WO2017115455A1

WO2017115455A1 - Water treatment system, water treatment method , and water production method

Info

Publication number: WO2017115455A1
Application number: PCT/JP2016/004855
Authority: WO
Inventors: 若狭　浩之; 高志西田
Original assignee: 王子ホールディングス株式会社
Priority date: 2015-12-28
Filing date: 2016-11-10
Publication date: 2017-07-06
Also published as: JP2020192533A; JPWO2017115455A1; SG11201805603SA

Abstract

When performing water treatment using a hollow fiber membrane filtration module, the present invention achieves increased efficiency of filtration and reduction of membrane clogging and also makes it possible to improve the washing efficacy of air backwashing, etc. Prior to performing filtration of raw water using a hollow fiber membrane bundle, one end of which is not fixed, the turbidity of the raw water is measured and an inorganic flocculant is added in an amount that is adjusted on the basis of the measured turbidity. By thereby forming flocs of favorable size, increased efficiency of filtration and reduction of membrane clogging are achieved and it also becomes possible to improve washing efficacy.

Description

Water treatment system, water treatment method and water production method

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.

There are systems that use hollow fiber membrane filtration modules as systems for treating raw water such as river water and groundwater. Among them, the hollow fiber membrane filtration module disclosed in Patent Document 1 is a hollow fiber membrane bundle composed of a number of hollow fiber membranes, one end (upper end) being fixed to a container and the other end (lower end) not fixed. By adopting a structure called “one-end free” using the above, it has superior characteristics as compared with those using a hollow fiber membrane bundle in which both ends are fixed. That is, when air scrubbing is applied to perform a cleaning process for removing deposits on the surface of the hollow fiber membrane, the non-fixed end side of the hollow fiber membrane moves freely, so that the effect of peeling the deposited material is high. Further, in the hollow fiber membrane filtration module of Patent Document 1, the hollow fiber membrane filtration module includes a rectifier tube extending from the fixed side of the hollow fiber membrane bundle toward the longitudinal direction of the hollow fiber membrane bundle, thereby entanglement of the hollow fiber membranes during cleaning. In addition, it is 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 raw water with high turbidity, an inorganic flocculant may be added and combined with treatment by a hollow fiber membrane filtration module. In order to perform effective water treatment, it is considered effective to add a high concentration of the inorganic flocculant. However, since the high concentration of the inorganic flocculant itself can cause membrane fouling and clogging, There is a concern that efficient filtration with a hollow fiber membrane (hereinafter simply referred to as filtration treatment) cannot be performed, and the life of the hollow fiber membrane is shortened. Therefore, when combined with the filtration treatment, the concentration or addition amount of the inorganic flocculant is generally kept low.

Japanese Patent No. 3686225 International Publication WO2013 / 099857

However, as a result of diligent investigations by the present inventor, when the inorganic flocculant has a low concentration, the size of the aggregate (hereinafter referred to as “floc”) generally becomes small, and on the contrary, the pores of the hollow fiber membrane are easily blocked. It has been found that the cleaning effect by air scrubbing is diminished by the water entering and staying between the hollow fibers.

Therefore, an object of the present invention is to realize the efficiency of the filtration process and the reduction of the clogging of the membrane and improve the cleaning effect when performing the water treatment using the hollow fiber membrane filtration module. .

Therefore, in one form of the present invention, in a water treatment system that treats raw water with a hollow fiber membrane bundle that is not fixed at one end, the turbidity of the raw water is measured prior to the filtration treatment with the hollow fiber membrane bundle. A turbidity measuring unit; and a flocculant adding unit for adding an amount of an inorganic flocculant adjusted based on the measured turbidity.

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

Furthermore, 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 the inorganic flocculant being added. The raw water is filtered by a hollow fiber membrane bundle whose one end is not fixed, and a water production method is provided.

According to the present invention, the turbidity of the raw water is measured prior to the raw water filtration using the hollow fiber membrane bundle not fixed at one end, and the amount adjusted based on the measured turbidity is measured. Add inorganic flocculant. Thereby, by forming the floc into a preferred size, it is possible to improve the efficiency of the filtration process and reduce the blockage of the membrane, and to improve the cleaning effect.

