JP4666600B2 - Water evaluation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for evaluating water using a filtration membrane, and in particular, feed water and concentration to a water treatment apparatus using a filtration membrane such as a reverse osmosis membrane (hereinafter sometimes abbreviated as “RO membrane”). The present invention relates to a water evaluation method suitable for water quality evaluation .

  Conventionally, water quality has been analyzed and measured using a filtration membrane. For example, there is a method of measuring very low turbidity called SDI and a method of measuring fine particles in very pure water. In addition to these methods, the material and pore size of membranes for analysis and water quality measurement have been controlled as important factors. Membrane materials are known to adsorb specific substances due to the hydrophilic / hydrophobic nature of the materials, the presence or absence of charge, and the properties of the yin and yang. As a result, this may cause measurement interference and error generation. It has been pointed out. Regarding the pore size of the membrane, it is known that, for example, when measuring fine particles, it is necessary to select a membrane having a pore size smaller than the fine particles to be measured.

  To explain the SDI measurement that is deeply related to the present invention, SDI is a method developed for the purpose of detecting very low turbidity in water. This is a method for confirming that sufficient pretreatment is performed so as not to cause a problem in the film. Specifically, the sampled water is pressurized and passed through a given membrane at a constant pressure (210 kPa), and the time required for the initial 500 mL filtration and the time required for 500 mL filtration after 15 minutes of continuous filtration. In this method, the rate of change per hour is evaluated, and if the value is not less than a certain value (for example, SDI = 4 or less), it is determined that the RO membrane water supply is insufficient. The maximum SDI is 100/15 = 6.7 when filtering is continued for 15 minutes from the numerical definition. However, if the water quality is poor and the filtration cannot be continued for 15 minutes, the filtration time may be shortened for measurement. For example, when the filtration duration is set to half of 7.5 minutes, the maximum value of SDI is 100 / 7.5 = 13.3. As the membrane used for the measurement, a pore diameter of 0.45 μm is prescribed, but a HAWPO membrane manufactured by Millipore (pore diameter: 0.45 μm, material: cellulose acetate / cellulose nitrate mixture) is adopted as standard, and is used for filtration. The form employs a dead-end filtration system that does not have the effect of stirring concentrated water.

  As described above, this SDI method is a method for measuring turbidity in water, but it has recently been reported that trouble occurs even if SDI shows a sufficient value. The reason is not clear, but RO membranes have a physical pore with a pore diameter of 0.45 μm because it is assumed that water penetrates the molecular gaps of macromolecules much smaller than the membrane used for SDI measurement. The membrane cannot fully evaluate the phenomenon that occurs in the RO membrane, and the SDI measurement is dead-end filtration, whereas the RO membrane filtration method is usually cross-flow filtration, and the mechanism of membrane contamination is different. Is inferred. It has also been pointed out that the microorganisms and microorganism metabolites that have entered the RO membrane module may cause the blockage of the RO membrane module. In this case, since the amount of microorganisms at the inlet grows at least in the module, it has been pointed out that it may not be determined even if the inlet water quality is measured. In any case, SDI measurement is a measurement of the necessary conditions, and it is considered that it can not be determined whether it can be used as RO water supply only by the SDI measurement result, and it is more RO as an alternative or supplement to SDI. It has also been proposed to measure water quality indicators in a manner close to treatment. However, even in such a case, studies on the difference in film material, difference in pore size, etc. have been made. However, as will be described later, the structure of the film surface focused on in the present invention, particularly the surface structure represented by irregularities on the film surface for measurement. It has not yet been proposed to control properties.

The characteristics of ordinary water treatment equipment equipped with RO membranes are excellent membranes and operation methods that can be operated stably for a longer period of time, and the structure of the membrane surface is smooth. There is a report example that it is more advantageous for maintaining the amount of permeated water than the difference in membrane material such as being a system material (Non-Patent Document 1). However, when measuring a water quality index, characteristics different from the RO device as a normal water treatment device, such as being able to measure a difference in water quality with high sensitivity and being able to measure in a short time, are required. Yes. Also, although the permeate flow rate does not decrease, the water flow differential pressure rises, and it is not possible to continue operation and chemical cleaning etc. are necessary. When converted to a predetermined pressure (the device maintains the permeate flow rate) Therefore, it is important to be able to expect an increase in the water flow differential pressure at the same time as the permeate flow rate decreases (because the operation pressure is increased).
J. of Membrane Science, 1997, p101

In view of the background art as described above, the object of the present invention is to focus on the surface structure of a filtration membrane for measurement that has not been focused on in the past, and by appropriately controlling or selecting the surface structure characteristics, it is possible to achieve high sensitivity and short time. It is an object of the present invention to provide a water evaluation method that can accurately measure the target items and can appropriately predict the degree of decrease in the amount of permeated water and the increase in water flow differential pressure.

