JPH1015307A - Coagulating filtration method of water and water treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coagulating filtration method by which filtered water is flowed out in a stable state and to provide an execution device thereof. SOLUTION: In the coagulating filtration method of water, raw water is clarified by adding a flocculant of set amount to raw water and passing the raw water through a coagulating filtration device 14 to perform coagulating filtration. When it is detected that differential pressure between inlet pressure and output pressure of a filter layer is measured by a differential manometer 36 at time for passing raw water and ascending speed of the measured differential pressure is lower than the ascending speed of standard differential pressure, the the amount of the flocculant to be added is increased so that the ascending speed of differential pressure at time for passing water nearly concides with the ascending speed of standard differential pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coagulating and filtering water and a water treatment apparatus for implementing the method.
River water, lake water, industrial water, sewage treatment water, etc. containing suspended matter is used as raw water, and purified water such as industrial water, tap water, etc. containing no suspended matter, or raw water such as pure water, ultrapure water, etc. The present invention relates to a method of coagulating and filtering water that can be stably produced and an apparatus for implementing the method.

[0002]

2. Description of the Related Art River water, lakes and marsh water are used as raw water, and a water treatment apparatus for clarifying the raw water includes a coagulation filtration apparatus and a membrane filtration apparatus using a microfiltration membrane or an ultrafiltration membrane. Connected in series along the flow, firstly dewatering the raw water with a coagulation filter, and then removing the remaining suspension with a membrane filter,
For example, there is a water treatment apparatus as disclosed in Japanese Patent Application Laid-Open No. 5-285478. As shown in FIG. 10, in the water treatment apparatus disclosed in the above-mentioned publication (hereinafter, referred to as a conventional water treatment apparatus), raw water is introduced into a raw water tank 12 and a coagulant is added thereto. , And the suspension in the raw water is subjected to coagulation filtration to obtain primary filtered water. This primary filtered water is filtered by a membrane filter 18 to remove fine suspensions that could not be removed by the aggregating filter 14 to obtain turbidity-treated water. As described above, in the conventional water treatment apparatus, the coagulant is added to the raw water upstream of the coagulation filter
By performing the coagulation filtration in 4, the amount of the suspension in the primary filtered water is reduced, and the load on the membrane filtration device 18 is reduced. 24 is a coagulant injection equipment.

[0003] In such a water treatment apparatus, the amount of the flocculant to be added is generally low enough to allow the suspension in the raw water to aggregate by the action of the flocculant to form micro flocs. It is not necessary to add a flocculant in a high addition amount as in the case where components are removed by a flocculation settling apparatus. still,
In this specification, the added amount of the coagulant or the added amount of the coagulant is the weight of the coagulant added per unit volume of the raw water amount, and the added amount of the coagulant or the added amount of the coagulant = (coagulant weight ) /
(Raw water volume). For example, when PAC (polyaluminum chloride) is used as a coagulant, the amount of addition is generally 3 to 1
It is in the range of 0 mg / l, whereas in the case of coagulating sedimentation equipment, it is often in the range of 20 to 60 mg / l. Further, since the quality of raw water does not fluctuate so much, it is often operated with a substantially constant addition amount throughout the year.

[0004]

In the above-mentioned conventional water treatment apparatus, apart from the regular or regular increase of the normal transmembrane pressure in the membrane filtration device, the transmembrane pressure is irregular. However, there is a problem that the phenomenon that the flow rate of the permeated water suddenly decreases and the flow rate of the permeated water suddenly decreases occurs several times a year. The present inventor investigated the problem that the transmembrane pressure of the membrane filtration device was irregular and rapidly increased, and the cause was that the amount of the suspended matter in the primary filtered water flowing out of the coagulation filtration device was for some reason. And the large amount of the suspension flows into the membrane filtration device together with the primary filtered water,
It was found that the filtration membrane was blocked and the flow rate of the permeated water decreased. In addition, since the blocking of the filtration membrane is often not noticed by the operator, the failure of the water treatment device can be detected only when the flow rate of the permeated water decreases. In this case, it was difficult to operate the water treatment apparatus in a stable state, and it was not possible to constantly supply permeated water at a predetermined flow rate. In the above description, Japanese Patent Application Laid-Open No.
Although the water treatment apparatus disclosed in Japanese Patent No. 285478 is taken as an example, the rapid increase in the suspension of the primary filtered water flowing out of the above-mentioned coagulation filtration apparatus is the same in the case of other coagulation filtration apparatuses. is there.