It is a side view which shows a partially broken example of a hollow fiber membrane filtration module applicable to the present invention. It is a block diagram which shows typically one Embodiment of this invention water treatment system 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 process with respect to five samples prepared by varying the kind and density | concentration of the inorganic flocculant added to raw | natural water. It is a graph which shows the result of having compared the water permeability after filtration with respect to three samples prepared by varying the density | concentration of the inorganic flocculant added to raw | natural water about one sample of FIG. 5A. It is a graph which shows the result of having measured the relationship between the density | concentration of the inorganic flocculant added with respect to the raw | natural 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 | cleaning with respect to five samples prepared by varying the kind and density | concentration of the inorganic flocculant added to raw | natural water. It is a graph which shows the result of having compared the recoverability of the filtration performance after washing | cleaning with respect to three samples prepared by varying the density | concentration of the inorganic flocculant added to raw | natural water about one sample of FIG. 7A. It is explanatory drawing which shows the relationship between the density | concentration in the case of adding a sulfuric acid band as an inorganic flocculant, and an SDI value. It is explanatory drawing which shows the relationship between the turbidity of raw | natural water, and the preferable density | 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, ground water, various wastewater after treatment, etc., and can be reused as industrial water by removing turbidity. .

Turbidity is an index representing the degree of turbidity of water defined in JIS K 0101. When 1 mg of kaolin or formazine as a standard substance is uniformly dispersed in 1 L (liter) of purified water. It is determined by comparing the turbidity of the suspension (defined as “1 degree of turbidity”) 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 is needless to say that formazine can be used as a standard substance.

Further, the inorganic flocculant includes aluminum-based and iron-based ones. In the following embodiments, a case where a sulfate band (aluminum sulfate) and ferric chloride are used is exemplified. (Polyaluminum chloride) or iron-based polyferric sulfate 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, a hollow fiber membrane filtration module (hereinafter simply referred to as a filtration module) denoted by reference numeral 100 as a whole is a hollow fiber membrane bundle that can be a microfiltration membrane or an ultrafiltration membrane comprising a number of hollow fiber membranes. 1 has a container 3 containing 1. Here, one end side (lower end side in FIG. 1) of each hollow fiber membrane is sealed and is a free end not fixed to the container 3. On the other hand, the other end side (the upper end side in FIG. 1) of each hollow fiber membrane is opened and is a fixed end fixed to the container 3 by a fixing member 6. That is, the hollow fiber membrane bundle 1 is converged and fixed while maintaining the open state on the fixed end side of each hollow fiber membrane, and the filtered water flows into the container 3 so as to exit from the opening on the fixed end side. Contained.

A lower end portion of the container 3, that is, an end portion on the free end side of the hollow fiber membrane bundle 1 is formed as a raw water introduction portion 7 for introducing raw water, and an air introduction portion 9 for introducing compressed air therein. Is connected. On the other hand, the upper end of the container 3, that is, the end on the fixed end side of the hollow fiber membrane bundle 1, is formed as a treated water outlet 11 for discharging filtered water (hereinafter referred to as treated water), Further, an exhaust part 13 is provided in the vicinity of 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 is extended so as to extend 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.

Raw water is introduced into the container 3 from the raw water introduction section 7 and filtered through the hollow fiber membrane bundle 1, and the treated water flows out through the outlet section 11. On the other hand, by introducing compressed air into the container 3 through the air introduction unit 9 and causing movement of the fluid inside the container 3, the hollow fiber membrane bundle 1 is washed (air scrubbing; hereinafter referred to as air backwashing). Say). As described in Patent Document 1, if a rectifying tube is provided, the movement of the hollow fiber membranes during backwashing with air is suppressed and entanglement is prevented. In addition, the air introduced at the time of air backwashing is discharged | emitted via the exhaust part 13. FIG.

FIG. 2 schematically shows an embodiment of the water treatment system of the present invention using the filtration module 100 of FIG. In this system, a plurality of (four in the illustrated example) filtration modules 100 are disposed, and the raw water introduction part 7 and the air introduction part 9 are connected in common to the raw water pipe 70 and the air pipe 90, respectively. The raw water is supplied to each filtration module 100 at a pressure of, for example, 0.1 MPa (gauge pressure) through the raw water pipe 70 and the raw water introduction unit 7 by the pump 72. On the other hand, at the time 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 through the air pipe 90 and the air introduction unit 9. In this embodiment, the raw water introduction part 7 is also used as a drain removal part of the filtration module 100, and the terminal side of the raw water pipe 70 is a drain discharge pipe 76.

The treated water outlet 11 and the exhaust 13 of the filtration module 100 are connected in common 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 part 11 through the treated water pipe 110, and is used as, for example, industrial water. 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 inserted 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 at the time of filtration processing, air backwashing, and the like, and can open / close the flow path of each pipe. Further,

pressure sensors

78 and 118 can be disposed 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 reduced. Can be used for judgment.