In order to solve the above-described problems, a water evaluation method according to the present invention is a method for evaluating water supply and / or concentrated water of a filtration membrane, wherein the amount of permeated water that permeates the filtration membrane and / or the water supply inlet of the filtration membrane. And the difference between the pressure difference between the outlet of the concentrated water and the average value of the height difference of the surface irregularities as the surface structure characteristics of the filtration membrane, and the amount of permeated water permeating the filtration membrane and / or the feed inlet of the filtration membrane from the relationship The surface structure which determines the specific range or specific reference value of the average value of the height difference of the surface irregularities to be used for the measurement of the differential pressure between the water outlet and the concentrated water outlet, and satisfies the determined specific range or specific reference value The method comprises measuring a time-dependent change in the amount of permeated water permeating through the filter membrane and / or a time-dependent change in the differential pressure between the feed water inlet and the concentrated water outlet of the filter membrane .

In this water evaluation method, a cross flow method that continuously obtains permeated water that permeates the filtration membrane and concentrated water that does not permeate the filtration membrane can be used as the water flow method.

As the surface structure characteristics, an average value of the height difference of the surface irregularities is used . Height difference between the surface roughness is preferably in the range of ± 50% against the average value thereof. If a filtration membrane with too much variation is used, the meaning of controlling the surface structure characteristics, particularly the height difference of the surface irregularities, to a specific range or a specific value is lost.

In the evaluation method of the water according to the present invention, the average value of the height difference of the surface unevenness of the filtration membrane used for evaluation of water, is equipped to a device that actually water treatment target water Evaluation of the water It is preferable that the average value of the height difference of the surface irregularities of the filtration membrane is different. That is, the filtration membrane to be mounted to a device that is actually water treatment, as described above, to allow long-term stable operation, but the film surface preferably smooth filtration membrane, in the case of evaluation of water, In order to enable measurement in a short time and with high sensitivity (that is, in order to accelerate the filtration operation [detection operation for a measuring device]), a filtration membrane with a large difference in surface irregularities is used, and a specific measurement item is selected. On the other hand, it is preferable to greatly improve the measurement performance.

In particular, the average value of the height difference of the surface unevenness of the filtration membrane used for evaluation of water, the height of the surface irregularities of the filtration membrane to be mounted to the device that actually water treatment target water Evaluation of the water It is preferable that the difference is 50% or more compared to the average value of the differences. For example, the average value of the height difference of the surface unevenness of the filtration membrane used for evaluation of water, the height of the surface irregularities of the filtration membrane to be mounted to the device that actually water treatment target water Evaluation of the water It is preferably 50% or more larger than the average difference.

In addition, the measurement items for the evaluation of the water include measurement of the change with time of the amount of permeated water that permeates the filtration membrane . Alternatively, in addition to the measurement of the amount of permeated water or together with the measurement of the amount of permeated water, the measurement items for evaluating the water include measurement of the differential pressure between the water supply inlet and the concentrated water outlet of the filtration membrane .

In such a water evaluation method according to the present invention, a reverse osmosis membrane can be used as a filtration membrane for water evaluation . Thereby, even when a reverse osmosis membrane is used in an actual water treatment apparatus, it becomes possible to accurately measure the water quality in a form corresponding to the reverse osmosis membrane.

According to the method for evaluating water according to the present invention, by using a measurement filter membrane having a surface structure characteristic in a specific range, and further by controlling the surface structure, the measurement sensitivity can be improved and the measurement time can be reduced. While achieving the shortening, the water quality of the measurement target water can be accurately evaluated . In addition, it will be possible to properly predict the degree of decrease in the amount of permeated water and the increase in water flow differential pressure that occur in a normal RO device as a water treatment device, making it possible to evaluate water in accordance with the actual usage pattern. Become.