Accordingly, an object of the present invention is to provide a flocculation filtration method capable of stably discharging filtered water containing no suspended matter, and to provide an apparatus for implementing the method.

[0006]

The present inventor first investigated the cause of the increase in the amount of suspended matter in the primary filtered water, and as a result, determined the turbidity or the amount of suspended matter in the raw water and the suspended amount of the primary filtered water. It is not necessarily directly related to the increase in the amount of turbid matter, and the fact that an increase in a certain component (hereinafter referred to as X component) in raw water causes a sudden increase in transmembrane pressure will occur. I found it. This is because when the water treatment equipment is operated with a fixed amount of coagulant added to the raw water and the river water with many suspended matters during the typhoon is used as the raw water, for example, the transmembrane pressure difference necessarily increases. Is not produced, but when a large amount of snowmelt is mixed into the river water, the transmembrane pressure rises sharply, despite the fact that the amount of suspended matter is not so large. .

Further research has shown that when the X component is mixed into raw water, the suspended matter in the raw water causes poor coagulation, and as a result, the raw water is suspended in the coagulation filtration device in a state of poor coagulation. When the primary filtration water containing a large amount of unagglomerated suspension flows out from the coagulation filtration device when the suspended matter removal rate in the coagulation filtration device is reduced, and such coagulation failure occurs, the coagulation Since the suspension is not trapped by the filtration device, the rising speed of the differential pressure between the inlet and the outlet of the coagulation filtration device is, as shown in FIG. I found that it was lower than that.

[0008] It is technically difficult to predict the occurrence of poor coagulation of a suspension due to the fluctuation of water quality as described above, and the cause of the poor coagulation is unknown. In order to prevent this, it is necessary to periodically sample raw water and perform a jar test or a coagulation filtration test to determine the optimum amount of coagulant to be added, and to increase or decrease the amount of coagulant added each time. However, it is cumbersome to sample the raw water to determine the optimal amount of flocculant to be added and to periodically increase or decrease the amount of flocculant to be added. Poor aggregation of the suspension may occur in the raw water when not performed. Then, the present inventor promptly states that poor aggregation of the suspension has occurred,
As a result of intensive research on a method for reliably and reliably detecting, when the flocculation of the suspension is poor, the differential pressure rise rate of the flocculation filtration device is smaller than normal, and the turbidity of the primary filtered water is significantly increased. That is, the inventors have come to think that it is possible to detect the occurrence of poor aggregation by utilizing the above-described phenomenon found by the present inventors.

The present inventor has found that when the above-mentioned coagulation failure occurs, the coagulation agent can be normally coagulated by increasing the amount of the coagulant added. As a result of examining the relationship between the amount of the coagulant added and the pressure difference between the inlet and the outlet of the coagulation filtration device when the addition amount of the coagulant was variously changed, it was shown in FIG. It has been found that as the amount of the coagulant added increases, the rate of increase of the differential pressure (that is, the magnitude of the differential pressure that increases per unit time) increases in proportion thereto. From the above, if the relationship as shown in FIG. 4 is obtained in advance with respect to the raw water to be treated, when the coagulation failure occurs, the amount of the coagulant to be added can be increased to what extent to coagulate normally. Know what you can do. That is,
As a result of increasing the addition amount of the coagulant from the addition amount at the time when the coagulation failure occurs, the differential pressure increase speed of the coagulation filtration device is, for example, the differential pressure increase speed (reference differential pressure increase) obtained from the relationship diagram of FIG. If the measured differential pressure rise rate is smaller than the reference differential pressure rise rate, it can be determined that the coagulation failure has not been eliminated yet. It can be determined that it is necessary to further increase the amount added.

[0010] Based on the above findings, in order to achieve the above object, the method for coagulating and filtering water according to the present invention (hereinafter referred to as the first invention method) is to filter raw water to which a coagulant is added in a set amount. A method for removing raw water by passing water through the bed and performing coagulation filtration, wherein the rising speed of the differential pressure between the inlet pressure and the outlet pressure of the filtration layer during passing of the raw water is lower than the reference differential pressure rising speed. When this is detected, the amount of the coagulant added is increased so that the rate of rise in differential pressure at the time of passing water substantially matches the reference rate of rise in differential pressure.

The coagulation filtration apparatus according to the present invention for carrying out the method of the first invention is a coagulation filter for removing raw water by passing a raw water to which a coagulant is added in a set amount through a filtration layer and performing coagulation filtration. In the filtration device, adjusting means for adjusting the addition amount of the flocculant, differential pressure detecting means for detecting the differential pressure between the inlet pressure and the outlet pressure of the flocculant filtration device, and the difference in water flow detected by the differential pressure detecting means A calculating means for calculating a differential pressure rising rate based on a temporal change in pressure, and a preset reference differential pressure rising rate and a differential pressure rising rate calculated by the calculating means are compared to calculate a calculated differential pressure rising rate. Control means for issuing a command to the adjusting means that the amount of coagulant to be added should be increased so that the calculated differential pressure rise rate substantially coincides with the reference differential pressure rise rate when is smaller than the reference differential pressure rise rate. It is characterized by.

The filter medium of the coagulation filter used in the apparatus for carrying out the method of the first invention and the method of the second invention described later is not particularly limited, but is preferably a high-speed filter using, for example, a fiber bundle or a fiber mass as the filter medium. Fiber filtration devices are preferred. The adjusting means for adjusting the amount of the coagulant is a known means,
For example, it comprises a flocculant tank containing a flocculant, means for injecting the flocculant from the flocculant tank into raw water (for example, a combination of a pipe and a pump), and a flow control valve provided in the pipe. Further, a variable displacement injection pump may be used instead of the flow control valve. The rising speed of the differential pressure can be obtained by differentiating the time-dependent change curve of the differential pressure detected by the differential pressure detecting means with respect to time. On the other hand, the reference differential pressure rise rate is determined by using the actual coagulation filtration apparatus or coagulation filtration experimental apparatus, and using the amount of coagulant added as a parameter to pass the normal raw water (in other words, the average raw water over a long period of time). Data obtained by calculating the differential pressure rise rate by watering,
For example, data as shown in FIG. 4 is an example. If the measured rate of increase in the differential pressure is lower than the reference rate of increase in the differential pressure, it means that poor coagulation occurs. Therefore, the coagulant is increased to eliminate the poor coagulation.

Further, the present inventor has also conducted experiments that the turbidity of the primary filtered water flowing out of the coagulation filtration device increases when the suspension is insufficiently captured by the coagulation filtration device due to poor coagulation. After confirming and monitoring the turbidity of the primary filtered water and paying attention to the fact that when the turbidity increases, it can be determined that coagulation failure has occurred, the present second invention has been completed. Therefore, in order to achieve the above object, another method of coagulating and filtering water according to the present invention (hereinafter referred to as the second invention method) is to pass raw water to which a coagulant has been added at a set addition amount through a filtration layer. Is a method for removing turbidity of raw water by coagulation filtration, wherein when it is detected that the turbidity of the filtered water flowing out of the filtration layer is higher than the reference turbidity, the turbidity of the filtered water is set to the reference turbidity. It is characterized in that the addition amount of the coagulant is increased so as to be not more than the degree.

The coagulation filtration apparatus according to the present invention for carrying out the method of the second invention is a coagulation filter for removing raw water by passing the raw water to which a coagulant is added in a set amount through a filtration layer and performing coagulation filtration. In the filtration device, adjusting means for adjusting the addition amount of the flocculant, turbidity measuring means for measuring the turbidity of the filtered water flowing out of the flocculating filtration device, and a preset reference turbidity and turbidity measuring means By comparing the measured turbidity with the measured turbidity, when the measured turbidity is higher than the reference turbidity, a command is issued to the adjusting means to increase the amount of the coagulant added so that the measured turbidity is equal to or less than the reference turbidity. Control means.

As the turbidity measuring means, a known turbidity meter of a transmitted light type, a scattered light type or the like can be used. The reference turbidity is
Using the actual coagulation filtration device or coagulation filtration test device, the turbidity of primary filtered water is passed by passing raw water at normal time (in other words, average raw water over a long period of time) with the amount of coagulant added as a parameter. May be obtained by measuring the turbidity of the primary filtered water, or may be considered as an allowable upper limit of the turbidity of the primary filtered water. If the measured turbidity is higher than the reference turbidity, it means that poor coagulation occurs. Therefore, the coagulant is increased to eliminate the poor coagulation.

Further, a water treatment device may be constituted by the coagulation filtration device according to the present invention, and a membrane filtration device connected in series downstream of the coagulation filtration device along the water flow path. The type of the membrane filtration device is not particularly limited.

[0017]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[0018]

Embodiment 1 Embodiment 1 is an example of implementing the first invention method.
Is a flow sheet of the water treatment apparatus 10 for implementing the first invention method. Note that devices having the same functions as those used in the conventional water treatment apparatus shown in FIG. 10 are denoted by the same reference numerals. As shown in FIG. 1, the water treatment device 10 includes a raw water tank 12 for storing raw water such as river water and industrial water, a coagulation filtration device 14, and a primary filtered water tank 1 along the flow of raw water.
6, a membrane filtration device 18, a first water supply pump 20 for supplying raw water from the raw water tank 12 to the coagulation filtration device 14, and a second water supply pump for supplying primary filtered water from the primary filtration water tank 16 to the membrane filtration device 18. 22, and a coagulant injection facility 24 for injecting the coagulant into the raw water tank 12.

The coagulation filtration device 14 is a so-called high-speed flow type fiber filtration device, and forms a fiber bundle or a fiber lump in which a large number of fibrils are aggregated so that a suspended matter can be captured between the fibrils. This is a filtration device in which a large number of carriers for capturing a suspension are incorporated in a container. For example, the thickness of the fibrous filter medium is 1
A large number of long fiber bundles are used in which a large number (for example, several tens to several hundreds) of non-combustible single fibers such as acrylic fibers, polyester fibers, and polyamide fibers having a length of about 0 μm to 80 μm and a length of several tens cm to several meters are bundled. . The lower end of such a long fiber bundle is fixed to a perforated plate provided at the lower part inside the container, and each upper end of the long fiber bundle is extended upward of the container to form a free end broom-shaped filter medium.
By passing raw water in a downward flow through the coagulation filtration device 14 having such a filter material of a long fiber bundle, a suspended matter can be efficiently captured.

The specifications of the membrane filtration device 18 are not particularly limited, but in the present embodiment, the membrane filtration device 18 is constituted by a cross-flow type membrane filtration device using an ultrafiltration membrane (UF). As the membrane, inorganic membrane such as ceramic, or cellulose acetate, polysulfone, polypropylene,
An organic film made of a high molecular compound such as polyethylene, polyacrylonitrile, or silicone is used in the form of a tube, pleated, hollow fiber, spiral, or flat film. In the case of treating a large amount of primary filtered water, a modular membrane filtration device in which hundreds to thousands of hollow fiber membranes are bundled and put in a case can be used. still,
The membrane filtration device 18 may be a total filtration type, or may use a microfiltration membrane (MF).

The coagulant injection equipment 24 includes a coagulant tank 26 for storing a coagulant, an injection pump 28, an injection pipe 30 from the coagulant tank 26 via the injection pump 28 to the raw water tank 12, and an injection pipe 30. And a flow control valve 32 provided. With the above configuration, the coagulant injection equipment 24 can inject the coagulant at a set flow rate into the raw water tank 12 under the control of the flow control valve 32.
In this embodiment, the coagulant is injected into the raw water tank 12. However, the coagulant may be injected into the raw water in front of the coagulation filtration device 14, and the coagulant may be injected into the pipe from the raw water tank 12 to the coagulation filtration device 14. May be injected. Further, instead of the flow control valve 32, the injection pump 28 may be a variable displacement pump so that the injection amount of the coagulant may be adjusted. Various coagulants such as polyaluminum chloride, sulfuric acid band, and ferric chloride can be used.

The water treatment apparatus 10 further includes a controller 34
The reference differential pressure increase rate is input in advance. The reference differential pressure rise rate is determined by adding a coagulant in a predetermined amount to raw water in normal or normal time (which may be referred to as average raw water over a long period of time), and then performing coagulation filtration apparatus 14 or coagulation filtration experiment apparatus. And the rate of increase of the differential pressure using the amount of added coagulant as a parameter, which is obtained by measuring the differential pressure at that point in time with respect to the elapsed time of water passage, for example, as shown in FIG. It is a correlation between the quantity and the rate of rise of the differential pressure. The controller 34 calculates the differential pressure rise rate based on the measurement value of the differential pressure gauge 36 that detects the differential pressure of the flocculation filtration device 14, and increases the set flow rate of the flocculant when it is smaller than the reference differential pressure rise rate. Flow control valve 3
Fire at 2.

Hereinafter, an operation method of the water treatment apparatus 10 will be described. Raw water at a predetermined flow rate is received in the raw water tank 12 and a coagulant at a predetermined flow rate is injected into the raw water tank 12 by the coagulant injection equipment 24. Raw water is passed through the coagulation filtration device 14 by the first water supply pump 20. Most of the suspension is aggregated by the action of the flocculant to form relatively large flocs, which are removed from the raw water by the filtering action of the flocculation and filtration device 14. The raw water from which most of the suspension has been removed enters the filtered water tank 16 as primary filtered water. Coagulation filtration device 14
After the elapse of a predetermined time from the start of water supply or when the differential pressure measured by the differential pressure gauge 36 reaches a set value, the water supply is temporarily stopped, and then backwashing is performed. Thereafter, the water flow cycle of this procedure is repeated.

Subsequently, the primary filtered water is supplied to the filtered water tank 1
From 6, water is passed through the membrane filtration device 18 by the second water supply pump 22. The membrane filtration device 18 removes fine suspended matter that has passed through the coagulation filtration device 14 and flows out the turbidity-treated water.
In the present embodiment, the membrane filtration device 18 is operated in a cross flow system, and the circulating water returns to the filtration water tank 16 and is sent to the membrane filtration device 18 together with the primary filtration water. After a lapse of a predetermined time from the start of water passage, the water filtration of the membrane filtration device 18 is temporarily stopped, and backwashing is performed. Thereafter, the water flow cycle of this procedure is repeated.

The differential pressure of the coagulation filtration device 14 is continuously measured by a differential pressure gauge 36, an output signal from the differential pressure gauge 36 is input to a control device 34, and an output signal from the control device 34 is input to a flow control valve 32. The input coagulant injection amount is adjusted.

Here, it is assumed that the X component that causes poor coagulation flows into the raw water. Since the suspension in the raw water cannot sufficiently coagulate before entering the coagulation filtration device 14 due to the X component, a large amount of the suspension passes through the coagulation filtration device 14 and is introduced into the subsequent membrane filtration device 18. As a result, the suspended solids removal load of the membrane filtration device 18 increases. At this time, the differential pressure increasing speed of the coagulation filtration device 14 is a small value as compared with the case where the coagulation of the suspension normally occurs as shown in FIG. In the control device 34, the differential pressure increasing speed of the flocculation filtration device 14 is calculated at regular time intervals or at every water passage cycle, and is compared with a reference differential pressure increasing speed having a preprogrammed coagulant addition amount as a parameter. .

When the differential pressure rise rate based on the differential pressure measured by the differential pressure gauge 36 (hereinafter referred to as the measured differential pressure rise rate) is lower than the reference differential pressure rise rate, a command from the control device 34
The coagulant injection equipment 24 increases the amount of coagulant added to the raw water stepwise or continuously, and injects the coagulant until the difference between the measured differential pressure rise rate and the reference differential pressure rise rate falls within a certain range. Increase quantity. Referring to FIG.
In the first stage (the period indicated by 1 in FIG. 5, the same applies hereinafter), no aggregation failure has occurred, so the measured differential pressure rise rate is:
It substantially coincides with the reference differential pressure increasing speed, and in the second stage, the measured differential pressure increasing speed is lower than the reference differential pressure increasing speed. Therefore, when the second stage is started, the addition amount of the coagulant is increased, and as a result, the coagulant addition amount is made constant when the measured differential pressure rise rate becomes equal to or greater than the reference differential pressure rise rate (the second step). 3 steps). After a few cycles of operation with the increased amount of coagulant added, when the water quality of the raw water is assumed to have almost returned to the original value, the amount of coagulant added was returned to the initial set value again. The continuous operation is continued while repeating the procedure of calculating the rising speed, comparing the measured differential pressure rising speed with the reference differential pressure rising speed, and then repeating the procedure of changing the amount of the flocculant added (fourth stage). In FIG. 5, each valley portion of the line indicating the change in the water flow differential pressure indicates that the differential pressure has been restored to the original state by backflow washing the coagulation filtration device that has finished water flow for a predetermined time. Is shown.

The initial setting value of the amount of the coagulant added may be determined in advance by experiments, but empirically, _{2 to 5} mg / l as PAC (0.2 to 0.5 mg as Al ₂ O ₃₎
/ L) is appropriate. In addition, since it takes 24 to 72 hours empirically from the change of the properties of the raw water to the occurrence of poor coagulation and the return to the normal raw water state, this time is stored in the controller 34 in advance, It is preferable to control the amount of the coagulant to be automatically returned to the initial set value after the lapse of the above-mentioned time from the increase in the amount of the coagulant to be added due to poor coagulation.

Experimental Example 1 The water treatment apparatus 10 of Example 1 was continuously operated under the following conditions.
The water pressure difference of the coagulation filtration device 14 and the membrane pressure difference of the membrane filtration device 18 were measured according to the passage of water time. Niigata industrial water is used as raw water, a high-speed fiber filtration device filled with an acrylic long fiber bundle is used for the coagulation filtration device 14, a UF membrane (Asahi Kasei Kogyo LNV-5010) is used for the membrane filtration device 18, and a coagulant Used polyaluminum chloride. FIG. 6 shows the time change of the pressure difference in water passing through the coagulation filtration device 14 and the time change of the pressure difference between the membranes of the membrane filtration device 18 when the water treatment device 10 is operated.
As shown in FIG. 6, in the example in which the water treatment apparatus 10 of the first embodiment is used, in the first stage (the period indicated by 1 in FIG. 6, the same applies hereinafter), the initial addition amount of the coagulant is set to Al ₂ O _3. At 0.3m
g / l, and in the second stage where the differential pressure rise rate is smaller than the reference differential pressure rise rate, the addition amount is 0.6 mg / Al ₂ O _3.
In the third stage where the addition amount was further increased and the addition amount was further increased, the addition amount was set to 0.9 mg / l with Al ₂ O ₃ , and in the fourth stage the addition amount was returned to the initial set rate.

For comparison, the conventional water treatment apparatus shown in FIG. 10 was operated under the same conditions as those of the water treatment apparatus 10, and similarly, the differential pressure of water passing through the coagulation filtration device 14 and the membrane pressure of the membrane filtration device 18 were similarly measured. The differential pressure was measured as the water passage time passed. FIG. 7 is a graph showing the change in the pressure difference in water passing through the coagulation filtration device 14 and the change in turbidity of the primary filtered water when the conventional water treatment device is operated, and the change in the membrane filtration device
5 shows the change over time in the transmembrane pressure difference.

As is clear from the rising tendency of the pressure difference in water passing through the flocculation filtration device 14 and the rising tendency of the turbidity and the transmembrane pressure difference of the primary filtered water shown in FIGS. In Experimental Example 1 in which the amount of the coagulant added was controlled using the water treatment device 10,
It was confirmed that the phenomenon of lowering of the suspended solids removing ability of the coagulation filtration device 14 occurred only temporarily, there was no increase in the transmembrane pressure difference of the membrane filtration device 18, and the water treatment device 10 could be operated stably. I have.

Embodiment 2 Embodiment 2 is an example of implementing the second invention method.
Is a flow sheet of the water treatment apparatus 40 for implementing the second invention method. The water treatment device 40 has the same configuration as that of the water treatment device 10 shown in FIG. 1 except for the differences described below. The difference is that a turbidity meter 42 is attached to the outlet of the coagulation filtration device 14 in place of the differential pressure gauge 36 of the water treatment device 10. In this embodiment, the upper limit value (reference turbidity) of the turbidity of the primary filtered water measured at the outlet of the coagulation filtration device 14 is set in the control device 34 in advance. The turbidity of the primary filtered water at the outlet of the flocculation filtration device 14 is continuously measured by a turbidity meter 42, and an output signal from the turbidity meter 42 is input to the control device 34. Further, an output signal from the control device 34 is input to the flow control valve 32, and the injection amount of the coagulant is adjusted by changing the valve opening.

Here, it is assumed that the X component causing poor coagulation flows into the raw water. Since the suspension in the raw water cannot sufficiently coagulate before entering the coagulation filtration device 14 due to the X component, a large amount of the suspension is formed by the coagulation filtration device 14.
And is introduced into the membrane filtration device 18 together with the primary filtered water. For this reason, the suspended solids removal load of the membrane filtration device 18 increases, and a clogging phenomenon of the membrane occurs.

Therefore, as shown in FIG. 8, the first stage in which the measured turbidity is lower than the reference turbidity (the period indicated by 1 in FIG. 8,
The same applies to the following), the coagulant is added at the initial addition amount,
When the turbidity enters the second stage in which the turbidity exceeds the reference turbidity, the control device 3
4. A command is issued from step 4 and the flow control valve 3 is stepwise or continuously.
2, the valve opening is increased, and the amount of the coagulant added is increased. The addition amount of the coagulant is increased until the turbidity at the outlet of the coagulation filtration device 14 becomes equal to or less than the reference turbidity set in the control device 34. In the third stage when the measured turbidity becomes lower than the reference turbidity, the coagulant injection amount is made constant. Subsequently, the operation was performed with the increased amount of the flocculant added, and in the fourth stage in which the water quality of the raw water was assumed to have substantially returned to the original state, the flocculant added amount was returned to the initial set value again, and the primary filtration water turbidity was measured. Continuous operation is continued while repeating the procedure of comparing the measured turbidity with the reference turbidity and then changing the amount of the flocculant added.

Although the standard turbidity depends on the performance of the subsequent membrane filtration device, it is empirically set to one or less.

Experimental Example 2 The water treatment apparatus 40 of Example 2 was continuously operated under the following conditions.
The water pressure difference of the coagulation filtration device 14 and the membrane pressure difference of the membrane filtration device 18 were measured according to the passage of water time. The raw water is Niigata industrial water, the coagulation filtration device 3 is a high-speed fiber filtration device filled with an acrylic long fiber bundle, the membrane filtration device 5 is a UF membrane (LNV-5010 manufactured by Asahi Kasei Kogyo), and the coagulant is polychlorinated. Aluminum was used. The reference turbidity at the outlet of the membrane filtration device 18 was set to 1 degree (kaolin).

FIG. 9 shows the temporal change of the turbidity of the primary filtered water at the outlet of the flocculation filtration device 14 and the temporal change of the transmembrane pressure of the membrane filtration device 18 when the water treatment device 40 is operated. .
As shown in FIG. 9, in the example using the water treatment apparatus 40 of the first embodiment, in the first stage (the period indicated by 1 in FIG. 9, the same applies hereinafter), the initial addition amount of the coagulant is set to Al ₂ O _3. At 0.3m
g / l, and in the second stage where the turbidity of the primary filtered water is higher than the reference turbidity (upper limit of turbidity), the addition amount is set to 0.6 mg / l with Al ₂ O ₃ and further added. The third that increased
In the step, the addition amount was set to 0.9 mg / l with Al ₂ O ₃ , and in the fourth step, the addition amount was returned to the initial set amount.

As is clear from the turbidity of the primary filtered water and the tendency of increasing the transmembrane pressure shown in FIGS. 7 and 9 showing the results obtained by the conventional apparatus, the coagulation was performed using the water treatment apparatus 40 of Example 2. In Experimental Example 2 in which the additive amount was controlled,
It has been confirmed that the rise in the turbidity at the outlet is eliminated in a short time, and there is no increase in the transmembrane pressure of the membrane filtration device 18 and the stable operation of the water treatment device 40 can be ensured.

[0039]

According to the method of the present invention, the differential pressure between the inlet pressure and the outlet pressure of the coagulation filtration device is measured, and when the differential pressure rising speed is lower than the reference differential pressure rising speed obtained in advance, the raw water in the raw water is measured. It is determined that poor aggregation of the suspension has occurred, and the amount of the aggregating agent added is increased. Further, the turbidity of the primary filtered water flowing out of the coagulation filtration device is measured, and when the turbidity is higher than a predetermined reference turbidity, it is determined that poor coagulation of the suspension in the raw water has occurred, and the amount of the coagulant added Increase. Therefore, when the quality of the raw water fluctuates and poor aggregation of the suspension occurs in the raw water, according to the method of the present invention, the occurrence of poor aggregation is detected and the amount of the coagulant added is increased. Thereby, the aggregation failure phenomenon can be quickly eliminated. When a membrane filtration device is provided downstream of the coagulation filtration device, it is possible to predict the occurrence of membrane blockage of the membrane filtration device, which has been difficult to predict in the past, and to prevent the occurrence.

The water treatment apparatus according to the present invention realizes an optimum apparatus for carrying out the method of the present invention, and even if there is a change in the properties of raw water, the ability to remove suspended solids in the flocculation filtration apparatus is not affected. No stable operation of the subsequent membrane filtration device can be ensured.

[Brief description of the drawings]

FIG. 1 is a flow sheet of a water treatment apparatus 10 for implementing a first invention method.

FIG. 2 is a flow sheet of a water treatment apparatus 40 for implementing the method of the second invention.

FIG. 3 is a graph showing a relationship between a water flow time of a coagulation filtration device and a differential pressure.

FIG. 4 is a graph showing a correlation between a coagulant addition amount and a differential pressure rise rate.

