JPH07204476A - Water purifying apparatus and operation thereof - Google Patents

Abstract

PURPOSE:To control the clogging of a filter membrane module by controlling the backwashing of the filter membrane module using the ratio of flux at the start time of filtering after the completion of backwashing and the flux during the elapse time up to next backwashing. CONSTITUTION:The backwashing of a filter membrane module is controlled using the ratio of flux at the start time of filtering after the completion of backwashing and the flux during the elapse time up to next backwashing. In backwashing, the change of backwashing pressure, the change of backwashing frequency, the change of a backwashing time and the addition of chemicals or the change of the addition condition thereof may be executed independently or in combination. In order to change the flow rate of backwashing water using the flux ratio, a backwashing automatic valve 19, a pump 18, a chemical injection pump 22 and a chemical injection automatic valve 25 may be automatically or manually controlled on the basis of the control signals sent from a flux ratio measuring device 31 and an operational operator 32 through the control signal cable shown by a broken line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water purification system using a filtration membrane module and a method of operating the same, and more specifically, backwashing the filtration membrane module using the change in the flux ratio as an index. The present invention relates to a water purification system for controlling clogging of a filtration membrane module and a method of operating the same.

[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, practical application of a water purification system using a filtration membrane module that does not require the above-mentioned vast facilities 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 that have not been permeated accumulate 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. In this way, a large amount of raw water is lost along with suspended substances.
The system shown in is being considered.

The operation of the water purification system shown in FIG. 2 includes the production of permeated water by cross flow filtration and the clogging of the hollow fiber UF membrane module 12 (the filtration membrane module by the non-permeable component).
Backwash to prevent accumulation of permeated water at the permeate outlet). 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 cross-flow filtration, raw water is supplied with the permeated water automatic valve 13 open, the wash water discharge automatic valve 14 and the backwash automatic valve 19 closed, and the circulating water amount is about 10 times the raw water inflow amount. Filtration with a hollow fiber UF membrane module is performed, and the generated permeated water is stored in the tank 17. On the other hand, in the backwashing of the hollow fiber UF membrane module, the permeated water automatic valve 13 is closed, the wash water discharge automatic valve 14 and the backwash automatic valve 19 are opened at a rate of about once every 30 to 60 minutes. A part of the permeated water is pumped by the pump 18 in the direction opposite to the direction in which the permeated water is generated.
The turbid component on the inner surface of the raw water side of the filtration membrane module is supplied to the module 12 and the turbid component containing the turbid component at a high concentration is passed through the route 15 to the outside of the system from the lavage water discharge automatic valve 14. Let it drain. As described above, a large amount of raw water is lost together with turbidity components, and the system shown in FIG. 2 is being studied to prevent this.

[0006]

The main obstacle in the operation of such a water purification system is the shutdown due to clogging of the filtration membrane module. Therefore, various methods have been tried for controlling the backwash using the information obtained from the raw water or the water treatment system as an index. Water Supply Association Magazine (Vo
l. 61, No. 11, 19-26, 1992),
In the quantitative filtration method in which the membrane permeate flow rate is constant, an example is described in which, when the pressure on the circulating water side of the water purification system exceeds a set value, periodic backwashing is performed depending on the turbidity of the raw water. . However, backwashing depending on the raw water turbidity cannot eliminate the performance degradation of the filtration membrane module when the raw water turbidity does not correspond to the clogging state of the filtration membrane module, or This leads to a reduction in the permeated water recovery rate due to unnecessary backwashing. Further, Japanese Patent Application Laid-Open No. 4-247226 discloses a method of controlling raw water turbidity and the amount of filtered water as indexes, and Japanese Patent Application Laid-Open No. 4-326927 discloses a filter membrane module.
A method is disclosed in which the flow rate of circulating water discharged from the tank and transferred to the circulation system is used as an index. However, there are various problems such that information on both the raw water and the water treatment equipment side is required, or it can be implemented only with a defined circulating water flow path. That is, in the water purification system using these filtration membrane modules, a simple control mechanism that can solve the clogging of the filtration membrane module in response to changes in the raw water supply and can also be applied to various water treatment systems There is a strong demand for the development of driving methods based on.

