JP2020192533A - Water treatment system, water treatment method and water production method - Google Patents

Abstract

To make it possible, upon water treatment using hollow fiber membrane filtration modules, to improve efficiency of filtration treatment, reduce clogging of membrane, and improve cleaning effect by means of air backwash or the like.SOLUTION: Before subjecting raw water to filtration treatment using a hollow fiber membrane bundle with one end not fixed, the turbidity of raw water is measured, and an inorganic flocculant is added thereto in an amount adjusted in accordance with the turbidity measured. This makes it possible to form flocs having preferred sizes, which improves the efficiency of the filtration treatment and reduces clogging of the membrane, and also improves the cleaning effect.SELECTED DRAWING: Figure 2

Description

The present invention relates to a water treatment system, a water treatment method, and a water production method, and more particularly to a technique suitable for treating raw water such as river water and groundwater and reusing it as industrial water.

As a system for treating raw water such as river water and groundwater, there is a system using a hollow fiber membrane filtration module. Among them, the hollow fiber membrane filtration module disclosed in Patent Document 1 has a hollow fiber membrane bundle composed of a large number of hollow fiber membranes in which one end (upper end) is fixed to the container but the other end (lower end) is not fixed. By adopting a structure called "one-end free", it has excellent features as compared with the one using a hollow fiber membrane bundle in which both ends are fixed. That is, when the cleaning treatment for removing the deposits on the surface of the hollow fiber membrane is performed by applying air scrubbing, the non-fixed end side of the hollow fiber membrane moves freely, so that the effect of peeling the deposits is high. Further, the hollow fiber membrane filtration module of Patent Document 1 is provided with a rectifying tube extending from the fixed side of the hollow fiber membrane bundle toward the longitudinal direction of the hollow fiber membrane bundle, so that the hollow fiber membranes are entangled with each other during cleaning. It is also possible to prevent the hollow fiber membrane from being broken due to the cutting of the hollow fiber membrane or the stress concentration on the fixed end side of the hollow fiber membrane.

On the other hand, in order to treat the raw water having high turbidity, an inorganic flocculant may be added and combined with the treatment by the hollow fiber membrane filtration module. It is considered effective to add an inorganic flocculant at a high concentration for effective water treatment. However, a high concentration of the inorganic flocculant itself can cause membrane fouling and clogging. There was a concern that efficient filtration treatment with a hollow fiber membrane (hereinafter, simply referred to as filtration treatment) could not be performed, or the life of the hollow fiber membrane could be shortened. Therefore, when combined with the filtration treatment, the concentration or the amount of the inorganic flocculant added is generally kept low.

Japanese Patent No. 3686225 International Publication WO2013 / 099857

However, as a result of diligent studies by the present inventor, when the concentration of the inorganic flocculant is low, the size of the agglomerates (hereinafter referred to as flocs) is generally small, and the pores of the hollow fiber membrane are easily blocked, and flocs It was found that the cleaning effect of air scrubbing was diminished by easily entering and staying between the hollow fibers.

Therefore, it is an object of the present invention to realize efficiency of filtration treatment and reduction of membrane blockage when water treatment is performed using a hollow fiber membrane filtration module, and to improve the cleaning effect. ..

Therefore, in one embodiment of the present invention, in a water treatment system in which raw water is treated by a hollow fiber membrane bundle whose one end is not fixed, the turbidity of the raw water is measured prior to performing filtration treatment by the hollow fiber membrane bundle. It includes a turbidity measuring unit and a coagulant adding unit that adds an amount of an inorganic flocculant adjusted based on the measured turbidity.

Further, in another embodiment of the present invention, in a water treatment method for treating raw water with a hollow fiber membrane bundle whose one end is not fixed, the turbidity of the raw water is measured prior to performing filtration treatment with the hollow fiber membrane bundle. It comprises a step and a step of adding an amount of the inorganic flocculant adjusted based on the measured turbidity.

Further, another embodiment of the present invention includes a step of measuring the turbidity of raw water, a step of adding an amount of an inorganic flocculant adjusted based on the measured turbidity, and a step of adding the inorganic flocculant. There is a step of filtering the raw water with a hollow fiber membrane bundle whose one end is not fixed, and a method of producing water.