Hereinafter, preferred embodiments of the present invention will be described mainly with reference to experimental examples with reference to the drawings.
For four types of commercially available reverse osmosis membranes (membrane types A to D), the height difference of the surface irregularities of the membrane in a wet state was analyzed and measured by an AFM (atomic force electron microscope). The measurement conditions are as follows.
・ Device: SPA-400 (Seiko Instruments Inc. [current SII Nano Technology)
・ Cantilever: Made of silicon (spring constant: 15N / m)
・ Scanning area: 5 × 5μm
・ Scanning speed: 0.25Hz
Measurement environment: Table 1 shows the measurement and measurement results when the sample film was wet in pure water.

  Each membrane shown in Table 1 was used as a filtration membrane in the experiment. Since the appropriate operating pressure differs depending on the type of membrane, the initial filtration rate per membrane area was set to 1 m / d, and the crossflow flow rate was set to the operating pressure and flow rate conditions at 10 cm / sec at the membrane device inlet. . These are the operating conditions of a typical actual device. Although a 4-inch spiral element was used in the experiment, since the basic structure of the spiral element is a flat membrane, it has been confirmed that the same result can be obtained even in a small-area flat membrane device in the case of a water quality measuring device.

  In the water supply in the experiment, pure water, pure water + industrial water, pure water + biologically treated water, from the viewpoint of preventing disturbance of inorganic substances etc. (Of course, even if they are mixed, it can be measured practically) Pure water + surfactant was used. In addition, the characteristics of a, b, c, and d shown in the following figures show the characteristics when the filtration membranes A, B, C, and D are used.

Experiment 1
Figure 1, Figure 2, in the case of pure water and water supply, aging (indicated by F / F ₀₎ and passing jugs pressure on the permeate water (unit pressure and unit area basis) - of (inlet pressure outlet pressure) A change with time (indicated by ΔP / ΔP ₀ ) was shown. Since membrane fouling does not occur in pure water, naturally, the amount of permeated water and water flow differential pressure did not change.

Experiment 2
FIG. 3 and FIG. 4 show changes over time when pure water + industrial water (30%) blended water is used as feed water. As industrial water, Toda City industrial water was used, and the average turbidity during the experiment was about 0.6. Regarding the A and B membranes, the amount of permeated water gradually decreased and the water flow differential pressure gradually increased. Similar variations were observed for the C and D films, but the variations were much smaller.

Experiment 4
FIG. 5 and FIG. 6 show the change over time when pure water + biologically treated water (20%) blend water is used as the feed water. For biological treatment, add trace amount salt using glucose as a substrate, use BOD load 2kg / m ³ / day, aerobic biological treatment method using fibrous activated carbon as carrier, and filter the whole amount with a 20 micron safety filter Blended with pure water. In the A, B, C, and D membranes, the decrease in the permeated water amount was not remarkable, but the increase in the water flow differential pressure of the A, B, and C membranes occurred relatively remarkably.

Experiment 5
FIG. 7 and FIG. 8 show changes with time when pure water + surfactant (alkyldimethylbenzene ammonium chloride: 100 ppm) added water is supplied. Although the decrease in the amount of permeated water in the A, B, and C membranes was remarkable, no decrease in the amount of permeated water occurred in the D membrane. None of the membranes caused an increase in water differential pressure.

Experiment 3
FIG. 9 and FIG. 10 show changes over time when pure water + industrial water (60%) blend water is used as the feed water. As industrial water, Toda City industrial water was used, and the average turbidity during the experiment was about 0.5. A~D even relates to any of the membrane, permeate flow decreased, increased through pitcher pressure was observed. The degree was greater than in Experiment 2.

Experiment 6
An experiment similar to Experiment 2 was performed except that the initial filtration rate per membrane area was 1.5 m / d, which was 1.5 times (Measurement Promotion Experiment 1). The results are shown in FIG. 11 and FIG. 12. For any of the membranes A to D, the decrease in the permeated water amount and the increase in the water flow differential pressure were promoted more than in Experiment 2, but in particular, the decrease in the permeated water amount of the A to C membranes was promoted. It was done.

Experiment 7
An experiment similar to Experiment 2 was carried out except that the cross flow velocity was set to 20 cm / sec, which was 2.0 times at the entrance of the membrane device (Measurement Promotion Experiment 2). The results are shown in FIG. 13 and FIG. 14. For any of the membranes A to D, the decrease in the permeate flow rate and the increase in the water flow differential pressure were promoted more than in Experiment 2, but in particular the decrease in the permeate flow rate of the A to C membranes, and The increase in the water flow differential pressure of the A to D membranes was promoted.

