JP2009233511A - Method of operating membrane filtration system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane filtration system which can operate stably for a long time by forecasting operating conditions through evaluating a membrane module for evaluation, in conjunction with a membrane filtering method for obtaining permeant water by filtering, through a membrane, water to be treated such as underground water, river water, lake/marsh water, sewage water to be secondarily treated. <P>SOLUTION: This membrane filtering system is equipped with a precise filtration membrane and/or ultrafiltration membrane, as well as the membrane module for valuation which evaluates the same water to be treated as in the case with the membrane filtration system body by accelerated velocity test. The method of operating the membrane filtration system is to optimize the operating conditions of the membrane filtration system body, considering the ascending degree of filtration resistance of the membrane module for evaluation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of operating a membrane filtration system using a microfiltration membrane and / or an ultrafiltration membrane used for water treatment such as water purification, industrial water production, sewage treatment, and reverse osmosis membrane pretreatment.

  Separation membranes such as microfiltration membranes and ultrafiltration membranes are used in various fields such as the food industry, the medical field, water production, and wastewater treatment fields. Particularly in recent years, separation membranes are increasingly used in the beverage manufacturing field, that is, in the process of water purification. Compared with water treatment by slow filtration or rapid filtration, water treatment by membrane filtration can remove impurities in raw water reliably and stably, and the installation area of equipment is small and requires less land. It is very advantageous in that there are few. For this reason, it is considered that the need for water treatment by membrane filtration will increase as a method for stably producing safer water in the future.

  However, on the other hand, the accumulation of dirt in the separation membrane accompanying the increase in the total amount of filtered water, that is, performance degradation due to membrane fouling occurs. Natural water sources such as river water and lake water have various water quality and contain various impurities. Therefore, the progress of membrane fouling, that is, the performance transition of the membrane also changes depending on the water source water quality. Therefore, in designing the membrane filtration process, it is important to set the membrane filtration flux and cleaning conditions according to the quality and cost of the membrane supply water, and the selection of pretreatment, but the components contained in the treated water are various. It is difficult to specify the fouling component of the membrane, and empirically setting the membrane filtration flux and cleaning conditions and selecting the pretreatment. Therefore, it is often disadvantageous in terms of cost by setting a membrane filtration flux with an excessively high safety factor or adding an excessive pretreatment process. Moreover, the water quality changes every day, and the transmembrane pressure difference may increase rapidly. Once the differential pressure has risen, the operation must be stopped and the chemicals must be washed. For this reason, it is necessary not only to operate under optimal conditions as a membrane filtration system, but also to detect daily water quality changes quickly and change to optimal operating conditions for long-term, low-cost and stable operation. Become.

  For this reason, it is necessary to predict the operating conditions of the membrane filtration system. For example, as described in Non-Patent Document 1, in order to estimate the actual liquid permeation performance in practical applications, (a) Using the liquid itself, or a representative actual liquid, or a model liquid close to the actual liquid, (b) the module to be used is a module of a scale that is as practical as possible, and (c) by an operation method that is as close to practical filtration operation as possible ( d) “Actual liquid evaluation” is essential for operation for a certain period of time. Therefore, in the end, if you do not actually drive, you will not know how long and how long you can drive stably under which operating conditions.

  Patent Document 1 discloses a method for estimating the degree of contamination of a separation membrane used in a membrane separation activated sludge apparatus, but the water to be used for evaluation uses a supernatant of sludge and separates solids. It requires a lot of work to do so, and the dilution ratio, filtration flow rate, and evaluation time of the supernatant are not determined.

