JP5151009B2 - 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). As this membrane cleaning, backwashing is often performed in which a cleaning fluid such as membrane filtered water is allowed to flow from the secondary side to the primary side of the membrane separation device.

  Water backwashing with membrane filtered water is usually performed at a high frequency of about once every 30 seconds to 60 minutes. Even if this water backwashing is performed, dirt gradually accumulates in the film and cannot be removed by water backwashing. Therefore, the film is washed with a chemical solution at a low frequency of about once every 0.5 days to 10 days. As this chemical solution, an acid or an alkali is often used. This chemical cleaning is performed periodically or when the filtration differential pressure does not recover even after backwashing with water. After this chemical cleaning, the membrane is rinsed with clean water and then returned to normal filtration operation.

Regarding the above control method of backwashing using filtered water, Japanese Patent No. 2876978 detects the organic substance concentration and turbidity in the water to be treated, and the ratio of the organic substance concentration or the organic substance concentration to turbidity. It is described that the cleaning time or filtration time of the membrane is controlled according to the size of the film.
Japanese Patent No. 2876978

  Japanese Patent No. 2876978 does not disclose how to control the frequency of chemical cleaning of the separation membrane.

  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 chemical cleaning of a separation membrane obtained by filtering organic substance-containing water.

The membrane separation device according to claim 1 is a membrane separation means for supplying water to be treated from the primary side and discharging filtered water that has permeated through the separation membrane from the secondary side, and water or washing on the secondary side of the membrane separation means. In a membrane separation apparatus having a cleaning means for supplying a chemical solution and discharging the liquid that has passed through the separation membrane from the primary side to wash the separation membrane, an ultraviolet absorbance in the wavelength range of 200 to 400 nm and a wavelength of 400 to 800 nm Organic substance concentration measuring means for measuring the organic substance concentration in the water to be treated from the difference in visible light absorbance within the range, and the membrane separation means are backwashed with water once every 10 to 180 minutes, and the organic substance concentration The higher the measurement value of the measurement means, the shorter the cleaning interval of the membrane separation means with the cleaning chemical solution, and the chemical solution cleaning frequency is 1 in 6 to 12 hours when the organic substance concentration is 2.3 to 4.5 mg / L. Control to control the frequency of times It is characterized in that it has a stage.

A membrane separation apparatus according to a second aspect of the present invention is the membrane separation apparatus according to the first aspect, wherein the control means increases the concentration of the cleaning chemical as the concentration of organic matter in the water to be treated increases.

The membrane separation method according to claim 3 includes a step of supplying treated water to the membrane separation means to obtain membrane filtered water, and a liquid that supplies water or a cleaning chemical to the secondary side of the membrane separation means and permeates the separation membrane. In the membrane separation method having a separation membrane cleaning step of discharging the primary side from the primary side, the organic matter in the treated water is determined from the difference between the ultraviolet absorbance in the wavelength range of 200 to 400 nm and the visible light absorbance in the wavelength range of 400 to 800 nm. Concentration is measured, and the membrane separation means is backwashed with water once every 10 to 180 minutes, and the higher the measured value of the organic substance concentration, the shorter the cleaning interval of the membrane separation means with the cleaning chemical solution, And when an organic substance density | concentration is 2.3-4.5 mg / L, a chemical | medical solution washing | cleaning frequency is made into the frequency once for 6 to 12 hours, It is characterized by the above-mentioned.

According to a fourth aspect of the present invention, the membrane separation method according to the third aspect is characterized in that the concentration of the cleaning chemical is increased as the concentration of organic matter in the water to be treated is higher.

Even if organic matter concentration in the water to be treated is high, by controlling the cleaning interval by the wash liquor during the chemical cleaning of the separation membrane, it has been found that the filtration performance of the separation membrane is sufficiently restored. The present invention is based on such knowledge. According to the present invention, the membrane filtration performance can be sufficiently recovered.

  Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a system diagram of a membrane separation apparatus according to an embodiment.

  The raw water is sent from the raw water tank 1 to the primary side 3a of the membrane module 3 through the raw water pump 2 and the valve 2a. In this embodiment, the membrane module 3 is a total filtration method, but may be a cross flow method. The membrane permeated water (filtrated water) that has permeated the membrane and entered the secondary side 3b is introduced into the filtered water tank 5 through the pipe 4 having the valve 4a, and is taken out from the pipe 6 as membrane filtered water. A pipe 20 for backwash drainage having a valve 21 is connected to the primary side 3 a of the membrane module 3.

