JPH11179163A - Method for back washing of inner pressure type membrane module for removing pollutant by fluctuation of flow rate and pressure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve back washing efficiency and lower the frequency of washing with a chemical agent by repeating operations of high speed circulation washing and circulation stop or operations of high speed circulation washing and low speed circulation washing in the membrane back washing process in membrane module filtration carried out by using an inner pressure type hollow fiber membranes. SOLUTION: In this method comprising a back washing process for back washing an inner pressure type hollow fiber membrane module 5 for removing pollutants with back washing water in the presence of a sterilizer after a filtration process for providing filtered water from raw water by the membrane module 5, during the operation for switching the filtration process to the back washing process, an acid and/or a sterilizer to be used as an oxidizing agent are injected to a raw water flowing-in pipeline system 10 or a raw water circulation pipeline system 12 from respective storage tanks 8, 9 in order to accelerate decomposition and separation of pollutants and organic matters adhering to the membrane. Then, operations of high speed circulation washing and circulation stop or operations of high speed circulation washing and low speed circulation washing are repeatedly carried out to efficiently discharge and remove pollutants and organic matter in the inside and the outside of the hollow fiber membranes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for filtering using river water, industrial water, or the like as raw water using a hollow fiber membrane, comprising a flux (unit example of filtered water flow rate: m ³ / m ² /
The present invention provides an efficient backwashing method for stably obtaining the day) for a long period of time. The present invention can be applied to a cross flow system using an internal pressure type membrane module and an operation method of a total filtration system. As the shape and material of the membrane, any hollow fiber membrane can be used regardless of UF membrane (ultrafiltration membrane), MF membrane (microfiltration membrane) or the like. The present invention, as raw water,
The present invention can be suitably used when river water, lake water, groundwater, and industrial water obtained by primary treatment of these are used, and when raw water containing iron, aluminum, or the like as a turbid component is recovered and reused.

[0002]

2. Description of the Related Art The operation of a conventional internal pressure type, cross flow type hollow fiber membrane module filtration apparatus will be described with reference to FIG. The filtration step is performed as follows. The raw water 1 is pumped up by a raw water pump P-1, and large turbidity is removed by an automatic filter 3 having an aperture of 80 to 100 mesh or a high-speed filter having a similar performance. Manual valve 1 of system 12 (cross flow piping)
9. Opening the circulation valve AV-1 and the filtration outlet valve AV-2 of the filtered water outflow piping system 13 from the top of the membrane module or from the filtration outlet valve AV-2 and the backwash water lower inlet valve AV-
5. The backwash water upper inlet valve AV-4 is also opened, and the circulating pump P-2 is activated from above and below the membrane module 5 to circulate the raw water to obtain the filtered water 7 in the filtered water tank 6. The ratio between the raw water circulation flow rate and the filtered water flow rate is 95: 50: 5 to 50, and varies greatly depending on the raw water quality. Recently, the degree of opening of each valve was adjusted, and the circulating pump P-2 was controlled by an inverter.
In many cases, the ratio is about 0:40 to 50, and the ratio of filtered water is increased to reduce the power cost.

[0003] After the completion of the filtration step for 10 to 45 minutes, a backwashing step for a short time of about 40 seconds to 2 minutes is usually performed as described below. From the upper part (filtration water outlet, circulating water outlet side) of the membrane module 5 to the lower part (raw water inlet, backwashing drain outlet side), the flow rate of the membrane module 5 at the time of filtration is 1.4 to 1.4.
2.5 times higher flow rate and membrane module 5 at the time of filtration
The backwash water upper inlet valve AV-4, backwash drain lower outlet valve AV-6, and backwash water main valve AV-3 are opened at a pressure of about 1.1 to 2.0 times the inlet pressure, and the backwash water is backwashed. Start the water pump P-3 and start 2
By passing water from the outside (filtration water side) to the inside (raw water side) of the hollow fiber membrane for about 0 to 30 seconds, the turbid component that is attached to the inner surface of the membrane and trapped during filtration is discharged out of the system. Perform backflow backwash.

At this time, Cl ₂ is converted from the disinfectant / oxidant storage tank 8 to Cl ₂ by the sodium hypochlorite injection pump P-4.
About 5 mg / liter is injected into, for example, * 1 of the backwash water piping system 11 so that the residual chlorine in the backwash wastewater is generally about 0.2 to 3.0 mg / liter. Similarly, upward backwash is performed from the lower part of the module to the upper part. The manual valve 19 of the raw water circulation piping system 12 is kept open except during chemical cleaning. Further, thereafter, referred to as a flushing step, the raw water pump P-1 and the backwash pump P-3 are activated from the lower part of the module to the upper part of the raw water and the backwash water,
Open the backwash water main valve AV-3, backwash water lower inlet valve AV-5, and backwash drain upper outlet valve AV-7 to allow raw water and backwash water to flow at the same time. Is periodically discharged from the inner surface of the hollow fiber membrane to the outside of the system.

[0005] Sodium hypochlorite as a fungicide, ie C
It is known to carry out backwashing using backwash water into which l ₂ has been injected, and it has been found that there is an effect of stabilizing the flux. For example, the 1989 JOURRNARL AW
In WA NOVEMBER, there is a specific description that it is more effective to inject 3.5 mg / liter as free chlorine using sodium hypochlorite in backwash water to reduce membrane contamination of UF membrane. Can be When such a [filtration step-backwash step] is repeated, the flux of the membrane module gradually decreases. The inverter control of the circulation pump P-2 and the opening degree of each valve are adjusted, and the membrane inlet pressure is gradually increased so that a desired flux can be obtained. However, if the membrane inlet pressure rises to two to three times the initial operation, chemical cleaning is performed, for example, after one week to several months to recover the initial flux as much as possible.
Even in the case of industrial water in which river water or the like has been subjected to primary treatment, the flux gradually decreases, depending on the structure of the membrane module and backwashing conditions, and chemical cleaning is required every one to several months.

In general, chemical cleaning is often performed manually, and is performed by the following operation. After the operation of the apparatus is stopped, the manual valve 19 of the raw water circulation piping system is closed, the manual valve 16 and the manual valve 17 of the filtered water circulation system 14 are opened, and the raw water circulating water * 5,
The circulating water * 4 of the filtered water is returned to the chemical cleaning tank 20. And the manual valve 1 connected to the circulation pump P-2
8. Open the circulation valve AV-1 and activate the chemical cleaning pump P-7 or the circulation pump P-2 to create a circulation piping system for the chemical cleaning liquid. Then, an appropriate chemical that can withstand the film material is dissolved and introduced into the chemical cleaning tank 20, and the chemical is increased by about 30 to 50% from the combined water amount of the membrane module 5 and each circulation piping system. The concentration is adjusted to an appropriate value for the amount of the washing liquid, and circulating washing is performed. At this time, an immersion treatment may be performed after the circulation. Generally 0.5-2.5%
Chemical cleaning using about a citric acid solution, followed by ordinary backwashing without injecting Cl ₂ for replacement blow of the washing waste liquid, and then about 50 to 500 mg / L of sodium hypochlorite or other Chemical cleaning is often performed using chemicals. The chemical cleaning conditions are the chemical resistance of the membrane,
It is determined by the state of contamination of the membrane generated according to the raw water state. As a chemical, if the film material can withstand,
In addition to hydrogen peroxide, ozone, caustic soda, hydrochloric acid, citric acid, oxalic acid having a chelating action, other organic acids, EDTA and the like are also used.

