NOVEL CONDUCTIVE MEMBRANE FILTRATION SYSTEM FOR DEGRADATION OF ORGANIC POLLUTANTS FROM WASTEWATER

Abstract

This invention relates to a novel conductive organic membrane-coupled filtration system for the degradation of organic pollutants from wastewater. The system comprises a connected water pump and a reactor. The upper end of the reactor contained a water inlet, and the lower end consisted of a water outlet. A counter electrode and a membrane electrode are fixed on the reactor between the water inlet and water outlet. The counter electrode and membrane electrode constitute a two-electrode system connected to an external potentiostat through metal wires. The membrane electrode is made of carbon-based polyvinylidene fluoride (PVDF) membrane that can be used to enhance the electrochemical separation of small molecules and the removal of organic pollutants.

Claims

1. The novel conductive organic membrane-coupled filtration system comprises a connected water pump and a reactor, upper end of the reactor contains a water inlet and the lower end is provided with a water outlet, a counter electrode and a membrane electrode are fixed on the reactor between the water inlet and water outlet, the counter electrode and membrane electrode constitute a two-electrode system connected to an external potentiostat through metal wires, the membrane electrode is a carbon-based PVDF membrane.

2. The conductive organic membrane-coupled filtration system described by claim 1 comprises a metal wire made of titanium.

3. The conductive organic membrane-coupled filtration system described by claim 1 comprises a counter electrode and a membrane electrode embedded in the electrode slot of the reactor and fixed by waterproof glue, Vaseline, and silica gel gasket.

4. The conductive organic membrane-coupled filtration system described by claim 1 comprises a counter electrode located directly above the membrane electrode.

5. The conductive organic membrane-coupled filtration system described by claim 1 comprises a vertical distance between the membrane electrode and the counter electrode set to 1-3 cm.

6. The conductive organic membrane-coupled filtration system described by claim 1 comprises a counter electrode made of platinum mesh, titanium mesh, or stainless steel mesh.

7. The conductive organic membrane-coupled filtration system described by claim 1 comprises a potentiostat with output voltages ranging from 0 to 3 V.

8. The conductive organic membrane-coupled filtration system described by claim 1 comprises a membrane electrode prepared by coating the PVDF casting solution on pretreated dry carbon fiber by scraping the membrane to yield a coating thickness of 300-400 μm, the modified carbon fiber is then left to stand in the air for 1-5 min followed by immersion in deionized water overnight to form the PVDF coating substrate membrane, after vacuum drying, a smooth and uniform carbon-based-PVDF membrane is obtained by the phase inversion method.

9. The conductive organic membrane-coupled filtration system described by claim 8 comprises a carbon fiber made of polyacrylonitrile.

10. The conductive organic membrane-coupled filtration system described by claim 8 states that the carbon fiber is pretreated by ultrasounds in acetone, ethanol, and deionized water solution respectively for 60-80 min to remove organic matter and other impurities attached to it followed by drying at 50-80° C. for 4-5 hours.

11. The conductive organic membrane-coupled filtration system described by claim 8 states that the PVDF casting solution is prepared by dissolving PVDF powder and PVP in DMF under magnetic stirring for 10-12 hours, the mixture is then vacuum degassed at 50-80° C. for 3-5 hours to yield a PVDF casting solution. The mass ratio of PVDF powder to those of PVP and DMF is 12:2:86.

12. The conductive organic membrane-coupled filtration system described in claim 8 states that the vacuum drying conditions are set to 50-80° C. and 50-70 min.

13. The conductive organic membrane-coupled filtration system described by claim 8 states that the phase conversion method is used by first coating the PVDF casting solution onto the PVDF coated base membrane by scraping, the resulting base membrane is then fixed on the glass plate, and the coating thickness is adjusted to 200-400 μm, after standing in the air for 1.sup.˜3 min, the glass plate is slowly immersed in 25-28° C. constant temperature deionized water, this process transforms the gel structure into a three-dimensional macromolecular network, which is cured after phase transformation.

14. A method for degrading organic wastewater by the conductive organic membrane-coupled filtration system described by claim 1 comprises the following steps: a reactor is used to pretreat the pure water passing through the system for 20-30 minutes to stabilize the membrane electrode, after pretreatment, a stable voltage is applied by the potentiostat to the counter electrode and membrane electrode, the organic wastewater is then continuously pumped into the reactor to yield purified wastewater flowing naturally out of the outlet.

15. The degradation method of organic wastewater described by claim 14 states that organic wastewater passing through the counter electrode and membrane electrode flows at the rate of 3-5 mL/min.