  In order to back-wash the membrane module 3 with water or to rinse it after chemical cleaning, water in the filtered water tank 5 can be supplied to the pipe 4 upstream of the valve 4a via the valve 7, the pipe 8, and the pump 9. It is said that. Further, in order to perform chemical cleaning of the membrane module 3, the acid solution in the acid storage tank 10 can be supplied to the pipe 4 upstream of the valve 4a via the valve 11, the pump 12, and the pipe 13. The alkaline solution in the alkaline storage tank 14 can be supplied via a valve 15, a pump 16 and a pipe 17.

  When the membrane module 3 is back-washed with water or rinsed after chemical cleaning, the pump 2 is stopped, the valves 2a, 4a, 11, 15 are closed, the valves 7, 21 are opened, and the pump 9 is operated. As a result, the filtered water in the filtered water tank 5 is supplied to the secondary side 3b of the membrane module 3 via the pipes 8 and 4 and permeates the membrane in the reverse direction to the primary side 3a. Discharged.

  When the membrane module 3 is chemically cleaned with acid or alkali, the pump 2 is stopped, the valves 2a and 4a are closed, the valve 11 or 15 is opened and the valve 21 is opened, and the pump 12 or 16 is operated. The valve 9 is opened and the pump 9 is operated to send a predetermined amount of water from the filtered water tank 5 to the pipe 4 and to the membrane module 3 while diluting acid or alkali.

  In addition, when changing the density | concentration of the acid or alkali supplied to the membrane module 3, the injection amount of an acid or an alkali is changed by carrying out inverter or pulse control of the pump 12 or 16. FIG.

  An organic substance concentration sensor 23 is installed in the raw water tank 1, and the detected value is input to the controller 24. The controller 24 controls the frequency of chemical cleaning and / or the concentration of chemical supplied to the membrane module 3 (acid or alkali injection amount from the tank 10 or 14) according to the detection value of the organic substance concentration sensor 23.

  The raw water may be first coagulated and then supplied to the raw water tank 1. In this case, a flocculant adding means and a solid-liquid separation means for separating the coagulated flocs are provided upstream of the raw water tank 1. However, there is no need for solid-liquid separation means.

  The treated water to be treated by the membrane separation apparatus and the membrane separation method of the present invention includes organic substances, and examples include natural water such as river water and groundwater, various factory wastewater, agricultural wastewater, and sewage. The The organic matter contained in the water to be treated 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.

  Examples of the separation membrane include an MF membrane, a UF membrane, and an NF membrane.

  As described above, the membrane separation device may be of a cross flow type or a whole amount filtration type.

  The concentration of organic matter in the water to be treated may be measured with a TOC meter or a COD meter, but it is preferable because it is simple, quick, and preferable from the difference in absorbance between ultraviolet light and visible light. As the ultraviolet light, a wavelength of 200 to 400 nm is suitable, and the absorbance at this wavelength is the total value of the absorbance of the organic substance and the absorbance of the turbidity component mainly composed of inorganic clay mineral. The visible light preferably has a wavelength of 600 to 800 nm, and the absorbance at this wavelength is the absorbance due to the turbidity component. Therefore, the organic substance concentration in the for-treatment water can be detected from the difference in absorbance at both wavelengths.

In the present invention, the membrane of the membrane module is preferably backwashed with water at a high frequency of about once every 10 to 180 minutes, and with a chemical solution at a low frequency of about once every 0.5 to 7 days. In the present invention, the chemical concentration and / or the cleaning interval (cleaning frequency) for chemical cleaning are controlled according to the organic matter concentration in the raw water. Normally, the higher the concentration of organic matter in the raw water, the higher the chemical concentration or the greater the frequency of cleaning.

  In the present invention, when the concentration of the chemical solution or the cleaning frequency is increased as the concentration of the organic substance in the water to be treated increases, the organic substance concentration and the chemical solution concentration or the cleaning frequency may be linearly proportional, and as the organic matter concentration increases. The chemical concentration or the cleaning frequency may be increased stepwise. For example, the relationship between the concentration of organic substances in the water to be treated and the necessary minimum chemical concentration or washing frequency to sufficiently recover the filtration performance is obtained in advance by experiments, and this relationship is mathematically expressed or stored in the computer memory as it is. In addition, the chemical concentration or the cleaning frequency 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 water to be treated and the cleaning frequency necessary to sufficiently recover the membrane filtration differential pressure. is there.