[0007]

[Means for Solving the Problems] In view of such a current situation,
When the present inventors examined the change in flux due to backwashing in detail, the elapsed time t with respect to the flux (Flux ₀ ) at the start of filtration after the end of backwashing within the elapsed time between backwashing and the next backwashing was examined. Ratio with Flux (Flux _t ) or Fl
ux _t / Flux ₀ (hereinafter, referred to as flux ratio) is
The present inventors have completed the present invention by discovering that the water treatment capacity of the filtration membrane module is accurately shown and that by using this flux ratio, the backwashing of the filtration membrane module can be controlled simply and accurately.

That is, according to the present invention, in a continuous operation including backwashing of the filtration membrane module of a water purification system using the filtration membrane module by cross flow filtration, flux (Flux) at the start of filtration after the backwashing is completed. ₀ ) and the flux (Flux _t ) at the elapsed time t until the next backwashing are controlled to control the backwashing of the filtration membrane module, and a method for operating the same. To do.

The present invention will be described in detail below. The operation method according to the present invention is intended for a water purification system using a filtration membrane module by cross-flow filtration, and as the filtration membrane module, an ultrafiltration membrane, a microfiltration membrane or the like can be used. The membrane form of the filtration membrane module is
Examples include and-frame type, pleated type, spiral type, tubular (tubular) type, and hollow fiber type, with hollow fiber type being 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. Further, as the material of the film, hydrophilic polymer materials such as polyethersulfone, polyacrylonitrile copolymer, and cellulose acetate can be used, and cellulose acetate is most suitable.

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

Generally, the reduction of water treatment capacity in the operation of the water purification system is due to the clogging of the filtration membrane module. In the present invention, the water treatment capacity of the water purification system is defined as flux (permeate flow rate per unit area / hour (liter /
m ² · h). ). Fluctuations in the flux when backwashing is performed every 30 minutes are schematically shown in FIG. 1 (A). The flux increased by backwashing drops with the elapse of filtration time, and rises again by the next backwashing. , Repeat this for each backwash. On the other hand, the change in flux filtration membrane module at that time - may indicate that Le state transitions typically flux filtration beginning L _T line (or nadir of the state of the filtration membrane module Read the changes on the L _B line, and so on). However, as the flux ratio in the present invention, the flux on these lines is not used, but the ratio within the elapsed time between backwash and the next backwash is used. That is, if the flux at the start of filtration after the backwashing is Flux ₀ and the flux at the elapsed time t until the next backwashing is Flux _t , the flux ratio (Flux _t / Flu at the time t.
x ₀ ) is obtained and this flux ratio is used as an index of the water treatment capacity of the water purification system. FIG. 1 (B) is a schematic diagram showing changes with time of the flux ratio in a single backwash.

The raw water in the water purification system always contains turbid components, and the flux corresponding to the accumulation of these unpermeated substances in the filtration membrane module or the peeling by backwashing keeps the vertical movement by backwashing. The L _T line gradually rises or falls. The flux on the L _T line is considered to represent the filtration capacity of the filtration membrane module, but the same level of flux on the L _T line during the ascending phase (filtering capacity recovery phase) or the falling phase (filtering capacity decrease phase) was compared. In this case, the flux ratio in the ascending period is larger than the flux ratio in the descending period. That is, an increase in the flux ratio indicates that the filtration capacity tends to recover further, and a decrease in the flux ratio indicates that the filtration capacity tends to decrease further. Therefore,
As an indication of filtration capacity of the filter membrane modules by using the flux ratio, the change due to the flux take days at L _T line, it can be represented in a single measurement. The present invention uses this flux ratio to control backwashing. As the flux ratio, it is preferable to use the flux ratio at a preset time t such as 15 minutes or 30 minutes after backwashing as an index, and the cumulative flux ratio up to the preset time t may be used.

The flux ratio may be measured by a continuous monitor for 24 hours, but may be measured once or several times a day at a predetermined time.

