WO2020172935A1 - Method for mitigating ultrafiltration membrane pollution on basis of morphological matching of precursor and flocculant - Google Patents

Abstract

A method for mitigating ultrafiltration membrane pollution on the basis of the morphological matching of a precursor and a flocculant, comprising the following steps: (1) during a process of preparing drinking water from a natural body of water, before electroflocculation-membrane separation, detecting a body of water to be subjected to electroflocculation-membrane separation to obtain a SUVA value and a concentration value of the precursor; fitting a correlation coefficient R; (2) using an electroflocculation-ultrafiltration collaborative water treatment device to introduce the body of water; (3) adjusting the current density and a pH value according to R; (4) performing an electroflocculation-membrane separation treatment, starting up a suction filter pump, and the body of water subjected to the electroflocculation-membrane separation treatment entering into a chlorination disinfection step. The described method is simple to use and operate and is easy to implement, and may mitigate membrane pollution and extend the service life of the membrane.

Description

Method for reducing pollution of ultrafiltration membrane based on matching of precursor and flocculant morphology Technical field

The invention belongs to the technical field of environmental protection, and in particular relates to a method for slowing down ultrafiltration membrane pollution based on the matching of precursor and flocculant forms.

Background technique

Drinking water disinfection is to kill pathogenic microorganisms in water that are harmful to human health and prevent diseases transmitted through water; disinfection does not kill all microorganisms in the water, but only eliminates the hidden dangers of pathogenic microorganisms in the water; chlorination disinfection is currently The most commonly used method in drinking water disinfection in China; however, while chlorination disinfection kills pathogenic microorganisms in the water, chlorine reacts with natural organic matter in the water to produce a series of halogenated disinfection by-products (mainly including trihalomethane and haloacetic acid). Halogenated substances in drinking water have been proved to be teratogenic, carcinogenic and mutagenic main disinfection by-products; it is of vital significance to remove the generation of halogenated disinfection by-products in drinking water.

There are three main methods for removing halogenated disinfection by-products in drinking water: one is to remove the precursors of disinfection by-products, including enhanced coagulation, granular activated carbon adsorption and membrane separation; the second is to change the disinfection process parameters or disinfection methods; It is to remove the disinfection by-products that have been produced, which can be removed by biological, physical and chemical methods; however, since disinfection is the last step in drinking water treatment, it is difficult to remove the disinfection by-products once they are generated. Therefore, remove drinking water In the halogenated disinfection by-products, it is fundamentally necessary to remove the precursors that cause the generation of halogenated disinfection by-products.

Electric flocculation-ultrafiltration is an important technical method to remove the precursors of halogenated disinfection by-products; in recent years, people have gradually formed a more consistent view that the removal rate of halogenated disinfection by-products is used to characterize the removal of halogenated disinfection by-products. Feasible; however, when the concentration of natural organic matter in the raw water is low, even if the halogenated disinfection by-product precursor removal rate meets the requirements, the combination with the ionized flocculant is low, the natural organic matter and flocculant remaining in the water will still adhere to The membrane surface, thereby increasing membrane pollution and reducing membrane service life.

Summary of the invention

The purpose of the present invention is to provide a method for mitigating the pollution of ultrafiltration membranes based on the matching of precursors and flocculants, providing flocculants with different advantageous forms through electric flocculation, matching with different current densities, and aiming at low-concentration halogenated drinking water Different predominant forms in the precursors of disinfection by-products realize the maximum removal of halogenated disinfection by-products, slow down membrane pollution and extend the service life of membranes.

The method of the present invention includes the following steps:

1. The process of preparing drinking water from natural water bodies includes electro-flocculation-membrane separation steps and chlorination and disinfection steps; among them, before electro-flocculation-membrane separation, the water body that will be electro-flocculation-membrane separation is tested, and the measurement Among them, the characterization parameter SUVA value of aromatic carbon content, and the concentration value of halogenated disinfection by-product precursor is measured; according to the SUVA value and the concentration value of halogenated disinfection by-product precursor, the correlation coefficient R value of the two is fitted ；

2. Adopt electric flocculation-ultrafiltration combined water treatment device, the cathode and anode of the device are made of aluminum, and the water body that is about to undergo electro-flocculation-membrane separation is passed through the water inlet to the device;

