JPH1157739A - Water purifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a decrease in the amt. of permeated water at the time of separating the fine grain and floc of suspensoid formed by the injection of a flocculant by the use of a membrane by controlling the injection of the flocculant based on the ratio of the diameter of the floc to the diameter of the pore of the membrane. SOLUTION: A flocculant 10 is injected into the raw water RW freed from large-diameter sand or the like, in a rapid mixing basin 3 to form the microfloc of the suspensoid and org. matter, and the microfloc is grown into a large floc. The water flowing out of the rapid mixing basin 3 is supplied to a membrane treating device 11 to separate the floc, and the filtered water FW is sterilized with chlorine and supplied to a consumer as service water. In this case, the diameter of the floc after the flocculant is injected is measured based on the output of the first monitor 13 for the microfloc set in the rapid mixing basin 3 and that of the second monitor 23 for the floc, and a flocculant injection corrector 500 is controlled so that the ratio of the diameter of the floc to the diameter of the pore of the membrane or the like is adjusted in a preset appropriate range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water purification method in which a flocculant is injected into raw water taken in a water purification plant or the like to form fine and turbid flocs in the raw water, and the flocs are separated using a membrane. About.

[0002]

2. Description of the Related Art Generally, in a water purification plant, turbid matter in raw water is mainly removed by coagulation and sedimentation treatment and subsequent sand filtration. According to this method, a turbid component having a relatively large particle size can be removed. However, fine particles that do not settle by gravity are difficult to remove by sand filtration.
In recent years, a membrane treatment method for treating raw water directly using a microfiltration or ultrafiltration membrane has been widely used. This type of film processing method is disclosed in JP-A-8-229362 and JP-A-8-2900.
It is known in Japanese Patent Publication No. 45 and the like.

In this membrane treatment method, a filtrate adheres and deposits on the membrane surface as the operation time of the membrane treatment elapses. As a result, the water flow resistance increases and the amount of permeated water passing through the membrane decreases, so that the membrane is washed every predetermined time (about 0.5 h). As a method for cleaning the membrane, a part of the permeated water (filtration water) is used for back pressure cleaning from the permeated water side to the permeated water side of the membrane to remove the deposits deposited on the membrane surface or clogging substances in the membrane. The removal method is adopted.

Further, the floc properties after the coagulant is injected fluctuate depending on the concentration of organic substances and turbidity in the water to be treated, which may result in poor coagulation. In order to cope with the above problem, as a conventional technique of flocculant injection control, a method of monitoring the state of floc formation, judging whether floc formation is good or not, and controlling the flocculant injection amount (JP-A-63-252512). is there. Specifically, the floc is image-processed, the logarithmic average diameter of the floc is obtained from the recognized image, the quality of the floc is determined based on the logarithmic average diameter, and the coagulant injection amount is controlled.

[0005]

In the above-mentioned membrane treatment method, among the fine particles to be filtered, fine particles having a relatively large particle diameter are captured by filtration on the membrane surface. However, fine particles close to or smaller than the pore diameter of the membrane penetrate into the pores of the membrane.If these fine particles increase, clogging of the membrane progresses, water resistance increases, and the amount of permeated water increases. Decrease.

[0006] For this reason, as disclosed in, for example, Japanese Patent Application Laid-Open No. 5-185093, a method of injecting a coagulant into raw water to be treated water to coagulate fine particles in the raw water has been adopted. According to this method, fine particles before and after the pore diameter of the membrane are aggregated to form flocs having a large particle diameter, so that it is possible to suppress penetration into the inside of the pores of the membrane. However, if the particle size of the floc generated by the aggregation is too large, the strength of the floc is weakened, so that the floc is broken and adheres to the film surface, and covers the pores of the film. As a result, there arises a disadvantage that the water flow resistance of the membrane increases and the amount of permeated water decreases.

Further, the above-mentioned prior art relating to the coagulant injection control (JP-A-63-252512) is directed to a water purification process comprising a floc forming pond and a sedimentation pond. The purpose of monitoring the state of floc formation is to form flocs that tend to settle in the sedimentation basin. When the coagulant is injected before the membrane treatment device, the water flow resistance of the membrane changes depending on the floc properties and the pore diameter of the membrane. In the prior art, the relationship between the floc diameter and the pore diameter of the membrane is not taken into account, so that flocs that easily precipitate can be generated, but there is a problem that the water flow resistance of the membrane is increased.