Patent Document 2 discloses a method for estimating a long-term stable membrane filtration flux of a membrane filtration plant from measurement data of membrane filtration characteristics at the initial stage of membrane filtration. However, it is necessary to determine operating conditions other than the flux in advance. is there. Actually, if the operation is continued at a constant flux, a sudden increase in the differential pressure often occurs due to natural changes caused by typhoons and seasonal fluctuations. Once the pressure difference between the membranes has increased, the membrane filtration system must be stopped once, and chemical cleaning must be performed, which is disadvantageous in terms of cost.
Membrane Experimental Method-Artificial Membrane Edition-Published by the Japanese Membrane Society 2006pp163-164 JP 2007-125465 A International Publication No. 2006/059658 Pamphlet

  As described above, it is difficult to predict the operation by a simple method, and since the water quality changes every day, it is difficult to continue the stable operation under one operation condition. The present invention predicts appropriate operating conditions from a membrane module for evaluation in a membrane filtration system that obtains permeate by subjecting treated water such as groundwater, river water, lake water, seawater, and secondary treated water to membrane filtration. An object of the present invention is to provide a method for operating a membrane filtration system that can be stably operated for a long time.

As a result of intensive studies to solve the above problems, the inventors know that the operating conditions of the membrane filtration system can be determined by intermittently evaluating the degree of increase in the filtration resistance of the membrane module for evaluation. It came. That is, the present invention
(1) In a membrane filtration system equipped with a microfiltration membrane and / or an ultrafiltration membrane, the same treatment as the membrane filtration system main body having a filtration membrane having a smaller membrane area than the filtration membrane used in the membrane filtration system main body This is a membrane filtration system operation method that includes an evaluation membrane module that evaluates water, measures the degree of increase in filtration resistance with the evaluation membrane module, and optimizes the operating conditions of the membrane filtration system based on the results. The operation method is a constant flow operation or a constant pressure operation, and the evaluation test module module has a flux or pressure of 1.1 to 10 times that of the membrane filtration system. The operation method of the membrane filtration system characterized.
(2) In the membrane module for evaluation, when the increase in filtration resistance is 0.5 × 10 ¹² m ⁻² or more, the flocculant is 5 ppm or more and 100 ppm or less, and / or the reverse flow physical cleaning is performed. The method for operating a membrane filtration system according to claim 1, wherein sodium chlorite is added in an amount of 10 ppm to 500 ppm.

  To provide a method for operating a membrane filtration system that can be stably operated for a long period of time in a membrane filtration system that obtains permeate by subjecting treated water such as groundwater, river water, lake water, seawater, and sewage secondary treated water to membrane filtration. Therefore, it is possible to provide a membrane filtration system that suppresses the high water production cost by stopping operation, cleaning chemicals, and changing membranes.

  The membrane filtration system of the present invention is a microfiltration membrane and / or an ultrafiltration membrane used for membrane filtration of at least one kind of treated water selected from groundwater, river water, lake water, seawater, and sewage secondary treated water. In a membrane filtration system equipped with a filtration membrane, a membrane having the same filtration membrane having a membrane area smaller than that of the filtration membrane used in the membrane filtration system main body in front of or in parallel with the microfiltration membrane and / or ultrafiltration membrane The membrane module for evaluation which evaluates the to-be-processed water same as the filtration system main body is provided, It is characterized by the above-mentioned. In the method according to the present invention configured as described above, the same treated water to be filtered by the membrane filtration system main body can be filtered by the accelerated test evaluation by the evaluation membrane module. Accordingly, fouling of the evaluation membrane module proceeds earlier than that of the membrane filtration system body, and it becomes possible to know in advance the increase in the filtration differential pressure in the membrane filtration system body.

  When the pores of the filtration membrane are clogged and the water permeation amount decreases, the filtration resistance increases. For this reason, in previous studies, it was considered that the use of a membrane in which the filtration resistance hardly increases in one filtration step leads to stable operation. However, since the membrane filtration method in which the filtration step and the physical cleaning step are alternately performed in the actual operation is the mainstream, in order to enable stable operation, the increase in the filtration resistance in one filtration step is suppressed rather than the physical resistance. It is required to suppress an increase in filtration resistance in continuous operation including a washing step.

