CN114988535A - Electrochemical-mediated osmotic wastewater treatment system and preparation method and application thereof - Google Patents

Abstract

The invention discloses an electrochemical-mediated permeation wastewater treatment system, a preparation method thereof and application of the electrochemical-mediated permeation wastewater treatment system in treatment of antibiotic wastewater, heavy metal wastewater, printing and dyeing wastewater or landfill leachate. Mixing PMIA polymer, LiCl, CNTs and the like to form a membrane casting solution, casting the membrane to obtain a CNTs basal membrane, immersing the surface of the membrane in MPD aqueous solution, and exposing the surface of the membrane to Isopar-G solution to obtain a CNTs TFC membrane; assembling the membrane assembly, the silica gel gasket, the metal sheet, the silica gel gasket, the separation layer, the silica gel gasket, the separation grid layer, the CNTs TFC membrane, the separation grid layer, the silica gel gasket and the membrane assembly. The invention organically combines electrochemistry and a permeable membrane technology, utilizes a space electric field or an electrode potential to strengthen/optimize a permeation process, takes the CNTs conductive membrane as an electrode, couples a forward osmosis or reverse osmosis technology, realizes selective separation of pollutants by regulating and controlling particle transmission characteristics, improves water flux and slows down membrane pollution.

Description

Electrochemically mediated osmotic wastewater treatment system, preparation method and application thereof

technical field

The invention relates to an electrochemically mediated permeable membrane wastewater treatment system, which can effectively apply water treatment and reuse, and belongs to the technical field of environmental protection.

Background technique

The relative scarcity of water resources and the deterioration of water quality have increasingly seriously affected human life and health and restricted economic development. Governments and social groups have strategically realized that future peace and development will be closely related to access to clean water and fresh water.

Thin-film Composite (TFC) membrane is the mainstream of the current research and development of forward osmosis and reverse osmosis membrane materials. Usually, a thin and dense active layer is formed on the top of the porous base membrane. This layer of active layer generally passes through the interface of monomers The formation of films formed by the polymerization (IP) reaction largely depends on the structure and properties of the base film. Despite the advantages of highly cross-linked PA membranes such as high rejection and water flux, the PA layer structure is easily destroyed when TFC membranes are operated in a high-chlorine environment, which is the most commonly used disinfection process. Therefore, this greatly affects the development of TFC membranes. In addition, the PA layer has a nano-scale ridge-valley structure, which has a high specific surface area and is easy to accumulate dirt. In addition, the high density of carboxyl groups and the hydrophobicity of the PA layer are also very likely to cause the pollution of the TFC membrane. In addition, organic pollutants are not only adsorbed on the membrane surface, but also easily block membrane pores through strong interactions such as electrostatic attraction and hydrophobic force during transportation. While simple physical cleaning can remove a small fraction of the adsorbed molecules on the membrane surface, stubborn contaminants in the membrane pores can only be removed by chemical cleaning, which may cause irreversible damage to the membrane material.

Improving the hydrophilicity of membranes is a common method to improve the fouling resistance of membranes. The antifouling performance is reported to come from the strong hydration layer on the hydrophilic surface, which inhibits the adsorption of pollutants. Since most organic pollutants are negatively charged, another commonly used method is to apply a negative charge to the membrane surface to electrostatically repel the attachment of negatively charged organic pollutants and bacteria. In addition, by introducing an electric field during the operation of the permeation system, the stubborn pollutants in the membrane pores can be removed by means of electrocatalysis, which can effectively improve the water flux of the membrane and improve the stability of the membrane. Among the various additives used to produce composite conductive films, highly conductive carbon nanotubes are the most common. As a representative one-dimensional carbon nanomaterial, carbon nanotubes have the advantages of stability and electrical conductivity. Carbon nanotubes can be prepared as free-standing membranes or porous layers on substrates, and thus have been extensively studied for membrane applications.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is: how to improve water flux and alleviate the membrane fouling problem of forward osmosis/reverse osmosis technology by means of electric field action.

