JP4872391B2 - Membrane separation device and membrane separation method - Google Patents

Description

  The present invention relates to a membrane separation apparatus and a membrane separation method for subjecting water to be treated to membrane filtration with a separation membrane such as a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), and a nanofiltration membrane (NF membrane).

  When the water to be treated is filtered by this type of membrane separation apparatus, dirt adheres to the separation membrane, and thus membrane cleaning is performed by intermittently supplying a cleaning fluid (water and / or gas). In this membrane cleaning, backwashing is often performed by flowing a cleaning fluid such as membrane filtered water from the secondary side to the primary side of the membrane separation apparatus. However, flushing that distributes the cleaning fluid to the primary side of the separation membrane is performed. Sometimes done.

Regarding this backwashing control method, Japanese Patent No. 2876978 detects the organic substance concentration and turbidity in the water to be treated, and the film concentration depends on the organic substance concentration or the ratio of the organic substance concentration and turbidity. Controlling the washing time or filtration time is described.
Japanese Patent No. 2876978

  As the inventor conducted various studies, it was found that the filtration performance of the separation membrane may not be sufficiently recovered even if the membrane cleaning time is increased as the concentration of organic matter in the water to be treated increases. It was.

  An object of the present invention is to provide a membrane separation apparatus and a membrane separation method in which filtration performance is reliably and sufficiently recovered by washing a separation membrane obtained by filtering water containing organic matter.

The membrane separation apparatus according to the present invention (Claim 1) supplies the raw water from the primary side, discharges the permeated water that has permeated the separation membrane from the secondary side, and supplies the cleaning fluid to the separation membrane. Separation membrane cleaning means for cleaning, organic substance concentration measuring means for measuring the organic substance concentration in the permeated water, and control means for controlling the supply speed of the cleaning fluid based on the measured value of the organic substance concentration measuring means A membrane separation apparatus, wherein the cleaning means supplies the cleaning fluid from the secondary side of the membrane separation means, and discharges the cleaning fluid that has permeated the separation membrane from the primary side to backwash the separation membrane. And the control means increases the backwash speed when the measured value of the organic substance concentration measuring means becomes a predetermined value or more .

Membrane separation apparatus of claim 2, Oite to claim 1, wherein the organic substance concentration measuring means is characterized in that it is designed to measure the concentration of organic substances from the ultraviolet absorbance in the wavelength range of 200 to 400 nm.

The membrane separation method of the present invention (Claim 3 ) includes a membrane separation step of supplying raw water from the primary side of the membrane separation means and discharging permeated water that has passed through the separation membrane from the secondary side of the membrane separation means, and a cleaning fluid And a separation membrane cleaning step of cleaning the separation membrane by supplying water, measuring an organic substance concentration in the permeated water, and controlling a supply rate of the cleaning fluid based on the measured value of the organic substance concentration In the membrane separation method, the washing step supplies the washing fluid from the secondary side of the membrane separation means, discharges the washing fluid that has passed through the separation membrane from the primary side, and backwashes the separation membrane. It is a process and is characterized in that the backwashing speed is increased when the measured value of the organic substance concentration becomes a predetermined value or more .

A membrane separation method according to a fourth aspect is characterized in that, in the third aspect , the organic matter concentration in the permeated water is measured from the absorbance of ultraviolet light within a wavelength range of 200 to 400 nm.

  According to the present invention, by controlling the supply rate of the cleaning fluid based on the organic matter concentration of the permeated water, the membrane filtration performance can be sufficiently recovered according to the organic matter concentration even when the organic matter concentration in the water to be treated is high. be able to. Further, it is possible to prevent the cleaning fluid from being supplied in large quantities and the product water from being wastedly consumed for cleaning the membrane or deteriorating the membrane.

