Patent Application
20200001240
The present invention relates to a membrane separation device and a membrane separation method in which, while air is diffused toward a separation membrane provided so as to be immersed in drained water containing organic substances, treated water that has passed through the separation membrane is obtained.
As a method for treating drained water containing organic substances (hereinafter, referred to as “treatment target water”), a membrane bioreactor (MBR) is used in which organic substances in treatment target water are decomposed using microorganisms and the treatment target water is filtered by a separation membrane to be separated into solid and liquid. In filtering using the separation membrane, as the separation membrane continues to be used, contaminants adhere to the surface of the separation membrane or into the pores of the separation membrane and thus clogging may occur, whereby filtering performance gradually deteriorates.
Therefore, the following method is used: a diffuser device is provided below the separation membrane, aeration with air or the like is performed toward the separation membrane from the diffuser device, the adhering materials on the separation membrane surface are peeled by bubbles and ascending flow of the treatment target water, thereby suppressing clogging. The energy cost required for this aeration is calculated to reach approximately half the entire operation cost. Accordingly, various techniques for suppressing the aeration amount are being developed.
Patent Document 1 proposes a method in which the transmembrane pressure (TMP) of a filtration membrane is measured and the aeration flow amount is controlled so that the transmembrane pressure is maintained at a predetermined increase speed set in advance. Specifically, a reference value for the transmembrane pressure is updated and set so as to automatically increase every certain period, the next target value for the aeration flow amount is set on the basis of a difference value between the reference value and a measurement value of the transmembrane pressure for each time, and the aeration flow amount is controlled in accordance with the target value.
Patent Document 2 proposes that a negative operation pressure difference inside a flat membrane unit is measured by a pressure meter, and the amount of diffused air from a diffuser device and an intermittent operation time ratio of operation and stop of a suction pump are controlled on the basis of the rate of change in the increase speed of the operation pressure difference. In addition, an optimum pattern for the diffused air amount and the intermittent operation time ratio is estimated, and automatic control is performed on the basis of the estimation.
However, in the method of controlling the aeration flow amount on the basis of the transmembrane pressure (hereinafter, may be referred to as TMP) of the filtration membrane as shown in the above Patent Documents 1, 2, the water quality of the treatment target water to be subjected to solid/liquid separation by the separation membrane is not measured, and therefore an excessive aeration flow amount is sometimes needed for maintaining the aeration flow amount at the target value therefor. Thus, under such a condition, there is a possibility that an excessive aeration flow amount is required.
The present invention has been made to solve the above problem, and an object of the present invention is to obtain a membrane separation device and a membrane separation method that enable reduction of operation cost by reducing a membrane surface aeration flow amount.
A membrane separation device according to the present invention includes: a separation membrane which filters treatment target water in a membrane separation tank; a membrane surface aeration device which supplies air for performing membrane surface aeration for the separation membrane; organic substance concentration measurement means which measures an organic substance concentration in the treatment target water; a pressure measurement unit which measures a transmembrane pressure of the separation membrane; transmembrane pressure increase speed comparing means which compares a transmembrane pressure increase speed RT selected on the basis of a value of the organic substance concentration measured by the organic substance concentration measurement means, with a transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit; and a control unit which controls a membrane surface aeration flow amount of the membrane surface aeration device, wherein the control unit changes the membrane surface aeration flow amount on the basis of the difference, obtained by the transmembrane pressure increase speed comparing means, between the transmembrane pressure increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means and the transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit.
Another membrane separation device according to the present invention includes: a separation membrane which filters treatment target water in a membrane separation tank; a membrane surface aeration device which supplies air for performing membrane surface aeration for the separation membrane; first organic substance concentration measurement means which measures an organic substance concentration in the treatment target water; second organic substance concentration measurement means which measures an organic substance concentration in filtered water filtered by the separation membrane; a pressure measurement unit which measures a transmembrane pressure of the separation membrane; transmembrane pressure increase speed comparing means which compares a transmembrane pressure increase speed RT selected on the basis of an organic substance concentration difference obtained by subtracting a value of the organic substance concentration measured by the second organic substance concentration measurement means from a value of the organic substance concentration measured by the first organic substance concentration measurement means, with a transmembrane pressure increase speed RM calculated from the transmembrane pressure measured by the pressure measurement unit; and a control unit which controls a membrane surface aeration flow amount of the membrane surface aeration device, wherein the control unit changes the membrane surface aeration flow amount on the basis of the difference, obtained by the transmembrane pressure increase speed comparing means, between the transmembrane pressure increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means and the transmembrane pressure increase speed R calculated from the transmembrane pressure measured by the pressure measurement unit.
A membrane separation method according to the present invention includes: filtering a treatment target water in a membrane separation tank by a separation membrane; measuring an organic substance concentration in the treatment target water when performing membrane surface aeration for supplying bubbles by a diffuser pipe from below the separation membrane; selecting a transmembrane pressure increase speed as a target on the basis of a measured value of the organic substance concentration; comparing the target transmembrane pressure increase speed with an increase speed of a transmembrane pressure of the separation membrane; and setting a flow amount of the membrane surface aeration so that a difference between the transmembrane pressure increase speed and the increase speed becomes small.
The present invention changes the TMP increase speed by changing the membrane surface aeration flow amount on the basis of the concentration of organic substances contained in the treatment target water in the membrane separation tank, thereby enabling reduction of operation cost required for aeration and thus providing a significant effect that has not been achieved conventionally.
Hereinafter, a membrane separation device according to embodiment 1 of the present invention will be described with reference to
As shown in
Here, the case where activated sludge is contained in the treatment target water 9 will be described. However, activated sludge does not necessarily need to exist in the treatment target water 9.
Inflow water 8 flows into the membrane separation tank 1, and the filtered water pipe 3 is connected to the membrane separation tank 1 via the separation membrane 2. The membrane separation tank 1 is required to receive the inflow water 8 and store the treatment target water 9, and the material and the structure thereof are required to be ones that prevent water leakage, e.g., concrete, stainless steel, or resin. The separation membrane 2 is required to be means such as a hollow fiber membrane or a flat membrane that is capable of separation into solid and liquid, and is not limited to an RO membrane, an NF membrane, a UF membrane, an MF membrane, or the like. The separation membrane 2 is connected to the filtration pump 4 via the filtered water pipe 3. The separation membrane 2 is immersed in the membrane separation tank 1, and the diffuser pipe 7 is provided directly under the separation membrane 2, at the lower part of the membrane separation tank 1.