In other words, not the degree of clogging that occurs in the filtration process, but the change in filtration resistance including the cleaning recovery property is important. Even if the filtration resistance increases in one filtration step, if the component that caused the clogging in the physical washing step can be removed, the amount of water permeation increases and the filtration resistance decreases at the start of the next filtration step. Thus, the total filtration water amount (m ³ / m ² ) when the filtration step and the physical washing step were alternately repeated was plotted on the horizontal axis, and the filtration resistance (1 / m) calculated from Equation 1 was plotted on the vertical axis. In FIG. 1, the slope of the straight line connecting the filtration resistance at the start of each filtration step was defined as the increase in filtration resistance. The lower the degree of increase in filtration resistance, the longer the stable operation is possible in the membrane filtration operation that repeats filtration and backflow physical washing.

In the membrane filtration operation evaluation that repeats filtration and backflow physical washing with the membrane module for evaluation in the evaluation, the inventors of the membrane resistance of the filtration resistance obtained with the membrane module for evaluation, even without the scrubbing washing operation as in the membrane filtration system main body. We found that there is a correlation between the degree of increase and the increasing pressure difference of the membrane filtration system. In addition, the increase in the filtration resistance obtained when evaluating the acceleration test with the membrane module for evaluation increased from the differential pressure of the membrane filtration system, the differential pressure of the membrane filtration system increased to that pressure. It was found that there was a correlation with the increasing pressure differential.
(Formula 1)
Filtration resistance (1 / m) = (filtration pressure (Pa)) × (density (g / cm ³ )) × 10 ⁶ × (membrane area (m ² )) / ((viscosity (Pa · s) × (unit time Permeated water volume (g / s))
Here, a microfiltration membrane or an ultrafiltration membrane is a separation membrane that removes 90% or more of a component of 5 μm or more and less than 90% of a component of 0.005 μm or less from components contained in raw water supplied to the membrane. It is. The material of the microfiltration membrane or ultrafiltration membrane includes polyacrylonitrile, polysulfone, polyether sulfone, polyphenylene sulfone, polyphenylene sulfide sulfone, polyvinylidene fluoride, polymer materials such as cellulose acetate, polyethylene and polypropylene, and inorganic materials such as ceramics. Although a raw material etc. can be mentioned and it does not specifically limit, The case where it consists of a polyvinylidene fluoride type-resin with high chemical resistance and water permeability is preferable when stable operation is considered. The shape of the filtration membrane may be a hollow fiber shape or a flat membrane shape.

  The evaluation membrane module is installed in front of or in parallel with the main body of the membrane filtration system in order to evaluate the same treated water. The hollow fiber membrane module has the same shape as the main body of the membrane filtration system. The size is not particularly limited, but one to 100 hollow fibers having a length of 10 cm to 50 cm are stored in a cylindrical container and sealed at both ends. Is preferred. In the case of a flat membrane module, the size is not particularly limited, but a membrane cut out on a circle having a diameter of 15 mm to 300 mm and sealed on the base with an O-ring or the like is preferable. Since the flow rate and pressure of filtration and backflow physical washing of the evaluation membrane module are adjusted separately from the main body of the membrane filtration system, it is preferable to include a flow rate adjustment valve and a pressure gauge, respectively.

In the accelerated test evaluation, first, the filtration flow rate per unit area of the membrane filtration system main body, the backflow physical washing amount and the filtration flow rate per unit area of the evaluation membrane module, and the backflow physical washing amount are the same. Set to. In constant flow acceleration operation evaluation, the flux (m ³ / m ² · s) obtained from the amount of water movement (m ³ / s) per unit area (m ² ) is 1.1 times or more that of the membrane filtration system. The evaluation membrane module is operated under a constant flow rate condition of 10 times or less. If it exceeds 10 times, the filtration pressure of the membrane module for evaluation will increase, causing problems such as the membrane being crushed. If it is less than 1.1 times, it will not be an accelerated evaluation, so the response to changes in the membrane filtration system body will be delayed. There is a case. Preferably they are 1.1 times or more and 3 times or less.