  That is, by controlling the supply rate of the cleaning fluid to the separation membrane based on the organic matter concentration of the permeated water, it is possible to adopt appropriate cleaning conditions corresponding to the quality of the raw water and the permeated water, resulting in a water recovery rate. Can be maintained at a high value, and the permeation flux of the membrane can be stabilized at a high value.

  Although it is conceivable to control the supply rate of the cleaning fluid based on the organic matter concentration of the raw water, contamination of the organic matter concentration detection sensor (for example, an optical acid cell) progresses by continuing the treatment for a long period of time. As a result, the control of the supply speed of the cleaning fluid is insufficient due to measurement errors. On the other hand, if the organic substance concentration of the permeated water, stable control can be performed over a long period of time without the problem of measurement errors due to such sensor contamination.

In addition, the organic substance density | concentration of permeated water can be easily measured from the light absorbency of the ultraviolet light within the range of wavelength 200-400 nm (Claim 2 , 4 ). Although the organic substance concentration in the permeated water can be measured by a TOC meter or a COD meter, the absorbance of ultraviolet light is preferable because the organic substance concentration can be easily and quickly obtained.

  Hereinafter, embodiments of the membrane separation apparatus and the membrane separation method of the present invention will be described in detail.

  The raw water to be treated by the present invention contains organic matter, and examples include natural water such as river water and groundwater, as well as various factory wastewater, agricultural wastewater, and sewage. The organic matter contained in the raw water is not particularly limited. Natural water often contains humic acid, but naturally this humic acid is also a kind of organic matter of the present invention.

  In the present invention, when washing the separation membrane for performing the membrane separation treatment of raw water, the concentration of organic substances in the permeated water is measured, and the washing conditions of the separation membrane are controlled based on this measured value.

  The organic substance concentration in the permeated water may be measured with a TOC meter or a COD meter, but it is convenient and quick to obtain it from the absorbance of ultraviolet light. Ultraviolet light having a wavelength of 200 to 400 nm, for example, a wavelength of 260 nm is suitable, and this absorbance corresponds to the absorbance of organic matter in the permeated water. The absorbance may be measured continuously or intermittently once every 1 to 10 minutes. Further, an average value of absorbance measurement values for 30 seconds to 1 day may be obtained, and this value may be used as an index value for control.

  Examples of the separation membrane that separates raw water from the membrane include MF membranes, UF membranes, NF membranes, and RO membranes. The membrane separation device may be of a cross flow type or a whole amount filtration type.

Separation membrane cleaning methods include:
(1) Ordinary backwash (wash water without chemicals (treated water (membrane permeate), city water, industrial water, etc.) is supplied from the secondary side of the membrane, permeated through the separation membrane, and discharged from the primary side. What)
(2) Backwashing with chemicals (supplying chemicals from the secondary side of the membrane, permeating through the separation membrane and discharging from the primary side)
(3) Ordinary chemical cleaning (circulating cleaning chemicals to the primary side of the membrane)
(4) Flushing cleaning (Flushing fluid to the primary side of the membrane)
And two or more of these may be used in combination.

  Among these, in particular, in the case of backwashing with the chemical solution (2), a method of alternately adding an acid and alkali in the vicinity of an equal specified concentration to the backwashing water is preferably used. In this case, after backwashing with one of the acid and alkali cleaning chemicals, it is allowed to stand for a certain period of time, and then backwashed with water to which no cleaning chemicals are added (treated water, city water, industrial water, etc.), then acid And after washing back with the other cleaning chemical solution of alkali, it may be allowed to stand for a certain period of time, and finally backwashed with water to which no chemical solution is added (treated water, city water, industrial water, etc.). Ordinary backwashing and chemical backwashing may be alternately performed.

  The alkali of the cleaning chemical is preferably sodium hypochlorite or sodium hydroxide, and examples of the acid include sulfuric acid, hydrochloric acid, nitric acid, citric acid, oxalic acid, ascorbic acid, sodium bisulfite and the like. It is not limited to these. An alkali and an acid may be used individually by 1 type, and may use 2 or more types together.