The diffuser pipe 7 is required to be capable of supplying bubbles 11, and may be made from glass, stainless steel, sintered metal, resin, or the like. The diffuser pipe 7 is connected to the membrane surface aeration device 5 via the aeration pipe 6. The membrane surface aeration device 5 is required to be a device such as a blower that is capable of pressure-feeding air. Organic substance concentration measurement means 19 is provided for the treatment target water 9 in the membrane separation tank 1. The organic substance concentration measurement means 19 is required to be means such as a total organic carbon concentration meter, an ultraviolet absorbance meter, or a fluorescence intensity meter, that is capable of directly or indirectly measuring organic substances in water. An organic substance concentration sensor such as a total organic carbon concentration meter, an ultraviolet absorbance meter, or a fluorescence intensity meter may be immersed in the membrane separation tank 1, to perform measurement, or the treatment target water 9 in the membrane separation tank 1 may be supplied to the organic substance concentration sensor, to perform measurement.
A pressure measurement unit 17 is provided to the filtered water pipe 3 between the separation membrane 2 and the filtration pump 4. The pressure measurement unit 17 is a meter that is capable of measuring a pressure, and may be either a digital type or an analog type. Preferably, the pressure measurement unit 17 is provided with a mechanism that can store pressure values measured over time. The organic substance concentration measurement means 19 and the pressure measurement unit 17 are included in the TMP increase speed changing means 12, and the TMP increase speed changing means 12 is connected to the membrane surface aeration device 5 via a signal line 54.
Next, the configuration of the TMP increase speed changing means 12 will be described. The TMP increase speed changing means 12 includes target TMP increase speed setting means 13, TMP increase speed measurement means 14, TMP increase speed comparing means 15, and membrane surface aeration flow amount control unit 16. The membrane surface aeration flow amount control unit 16 is connected to a database 20 described later via a signal line 70.
The target TMP increase speed setting means 13 includes the organic substance concentration measurement means 19, the database 20, and a target TMP increase speed selecting unit 21. The organic substance concentration measurement means 19 and the target TMP increase speed selecting unit 21 are connected via a signal line 56, and the database 20 and the target TMP increase speed selecting unit 21 are connected via a signal line 57. The target TMP increase speed selecting unit 21 is connected to the TMP increase speed comparing means 15 via a signal line 51.
In the database 20, water quality, temporal changes in TMP, and the like acquired by the past water treatments are recorded and stored as a database. The target TMP increase speed selecting unit 21 compares the data stored in the database 20 and data acquired by the organic substance concentration measurement means 19, and selects a target TMP increase speed RT. Preferably, the target TMP increase speed RT is 0.01 to 40 kPa/h.
As shown in
By supplying the treatment target water 9 in the membrane separation tank 1 to the organic substance index measurement means 27, it is possible to measure at least one organic substance index of UV, TOC, COD, BOD, a humic acid concentration, a sugar concentration, and a protein concentration. It has been confirmed that the substances corresponding to these indexes are readily captured by the separation membrane 2 and can be used as indexes for clogging, whereby organic substances that can cause clogging in the membrane can be accurately measured.
Here, the present invention is implemented under the condition that the UV value is 0 to 10 Abs/cm, the TOC value is 1 to 500 mg/L, the COD value and the BOD value are 1 to 500 mg/L, and the humic acid concentration, the sugar concentration, and the protein concentration are 0 to 500 mg/L.
The TMP increase speed measurement means 14 includes the pressure measurement unit 17 and a TMP increase speed calculation unit 18 which are connected via a signal line 55. The TMP increase speed calculation unit 18 is connected to the TMP increase speed comparing means 15 via a signal line 52. The TMP increase speed calculation unit 18 calculates the TMP from a pressure measured by the pressure measurement unit 17, and calculates a TMP increase speed RM on the basis of temporal change in the TMP.
The TMP increase speed comparing means 15 is connected to the membrane surface aeration flow amount control unit 16 via a signal line 53. The TMP increase speed comparing means 15 is connected to the target TMP increase speed selecting unit 21 via the signal line 51, and connected to the TMP increase speed calculation unit 18 via the signal line 52. The TMP increase speed comparing means 15 compares the TMP increase speed RM calculated by the TMP increase speed calculation unit 18 and the target TMP increase speed RT selected by the target TMP increase speed selecting unit 21, and sends the difference therebetween to the membrane surface aeration flow amount control unit 16 via the signal line 53.
The membrane surface aeration flow amount control unit 16 controls the membrane surface aeration flow amount of the membrane surface aeration device 5 on the basis of the signal obtained from the TMP increase speed comparing means 15. Further, data used in the control is sent to the database 20 via the signal line 70, and thus data about the membrane surface aeration flow amount is accumulated.
Hereinafter, a procedure of control for the membrane surface aeration flow amount will be described. Aeration is performed with a gas such as air from the diffuser pipe 7 provided below the separation membrane 2, and the adhering materials on the surface of the separation membrane 2 are peeled by bubbles 11 and ascending flow of the treatment target water 9 caused by the bubbles, whereby clogging of the separation membrane 2 is suppressed. The TMP increase speed varies depending on the extent to which clogging is suppressed, and as the membrane surface aeration flow amount increases, clogging becomes less likely to occur. Here, preferably, the membrane surface aeration flow amount per membrane area of the separation membrane 2 is controlled to be 0.01 to 10 m3/hr/(membrane filtration area m2).
The extent of clogging of the separation membrane 2 can be grasped from the value measured by the pressure measurement unit 17. As membrane filtration is continuously performed by the filtration pump 4, the separation membrane 2 is gradually clogged and the TMP increases. This is grasped from data of TMP and time sent from the pressure measurement unit 17 via the signal line 55 at the TMP increase speed calculation unit 18, and the temporal change of the TMP is calculated as the TMP increase speed RM. Preferably, the interval of measurement of TMP for calculating the TMP increase speed is once a second to once a day, and preferably, the TMP increase speed RM is calculated from temporal change in the TMP over a range of one minute to one month. The TMP increase speed RM is sent to the TMP increase speed comparing means 15 via the signal line 52.
Meanwhile, the organic substance concentration measurement means 19 measures the organic substance concentration in the treatment target water 9 over time. The measurement interval may be once a minute to once an hour, or may be once a day. The value of the measured organic substance concentration is sent to the target TMP increase speed selecting unit 21 via the signal line 56. The target TMP increase speed selecting unit 21 selects a target TMP increase speed RT on the basis of the organic substance concentration obtained from the organic substance concentration measurement means 19 and the data in the database 20 in which association between a TMP increase speed and water quality such as organic substance concentration, water temperature, and solid material concentration in the past is stored as data. The selected TMP increase speed RT is sent to the TMP increase speed comparing means 15 via the signal line 51.