According to the present invention, the turbidity of the raw water is measured and the amount adjusted based on the measured turbidity prior to performing the filtration treatment of the raw water using the hollow fiber membrane bundle whose one end is not fixed. Add an inorganic flocculant. As a result, by forming the flocs into a preferable size, the efficiency of the filtration process and the reduction of the blockage of the membrane can be realized, and the cleaning effect can be improved.

It is a side view which shows an example of the hollow fiber membrane filtration module applicable to this invention partially broken. It is a block diagram which shows typically one Embodiment of the water treatment system of this invention using the hollow fiber membrane filtration module of FIG. It is a block diagram which shows the outline of the control system for operating the water treatment system of FIG. It is a flowchart which shows an example of the control procedure of the water treatment system by the control system of FIG. It is a graph which shows the result of having compared the water permeability after the filtration treatment with respect to 5 samples prepared with different types and concentrations of the inorganic flocculants added to raw water. It is a graph which shows the result of having compared the water permeability after the filtration treatment with respect to three samples prepared with different concentrations of the inorganic flocculants added to raw water about one sample in FIG. 5A. It is a graph which shows the result of having measured the relationship between the concentration of the inorganic flocculant added to the raw water of turbidity 25 and water permeability. It is a graph which shows the result of having compared the recoverability of the filtration performance after washing with respect to 5 samples prepared with different types and concentrations of the inorganic flocculants added to raw water. It is a graph which shows the result of having compared the recoverability of the filtration performance after washing with respect to three samples prepared by making the concentration of the inorganic flocculant added to raw water different with respect to one sample of FIG. 7A. It is explanatory drawing which shows the relationship between the concentration and SDI value at the time of adding a sulfuric acid band as an inorganic flocculant. It is explanatory drawing which shows the relationship between the turbidity of raw water and a preferable concentration of an inorganic flocculant.

Hereinafter, the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the embodiments described below.

(Definition)
In the present specification and claims, raw water refers to river water, lake water, groundwater, various types of wastewater after treatment, etc., and refers to water that can be reused as industrial water by removing turbidity. ..

The turbidity is an index indicating the degree of turbidity of water specified in JIS K 0101, and when 1 mg of kaolin or formazine, which is a standard substance, is uniformly dispersed in 1 L (liter) of purified water. It refers to what is determined by comparing the turbidity of the suspension (defined as "turbidity 1 degree") with the sample (raw water). In the following embodiments, kaolin is used as a standard substance and is simply labeled as "turbidity 50", but it goes without saying that formazine can be used as a standard substance.

Further, the inorganic flocculant includes aluminum-based and iron-based ones, and in the following embodiments, a case where a sulfate band (aluminum sulfate) and ferric chloride are used will be exemplified, but PAC is also used as an aluminum-based one. (Polyaluminum chloride) or iron-based ones such as ferric polysulfate) can be used.

(Embodiment of water treatment system)
FIG. 1 is a side view showing a partially broken example of a hollow fiber membrane filtration module applicable to the water treatment system of the present invention. In FIG. 1, the hollow fiber membrane filtration module (hereinafter, simply referred to as a filtration module) whose whole is indicated by reference numeral 100 can be a microfiltration membrane or an ultrafiltration membrane composed of a large number of hollow fiber membranes. It has a container 3 containing 1. Here, one end side (lower end side in FIG. 1) of each hollow fiber membrane is sealed and has a free end that is not fixed to the container 3. On the other hand, the other end side (upper end side in FIG. 1) of each hollow fiber membrane is opened and is a fixed end fixed to the container 3 by the fixing member 6. That is, the hollow fiber membrane bundle 1 is converged and fixed while maintaining the opening state on the fixed end side of each hollow fiber membrane, and is placed in the container 3 so that the filtered water exits from the opening on the fixed end side. It is contained.

The lower end of the container 3, that is, the end of the hollow fiber membrane bundle 1 on the free end side is formed as a raw water introduction portion 7 for introducing raw water, and an air introduction portion 9 for introducing compressed air there. Is connected. On the other hand, the upper end portion of the container 3, that is, the end portion on the fixed end side of the hollow fiber membrane bundle 1 is formed as a treated water outlet portion 11 for discharging the filtered water (hereinafter referred to as treated water). Further, an exhaust portion 13 is provided near the upper end of the container 3. Although not shown in the figure, as described in Patent Document 1, the hollow fiber membrane bundle 1 extends from the fixed end side to the free end side of the hollow fiber membrane bundle 1. A rectifier tube can be arranged near the center.