In addition, when using an acid and an alkali together, it is preferable that each density | concentration is the substantially same prescription | regulation (N). Usually, the acid and alkali concentrations are preferably about 1 × 10 ^{−3 to} 0.5N.

  In such a separation membrane cleaning process, the supply rate of the cleaning fluid is controlled.

  A more specific method for controlling the cleaning conditions is as follows.

(1) In the case of normal backwashing Simple water backwashing without adding chemicals is usually performed at a rate of once every 30 seconds to 6 hours, preferably 5 minutes to 3 hours, particularly preferably 10 minutes to 3 hours. Is done. The supply speed of the cleaning fluid at this time is controlled by fluctuations in the organic substance concentration of the permeated water. Specifically, it is preferable to set about 1 to 10 threshold values of the organic substance concentration serving as a control reference, and to set the supply rate of the cleaning fluid in the backwashing with water (permeation flux of the cleaning fluid). .

(2) Backwashing with a chemical solution The chemical solution backwashing is preferably performed in combination with the above-described normal backwashing. In this case, normal backwashing is performed at the above-described cleaning intervals, and further, chemical backwashing is performed once every 0.5 to 10 days. The supply rate of the cleaning fluid in this chemical liquid backwashing is controlled by the variation in the organic matter concentration of the permeated water. Specifically, one to three organic substance concentration thresholds serving as control criteria are set, and the cleaning fluid supply speed is set for each.

Note that the supply rate of the cleaning fluid in the chemical backwashing may be controlled and the cleaning fluid supply rate in the normal backwashing may be controlled based on the organic matter concentration of the permeated water. Is constant, and only the supply rate of the cleaning fluid for chemical backwashing can be controlled based on the organic matter concentration of the permeated water, or vice versa .

  In addition, when sodium hypochlorite is used as a chemical solution, it may be used in the same manner as the above-described “normal backwashing”. That is, when sodium hypochlorite is used as a chemical solution, the washing interval is 30 seconds to 6 hours, preferably 5 minutes to 3 hours, particularly preferably once every 10 minutes to 3 hours. Or may be used in combination with other chemical solutions or chemical solution backwashing using high-concentration sodium hypochlorite.

(3) Ordinary chemical cleaning Basically, chemical cleaning is performed when the membrane differential pressure exceeds a set value or when the converted membrane permeation flux (the membrane permeation flux when the temperature and pressure are set to predetermined values). However, in the present invention, the supply rate of the cleaning fluid in the chemical cleaning may be controlled by, for example, the integrated value of the organic matter concentration of the permeated water described above.

(4) Gas cleaning As for the gas cleaning, the supply rate of the cleaning fluid may be controlled in the same manner as in the case of the above normal back cleaning.

  Further, in (2) chemical liquid backwashing and (3) chemical washing, the chemical concentration can be controlled according to the organic substance concentration in the permeated water. In this case, the chemical concentration may be increased in proportion to the organic matter concentration of the permeated water, and threshold control may be performed.

  Also in this case, the supply speed of the cleaning fluid may be increased in proportion to the organic substance concentration of the permeated water, or threshold control may be performed.

  In the present invention, the higher the organic matter concentration in the permeated water, the higher the cleaning condition, that is, the higher the supply speed of the cleaning fluid, which is controlled. In this case, the organic matter concentration of the permeated water and the supply of the cleaning fluid are controlled. The speed may be linearly proportional, and the supply rate of the cleaning fluid may be increased stepwise as the organic concentration increases. For example, the relationship between the concentration of organic substances in the permeated water and the minimum required cleaning fluid supply speed that sufficiently restores the filtration performance is obtained in advance by experimentation, and this relationship can be mathematically expressed or stored directly in the computer memory. The supply speed of the cleaning fluid may be determined based on this.

  FIG. 2 is a graph schematically showing the results obtained by the inventor's study on the relationship between the humic acid concentration in the permeated water and the supply rate of the cleaning fluid necessary to sufficiently recover the membrane differential pressure. It is.