In order to solve the above-mentioned technical problems, the present invention provides a preparation method of an electrochemically mediated osmotic membrane wastewater treatment system, comprising the following steps:

Step 1): Mix the vacuum-dried PMIA polymer, LiCl, DMac, acetone, and CNTs to form a casting liquid;

Step 2): Spread the film base on the glass plate, use a film casting knife to quickly cast the degassed film casting solution on the film base, and quickly immerse the cast glass plate in a water-coagulation bath to ensure that Complete precipitation to obtain CNTs base film;

Step 3): the membrane surface of the CNTs-based membrane obtained in Step 2) is immersed in the MPD aqueous solution, and the residual solution on the membrane surface is removed with a hair dryer; the membrane surface is exposed to the Isopar-G solution, and the excess organic solution is poured out, and the membrane is removed. Vacuum drying to improve the cross-linking degree of PA to obtain CNTs TFC film;

Step 4): Assemble the membrane assembly-silicone gasket-metal sheet-silicone gasket-separation layer-silicone gasket-separation grid layer-CNTs TFC membrane-separation grid layer-silicone gasket-membrane assembly in sequence, The CNTs TFC membrane is used as the anode, the active layer is facing the feed liquid side, the metal sheet is used as the cathode, and the separation grid layer is used for mechanical support;

Step 5): connect the cathode and the anode respectively to the power supply, leave the water inlet and the water outlet on the left and right sides of the membrane module to connect the raw material liquid and the drawing liquid respectively, the drawing liquid is placed on an electronic balance to record the quality, and a conductivity meter is placed in the raw material liquid for observation. The conductivity of the raw material liquid changes; at the same time, the electronic balance and conductivity meter system are respectively connected to the computer to record the changes of quality and conductivity in real time, and analyze the water flux.

Preferably, in the step 1), the mass percentage of PMIA in the casting solution is 10-15%, the mass percentage of LiCl is 2-5%, the mass percentage of CNTs is 5-20%, and the volume ratio of DMac and acetone is 8:2.

Preferably, in the step 2), the film substrate is conductive carbon paper or conductive carbon cloth; the film thickness set by the film casting knife is 80-120 μm.

Preferably, the temperature of the hydraulic bath in the step 2) is 50-70°C.

Preferably, in the step 3), the CNTs-based membrane is immersed in a 1.5 mol/L NaOH solution for 1 hour before being immersed in the MPD aqueous solution, so as to improve the hydrophilicity of the membrane.

Preferably, in the step 4), the size of the effective membrane pool of the membrane module is 20mm×60mm×4mm; the separation grid layer is a non-conductive plastic grid; the metal sheet is a titanium sheet, a platinum sheet or a nickel sheet; The size of the layer is consistent with the size of the membrane module, and the water passage is reserved in the middle of the separation layer.

Preferably, the power supply in the step 5) is pulsed electricity, and the voltage is 1-3V.

Preferably, in the step 5), the operating flow rate of the CNTs TFC membrane is 10-20 cm/s, and a constant temperature water bath is used to keep the temperature of the raw material liquid and the drawing liquid at 25±0.1°C.

The present invention also provides the electrochemically mediated permeable membrane wastewater treatment system prepared by the above preparation method.

The invention also provides the application of the electrochemically mediated osmotic membrane wastewater treatment system in treating antibiotic wastewater, heavy metal wastewater, printing and dyeing wastewater or landfill leachate.

The invention organically combines electrochemistry and permeable membrane technology, and utilizes space electric field or electrode potential to strengthen/optimize forward osmosis and reverse osmosis processes. Using the CNTs conductive membrane as the electrode, coupled with the forward osmosis and reverse osmosis membrane technologies, can control the particle transport characteristics to achieve selective separation, improve water flux and slow down membrane fouling.

Compared with the prior art, the beneficial effects of the present invention are:

The electric field-mediated forward osmosis system is an organic combination of electrochemistry and permeable membrane technology, which can use space electric field or electrode potential to strengthen/optimize the permeable membrane process. It has the following characteristics: 1) Improve the retention rate: charged substances in water are simultaneously subjected to electrostatic repulsion and membrane pore steric hindrance screening, resulting in a stronger interception effect; 2) Improve water flux: membrane separation can produce electricity under electrical regulation. Higher selectivity; 3) Membrane fouling mitigation: electrostatic repulsion and electrochemical reaction can effectively alleviate organic, inorganic and biological pollution in the membrane separation process.