The TMP increase speed comparing means 15 compares the TMP increase speed RM calculated by the TMP increase speed calculation unit 18 and the TMP increase speed RT selected by the target TMP increase speed selecting unit 21, and sends the difference therebetween to the membrane surface aeration flow amount control unit 16 via the signal line 53. The membrane surface aeration flow amount control unit 16 sets the value of the membrane surface aeration flow amount so that the difference becomes small or zero, and sends the set value to the membrane surface aeration device 5 via the signal line 54.
In the case where the value of the TMP increase speed RM calculated by the TMP increase speed calculation unit 18 is greater than the TMP increase speed RT selected by the target TMP increase speed selecting unit 21, it is necessary to increase the membrane surface aeration flow amount. On the other hand, in the case where the value of the TMP increase speed RM calculated by the TMP increase speed calculation unit 18 is smaller than the TMP increase speed RT selected by the target TMP increase speed selecting unit 21, it is necessary to decrease the membrane surface aeration flow amount.
The membrane surface aeration device 5 is controlled by an inverter and sends a gas such as air through the aeration pipe 6 to the diffuser pipe 7 so as to achieve the membrane surface aeration flow amount according to the value from the membrane surface aeration flow amount control unit 16, thereby performing membrane surface aeration. The TMP increase speed RM and the organic substance concentration in the treatment target water 9 are measured periodically, and the above operation is repeated. Such data are all sent from the membrane surface aeration flow amount control unit 16 via the signal line 70 to the database 20 and accumulated therein. In the case where the TMP reaches a certain value, e.g., 25 kPa, membrane filtration operation is stopped and the separation membrane 2 is washed. A specific method for determining the value of the aeration flow amount will be described later.
The present inventors have earnestly investigated the relationship among the TMP increase speed, the membrane surface aeration flow amount, and the water quality of treatment target water, and as a result, have found that there is a relationship as shown in
As shown in
On the other hand, if the membrane surface aeration flow amount becomes great, microorganisms, contaminants, and the like are less likely to adhere to the separation membrane surface, and thus the TMP increase speed can be reduced to be low. Existence of the point where the TMP increase speed sharply increases, i.e., the inflection point, is a discovery, and it is possible to indirectly grasp the condition of adhesion of microorganisms, contaminants, and the like to the separation membrane surface by monitoring the TMP increase speed. Further, from the result at this time, it has been found that increase in the TMP increase speed is caused due to two factors.
That is, the two factors are adhesion of microorganisms, contaminants, and the like to the separation membrane surface and adhesion of organic substances to inside of the separation membrane. Adhesion of microorganisms, contaminants, and the like to the separation membrane surface rapidly causes clogging of the separation membrane surface, and thus contributes to sharp increase in the TMP increase speed where the membrane surface aeration flow amount is at the inflection point or lower. On the other hand, the pace of adhesion of organic substances to the inside of the separation membrane is slow, and thus contributes to gradual change in the TMP increase speed where the membrane surface aeration flow amount is at the inflection point or higher. This discovery is significantly important knowledge for controlling the TMP increase speed.
Further, it has been discovered that: as the organic substance concentration in the treatment target water 9 increases, the membrane surface aeration flow amount needed for reducing the same TMP increase speed increases; as the organic substance concentration in the treatment target water 9 increases, the membrane surface aeration flow amount at the inflection point increases; and, as the organic substance concentration in the treatment target water 9 increases, the TMP increase speed where the membrane surface aeration flow amount is at the inflection point or higher, increases. As the membrane surface aeration flow amount decreases, the amount of microorganisms, contaminants, and the like adhering to the separation membrane surface increases, and also, the thicknesses thereof increase. At this time, organic substances existing in the treatment target water 9 and spaces among microorganisms and contaminants serve as binders, so that the materials adhering on the separation membrane surface become less likely to be peeled from the separation membrane surface by bubbles supplied by membrane surface aeration and flow of the treatment target water 9 by the bubbles. Therefore, if the organic substance concentration in the treatment target water 9 increases, the membrane surface aeration flow amount needed for removing the materials adhering to the separation membrane surface also increases.
In the case of the membrane surface aeration flow amount below the inflection point, the function of the organic substances as a binder is more significant than the function of the organic substances as a binder when the membrane surface aeration flow amount is above the inflection point, and thus the TMP increase speed sharply increases due to the materials adhering to the separation membrane surface. On the other hand, in the case of the membrane surface aeration flow amount above the inflection point, the amount of materials adhering to the separation membrane surface is reduced and thus the contribution thereof to the TMP increase speed becomes small. However, in contrast to this, clogging of the separation membrane progresses due to adhesion of the organic substances to the inside of the separation membrane. From the above, it can be explained that, as the organic substance concentration in the treatment target water 9 increases, the separation membrane becomes more likely to be clogged, the TMP increase speed increases, and the membrane surface aeration flow amount at the inflection point also increases.
Here, preferably, the organic substance concentration is a value obtained with contaminants and turbidity excluded. That is, the organic substance concentration is measured after contaminants and turbidity are excluded through centrifugal separation, filtration, or the like in advance, whereby the relationships of the membrane surface aeration flow amount and the TMP increase speed with respect to each value of the organic substance concentration can be enhanced in accuracy.
Here, with reference to
That is, by measuring the organic substance concentration in the treatment target water 9 and setting the membrane surface aeration flow amount on the basis thereof, it becomes possible to greatly reduce the membrane surface aeration flow amount, though the TMP increase speed slightly increases. The energy cost required for membrane surface aeration is significantly large as compared to the operation cost for washing or the like. Therefore, even if the frequency of washing increases due to the slight increase in the TMP increase speed as shown in
Hereinafter, with reference to
The inflow water 8 varies from moment to moment, and along with this, the organic substance concentration in the treatment target water 9 varies depending on the operation conditions such as a solid retention time (SRT) in the membrane separation device and the dissolved oxygen concentration in the treatment target water 9. In accordance with whether the organic substance concentration is high, middle, or low, the target TMP increase speed RT, i.e., the membrane surface aeration flow amount QT at the inflection point in
High, middle, and low organic substance concentrations can be represented by using, for example, the absorbance of an ultraviolet ray having a wavelength of 220 to 270 nm, as follows. High: 2.000 Abs/cm or greater, middle: 0.001 to 1.999 Abs/cm or greater, low: 0.000 to 0.001 Abs/cm. Regarding a wavelength for ultraviolet absorbance measurement, 254 nm or 260 nm may be used as a first preferential candidate. The membrane surface aeration flow amount is set in a range of 0.01 m3/hr/m2 to 10 m3/hr/m2. The filtration area per one bar or one sheet of the separation membrane 2 is 0.01 to 100 m2.