On the other hand, in the total filtration method, it is not necessary to provide a cross flow pipe during the filtration step.
There is no V-1 and there is no circulation pump P-2. Instead,
A chemical cleaning circulation pump P-7 that supplies and circulates the chemical cleaning liquid * 6 in the chemical cleaning storage tank 20 and a pipe required for circulation are separately provided. Since there is no circulation pump P-2 and filtered water is obtained by starting the raw water pump P-1 at the time of filtration, the power cost is generally reduced.

However, since the cross-flow does not flow on the inner surface of the hollow fiber membrane at the time of filtration, the ratio of turbid matter adhering to the inner surface of the membrane and the degree of penetration into the film thickness generally increase.
In the backwashing step, as in the above-mentioned cross-flow method, downflow backwashing, upflow backwashing, etc. are performed. More. Chemical cleaning is generally performed once every several days to once a month, although it depends on the raw water quality, the structure of the membrane module, the backwashing method, and the like. In addition, the contact time between the generally used cleaning chemicals and the membrane is lengthened to recover the flux in many cases. In the case of the total filtration method, the frequency of chemical cleaning increases, and when the decrease in flux is large, it takes time to recover the flux, and the recovery may be insufficient. Including maintenance, the total average running cost cannot be said to be significantly lower than the cross-flow method. Therefore, its application requires caution.

[0009] The problems of the conventional technology described above are summarized as follows. 1) The frequency of chemical cleaning is high, and the time required for the chemical cleaning operation is often as long as several hours to about two days, during which time the apparatus stops and filtered water cannot be obtained. 2) Since the frequency of chemical cleaning is high, there are many manual operations such as chemical dissolution, and maintenance is troublesome. In addition, it is necessary to consider a treatment device for high-concentration waste liquid used for chemical cleaning.

3) When the turbid components of the raw water tend to adhere to the inside and outside of the membrane, and as the water temperature of the raw water becomes lower, such as 10 ° C. or lower, 1/2 to 1% of the normal flux
/ 4 low flux. There is a limit to obtaining the desired flux by gradually increasing the inlet pressure of the membrane without lowering the flux. Under such conditions, running costs such as pump power costs and cleaning chemicals costs are increased, and under such conditions, the flux is easily accelerated, and the continuous operation time tends to gradually decrease. 4) Therefore, in order to maintain the design flow rate stably, it is necessary to give a considerable margin to the device, and there is a disadvantage that the device capacity must be increased or the number of series must be increased at the time of design. Therefore, there is a problem that the merit of applying the film is reduced as compared with the conventional general processing method. Originally, there is a demand for a filtration and backwashing method that can stably obtain a high flux of a membrane for a long time and that is easy to maintain.

[0011]

SUMMARY OF THE INVENTION The present invention uses an internal pressure type hollow fiber membrane, does not depend on the type of filtration system, such as a cross flow system or a total filtration system, as an operation method, and uses a UF membrane of a membrane material. It can be applied to any type of MF membrane filtration device, provides a stable design flux, provides a simple backwashing method, and provides an appropriate (filtration-backwashing) operation method. The task is to

[0012]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors examined the conditions of raw water, filtration, backwashing, and flux. As a result, it was found that the problems to be solved can be summarized into two points: prevention of the progress of membrane contamination, and countermeasures when the raw water temperature drops. Among them, is a basic problem mainly related to the raw water state and the backwashing method, and the influence of the module structure, the membrane material, the filtration time (the amount of turbid matter trapped per filtration step) and the like is considerably large. Is a real problem. Water temperature below 15 ℃, especially in winter
Below ℃, the flux increases by 15 due to an increase in the viscosity of water.
At present, the temperature has to be reduced to 1/2 to 1/4 of the temperature at 25C. Are closely related to each other, and in order to solve the two at the same time, as a result of earnest research, we have found concrete causes that cause the above problems, and we have found means to solve these causes. Was.

(1) As a result of the investigation, the following three points were considered to be the causes of the decrease in the flux and the increase in the pressure at the inlet of the membrane module. 1) The turbidity, organic matter, etc., which could not be discharged by the normal backwashing, grow on the inner surface of the hollow fiber membrane at every operation of (filtration step-backwashing step), and a phenomenon occurs that the inner surface of the membrane is gradually closed.
And the number of effective hollow fiber membranes, that is, the effective membrane area is gradually reduced. A turbid substance, an organic substance, or a mixture thereof, which blocks the inner surface of the membrane, cannot be discharged by ordinary backwashing. This phenomenon seemed to have the greatest influence on the above-mentioned causes.

2) In the case of a UF film having a skin layer (pore size: about 0.01 μm or less), the ratio of turbidity or the like entering the film thickness is MF film (pore size: 0.05 to
(About 0.5 μm). This is because most of the turbidity in the water is mainly larger than 0.01 μm, and it is difficult to close the pores of the membrane. On the other hand, it is considered that the pore size of the MF membrane is large, and the proportion of the suspended matter that gets into and closes the pores (within the film thickness) of the MF membrane is high due to the size distribution of the suspended matter in water. Organic matter is also present in UF membranes.
Although it depends on the pore size (fraction molecular weight), it often penetrates and leaks toward the filtered water in many cases.
This causes a problem in the quality of the filtered water, and it is necessary to separately consider, for example, injecting a flocculant such as PAC into raw water to remove chromaticity, TOC, and the like due to the leaked organic matter. However, it is sufficiently conceivable that a high molecular organic substance enters and remains in the film thickness. 3) Since Cl ₂ is injected during normal backwashing, if ionic manganese is present in the raw water, it passes through the membrane, undergoes chlorine oxidation, and gradually adheres to the outer surface (filtration water side) of the membrane. This results in lower flux and higher membrane inlet pressure.

(2) A film having high hydrophilicity is used as a film material. The greater the hydrophilicity, the easier it is to solve the above problem. For example, when comparing a cellulose-based membrane having high hydrophilicity with a polyester-based membrane which is not sufficiently hydrophilic even after being chemically modified, the problem with the cellulose-based membrane is clearly smaller. Regardless of the film material, a material having higher hydrophilicity is suitable.

(3) At regular intervals in the usual operation method of injecting a bactericide such as sodium hypochlorite into the backwashing water [filtration step-backwashing step], that is, membrane contamination considerably proceeds. Before or if necessary, during the backwashing process, instead of the usual injection of sodium hypochlorite, citric acid is used as a low-concentration acid that is different from the conventional concept of high-concentration chemical cleaning. Circulation washing is performed using a single acid or a mixed acid of citric acid and hydrochloric acid. The circulation valve AV-1 is opened, and the raw water inflow piping system 10, the membrane module 5, the raw water circulation piping system 12,
The filtered water circulation outlet valves AV-8 and AV-9 are also opened, and the circulation pump P-2 is started via the filtered water circulation system 14 to form a circulation system capable of high flow velocity. And the circulation pump P-
Raw water inflow piping system 10 between before and after 2 and the inlet of the membrane module 5 or the circulation pump P-
As the concentration of citric acid in the raw water circulation piping system 12 up to 2, 50 to 1500 mg / liter heated to 15 ° C. to 35 ° C., preferably 18 ° C. in consideration of running cost
Inject 200-600 mg / liter warmed to ２５25 ° C.