3. The cathode and anode of the electro-flocculation-ultrafiltration cooperative water treatment device are energized through the power supply; according to the measured R value, the current density between the cathode and the anode in the electro-flocculation-ultrafiltration cooperative water treatment device is adjusted, and the current density is adjusted at the same time. The pH value of the water body undergoing electro-flocculation-membrane separation; when R<0, adjust the pH value to 5.0≤pH value<5.5, and current density 5≤I<10A/m ² ; when 0≤R<0.70, adjust the pH value Value to 5.5≤pH value<6.5, current density 10≤I<30A/m ² ; when R≥0.7, adjust pH value to 6.5≤pH value≤7.5, current density 30≤I≤50A/m ² ;

4. After the adjustment of pH value and current density is completed, the water body that is about to be electro-flocculated-membrane separated is processed by the electro-flocculation-ultrafiltration cooperative water treatment device, and the suction filter pump is started to perform suction filtration to form a membrane. After filtering, the water that has been treated by electro-flocculation-membrane separation is discharged by the suction filter and enters the chlorination disinfection step.

The aforementioned halogenated disinfection by-product precursors are trihalomethanes (THMs) precursors or haloacetic acid (HAAs) precursors; the trihalomethanes are trichloromethane, dichloromonobromomethane or tribromomethane; the halogen Acetic acid is monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), dichloroacetic acid (DCAA), dibromoacetic acid (DBAA) or trichloroacetic acid (TCAA).

In the above method, the determination method of the SUVA value is to use the organic carbon concentration (TOC) to standardize the 254nm ultraviolet absorbance (UV ₂₅₄ ) of the humic acid solution to obtain the unit organic carbon UV ₂₅₄ , as the SUVA, the unit L/(mg ·Cm).

In the above method, the unit of the concentration of the halogenated disinfection by-product precursor is L/(mg·cm).

The calculation formula of the R value in the above method is:

In the formula, Cov(X,Y) is the covariance of X and Y, Var[X] is the variance of X, Var[Y] is the variance of Y, X is the SUVA value, and Y is the precursor of halogenated disinfection by-products Concentration value.

In the above method, after the water body separated by the electrocoagulation-membrane separation is discharged from the water outlet, the dissolved organic carbon concentration, the water outlet membrane flux and the ultraviolet absorption value (UV ₂₅₄ ) at 254 nm are tested.

The method for judging the different forms of the precursors of the disinfection by-products of the present invention is: taking humic acid and fulvic acid, which are the precursors of the typical halogenated disinfection by-products in natural water bodies, as the main components, and using the characterization parameter SUVA value of aromatic carbon content in natural water bodies (The ratio of UV ₂₅₄ to the concentration of soluble organic carbon TOC), the correlation with the precursors of halogenated disinfection by-products, and the structure distribution law of the precursors of disinfection by-products.

The present invention proposes that for the natural water bodies with the dominant form distribution law of the precursors of different halogenated disinfection by-products, by adjusting the current density, the corresponding flocculant form with the advantageous removal ability is ionized; the precursor form and the ionized flocculant form are used The matching relationship significantly improves the removal efficiency of low-concentration disinfection by-product precursors in natural waters, thereby reducing membrane pollution; the principle is: through electro-flocculation, the structure of pollutants is changed, the size of particles is adjusted, and the membrane surface is hydrophilic and porous. The filter cake layer slows down membrane pollution, performs solid-liquid separation through membrane filtration, and further improves the quality of the effluent; the invention regulates the form and structure of flocs through induction electric flocculation, reduces the accumulation of pollutants on the membrane surface, and controls pollution through electrode reaction The direct and indirect oxidation of substances changes the molecular structure and polarity of pollutants, and forms a highly porous and hydrophilic filter cake layer on the membrane surface; and the filter cake layer is polarized by the electric field between the plates. The enhanced properties further enhance the hydrophilic properties of the filter cake layer and further reduce membrane pollution. Unlike the traditional electro-flocculation-ultrafiltration process, the present invention focuses on the matching relationship between the precursor form of the halogenated disinfection by-product and the form of the flocculant, and Strengthen the generation of the in-situ form of the flocculant under the corresponding water quality, thereby greatly improving the efficiency of removing halogenated disinfection by-product precursors in the electro-flocculation-membrane separation process, effectively controlling the generation of disinfection by-products after chlorination disinfection, and significantly slowing down the membrane Pollution.

