Device for relieving membrane pollution of forward osmosis membrane bioreactor and use method

Abstract

The invention discloses a device for relieving membrane pollution of a forward osmosis membrane bioreactor and a method for treating wastewater, the device utilizes the lightning rod effect of a local strong electric field (LEEFT), a nano-cathode is placed on one side, close to a feed liquid cell, of the surface of a forward osmosis membrane in a water inlet separation net form, and low voltage (within 2V) is applied to the nano-electrode, so that the membrane pollution of the forward osmosis membrane bioreactor is relieved. On one hand, the cross flow speed is enhanced by utilizing the hydraulic action to slow down the forward osmosis membrane pollution process, and on the other hand, a local strong electric field is formed on the surface of the forward osmosis membrane to influence the migration of pollutants through electrophoresis and dielectrophoresis to relieve the formation of a biological membrane on the surface of the forward osmosis membrane; meanwhile, a micro electric field is mainly used in a main solution to influence microbial community composition and metabolic behaviors, so that forward osmosis membrane pollution formation is further regulated and controlled. The device can overcome the defect of membrane pollution of the forward osmosis membrane bioreactor, the treatment efficiency is improved, the treatment cost is saved, and extremely high environmental significance and good economic benefits are embodied.

Description

Technical Field

[0001] The invention relates to a device for alleviating membrane pollution of a forward osmosis membrane bioreactor and a use method thereof, belonging to the technical field of industrial wastewater treatment. Background Art

[0002] The forward osmosis membrane bioreactor (OMBR) is a wastewater treatment system that integrates the forward osmosis (FO) interception and biodegradation. It obtains high-quality effluent from wastewater through the FO membrane, and can effectively intercept trace pollutants (such as pathogenic microorganisms, antibiotics, etc.) in wastewater to achieve the purpose of wastewater resource utilization. It has the advantages of high wastewater reuse rate and low energy consumption. However, membrane fouling caused by the accumulation of inorganic salts and pollutants on the raw liquid side is still a key factor affecting the economic efficiency and operational stability of this technology. Due to the high interception rate of the FO membrane and the reverse solute diffusion (RSD) of the draw liquid into the feed liquid, the dissolved components accumulate in the bioreactor, resulting in a decrease in the driving force on the FO membrane and the biological activity in the bioreactor, thereby reducing the efficiency of the system in water recovery. The electrochemical effect generated by the applied voltage can effectively alleviate the membrane fouling problem in the OMBR, which has the advantages of simplicity and stable effect. However, the single electric field it generates has limited effect, and there are problems such as high energy consumption, secondary pollution, and damage to forward osmosis (FO) membranes. Summary of the invention

[0003] Purpose of the invention: The first purpose of the present invention is to provide a device for alleviating membrane fouling of a forward osmosis membrane bioreactor. The second purpose of the present invention is to provide a method for treating wastewater using the device for alleviating membrane fouling of a forward osmosis membrane bioreactor.

[0004] Technical solution: The device for alleviating membrane fouling of a forward osmosis membrane bioreactor described in the present invention comprises a forward osmosis membrane bioreactor unit and an electrode unit, characterized in that the forward osmosis membrane bioreactor unit comprises a feed liquid cell and an extraction liquid cell separated by a forward osmosis membrane, the feed liquid cell is filled with activated sludge; the extraction liquid cell is a forward osmosis extraction liquid that is pumped in a cycle, the electrode unit comprises an anode and a nano cathode, wherein the anode is placed in the feed liquid cell, and the nano cathode is placed on the surface of the forward osmosis membrane on one side of the feed liquid cell, and a voltage greater than 0 and less than or equal to 2V is applied to the electrode unit, so that a local strong electric field can be formed on the surface of the forward osmosis membrane, thereby producing a "lightning rod effect".

[0005] Furthermore, an inlet is provided at the lower part of one side of the feed liquid cell, an overflow is provided at the upper part of the other side of the feed liquid cell corresponding to the inlet and outlet, an inlet for drawn liquid is provided at the lower part of the drawn liquid cell, and an outlet for drawn liquid is provided at the upper part of the other side of the drawn liquid cell corresponding to the inlet for drawn liquid, the inlet and the overflow are respectively connected to the wastewater pool outside the device, and the inlet and the outlet for drawn liquid are respectively connected to the forward osmosis drawn liquid pool outside the device.