[0008] The membrane used in the water purification treatment has a pore diameter of nm.
Ultrafiltration membranes (hereinafter, UF membranes) on the order and microfiltration membranes (hereinafter, MF membranes) on the order of μm are mainly used. The MF membrane is advantageous from the viewpoint of water flow resistance and the amount of treated water. The pore size of the MF membrane is 0.
The particle size is in the range of 01 to 1 μm, and has a small effect on the membrane water flow resistance, and is in the range of 1 to 50 μm when the MF membrane of 0.1 μm is used. In the prior art, because the purpose is to monitor flocks that tend to settle,
The maximum diameter of the flock to be measured is 4 to 5 mm. Therefore, in the above-described embodiment of the prior art, the data processing accuracy of one pixel is 0.1 mm from the relationship between the size of the flock image processing screen and the number of pixels. For this reason, flocs of several tens of μm are not detected, and it is impossible to recognize flocs of several tens of μm necessary for controlling the membrane water flow resistance.

The present invention addresses the above-mentioned problems of the prior art. An object of the present invention is to achieve a membrane treatment suitable for controlling the flocculant injection amount by monitoring the floc properties by a monitoring device and suppressing a decrease in the amount of permeated water.

[0010]

According to the water purification treatment method of the present invention, the floc particle size after the coagulant injection is measured, and the coagulant injection amount is controlled based on the ratio between the floc particle size and the pore size of the membrane. It is characterized by doing. Further, the amount of the coagulant injected is controlled based on the difference between the floc particle size and the pore size of the membrane. Further, the water purification treatment method of the present invention is provided with two types of floc monitoring devices for measuring the floc particle size, and based on the ratio or difference between the floc diameter and the pore size of the membrane determined by these devices, a flocculant is used. It is characterized in that the injection amount is controlled.

In the present invention, of the two types of floc monitoring devices, the first floc monitoring device is 1 to 100 μm.
(Hereinafter referred to as micro floc)
The second floc monitoring device measures a floc of 0.1 mm to 5 mm (hereinafter referred to as a floc).

Based on the output result of the monitoring device, a micro-flock diameter d1 and a number N1 of micro-flocks are calculated by a computing device.
After calculating the floc diameter d2 and the floc number N2, the average particle diameter d3 = (d1 × N1 + d2 ×
N2) / (N1 + N2) is calculated. The ratio or difference between d3 and the previously input pore diameter of the membrane is determined, and compared with a control threshold value in the ratio or difference between the pore diameter and the floc particle diameter of the membrane where the water flow resistance of the membrane decreases, Manipulate the injection volume. Further, in order to obtain a stable amount of treated water, a difference value between the pressure before the water flow through the membrane and the pressure after the water flow is obtained, and when the difference value exceeds an allowable value, the membrane is back-pressure washed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have investigated the relationship between the ratio of the average particle size of flocs to the pore size of a membrane after injecting a flocculant into raw water and the flux permeating the membrane in order to achieve the above-mentioned object. As a result, as shown in FIG. 2, if the ratio of the average particle size of the floc to the pore size of the membrane before membrane filtration is too large, the flux permeating through the membrane is reduced. Conversely, even if the ratio of the average particle size of the floc to the membrane pore diameter is too small, the membrane permeation flux is reduced. Was found to exist.
That is, when the coagulant is injected into the raw water and then the membrane is filtered, the ratio of the average particle size of the floc to the pore size of the membrane is maintained in an appropriate range to suppress the decrease in the membrane permeation flux and increase the permeated water amount. I found out. Next, the present inventors investigated the relationship between the ratio of the average particle size of the floc and the pore size of the membrane when the coagulant concentration was changed, and the coagulant injection concentration. As shown in FIG. 3, as the flocculant concentration increases, the ratio between the floc average particle diameter and the membrane pore diameter increases, and by controlling the flocculant concentration, the ratio between the floc average particle diameter and the membrane pore diameter is adjusted. can do.