The principle of electro-flocculation treatment is: placing a metal electrode (aluminum or iron) in the water to be treated as an anode and applying a direct current. At this time, the metal anode is oxidized and electrochemically reacted, and metal cations such as Al ³⁺ or Fe ^{2+ are} dissolved in the water. Hydrolysis-polymerization reaction occurs, and then it performs its coagulation or flocculation effect like a traditional chemical coagulant; the electrode materials usually used in electrocoagulation are aluminum and iron; for water treatment, aluminum is generally used as the anode; In the anode, iron consumption is 3-10 times that of aluminum, and polarization and passivation will occur.

The main reactions that occur when Al is used as the anode are as follows.

The anode is mainly Al electrolysis to generate Al ³⁺ reaction:

Al → Al ³⁺ + 3e ^-;

The cathode mainly undergoes electrolysis of H ₂ O, releasing H ₂ :

_{2H 2 O + 2e → H 2} + 2OH -;

Under different pH, the system has the functions of compressing the electric double layer, adsorbing and neutralizing, bridging and sweeping; the gas generated by the electrolysis accelerates the mixing of the system, and the apparent density will rise when the apparent density is small, and sink when the apparent density is large, thereby achieving separation.

The method of the present invention is simple, simple to use and easy to implement; it adopts electro-flocculation-ultrafiltration cooperative water treatment device, uses aluminum plate to ionize flocculant, aluminum plate can be used repeatedly, and has low cost; the concentration of precursors of halogenated disinfection by-products is relatively low. At low time, use the matching of different halogenated disinfection by-product precursor forms and the in-situ form of flocculant to optimize the process parameters of electroflocculation-membrane separation to remove halogenated disinfection by-product precursors, slow down membrane pollution, and extend electro-flocculation-ultrafiltration The service life of the membrane in the cooperative water treatment device.

detailed description

In Example 1 of the present invention, a mixed aqueous solution of humic acid and fulvic acid is used to simulate natural water (a body of water that is about to undergo electro-flocculation-membrane separation), and the mixed aqueous solution is molar ratio of humic acid: fulvic acid = 1:2～2 :1, and the concentration of dissolved organic carbon DOC is 3-10mg/L.

In step 3 of the present invention, the stirring speed when adjusting the pH value is 200-300 rpm, and the stirring speed after adjusting the pH value is 30-50 rpm.

The electro-flocculation-ultrafiltration synergistic water treatment device used in the embodiments of the present invention is an experimental device described in "Electro-flocculation-ultrafiltration synergistic removal of humic acid in water" (Journal of Environmental Engineering, Vol.11.No.7).

The electro-flocculation-ultrafiltration synergistic water treatment device used in the embodiment of the present invention includes a reactor. The reactor is provided with two electrode plates and a hollow fiber ultrafiltration membrane. The two electrode plates are respectively connected to the two poles of the power supply. The fiber ultrafiltration membrane is assembled with the suction filter pump; the water inlet of the reactor is connected with the water outlet of the water inlet pump, and the water inlet of the water inlet pump is connected with the raw water tank; the water outlet of the reactor is connected with the water inlet of the water outlet pump. The water outlet of the water pump is connected with the raw water tank; the bottom of the reactor is equipped with a magnetic stirring device.

In the embodiment of the present invention, the outlet of the suction filter pump is connected with the filtered water tank.

The electro-flocculation-ultrafiltration cooperative water treatment device in the embodiment of the present invention is also provided with a pH meter to detect the pH value of the materials in the reactor.

In the embodiment of the present invention, when the current density and pH value are adjusted, when the suction filter pump is started, the water outlet pump is turned on at the same time to return part of the water in the reactor to the original water tank to keep the water volume in the reactor fixed. The pH value adjustment includes The water in the raw water tank.

The reactor in the embodiment of the present invention is a 140mm×50mm×150mm plexiglass tank, and the distance between the plates is 20mm; it uses DH1765-1 type programmable DC stabilized current power supply (35V, 3A); it uses a magnetic stirrer to stir the solution , So that the processed materials are evenly dispersed in the reactor; the water that is about to undergo electro-flocculation-membrane separation enters the reactor through the water inlet pump, part of the water flows out through the membrane separation, and the other part gradually stays in the reactor due to the decrease in membrane flux The water in the water is returned to the raw water tank through the return pump.

The calculation method of the R value in the embodiment of the present invention is to use Excle to calculate: First, respectively input the SUVA value and the concentration value of the halogenated disinfection by-product precursor into Excle as two sets of data; select these two sets of data, click Insert, select the scatter graph, select the scatter, click to add a trend line; select linear, check the display formula, display R, get the result R ² , use the computer to prescribe the R value.