Marginal membrane filtration flux Jc in FIG. 2, when the organic substance concentration is the same concentration of the raw water, when set to more membrane filtration flux, the rate of increase of transmembrane pressure difference ΔP increases rapidly, membrane filtration Indicates the limit value at which operation becomes impossible.

In FIG. 2, f ₁ , f ₂ , and f ₃ are the frequency of chemical cleaning, and f ₁ <f ₂ <f ₃ . When the membrane flux is controlled so that the filtration flux recovers to A [m / d] and the filtration operation is performed with this filtration flux, the frequency of chemical washing is f ₁ when the humic acid concentration is 0.8a or less. and then, the frequency of 0.8a~0.8b the chemical cleaning and _{f 2,} and _{f 3} the frequency of chemical cleaning at 0.8B～0.8C. When the humic acid concentration C ₀ is a and the frequency of chemical cleaning is f ₁ when the humic acid concentration C ₀ is a, the reverse filtration flux becomes the limiting membrane filtration flux, and the pressure factor is rapidly increased. This is because there is a risk of the rise.

  Although not shown, it was recognized that there is a relationship shown in FIG. 2 between the organic substance concentration and the chemical concentration in the raw water.

  Thus, by increasing the concentration of the cleaning chemical and the frequency of chemical cleaning as the concentration of the organic substance in the water to be treated increases, the membrane filtration performance of the separation membrane can be reliably and sufficiently recovered even when the concentration of the organic substance is high. In addition, when the organic matter concentration in the water to be treated is low, the chemical solution concentration is lowered or the chemical cleaning frequency is lowered accordingly, so that the consumption of the cleaning chemical solution is small and the cleaning chemical solution can be saved. Can be prevented. When membrane filtered water is used as rinsing water after chemical cleaning, the water recovery rate can be increased by saving the frequency of chemical cleaning.

  As a result of various experiments, it was found that when the frequency of chemical cleaning is increased in accordance with the increase in the concentration of organic substances in the raw water, a sufficient chemical cleaning effect can be obtained even if the concentration of the chemical is decreased. .

  As the alkali of the cleaning chemical solution, sodium hypochlorite and sodium hydroxide are suitable, and as the acid, one or two of sulfuric acid, hydrochloric acid, nitric acid, citric acid, oxalic acid, ascorbic acid, sodium bisulfite are used. Although seed | species or more is illustrated, it is not limited to this.

In addition, when using an acid and an alkali together like FIG. 1, 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.

Example 1
In the membrane separation apparatus shown in FIG. 1, as a membrane module 3, a small laboratory module (membrane area: 0.14 m ² ) of Kuraray's internal pressure hollow fiber ultrafiltration membrane (hydrophilic polysulfone, molecular weight cut off 150,000). Was used. As the organic substance concentration sensor 13, a UV turbidity two-wavelength measuring sensor having wavelengths of 260 nm and 660 nm was used. As raw water, humic acid dissolved in tap water at 4.5 mg / L was used. The difference between the absorbance at a wavelength of 260 nm and the absorbance at 660 nm of this raw water was 0.5 abs at an optical path of 50 mm. The absorbance difference before adding the humic acid in tap water and the absorbance at a wavelength of 260 nm were both 0.035 abs.

  Membrane filtration was performed with the filtration flux kept constant at 3 m / d, and the filtration step and the backwashing step were repeated in a cycle of 29 minutes for water flow and 1 minute for backwashing. And the chemical | medical solution washing | cleaning was performed once every 12 hours. Table 1 shows the rate of increase in membrane differential pressure (kPa / d) in this 29 minute filtration step.

  In addition, sulfuric acid (concentration 100 g / L) was used as the acid, and sodium hydroxide (concentration 100 g / L) was used as the alkali.

The chemical cleaning process is as follows.
First step: The water pump 9 and the acid pump 12 are operated, and an acid solution having a sulfuric acid concentration of 1225 mg / L is passed through the water at a linear velocity of 5 m / d for 1 minute.
Second step: Stop the acid flow and leave the membrane module 3 immersed in acid, and continue this for 28 minutes.
Third step: Only the pump 9 is operated, and filtered water is passed through the reverse permeation flux at 5 m / d for 1 minute.
Fourth step: The water pump 9 and the alkali pump 16 are operated, and a sodium hydroxide solution having a concentration of 1000 mg / L is passed for 1 minute at a reverse permeation flux of 5 m / d.
Fifth step: Alkaline water flow is stopped, the membrane module is immersed in alkali, and this is continued for 28 minutes.
Sixth step: Only the pump 9 is operated, and the filtered water is passed once a minute at a reverse permeation flux of 5 m / d.