Further, a turbidity measuring device 202 that measures turbidity prior to distributing raw water to the filtration module 100 and a flocculant addition that adds an inorganic flocculant to the raw water based on the measured turbidity are added to the raw water pipe 70. A device 204 is provided. These are the constituent elements that characterize the present embodiment, but those in appropriate forms can be used. For example, although the turbidity measuring device 202 can use an automatic turbidity measuring device based on JIS K 0801, it is preferable that the measured turbidity information can be presented to a controller described later. Moreover, it is preferable that the flocculant addition apparatus 204 includes an inorganic flocculant storage unit and an input unit that inputs an amount of the inorganic flocculant into the raw water pipe 70 in accordance with an instruction from a controller or the like described later.

(Control of water treatment system)
FIG. 3 is a block diagram showing a configuration example of a control system applicable to the configuration of the system shown in FIG. The illustrated control system is mainly configured by 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. Control targets of the controller 200 are

valves

74, 94, 114, 134, a pump 72, a compressed air supply source (such as an air compressor) 92, and a charging unit 204, which are driving units 212, 214, Driven through 216 and 218. In addition, measurement information of the turbidity measuring device 202 is input to the controller 200, and 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 based on time, for example, at a timing of every 15 to 30 minutes. Accordingly, the cleaning timing defining unit 220 can include a timer unit that manages time. However, the air backwashing may be performed by judging other conditions and the performance deterioration of the hollow fiber membrane bundle 1, and in that case, the cleaning timing defining part 220 is set to the detection values of the

pressure sensors

78 and 118, for example. A comparator or the like for comparison may be included. Further, chemical cleaning performed by appropriately putting chemicals such as sodium hypochlorite into the filtration module 100 can be combined. The timing of chemical cleaning can be performed based on time, for example, and can be performed every 1-2 days, for example.

FIG. 4 shows an example of the control procedure of the water treatment system of FIG. 2 using the control system of FIG. When this procedure is started, first, the valve 114 is opened and the

valves

74, 94 and 134 are closed in step S1, 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 gas are exhausted. Tube 130 is closed. In step S5, the turbidity measuring device 202 measures the turbidity of the raw water, and in step S7, the flocculant adding device 204 is driven to appropriately determine the turbidity and the flow rate of the raw water to be processed. An amount of inorganic flocculant is charged. Thereby, 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 the floc is formed to a preferred size by adjusting the concentration of the inorganic flocculant, and the hollow fiber membranes are less likely to block the holes and stay between the hollow fibers. It will be a thing. The measurement of turbidity and the adjustment of the amount of inorganic flocculant added in accordance therewith may be performed at an appropriate timing, not always.

Next, in step S11, it is determined whether or not the cleaning timing is due to air backwashing. If the determination is negative, the process returns to step S5. If the determination is affirmative, the process proceeds to step S13, and the valve 114 is closed and the valve 74 is closed. , 94 and 134 are opened. Thereby, the flow of the raw water from the raw water pipe 70 to each filtration module 100 and the flow of the 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 gas are exhausted. A flow path through the tube 130 is established.

In step S15, the driving of the flocculant adding device 204 is stopped, and the air compressor 92 is driven in step S15. Thereby, air backwashing of the hollow fiber membrane bundle 1 is performed by supplying compressed air to the filtration module 100 via the air pipe 90. Fluid containing flocs floating in the container 3 or flocs separated from the hollow fiber membrane bundle 1 by this air backwashing is transferred from the exhaust unit 13 to the drain discharge pipe 76 via the exhaust pipe 130. Moreover, in this embodiment, since the raw | natural water introduction part 7 of the lower end side of the container 3 serves as a drain discharge port, the floc settled in the raw | natural water introduction part 7 by driving the pump 72 also at the time of air backwashing. Can be transferred to the drain discharge pipe 76.

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

(About the amount of inorganic flocculant added)
Through various experiments as described below, the present inventor appropriately added an inorganic flocculant to achieve an efficient filtration process and a reduced membrane clogging, and to improve the cleaning effect. The amount was examined.

First, FIG. 5A is a graph showing experimental results comparing the water permeability after filtration treatment according to the type and concentration of the inorganic flocculant added to the raw water. The experiment included the following five samples:
Sample 1: raw water not containing inorganic flocculant (turbidity 25),
Sample 2: Raw water to which 5 ppm of sulfuric acid band was added,
Sample 3: raw water to which 10 ppm of sulfuric acid band was added,
Sample 4: Raw water to which 5 ppm of ferric chloride was added, and Sample 5: Raw water to which 10 ppm of ferric chloride was added,
Prepared. Then, the hollow fiber membrane of PUREA (registered trademark) GS manufactured by Kuraray Aqua Co., Ltd., which is a filtration module having the structure as shown in FIG. 1, is cut so that the total area becomes 0.0152 m ^2. Was bundled on the side opposite to the free end, and used as a test membrane. Raw water was supplied to the filtration membrane at a pressure of 0.1 MPa.