[0006] Furthermore, the anode and the nano cathode are connected to a direct current power source through a conductive metal wire and a resistance wire.

[0007] Furthermore, the conductive metal wire is a titanium wire or a metal wire with good conductive performance; the resistance of the resistance wire is 1 to 1000Ω; the DC power supply is an adjustable DC power supply, and the load voltage range is 0.6 to 4V.

[0008] Furthermore, the anode includes activated carbon particles applied to conductive carbon cloth, and the nano cathode is a copper oxide nano electrode.

[0009] Furthermore, the nano cathode includes a copper mesh as a substrate, and copper oxide nanowires are grown on the surface of the copper mesh through oxidation treatment.

[0010] Furthermore, the forward osmosis membrane bioreactor unit is a box-type or columnar structure.

[0011] Furthermore, the forward osmosis membrane is a cellulose triacetate membrane (CTA), a thin layer composite polyamide membrane (TFC) or a modified membrane thereof.

[0012] Furthermore, the distance between the anode and the nano cathode is 1 to 2 cm.

[0013] Furthermore, the preparation method of the nano cathode, i.e., the copper oxide nano electrode, comprises the following steps:

[0014] (A1) Cleaning: Rinse the copper mesh with acid and then with deionized water;

[0015] (A2) Reaction: calcining the cleaned copper mesh in step (A1), cooling and oxidizing, and vertically growing copper oxide nanowires on the surface of the copper mesh;

[0016] (A3) Coating: The copper mesh with copper oxide nanowires grown in step (A2) is transferred to a hydrochloric acid methyl acid buffer solution in which dopamine is dissolved, and the reaction is heated in a water bath so that dopamine is coated on the surface of the copper oxide nanowires to form a protective layer.

[0017] Furthermore, in step (A1), the acid is hydrochloric acid, and the concentration of the acid is below 0.1 mol / L.

[0018] Furthermore, in step (A2), the calcination temperature is 400-500°C, the calcination time is more than 2 hours, the cooling and oxidation temperature is room temperature, and the cooling and oxidation time is more than 12 hours.

[0019] Furthermore, in step (A3), the concentration of the hydrochloric acid methyl acid buffer in which dopamine is dissolved is 2 g / L, the temperature of the water bath heating reaction is about 40°C, the time of the water bath heating reaction is more than 4 hours, and the thickness of the protective layer formed by the dopamine fluoride coating on the surface of the copper oxide nanoelectrode is 12-30 nm.

[0020] A method for using the device for alleviating membrane fouling of a forward osmosis membrane bioreactor according to the present invention comprises the following steps:

[0021] (B1) The wastewater enters the feed liquid cell of the forward osmosis membrane bioreactor unit, a low voltage is applied to the electrode unit, the wastewater is intercepted by the forward osmosis membrane, and contacts and reacts with the microorganisms in the activated sludge in the feed liquid cell;

[0022] (B2) The wastewater in the feed liquid cell is stretched, permeates through the forward osmosis membrane and diffuses into the draw liquid cell, where it is mixed with the forward osmosis draw liquid pumped into the draw liquid cell. The wastewater overflowing from the feed liquid cell flows back to the wastewater pool outside the device, and the treated wastewater in the draw liquid cell is returned to the forward osmosis draw liquid pool outside the device.

[0023] Furthermore, in step (B1), the organic pollutants are consumed and decomposed by the microorganisms, while the trace pollutants are retained by the forward osmosis membrane in the feed liquid compartment and then metabolized and decomposed by the microorganisms.

[0024] Furthermore, in step (B1), the low voltage is a voltage greater than 0 and less than or equal to 2V. The low surface curvature of the nanocathode increases the charge density of the nanocathode to form a local strong electric field, thereby producing a "lightning rod effect", which increases the electric field strength on the surface of the nanocathode by several orders of magnitude (greater than 100 kV / cm). The electrostatic repulsion of the local strong electric field is used to move negatively charged pollutants away from the surface of the forward osmosis membrane, thereby alleviating the formation of membrane pollution.