At this time, the flow rate of the filtered water circulation system 14 may be about 2 to 20% of the total flow rate. It easily adheres to the outer surface of the hollow fiber membrane. It suffices if contaminants such as manganese generated by chlorine oxidation can be dissolved and removed. By performing such an operation, it is possible to promote the decomposition of turbid matter, the decomposition of organic matter, or the separation of the suspended matter adhered to the inner and outer surfaces of the film, within the film thickness, or adhered to the inner surface of the film and closed. In the case of citric acid, the temperature of the solution is particularly important. If the temperature is 15 ° C. or lower, the effect of the chelating action is reduced and the washing is not effective. Therefore, the liquid temperature is set as described above. If there is enough time, it is effective to perform the immersion treatment for several hours in total.

At the time of this high-flow circulation cleaning, the operation of [high-flow circulation cleaning-recirculation stop] or [high-flow circulation cleaning-low-flow circulation cleaning] is repeated to change the flow rate and pressure fluctuation on the inner and outer surfaces of the hollow fiber membrane. It was found that the effect was further enhanced by repeating the given operation several times. Finally, the replacement blow process of the washing wastewater held by the entire system including the inside of the membrane module and the piping is performed at a high flow rate using raw water and / or filtered water or at a flow rate appropriate for the replacement blow. This replacement blow step is performed once or twice even during the operation of [high-flow circulation cleaning-stop circulation] or [high-flow circulation cleaning-low-flow circulation cleaning] at the time of the circulation cleaning, and the suspended matter in the membrane module is removed. It is more effective if the wastewater containing organic matter is blown by displacement.

In order to replace and blow the washing wastewater, the above-mentioned chemical is not injected using the raw water, the circulation valve AV-1 is closed to stop the circulation, and the backwash wastewater provided immediately above the circulation valve AV-1. Open the upper outlet valve AV-7 and set the filtered water circulation outlet valve A
V-8 and AV-9 are also opened to activate the raw water pump P-1 and the circulation pump P-2, and to wash the entire piping system including the membrane module at a high flow rate or at a flow rate appropriate for displacement blow. Drain the wastewater. Once the replacement blow process has progressed to some extent, the circulation valve AV-1 is once opened and the circulation valve AV-
The washing drainage in the piping remaining between the pump 1 and the circulation pump P-2 is also drained. If necessary, backwash pump P
Using -3, each valve is opened and closed in the same manner as above by upflow backwash using filtered water without injection of Cl ₂ , and replacement piping of the entire piping system of the apparatus is performed so that no acid remains. .

(4) When the film is contaminated with organic matter (including microbial contamination), sodium hypochlorite or the like is used as Cl ₂ , depending on the film material, but 20 to 300 mg / l.
It is preferably about 20 to 60 mg / liter, and it is always present in the membrane module during circulating washing, and the flow rate and the pressure are changed several times in the same manner as in the case of the citric acid. Circulation washing while giving. In the case of sodium hypochlorite, in order to further reduce the contamination of organic substances, it is effective to perform immersion treatment for several hours as needed. The method of replacing and blowing the cleaning wastewater held in the module and in the entire system such as piping, etc. may be performed in the same manner as in the case of the above-mentioned acid. After the displacement blow, Cl ₂ is prevented from remaining like the acid described above. The liquid temperature of sodium hypochlorite as an oxidizing agent at the time of circulation cleaning is set to 15 to 35 ° C. as in the case of acid. Higher is more effective, but about 18 to 25 ° C. is sufficient in consideration of running costs.

(5) When the raw water temperature is low, heating is not performed during filtration and during normal backwashing, but the membrane module is mainly used during backwashing in which the above-mentioned acid and oxidizing agents are used for circulating washing. It is preferable to heat the retained water containing the acid or the oxidizing agent in the entire system circulation piping system. The heating device 15 may be provided with, for example, an electric heater or a heat exchanger using steam in a raw water circulation piping system, and may be heated. If the heating takes too long, a heating storage tank (not shown) that stores more than the amount of water held in the entire circulation piping system of the device is provided separately.
It is one idea to make the heating water in advance with a heating device.

(6) The degree of fluctuation of the flow rate and pressure applied to the membrane module during circulating washing is determined by the fact that the hollow fiber membrane breaks (burst: meaning tearing, breaking, etc.) and buckling (meaning shape change such as dent). Is performed so that no Since the burst pressure and buckling pressure, which are indicators of the strength of the membrane in the following examples, decrease with deterioration of the membrane, the flow rate and the degree of pressure fluctuation should be set to less than half of the buckling pressure value when new. Be careful. Example) cellulosic membrane burst pressure (when new): 15 kgf / cm ² degree seat屈圧(when new): the high flow rate used in the 6 kgf / cm ² about the present invention, the inlet in the circulatory system membrane module during filtration The flow rate is about 1.0 to 2.0 times the flow rate, and the flow rate of the pressure loss that can sufficiently withstand the strength of the hollow fiber membrane is better. However, considering the power cost of the circulation pump and backwash pump,
It may be about twice. As a method of increasing the flow rate, a circulation valve AV
There is a means of adjusting the opening degree such as -1 or controlling the circulation pump P-2 and the backwash pump P-3 with an inverter. or,
There is also a means in which the circulation valve AV-1 is divided into two parts to be used for normal filtration and for high flow rate during circulation washing. Circulation can be stopped by a simple operation to stop the circulation pump. The low flow rate may be about the flow rate of the filtered water outflow piping system 13 during filtration.

Since the set value of the pressure gives a sudden change, the material of the membrane, the strength of one hollow fiber membrane (outer diameter, film thickness, etc.), so that the hollow fiber membrane does not break (break, buckle), It is important that the strength (mainly the structure) of the entire membrane module be sufficiently considered and set. Although it varies depending on the membrane material, the pressure is set to about 1.5 to 4.0 times the pressure at the membrane module inlet at the time of filtration immediately before the flow rate and pressure fluctuation are applied. For example, in the case of a cellulose-based hollow fiber membrane having an outer diameter of 1000 to 1500 μm, it is safe to perform the process at a maximum of about 2.5 kgf / cm ² or less. The operation procedure for giving specific fluctuations in the flow rate and pressure is as follows, taking [high-speed circulation cleaning-circulation stop] as an example.

1) High flow circulation washing: 20 to 200 cm / sec with respect to the inner surface of the hollow fiber membrane (corresponding to about 1.0 to 2.0 times the flow rate at the time of filtration at the inlet of the above-mentioned membrane module). Perform for a few minutes. 2) At the end of the operation of 1), with the circulation pump P-2 activated, the backwash valve AV-1 and the like are closed and the lower pressure (or upper pressure) of the raw water circulation piping system 12 of the membrane module is set to, for example, 2 When the pressure reaches about 0.0 kgf / cm ² , the circulation pump P-2 is stopped. Then, it is held for 10 seconds to several 10 seconds. At this time, the pressure is monitored and controlled by a pressure switch or the like so as not to increase. 3) Then, start the circulation pump P-2 and 2)
The backwash valve AV-1 and the like, which were closed by, are suddenly opened, and the flow rate and the pressure are varied. 4) Repeat steps 1) to 3) several times.

