to stir the flocculant, so that the differential pressure increase rate was the same as that of Comparative Example 1. From these results, the superiority of in-line agglutinating membrane filtration by an in-line mixer was shown.

FIG. 5 shows the difference in treated water quality depending on the rotation speed (G value) of the in-line mixer. It was confirmed that the treated water quality can be improved by changing the rotation speed of the in-line mixer. By using the in-line mixer, it was possible to perform agglutinating membrane filtration without providing a mixing tank. By installing an inverter in the in-line mixer and controlling the number of revolutions, the quality of treated water could be further improved.

In this way, in the membrane filtration method in which a flocculant is added to the water to be treated and the membrane filtration treatment is performed by the method of the example, the occurrence of membrane clogging is suppressed and the treatment of good treated water quality is performed even if a mixing tank is not provided. Water was obtained.

1,3,5 film filtration device, 10,50 water tank to be treated, 12 in-line mixer, 14,54 filtration device, 16,56,58 pump, 18 motor, 20 stirring blades, 22,62 water to be treated pipe, 24, 64 Processed water supply pipe, 26,66 Coagulant-added water pipe, 28,68 Treated water pipe, 30,70 Coagulant-added pipe, 32 Rotation control device, 34 flow path, 52 mixing tank, 60 stirring device.

Claims (10)

A coagulant addition means for adding a coagulant to the water to be treated,
Membrane filtration means for performing membrane filtration treatment of the coagulant-added water to which the coagulant has been added using at least one of a microfiltration membrane or an ultrafiltration membrane.
It has a flow path provided between the coagulant addition means and the membrane filtration means through which the coagulant-added water flows, and a stirring blade provided in the flow path and rotated by power, and the coagulation. A stirrer that stirs the additive-added water and
With
The agitator is an in-line mixer and
A membrane filtration device characterized in that the stirring intensity G value in the stirring device is in the range of 500 to 1900 / s. The membrane filtration device according to claim 1.
The agitator is a membrane filtration device further comprising a rotation speed control device for controlling the rotation speed of the stirring blade. The membrane filtration apparatus according to claim 1 or 2.
A membrane filtration apparatus characterized in that a coagulation aid adding means for adding an inorganic coagulation aid to the water to be treated is provided in front of the coagulant adding means. The membrane filtration apparatus according to any one of claims 1 to 3.
A membrane filtration device characterized in that the power in the in-line mixer is a motor. The membrane filtration apparatus according to any one of claims 1 to 4.
A membrane filtration device characterized in that the stirring intensity G value is represented by the following formula.
G = [ρCΣ _i (A _i v _i ³ ) / 2μV] ^1/2
ρ: Water density (kg / m) ³ , 20 ° C)
C: Drag coefficient of stirring blade
a _i : Area (m) perpendicular to the direction of movement of the stirring blade i ² )
v _i : Average speed of stirring blade i (m / s)
μ: Viscosity coefficient of water (kg / m · s, 20 ° C)
V: Capacity of agitator (m ³ ) The coagulant addition step of adding the coagulant to the water to be treated, and
A membrane filtration step in which the coagulant-added water to which the coagulant is added is subjected to a membrane filtration treatment using at least one of a microfiltration membrane or an ultrafiltration membrane.
Including
Between the coagulant addition step and the membrane filtration step, the coagulant is provided by a flow path through which the coagulant-added water flows and a stirring device provided in the flow path and having a stirring blade that is rotated by power. Stir the added water and
The agitator is an in-line mixer and
A membrane filtration method characterized in that the stirring intensity G value in the stirring device is in the range of 500 to 1900 / s. The membrane filtration method according to claim 6.
The membrane filtration method further includes a rotation speed control device for controlling the rotation speed of the stirring blade. The membrane filtration method according to claim 6 or 7.
A membrane filtration method comprising a coagulation aid addition step of adding an inorganic coagulation aid to the water to be treated before the coagulant addition step. The membrane filtration method according to any one of claims 6 to 8.
A membrane filtration method characterized in that the power in the in-line mixer is a motor. The membrane filtration method according to any one of claims 6 to 9.
The membrane filtration method, wherein the stirring strength G value is represented by the following formula.
G = [ρCΣ _i (A _i v _i ³ ) / 2μV] ^1/2
ρ: Water density (kg / m) ³ , 20 ° C)
C: Drag coefficient of stirring blade
a _i : Area (m) perpendicular to the direction of movement of the stirring blade i ² )
v _i : Average speed of stirring blade i (m / s)
μ: Viscosity coefficient of water (kg / m · s, 20 ° C)
V: Capacity of agitator (m ³ )

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