[0025] Furthermore, in step (B2), due to the osmotic pressure difference between the feed liquid compartment and the draw liquid compartment, the water in the feed liquid compartment is stretched, permeates through the forward osmosis membrane and diffuses into the draw liquid compartment.

[0026] Furthermore, in step (B2), in order to avoid the resulting decrease in osmotic pressure driving force, it is necessary to circulate the draw liquid into the draw liquid cell to maintain a stable osmotic pressure difference and thus ensure a high water flux.

[0027] Furthermore, in step (B2), the forward osmosis draw solution is a salt solution, which can be one or more of CaCl2, NaCl, and NH4Cl.

[0028] Furthermore, in step (B2), there is a salinity gradient on both sides of the forward osmosis membrane. Due to the salinity gradient on both sides of the forward osmosis membrane, part of the salt in the draw liquid cell will penetrate into the feed liquid cell due to the reverse diffusion of the solute, resulting in a decrease in the draw liquid concentration and salt accumulation, which in turn leads to a decrease in water flux, which in turn causes the water to be unable to be stretched into the draw liquid cell in time, so that the wastewater overflowing from the feed liquid cell flows back to the wastewater pool.

[0029] The present invention applies a low voltage (greater than 0 and less than or equal to 2V) to the electrode unit. Since the wastewater continuously or indirectly enters the feed liquid cell of the forward osmosis membrane bioreactor unit, the inorganic, organic and biological pollutants in the wastewater will adhere to the surface of the forward osmosis membrane to form a membrane pollution layer, which will cause the water flux to decrease and affect the system performance. Therefore, a nano cathode with copper oxide nanowires grown on the surface is placed on the side of the feed liquid cell on the surface of the forward osmosis membrane, and a low voltage (greater than 0 and less than or equal to 2V) is applied to the electrode unit through a DC power supply. On the one hand, the adhesion of pollutants on the nano cathode and the forward osmosis membrane surface can be reduced through hydraulic action, and on the other hand, the "lightning rod effect" of the local strong electric field can be achieved. The "bactericidal effect" removes the biofilm formed on the surface of the nano cathode and forward osmosis membrane, slows down the formation of biological composite pollution, avoids the decline of water flux and the reduction of system performance; at the same time, the microorganisms and organic matter in the feed liquid cell are in a micro-electric field environment, which can promote the metabolism of microbial cells, enhance microbial activity, and promote the degradation of pollutants; at the same time, the micro-electric field environment will affect the structure of the microbial community, further affect the utilization and metabolic behavior of microorganisms on substances, thereby affecting the formation of membrane pollution; in addition, the induced current will cause an oxidation reaction near the anode, which can cooperate with microorganisms to oxidize and degrade organic pollutants and can oxidize and break difficult-to-biodegrade macromolecular pollutants into small molecular intermediates for microbial use.