16. The degradation method of organic wastewater described by claim 14 states that organic wastewater is made by water containing methyl orange or humic acid.

Description

DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 shows a schematic diagram of the conductive organic membrane-coupled filtration system in Embodiment 1. The different components can be described as: (1) Water pump, (2) Water inlet, (3) Counter electrode, (4) Membrane electrode, (5) Water outlet, (6) Potentiostat, and (7) Reactor.

[0028] FIG. 2 displays scanning electron microscopy (SEM) images of the carbon fiber, basement membrane, and CC/PVDF membrane in Embodiment 1.

[0029] FIG. 3 illustrates a confocal laser scanning microscopy (CLSM) image of the carbon fiber in Embodiment 1.

[0030] FIG. 4 represents a CLSM image of the basement membrane in Embodiment 1.

[0031] FIG. 5 refers to a CLSM image of the CC/PVDF membrane in Embodiment 1.

[0032] FIG. 6 exhibits a SEM image of the CC/PVDF membrane in Embodiment 2 after the passage of organic wastewater through the system for 30 min.

[0033] FIG. 7 displays a ATR-FTIR spectrometry image of the CC/PVDF membrane in Embodiment 2 after the passage of organic wastewater through the system for 30 min.

[0034] FIG. 8 shows the voltage-current curves of methyl orange solutions at different concentrations passing through CC/PVDF membrane in Embodiment 2.

[0035] FIG. 9 illustrates a SEM image of the CC/PVDF membrane under 0 V voltage in Embodiment 4 after the passage of organic wastewater through the system for 30 min.

[0036] FIG. 10 is a SEM image of the CC/PVDF membrane under applied 1 V in Embodiment 4 after the passage of organic wastewater through the system for 30 min.

[0037] FIG. 11 presents a SEM image of the CC/PVDF membrane under an applied 2 V voltage in Embodiment 4 after passing the organic wastewater through the system for 30 min.

[0038] FIG. 12 shows a SEM image of the CC/PVDF membrane under an applied 3 V voltage in Embodiment 4 after passing organic wastewater through the system for 30 min.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0039] The proposed invention is described in combination with the drawings and specific embodiments, but the protection scope of the invention is not limited to the described.

[0040] Meanwhile, the experimental methods described in the following embodiments are conventional without special instructions. The reagents, materials, and equipment can be obtained from commercial providers without special instructions.

[0041] In the embodiment, the electrochemical equipment is a CH11030C multi-channel potentiostat sold by Shanghai Chenhua Instrument Co., Ltd. The titanium 60 mesh is sold by Cangzhou Kangwei metal products Co., Ltd. The carbon fiber is made of polyacrylonitrile commercialized by Shanghai Hesen Electric Co., Ltd. The conductive adhesive, titanium wire, waterproof adhesive, Vaseline, silica gel gasket, PVDF, methyl orange, and humic acid are all commercial products.

Embodiment 1

[0042] As shown in FIG. 1, the conductive organic membrane coupled-filtration system consists of a water pump 1 and a reactor 7 made of a closed plexiglass column with an effective volume of 12 L. Water inlet 2 is arranged at the upper end of reactor 7, and water outlet 5 is arranged at the lower end. Water inlet 2 is connected to water pump 1. Also, counter electrode 3 and membrane electrode 4 are embedded in reactor 7 between the water inlet 2 and water outlet 5. Counter electrode 3 is made of a 60 mesh titanium mesh, and membrane electrode 4 is composed of a carbon-based PVDF membrane (CC/PVDF membrane). Counter electrode 3 is located above membrane electrode 4 at a vertical distance of 1 cm. The interception of the membrane electrode 4 accumulates the pollutants in the organic wastewater between the two electrodes, leading to their degradation to a greater extent due to prolonged redox reactions by increasing the residence time. The membrane electrode 4 and counter electrode 3 constitute two-electrode systems, connected to the external potentiostat 6 through the conductive adhesive and titanium wire.

[0043] Membrane electrode 4 is made of carbon-based PVDF membrane prepared by first dissolving PVDF powder and PVP in DMF under magnetic stirring for 12 hours. After complete dissolution, the PVDF casting solution is prepared after vacuum degassing at 50° C. for 4 hours. Next, the PVDF casting solution is coated on the surface of pretreated dried carbon fiber through scraping to form a coating thickness of 300 μm. The modified substrate is then left to stand in the air for 3 min followed by immersion in deionized water overnight to form the PVDF coating base membrane. Afterward, the membrane is vacuum dried at 80° C. for 70 minutes, and then fixed on the glass plate for coating with the PVDF casting solution twice to yield a thickness of 200 μm. The glass plate modified membrane is left to stand in the air for 2 minutes and then slowly immersed in 25° C. constant temperature deionized water to form a smooth and uniform CC/PVDF membrane by phase transformation. As shown in FIG. 2-5, the smooth surface morphology of carbon fiber, basement membrane and CC/PVDF membrane gradually increases, while surface roughness decreases significantly. These features would improve the mechanical stability of CC/PVDF membrane.