Electrochemical advanced oxidation processes can efficiently remove many stubborn organic pollutants. During electrochemical oxidation, organic compounds are reduced through two different mechanisms. In the mediated mechanism, the highly reactive hydroxyl radicals generated on the anode surface by water oxidation will be able to react non-selectively with a variety of stubborn pollutants, thereby degrading them indirectly. Alternatively, electrons can be transferred from contaminants to the anode surface to be directly oxidized.

When a voltage is applied to the carbon nanotube conductive membrane to increase the surface charge density of the membrane, the Donnan potential difference between the membrane and the solution increases, which can improve the retention rate of the membrane without reducing the water flux. The conductive film of CNTs can not only reduce organic pollution but also inhibit bacterial attachment by applying a small potential. And the forward osmosis/reverse osmosis with carbon paper as the continuous conductive phase can form an interpenetrating structure with the base polymer, which has the advantages of good stability and low resistance. Besides, under the indirect electric field mediation, the pollutants in the pores of the forward osmosis/reverse osmosis membrane can be successfully degraded under the electrocatalysis of CNTs, and the water flux in the forward osmosis/reverse osmosis process can be restored, Mitigates membrane fouling, which helps increase the life of your forward osmosis/reverse osmosis membranes.

Description of drawings

1 is a schematic diagram of an electrochemically mediated permeation system of the present invention;

Figure 2 is the impedance value of the CNTs TFC permeable membrane;

Figure 3 is a comparison diagram of the water flux of wastewater under the electrochemically mediated permeable membrane system;

Fig. 4 is the influence of different draw fluids on the water flux of electrochemically mediated permeable membrane system;

Figure 5 shows the effect of conductive films prepared with different CNTs concentrations on the water flux of antibiotic wastewater;

Figure 6 is a comparative data diagram of the water flux recovery of the permeable membrane system under the backwash method and the intermittent electric field mediated action.

Detailed ways

In order to make the present invention more obvious and comprehensible, preferred embodiments are described in detail below with reference to the accompanying drawings.

The electrochemically mediated permeable membrane system provided in Examples 1-5 is shown in Figure 1, which includes an anode 7 and a cathode 6, the anode 7 is a CNTsTFC conductive membrane, the cathode 6 is a titanium sheet, and the anode 7 and the cathode 6 are Silicone gasket-titanium sheet-silicone gasket-separator layer-silicone gasket-separation grid layer-CNTs TFC membrane-separation grid layer-silicone gasket are sequentially connected and placed in the membrane module housing 8, so that the membrane Component-silicone gasket-titanium sheet-silicone gasket-separator layer-silicone gasket-separation grid layer-CNTs TFC membrane-separation grid layer-silicone gasket-membrane components are connected in sequence, anode 7, cathode 6 external power supply 5. The inlet ends on both sides of the membrane module are respectively connected to the drawing liquid and the raw material liquid through a pump 4, and the outlet ends on both sides of the membrane module are respectively connected to the drawing liquid and the raw material liquid through an automatic counting device 3, and the two automatic counting devices 3 are respectively connected. It is used to measure the quality of the drawn liquid and the conductivity of the raw material liquid; the bottom of the drawn liquid is provided with an analytical balance 2, the analytical balance is connected to the PC end 1, and the raw material liquid is equipped with a magnetic stirrer 9. The power source 5 controls the electric field intensity, and the automatic counting device 3 automatically records the quality change of the drawn liquid and the conductivity change of the raw material liquid every 5 minutes to determine the water flux and salt backmixing flux.

Example 1

A preparation method of an electrochemically mediated osmotic membrane wastewater treatment system, comprising the following steps:

(1) PMIA membrane substrate was prepared by phase inversion method. The 12wt% PMIA polymer dried in vacuum was dissolved in a mixture of DMac (8mL) and acetone (2mL) and stirred evenly, while slowly adding 5-15wt% CNTs and 2wt% LiCl to form a casting solution.

(2) Spread the conductive carbon paper flat on the glass plate, and use a film-casting knife to rapidly cast the film-casting liquid after degassing overnight on the conductive carbon paper. Immerse the glass plate after film casting in a hydrogel bath at 60°C for 30 minutes to ensure complete precipitation of the film.