The vertical axis in FIG. 5A indicates the flow rate of the treated water, and indicates how many liters of treated water are obtained per hour for the membrane 1 m ² . From this graph, it is better to add inorganic flocculant to raw water, water permeability is better, and efficient filtration without membrane clogging is possible, and higher addition rate (concentration) of inorganic flocculant is higher. The knowledge that it becomes efficient was obtained. This is considered to be derived from the fact that the floc is formed in a preferable size.

Therefore, the present inventor selected a sulfuric acid band as the inorganic flocculant, added to the 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,
The water permeability was verified in the same manner. FIG. 5B is a graph showing the experimental results. From this graph, sample 3-2 having a higher addition rate (concentration) of the inorganic flocculant than sample 3 has higher water permeability, but sample 3-3 to which the inorganic flocculant is added at a higher concentration is more water permeable. 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
Chromaticity: 30-50
Electrical conductivity: 1.80-5.34 mS / cm
Salinity: 0.3%
Ca: 250 to 870 mg / L
SiO ₂ : 7 mg / L
NH ₄ ⁺ : 0.2 to 0.7 mg / L
CaCO ₃ : 150 to 200 mg / L

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

On the other hand, the 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 described above, and then physical cleaning (backwashing with air) and (chemical cleaning) were performed.

FIG. 7A is a graph showing how much the performance of the membrane has recovered after washing, as a flow rate ratio when the water permeability before supply is 100%. From this graph, it is generally found that the addition of the inorganic flocculant to the raw water has better recoverability, and considering the water permeability shown in FIG. 5A, it is preferable to add the inorganic flocculant at a concentration of 10 ppm or more. It was. This is also considered to be derived from the fact that the floc is formed in a preferred 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 using a sulfuric acid band, it is possible to add a concentration of about 15 ppm (for example, in the range of 12.5 to 17.5 ppm) with respect to raw water with a turbidity of 25. It was confirmed that it was preferable also 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.

Furthermore, the present inventor, according to the method described in the specification of Patent Document 2, in accordance with the provisions of US ASTM D 4189, the amount of turbidity component of raw water (SDI (Silt Density とき Index) value when 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. However, when a sulfuric acid band is added, water is treated more than when UF (ultrafiltration membrane) indicated by “x” is treated. Was confirmed to be an excellent SDI value.

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

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

(Other)
Note that the present invention is not limited to the above-described embodiment and the modifications described in various places. For example, the preferred concentration for 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 iron-based inorganic flocculants such as ferric chloride and polysulfuric acid Needless to say, an appropriate addition amount can be determined in the same manner when using ferric iron or the like. Also, depending on the specifications of the hollow fiber membrane (such as the diameter and pore diameter of the hollow fiber), or depending on the use conditions and environmental conditions (water temperature, etc.) of the filtration system, the type, concentration or amount of addition of the inorganic flocculant used Of course, it can be determined.

In addition, in the above-described embodiment, a water treatment system that automatically performs turbidity measurement and inorganic flocculant addition is illustrated, but in light of the spirit of the present invention embodied in a water treatment method or a water production method, At least a part may be performed in accordance with an operator's instruction or operation. The water treated according to the present invention may be used directly as industrial water or the like, or may be subjected to additional treatment.

Claims

In a water treatment system for treating raw water with a hollow fiber membrane bundle whose one end is not fixed,
Prior to performing the filtration treatment with the hollow fiber membrane bundle, a turbidity measuring unit for measuring the turbidity of raw water,
A flocculant addition unit for adding an inorganic flocculant in an amount adjusted based on the measured turbidity;
A water treatment system comprising:
When the turbidity measured by the turbidity measurement unit is X degree (kaolin), the flocculant addition unit has a concentration Y (ppm) determined by the following formula:
Y = 0.45 × X + 5
The water treatment system according to claim 1, wherein the inorganic flocculant is added so that
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, wherein 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 of treating raw water with a hollow fiber membrane bundle whose one end is not fixed,
Prior to performing the filtration treatment with the hollow fiber membrane bundle, measuring the turbidity of the raw water,
Adding an inorganic flocculant in an amount adjusted based on the measured turbidity;
A water treatment method comprising:
Measuring raw water turbidity;
Adding an amount of inorganic flocculant adjusted based on the measured turbidity;
A step of filtering the raw water to which the inorganic flocculant is added with a hollow fiber membrane bundle whose one end is not fixed;
A water production method comprising: