JPH07204475A - Water purifying apparatus and continuous operation thereof - Google Patents

Abstract

PURPOSE:To prevent the clogging of a filter membrane module by executing the backwashing of the filter membrane module by changing the flow rate of backwashing water corresponding to flux to allow the module to quickly correspond even to surface flowing water large in the fluctuation width of turbidity. CONSTITUTION:In continuous operation containing the backwashing of the filter membrane module 12 of a water purifying system, the backwashing of the filter membrane module 12 is executed on the basis of the change of the flow rate of backwashing water corresponding to flux. In backwashing, the change of backwashing pressure, the change of backwashing frequency and the change of a backwashing time may be executed independently or in combination. In the backwashing corresponding to the flow rate of backwashing water to the flux, a backwashing automatic valve 19 and a pump 18 may be controlled automatically or manually on the basis of the control signals sent from a flux measuring device 31 and an operational controller 32 through the control signal cable shown by a broken line. Herein, the control signal from the operational controller 32 is returned to a chemical injection pump 22 and a chemical injection automatic valve to also automatically control both of them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a water purification system using an ultrafiltration membrane module or a precision filtration membrane module. The permeated water can be collected at a specified rate, and the flux (FLU
The present invention relates to a continuous operation method of a water purification system for backwashing a filtration membrane module using the change of X) as an index.

[0002]

2. Description of the Related Art Conventionally, as a water purification system for obtaining tap water from surface water such as river water or lake water, it is common to go through a coagulation-precipitation-sand filtration-chlorine sterilization process. In order to realize such a process, a flocculation basin, a sedimentation basin, a sand filtration basin, and chlorine sterilization equipment are required, and a vast installation space is required. In addition, it has been proposed in recent years to add an activated carbon treatment system or an ozone treatment system to cope with pollution of water sources such as rivers, but these have caused a further increase in installation space and have become a new problem. On the other hand, the practical use of a water purification system using an ultrafiltration membrane module or a microfiltration membrane module that does not require the vast facility described above and a continuous operation method thereof have been studied.

An example of a water purification system using a filtration membrane module will be described with reference to FIG. Raw water such as river water introduced through the check valve 10 is pressurized by a pump 11 and supplied to a hollow fiber ultrafiltration membrane module (hereinafter referred to as a hollow fiber UF membrane module) 12. The hollow fiber UF membrane module 12 is an assembly of a large number of hollow fiber ultrafiltration membranes, and when raw water containing suspended matter is supplied to the inside of this hollow fiber membrane, suspended matter is removed. The permeated water can be obtained outside the hollow fiber membrane. Next, the permeated water from which the suspended components have been removed is stored in the tank 17 through the permeated water automatic valve 13.

In the hollow fiber UF membrane module 12, turbid components which have not been permeated are accumulated on the inner surface of the hollow fiber membrane,
This will reduce the permeate generation capacity and eventually cause an operation stop.
Therefore, generally, so-called cross flow filtration, which has an effect of supplying raw water to the inner membrane of the hollow fiber UF membrane module 12 at a high speed and stripping the suspended matter components adhering to the inner membrane surface by a high-speed water flow, carry out. The raw water supplied at a high speed is partially permeated by the hollow fiber UF membrane module 12, and the unpermeated supply water passes through the circulation path 16 and joins with the raw water. In this case, turbidity components accumulate in the hollow fiber UF membrane module 12 at a high concentration. Therefore, the water containing a large amount of turbidity components is discharged from the automatic flush water discharge valve 14 through the route 15 branched from the circulation route 16.

The above-mentioned water purification system is operated by the production of permeated water by cross flow filtration and the hollow fiber UF membrane module 1.
Alternately, backwash to prevent the second clogging (accumulation of the filtration membrane module at the permeate outlet by non-permeate components). Backwashing is to supply permeate to the filtration membrane module in the direction opposite to that for producing permeate in order to remove turbid components adhering to the inner surface of the filtration membrane module on the raw water side. The quality component is peeled off and the turbidity component is discharged out of the system. That is, in the cross flow filtration, the permeated water automatic valve 13
The raw water is supplied in a state where the automatic wash water discharge valve 14 and the backwash automatic valve 19 are closed, and the hollow fiber UF membrane module performs filtration with a circulating water amount of about 10 times the raw water inflow amount. The generated permeated water is stored in the tank 17. On the other hand, hollow fiber U
For backwashing of the F membrane module, the permeate water automatic valve 13 is closed and the wash water discharge automatic valve 14 is once every 30 to 60 minutes.
The backwash automatic valve 19 is opened, and a part of the permeate is supplied to the hollow fiber UF module 12 by the pump 18 in the direction opposite to that at the time of producing the permeate, so that the turbidity of the inner surface of the filtration membrane module on the raw water side. The components are peeled off, and the cleaning water containing the turbidity component at a high concentration is discharged from the automatic cleaning water discharge valve 14 to the outside of the system through the path 15.

[0006]

The main obstacle in continuous operation of such a water purification system is the shutdown due to clogging of the filtration membrane module. The state of the raw water supplied is not constant, and due to a sudden change in the turbidity of the raw water, a periodic backwash cannot solve the outage. Water Supply Association Magazine (Vol. 61, No. 11, 19-26, 19
92) is an example of performing regular backwash depending on the turbidity of raw water when the pressure on the circulating water side of the water purification system exceeds a set value in the quantitative filtration method in which the flow rate of the permeated water is constant. Is listed. However, backwashing that depends on raw water turbidity leads to a reduction in permeate recovery rate due to unnecessary backwashing when the raw water turbidity does not correspond to the clogging state of the filtration membrane module, which is artificial. There is a problem in that only a regular backwash with the backwash frequency set to 1 causes clogging of the filtration membrane module depending on the set value, making continuous operation impossible.

Further, the UF membrane module has the ability to separate substances having a size of 0.01 μm or more, which makes it possible to obtain permeated water from which general bacteria have been removed. The post-chlorination that is being carried out can be reduced, and the production of chlorinated organic compounds such as trihalomethane can be expected to be reduced. However, since general bacteria accumulate in the circulating water, these accumulated general bacteria also need to be discharged out of the system. Since a part of the permeated water is used for backwashing, efficient backwashing of non-permeated substances such as turbid components and general bacteria is required to collect permeated water at a high rate. That is, in the water purification system using these filtration membrane modules, it is possible to respond to changes in the raw water supply, and the filtration membrane module can be agile.
There is a strong demand for the development of a continuous operation method that can solve permeated water with a high recovery rate and that is stable over a long period of time.

[0008]

[Means for Solving the Problems] In view of such a current situation,
The present inventors have found that clogging of the filtration membrane module is prevented by capturing the change in permeated water flux of the water purification system as a change in the raw feed water and performing backwashing corresponding to the flux. The present invention has been completed.

That is, in the present invention, the flux is dealt with in the continuous operation including backwashing of the filtration membrane module of the water purification system using the UF membrane module or the microfiltration membrane module by the cross flow filtration. Provided is a water purification system characterized by performing backwashing of the filtration membrane module by changing the backwash water flow rate, and a continuous operation method thereof. The present invention will be described in detail below.

The continuous operation method according to the present invention is intended for a water purification system using an ultrafiltration membrane module or a microfiltration membrane module by cross flow filtration, and the membrane configuration of the filtration membrane module is not Plate and frame type, pleated type, spiral type, tubular (tubular)
Examples thereof include a mold and a hollow fiber type, but the hollow fiber type is preferable. Further, when using the hollow fiber type filtration membrane module, an internal pressure system in which raw water is flown into the hollow fiber membrane is preferable. Furthermore, as the material of the film, hydrophilic polymer materials such as polyethersulfone, polyacrylonitrile copolymer, and cellulose acetate can be used.
The best is.

Surface water such as river water or lake water can be used as the raw water supplied for purification.

Generally, the decrease in water treatment capacity in continuous operation of the water purification system is due to clogging of the filtration membrane module. In the present invention, it is possible to monitor the change in the water treatment capacity of the water purification system by using the raw water supply amount, the circulating water side pressure by cross flow filtration, the integrated permeated water amount from the filtration membrane module, the flux and the like as indexes. The flux is the flow rate (liter / m ² · h) per unit area / time of the permeated water in the filtration membrane module. In the present invention, it is particularly preferable to use the flux as an index. Therefore, the water treatment capacity of the water purification system can be maintained constant by performing backwashing corresponding to the flux. In this case, the backwash can be performed in accordance with the level of flux (a set value with a width) or in accordance with the fluctuation of flux (the amount of change over time). In addition, backwashing is performed by changing the backwashing water flow rate per unit time, and by changing the backwashing pressure during backwashing, or by changing the backwashing time per time or the backwashing frequency. It can also be adjusted.

When the backwash pressure is changed in accordance with the flux level, the backwash pressure is selected in the range of 1.0 times or more and 3 times or less that in the cross flow filtration operation, depending on the monitored flux level. The flux level depends on the filter membrane module used, and is set appropriately by preliminary tests. In addition, when responding by changing the backwash time,
The backwash time is usually selected in the range of 10 seconds to 3 minutes depending on the monitored flux level. Further, when the backwashing frequency is changed, the backwashing frequency is selected every several minutes to 2 hours depending on the monitored flux level. In the case of dealing with fluctuations in the flux, the backwash pressure and backwash time are manipulated in the same manner as above depending on the amount of change in the flux over time. Furthermore, a chemical such as a bactericidal agent or an oxidizing agent can be used in combination with the backwash water. Examples of agents that can be used in combination during backwashing include soda hypochlorite, chlorine, hydrogen peroxide, and oxidizing bactericides such as ozone. In the above backwashing, changes in backwashing pressure, changes in backwashing frequency, and changes in backwashing time may be carried out individually or in combination. The backwash corresponding to the flow rate of the backwash water with respect to the flux is performed by automatically controlling the backwash automatic valve 19 and the pump 18 by a control signal sent from the flux measuring device 31 and the arithmetic and control unit 32 of FIG. Control or manual control operation may be performed. Here, the control signal from the arithmetic and control unit 32 is changed to the chemical injection pump 22.
It is also possible to transmit the information to the automatic drug injection valve 25 or the like for automatic control.

The UF membrane module or the microfiltration membrane module filters out general bacteria, but bacteria remaining on the feed water side accumulates turbidity accumulated at the outlet of the filtration membrane module over time. There is a possibility that they will adhere to the quality components or filtration membrane modules and propagate. In the continuous operation method of the present invention, the bacteria thus locally accumulated can be efficiently treated by using a bactericide in the backwash water and discharged to the outside of the system. Moreover, the bactericide has a bactericidal effect as well as a decomposition and cleaning effect on the film surface deposits, so that the backwashing effect can be increased.

[0015]

The present invention will be described in more detail below with reference to Reference Examples and Examples, but the present invention is not limited thereto.

(Reference Example) Hollow fiber UF membrane module of the present invention
An example of a water purification system using a battery will be described with reference to FIG. It should be noted that the same can be done by using a precision filtration membrane module.

The water treatment system has a check valve 1 similar to the conventional one.
0, pump 11, hollow fiber UF membrane module 12, permeate automatic valve 13, wash water discharge automatic valve 14, permeate tank 17 for accumulating permeate, and pump for pressurizing backwash water during backwashing 18, a backwash passage 20 including an automatic backwash valve 19, and a bactericide injection route 24 including a chemical tank 21, a chemical injection pump 22, and a check valve 23 as means for injecting a bactericide into the backwash route 20. Is provided. The bactericidal agent prevents damage to the permeable membrane of the hollow fiber UF membrane module 12 by microorganisms contained in raw water, and is an oxidative bactericidal agent such as sodium hypochlorite, chlorine, hydrogen peroxide and ozone. In addition to this, a decomposing effect on the film surface deposit can be expected.

The operation of this processing system is performed as follows. In the cross flow filtration operation, the permeated water automatic valve 13 is opened, the concentrated water discharge automatic valve 14 and the backwash automatic valve 19 are both closed, and the pump 18 is stopped.
In this way, the raw water introduced through the check valve 10 is
The hollow fiber UF membrane module 1 is pressurized by the pump 11
2 is supplied. In the hollow fiber UF membrane module 12, the permeated water from which the suspended components have been removed by the filtration action of the filtration membrane is
It is accumulated in the permeate tank 17 through the permeate automatic valve 13.

At the time of backwashing, the supply of raw water is stopped, the permeate water automatic valve 13 is closed, both the wash water discharge automatic valve 14 and the backwash automatic valve 19 are opened, the pump 11 is stopped, and the pump 18 is turned on. drive. In this way, a part of the permeated water accumulated in the permeated water tank 17 is used to backwash the hollow fiber UF membrane module 12, and the turbidity stripped from the inner surface of the hollow fiber membrane by the backwash. The quality component is discharged as cleaning water to the outside of the system through the automatic cleaning water discharge valve 14. The amount of backwash water is equal to the amount of wash water discharged. When the backwashing treatment of the filtration membrane module with respect to the monitored flux fluctuation is carried out as the backwashing pressure corresponding to the flux level, the pressure of the pump 18 is adjusted, and when it is carried out as the backwashing time, the above-mentioned is carried out. When the set time of the automatic valve and pump is extended or shortened, and when a chemical such as a sterilizing agent is used in combination with the permeated water, the chemical pump 22 is opened and backwash is performed in addition to the setting of the automatic valve and pump.