[0044] The mass ratio of PVDF powder to those of PVP and DMF is 12:2:86.

Embodiment 2

[0045] The degradation of organic wastewater in Embodiment 1 comprises the following steps:

[0046] Reactor 7 is pretreated by passing pure water through the system for 20 min to stabilize the membrane electrode. The potentiostat 6 is then turned on and stable voltages of 1 V, 2 V, and 3 V are subsequently applied to the titanium mesh and CC/PVDF membrane. Afterward, the organic wastewater is continuously pumped into reactor 7 and passed through the titanium mesh and CC/PVDF membrane at a flow rate of 4 mL/min to flow out purified wastewater at the outlet.

[0047] In this invention, water containing 10 mg/L methyl orange and 10 mm NaCl aqueous solution is used as organic wastewater.

[0048] To evaluate the quality of organic wastewater after 30 min operation in this embodiment, the removal efficiency of organic wastewater is tested under stable voltages of 1 V, 2 V, and 3 V. The removal rates of methyl orange are estimated to 21%, 88% and 92%, and membrane water fluxes are 70%, 86% and 92%, respectively. As shown in FIG. 6 and FIG. 7, no obvious differences in surface morphologies and chemical compositions are noticed between the CC/PVDF membrane that passes through the organic wastewater for 30 min, as well as CC/PVDF membrane that does not pass through the organic wastewater. Thus, almost no adhesion or degradation of methyl orange occurs on the membrane, effectively inhibiting the membrane fouling. As shown in FIG. 8, the oxidation potential changes during the passage of organic wastewater through the CC/PVDF membrane. Hence, direct electron transfer takes place in the CC/PVDF membrane.

Embodiment 3

[0049] As described in Embodiment 2, the only difference between this Embodiment and the method used for degrading organic wastewater in Embodiment 1 is the concentration of organic wastewater that is set to 20 mg/L humic acid aqueous solution.

[0050] The quality of organic wastewater after 30 min operation in this embodiment is tested under stable voltages of 1 V, 2 V, and 3 V. The removal rates of humic acid are 71%, 76% and 82%, and the membrane water fluxes are 65%, 81% and 85%, respectively.

Embodiment 4

[0051] As described in Embodiment 2, the only difference with the method used for organic wastewater degradation in Embodiment 1 is the organic wastewater solution that contained 10.sup.5 CFU/mL E. coli.

[0052] To test the quality of purified water after 30 min operation in this embodiment, the effect of pollutant removal is recorded under the stable voltages of 1 V, 2 V, and 3 V. The bacterial mortality of the effluent reaches 100% at all voltages, and the membrane water fluxes are 71%, 80% and 85%, respectively. As shown in FIG. 9-12, the E. coli cell rupture and death are detected. As voltage increases, the cell rupture declines. Thus, the conductive organic membrane coupled filtration system has an efficient bactericidal ability.

[0053] Contrasting Case 1

[0054] A common ultrafiltration system used for removal of organic wastewater consists of PVDF ultrafiltration membrane sold by sterlitech company as a conductive organic membrane. In this experiment, a voltage of 3 V is applied by the potentiostat to the system and filtered water is collected after 30 min. The removal rate of methyl orange in the test organic wastewater treatment is estimated to 36%, and the water flux of the membrane is 55%.

[0055] Contrasting Case 2

[0056] As described in Embodiment 2, the difference from the method used to degrade organic wastewater in Embodiment 1 is the applied voltage by the potentiostat, which is set to 0 V. The filtered water under these conditions is then collected after 30 min to test the efficiency of the organic wastewater treatment. The removal rate of methyl orange under these conditions is less than 20%, and water flux of the membrane is 60%.

[0057] Contrasting Case 3

[0058] As described in Embodiment 2, the difference from the method used to degrade the organic wastewater in Embodiment 1 is the applied voltage by the potentiostat, which is set to 0 V. The filtered water is collected after 30 min to test the efficiency of organic wastewater treatment. The removal rate of humic acid, in this case, is recorded as 65%, and the water flux of the membrane is 40%.