However, when the sudden closing and sudden opening operations of the circulation valve AV-1 etc. are problems in pressure detection, the risk of breakage of the membrane module, the stable operation of the apparatus, etc., the sudden closing and sudden opening operations are performed. And adjust so that the flow rate and pressure fluctuate slowly. When the circulation pump P-2 is started, the fluctuation may temporarily become excessive. Therefore, it is important that the performance of the pump is well understood and selected. Also, circulation pump P-2
Care must be taken from a different point of view when choosing the right choice. That is, if the closing pressure of the circulation pump P-2 is too high, the above-mentioned 2.0 kgf /
When a pressure switch or the like does not operate normally at a pressure setting of about cm ² , the target pressure is set to the circulation pump P.
There is a high risk of causing a breakage of the membrane module due to a high cutoff pressure of -2. It is also important to select a cut-off pressure that is as close as possible to the set value aimed at by the present invention. This can be said for the raw water pump P-1 and the backwash pump P-3, and the selection thereof requires sufficient care.

When the high-speed circulation cleaning is started after the circulation pump P-2 is stopped, the above-mentioned pressure, for example, about 2.0 kgf / cm ² rapidly drops, and the set high-flow conditions, the turbidity of the membrane module, The degree of the pressure drop depends on the degree of removal of the organic matter and the like. Therefore, for example, how many times the [high-speed circulation cleaning-circulation stop] operation is repeated is determined by judging the recovery status of the membrane module inlet pressure or outlet pressure for each time. In the case of [high-flow circulation cleaning-low-flow circulation cleaning], at the time of low-flow circulation cleaning, each outlet valve from the membrane module is rapidly closed so that the pressure becomes about 2.0 kgf / cm ² as in the above example, and the circulation valve is closed. The opening degree of the AV-A1 and the number of revolutions of the circulation P-2 are controlled by an inverter to adjust the flow rate at a low flow rate. Then, the process is repeated in the same manner as in the case of [high-speed circulation cleaning-circulation stop]. This method is based on the circulation pump P-2 described above.
This is a method that can substantially avoid temporary excessive pressure, mainly when moving from stop to start. Which method is to be used is determined based on its effect, ease of operation, durability of the membrane module, and the like.

(7) If the present invention is carried out in consideration of such considerations, removal and discharge of manganese, particularly manganese, adhering to the inner surface of the hollow fiber membrane, turbidity and organic substances in the film thickness, or the outer surface of the membrane by chlorine oxidation can be prevented. You can. The longer the circulation time or the immersion treatment time and the higher the heating temperature, the more effective. However, in the present invention, the effect is determined by the degree and number of fluctuations of the flow rate and the pressure. A circulation time of about 3 to 10 minutes is sufficient. The set time from the high-speed circulation cleaning to the target pressure, the holding time of the set pressure after stopping the circulation pump P-2, and the activation of the circulation pump P-2 again give a variation in flow rate and pressure. The time per cycle may be as short as about 0.5 to 3 minutes. It is sufficient that the number of times of the fluctuation shock is about 2 to 5 times. Even if the time required for the replacement blow step of the washing wastewater is added, the time required for implementing the present invention is about 5 minutes to a maximum of about 20 minutes. Although the frequency of implementation of the present invention varies depending on the raw water condition and the operating conditions, it is about once or twice per day, or about once or twice per week to one month, and the proportion of the total operating time is extremely small. .

(8) The present invention also relates to a conventional method (filtration step →
At a certain frequency of the backwashing step) and, if necessary, at the time of the backwashing step in which sodium hypochlorite is injected at a few ppm / liter, as described above, [high-speed circulation washing-circulation stop] or [high It is also effective to carry out the operation of [flow rate circulation cleaning-low flow rate circulation cleaning] and / or the replacement blow operation in the above-mentioned flow rate and pressure conditions in about 1 to 3 times in a short time. At this time, even if sodium hypochlorite does not exist,
The effect is almost unchanged. This is an operation in which the flow rate and pressure are changed in addition to the conventional flushing cleaning, in which turbid substances such as colloidal Fe and Al accumulated on the inner surface of the hollow fiber membrane are circulated at a high upward flow velocity, and the replacement blow operation is performed. As a result, the liquid can be physically discharged considerably out of the system as backwash wastewater.

(9) However, in the present invention, it is not necessary to perform all of these operation conditions, and the operation steps and conditions are appropriately combined depending on the properties of the raw water to shorten the backwashing time and reduce the backwashing drainage. And so on. The present invention
As described above, the operation of mainly giving fluctuations in flow rate and pressure is performed in the presence of citric acid alone, a mixed acid of citric acid and hydrochloric acid alone, and depending on the material of the membrane, 20 to 300 mg / liter of sodium hypochlorite. It is performed in the presence of a high concentration, usually several ppm / liter. Then, by appropriately combining the respective operations and performing the operations before the flux reduction at the time of filtration progresses, a long-term continuous operation can be performed. Further, the present invention may be carried out under the absence of chemicals, and may be carried out in the absence of a cleaning agent such as acid or sodium hypochlorite for physical cleaning in which a fluctuation in flow rate and pressure is applied. Although the effect is inferior, a certain effect can be obtained.

(10) Organic acids other than citric acid can be used, but considering the safety in handling, the safety in the event of leakage into filtered water, the concentration used and its effect (running cost), Acids are suitable. Citric acid is not a deleterious or poisonous substance and is also approved as a food additive. Further, even if the hydrochloric acid slightly leaks into the filtered water, it reacts with the bicarbonate in the filtered water to generate only CO _2, and does not cause a problem of the pH of the filtered water. With the citric acid solution alone, filamentous fungi such as mold and yeast may be mixed from the atmosphere and proliferate. To prevent this, hydrochloric acid is mixed with the citric acid solution. The amount is small, and 0.2-2.
What is necessary is just to inject | pour and mix so that it may become about 0%.

(11) If sodium hypochlorite and acid, which are used both as a bactericide and an oxidant, are mixed together, the strength of the hollow fiber membrane may be deteriorated. In some cases, it is carried out after the acid has been sufficiently replaced from the entire system piping system. The same is true for the opposite case.
In the present invention, citric acid is mainly used as an acid. When citric acid is discharged as backwash wastewater, about 35 to 40% of the citric acid concentration is discharged as a COD value. In the present invention, low concentration citric acid is used.
With a filtration device of 00 m ³ / day, the drainage amount is about 6 m ³ per time, and the COD is about 25 to 50 mg / l. Such citric acid effluent can be easily treated by separately collecting and performing biological treatment. Existing biological treatment equipment often does not require a new biological treatment equipment.

As described above, the means by which the present invention can solve the problems are summarized as follows. (1) During the operation of the filtration treatment for obtaining filtered water from raw water using an internal pressure type degaussing membrane module composed of a hollow fiber membrane, after the filtration step, backwash with backwash water in the presence of a bactericide. In the operation method in which the backwashing step is performed and the filtration step is started again, during the operation of switching from the filtration step to the backwashing step, decomposition of turbidity adhering to the membrane, decomposition of organic substances, or exfoliation thereof are promoted. For this purpose, a low-concentration acid and / or the disinfectant is injected into the raw water inflow piping system from the circulation pump to the module inlet or the raw water circulation piping system from the upper part of the membrane module to the circulation pump so as to be used as an oxidizing agent. Circulating and washing the membrane module at high flow rate through the circulation pump, raw water inflow piping system, membrane module, raw water circulation piping system, and filtered water circulation piping system. Step repeated operation of the washing → circulatory arrest], or [high flow rate recirculation washing → low flow rate recirculation washing],
By combining the step of replacing and blowing water in the module with raw water and / or filtered water, the hollow fiber membrane of the membrane module is given a repetition of fluctuations in flow rate and pressure, and turbidity inside and outside the hollow fiber membrane is reduced. A method for backwashing an internal pressure type turbidity membrane module, comprising discharging and removing organic matter.