(Example) Purification of surface water was carried out at a water purification plant based on the operation method by the water purification system of FIG. The operating conditions were as follows: Cellulose acetate was used as the material of the hollow fiber UF membrane module 12, the membrane area was 5 m ² , and the average operating pressure was 0.5.
It was set to kg / cm ² . Flux is 5 ℃, 0.5kg /
Converted as cm ² , when the flux (converted value) is 50 liters / m ² · h or more, once every 30 minutes for 60 seconds,
When the backwashing pressure is 1.5 kg / cm ² , and the flux (converted) is less than 50 liters / m ² · h, the backwashing frequency is once every 30 minutes for 120 seconds, and the backwashing pressure is 1.5 kg / c
It was carried out at m ² . If the backwashing frequency decreases due to the decrease in flux, the flux (converted) is restored to 80 liters / m ² · h, and the same value is maintained at the same frequency until the measured value is maintained twice the same value. Was backwashed. Sodium hypochlorite was used as a chemical agent used in combination with the backwash water. Figure 2 shows the operation modes such as backwashing and chemical combination during the implementation period, as well as the flux and permeated water recovery rate.
Shown in. In the figure, the vertical axis on the left side shares the turbidity with the flux.

The turbidity of the raw water varied from measurement to measurement in the range of 5 to 145 degrees, but did not coincide with the change in flux. When the backwash frequency was manually adjusted according to the flux level regardless of the fluctuation of turbidity in such raw water, the decrease in flux was immediately improved immediately after the treatment, and then 3 months before the end of the experiment. The stable flux could be maintained for a while. Increasing the backwash water flow rate lowers the permeate recovery rate, but the filtration membrane module does not respond to the decrease in flux.
Since the water treatment capacity of the water is rapidly improved, it is possible to prevent the loss of backwash water, and the average recovery rate during 85 days of operation is 94.
It was 1%.

[0022]

According to the continuous operation method of the present invention, in a water purification system using a filtration membrane module, the backwash water flow rate corresponding to the flux is changed to thereby cause clogging of the filtration membrane module. It is possible to prevent this, and therefore continuous operation is possible for a long period of time. Flux accurately grasped the treatment capacity of the water purification system, and as a result, was able to respond swiftly to surface water with large fluctuation range of turbidity. According to the operating method of the present invention, the flux recovery is fast and the backwash water is not wastefully used, so that a permeated water recovery rate of 94% or more can be finally obtained.

[Brief description of drawings]

FIG. 1 is a water purification system using the filtration membrane module used in the examples.

[Fig. 2] Example of a water purification plant.

FIG. 3 is a conventional water purification system using a hollow fiber UF membrane module.

[Explanation of symbols]

 10, 23 Check valve 11, 18 Pump 12 UF membrane module 13 Permeate automatic valve 14 Concentrated water discharge automatic valve 17 Permeate tank 19 Backwash automatic valve 21 Chemical tank 22 Chemical injection pump 24 Disinfectant injection path 31 Flux Measuring instrument 32 Arithmetic control device

Claims (7)

[Claims] 1. In a continuous operation including backwashing of the filtration membrane module of a water purification system using an ultrafiltration membrane module or a microfiltration membrane module by cross flow filtration, in response to flux. A continuous operation method of a water purification system, characterized in that backwashing of the filtration membrane module is carried out by changing a backwash water flow rate. 2. A continuous operation method for a water purification system, wherein the raw water according to claim 1 is surface water. 3. A continuous operation method for a water purification system, wherein the membrane material of the filtration membrane module according to claim 1 is cellulose acetate. 4. A continuous operation method of a water purification system, wherein the filtration membrane module according to claim 1 is a hollow fiber type, and the cross flow filtration is an internal pressure system. 5. A continuous operation method for a water purification system, wherein the backwash water according to claim 1 is used in combination with a bactericide. 6. The water characterized in that the disinfectant of the water purification system according to claim 5 is an oxidizing disinfectant selected from sodium hypochlorite, chlorine, hydrogen peroxide and ozone. Continuous operation method of purification system. 7. A water purification system using a filtration membrane module by cross flow filtration, comprising a flux measuring device for monitoring the flux and an operation control device for calculating the backwash condition based on the flux.