  The membrane permeation flux Jc of FIG. 2 increases rapidly when the organic permeate concentration is the same, and when the permeate flux is set to a higher membrane permeation flux, Indicates the limit value at which operation becomes impossible.

In FIG. 2, u ₁ , u ₂ , and u ₃ are the supply speeds of the cleaning fluid, and u ₁ <u ₂ <u ₃ . When the membrane cleaning is controlled so that the permeation flux recovers to A [m / d] and the operation is performed with this permeation flux, the supply rate of the washing water is set to u ₁ when the humic acid concentration is 0.8 a or less. and then, and _{u 2} the feed rate of the wash water in 0.8A～0.8B, the feed rate of the wash water in 0.8b~0.8c and _{u 3.} When the humic acid concentration C ₀ is a and the washing water supply rate is u ₁ , the permeation flux becomes the critical membrane permeation flux and the differential pressure increases rapidly. It is because there is a possibility of doing.

  Thus, by increasing the supply rate of the cleaning fluid as the organic matter concentration in the permeated water increases, the membrane performance of the separation membrane can be reliably and sufficiently recovered even when the organic matter concentration in the raw water is high. In addition, when the organic substance concentration in the permeated water is low, the supply rate of the cleaning fluid is reduced accordingly, so that the consumption of cleaning fluid such as cleaning chemicals is small, and deterioration of the membrane can be prevented. When membrane permeated water is used as rinsing water or cleaning fluid after chemical cleaning, the water recovery rate can be increased by reducing the supply rate of the cleaning fluid.

Embodiments of a membrane separation apparatus and a membrane separation method of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a system diagram showing an embodiment of the membrane separation apparatus of the present invention.

  In FIG. 1, 1 is a raw water tank, 2 is a membrane module, 3 is a permeated water tank, 4 is an organic substance concentration sensor, 5 is a control device, 6 is an alkali storage tank, and 7 is an acid storage tank. The pipe 12 for supplying the raw water in the raw water tank 1 to the membrane module 2 includes a water supply pump 12P and a bubble 12V. A bubble 13V is provided in the pipe 13 for supplying the membrane permeated water of the membrane module 2 to the permeated water tank 3, and the alkali in the alkali storage tank 6 passes through the pipe 17 from the alkali chemical injection pump 17P. It is arranged so that the acid in the acid storage tank 7 is supplied via the pipe 18 by the acid chemical injection pump 18P, and the permeate in the permeate tank 3 is supplied via the pipe 15 by the backwash pump 15P. ing.

  Reference numeral 16 denotes a backwash drain discharge pipe, and reference numeral 14 denotes a membrane permeate (treated water) discharge pipe. Each pipe 13, 15, 16, 17, 18 is provided with a valve 13 V, 15 V, 16 V, 17 V, 18 V, and the detected value of the organic substance concentration sensor 4 is input to the control device 5, and from the control device 4 A control signal is output to each pump 12P, 15P, 17P, 18P and each valve 12V, 13V, 15V, 16V, 17V, 18V.

  When the raw water is subjected to membrane separation treatment, the valves 12V and 13V are opened, the other valves are closed and the pump 12P is operated, and the raw water introduced into the raw water tank 1 from the pipe 11 is connected to the feed water pump 12P and the valve 12V from the pipe 12. To the primary side 2a of the membrane module 2. In this embodiment, the membrane module 2 is a total filtration method, but may be a cross flow method. The membrane permeated water that has permeated the membrane and entered the secondary side 2b is introduced into the permeated water tank 3 through the pipe 13, and is discharged out of the system through the pipe 14. A pipe 16 for taking out backwash drainage is connected to the primary side 2 a of the membrane module 2.