The raw water is introduced into the container 3 from the raw water introduction section 7, is filtered by passing through the hollow fiber membrane bundle 1, and the treated water flows out through the lead-out section 11. On the other hand, by introducing compressed air into the container 3 via the air introduction section 9 and causing the movement of the fluid inside the container 3, the hollow fiber membrane bundle 1 is washed (air scrubbing; hereinafter, also referred to as air backwashing). ) Is performed. As described in Patent Document 1, if the rectifying tube is provided, the movement of the hollow fiber membranes during air backwashing is suppressed, and entanglement is prevented. The air introduced during the air backwash is discharged through the exhaust unit 13.

FIG. 2 schematically shows an embodiment of the water treatment system of the present invention using the filtration module 100 of FIG. A plurality of (4 in the illustrated example) filtration modules 100 are arranged in this system, and the raw water introduction unit 7 and the air introduction unit 9 are commonly connected to the raw water pipe 70 and the air pipe 90, respectively. The raw water is supplied to each filtration module 100 by a pump 72 via the raw water pipe 70 and the raw water introduction section 7 at a pressure of, for example, 0.1 MPa (gauge pressure). On the other hand, in the case of air backwashing, compressed air of 0.1 MPa or more is introduced into each filtration module 100 from the compressed air supply source (air compressor or the like) 92 via the air pipe 90 and the air introduction section 9. In the present embodiment, the raw water introduction section 7 is also used as a drain drain section of the filtration module 100, and the end side of the raw water pipe 70 is a drain discharge pipe 76.

The treated water outlet section 11 and the exhaust section 13 of the filtration module 100 are commonly connected to the treated water pipe 110 and the exhaust pipe 130, respectively. That is, the treated water filtered by passing through the hollow fiber membrane bundle 1 of the filtration module 100 is led out from the lead-out unit 11 via the treated water pipe 110 and is used as, for example, industrial water. Further, the end of the exhaust pipe 130 is connected to the drain discharge pipe 76.

Valves 74, 94, 114 and 134 in the form of on-off valves are interposed in the drain discharge pipe 76, the air pipe 90, the treated water pipe 110 and the exhaust pipe 130 at the end of the raw water pipe 70, respectively. These valves are appropriately controlled during filtration processing, air backwashing, etc., and can open / close the flow path of each pipe. Further, pressure sensors 78 and 118 can be arranged in the raw water pipe 70 and the treated water pipe 110, respectively. For example, by detecting the pressure difference between the raw water introduction side and the discharge side, the performance of the hollow fiber membrane is deteriorated. Can be used for judgment.

Further, the raw water pipe 70 is provided with a turbidity measuring instrument 202 that measures turbidity prior to distributing the raw water to the filtration module 100, and a coagulant that adds an inorganic flocculant to the raw water based on the measured turbidity. The device 204 and the device 204 are arranged. These are the components that are characteristic of this embodiment, but those of an appropriate form can be used. For example, the turbidity measuring instrument 202 can use an automatic turbidity measuring instrument conforming to JIS K 0801, but it is preferable that the measured turbidity information can be presented to a controller or the like described later. Further, it is preferable that the coagulant adding device 204 includes a storage unit for the inorganic coagulant and a charging unit for charging the amount of the inorganic coagulant according to the instruction of the controller or the like described later into the raw water pipe 70.

(Control of water treatment system)
FIG. 3 is a block diagram showing a configuration example of a control system applicable to the system configuration shown in FIG. The illustrated control system is mainly composed of a controller 200 having a CPU that executes a control procedure described later with reference to FIG. 4, a ROM that stores a program corresponding to the control procedure, a working RAM, and the like. The control targets of the controller 200 are the valves 74, 94, 114, 134, the pump 72, the compressed air supply source (air compressor, etc.) 92, and the input unit of the coagulant addition device 204, which are the drive units 212, 214, respectively. Driven via 216 and 218. Further, the measurement information of the turbidity measuring instrument 202 is input to the controller 200, and the information from the cleaning timing defining unit 220 that defines the cleaning timing by air backwashing or the like is input.