  For example, when the membrane filtration system is operated at a flux of 1.5 m / d, the evaluation membrane module is preferably operated at 2.0 m / d. It is preferable to match the reverse flow physical washing flux with the acceleration rate of the filtration flux. In the constant pressure acceleration operation evaluation, the evaluation membrane module is operated under a constant pressure condition in which the pressure is 1.1 to 10 times that of the membrane filtration system main body. If it exceeds 10 times, the filtration pressure of the membrane module for evaluation will increase, causing problems such as the membrane being crushed. If it is less than 1.1 times, it will not be an accelerated evaluation, so the response to changes in the membrane filtration system body will be delayed. There is a case. Preferably they are 1.2 times or more and 5 times or less. For example, if the filtration differential pressure of the membrane filtration system body is 20 kPa to 40 kPa, the evaluation membrane module is 50 kPa. If the filtration differential pressure of the membrane filtration system body is 40 to 60 kPa, the evaluation membrane module is 80 kPa. Is preferred. At this time, it is preferable to match the backflow physical washing pressure with the acceleration magnification of the filtration pressure. When more accelerated operation is evaluated, the filtration flow rate per unit area of the evaluation membrane module and the backflow physical cleaning amount may be increased.

It is necessary to repeat the filtration process and the backflow physical washing process at least five times in one evaluation. This evaluation may be performed every day or once every few days. Since water quality changes from day to day, early assessment of the membrane filtration system is possible by daily assessment. The evaluation membrane module can be evaluated any number of times while attached to the apparatus. However, it is preferable to replace the membrane module for evaluation whose filtration resistance rise value is 1.0 × 10 ¹² m ⁻² or more with a new one.

The degree of increase in filtration resistance is evaluated by starting each filtration step in Fig. 1 where the total filtered water volume (m ³ / m ² ) is plotted on the horizontal axis and the filtration resistance (1 / m) calculated from Equation 1 is plotted on the vertical axis. It refers to the slope of a straight line connecting the five filtration resistance points. However, when 5 points do not lie on the straight line, the slope of the straight line is obtained by linear approximation to determine the increase in filtration resistance.

If the value of the increase in filtration resistance is less than 0.5 × 10 ¹² m ⁻² , especially 0.3 × 10 ¹² m ⁻² or less, the differential pressure of the membrane filtration system body does not change greatly and is stable. Long-term operation is possible. When the value of the increase in filtration resistance is 0.5 × 10 ¹² m ⁻² or more, the transmembrane pressure difference of the membrane filtration system body gradually increases, especially 1.0 × 10 ¹² m ⁻² or more. In this case, the transmembrane pressure difference of the membrane filtration system main body increases rapidly.

Therefore, in the present invention, when the value of the increase in filtration resistance is 0.5 × 10 ¹² m ⁻² or more, or when it is 1.0 × 10 ¹² m ⁻² or more, membrane filtration is performed as a pretreatment. Add flocculant such as aluminum salt such as polyaluminum chloride and iron salt such as iron sulfate to the treated water entering the system body and / or hypochlorous acid to the membrane filtration system body by backflow physical cleaning It has been found that stable operation can be maintained by adding 10 ppm to 500 ppm of sodium.

  In consideration of the effect and cost of the additive, the flocculant is more preferably 5 ppm to 50 ppm and the sodium hypochlorite is 10 ppm to 300 ppm. In addition, although the effect is not so high, the operating conditions of the membrane filtration system main body such as reducing the filtration flux, shortening the filtration time, increasing the backflow physical washing flux, increasing the backflow physical washing time, etc. It may be changed. The operating conditions of the membrane filtration system to be changed may be determined based on the required water permeability and cost estimation.

The membrane module for evaluation measures the degree of increase in the filtration resistance of water to be treated without adding a flocculant and sodium hypochlorite, and the operating conditions can be determined from the value of the degree of increase in filtration resistance. Therefore, the water to be treated is changed, the value of the increase in filtration resistance is 0.5 × 10 ¹² m ⁻² or more, and after the operation is continued by adding a flocculant or the like, the value is again 0.5 × 10 10. ^{In the case of 12} m ⁻² or more and less than 0.5 × 10 ¹² m ⁻² , conditions such as addition of a flocculant are not necessary. Thus, it is an effect of the present invention that the operation of the membrane filtration system main body can be stably operated over a long period of time under appropriate conditions with minimum cost and environmental load.