Regarding the above results, Table 2 summarizes the time when the permeated water amount decreased to 80% of the initial value and the time when the water flow differential pressure increased by 20% from the initial value. In Table 2, F / F ₀ = 0.8 and ΔP / ΔP ₀ = 1.2 are numerical values that depend on the accuracy sensitivity of the measurement system. For example, if the change can be reliably detected even if the change in F / F ₀ is small, the sensitivity is high. I can say that. However, there is an unknown part that cannot be actually controlled, and in the experiment, 0.8 was set as a realistic value. In addition, the display of “∞” in Table 2 indicates a case where the predetermined value was not reached during the experiment period.

  Experiments 1, 2, and 3 are considered to be experiments with varying concentrations. When the causative substance has the same concentration, for example, 30%, it can be said that the detection time is early because the A film having large irregularities among the A, B and C films reaches the set value at an early stage. Further, when viewed on the same film, when the concentration of the causative substance increases, the time to reach the set value is shortened, and it can be determined that the time to reach the set value is correlated with the concentration of the causative substance. Therefore, if you use a membrane that controls the level difference of surface irregularities within a specific range, it can be used to measure the concentration of the causative substance by measuring the time it takes for the change in permeate flow or change in water flow differential pressure to reach the set value. Further, it can be seen that the detection time can be shortened and the sensitivity can be substantially improved by controlling the uneven size to a large value. For example, when a B film is used in an actual device, if measurement is performed with a film corresponding to the A film and having surface irregularities larger than the B film, the detection time and detection sensitivity can be improved, and the trouble can be predicted more quickly. Is possible.

  In Experiment 4, even when SDI is 4 or less and it is judged that the standard is good, film contamination clearly occurs. The larger the surface roughness, the greater the degree of contamination. In Experiment 5, SDI does not detect it. It was confirmed that the surfactant can also be detected by this measuring apparatus.

In addition, sensitivity can be increased and measurement time can be shortened by adjusting the operating conditions of the measuring device. In Experiment 6, as a result of setting the initial filtration rate higher than that in Experiment 2, it was confirmed that the amount of contaminants deposited on the film surface increased rapidly, and as a result, F / F ₀ rapidly decreased. As a method of setting a large initial filtration rate, in addition to pressurization by a pump, if a membrane with a large permeated water amount at the same pressure is used as compared with a membrane used in a measuring device, a membrane used in a measuring device is equivalent to the actual device. It is possible to set the filtration rate to a large value with the pressure of. In Experiment 7, it was confirmed that it is possible to increase contaminants flowing into the membrane module by setting the cross flow speed large, and as a result, it is possible to quickly detect a decrease in permeate flow rate and an increase in water flow differential pressure. In addition to the operating conditions of the measuring device, it is also possible to measure the water flow differential pressure with high sensitivity by increasing the cross flow speed during measurement.

  Furthermore, even for membranes of the same material system, there is a difference in the degree of permeate flow reduction and increase in water flow differential pressure, and the tendency depends on the unevenness of the membrane surface. In other words, a decrease in permeated water volume and an increase in water flow differential pressure may occur at the same time or separately, and both phenomena can be measured with PA-based membranes, especially when a membrane with a large uneven structure is used. As a result, reliable measurement values cannot be obtained unless the surface roughness of the membrane used for measurement is controlled within a specific range. On the other hand, the degree of desalting performance has a large effect on the measurement results. It became clear that there was no.

  In FIG. 15, the water supply 2 by the pump 1 is measured with the measuring device No. 2 for the actual device 4 including the water treatment device in which the RO devices 3 are arranged in multiple stages in a Christmas tree shape. 1 (5), the intermediate concentrated water 6 is added to the measuring device No. 2 (7), the concentrated water 8 is added to the measuring device No. 3 (9) shows an example of the arrangement of the measuring device in the case where water is supplied for measurement. It is possible to improve detection time and detection sensitivity by measuring concentrated water instead of water supply. However, the final concentrated water of the actual device is often set to a concentration close to the upper limit value at which inorganic precipitation does not occur. Since it is considered that the rise is likely to occur, it is desirable to supply the intermediate concentrated water to the measuring device. In this case, correction of the osmotic pressure or the like is necessary, but it is possible to evaluate a biofilm derived from bacteria living in the RO apparatus from the measurement results of the actual apparatus water supply and concentrated water. In addition, the code | symbol 10 in FIG. 15 has shown the permeated water. In addition, although valves, pressure gauges, flow meters, and the like necessary for operation adjustment are not shown, they can be installed as necessary.