Example 1

Dissolve humic acid and fulvic acid in water to prepare a simulated water sample of the water body that will undergo electro-flocculation-membrane separation. As the experimental water sample, the mass ratio of humic acid to fulvic acid in the experimental water sample is 1:2 , The dissolved organic carbon TOC concentration in the experimental water samples is 5mg/L; the method for determining the SUVA value is to use the organic carbon concentration (TOC) to standardize the 254 nm ultraviolet absorbance (UV ₂₅₄ ) of the humic acid solution to obtain the unit organic Carbon UV ₂₅₄ , as SUVA, unit L/(mg·cm);

Detect the characterization parameter SUVA value of aromatic carbon content and the concentration value of halogenated disinfection by-product precursor; according to the SUVA value and halogenated disinfection by-product precursor concentration value, fit the correlation coefficient R value of the two;

The electro-flocculation-ultrafiltration combined water treatment device is adopted. The cathode and anode of the device are made of aluminum, and the experimental water sample is passed into the device through the water inlet; the experimental water sample is located in the raw water tank and is passed into the reactor through the inlet pump;

The cathode and anode are energized through the power supply; measured R=0.945, the initial concentration of TCAA precursor is 68.4ug/mg C; adjust the current density between the cathode and anode in the electro-flocculation-ultrafiltration water treatment device, and adjust the experiment at the same time The pH value of the water sample; adjust the pH value to 6.5～7.5, and the current density is 50A/m ² ;

After the adjustment of pH and current density is completed, the experimental water sample is processed, and the suction filter pump is started for suction filtration to form membrane filtration. The processed experimental water sample passes through the hollow fiber ultrafiltration membrane, and then is discharged by the suction filter pump , Complete the electric flocculation-membrane separation treatment, enter the chlorination disinfection step; at this time, turn on the water outlet pump to keep the amount of materials in the reactor in a constant state;

The water after electrocoagulation-membrane separation treatment enters the filtered water tank first to test its dissolved organic carbon concentration, water membrane flux and ultraviolet absorption value (UV ₂₅₄ ) at 254nm; then chlorination disinfection;

After the electroflocculation-membrane separation reaction, the TCAA precursor concentration is 10ug/mg C, which is 67% higher than the traditional electroflocculation-membrane separation efficiency.

Example 2

Using the water body that will undergo electro-flocculation-membrane separation, it is measured that R=0.625, and the initial concentration of the DCAA precursor is 30ug/mg C;

The method is the same as in Example 1, the difference is:

Adjust pH value to 5.6～6.5, current density 10A/m ² ;

After the electro-flocculation-membrane separation treatment, the DCAA precursor concentration reached 10.6ug/mg C, which is 30.2% higher than the traditional electro-flocculation-membrane separation efficiency.

Example 3

Using the water body that is about to undergo electro-flocculation-membrane separation, it is measured that R=0.678, and the initial concentration of CHCl ₃ precursor is 20.1ug/mg C;

The method is the same as in Example 1, the difference is:

Adjust pH value to 5.6～6.5, current density 15A/m ² ;

After electro-flocculation-membrane separation treatment, the CHCl ₃ precursor concentration reached 10.9ug/mg C, which was 51.1% higher than the traditional electro-flocculation-membrane separation efficiency.

Example 4

Using a water body that is about to undergo electro-flocculation-membrane separation, it is measured that R = -0.516, and the initial concentration of the TCAA precursor is 8ug/mg C;

The method is the same as in Example 1, the difference is:

Adjust pH value to 5～5.4, current density 5A/m ² ;

After electro-flocculation-membrane separation treatment, the concentration of TCAA precursor reaches 6ug/mg C, which is 67.1% higher than traditional electro-flocculation-membrane separation.

Example 5

Using the water body that is about to undergo electro-flocculation-membrane separation, it is measured that R=0.9, and the initial concentration of the DBAA precursor is 30.1ug/mg C;

The method is the same as in Example 1, the difference is:

Adjust pH to 6.5～7.5, current density 45A/m ² ;

After the electro-flocculation-membrane separation treatment, the DBAA precursor concentration reached 8.3ug/mg C, which was 81.2% higher than the traditional electro-flocculation-membrane separation efficiency.