(2) The above-mentioned (1), wherein the operation of [high-speed circulation washing → stop circulation] or [high-speed circulation washing → low-speed circulation washing] is repeated also in the displacement blowing step.
A method for backwashing the internal pressure type opacity membrane module according to the above. (3) Using citric acid alone or a mixed acid of citric acid and hydrochloric acid as an acid, sodium hypochlorite as a disinfectant and oxidizing agent, and adjusting the temperature of the liquid retained in the entire circulation piping system of the apparatus including the membrane module to 18 The method for backwashing an internal pressure type opaque membrane module according to the above (1) or (2), wherein the membrane module is heated to a temperature of from 35 ° C to 35 ° C. (4) At regular intervals of normal (filtration process → backwash process) operation, during the backwash process, repeat the operation of [high flow circulation wash → circulation stop] or [high flow circulation wash → low flow circulation wash]. The method according to any one of (1) to (3), wherein:

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on a cross flow system shown in FIG. 1 which is an example of the present invention. The following specific figures all show the case of one membrane module having a membrane area of 50 m ² . (1) Filtration process example Raw water 1 is pumped up with a raw water pump P-1, and openings 80-1
After removing large turbidity with the automatic filter 3 of about 00 mesh, the circulation valve AV-1 of the raw water circulation piping system (cross flow piping) 12 and the filtered water outlet of the filtered water outflow piping system 13 via the membrane module 5. The valve AV-2 is opened, and the circulating pump P-2 is started to circulate the raw water to obtain the filtered water 7 in the filtered water tank 6. At this time, backwash water lower inlet valve A
V-5, the backwash water upper inlet valve AV-4 may also be opened to obtain filtered water from above and below the membrane module 5.

The ratio between the circulating water amount of the raw water and the filtered water amount is, for example, 60 to 55:40 in the case of industrial water obtained by primary treatment of river water or the like.
About 45 is possible. However, as the amount of organic matter and turbidity in raw water increases, and the turbidity tends to adhere, it is necessary to reduce the ratio of filtered water, increase the flow velocity on the inner surface of the membrane, and make it difficult to adhere. At the time of filtration, the circulation pump P-2 is controlled by an inverter, and the circulation valve AV-
1, the filtered water outlet valve AV-2 of the filtered water outflow piping system 13 is opened, the flow rate of each system, the inlet pressure of the membrane module 5, the pressure of the raw water circulation piping system 12, the filtered water outflow. The operation is performed by appropriately adjusting the pressure of the piping system 13. It is preferable that the filtered water outlet valve AV-2 is fully opened so as not to have a back pressure as much as possible.

A specific example of the setting of the filtration step is shown below. Example) filtration step setting example raw industrial water temperature: 4 to 15 ° C. membrane module 50 m ² membrane area one, Material: CA membrane, UF membrane filtration time 30-40 minutes: set value, 30 minutes flux 1.5-2. 5 m ³ / m ² . Day: Set value, 100 m ³ / day (2.0 m ³ / m ² .day) Membrane module inlet flow rate: 9.6 m ³ / day Raw water circulation flow rate: 5.3 m ³ / day Filtration water flow rate: 4.3 m ³ / Day pressure Membrane module inlet pressure: 0.60 to 0.85 kgf / cm ² Raw water circulation pressure: 0.34 to 0.41 kgf / cm ² Filtration water pressure: 0.14 kgf / cm ²

In the case of the total filtration system, the circulation pump P-2 is not required, and the power cost during filtration is mainly the raw water pump P-1. However, in order to reduce the strength of adhesion of the suspended matter to the inner surface of the membrane, the filtration time is often set short and the flux is set small. A specific setting example of the filtration step is shown below. Example) Filtration process example Raw water Industrial water Water temperature: 4 to 15 ° C Membrane module 50m ² One membrane area, material: CA membrane, UF membrane Filtration time 20 to 30 minutes: Set value, 20 minutes Flux 1.0 to 1.5m ³ / m ² . Day: set value, 75 m ³ / day (1.5 m ³ / m ² .day) Membrane input pressure 0.6 to 0.9 kgf / cm ² (filtration water pressure at the membrane outlet: 0.1 to 0.14 kgf / cm ² )

The backwashing method is basically the same for both the cross-flow method and the total filtration method. However, in the total filtration system, the frequency of backwashing is generally higher than that in the cross flow system. Usually, filtered water 7 is used in both systems as backwashing water in the backwashing step. The difference is that the circulation of the chemical cleaning liquid is performed by the circulation pump P-2 in the cross flow system, and the chemical cleaning pump P- connected to the chemical cleaning tank 20 shown in FIG.
7. Hereinafter, the cross flow method will be described as an example. The specific figures given below are all membrane areas of 50
It is shown for the case of the membrane module one m ^2.

(1) Example of Backwashing Step of Injecting Disinfectant at Normal Time This is a usual general backwashing step. From the upper part (filtration water outlet, circulating water outlet side) of the membrane module 5 to the lower part (raw water inlet, backwash drainage outlet side) at a high flow rate of about 1.0 to 2.0 times the flow rate of the membrane module 5 inlet at the time of filtration. , And about 1.2 to 2.5 times the inlet pressure of the membrane module 5 at the time of filtration,
The backwash water main valve AV-3, the backwash water upper inlet valve AV-4, and the backwash drain lower outlet valve AV-6 are opened, and the backwash water pump P-3 is opened.
Is started, and water is passed from the outside (filtration water side) to the inside (raw water side) of the hollow fiber membrane for about 20 to 30 seconds, so that the turbid components adhering to the inside of the membrane and trapped during filtration are collected. Downflow backwashing to discharge outside is performed. At this time, about 3 to 5 mg / liter of Cl ₂ is injected from the disinfectant / oxidizing agent storage tank 8 into the backwash water piping system 11, for example, * 1, by the sodium hypochlorite injection pump P-4. Cl ₂ in the washing wastewater is generally about 0.2 to 3.0 mg / liter,
So that the microorganisms in the membrane module are killed. When the backwash water already contains a bactericide, it is not necessary to supply sodium hypochlorite from the storage tank 8, and if it is insufficient even if it is contained. What is necessary is just to supply the quantity which compensates for a shortage.

Similarly, the backwash drain upper outlet valve AV-7 is opened from the lower part to the upper part of the membrane module 5, and the upward backflow is performed. An example of the backwashing step is shown below. Downflow backwash 20 seconds Cl ₂ 3 mg / l backwash water flow rate: 10m ³ / hr, a pressure: 1.15kgf / cm ² upflow backwash 20 seconds Cl ₂ 3 mg / l backwash water flow rate: 10 m ³ / hr, pressure: 1.15 kgf / cm ² Therefore, the backwash time is 40-60 seconds. Depending on the raw water or only one of them may be performed.
If free chlorine does not remain in the filtered water, the subsequent step may be performed without injecting free chlorine. Further, a step of replacing and blowing blown water in the membrane module 5 and each pipe using backwash water or raw water containing no free chlorine may be provided.