  In this way, the chemical solution was washed once for 60 minutes in total of 1 minute of acid passing water, 28 minutes of acid retention, 1 minute of rinsing, 1 minute of alkaline water flow, 28 minutes of alkali retention, and 1 minute of rinsing.

Example 2
The filtration step was performed in the same manner as in Example 1 except that the frequency of chemical cleaning was doubled once and every 6 hours, and the acid and alkali concentrations were 610 mg / L, 500 mg / L and 1/2, respectively. The backwashing process was repeated, and the rate of increase in the membrane differential pressure in the filtration process was measured. The results are shown in Table 1.

Comparative Example 1
Except that the tap water was used as it was without adding humic acid as raw water, the filtration step, back washing step and chemical washing were repeated in the same manner as in Example 1, and the rate of increase in membrane differential pressure in the filtration step was measured. . The results are shown in Table 1.

Comparative Example 2
Except that no acid or alkali was added at the time of chemical cleaning, the filtration step, back washing step and chemical cleaning were repeated in the same manner as in Example 1, and the rate of increase in the membrane differential pressure in the filtration step was measured. The results are shown in Table 1.

Examples 3 and 4 and Comparative Example 3
The filtration step, back washing step and chemical solution washing were repeated in the same manner as in Example 1, Example 2 and Comparative Example 2, except that the raw water used was one having a humic acid concentration of 2.0 mg / L. The rate of increase in the membrane differential pressure was measured. The results are shown in Table 2.

  From Tables 1 and 2, it is clear that by increasing the chemical cleaning frequency as the humic acid concentration increases, the increase in the membrane pressure difference is suppressed as in Examples 1, 2, 3, and 4. In Examples 2 and 4, the cleaning frequency of Examples 1 and 3 was doubled and the chemical concentration was halved. However, the chemical cleaning effects of Examples 2 and 4 were respectively implemented. It was found to be equivalent to Example 1 and Example 3.

It is a systematic diagram of the membrane separator which concerns on embodiment. It is a graph which shows typically the relation between humic acid concentration and membrane filtration rate.

Explanation of symbols

3 Membrane Module 5 Filtration Water Tank 13 Organic Concentration Sensor 14 Controller

Claims (4)

Membrane separation means for supplying water to be treated from the primary side and discharging filtered water that has passed through the separation membrane from the secondary side;
In a membrane separation apparatus having a cleaning means for supplying water or a cleaning chemical to the secondary side of the membrane separation means and discharging the liquid that has passed through the separation membrane from the primary side to wash the separation membrane,
Organic substance concentration measuring means for measuring the organic substance concentration in the water to be treated from the difference between the ultraviolet absorbance within the wavelength range of 200 to 400 nm and the visible light absorbance within the wavelength range of 400 to 800 nm;
The membrane separation means is backwashed with water at a frequency of once every 10 to 180 minutes, and the higher the measurement value of the organic substance concentration measurement means, the shorter the cleaning interval of the membrane separation means with the cleaning chemical solution, and the organic matter And a control means for controlling the chemical cleaning frequency to be once every 6 to 12 hours when the concentration is 2.3 to 4.5 mg / L. 2. The membrane separation apparatus according to claim 1, wherein the control means increases the concentration of the cleaning chemical as the concentration of organic matter in the water to be treated increases. A step of supplying treated water to the membrane separation means to obtain membrane filtrate, and a separation membrane for supplying water or a cleaning chemical to the secondary side of the membrane separation means and discharging the liquid that has passed through the separation membrane from the primary side A membrane separation method having a washing step,
The organic substance concentration in the water to be treated is measured from the difference between the ultraviolet absorbance in the wavelength range of 200 to 400 nm and the visible light absorbance in the wavelength range of 400 to 800 nm, and the membrane separation means is used once every 10 to 180 minutes. chemical when in addition to backwashing water, the wash interval by wash liquor of the membrane separation means higher measured value of the concentration of organic substances is short and the concentration of organic substances is 2.3~4.5mg / L A membrane separation method characterized in that the washing frequency is once every 6 to 12 hours. 4. The membrane separation method according to claim 3, wherein the concentration of the cleaning chemical is increased as the concentration of the organic substance in the water to be treated is higher.

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