The organic substance concentration measurement means 19 measures the organic substance concentration in the treatment target water 9. The target TMP increase speed selecting unit 21 selects the target TMP increase speed RT based on the measured organic substance concentration from the data in the database 20. In addition, the pressure measurement unit 17 measures the TMP, and the TMP increase speed calculation unit 18 calculates the TMP increase speed RM from the TMP measured by the pressure measurement unit. Next, the TMP increase speed RM calculated by the TMP increase speed calculation unit 18 and the target TMP increase speed RT selected by the target TMP increase speed selecting unit 21 are compared with each other.
If the TMP increase speed RM is equal to the target TMP increase speed RT or the absolute value of a difference between the TMP increase speed RM and the target TMP increase speed RT is smaller than an optionally set value a, the membrane surface aeration flow amount is maintained. If the TMP increase speed RM is greater than the target TMP increase speed RT or the TMP increase speed RN is greater than the target TMP increase speed RT by the optionally set value a or greater, the membrane surface aeration flow amount is increased by ΔQ. If the TMP increase speed RM is smaller than the target TMP increase speed RT or the TMP increase speed RM is smaller than the target TMP increase speed RT by the optionally set value a or greater, the membrane surface aeration flow amount is decreased by ΔQ. The optionally set value a can be optionally set in consideration of measurement error of the transmembrane pressure increase speed and convenience for operation in flow amount control. The change amount ΔQ for the membrane surface aeration flow amount can be optionally set, and may be set on the basis of a difference between the TMP increase speed RM and the target TMP increase speed RT or the change rate of the TMP increase speed RM, or may be set on the basis of the organic substance concentration or the amount of change in the organic substance concentration.
After the membrane surface aeration flow amount is maintained or increased/decreased, the TMP increase speed RM is calculated again. Further, the TMP increase speed RM and the target TMP increase speed RT are compared with each other, and the membrane surface aeration flow amount is adjusted by the method described above. Such a procedure is repeated until reaching to a step of measuring the next organic substance concentration. Thus, the value of the membrane surface aeration flow amount is set so that the TMP increase speed RM is controlled to be equal to the target TMP increase speed RT or the absolute value of the difference therebetween is controlled to be smaller than the optionally set value a. If the step of measuring the next organic substance concentration is reached, the organic substance concentration is measured and the above process is repeated.
As described above, in the invention according to embodiment 1, the target TMP increase speed RT is set on the basis of the concentration of organic substances contained in the treatment target water 9, and the membrane surface aeration flow amount is controlled so that the TMP increase speed is maintained at the target TMP increase speed RT. Therefore, it is possible to reduce the membrane surface aeration flow amount and reduce the operation cost for the entire device.
Next, a membrane separation device according to embodiment 2 of the present invention will be described with reference to
As shown in
The database update means 40 is connected to the membrane surface aeration flow amount control unit 16 via a signal line 71, and is connected to the database 20 via a signal line 72. The other configurations are the same as those in embodiment 1. Therefore, the same or corresponding parts are denoted by the same reference characters and the description thereof is omitted.
As filtration operation continues, variation in property of the filtration membrane, accumulation of inorganic substances, or the like can occur. These are factors that cause the TMP increase speed to change without depending on the organic substance concentration in the treatment target water 9. Therefore, as shown in
Accordingly, it is necessary to update the database as appropriate by comparing the relationship between the organic substance concentration in the treatment target water 9 and the TMP increase speed stored in the database 20, and the relationship between the organic substance concentration in the treatment target water 9 and the TMP increase speed under actual operation.
As shown in
The membrane surface aeration flow amount comparing means 41 is connected to the membrane surface aeration flow amount control unit 16 via a signal line 71a, connected to the database 20 via a signal line 72a, and connected to the target TMP increase speed calculation means 42 via a signal line 73. The membrane surface aeration flow amount change command unit 44 is connected to the membrane surface aeration flow amount control unit 16 via a signal line 71b. The target TMP increase speed calculation unit 45 is connected to the TMP increase speed calculation unit 18 via a signal line 74. The database update unit 43 is connected to the target TMP increase speed calculation means 42 via a signal line 75, and connected to the database 20 via a signal line 72b.
Next, a procedure for updating the database in embodiment 2 will be described. The membrane surface aeration flow amount control unit 16 performs control so that the TMP increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means 19, and the TMP increase speed RM calculated from the TMP measured by the pressure measurement unit 17, become equal to each other.
The value of the membrane surface aeration flow amount QM when the TMP increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means 19 and the TMP increase speed RM calculated from the TMP measured by the pressure measurement unit 17 have become equal to each other through control, is sent to the membrane surface aeration flow amount comparing means 41 via the signal line 71a. The value of the membrane surface aeration flow amount QT corresponding to the target TMP increase speed RT stored in the database is sent to the membrane surface aeration flow amount comparing means 41 via the signal line 72a. The membrane surface aeration flow amount comparing means 41 compares the membrane surface aeration flow amount QM when the TMP increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means 19 and the TMP increase speed RM calculated from the TMP measured by the pressure measurement unit 17 have become equal to each other through control, with the membrane surface aeration flow amount QT corresponding to the target TMP increase speed RT stored in the database, and sends the difference therebetween to the target TMP increase speed calculation means 42 via the signal line 43.
In the target TMP increase speed calculation means 42, if the membrane surface aeration flow amount QH when the TMP increase speed RT selected on the basis of the value of the organic substance concentration measured by the organic substance concentration measurement means 19 and the TMP increase speed RM calculated from the TMP measured by the pressure measurement unit 17 have become equal to each other through control, is equal to the membrane surface aeration flow amount QT corresponding to the target TMP increase speed RT stored in the database, update for the database is not performed. On the other hand, if these values are different from each other, a new target TMP increase speed RT′ and a membrane surface aeration flow amount Q=′ corresponding to the new target TMP increase speed RT′ are calculated, and the calculated values are sent to the database update unit 43 via the signal line 75.