Further, the relationship between the difference between the average particle size of the floc and the pore size of the membrane after injecting the flocculant into the raw water and the flux permeating through the membrane was examined. As a result, as shown in FIG. 4, if the difference between the average particle size of the floc before membrane filtration and the pore size of the membrane is too large, the membrane permeation flux decreases. Conversely, even if the difference between the average particle size of the floc and the pore size of the membrane is too small, the membrane permeation flux is reduced. We found that there was a difference. That is, when the coagulant is injected into the raw water and then the membrane is filtered, the difference between the average particle size of the floc and the pore size of the membrane can be maintained at an appropriate value to suppress the decrease in the membrane permeation flux and increase the amount of permeated water. Was determined. Next, the present inventors examined the relationship between the difference between the average particle size of the floc and the pore diameter of the membrane when the coagulant concentration was changed, and the coagulant injection concentration. As shown in FIG. 5, as the flocculant concentration increases, the difference between the floc average particle diameter and the membrane pore diameter increases, and by controlling the flocculant concentration, the difference between the floc average particle diameter and the membrane pore diameter is adjusted. can do.

From the above results, in order to suppress a decrease in the permeation flux of the membrane when the coagulant is injected and thereafter the membrane is filtered, the average particle size of the floc and the pore diameter of the membrane after the coagulant injection are controlled. If the flocculant concentration is controlled so that the particle size ratio or difference becomes a preset particle size ratio or difference, the floc particle size suitable for membrane filtration can be maintained.

The operation in such a case will be described. As described above, particles in water are divided into micro flocs and flocs and monitored. From the micro floc and floc monitoring results, the average floc diameter in the water to be treated supplied to the membrane processing apparatus is determined, and the ratio or difference between the average floc particle diameter and the pore diameter of the membrane in a region where the water flow resistance of the membrane is reduced. Compared with the control threshold value, if the value is lower or higher than the target range, the coagulant injection amount is adjusted. As described above, according to the present invention, the micro floc diameter and the floc diameter are monitored, and the aggregation or flocculation is performed in consideration of the ratio or difference between the floc diameter in the liquid before the membrane supply and the pore diameter of the membrane, which has not been considered in the past. By controlling the injection amount
Clogging of the membrane can be prevented, and a decrease in the amount of treated water can be suppressed.

An embodiment of the present invention will be described below with reference to the drawings.

Here, an example is shown in which a floc monitoring device is installed in a rapid mixing pond in a water purification plant in which a membrane treatment device is disposed downstream of the rapid mixing pond.

First, the flow of the water purification process will be described.
In the process flow of the water purification plant shown in FIG. 1, raw water RW taken from a river or the like is guided to a rapid mixing pond 3 via a landing well 2 after sand having a large particle size is removed in a sand basin 1. A coagulant 10 such as a sulfuric acid band or PAC (polyaluminum chloride) is injected from the coagulant injection device 200 into the rapid mixing pond 3. By the action of the coagulant, the turbid particles and the organic matter form large flocs after forming fine flocs.
A power pump 8 is arranged at the subsequent stage of the rapid mixing pond 3, and supplies the effluent of the mixing pond 3 to the membrane treatment device 11. Power pump 8
May be omitted in the case of a membrane that can be filtered at a low pressure. Here, a floc of 1 to 100 μm is referred to as a micro floc,
A floc of 0.1 mm to 5 mm is defined as a floc. The micro flocs and flocs are separated by the membrane processing device 11. The filtered water FW is temporarily stored in the water purification tank 12, and is supplied to the customer as tap water after chlorine sterilization. The non-filtered water from the membrane treatment device 11 is returned to the rapid mixing pond 3 as circulating water SW. The membrane treatment apparatus 11 performs backwash with the filtered water FW using the backwash pump 14 as a power source, and removes deterrents in the pores of the membrane and on the membrane surface. The retained matter is separated by the sludge discharge device 7, and the backwash water FBW is returned to the preceding stage of the landing well 2.

In the case of the above configuration, the operation will be described below.

A turbidity meter 24 and an alkalinity meter 25 are installed on the effluent of the landing well 2 to measure turbidity and alkalinity.
It is input to the flocculant injection concentration calculation device 100. In the coagulant injection concentration calculation device 100, the coagulant injection concentration DL is calculated based on the equation (1). The calculated injection concentration DL is input to the coagulant injection correction device 500.