[0030] The technical problem to be solved by the present application is the technical problem that the membrane pollution of the forward osmosis membrane bioreactor in the prior art leads to the decline of system performance, and provides a device and a method for using the membrane pollution of the forward osmosis membrane bioreactor. This method utilizes the "lightning rod" effect of the local strong electric field (LEEFT). By placing the nano cathode on the membrane surface in the form of a water inlet screen, on the one hand, the hydraulic action is used to enhance the cross-flow speed and slow down the membrane pollution process. On the other hand, a strong electric field is formed on the membrane surface, which affects the migration of pollutants through electrophysical action and reduces the attachment of pollutants on the membrane surface; it can also mainly affect the composition and metabolic behavior of the microbial community in the main solution with the micro-electric field, and alleviate the formation of OMBR membrane pollution; because the added voltage is relatively low (greater than 0 and less than or equal to 2V), the local strong electric field generated by the device is theoretically mainly electrophysical, which reduces the electrochemical action, reduces the generation of by-products, reduces the risk of secondary pollution and damage to the FO membrane structure, saves the processing cost, and reflects the extremely high environmental significance and good economic benefits.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0032] The device of the present invention utilizes the "lightning rod" effect of the local strong electric field (LEEFT). By placing the nano cathode on the membrane surface in the form of a water inlet screen, on the one hand, the hydraulic effect is used to enhance the cross-flow speed to slow down the membrane fouling process, and on the other hand, a strong electric field is formed on the membrane surface to affect the migration of pollutants through electrophysical effects, thereby alleviating the formation of a membrane fouling layer. It can also mainly affect the composition and metabolic behavior of the microbial community in the main solution through a micro-electric field, activate the activity of microorganisms to further improve the biodegradability of the reactor, and further improve the membrane fouling situation. Since the added voltage is relatively low (within 2V), the local strong electric field generated by the LEEFT device is theoretically mainly electrophysical, which reduces electrochemical effects, reduces the generation of by-products, reduces the risk of secondary pollution and damage to the FO membrane structure, saves processing costs, and reflects extremely high environmental significance and good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the structure of the device for alleviating membrane fouling of a forward osmosis membrane bioreactor as described in Example 1;

[0034] Figure 2 for Figure 1 A top view of the forward osmosis membrane bioreactor unit and the electrode coupling device of the electrode unit;

[0035] Figure 3 for Figure 1 Left view of the forward osmosis membrane bioreactor unit and the electrode coupling device of the electrode unit;

[0036] Figure 4 for Figure 1 Right view of the forward osmosis membrane bioreactor unit and the electrode coupling device of the electrode unit;

[0037] Figure 5 for Figure 1 Front view of the forward osmosis membrane bioreactor unit and the electrode coupling device of the electrode unit;

[0038] Figure 6 for Figure 1 Rear view of the forward osmosis membrane bioreactor unit and the electrode coupling device of the electrode unit;

[0039] Figure 7 Detailed diagram of the electrode unit electrode.

[0040] Among them, 1. forward osmosis membrane bioreactor unit; 2. electrode unit; 3. forward osmosis membrane; 4. feed liquid cell; 5. extraction liquid cell; 6. feed liquid inlet; 7. feed liquid outlet; 8. extraction liquid inlet; 9. extraction liquid outlet; 10. anode; 11. nano cathode; 12. conductive metal wire; 13. resistance wire; 14. DC power supply. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0042] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0043] Example 1

[0044] like Figure 1-6 As shown, the device for alleviating membrane pollution of a forward osmosis membrane bioreactor described in the present invention comprises a box-type forward osmosis membrane bioreactor unit 1 and an electrode unit 2. The forward osmosis membrane bioreactor unit 1 comprises a feed liquid cell 4 and an extraction liquid cell 5 separated by a forward osmosis membrane 3, wherein the feed liquid cell 4 contains activated sludge; the extraction liquid cell contains the forward osmosis extraction liquid that is circulated and injected; the electrode unit 2 comprises an anode 10 and a nano cathode 11, wherein the anode 10 is placed in the feed liquid cell 4, and the nano cathode 11 is placed on the surface of the forward osmosis membrane 3, biased towards the feed liquid cell 4. When a voltage of less than 0.6V is applied to the electrode unit 2, a local strong electric field can be formed on the surface of the forward osmosis membrane 3, thereby producing a "lightning rod effect".

[0045] Among them, a water inlet 6 is provided at the lower part of one side of the feed liquid cell 4, and an overflow port 7 is provided at the upper part of the other side of the feed liquid cell 4 corresponding to the water inlet and outlet 6. A drawn liquid water inlet 8 is provided at the lower part of the drawn liquid cell 5, and an drawn liquid water outlet 9 is provided at the upper part of the other side of the drawn liquid cell 5 corresponding to the drawn liquid water inlet 8. The water inlet 6 and the overflow port 7 are respectively connected to the wastewater tank outside the device, and the drawn liquid water inlet 8 and the drawn liquid water outlet 9 are respectively connected to the forward osmosis drawn liquid tank outside the device.