Example 6

Using a water body that is about to undergo electro-flocculation-membrane separation, it is measured that R = -0.231, and the initial concentration of MBAA precursor is 54.3ug/mg C;

The method is the same as in Example 1, the difference is:

Adjust pH value to 5～5.4, current density 8A/m ² ;

After electroflocculation-membrane separation treatment, the concentration of MBAA precursor reached 13.1ug/mg C, which was 38.4% higher than the traditional electroflocculation-membrane separation efficiency.

Example 7

Using the water body that is about to undergo electro-flocculation-membrane separation, it is measured that R=0.876, and the initial concentration of MCAA precursor is 71.3ug/mg C;

The method is the same as in Example 1, the difference is:

Adjust pH value to 6.6～7.5, current density 40A/m ² ;

After electro-flocculation-membrane separation treatment, the TCAA precursor concentration reached 13.8ug/mg C, which was 71.9% higher than the traditional electro-flocculation-membrane separation efficiency.

Although the specific embodiments of the present invention are described above, those skilled in the art should understand that the specific embodiments described by us are only illustrative, and are not used to limit the scope of the present invention. The equivalent modifications and changes made by the skilled person in accordance with the present invention should all fall within the protection scope of the claims of the present invention.

Claims (5)

1. A method for mitigating the pollution of ultrafiltration membranes based on the matching of precursors and flocculants, which is characterized by comprising the following steps:

   (1) The process of preparing drinking water from natural water bodies includes electro-flocculation-membrane separation steps and chlorination and disinfection steps; among them, before electro-flocculation-membrane separation, the water body that will be electro-flocculation-membrane separation is tested. Obtain the characterization parameter SUVA value of aromatic carbon content, and measure the concentration value of halogenated disinfection by-product precursor; according to the SUVA value and halogenated disinfection by-product precursor concentration value, fit the correlation coefficient R between the two value;

   (2) Adopt electric flocculation-ultrafiltration combined water treatment device, the cathode and anode of the device are made of aluminum, and the water body that is about to undergo electro-flocculation-membrane separation is passed through the water inlet to the device;

   (3) The cathode and anode of the electro-flocculation-ultrafiltration cooperative water treatment device are energized through the power supply; according to the measured R value, the current density between the cathode and the anode in the electro-flocculation-ultrafiltration cooperative water treatment device is adjusted and adjusted simultaneously The pH value of the water body about to undergo electro-flocculation-membrane separation; when R<0, adjust the pH value to 5.0≤pH value<5.5, and the current density 5≤I<10A/m ² ; when 0≤R<0.70, adjust pH value to 5.5≤pH value<6.5, current density 10≤I<30A/m ² ; when R≥0.7, adjust pH value to 6.5≤pH value≤7.5, current density 30≤I≤50A/m ² ;

   (4) After the adjustment of the pH value and the current density is completed, the water body that is about to be electro-flocculated-membrane separated is processed by the electro-flocculation-ultrafiltration cooperative water treatment device, and the suction filter pump is started for suction filtration to form Membrane filtration, the water that has been treated by electro-flocculation-membrane separation is discharged through a suction filter and enters the chlorination disinfection step.
2. The method for mitigating the pollution of ultrafiltration membranes based on the morphological matching of precursors and flocculants according to claim 1, wherein the halogenated disinfection by-product precursor is a trihalomethane precursor or a haloacetic acid precursor; The trihalomethane is trichloromethane, dichloromonobromomethane or tribromomethane; the haloacetic acid is monochloroacetic acid, bromoacetic acid, dichloroacetic acid, dibromoacetic acid or trichloroacetic acid.
3. The method for mitigating ultrafiltration membrane pollution based on the matching of precursor and flocculant morphology according to claim 1, wherein the method for measuring the SUVA value is to measure the 254nm UV absorbance of the humic acid solution by the organic carbon concentration. Standardized to obtain UV ₂₅₄ per unit of organic carbon, as SUVA, in L/(mg·cm).
4. The method for mitigating the pollution of ultrafiltration membranes based on the morphological matching of precursors and flocculants according to claim 1, wherein the unit of the concentration of the precursors of halogenated disinfection by-products is L/(mg·cm).
5. The method for mitigating the pollution of ultrafiltration membranes based on the matching of precursors and flocculants according to claim 1, characterized in that the formula for calculating the R value is:

   

   In the formula, Cov(X,Y) is the covariance of X and Y, Var[X] is the variance of X, Var[Y] is the variance of Y, X is the value of SUVA, and Y is the precursor of halogenated disinfection by-products Concentration value.