DL = a + b × Tu + c × AL (1) where Tu: turbidity and AL: alkalinity. A, b, and c are eigenvalues of the water treatment plant,
0.15 to 0.2, 0.2 to 0.3.

In the coagulant injection correction device 500, the flow meter 6
By multiplying the flow rate Q after passing through the landing well measured at 0 and the coagulant injection concentration DL, the coagulant injection amount Mp is calculated as in equation (2).

Mp = DL × Q (2) The injection amount Mp is output to the coagulant injection device 200. The coagulant injection device 200 injects the coagulant into the rapid mixing pond 3 so as to have an injection amount Mp.

The rapid mixing pond 3 is provided with a first monitoring device 13 for monitoring micro flocs and a second monitoring device 23 for monitoring flocs. The first monitoring device 13 includes, for example, an ITV camera 50, a microscope 51, and a flow cell 52. FIG. 6 shows an example of the configuration. After the coagulant is injected, the mixing pond water is sampled and passed to the flow cell 52. The flow cell 52 is made of, for example, flat hollow glass, and the flocs in the water can be observed from the outside. A lamp 53 is installed before and after the flow cell 52 to illuminate the flock, and the flock is continuously photographed by the ITV camera 50 and the microscope 51. The captured floc image is visualized by the ITV camera 50, and the video data is sent to the arithmetic unit 300 in FIG. The arithmetic unit 300 calculates the number of flocks n1 and the average floc diameter d1 of 0.1 mm or less per unit volume, and outputs the values to the arithmetic unit 350. For example, assuming that the objective lens magnification of the microscope 51 is 10 times in FIG.
The measurement visual field range of the screen is 0.6 mm × 0.6 mm. If one screen is processed by an image processing apparatus having a memory of 512 pixels × 512 pixels, the size of each pixel is 1.2 μm.
The actual measurement range is from 1.2 μm to 0.6 mm, and the detection of micro flocs becomes possible. The image data sent to the arithmetic unit 300 by the ITV camera 50 recognizes a micro floc after the binarization processing. The area di of each of the recognized n1 micro flocs is assumed to be the same equivalent circle, and the diameter di is obtained by Expression (3).

Di = (2si / π) ^0.5 (3) d1 = (Σni × di) / n1 (4) From the equation (4), the average microfloc diameter d1 is obtained.

The second monitoring device 23 comprises, for example, a lamp 53 and an ITV camera 50. FIG. 7 shows an example of the configuration. Back screen 5 illuminated by lamp 53
6 is monitored by the ITV camera 50. IT
Flocked video data captured by the V camera 50 is sent to the arithmetic unit 320 in FIG. The arithmetic unit 320
Number of flocks n2 per unit volume and average floc diameter d
2 is calculated and the value is output to the arithmetic unit 350. For example, in FIG. 7, the measurement visual field range of one screen captured by the ITV camera 50 is set to 50 mm × 50 mm, and the one screen is processed by an image processing apparatus having a memory of 512 pixels × 512 pixels. Become. The actual measurement range is from 0.1 mm to 50 mm, and the flock can be detected. The image data sent to the arithmetic unit 320 by the ITV camera recognizes a block after binarization processing. The diameter dj is obtained assuming that the area sj of each of the recognized n2 flocs is an equivalent circle. The average diameter d2 of the entire floc can be obtained by the same method as in the equations (3) and (4).
The arithmetic unit 350 calculates the average floc diameter d3 of the particles present in the water supplied to the film processing apparatus according to the equation (3), and outputs the value of d3 to the arithmetic unit 370.

D3 = (d1 × n1 + d2 × n2) / (n1 + n2) (5) The arithmetic unit 370 calculates the ratio d3 / D between d3 and the pore diameter D of the membrane previously input. The operation result d3 / D is output to the comparison circuit 400. The comparison circuit 400 determines the correction amount of the coagulant injection amount according to the equations (6), (7), and (8).

E1 <d3 / D <e2 (6) e1 ≧ d3 / D (7) e2 ≦ d3 / D (8) Here, e1 and e2 are determined from the ratio between the pore diameter and the floc diameter of the membrane. It is a control target value, for example, M having a pore diameter of 0.1 μm.
For the F film, it is 10,500 respectively.