(2) Normal reverse injection of fungicide according to the present invention
Washing process example The present invention is suitable for the setting example of the cross-flow filtration process.
An example of each process combination in the case of using is shown below. 1) Upflow backwash of the above item (1): flow rate, 12 m^Three
/ Hr, 20 seconds, Cl _Two3 to 5 mg / liter 2) Backwashing by [high-flow circulation washing → circulation stop] operation High-flow circulation washing: After the end of filtration, start circulation pump P-2.
Dynamic, circulation valve AV-1, filtered water circulation valve AV-8, AV-9
Was opened. Flow rate: 12m^Three/ Hr, pressure: 1.25kgf / cm^Two(water temperature:
17 ° C) Time: 2 minutes Flow rate of filtered water circulation piping system: 1.2m^Three/ Hr

Conditions of flow rate and pressure fluctuation: 40 seconds after high-speed circulation cleaning, the filtered water circulation valves AV-8 and AV-9 are closed, and the circulation valve AV-1 is gradually closed. The inlet pressure was set at 2.0 kgf / cm ² . Then, the circulation pump P-2 was stopped for 20 seconds, and after maintaining the pressure as it was, the system was restarted and high-speed circulation cleaning was performed for 1 minute.
(High-speed circulation cleaning → pressure increase → pressure release, high-speed circulation cleaning) operation was performed once. Substitution blow conditions: raw water pump P-1, circulating pump P-
2, the upper backwash drainage outlet valve AV-7, the filtered water circulation valves AV-8 and AV-9 are opened, the circulation valve AV-1 is closed, and the membrane module and the flow rate are 12 m ³ / hr for 2 minutes. A water displacement blow of the piping was performed. Flow rate of filtered water circulation piping system: 1.2 m ³ / hr

(3) Example of Acid Injection Heating Backwashing Step According to the Present Invention The following step combination example was adopted. Raw water was industrial water and the water temperature was 7 to 10 ° C. 1) Injection of a mixture of 10% citric acid and 0.3% hydrochloric acid and high-speed circulating heating / washing step After the filtration, the circulation valve AV-1, the filtered water circulation valves AV-8 and AV-9, and the upper part of the backwash water Inlet valve A
V-4, the backwash water lower inlet valve AV-5 was also opened, the circulation pump P-2 was started, and filtered water was discharged from above and below the membrane module 5 to form a circulation system of 14 m ³ / hr. Further, about 80 liters of water retained in the circulation system was heated to 22 ° C. for 10 minutes by the heating device 15 using steam. In the meantime, the above-mentioned mixed solution is injected from the citric acid solution storage tank 9 into the raw water inflow piping system 10 at * 3 for 3 minutes by the acid injection pump P-6, and the water volume of all the devices (membrane module, piping, etc.) The citric acid concentration was adjusted to about 400 mg / liter for about 80 liters. The flow rate of the filtered water circulation piping system 14 was about 1.4 m ³ / hr, which is 10% of the total flow rate.

2) Step of giving flow rate and pressure fluctuations After 10 minutes from the end of heating, filtered water circulation valve AV-8,
After opening the AV-9, the backwash water upper inlet valve AV-4 and the backwash water lower inlet valve AV-5, the circulating valve AV-1 is slowly closed with the circulating pump P-2 started, and the membrane is opened. The pressure gauges above and below the module 5 automatically increased the pressure to about 2.0 kgf / cm ² while detecting the pressure. Then, the circulation pump P-2 was stopped. After holding for 20 seconds, the circulating pump P-2 was started, the circulating valve AV-1 was rapidly opened, and high-speed washing was performed again at 14 m ³ / hr for 2 minutes. At this time, the filtered water circulation valves AV-8 and AV-9, the backwash water upper inlet valve AV-4, and the backwash water lower inlet valve AV-5 were opened. At this time, the flow rate of the filtered water circulation piping system 14 was set at about 1.4 m ³ / hr, which is 10% of the total flow rate. After the high flow rate circulation, as described above, the operation of increasing the pressure to about 2.0 kgf / cm ² , the rapid opening of the circulation valve AV-1, and the high flow rate washing at 14 m ³ / hr again for 2 minutes are further performed. Steps of giving a flow rate and a pressure change three times in total were performed. During this time, the temperature control was performed with the temperature switch TS so that the temperature of the water held in the circulation system by the apparatus was maintained at about 20 to 22 ° C., and the heating device 15 was operated.

3) Substitution blow step After the third circulation washing in 2), with the circulation pump P-2 activated, the filtered water circulation valves AV-8 and AV-9, and further the backwash water upper inlet valve AV-4. The backwash water lower inlet valve AV-5 was also opened, the raw water pump P-1 was also started, the backwash drain upper outlet valve AV-7 was opened at 14 m ³ / hr, and the displacement blow operation was performed for 3 minutes. . The circulation valve AV-1 performs the displacement blow operation for two times.
It was opened after a minute. 4) Ordinary backwashing step Item (2), 1) Upflow backwashing was performed for 30 seconds without injecting Cl ₂ to prevent acid from remaining in the entire system of the apparatus.

(4) Oxidant Injection Heating Backwashing Step According to the Present Invention This step is performed when it is expected that the membrane module is contaminated with organic substances or the like. The operation may be performed almost in the same manner as the acid injection backwashing step. For example, sodium hypochlorite, which had been used as a disinfectant instead of acid, was used as an oxidizing agent, and the sodium hypochlorite injection pump P-5 was started, and the raw water inflow piping system 10, such as * 2 The circulating water was injected such that the free chlorine concentration was about 40 to 60 mg / liter. However, the oxidizing agent often reacts with an organic substance contaminating the film to lower the concentration. It is necessary to replenish the sodium chlorite as an oxidizing agent during circulation cleaning so as to maintain the above concentration during circulation cleaning so that the effect is not reduced. .
The oxidizing agent injection and high-speed circulation cleaning step, the method of heating the water retained in the apparatus, the step of giving a flow rate and pressure fluctuation, the displacement blowing step, and the ordinary backwashing step also include the acid injection heating reverse of the above item (3). This was performed in the same manner as the washing step.