The air backwash can be performed on a time basis, for example every 15 to 30 minutes. Therefore, the cleaning timing defining unit 220 may have a timer unit that manages the time. However, under other conditions, it may be determined that the performance of the hollow fiber membrane bundle 1 is deteriorated so that air backwashing may be performed. In that case, the cleaning timing defining unit 220 may be set to, for example, the detected values of the pressure sensors 78 and 118. It may have a comparator or the like to be compared. It is also possible to combine chemical cleaning performed by appropriately adding a chemical such as sodium hypochlorite into the filtration module 100. The timing of chemical cleaning can also be carried out, for example, based on time, and can be carried out, for example, every 1 to 2 days.

FIG. 4 shows an example of a control procedure of the water treatment system of FIG. 2 using the control system of FIG. When this procedure is activated, the valve 114 is first opened in step S1, the valves 74, 94 and 134 are closed, and then the pump 72 is driven in step S3. As a result, the flow of raw water from the raw water pipe 70 to each filtration module 100 and the flow of treated water from each filtration module 100 through the treated water pipe 110 are established, and the air pipe 90, the drain discharge pipe 76 and the exhaust are established. The pipe 130 is blocked. Then, in step S5, the turbidity of the raw water was measured by the turbidity measuring instrument 202, and in step S7, the coagulant addition device 204 was driven to appropriately determine the turbidity and the flow rate of the raw water to be treated. Add an amount of inorganic flocculant. As a result, the raw water to which the inorganic flocculant is added flows into the filtration module 100. Impurities contained in the raw water aggregate in this process, but by appropriately adjusting the concentration of the inorganic flocculant, the flocs are formed in a preferable size, and the pores of the hollow fiber membrane are less likely to be blocked or retention between the hollow fibers is unlikely to occur. It becomes a thing. The measurement of turbidity and the adjustment of the amount of the inorganic flocculant added accordingly may be performed at an appropriate timing instead of always.

Next, in step S11, it is determined whether or not the cleaning timing is due to air backwashing, and if a negative determination is made, the process returns to step S5. If the determination is positive, the process proceeds to step S13, the valve 114 is closed, and the valve 74 , 94 and 134 are open. As a result, the flow of raw water from the raw water pipe 70 to each filtration module 100 and the flow of treated water from each filtration module 100 through the treated water pipe 110 are blocked, and the air pipe 90, the drain discharge pipe 76 and the exhaust are blocked. A flow path is established through the pipe 130.

In step S15, the drive of the coagulant addition device 204 is stopped, and in step S15, the air compressor 92 is driven. As a result, the compressed air is supplied to the filtration module 100 via the air pipe 90, so that the hollow fiber membrane bundle 1 is backwashed with air. The fluid containing the flocs floating in the container 3 and the flocs separated from the hollow fiber membrane bundle 1 by this air backwash is transferred from the exhaust unit 13 to the drain discharge pipe 76 via the exhaust pipe 130. Further, in the present embodiment, since the raw water introduction portion 7 on the lower end side of the container 3 also serves as a drain discharge port, by driving the pump 72 even during air backwashing, the flocs settled in the raw water introduction portion 7 Can be transferred to the drain discharge pipe 76.

The period for performing cleaning by air backwash can also be managed by time, and when it is determined in step S19 that the cleaning is completed, the drive of the air compressor 92 is stopped in step S21. Then, by returning to step S1, normal water treatment is restarted. Although not shown in FIG. 4, a treatment step for carrying out chemical cleaning may be added.

(About the amount of inorganic flocculant added)
Through various experiments as shown below, the present inventor appropriately added an inorganic flocculant to improve the efficiency of filtration treatment and the reduction of membrane blockage, and also to improve the cleaning effect. The amount was examined.