D3 / D is higher than e1 as in equation (6),
If it is lower than e2, a signal indicating that the injection concentration has not been corrected is sent from the comparison circuit 400 to the coagulant injection correction device 500, and the coagulant is injected according to the value obtained by the coagulant injection concentration calculation device 100. d3 / D is equal to e1 as in equation (7).
If not, the comparison circuit 400 sends a signal to increase the coagulant in proportion to the deviation between e1 and d3 / D to the coagulant injection correction device 500, and increases the coagulant until a signal indicating that the injection concentration is not corrected is sent. I do. Also, d3 / D is equal to e as in equation (8).
If it is 2 or more, the comparison circuit 400 sends a signal for reducing the coagulant in proportion to the deviation between e2 and d3 / D to the coagulant injection correction device 500, and the coagulant is supplied until the signal of the unconcentrated injection concentration is sent. reduce weight.

In the above embodiment, the ratio between d3 and D has been described, but the difference between d3 and the pore D of the membrane may be used. In this case, the arithmetic unit 370 calculates the difference between d3 and the previously input pore diameter D of the membrane, d3-D. The calculation result d3-D is output to the comparison circuit 400. In the comparison circuit 400, Expression (9),
The correction amount of the coagulant injection amount is determined according to (10) and (11).

E3 <d3-D <e4 (9) e3 ≧ d3-D (10) e4 ≦ d3-D (11) Here, e3 and e4 are determined from the difference between the pore diameter and the floc diameter of the membrane. It is a control target value, for example, M having a pore diameter of 0.1 μm.
For the F film, it is 10,500 respectively.

D3-D is higher than e3 as in equation (9),
If it is lower than e4, a signal indicating that the injection concentration has not been corrected is sent from the comparison circuit 400 to the coagulant injection correction device 500, and the coagulant is injected according to the value obtained by the coagulant injection concentration calculation device 100. d3-D is equal to e as in equation (10).
If it is 3 or less, the comparison circuit 400 sends a signal to increase the coagulant in proportion to the deviation between e3 and d3-D to the coagulant injection correction device 500, and the coagulant is supplied until the signal of the injection concentration uncorrected is sent. Increase the amount. Further, if d3-D is equal to or more than e4 as in the equation (11), the comparison circuit 400 sends a signal for reducing the coagulant in proportion to the deviation between e4 and d3-D to the coagulant injection correction device 500, The coagulant is reduced until an uncorrected injection concentration signal is sent. A signal prompting the coagulant injection reduction is sent from the comparison circuit 400 to the coagulant injection correction device 500, and the coagulant is reduced until a signal indicating that the injection concentration is not corrected is sent.

With the above-described coagulant injection method, clogging of the film processing apparatus can be suppressed. Further, in order to obtain a stable amount of treated water, backwashing is performed. Hereinafter, the backwash method will be described.

The supply pressure Pin to the membrane processing apparatus is measured with a pressure gauge 1
At 5, the pressure Pfw of the permeated water is measured by the pressure gauge 16 and input to the arithmetic unit 550. The arithmetic device 550 calculates the differential pressure ΔP by the equation (12). The calculated ΔP is used as the comparison circuit 600
And compared with the upper limit value of loss Pe set in advance by the equation (13). The comparison circuit 600 instructs back-pressure cleaning for 30 seconds.

ΔP = Pin−Pfw (12) ΔP> Pe (13) Here, Pe is the upper limit of pressure loss.

If ΔP is higher than Pe as in the equation (13), the power pump 8 stops, then the valves 19 and 20 are closed, and the valves 21 and 22 are opened. The pump 14 is operated to backwash the membrane treatment apparatus 11 using the water in the water purifying pond 12, and the backwash water BW is returned to the preceding stage of the landing well 2 after the floc is removed from the sludge discharging apparatus 7. .

As described above, if the coagulant injection control is performed based on the floc data, a decrease in the amount of treated water due to a decrease in membrane performance is suppressed, and a stable amount of treated water can be obtained.