[0047]

The present invention will be described in detail with reference to the following examples. However, the present invention is not limited to these examples. Example 1 Processing of a cross-flow method using the processing float shown in FIG. 1 was performed. Table 1 shows the quality of raw water and filtered water. (1) Raw water: Industrial water (river water is primarily treated with a sulfuric acid band)

[0048]

[Table 1]

(2) Filtration step 1) Membrane module 50m ² membrane area, 1 module Membrane material CA membrane (UF membrane) 2) Operating method Filtration water recovery rate: 45% (45% of raw water circulating water amount is recovered Filtration time: 30 minutes Flux: 2.0 m ³ / m ² · day Filtration water volume: 100m ³ / day

(3) Backwashing step Each backwashing step was combined as follows. I: Sodium hypochlorite injection backwashing step at normal time It consists of the following steps. 1) upflow backwash 20 seconds Cl ₂ 3 mg / l backwash water flow rate: 10m ³ / hr, a pressure: 1.15kgf / cm ² downflow backwash 20 seconds Cl ₂ 3 mg / l backwash water flow rate: 10 m ³ / hr, pressure: 1.15 kgf / cm ²

II Acid Injection Heated Backwashing Step 1) Injection of a mixture of 10% citric acid and 0.3% hydrochloric acid and high-speed circulation washing step After the filtration is completed, circulation valve AV-1, filtered water circulation valve AV-8,
AV-9, the backwash water upper inlet valve AV-4, and the backwash water lower inlet valve AV-5 are also opened to start the circulating pump P-2 so that filtered water flows out from above and below the membrane module 5, and 14 m ^3.
/ Hr circulation system was formed. Further, a heating device 15 using steam
About 60 liters of water in the circulatory system up to 22 ° C
Circulation was warmed for 12 minutes. In the meantime, the above-mentioned mixed solution was injected from the citric acid solution storage tank 9 into the raw water inflow piping system 10 at * 3 for 3 minutes by the acid injection pump P-6 for 3 minutes with respect to the amount of water retained in the circulation system, about 60 liters. Acid concentration 300m
g / liter. The flow rate of the filtered water circulation piping system 14 was about 1.4 m ³ / hr.

2) Step of giving flow rate and pressure fluctuations After the heating is completed, the filtered water circulation valves AV-8 and AV-9, the backwash water upper inlet valve AV-4, and the backwash water lower inlet valve AV-5 are closed. After that, the circulation valve AV-1 is slowly closed with the circulation pump P-2 activated, and the pressure is automatically detected while detecting the pressure so that the pressure above and below the membrane module 5 becomes about 2.0 kgf / cm ^2. Performed at Then, the circulation pump P-2 was stopped. After holding for 20 seconds, the circulation pump P
-2 is restarted and the circulation valve AV-1 is rapidly opened,
High-speed circulation washing was performed again at 14 m ³ / hr for 2 minutes.
The valves to be opened at this time and the flow rate were the same. As described above, the operation of increasing the pressure to about 2.0 kgf / cm ² , rapidly opening the circulation valve AV-1, and performing the high-speed circulation washing again at 14 m ³ / hr for 2 minutes are further repeated twice. 3
The process of giving the flow rate and the pressure fluctuation each time was performed. During this time,
The temperature was controlled by the temperature switch TS so that the temperature of the water held in the circulating system by the device was maintained at about 20 to 22 ° C., and the heating device 15 was operated.

3) Substitution blow step After the third circulation washing in 2), with the circulation pump P-2 activated, the filtered water circulation valves AV-8 and AV-9, and further the backwash water upper inlet valve AV-4. Also, the backwash water lower inlet valve AV-5 is opened, the raw water pump P-1 is also started, and at 14 m ³ / hr, the backwash water upper outlet valve AV-7 is opened, and the displacement blow operation is performed three times.
Minutes. The circulation valve AV-1 was opened two minutes after the replacement blow operation. 4) Ordinary backwashing step The upward backwash of the above item 1) was performed for 30 seconds without injecting Cl _2, and it was confirmed by pH measurement that no acid remained in the entire system of the apparatus.

III Oxidizing Agent Injection Heating Backwashing Step Sodium hypochlorite, which had been used as a disinfectant instead of acid, was used as the oxidizing agent, and the sodium hypochlorite injection pump P-5 was started. , The concentration of free chlorine in the circulating water at * 2 in the raw water inflow piping system 10 is 40 to 6
When the concentration of Cl ₂ was lowered by reacting with an organic substance or the like so that the concentration became about 0 mg / liter, re-injection was performed. Injection of sodium hypochlorite as oxidizing agent and high-speed circulation cleaning process,
The method of heating the water held in the apparatus, the step of giving the flow rate and the pressure fluctuation, the displacement blow step, and the ordinary backwashing step were performed in the same manner as the above-mentioned acid injection heating backwashing step of section II. Finally, it was confirmed that there was no residual chlorine in the entire circulation system of the apparatus.

Implementation frequency of each backwashing step The raw water shown in Table 1 and the above operating conditions were used as follows. I. Normal sodium chlorite injection backwash step: Every cycle was performed. II. Acid injection heating backwashing steps: Steps 1), 2), 3) and 4) were performed once a week. III. Oxidant Injection Heated Backwashing Step: Immediately after the step II, the step was performed once a week. <Results> Although the continuous operation was performed for 6 months, the flux maintained the initial 2.0 m ³ / m ² .day (Q: 100 m ³ / day). In addition, the rise in the inlet pressure of the membrane module is also the initial value,
0.65 / cm ² at a water temperature of 15 ° C.
℃ 0.95kgf / cm ²
(Water temperature 5 ° C.). There was no need for chemical cleaning. Continuous operation was still possible.

Example 2 The raw water shown in Table 1 was subjected to the all-filtration processing according to the processing flow of FIG. There was no circulation valve AV-1 and no circulation pump P-2, and a chemical cleaning pump P-7 shown in FIG. 2 was used instead. (2) Backwashing step This is the same as the method shown in Example 1. The basic cleaning method is a method in which a film is fluctuated by a flow rate and a pressure by [high-speed circulation cleaning → circulation stop] to discharge turbidity, organic matter, and the like. Since the chemical cleaning tank 20 and the chemical cleaning pump P-7 shown in FIG. 2 are used instead of the circulation valve AV-1 and the circulation pump P-2, piping and a manual valve for them are provided as shown in FIG.

1) Injection amount of chemical: 350 mg / liter of citric acid Sodium hypochlorite injection amount: 40-60 mg / l 2) Frequency of execution: once a week 3) Order of execution I. Sodium hypochlorite injection backwashing process in normal time: every cycle II. Acid injection heating backwashing process: 1), 2), 3), 4) <Results> Continuous operation for about 5 months done. Five months later, the pressure at the inlet of the membrane module increased to 1.15 kgf / cm ² , necessitating chemical cleaning. Chemical cleaning is usually performed 2
After% of the cleaning of citric acid, 50 to 100 mg as Cl ₂
/ Liter of sodium hypochlorite was washed. The flux recovered to the set value of 1.0 m ³ / m ² .day, and the membrane module inlet pressure recovered to 0.7 kgf / cm ² which was close to the initial operation value.

Example 3 According to the processing flow shown in FIG. 1, the cross-flow processing was performed using the river water shown in Table 2. Except for the raw water conditions and the conditions shown below, the conditions are the same as in Example 1. (1) Raw water

[0059]

[Table 2]

(2) Method for giving flow rate and pressure fluctuation The operation was performed under almost the same conditions as in Example 1. However, the method of giving the flow rate and pressure fluctuation in the above-mentioned II and III was as follows. Basically, a method of [high-flow circulation cleaning → low-flow circulation cleaning] was used. High flow circulation washing: 14m ³ / hr, filtered water circulation piping system:
It was set to 1.4 m ³ / hr. After the heating, the filtered water circulation valves AV-8 and AV-9, the backwash water upper inlet valve AV-4, and the backwash water lower inlet valve AV-5 are closed, and then the circulation pump P-2.
Is started, the opening of the circulation valve AV-1 is gradually reduced, and the rotation speed of the circulation pump P-2 is controlled by an inverter.
The measurement was performed automatically while detecting the pressure and the flow rate so that the flow rate was about 0 kgf / cm ² and the flow rate was 3 to 5 m ³ / hr. Then, the operation state of the circulation pump P-2 was maintained as it was.
Then, after holding for 20 seconds, the circulation pump P-
2, the opening degree of the inverter and the circulation valve AV-1 is adjusted,
The high-speed circulating washing was rapidly performed again at 14 m ³ / hr for 2 minutes. The valves to be opened at this time were the same.