The target TMP increase speed calculation means 42 includes the membrane surface aeration flow amount change command unit 44 and the target TMP increase speed calculation unit 45. If the membrane surface aeration flow amount QM is smaller than the membrane surface aeration flow amount QT, the membrane surface aeration flow amount change command unit 44 issues a command to the membrane surface aeration flow amount control unit 16 via the signal line 71b to increase the membrane surface aeration flow amount. On the other hand, if the membrane surface aeration flow amount QM is greater than the membrane surface aeration flow amount QT, the membrane surface aeration flow amount change command unit 44 issues a command to the membrane surface aeration flow amount control unit 16 via the signal line 71b to decrease the membrane surface aeration flow amount. After the membrane surface aeration flow amount is changed by the membrane surface aeration flow amount control unit 16, the TMP increase speed calculation unit 18 calculates the TMP increase speed RM, and sends the calculated value to the target TMP increase speed calculation unit 45 via the signal line 74. Increase/decrease of the membrane surface aeration flow amount and calculation of the TMP increase speed RM are repeatedly performed until the membrane surface aeration flow amount reaches the membrane surface aeration flow amount QT.
The target TMP increase speed calculation unit 45 calculates an inflection point from the relationship between the TMP increase speed and the membrane surface aeration flow amount obtained through the above operation, and as described above, calculates the TMP increase speed at the inflection point as a new target TMP increase speed RT′, and calculates the membrane surface aeration flow amount at the inflection point as a membrane surface aeration flow amount QT′ corresponding to the new target TMP increase speed RT′. Regarding a calculation method for the inflection point, the inflection point may be calculated on the basis of a value obtained by dividing the amount of change in the TMP increase speed by the amount of change in the membrane surface aeration flow amount, i.e., the calculated value of the change rate of the TMP increase speed with respect to the amount of change in the membrane surface aeration flow amount. Alternatively, the inflection point may be calculated by using an expression for calculating operation cost using the membrane surface aeration flow amount and the TMP increase speed as parameters. For example, the following expression can be used. The TMP increase speed and the membrane surface aeration flow amount which are calculated by using the following expression and which minimize the operation cost, may be used as an inflection point.
[Operation cost]=f(TMP increase speed, membrane surface aeration flow amount)
Here, with reference to
The database update unit 43 sends the new target TMP increase speed RT′ and the membrane surface aeration flow amount QT′ corresponding to the new target TMP increase speed RT′ which are calculated by the target TMP increase speed calculation means 42, to the database 20 via the signal line 72b, thereby updating the database. Further, the membrane surface aeration flow amount change command unit 44 issues a command to the membrane surface aeration flow amount control unit 16 via the signal line 71b so as to cause the membrane surface aeration flow amount to be the membrane surface aeration flow amount QT′. After the membrane surface aeration flow amount control unit 16 performs control so that the membrane surface aeration flow amount becomes the membrane surface aeration flow amount QT′, the update procedure for the database is finished.
As shown in
Next, the membrane surface aeration flow amount QM and the membrane surface aeration flow amount QT are compared with each other. If the membrane surface aeration flow amount QM and the membrane surface aeration flow amount QT are equal to each other or the absolute value of a difference between the membrane surface aeration flow amount QT and the membrane surface aeration flow amount QT is smaller than an optionally set value b, update of the database is not performed. If the membrane surface aeration flow amount QM is smaller than the membrane surface aeration flow amount QT or the membrane surface aeration flow amount QM is greater than the membrane surface aeration flow amount QT by the optionally set value b or greater, the membrane surface aeration flow amount is increased by ΔQ. If the membrane surface aeration flow amount QM is greater than the membrane surface aeration flow amount QT or the membrane surface aeration flow amount QM is greater than the membrane surface aeration flow amount QT by the optionally set value b or greater, the membrane surface aeration flow amount is decreased by ΔQ. The optionally set value b can be optionally set in consideration of control error of the membrane surface aeration flow amount and convenience for operation in flow amount control. The change amount ΔQ for the membrane surface aeration flow amount can be optionally set, and may be set on the basis of a difference between the membrane surface aeration flow amount QM and the membrane surface aeration flow amount Q, or may be set on the basis of the change rate of the TMP increase speed. After the membrane surface aeration flow amount is increased/decreased, the TMP increase speed is calculated. The changing of the membrane surface aeration flow amount and the calculation for the TMP increase speed RM are repeatedly performed until the membrane surface aeration flow amount reaches the membrane surface aeration flow amount QT. In other words, while the membrane surface aeration flow amount is changed from the membrane surface aeration flow amount QM to the membrane surface aeration flow amount QT, the TMP increase speed is measured each time.
The target TMP increase speed calculation unit 45 calculates an inflection point from the relationship between the TMP increase speed RM and the membrane surface aeration flow amount QM obtained through the above operation, and as described above, calculates the TMP increase speed at the inflection point as a new target TMP increase speed RT′, and calculates the membrane surface aeration flow amount at the inflection point as a membrane surface aeration flow amount QT′ corresponding to the new target TMP increase speed RT′. The calculated new target TMP increase speed RT′ and the calculated membrane surface aeration flow amount QT′ corresponding to the new target TMP increase speed RT′ are sent to the database 20, whereby the database is updated. Finally, the membrane surface aeration flow amount is controlled so that the membrane surface aeration flow amount becomes the membrane surface aeration flow amount QT′, and thus the database update procedure is finished.
As described above, in the invention according to embodiment 2, the relationship between the organic substance concentration in the treatment target water and the TMP increase speed, stored in the database, is updated, so that the target TMP increase speed can be set accurately. Therefore, it is possible to reduce the membrane surface aeration flow amount and reduce the operation cost for the entire device.
Next, a membrane separation device according to embodiment 3 of the present invention will be described with reference to
As shown in
The organic substance concentration measurement means 19 for measuring the organic substance concentration in the treatment target water 9 in the membrane separation tank 1 is connected to the organic substance concentration difference value calculation unit 23 via a signal line 58, and the organic substance concentration measurement means 22 for measuring the organic substance concentration in the filtered water in the filtered water pipe 3 is connected to the organic substance concentration difference value calculation unit 23 via a signal line 59. The organic substance concentration difference value calculation unit 23 is connected to the target TMP increase speed selecting unit 21 via a signal line 60. The other configurations are the same as those in embodiment 1. Therefore, the same or corresponding parts are denoted by the same reference characters and the description thereof is omitted.
Next, operation of the membrane separation device in embodiment 3 will be described. The organic substance concentration measurement means 22 measures the organic substance concentration in the filtered water that is passing through the filtered water pipe 3 after the treated water is filtered by the separation membrane 2. The value of the organic substance concentration measured by the organic substance concentration measurement means 22 is sent to the organic substance concentration difference value calculation unit 23 via the signal line 59. The organic substance concentration difference value calculation unit 23 calculates a difference between the respective organic substance concentrations measured by the organic substance concentration measurement means 19 and the organic substance concentration measurement means 22, specifically, a value obtained by subtracting the organic substance concentration measured by the organic substance concentration measurement means 22 from the organic substance concentration measured by the organic substance concentration measurement means 19, and the organic substance concentration difference value calculation unit 23 sends the calculated value to the target TMP increase speed selecting unit 21 via the signal line 60.