First, FIG. 5A is a graph showing the experimental results comparing the water permeability after the filtration treatment according to the type and concentration of the inorganic flocculant added to the raw water. For the experiment, the following five samples, that is,
Sample 1: Raw water without an inorganic flocculant (turbidity 25),
Sample 2: Raw water to which 5 ppm of sulfuric acid band is added,
Sample 3: Raw water to which 10 ppm of sulfuric acid band is added,
Sample 4: Raw water containing 5 ppm of ferric chloride, and Sample 5: Raw water containing 10 ppm of ferric chloride.
I prepared. Then, the hollow fiber membranes of Puria (registered trademark) GS manufactured by Kuraray Aqua Co., Ltd., which is a filtration module having a structure as shown in FIG. 1, are cut, and several of them are cut so that the total area is 0.0152 m ^2. Was bundled on the opposite side of the free end and used as a test filtration membrane. Raw water was supplied to the filtration membrane at a pressure of 0.1 MPa.

The vertical axis of FIG. 5A shows the flow rate of the treated water, and shows how many L (liters) of treated water was obtained per 1 m ^{2 of} the membrane per hour. From this graph, it is better to add the inorganic flocculant to the raw water, the water permeability is better, the efficient filtration treatment without film blockage is possible, and the higher the addition rate (concentration) of the inorganic flocculant is, the better. It was found that it would be efficient. And this is considered to be due to the fact that the flocs are formed in a preferable size.

Therefore, the present inventor selected a sulfuric acid band as the inorganic flocculant and added it to sample 3.
Sample 3-2: Raw water to which 15 ppm of sulfuric acid band was added, and Sample 3-3: Raw water to which 25 ppm of sulfuric acid band was added.
Was prepared, and the water permeability was verified in the same manner. FIG. 5B is a graph showing the experimental results. From this graph, the water permeability of the sample 3-2, which has a higher addition rate (concentration) of the inorganic flocculant than that of the sample 3, is higher, but the water permeability of the sample 3-3 to which the inorganic coagulant is added at a higher concentration is rather higher. It turned out to be lower.

The present inventor further conducted an experiment to verify the water permeability by changing the addition rate of the sulfuric acid band with respect to the raw water (turbidity 25). The raw water used in this experiment had a water quality within the following range.
pH: 5.4 to 7.8
SS: 20-380 mg / L
Saturation: 30-50
Electrical conductivity: 1.80 to 5.34 mS / cm
Salt content: 0.3%
Ca: 250-870 mg / L
SiO ₂ : 7 mg / L
NH ₄ ⁺ : 0.2-0.7 mg / L
CaCO ₃ : 150-200 mg / L

FIG. 6 is a graph showing the experimental results. From this result, adding the inorganic flocculant to an appropriate concentration, that is, when using a sulfuric acid band, adding it to a concentration of about 15 ppm with respect to the raw water improves the water permeability. It was confirmed that it was preferable.

On the other hand, the present inventor conducted an experiment to confirm the cleaning effect according to the concentration of the inorganic flocculant. In the experiment, first, 50 L of the above samples 1 to 5 was supplied to the same filtration module as above, and then physical washing (air backwashing) and (chemical washing) were performed.

FIG. 7A is a graph showing how much the performance of the membrane has recovered after cleaning by the flow rate ratio when the water permeability before supply is 100%. From this graph, it was found that the recovery is generally better when the inorganic flocculant is added to the raw water, and it is preferable to add the inorganic flocculant at a concentration of 10 ppm or more in consideration of the water permeability shown in FIG. 5A. Was done. And this is also considered to be due to the fact that the flocs are formed in a preferable size.

Therefore, the present inventor selected a sulfuric acid band as the inorganic flocculant, prepared Sample 3, Sample 3-2 and Sample 3-3, and similarly verified the recoverability. FIG. 7B is a graph showing the experimental results. From this graph, when a sulfuric acid band is used, it is necessary to add it to a concentration of about 15 ppm (for example, in the range of 12.5 to 17.5 ppm) with respect to raw water having a turbidity of 25 for recovery after washing. It was confirmed that it was preferable from the viewpoint. In the present invention, the use of an inorganic flocculant having such a concentration is particularly suitable for the treatment of raw water having the above water quality.

Further, the present inventor, according to the method described in the specification of Patent Document 2, according to the provisions of ASTM 4189 in the United States, the amount of turbid component (SDI (Silt Density Index) value) of raw water when a sulfuric acid band is added. ) Was evaluated.