  If the measurement device is a flat membrane device simulating an actual device, it can measure with a small flow rate. However, when mounted on the actual device, there is a possibility that the flow rate has a margin, and a commercially available small element (2.5 inch spiral element) It is also possible to eliminate the influence of the measurement history by performing measurement using a 4-inch spiral element or the like, and replacing it with a new one for a certain period.

The water evaluation method according to the present invention includes a reverse osmosis membrane device for producing desalted water from industrial water and city water, a seawater desalination membrane device for producing fresh water from seawater, and water recovery from wastewater discharged from an industrial process. The present invention can be applied to any reverse osmosis membrane device such as a reverse osmosis membrane device and a reverse osmosis membrane device that performs water recovery after biological treatment of sewage and wastewater.

It is a time-dependent change characteristic view of the permeated water amount fall in Experiment 1. It is a time-dependent change characteristic view of the water flow differential pressure rise in Experiment 1. It is a time-dependent change characteristic view of the permeated water amount fall in Experiment 2. It is a time-dependent change characteristic view of the water flow differential pressure rise in Experiment 2. It is a time-dependent change characteristic view of the permeated water amount fall in Experiment 3. It is a time-dependent change characteristic view of the water flow differential pressure rise in Experiment 3. It is a time-dependent change characteristic view of the permeated water amount fall in Experiment 4. It is a time-dependent change characteristic view of the water flow differential pressure rise in the experiment 4. It is a time-dependent change characteristic view of the permeated water amount fall in Experiment 5. It is a time-dependent change characteristic view of the water flow differential pressure rise in Experiment 5. It is a time-dependent change characteristic view of the permeated water amount fall in Experiment 6. It is a time-dependent change characteristic view of the water flow differential pressure rise in Experiment 6. It is a time-dependent change characteristic view of permeated water amount fall in Experiment 7. It is a time-dependent change characteristic view of the water flow differential pressure rise in Experiment 7. It is a schematic equipment block diagram which shows the example of arrangement | positioning of the water quality measuring apparatus with respect to an actual apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pump 2 Water supply 3 RO apparatus 4 Actual apparatus which consists of a water treatment apparatus 5 Measuring apparatus No. 1
6 Intermediate concentrated water 7 Measuring device No. 6 2
8 Concentrated water 9 Measuring device no. 3
10 Permeated water

Claims (7)

A method for evaluating the feed water and / or concentrated water of a filtration membrane, wherein the amount of permeated water permeating through the filtration membrane and / or the differential pressure between the feed water inlet and the concentrated water outlet of the filtration membrane and the surface irregularities as surface structure characteristics of the filtration membrane The relationship between the height difference of the surface and the average value of the surface unevenness is determined in advance, and from this relationship, the amount of permeated water permeating the filtration membrane and / or the height of the surface irregularities to be used for measuring the differential pressure between the water supply inlet and the concentrated water outlet of the filtration membrane Determining a specific range or a specific reference value of an average value of the difference, a change over time of the amount of permeated water permeating through the filtration membrane using a filtration membrane having a surface structure that satisfies the determined specific range or the specific reference value, and A method for evaluating water , comprising measuring a time-dependent change in differential pressure between a feed water inlet and a concentrated water outlet of a filtration membrane . The water evaluation method according to claim 1, wherein a cross-flow method is used as the water flow method, which continuously obtains permeated water that permeates the filtration membrane and concentrated water that does not permeate the filtration membrane. The water evaluation method according to claim 1 or 2, wherein the difference in height of the surface irregularities is within a range of ± 50% of the average value. The average value of the height difference of the surface unevenness of the filtration membrane used for water evaluation is the height difference of the surface unevenness of the filtration membrane installed in the apparatus for actually treating the target water for the water evaluation . The water evaluation method according to claim 1, which is different from the average value. The average value of the height difference of the surface unevenness of the filtration membrane used for water evaluation is the height difference of the surface unevenness of the filtration membrane installed in the apparatus for actually treating the target water for the water evaluation . The water evaluation method according to claim 4, wherein the water evaluation value differs by 50% or more compared to the average value. The average value of the height difference of the surface unevenness of the filtration membrane used for water evaluation is the height difference of the surface unevenness of the filtration membrane installed in the apparatus for actually treating the target water for the water evaluation . The water evaluation method according to claim 5, wherein the water evaluation method is at least 50% larger than the average value. The filtration membrane for the evaluation of water using a reverse osmosis membrane, the evaluation method of water according to any one of claims 1-6.

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