The organic substance concentration measurement means 22 is means for measuring the concentration of organic substances contained in the filtered water, and may perform the measurement by an organic substance concentration sensor provided to the filtered water pipe 3, or may perform the measurement by the filtered water being supplied to the organic substance concentration sensor. Alternatively, the filtered water discharged from the filtration pump 4 may be sampled and the organic substance concentration thereof may be measured. The database 20 is connected to the target TMP increase speed selecting unit 21 via the signal line 57. In the database 20, water quality acquired by the past water treatments, e.g., the value obtained by subtracting the organic substance concentration measured by the organic substance concentration measurement means 22 from the organic substance concentration measured by the organic substance concentration measurement means 19, temporal change in TMP, and the like, are recorded and stored as a database.
The target TMP increase speed selecting unit 21 selects a target TMP increase speed RT on the basis of the data stored in the database 20 and the concentration difference calculated by the organic substance concentration difference value calculation unit 23 (the value obtained by subtracting the organic substance concentration measured by the organic substance concentration measurement means 22 from the organic substance concentration measured by the organic substance concentration measurement means 19). Preferably, the target TMP increase speed RT is 0.01 to 40 kPa/h. The other operations are the same as those in embodiment 1.
Here, not all the organic substances contained in the treatment target water 9 in the membrane separation tank 1 are necessarily cause of clogging of the separation membrane 2, and some of the organic substances pass through the separation membrane 2, to be contained in the filtered treated water 10. Therefore, by detecting a difference in the organic substance concentration between before and after passing through the separation membrane 2, i.e., by calculating the difference value between the concentration of organic substances contained in the treatment target water 9 in the membrane separation tank 1 and the concentration of organic substances contained in the filtered treated water 10, it is possible to grasp the amount of organic substances captured by the separation membrane 2, together with the amount of filtered water. That is, it is possible to indirectly calculate the amount of organic substances that can cause clogging of the separation membrane 2, and in particular, in the case of using an ultraviolet absorbance as the organic substance concentration, the amount of organic substances captured by the separation membrane 2 can be calculated accurately, and immediately because absorbance measurement can be instantly performed.
As described above, in the invention according to embodiment 3, it is possible to accurately calculate the concentration of organic substances that can cause clogging of the membrane, by calculating the difference value between the concentration of organic substances contained in the treatment target water 9 in the membrane separation tank 1 and the concentration of organic substances contained in the filtered water. Then, the target TMP increase speed RT is set in accordance with the difference value, and the membrane surface aeration flow amount is controlled so that the TMP increase speed is maintained at the target TMP increase speed RT. Therefore, it is possible to reduce the membrane surface aeration flow amount and reduce the operation cost for the entire device.
Next, a membrane separation device according to embodiment 4 of the present invention will be described with reference to
The organic substance concentration measurement means 19 in embodiment 4 of the present invention includes: a solid-liquid separation unit 24 which performs solid-liquid separation for suspended solids in the treatment target water 9 in the membrane separation tank 1, by any of filtration separation, centrifugal separation, and precipitation separation; and an organic substance concentration measurement unit 25 which measures the organic substance concentration in the liquid obtained through solid-liquid separation by the solid-liquid separation unit 24.
The treatment target water 9 in the membrane separation tank 1 is supplied to the solid-liquid separation unit 24, and is subjected to solid-liquid separation by any of filtration separation, centrifugal separation, and precipitation separation, whereby solid-liquid separated liquid 26 is obtained. The solid-liquid separated liquid 26 obtained by the solid-liquid separation unit 24 is supplied to the organic substance concentration measurement unit 25, and the organic substance concentration in the solid-liquid separated liquid 26 is measured.
In the case of performing filtration separation in the solid-liquid separation unit 24, preferably, the pore diameter of filter paper or a filtration membrane used for the filtration separation is 0.2 to 10 μm. However, this pore diameter is required to be greater than that of the separation membrane 2. If the pore diameter for the filtration separation is smaller than that of the separation membrane 2, the filter paper used for the filtration separation is to capture more organic substances than the separation membrane 2, in filtration separation. Therefore, it is impossible to accurately grasp the amount of organic substances that are captured by the separation membrane 2. The same applies for the case where the pore diameter of the filtration membrane is smaller than 0.2 μm. On the other hand, in the case where the pore diameter of the filtration membrane is greater than 10 μm, a solid material and a turbid component pass through the filter paper or the filtration membrane used for the filtration separation, so that the organic substance concentration cannot be measured accurately.
In the case of performing centrifugal separation in the solid-liquid separation unit 24, preferably, the centrifugal separation is performed with a gravitational acceleration of 1000 to 10000 G. If the gravitational acceleration is smaller than 1000 G, the solid-liquid separation is not sufficiently performed and a solid material and a turbid component pass through the filter paper or the filtration membrane used for the filtration separation. Therefore, the organic substance concentration cannot be measured accurately. If the gravitational acceleration is greater than 10000 G, the scale of the device is great and therefore the device cannot be installed on a side of the membrane separation device.
In the case of performing precipitation separation in the solid-liquid separation unit 24, the precipitation period is desired to be 15 minutes to 2 hours. If the precipitation period is shorter than 15 minutes, solid-liquid separation is not sufficiently performed and a solid material and a turbid component pass through the filter paper or the filtration membrane used for the filtration separation. Therefore, the organic substance concentration cannot be measured accurately. If the precipitation period is longer than 2 hours, the property of the treatment target water 9 changes, and therefore the organic substance concentration cannot be measured accurately.
Solid materials existing in the treatment target water 9, such as activated sludge, are deposited on the membrane surface, whereby clogging of the membrane occurs. However, this is suppressed by execution of membrane surface aeration. Some of organic substances in the treatment target water 9 stay at the surface of the separation membrane 2 and cannot reach the inside of the separation membrane 2 because the sizes thereof are large. Such organic substances can be removed by membrane surface aeration. The organic substances having smaller sizes penetrate into the separation membrane 2, so that some of them are captured by the separation membrane 2 and others pass through the separation membrane 2 to be discharged through the filtration pump 4 together with the filtered treated water 10. Such organic substances captured by the separation membrane 2 are clogging materials, which can cause increase in the TMP. The organic substances captured by the separation membrane 2 can be measured by the above-described method. That is, the organic substances in the treatment target water 9 that stay at the membrane surface and cannot reach the inside of the separation membrane 2, are removed in advance by filtration separation, centrifugal separation, precipitation separation, or the like, and the organic substance concentration of the treatment target water 9 from which such organic substances have been removed is measured, whereby the TMP increase speed can be accurately determined.