In the above-described embodiment, the first monitoring apparatus performs the image processing on the image to obtain the micro-flock. However, the first monitoring apparatus may obtain the micro-flock from the transmitted light intensity. For example, it may be composed of a flow cell, a light source and a light receiving converter. FIG. 8 shows an example of the configuration. Tungsten bulbs and lasers are used as light sources. After the coagulant is injected, the mixing pond water is sampled and passed to the flow cell. Light generated from a light source provided in front of the flow cell passes through the flow cell and reaches the detection unit. The output voltage drop of the light receiving converter corresponding to the area of the shadow projected by blocking the light by each particle in the flow cell is taken out as a pulse, and each pulse is taken as one particle and the pulse amplitude is taken as the particle size. Measure as The measured value is sent to the arithmetic unit 300. The arithmetic unit 300 calculates the number of flocks n1 and the average floc diameter d1 of 0.1 mm or less per unit volume, and outputs the values to the arithmetic unit 350.

The arithmetic unit 350 calculates the average floc diameter d3 of the particles present in the water supplied to the membrane processing apparatus by the following equation (5).
, And outputs the value of d3 to the arithmetic unit 370.

The arithmetic unit 370 calculates the ratio or difference between d3 and the pore diameter D of the membrane input in advance,
00 determines the correction amount of the coagulant injection amount.

Next, a case in which a membrane treatment device is disposed downstream of the sand filtration tank will be described.

First, the flow of water treatment will be described.
In the process flow of the water purification plant shown in FIG. 9, fine flocs are formed in the rapid mixing pond 3 as in FIG. Flock growth is promoted in the floc formation pond 4 at the subsequent stage, and the grown floc is settled and separated in the sedimentation pond 5. The sedimentation water SW from which flocs have been settled and separated through the above-described process is guided to the membrane treatment device 11, and microflocs that cannot be removed by sedimentation and separation are separated by the membrane treatment device 11. Backwash water FB
W is mixed with floc discharged from the sedimentation basin 5, the retained matter is separated by the sludge discharger 7, and the backwash water FBW is supplied to the landing well 2.
Returned to the previous stage.

Hereinafter, the present invention will be described in detail.

The coagulant injection amount Mp is obtained as in equation (2), and Mp is output to the coagulant injection device 200. The coagulant injection device 200 injects the coagulant into the rapid mixing pond 3.

A first monitoring device 13 for monitoring micro flocs and a second monitoring device 23 for monitoring flocs are installed in the floc forming pond 4. The arithmetic unit 350 calculates the average floc diameter d3 of the particles present in the water supplied to the membrane processing apparatus according to the equation (3), and calculates d3.
Is output to the arithmetic unit 370. In the arithmetic unit 370, the ratio of d3 to the pore diameter D of the membrane input in advance, d3 /
Calculate D. The operation result d3 / D is output to the comparison circuit 400. In the comparison circuit 400, the correction amount of the coagulant injection amount is determined by equations (14) and (15).

E5 ≧ d3 / D (14) e5 <d3 / D (15) Here, e5 is a control target value determined from the ratio between the pore diameter and the floc diameter of the membrane. It is 10 for the MF film.

When d3 / D is equal to or more than e5 as in the equation (14), a signal indicating that the injection concentration has not been corrected is sent from the comparison circuit 400 to the coagulant injection correction device 500, and the signal is obtained by the coagulant injection concentration calculation device 100. The flocculant is injected according to the value given. If d3 / D is less than e5 as in the equation (15), the comparison circuit 400 sends a signal to increase the coagulant in proportion to the deviation between e5 and d3 / D to the coagulant injection correction device 500, and the injection concentration Increase the flocculant until an uncorrected signal is sent.

In the above embodiment, the ratio between d3 and D has been described, but the difference between d3 and the pore D of the membrane may be used. In this case, the arithmetic unit 370 calculates the difference between d3 and the previously input pore diameter D of the membrane, d3-D. The calculation result d3-D is output to the comparison circuit 400. In the comparison circuit 400, the expression (1)
6) and (17), the correction amount of the coagulant injection amount is determined.

E6 ≧ d3-D (16) e6 <d3-D (17) Here, e6 is a control target value determined from the difference between the pore diameter and the floc diameter of the membrane. It is 10 for the MF film.

When d3-D is equal to or greater than e6 as in the equation (16), a signal indicating that the injection concentration has not been corrected is sent from the comparison circuit 400 to the coagulant injection correction device 500, and the signal is obtained by the coagulant injection concentration calculation device 100. The flocculant is injected according to the value given. If d3-D is less than e6 as in equation (17), the comparison circuit 400 sends a signal to increase the flocculant in proportion to the deviation between e6 and d3-D to the flocculant injection correction device 500, and the injection concentration Increase the flocculant until an uncorrected signal is sent.