As the backwash condition item that can be controlled by the measured flux ratio, the backwash water flow rate per unit time may be changed, or a chemical such as a bactericide or an oxidizing agent may be added to the backwash water, Alternatively, the addition amount may be changed. The change in the backwash water flow rate can be adjusted by changing the backwash pressure during backwash, changing the backwash time per wash, or the backwash frequency. The flux ratio, which is the boundary of whether or not to change the backwash conditions, is defined by the filtration membrane module used.
It may be set appropriately by a preliminary test or the like, but for example, a cellulose acetate hollow fiber ultrafiltration membrane module may be used.
In the case of backwashing every 30 minutes, the
If the flux ratio in lux ₃₀ ) is less than 0.92, the backwash is changed to a mode in which the backwash is performed at a higher level.
At 0.96, the backwash condition is continued as it is and 0.96
If it exceeds, it can be set to change the condition to more relax the backwash. In these cases, when the backwash pressure is changed as the control of the backwash, the backwash pressure may be 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 ratio. preferable. Further, in the case of responding by changing the backwash time, it is preferable to select the backwash time in the range of usually 10 seconds to 3 minutes according to the monitored flux ratio. Furthermore, if the change in backwash frequency is to be handled, the backwash frequency can be monitored.
It is preferable to select within a range of once every several minutes to 2 hours depending on the flux ratio. Further, as a control of the backwashing condition, it is possible to add a chemical such as a bactericidal agent or an oxidizing agent to the backwashing water together with the change of the various backwashing conditions.
Agents that can be added during backwash include sodium hypochlorite,
There are oxidizing germicides such as chlorine, hydrogen peroxide and ozone. In the above backwashing, changes in backwashing pressure, changes in backwashing frequency, changes in backwashing time, addition of chemicals and changes in conditions thereof may be carried out individually or in combination.
In order to change the backwash water flow rate using the flux ratio, for example, the backwash automatic flow is controlled by a control signal sent from the flux ratio measuring device 31 and the arithmetic and control unit 32 shown in FIG. The valve 19, the pump 18, the chemical injection pump 22, the automatic chemical injection valve 25, etc. may be automatically controlled, or these may be manually controlled.

The filtration membrane module filters out general bacteria, but the bacteria remaining on the feed water side, as time passes, the turbid components accumulated at the outlet of the filtration membrane module or the filtration membrane module, etc. May adhere to and propagate. Since the bactericide has a bactericidal effect as well as a decomposition / cleaning effect on the film surface deposit, the backwashing effect can be increased.

[0016]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

(Embodiment) As shown in FIG. 2, the water treatment system has a check valve 10, a pump 11, and a hollow fiber U, which are the same as those of the conventional one.
F membrane module 12, automatic permeate valve 13, automatic wash water discharge valve 14, permeate tank 17 for accumulating permeate
A pump 18 for pressurizing backwash water during backwashing, a backwash passage 20 including an automatic backwash valve 19, a chemical tank 21 as a means for injecting a bactericide into the backwash passage 20, and a chemical injection pump 2
2. A sterilizing agent injecting path 24 including a check valve 23 is provided. The bactericide is a hollow fiber U produced by microorganisms contained in raw water.
The permeable membrane of the F membrane module 12 is prevented from being broken or attacked and broken. In addition to this, if it is an oxidizing bactericidal agent such as sodium hypochlorite, chlorine, hydrogen peroxide, ozone, etc. You can also expect a decomposition effect on the kimono.

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 is carried out as the backwashing pressure corresponding to the flux level based on the monitored flux ratio, the pressure of the pump 18 is adjusted, and when it is carried out as the backwashing time. The automatic valve 19 and the pump 18
When the set time of (1) is extended or shortened and a drug such as a sterilizing agent is used in combination with permeated water, in addition to the settings of the automatic valve 19 and the pump 18, the drug pump 22 is operated and the automatic drug injection valve 25 is opened and the reverse. Perform a wash.

Based on the water purification system shown in FIG. 2, surface water was purified at a water purification plant, and changes with time of flux and correspondence with the flux ratio were investigated. Flux
₀ ) shall be regularly measured every day at 10 am during the operation period, and the flux ratio shall be continuously measured for 30 minutes after the start of filtration in the backwash, and the flux ratio shall be measured as Flux ₃₀ / F.
It was calculated as lux ₀ . The change with time of the flux is shown in FIG. 3 (A), and the flux ratio to the flux from the time of measurement to ◯ 12 is shown in FIG. 3 (B). The operating condition is that the material of the hollow fiber UF membrane module 12 is made of cellulose acetate.
The membrane area is 5 m ² and the average operating pressure is 0.5 kg /
It was set to cm ² . The flux was shown at a conversion value of 5 ° C. and 0.5 kg / cm ² . Backwash condition is once every 30 minutes for backwash, 45
The backwashing pressure was 1.5 kg / cm ² for ² seconds. Furthermore, two different kinds of backwash conditions (A and B modes) corresponding to the flux ratio and the flux during measurement were prepared.
The backwashing condition of the A mode is once every 30 minutes for backwashing for 120 seconds and backwashing pressure of 1.5 kg / cm ² . Further, soda hypochlorite was added to the backwash water. The backwashing condition of the B mode is once every 30 minutes for backwashing for 60 seconds, and the backwashing pressure is 1.
5 kg / cm ² , and sodium hypochlorite was added to the backwash water.