As described above, in the invention according to embodiment 4, the treatment target water in the membrane separation tank is subjected to solid-liquid separation by any of filtration separation, centrifugal separation, and precipitation separation, and the organic substance concentration in the liquid obtained by solid-liquid separation is measured, whereby the organic substances that can cause clogging of the membrane can be measured more accurately.
It is noted that the solid-liquid separated liquid 26 obtained by the solid-liquid separation unit 24 performing solid-liquid separation of the treatment target water 9 in the membrane separation tank 1, may be supplied to the organic substance index measurement means 27 of the organic substance concentration measurement means 19 described in embodiment 1. Thus, it is possible to measure the organic substance index of at least one of UV, TOC, COD, BOD, humic acid concentration, sugar concentration, and protein concentration. It has been confirmed that the substances corresponding to these indexes are readily captured by the separation membrane and can be used as indexes for clogging.
In
Next, a membrane separation device according to embodiment 5 of the present invention will be described with reference to
The target TMP increase speed setting means 13 in embodiment 5 of the present invention includes the database 20, the organic substance concentration measurement means 19, and the target TMP increase speed selecting unit 21, and in addition, includes at least one of: water temperature measurement means 28 for measuring the water temperature of the treatment target water in the membrane separation tank 1; MLSS measurement means 29 for measuring a mixed liquor suspended solid (MLSS, suspended solid in mixed liquor in aeration tank) concentration; and flux measurement means 30 for measuring the filtration flux of the separation membrane 2.
The water temperature measurement means 28 is connected via a signal line 65, the MLSS measurement means is connected via a signal line 66, and the flux measurement means is connected via a signal line 67, to the target TMP increase speed selecting unit 21. The other configurations are the same as those in embodiments 1 to 4, and therefore the description thereof is omitted.
Next, operation of the membrane separation device according to embodiment 5 will be described.
The water temperature measurement means 28 is means for measuring the water temperature of the treatment target water 9, and may perform the measurement by a water temperature sensor provided to the membrane separation tank 1, or may perform the measurement by the treatment target water 9 being supplied to the water temperature sensor. The MLSS measurement means 29 is means for measuring the MLSS concentration, the turbidity, the suspended solid (SS) concentration, or the like of the treatment target water 9, and may perform the measurement by an MLSS concentration sensor, a turbidity meter, or the like provided to the membrane separation tank 1, or may perform the measurement by the treatment target water being supplied to the MLSS concentration sensor, the turbidity meter, or the like. Alternatively, the treatment target water 9 may be sampled and the MLSS concentration, the SS concentration, the turbidity, or the like may be measured by manual analysis.
The flux measurement means 30 is means for measuring the filtration flux of the separation membrane 2, and performs the measurement by a flow rate sensor provided to the filtered water pipe 3, or calculates the flow rate by measuring the amount of water filtered per certain period. Further, the flow rate value is divided by the membrane area of the separation membrane 2, whereby the filtration flux can be measured. The values obtained by the water temperature measurement means 28, the MLSS measurement means 29, and the flux measurement means 30 are sent to the target TMP increase speed selecting unit 21 via the signal lines 65, 66, and 67, respectively.
The target TMP increase speed selecting unit 21 selects the membrane surface aeration flow amount appropriate for the water quality of the treatment target water 9 in the membrane separation device at present, on the basis of the past data of the TMP increase speed, the membrane surface aeration flow amount, the organic substance concentration, and the like sent from the database 20, the past operation data about the water temperature measurement means 28, the MLSS measurement means 29, and the flux measurement means 30, data about such matters obtained through experiments or the like in the past, and the like. In operation of the membrane separation device, preferably, the water temperature is 1 to 50° C. At a water temperature of 1° C. or lower or a water temperature of 50° C. or higher, the durability of the separation membrane 2 reduces, and thus it is difficult to perform stable operation of the membrane separation device. Preferably, the MLSS concentration and the SS concentration are 1 to 30000 mg/L.
Preferably, the turbidity of the treatment target water 9 is 0.1 to 10000 degrees. In the case where the MLSS concentration or the SS concentration is smaller than 1 mg/L or the turbidity is smaller than 0.1, filtration is not needed. In the case where the MLSS concentration or the SS concentration is 30000 mg/or higher, or the turbidity is 10000 degrees or higher, the separation membrane 2 is clogged in a short time, and therefore the treatment target water 9 having such water quality is not suitable to filtration. Preferably, the filtration flux of the separation membrane 2 is 0.01 to 10 m/day. If the filtration flux is smaller than 0.01 m/day, an enormous amount of separation membrane 2 is needed and this is not feasible in water treatment. If the filtration flux is 10 m/day or greater, the separation membrane 2 is clogged in a short time, and even if the separation membrane 2 is washed, the TMP is not restored. Therefore, filtration cannot be carried out.
Hereinafter, a specific control method for the membrane surface aeration flow amount will be described. As the water temperature decreases, the viscosity of the water increases, and thus the TMP increase speed increases. In addition, if the MLSS concentration, the SS concentration, the turbidity, or the like increases, the separation membrane 2 is more readily clogged, and thus the TMP increase speed increases. In addition, as the filtration flux increases, the rate at which the water passes through the separation membrane 2 increases, so that clogging is promoted and the TMP increase speed increases. Therefore, measuring such water quality items is important for operating the membrane separation device stably while keeping the TMP increase speed at an appropriate value, i.e., operating the membrane separation device while controlling the TMP increase speed.
Therefore, as the water temperature decreases, as the MLSS concentration, the SS concentration, or the turbidity increases, or as the filtration flux increases, the TMP increase speed increases. It is noted that one, some, or all of the water temperature measurement means 28, the MLSS measurement means 29, and the flux measurement means 30 may be used in combination.
As a database, the ones shown in
As shown in
In this case, even if not all of such data are prepared, it is possible to use them as a database by interpolating data thereamong. For example, in the case where data for water temperature of 15° C. and water temperature of 30° C. exist in the database, when operation is performed at a water temperature of 25° C., the average values of the membrane surface aeration flow amounts and the TMP increase speeds for both water temperatures may be used as a database. In this way, a new database may be formed by interpolation based on the existing database, or a relationship in which data are interpolated on the basis of the existing database may be prepared in advance to form a new database.