(3) The CNTs-based membrane obtained in step (2) was immersed in a 2 mol/L NaOH solution for 1 hour to improve the hydrophilicity of the membrane. Then the CNTs film was flattened and fixed on the coating tool for interfacial polymerization. The membrane surface was immersed in the MPD aqueous solution, and the solution remaining on the membrane surface was removed with a hair dryer. The membrane surface was exposed to Isopar-G solution, and the freshly prepared membrane was vacuum dried after decanting the excess organic solution to increase the cross-linking degree of PA. The prepared films are CNTs TFC films. The impedance values of the CNTs TFC films are shown in Figure 2.

(4) The CNTs TFC membrane was placed as the anode in the self-made membrane module, with the active layer facing the feed liquid side. Spacer layers are placed on both sides of the TFC membrane to provide certain mechanical support for the membrane and improve hydraulic conditions at the same time. The titanium sheet is placed on the other side of the separator layer as the cathode, and the membrane module-silicone gasket-titanium sheet-silicon gasket-separator layer-silica gasket-separation grid layer-CNTsTFC membrane-separation grid layer-silica gel Sequential assembly of gasket-membrane assemblies.

(5) Connect the cathode and the anode to the power supply, apply 2V voltage, use 1M NaCl as the drawing solution, and use 500 μg/L tetracycline solution as the raw material solution to analyze the water flux changes of the forward osmosis membranes under different CNTs contents, and the control flow rate is 15cm. /s, use a constant temperature water bath to keep the temperature of the raw material and the drawing liquid at 25±0.1 °C, and compare the change of water flux with the result of no voltage applied.

The results show that the impedance value of the CNTs TFC film is about 20Ω, showing that the film has ultra-high conductivity, which helps the space electric field to enhance the permeation process. It can be seen from Fig. 3 that the water flux in the permeation process after electrode strengthening is higher than that under the condition of no electric field. This is because the electric field improves the mass transfer characteristics between particles and relieves the pollution on the surface of the membrane pore collector.

Example 2

The difference between this example and Example 1 is: in step (5), the types of the liquid drawn are 1M NaCl, Na ₂ SO ₄ , NaHCO ₃ , NH ₄ HCO ₃ and MgSO ₄ , to observe the operation process of the forward osmosis system Influence of different draw fluids on pure water flux.

It can be seen from Figure 4 that the water flux using _MgSO4 solution is smaller than that using NaCl solution. The lower water flux may be due to the lower diffusion coefficient of magnesium ions than that of sodium ions, which increases the severity of intraconcentration polarization.

Example 3

The difference between this example and Example 1 is that: in step (5), the concentration of the extraction solution (NaCl) is 0.5M, 1M and 1.5M to observe the influence of the extraction solution concentration on the pure water flux.

It can be seen from Figure 5 that the greater the concentration of the drawn liquid, the greater the water flux, because with the increase of the NaCl concentration, the concentration gradient of the boundary layer increases, and the polarization degree of the concentration polarization increases.

Example 4

The difference between this example and Example 1 is that the raw material solution is 500 μg/L tetracycline solution, and the osmotic membrane system is operated for 3 hours without applying voltage, and then the osmotic membrane is backwashed for 30 minutes, and then connected to the power supply A voltage of 2 V was applied to strengthen the electric field to observe the change of the water flux of the permeable membrane.

It can be seen from Figure 6 that the water flux of the permeable membrane system decreased from 34LMH to 20LMH after 3 hours without the application of voltage. to 31.6LMH.

Example 5

The difference between this example and Example 1 is that 10wt% CNTs TFC membrane is selected as the conductive membrane of the osmotic system, and the raw material solutions in step (5) are respectively 1L of tetracycline solution, antimony-containing waste water, mixed dye waste water and The landfill leachate was distributed with water. Under the condition that the flow rate was set at 15cm/s, the permeation system was operated for 5 hours by applying voltages of 0V and 2V respectively, and the water flux changes of each raw material solution were analyzed.