Incidentally, the first monitoring device 13 and the second monitoring device 23 may be installed at the latter stage of the sedimentation basin.

As described above, if the flocculant injection control is performed based on the floc data, a decrease in the amount of treated water due to a decrease in membrane performance is suppressed, and a stable amount of treated water can be obtained.

In the above embodiment, a system using image processing and transmitted light intensity is used as the floc monitoring device, but an ultrasonic device may be used.

[0055]

According to the present invention, the load on the film can be reduced, and a decrease in the processing performance of the film can be suppressed.

[Brief description of the drawings]

FIG. 1 is a system diagram of coagulant injection control in a water purification plant showing one embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the ratio of the average particle size of the floc to the pore size of the membrane and the permeation flux.

FIG. 3 is a graph showing the relationship between the flocculant concentration and the ratio of the average particle size of the floc to the pore size of the membrane.

FIG. 4 is a graph showing the relationship between the difference between the average particle size of floc and the pore size of a membrane, and the permeation flux.

FIG. 5 is a graph showing the relationship between the difference between the average particle size of floc and the pore size of a membrane and the concentration of a flocculant.

FIG. 6 is a configuration diagram showing an embodiment of a first monitoring device for monitoring a micro floc.

FIG. 7 is a configuration diagram of a second monitoring device.

FIG. 8 is a configuration diagram showing another embodiment of the first monitoring device.

FIG. 9 is a system diagram of a coagulant injection control in a water purification plant showing another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sand basin, 2 ... Landing well, 3 ... Rapid mixing pond, 4 ... Floc formation pond, 5 ... Sedimentation basin, 6, 7 ... Sludge drainage device, 8, 14,
18, 55 pump, 9, 17 stirrer, 10 flocculant, 11 membrane treatment device, 12 water purification tank, 13 first monitoring device, 15, 16 pressure gauge, 19, 20, 21, 22
... Valve, 23 ... second monitoring device, 24 ... turbidity meter, 25
... alkalinity meter, 26 ... flow meter, 50 ... ITV camera,
51: microscope, 52: flow cell, 53: lamp, 54
... water sampling pipe, 56 ... back screen, 57 ... light source, 58
, Light, 59, light receiving converter, 100, flocculant injection concentration calculation device, 200, flocculant injection device, 300, 320, 35
0, 370, 550: arithmetic unit, 400, 600: comparison circuit, 500: coagulant injection correction device.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Naoki Hara 5-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Omika Plant of Hitachi, Ltd.

Claims (4)

[Claims] 1. A water purification treatment method in which a flocculant is injected into raw water that has been taken to aggregate fine particles and suspended matter in the raw water into flocs, and the flocs are separated and removed by a membrane. The water purification treatment method according to claim 1, wherein a coagulant injection amount is controlled such that a ratio or a difference between the floc particle diameter and the pore diameter of the membrane is within a predetermined appropriate range. 2. The method according to claim 1, wherein the floc particle size is measured by two types of floc monitoring devices, the first floc monitoring device measures 1 μm to 100 μm flocs, and the second floc monitoring device. To measure the floc of 0.1 mm to 5 mm, and control the coagulant injection amount so that the ratio or difference between the floc diameter and the pore diameter of the membrane obtained by these devices is within a predetermined appropriate range. A water purification method characterized by the following. 3. A flocculant is injected into the raw water that has been withdrawn to coagulate fine particles and turbidity in the raw water to form flocs. In the water purification method of separating and removing with a membrane,
The particle size of the floc flowing from the sedimentation basin is measured, and the coagulant injection amount is controlled such that the ratio or difference between the floc particle size and the pore size of the membrane falls within a predetermined appropriate range. Water treatment method. 4. The method according to claim 3, wherein the floc particle size is measured by two types of floc monitoring devices, the first floc monitoring device measures 1 μm to 100 μm flocs, and the second floc monitoring device. To measure the floc of 0.1 mm to 5 mm, and control the coagulant injection amount so that the ratio or difference between the floc diameter and the pore diameter of the membrane obtained by these devices is within a predetermined appropriate range. A water purification method characterized by the following.