That is, a formula for calculating the TMP increase speed may be prepared using the membrane surface aeration flow amount, the organic substance concentration, the water temperature, the MLSS concentration, and the filtration flux as parameters. For example, the following formula can be used.
It is noted that, instead of using the sum of all the parameters, a formula including multiplication, division, exponentiation, and logarithm in a mixed manner may be prepared, and it is important to prepare a formula that can reproduce the past operation data.
[TMP increase speed]=α[membrane surface aeration flow amount]+β[organic substance concentration]+γ[water temperature]+δ[MLSS concentration]+ε[filtration flux](α, β, γ, δ, and εare constants) (1)
As described above, in the invention according to embodiment 5, it is possible to set the target TMP increase speed more accurately even if at least one of the organic substance concentration, the water temperature, and the MLSS concentration of the treatment target water 9 in the membrane separation tank 1 and the filtration flux of the separation membrane 2 has changed.
Next, a membrane separation device according to embodiment 6 of the present invention will be described with reference to
In
As described above, not all the organic substances contained in the treatment target water 9 in the membrane separation tank 1 are necessarily cause of clogging of the separation membrane 2, and some of the organic substances pass through the separation membrane 2, to be contained in the filtered treated water 10. Therefore, by detecting a difference in the organic substance concentration between before and after passing through the separation membrane 2, i.e., by calculating the difference value between the concentration of organic substances contained in the treatment target water 9 in the membrane separation tank 1 and the concentration of organic substances contained in the filtered treated water 10, it is possible to grasp the amount of organic substances captured by the separation membrane 2, together with the amount of filtered water. Thus, it is possible to directly confirm the amount of organic substances captured by the separation membrane 2, and therefore, when the organic substance concentration in the treatment target water 9 varies, the degree of clogging of the separation membrane 2 can be easily grasped and it becomes easy to take measures for reducing the organic substance concentration in the treatment target water 9 by decreasing the water treatment load, increasing the SRT, or increasing the dissolved oxygen concentration, for example.
Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples.
In a membrane separation device shown in
In Example 1, using the separation membrane 2 having a membrane area of 1 m2, the treatment target water 9 in the membrane separation tank 1 was filtered at a filtration flux of 2.0 m/day. In order to measure the organic substance concentration in the treatment target water, the treatment target water 9 was filtered by a filter having a pore diameter of 1 μm, and the absorbance (UV254) of the filtered liquid for a wavelength of 254 nm was measured. Further, on the basis of the measured value of the UV254, a target TMP increase speed was selected with reference to the relationship between the membrane surface aeration flow amount and the TMP increase speed shown in
One hour later from the start of the filtration, the value of the UV254 was 0.05 Abs/cm and the TMP increase speed at the inflection point was 0.4 kPa/h. Then, the membrane surface aeration flow amount of the membrane surface aeration device was controlled at 0.60 m3/hr/m2 so that the TMP increase speed measurement value was maintained at the target TMP increase speed RT. One more hour later from the start of the filtration, the water quality of the inflow water changed, so that the water quality of the treatment target water 9 in the membrane separation tank 1 also changed and the UV254 increased to 0.10 Abs/cm. The target TMP increase speed RT at that time was 0.7 kPa/h as shown in the database in
In Example 2, the inflow water 8 was supplied to the membrane separation tank 1, and using the separation membrane 2 having a membrane area of 1 m2, the treatment target water 9 in the membrane separation tank 1 was filtered at a filtration flux of 2.0 m/day. In order to measure the organic substance concentration in the treatment target water, the treatment target water 9 was filtered by a filter having a pore diameter of 1 μm, and the UV254 of the filtered liquid was measured. Further, in order to measure the concentration of organic substances contained in the filtered treated water 10, the UV254 of the filtered water was measured. The UV254 of the filtered liquid of the treatment target water 9 and the UV254 of the filtered water were outputted to the organic substance concentration difference value calculation unit 23. Then, on the basis of the organic substance concentration difference value, a target TMP increase speed was selected with reference to the relationship between the membrane surface aeration flow amount and the TMP increase speed shown in
One hour later from the start of the filtration, a difference ΔUV254 between the UV254 of the treatment target water 9 and the UV254 of the filtered treated water 10 was 0.02 Abs/cm, and the TMP increase speed at the inflection point was 0.4 kPa/h. Accordingly, the membrane surface aeration flow amount of the membrane surface aeration device was controlled at 0.6 m3/hr/m2 so that the TMP increase speed measurement value was maintained at the target TMP increase speed RT. However, one more hour later from the start of the filtration, the water quality of the inflow water changed, so that the water quality of the treatment target water 9 in the membrane separation tank 1 also changed and a difference between the UV254 of the treatment target water 9 and the UV254 of membrane filtered water 3 increased to 0.07 Abs/cm. At that time, the target TMP increase speed RT was 0.7 kPa/h as shown in the database in
In the comparative example, the same filtration operation as in Example 1 was performed except that the target TMP increase speed RT was set to a fixed value in advance without measuring the organic substance concentration in the treatment target water 9. Target TMP increase speed input means 31 fixed the target TMP increase speed R7 at 0.4 kPa/h and outputs this target TMP increase speed to the TMP increase speed comparing means 15. Further, the membrane surface aeration flow amount per membrane area, of the membrane surface aeration device, was controlled at 0.6 m3/h/m2 so that the TMP increase speed measurement value was maintained at the target TMP increase speed RT. However, one more hour later from the start of the filtration, the water quality of the inflow water changed, so that the water quality of the treatment target water 9 in the membrane separation tank 1 also changed. Accordingly, in order to maintain the TMP increase speed at the target TMP increase speed 0.4 kPa/h, the membrane surface aeration flow amount was set at 1.2 m3/h/m2 as shown by broken-line circles in
In Example 1 and Example 2, as compared to the comparative example, the target TMP increase speed could be changed in accordance with the organic substance concentration in the treatment target water or a difference value between the organic substance concentration in the treatment target water and the organic substance concentration in the filtered water. Therefore, in Example 1 and Example 2, after the property of the treatment target water of the membrane separation tank 1 changed, the TMP increase speed could be maintained with the membrane surface aeration flow amount smaller than that in the comparative example, whereby power-saving operation of the membrane separation device was achieved.
It is noted that the TMP increase speed changing means 12 is configured from a processor 100 and a storage device 101 as shown in a hardware example in
Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments. Various design modifications may be made, and within the scope of the present invention, the embodiments may be freely combined with each other, or each of the embodiments may be modified or simplified as appropriate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-057090 | Mar 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/040283 | 11/8/2017 | WO | 00 |