FIG. 8 shows the result. Generally, water is required to be treated so that the SDI value is 3 to 4 or less, but when a sulfuric acid band is added, it is more than when it is treated with UF (ultrafiltration membrane) indicated by "x". It was confirmed that the SDI value was also excellent.

In addition, the present inventor conducted an experiment to determine the concentration of an inorganic flocculant (sulfuric acid band) preferable from the viewpoint of water permeability and recoverability after washing for various turbidities.

FIG. 9 shows the result, and from this result, it was confirmed that there is a substantially linear relationship between the turbidity and the amount of the preferable inorganic flocculant added. In the case of FIG. 9, the amount of inorganic coagulant added (ppm) = 0.45 x turbidity +5
The relationship is expressed by the formula of. Therefore, when applied to the water treatment system shown in FIGS. 2 and 3, an amount of the inorganic flocculant that can obtain a concentration corresponding to the flow rate of the raw water to be treated with respect to the turbidity measured by the turbidity measuring instrument 202. The flocculant addition device 204 may be controlled in step S7 of FIG. 4 so that When adding a preferable amount of the inorganic flocculant, for example, a table in which the turbidity, the amount added, and the flow rate of the raw water are tabulated in advance is stored in the ROM or the like of the controller 200, and this table is referred to. can do. Alternatively, the CPU of the controller 200 may calculate a preferable concentration and thus an addition amount according to the above formula based on the turbidity.

(Other)
It should be noted that the present invention is not limited to the above embodiments and modifications described everywhere. For example, the preferable concentration in the case of adding a sulfuric acid band as an inorganic flocculant has been specifically described, but this is merely an example, and PAC, or ferric chloride or polysulfate which is an iron-based inorganic flocculant. Of course, when ferric or the like is used, an appropriate addition amount can be determined in the same manner. In addition, the type, concentration, or amount of inorganic flocculant used depends on the specifications of the hollow fiber membrane (diameter and pore diameter of the hollow fiber itself, etc.), or according to the usage conditions and environmental conditions (water temperature, etc.) of the filtration system. Of course, it can be determined.

In addition, in the above-described embodiment, a water treatment system that automatically measures turbidity and adds an inorganic flocculant is exemplified, but in light of the gist of the present invention embodied in the water treatment method or the water production method. At least a part thereof may be performed according to the instruction or operation of the operator. Further, the water treated according to the present invention may be directly used as industrial water or the like, or may be additionally treated.

Claims (7)

In a water treatment system that treats raw water with hollow fiber membrane bundles with one end not fixed
Prior to performing the filtration process using the hollow fiber membrane bundle, a turbidity measuring unit that measures the turbidity of the raw water and a turbidity measuring unit.
A coagulant addition part that adds an amount of inorganic coagulant adjusted based on the measured turbidity,
A water treatment system characterized by being equipped with. When the turbidity measured by the turbidity measuring unit is X degree (kaolin), the flocculant addition unit has a concentration Y (ppm) determined by the following equation.
Y = 0.45 x X + 5
The water treatment system according to claim 1, wherein the inorganic flocculant is added so as to obtain the above. The water treatment system according to claim 1 or 2, wherein the hollow fiber membrane bundle is a microfiltration membrane or an ultrafiltration membrane. The water treatment system according to any one of claims 1 to 3, wherein aluminum sulfate is used as the inorganic flocculant. The water treatment system according to any one of claims 1 to 4, further characterized in that the hollow fiber membrane bundle is washed by introducing compressed air at a pressure of 0.1 MPa or more. In a water treatment method in which raw water is treated with a hollow fiber membrane bundle whose one end is not fixed,
Prior to performing the filtration treatment with the hollow fiber membrane bundle, the step of measuring the turbidity of the raw water and
The step of adding an amount of the inorganic flocculant adjusted based on the measured turbidity, and
A water treatment method characterized by being equipped with. The process of measuring the turbidity of raw water and
The step of adding an amount of the inorganic flocculant adjusted based on the measured turbidity, and
A step of filtering the raw water to which the inorganic flocculant is added by a hollow fiber membrane bundle having one end not fixed, and
A water production method characterized by being equipped with.

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