The flux and the flux ratio at the time of measurement decreased after the start of filtration, but the operation was continued without changing the backwash conditions of the filtration membrane module. After confirming the decrease of the flux during the measurement, the backwash condition was changed to the A mode in order to avoid the continuous decrease of the filtration capacity. At the time of measurement, after confirming a stable flux at, the backwash condition was changed to B mode.

(Results) The fall of the flux (converted value) from the start of measurement to the 8th day was 7.5 (liter / m ² · hr) on average on a daily basis. It took several days to determine the filtration capacity. However, the flux ratio, which was about 0.93 at the start of measurement, was about 0.90 at the time of measurement, and it could be predicted that the flux would further decrease unless the backwash conditions were changed.
In addition, the flux ratio accurately showed the same result as the measurement result by the flux for several days by one calculation. This had a flux ratio of 0.95 at the time of measurement, and showed a tendency of recovery of the filtration capacity.
The results were the same as the measurement results of the filtration membrane module for 10 days until the 8th day. Also, during the period when the filtration capacity of the filtration membrane module was relatively stable (during measurement to ∘12), the flux ratio was also stable in the range of 0.93 to 0.96. When changing the backwash condition using the flux ratio,
It was not necessary to measure the flux for 24 hours, and moreover, continuous operation was possible for a long period of time. Further, in the operation by the present water treatment system, the permeated water recovery rate could be increased by changing the backwash condition from the increase of the flux ratio.

[0023]

According to the operation method of the present invention, in a water purification system using a filtration membrane module, the backwash water flow rate using the flux ratio and the backwashing such as addition of a bactericide to the backwash water are performed. The clogging of the filtration membrane module could be controlled by controlling the conditions. For the flux ratio, the treatment capacity of the water purification system can be accurately grasped by measuring in a short time, and not only the filtration capacity of the filtration membrane module at the time of measurement but also the near future can be predicted from the flux and the flux ratio. . The flux ratio can be easily measured with a water treatment system using an ordinary filtration membrane module, and the control of backwash water by the flux ratio can be applied to water treatment systems using various filtration membrane modules.

[Brief description of drawings]

FIG. 1A is a schematic diagram of a flux change when a filtration membrane module is regularly backwashed. (B) is the flux ratio (Flux _t / Flu after 10, 20 and 30 minutes after the start of filtration to the flux (Flux ₀ ) at the start of filtration after the end of backwashing.
x ₀ ).

FIG. 2 is a water purification system using a filtration membrane module.

FIG. 3 (A) is a change in flux when the water treatment system in the water purification plant is continuously operated. (B) shows the relationship between the flux and the flux ratio at each measurement in the water treatment system operation.

FIG. 4 is a conventional water purification system using a filtration membrane module.

FIG. 5 is a water purification system using a filtration membrane module with backwash control based on the flux ratio.

[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 Chemical injection route 25 Chemical injection Automatic valve 31 Flux ratio measuring device 32 Arithmetic control device

Claims (7)

[Claims] 1. A filtration membrane module by cross flow filtration.
In a continuous operation including backwashing of the filtration membrane module of the water purification system using a filter, the flux (Flux ₀ ) at the start of filtration after the end of backwashing and the flux (Flux at the time t until the next backwashing) _t ) and the filtration membrane module
A method for operating a water purification system, which comprises controlling the backwashing of water. 2. A method for operating a water purification system, wherein the raw water according to claim 1 is surface water. 3. A method for operating a water purification system, wherein the membrane material of the filtration membrane module according to claim 1 is cellulose acetate. 4. A method for operating a water purification system, wherein the filtration membrane module according to claim 1 is a hollow fiber type, and the cross flow filter is an internal pressure system. 5. A method for operating 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. How to operate the purification system. 7. A flux (Flu
x ₀ ) and the flux (Fl
ux _t ) ratio (flux ratio) and a flux ratio measuring device and an arithmetic and control unit that calculates the backwash condition based on the flux ratio, by cross flow filtration using a filtration membrane module. Water purification system.