  The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples.

Using a hollow fiber membrane module made of polyvinylidene fluoride having an average pore size of 0.05 μm (membrane area 11.5 m ² ), a constant flow rate external pressure total filtration operation of Lake Biwa water was performed. The operating conditions were a filtration flux of 2.5 m / d, a reverse flow physical washing flux of 5.0 m / d, and a recovery rate of 95% (filtration 30 minutes, reverse flow physical washing 30 seconds, scrubbing washing 60 seconds).

FIG. 2 shows a hollow fiber membrane evaluation membrane module device connected in parallel to the membrane filtration system main body. A 15 mm long evaluation membrane module 1 (membrane area 0.004 m) in which six hollow fiber membranes made of polyvinylidene fluoride having the same average pore diameter of 0.05 μm as the membrane filtration system main body are housed in a cylindrical container and fixed at the ends. ² ) Installed. In the membrane filtration process, water to be treated is collected from the water inlet 2, the flow rate is adjusted by the flow rate adjusting valve 3, the pressure is adjusted by the pressure gauge 4, and the water is passed through the evaluation membrane module 1 connected to the end of the opened valve 5. Thus, filtered water 9 that has passed through the membrane from the tip of the opened valve 6 is obtained. At this time, the valve 7 and the valve 8 are closed. In the backflow physical cleaning process, the filtered water 9 that has passed through the membrane is adjusted by the flow rate adjusting valve 10, the pressure is adjusted by the pressure gauge 11, passed through the evaluation membrane module 1 connected to the end of the opened valve 8, and opened. Drain from the tip of the valve 7. At this time, the valve 5 and the valve 6 are closed. This filtration and backflow physical washing steps were repeated to determine the degree of increase in filtration resistance.

Example 1
The membrane filtration system was operated for 22 days. The evaluation membrane module was measured at a constant pressure acceleration operation every 5 days to measure the degree of increase in the filtration resistance of the evaluation membrane module. In the initial stage of operation, the transmembrane pressure difference of the membrane filtration system main body was 30 kPa, and the filtration pressure of the evaluation membrane module was 50 kPa. The increase in filtration resistance was approximately constant at 0.4 × 10 ¹² m ⁻² . At this time, the transmembrane pressure difference of the membrane filtration system main body was from 30 kPa to 40 kPa for 22 days, and could be operated stably.

Example 2
In the same period as in Example 1, the evaluation membrane module was operated at a constant flow rate acceleration, and the degree of increase in the filtration resistance of the evaluation membrane module was measured every 5 days. The filtration flux was 3.0 m / d and the reverse flow physical washing flux was 6.0 m / d. The increase in filtration resistance is 0.3 × 10 ¹² m ⁻² , which is almost constant. At this time, the transmembrane pressure difference of the membrane filtration system body is from 30 kPa to 40 kPa for 22 days. did it.

Comparative Example 1
At the same time as Example 1, the evaluation membrane module was measured at a constant pressure acceleration operation to measure the degree of increase in the filtration resistance of the evaluation membrane module. When the filtration pressure of the membrane module for evaluation was set to 450 kPa, which is 15 times the transmembrane differential pressure of 30 kPa of the membrane filtration system main body, the membrane was crushed and the amount of water permeation decreased, and the evaluation membrane module could not be evaluated.

Comparative Example 2
In the same period as in Example 1, the evaluation membrane module was subjected to constant flow acceleration operation, and the degree of increase in the filtration resistance of the evaluation membrane module was measured. When the filtration flux of the evaluation membrane module is increased to 30 m / d, which is 12 times 2.5 m / d, the filtration pressure rises rapidly, the membrane is crushed, and the water permeability is reduced. I couldn't.