  In order to backwash the membrane module 2 with water or to rinse after the chemical liquid backwashing, the water in the permeated water tank 3 can be supplied to the pipe 13 upstream of the valve 13V via the pipe 15. Further, in order to clean the membrane module 2 with the chemical solution, the acid solution in the acid storage tank 7 can be supplied to the pipe 13 upstream of the valve 13V via the pipe 18, and the alkali solution in the alkali storage tank 6 can be supplied. Can be supplied via the pipe 17.

  When the membrane module 2 is backwashed with water or rinsed after backwashing with a chemical solution, the pump 12P is stopped, the valves 12V, 13V, 17V, and 18V are closed, the valves 15V and 16V are opened, and the pump 15P is operated. Thereby, the permeated water in the permeated water tank 3 is supplied to the secondary side 2b of the membrane module 2 through the pipes 15 and 13 and permeates the membrane in the reverse direction to the primary side 2a. Discharged.

  When the membrane module 2 is backwashed with alkali or acid, the pump 12P is stopped, the valves 12V and 13V are closed, the valve 17V or 18V is opened, the valve 16V is opened, and the pump 17P or 18P is operated. Then, the valve 15V is opened to operate the pump 15P, and a predetermined amount of water is sent from the permeate tank 3 to the pipe 13 via the pipe 15, and sent to the membrane module 3 while diluting alkali or acid from the pipe 17 or 18.

  The control device 5 to which the detection value of the organic substance concentration sensor 4 such as an absorbance measuring device in the permeated water tank 3 is input is used for the backwashing fluid at the time of water backwashing or chemical backwashing according to the detection value of the organic substance concentration sensor 4. Control the feed rate. For example, the control device 5 controls the rotational speeds of the pumps 15P, 17P, and 18P so as to obtain a predetermined supply speed. As means for controlling the supply rate of the backwash fluid during this water backwashing or chemical solution backwashing, a method of changing the rotational speed of a centrifugal pump such as a centrifugal pump, or once holding the membrane permeated water in a pressure water tank, Examples include a method of changing the pressurized pressure of the water tank. Further, the frequency of chemical backwashing and / or the concentration of chemical supplied to the membrane module 2 (injection amount of alkali or acid from the tank 6 or 7) may be controlled. The control of the chemical concentration is controlled by the pumps 17P and 18P. This can be performed by using an inverter or pulse control using a variable discharge amount type pump or the like.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1
According to the present invention, raw water was treated in the order of raw water tank → membrane module.
As the membrane module, a small laboratory module (membrane area: 0.14 m ² ) of an internal pressure hollow fiber ultrafiltration membrane (hydrophilic polysulfone, molecular weight cut off 150,000) manufactured by Kuraray Co., Ltd. was used.

  As raw water, humic acid dissolved in tap water so as to be 4.5 mg / L was used.

  An S :: CAN sensor (S :: CAN MESSTECHNIK GMBH (Austria), cell width 50 mm), which can scan the ultraviolet to visible light region with a wavelength of 200 nm to 700 nm, is immersed in the permeating water tank as an absorbance measuring device. Was measured at a wavelength of 260 nm.

The membrane permeation flux in the membrane module was fixed at 3.0 m / d, and normal water backwashing was performed for 1 minute every 29 minutes. This water washing is performed by adjusting the flow rate so that the back washing speed per membrane area is 5 m / d. When the absorbance (E ₂₆₀ ) is 0.075 abs or more, the back washing speed is increased to 15 m / d. It was decided.

The rate of increase in the differential pressure of the separation membrane at this time was examined, and the results are shown in Table 1 together with the absorbance (E ₂₆₀ ) of the permeated water and the employed backwash rate.

Comparative Example 1
In Example 1, the treatment was performed in the same manner except that tap water without humic acid was used as raw water, the membrane permeation flux was 1.5 m / d, and the backwash rate was constant at 5 m / d. . At this time, the absorbance (E ₂₆₀ ) of the permeated water and the rate of increase in the membrane pressure difference were as shown in Table 1.