FIG. 5 is a graph showing the relationship between the water flow time of a coagulation filtration device and the pressure difference when the amount of coagulant added is changed.

FIG. 6 is a graph showing the results of Experimental Example 1, and is a graph showing the relationship between the water passage time, the water passage pressure difference of the coagulation filtration device, and the transmembrane pressure difference of the membrane filtration device.

FIG. 7 is a graph showing the results of measurement using a conventional water treatment apparatus, wherein the water passage time, the pressure difference between the water and the turbidity of the primary filtration water, and the membrane between the membranes of the membrane filtration apparatus. It is a graph which shows the relationship with a differential pressure.

FIG. 8 is a graph showing the relationship between the water flow time and the turbidity of the coagulation filtration device when the amount of the coagulant added is changed.

FIG. 9 is a graph showing the results of Experimental Example 2, and is a graph showing the relationship between the water passage time, the turbidity of the primary filtered water of the coagulation filtration device, and the transmembrane pressure of the membrane filtration device.

FIG. 10 is a flow sheet of a conventional water treatment apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Water treatment apparatus which implements 1st invention method 12 Raw water tank 14 Coagulation filtration apparatus 16 Primary filtration water tank 18 Membrane filtration apparatus 20 1st water supply pump 22 2nd water supply pump 24 Coagulant injection equipment 26 Coagulant tank 28 Injection pump 30 Injection pipe 32 Flow control valve 34 Control device 36 Differential pressure gauge 40 Water treatment device for implementing the second invention method 42 Turbidity meter

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Noriaki Watanabe 2-200 Momoyamacho, Niigata City, Niigata Tohoku Electric Power Co., Inc. Niigata Thermal Power Station (72) Inventor Masahiro Kuwata 1-4-9 Kawagishi, Toda City, Saitama Olga (72) Inventor Shuwa Murata 1-4-9 Kawagishi, Toda City, Saitama Prefecture Organo Research Institute

Claims (5)

[Claims] 1. A method for removing raw water by passing raw water to which a flocculant has been added in a set addition amount through a filtration layer and subjecting the raw water to coagulation filtration. When it is detected that the rate of increase of the differential pressure from the outlet pressure is lower than the reference differential pressure increase rate, the amount of the coagulant added is adjusted so that the differential pressure increase rate at the time of passing water substantially matches the reference differential pressure increase rate. A method for coagulating and filtering water, comprising increasing the concentration. 2. A method for removing turbidity of raw water by passing raw water to which a coagulant has been added in a set addition amount through a filtration layer and performing coagulation filtration, wherein the turbidity of the filtered water flowing out of the filtration layer is reduced. A method for coagulating and filtering water, comprising, when detecting that the turbidity becomes higher than a reference turbidity, increasing the amount of a coagulant added so that the turbidity of the filtered water is equal to or lower than the reference turbidity. 3. A coagulation filtration device for removing raw water by passing raw water to which a coagulant has been added in a set addition amount through a filtration layer and performing coagulation filtration, wherein an adjusting means for adjusting the coagulant addition amount; Differential pressure detecting means for detecting a differential pressure between the inlet pressure and the outlet pressure of the coagulation filtration device, and calculating means for calculating a rising speed of the differential pressure based on a temporal change of the differential pressure at the time of water passage detected by the differential pressure detecting means And comparing the preset reference differential pressure increase rate with the differential pressure increase rate calculated by the calculation means, and when the calculated differential pressure increase rate is lower than the reference differential pressure increase rate, the calculated differential pressure increase rate is A coagulation filtration device comprising: control means for issuing a command to the adjustment means to increase the amount of coagulant added so as to substantially coincide with the reference differential pressure rise rate. 4. An aggregating and filtering apparatus for removing raw water by passing raw water to which a flocculant has been added in a set addition amount through a filtration layer and performing flocculant filtration, comprising: an adjusting means for adjusting the amount of the flocculant added; The turbidity measurement means for measuring the turbidity of the filtered water flowing out of the coagulation filtration device is compared with a predetermined reference turbidity and the turbidity measured by the turbidity measurement means. A coagulation filtration device comprising: a control unit that issues a command to the adjustment unit that the amount of the coagulant to be added is increased so that the measured turbidity is equal to or lower than the reference turbidity when the turbidity is higher than the reference turbidity. 5. A water treatment apparatus, comprising: the coagulation filtration device according to claim 3 or 4; and a membrane filtration device connected in series downstream of the coagulation filtration device along a water flow path. .