Then, as described above, the operation of increasing the pressure to about 2.0 kgf / cm ² and the flow rate from 3 to 5 m ³ / hr to 14 m
^The operation of changing the flow rate to ³ / hr was repeated three times, and high-speed circulation washing was performed again for 2 minutes. A total of three steps of applying a flow rate and pressure fluctuation were performed. During this time, the temperature control was performed with the temperature switch TS so that the temperature of the water held in the circulation system by the apparatus was maintained at about 20 to 22 ° C., and the heating device 15 was operated. <Results> Since the raw water is river water, there is considerable fluctuation in turbidity. However, the nature of the turbid material was different from the fine, floc-like soft material such as iron or aluminum of the industrial water of Example 1 which was a mineral material that hardly adhered to the inner surface of a relatively hard film. The chromaticity was higher than the concentration of total iron and total manganese, and organic substances such as humic substances were present. Therefore, the treatment uses PAC as an aggregating agent and is not subjected to the aggregating treatment, so that the chromaticity of the filtered water shows a slightly high value. However, other water quality items were good as shown in Table 2.

Comparative Example In the processing flow of FIG. 1, the raw water shown in Table 1 of Example 1 was used and operated as follows according to a conventional method. (1) Filtration step: Shown by symbol →. 1) Filtration time: 30 minutes 2) Flux: 1.5 m ³ / m ² . 3) Conventional backwashing step: indicated by symbol A. The above-mentioned downward flow backwash Cl ₂ injection amount 5 mg / liter The above-mentioned upward flow backwash Cl ₂ injection amount 5 mg / liter The flushing step is indicated by symbol F. This step starts the raw water pump P-1 and the backwash pump P-3 in FIG.
In this step, the flow rate is set to 1.5 to 2.5 times the normal value, backflow is performed in an upward flow, turbidity and the like are backwashed, and turbidity and the like are discharged from the backwash drain upper outlet valve AV-7. .

4) Example of Operation Combination [A → A → A → F → A → A → A → F →] was repeated. <Results> Continuous operation was possible only for one to two months. In order to obtain the set flux of 1.5 m ³ / m ² .day, it was necessary to gradually increase the inlet pressure of the membrane module 5. From the initial of 0.6kgf / cm ² 1.4kgf / cm
^It rises to about ² . Note) At this time, the pressure on the filtered water outlet side is the value of the open condition.
It was 10 kgf / cm ² .

[0064]

According to the present invention, it is effective to remove turbidity in industrial water, river water, lake water, and recovered water. In the conventional method, the frequency of chemical cleaning is high and the continuous operation time is short. And during the chemical cleaning, the device is shut down for several hours to a few days, during which time no filtered water is obtained. According to the present invention, such a situation is eliminated, and a long-term continuous operation can be stably performed. Further, even if the water to be treated is at a low water temperature, continuous operation at a high flux has become possible over a long period of time.

[Brief description of the drawings]

FIG. 1 is a processing system diagram for explaining an embodiment of a method of operating an internal pressure type membrane module according to the present invention.

FIG. 2 is a processing system diagram for explaining an embodiment of a conventional operation method of an internal pressure type membrane module.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water 2 Raw water tank 3 Automatic filter 4 Drain piping of an automatic filter 5 Membrane module 6 Filtration water tank 7 Filtration water 8 Disinfectant and oxidizing agent storage tank 9 Citric acid chemical storage tank 10 Raw water inflow piping system 11 Backwash water piping system 12 Raw water circulation piping System (cross flow piping) 13 Filtration water outflow piping system 14 Filtration water circulation piping system 15 Heating device 16, 17, 18, 19 Manual valve 20 Chemical washing tank * 1 Disinfectant injection point into backwash water piping * 2 Raw water inflow Disinfectant injection point into pipe * 3 Acid injection point into raw water inflow pipe * 4 Circulating water of filtered water * 5 Circulating water of raw water * 6 Chemical cleaning solution AV-1 Circulating valve AV-2 Filtrated water outlet valve AV-3 Reverse Backwashing valve AV-4 Backwashing water upper inlet valve AV-5 Backwashing water lower inlet valve AV-6 Backwashing drainage lower outlet valve AV-7 Backwashing drainage upper outlet valve AV-8 Filtration water circulation valve (1) AV -9 Water circulation valve (2) P-1 Raw water pump P-2 Circulation pump P-3 Backwash water pump P-4 Disinfectant (sodium hypochlorite) injection pump P-5 Oxidizing agent (Sodium hypochlorite) injection Pump P-6 Acid injection pump (raw water inflow piping system) P-7 Circulation pump for chemical cleaning

Claims (4)

[Claims] 1. During the operation of a filtration process for obtaining filtered water from raw water using an internal pressure type turbidity membrane module comprising a hollow fiber membrane, after a filtration step, reverse filtration is carried out with backwash water in the presence of a disinfectant. In the operation method in which the backwashing step of washing is performed and the filtration step is started again, during the operation of switching from the filtration step to the backwashing step, the decomposition of turbidity adhering to the membrane, the decomposition of organic substances, or the separation thereof are performed. In order to promote the raw water inflow piping system from the circulation pump to the module inlet or the raw water circulation piping system from the top of the membrane module to the circulation pump, the low concentration acid and / or the sterilizing agent is used as an oxidizing agent. Meanwhile, at high flow rate, circulation pump, raw water inflow piping system,
A step of circulating and cleaning the membrane module through the membrane module, the raw water circulation piping system, and the filtered water circulation piping system. During this step, [high-speed circulation cleaning → circulation stop] or [high-speed circulation cleaning → low-flow circulation By repeating the step of (washing), the step of replacing and blowing water in the module using raw water and / or filtered water, the hollow fiber membrane of the membrane module is given a repetition of flow rate and pressure fluctuations, A method for backwashing an internal pressure type turbidity removing membrane module, comprising discharging and removing turbidity and organic matter inside and outside the hollow fiber membrane. 2. The internal pressure type opacity according to claim 1, wherein the operation of [high-speed circulation cleaning → circulation stop] or [high-speed circulation cleaning → low-flow circulation cleaning] is repeated during the displacement blowing step. Backwashing method for membrane module 3. Using citric acid alone or a mixed acid of citric acid and hydrochloric acid as an acid, sodium hypochlorite as a disinfectant and oxidizing agent, and the temperature of the liquid retained in the entire circulation piping system of the apparatus including the membrane module. 3. The method for backwashing a membrane module for internal pressure type turbidity according to claim 1 or 2, wherein the temperature is raised to 18 ° C to 35 ° C. 4. At regular intervals of normal (filtration step → backwash step) operation, during the backwash step, perform [high flow rate circulation wash → circulation stop] or [high flow rate circulation wash → low flow rate circulation wash]. The method according to any one of claims 1 to 3, wherein is repeated.