Comparative Example 2
In Comparative Example 1, the treatment was performed in the same manner except that the membrane permeation flux was 3.0 m / d. At this time, the absorbance (E ₂₆₀ ) of the permeated water and the rate of increase in the membrane pressure difference were as shown in Table 1.

Comparative Example 3
In Example 1, the treatment was performed in the same manner except that the backwash speed was fixed at 5 m / d. At this time, the absorbance (E ₂₆₀ ) of the permeated water and the rate of increase in the membrane pressure difference were as shown in Table 1.

Comparative Example 4
In Example 1, when the permeated water absorbance (E ₂₆₀ ) was 0.075 abs or more, instead of increasing the backwashing speed, a regular water backwashing was performed every 9 minutes with a backwashing speed of 5 m / min. The treatment was carried out in the same manner except that the treatment was carried out for 1 minute at d.

From Table 1, the following is clear.
In Comparative Examples 1 and 2 (membrane permeation flux 1.5 or 3.0 m / d) in which humic acid was not added to the raw water, the membrane differential pressure increase rate was stable at 1.0 kPa or less, In the case of Comparative Example 3 (membrane permeation flux 3.0 m / d) in which the absorbance (E ₂₆₀ ) of permeated water was significantly increased by adding 4.5 mg / L of humic acid, the rate of increase in the membrane differential pressure was It became 10 kPa / d or more, and it was impossible to continue stable operation.

On the other hand, Example 1 (membrane permeation flux 3) was added to the backwash speed of 15 m / d when the absorbance (E ₂₆₀ ) of permeated water was significantly increased by adding 4.5 mg / L of humic acid. In the case of 0.0 m / d), the rate of increase in the membrane differential pressure was stable at 1.0 kPa / d or less.

It is a systematic diagram which shows embodiment of the membrane separator of this invention. It is a graph which shows typically the relation between humic acid concentration and a limiting membrane permeation flux.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Membrane module 3 Permeated water tank 4 Organic substance concentration sensor 5 Control apparatus 6 Alkali storage tank 7 Acid storage tank

Claims (4)

Membrane separation means for supplying raw water from the primary side and discharging permeated water that has passed through the separation membrane from the secondary side;
A separation membrane cleaning means for cleaning the separation membrane by supplying a cleaning fluid;
An organic matter concentration measuring means for measuring the organic matter concentration in the permeated water;
A membrane separation device having control means for controlling the supply speed of the cleaning fluid based on the measurement value of the organic matter concentration measurement means ,
The cleaning means is means for supplying the cleaning fluid from the secondary side of the membrane separation means, discharging the cleaning fluid that has passed through the separation membrane from the primary side, and backwashing the separation membrane,
The control means increases the backwashing speed when the measured value of the organic substance concentration measuring means exceeds a predetermined value . Oite to claim 1, wherein the organic substance concentration measurement means, membrane separation device, characterized in that measures the concentration of organic substances from the ultraviolet absorbance in the wavelength range of 200 to 400 nm. A membrane separation step of supplying raw water from the primary side of the membrane separation means and discharging permeated water that has permeated through the separation membrane from the secondary side of the membrane separation means;
In a membrane separation method having a separation membrane cleaning step of cleaning the separation membrane by supplying a cleaning fluid,
A membrane separation method for measuring an organic substance concentration in the permeated water and controlling a cleaning speed of the cleaning fluid based on a measured value of the organic substance concentration ,
The cleaning step is a step of supplying the cleaning fluid from the secondary side of the membrane separation means, discharging the cleaning fluid that has passed through the separation membrane from the primary side, and backwashing the separation membrane,
A membrane separation method characterized by increasing the backwashing speed when the measured value of the organic substance concentration becomes a predetermined value or more . 4. The membrane separation method according to claim 3 , wherein the organic substance concentration in the permeated water is measured from the absorbance of ultraviolet light within a wavelength range of 200 to 400 nm.

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