Example 3
At a time different from Example 1, the membrane filtration system was operated for 15 days. The filtration differential pressure of the membrane filtration system main body in the initial operation was 35 kPa. The evaluation membrane module was operated at a constant pressure and the filtration pressure was 50 kPa. The increase in filtration resistance was 0.9 × 10 ¹² m ⁻² , and a sudden increase in the transmembrane pressure difference of the membrane filtration system was predicted. The polyaluminum chloride 10 mg / L was added to the to-be-processed water which enters into a membrane filtration system main part with 0.5 m / d. The transmembrane pressure difference of the membrane filtration system body became stable between 40 kPa and 50 kPa, and was 50 kPa even on the 15th day.

Comparative Example 3
At the same time as Example 3, the membrane filtration system was operated for 15 days. The filtration differential pressure of the membrane filtration system main body in the initial operation was 35 kPa. The evaluation membrane module was operated at a constant pressure and the filtration pressure was 50 kPa. The increase in filtration resistance was 0.9 × 10 ¹² m ⁻² respectively, and a sudden increase in the transmembrane pressure difference of the membrane filtration system was expected. With 2.5 m / d, 2 mg / L of polyaluminum chloride was added to the water to be treated entering the membrane filtration system main body. The transmembrane pressure difference of the membrane filtration system main body reached 50 kPa on the second day, the transmembrane pressure differential continued to rise, reached 120 kPa on the 15th day, and the operation was stopped.

Example 4
At the same time as Example 3, the membrane filtration system was operated for 15 days. The filtration differential pressure of the membrane filtration system main body in the initial operation was 35 kPa. The evaluation membrane module was operated at a constant pressure and the filtration pressure was 50 kPa. The increase in filtration resistance was 0.9 × 10 ¹² m ^-2 respectively, and a sudden increase in the transmembrane pressure difference of the membrane filtration system was expected. 20 ppm of sodium chlorite was added. The transmembrane pressure difference of the membrane filtration system body became stable between 45 kPa and 55 kPa, and was 55 kPa even on the 15th day.

Comparative Example 4
At the same time as Example 3, the membrane filtration system was operated for 15 days. The filtration differential pressure of the membrane filtration system main body in the initial operation was 35 kPa. The evaluation membrane module was operated at a constant pressure and the filtration pressure was 50 kPa. The increase in filtration resistance was 0.9 × 10 ¹² m ^-2 respectively, and a sudden increase in the transmembrane pressure difference of the membrane filtration system was expected. 5 ppm of sodium chlorite was added. The transmembrane pressure difference of the membrane filtration system body continued to rise and reached 150 kPa on the 15th day, and the operation was stopped.

The membrane filtration system of the present invention can be used for membrane filtration of groundwater, river water, lake water, seawater, sewage secondary treated water, and the like.

An example of the graph of the total amount of filtrate water-filtration resistance by a filtration experiment is shown. It is the schematic of the membrane module for evaluation.

Explanation of symbols

1: Membrane module for evaluation 2: Intake port 3: Flow rate adjusting valve 4: Pressure gauge 5: Valve 6: Valve 7: Valve 8: Valve 9: Filtrated water 10: Flow rate adjusting valve 11: Pressure gauge

Claims (2)

For membrane filtration systems equipped with microfiltration membranes and / or ultrafiltration membranes, evaluate the same treated water as the membrane filtration system body, which has a filtration membrane with a smaller membrane area than the filtration membrane used in the membrane filtration system body A membrane filtration system operating method for measuring the degree of increase in filtration resistance with the evaluation membrane module and optimizing the operating conditions of the membrane filtration system based on the results. A membrane characterized in that the operation method is a constant flow rate operation or a constant pressure operation, and the flux or pressure of the membrane module for evaluation is 1.1 to 10 times faster than that of the membrane filtration system main body. How to operate the filtration system. When the degree of increase in filtration resistance is 0.5 × 10 ¹² m ⁻² or more, add 5 ppm to 100 ppm flocculant and / or add 10 ppm to 500 ppm sodium hypochlorite by backflow physical cleaning The operation method of the membrane filtration system according to claim 1.

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