It can be seen from Figure 6 that the water fluxes of different wastewaters are improved under the action of the electric field. The water flux of tetracycline solution increased from 27.1LMH to 31.2LMH. The water flux of antimony-containing wastewater was increased from 27.4LMH to 35.7LMH. The water flux of mixed dye wastewater was increased from 24.6LMH to 27.9LMH. The water flux of landfill leachate distribution was increased from 21.3LMH to 30.2LMH. This is because CNTs improve the mass transfer between particles under the action of an electric field, and at the same time, the highly reactive hydroxyl radicals generated on the anode surface through water oxidation react non-selectively with various stubborn pollutants, thereby indirectly degrading them and alleviating The blockage of pollutants in the membrane pores is improved, and the increase of water flux is promoted.

Claims (10)

1. a preparation method of an electrochemically mediated osmotic membrane wastewater treatment system, is characterized in that, comprises the following steps: Step 1): Mix the vacuum-dried PMIA polymer, LiCl, DMac, acetone, and CNTs to form a casting liquid; Step 2): Spread the film base on the glass plate, use a film casting knife to quickly cast the degassed film casting solution on the film base, and quickly immerse the cast glass plate in a water-coagulation bath to ensure that Complete precipitation to obtain CNTs base film; Step 3): the membrane surface of the CNTs-based membrane obtained in Step 2) is immersed in the MPD aqueous solution, and the residual solution on the membrane surface is removed with a hair dryer; the membrane surface is exposed to the Isopar-G solution, and the excess organic solution is poured out, and the membrane is removed. Vacuum drying to improve the cross-linking degree of PA to obtain CNTs TFC film; Step 4): Assemble the membrane assembly-silicone gasket-metal sheet-silicone gasket-separation layer-silicone gasket-separation grid layer-CNTsTFC membrane-separation grid layer-silicone gasket-membrane assembly in sequence, wherein The CNTs TFC membrane is used as the anode, the active layer is facing the feed liquid side, the metal sheet is used as the cathode, and the separation grid layer is used for mechanical support; Step 5): connect the cathode and the anode respectively to the power supply, leave the water inlet and the water outlet on the left and right sides of the membrane module to connect the raw material liquid and the drawing liquid respectively, the drawing liquid is placed on an electronic balance to record the quality, and a conductivity meter is placed in the raw material liquid for observation. The conductivity of the raw material liquid changes; at the same time, the electronic balance and conductivity meter system are respectively connected to the computer to record the changes of quality and conductivity in real time, and analyze the water flux. 2. The preparation method of claim 1, wherein in the step 1), the mass percentage of PMIA in the casting solution is 10-15%, the mass percentage of LiCl is 2-5%, and the mass of CNTs is 2-5%. The percentage is 5-20%, and the volume ratio of DMac and acetone is 8:2. 3 . The preparation method according to claim 1 , wherein in the step 2), the film substrate is conductive carbon paper or conductive carbon cloth; the film thickness set by the film casting knife is 80-120 μm. 4 . 4. The preparation method of claim 1, wherein the temperature of the hydrogel in the step 2) is 50-70°C. 5. preparation method as claimed in claim 1 is characterized in that, in described step 3), CNTs base film is first immersed in the NaOH solution of 1.5mol/L before immersing MPD aqueous solution 1 hour, to improve the hydrophilicity of film . 6. preparation method as claimed in claim 1, is characterized in that, in described step 4), the size of the effective membrane pool of membrane module is 20mm * 60mm * 4mm; Separation mesh layer is non-conductive plastic mesh; The metal sheet is a titanium sheet, a platinum sheet or a nickel sheet; the size of the separation layer is consistent with the size of the membrane module, and a water passage is reserved in the middle of the separation layer. 7. The preparation method of claim 1, wherein the power supply in the step 5) is pulsed electricity, and the voltage is 1-3V. 8. preparation method as claimed in claim 1 is characterized in that, in described step 5), the running flow rate of CNTs TFC film is 10-20cm/s, and the temperature of raw material liquid and drawing liquid is kept at 25 using constant temperature water bath. ±0.1℃. 9. The electrochemically mediated permeable membrane wastewater treatment system prepared by the preparation method of any one of claims 1-8. 10. An application of the electrochemically mediated osmotic membrane wastewater treatment system of claim 9 in the treatment of antibiotic wastewater, heavy metal wastewater, printing and dyeing wastewater or landfill leachate.

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