[0046] The electrode unit 2 is composed of an electrode pair of an anode 10 and a nano cathode 11, wherein the anode 10 is made of a conductive carbon cloth coated with activated carbon particles on a base, and the nano cathode 11 is a copper oxide nano electrode. The anode 10 is placed in the middle of the feed liquid cell 4 of the forward osmosis membrane bioreactor unit 1, and the nano cathode 11 is placed on the surface of the forward osmosis membrane 3 of the forward osmosis membrane bioreactor unit 1, which is biased to the side of the feed liquid cell 4 (the effective surface of the forward osmosis membrane 3 is consistent with the effective surface of the nano cathode 11). The anode 10 and the nano cathode 11 are both connected to a DC power supply 14 through a conductive metal wire 12 and a resistance wire 13.

[0047] The forward osmosis membrane 3 is a cellulose triacetate membrane (CTA) or a thin layer composite polyamide membrane (TFC).

[0048] The conductive metal wire 12 is a titanium wire or metal wire with good conductivity; the resistance of the resistance wire 13 is 1-1000Ω; the DC power supply 14 is an adjustable DC power supply, and the load voltage is 0.6-4V. The distance between the anode 10 and the nano cathode 11 is 1-2cm.

[0049] The forward osmosis draw solution is one or more of CaCl2, NaCl, and NH4Cl solutions. The concentration of the forward osmosis draw solution is 1-2 mol / L. The amount of activated sludge used is 2000-3000 mg / L of wastewater.

[0050] The cathode 11, i.e., the copper oxide nanoelectrode, is specifically obtained in the following manner:

[0051] (A1) Cleaning: Rinse the copper mesh with 0.1 mol / L HCl and then rinse with deionized water;

[0052] (A2) Reaction: The cleaned copper mesh in step (A1) was moved to a muffle furnace, heated in air at 400-500° C. for 2 h, and then taken out and oxidized overnight for 12 h, so that the copper oxide nanowires grew vertically to the electrode surface;

[0053] (A3) Coating: The copper mesh on which the copper oxide nanowires were grown in step (2) was transferred to a 2 g / L dopamine-dissolved hydrochloric acid methyl acid buffer solution and heated in a water bath at about 40° C. for 4 h, so that the dopamine-fluorine-coated copper oxide nanoelectrode formed a protective layer on the surface, thereby obtaining copper oxide nanowires.

[0054] The method for treating wastewater using the above-mentioned device for alleviating membrane contamination of a forward osmosis membrane bioreactor comprises the following steps:

[0055] (B1) The wastewater enters the feed liquid cell 4 of the forward osmosis membrane bioreactor unit 1, and a low voltage is applied to the electrode unit 2. The wastewater is intercepted by the forward osmosis membrane 3 and contacts and reacts with the microorganisms in the activated sludge in the feed liquid cell 4;

[0056] (B2) The wastewater in the feed liquid cell 4 is stretched, permeates through the forward osmosis membrane 3 and diffuses into the draw liquid cell 5, and is mixed with the forward osmosis draw liquid pumped into the draw liquid cell 5. The wastewater overflowing from the feed liquid cell 4 flows back to the wastewater pool outside the device, and the treated wastewater in the draw liquid cell 5 returns to the forward osmosis draw liquid pool outside the device.

[0057] Specifically, the forward osmosis liquid in the forward osmosis liquid pool is pumped into the liquid cell 5 from the liquid inlet 8, and the wastewater in the wastewater pool continuously or indirectly enters the feed liquid cell 4 of the forward osmosis membrane bioreactor unit 1 from the water inlet 6. A low voltage of less than 0.6V is applied to the anode 10 and the cathode 11 through the DC power supply 14, and the wastewater is retained by the forward osmosis membrane 3 and fully contacts and reacts with the microorganisms in the activated sludge in the feed liquid cell 4. The organic pollutants are consumed and decomposed by the microorganisms, while the trace pollutants are retained by the forward osmosis membrane 3 in the feed liquid cell 4 and then metabolized and decomposed by the microorganisms; due to the osmotic pressure difference between the feed liquid cell 4 and the liquid cell 5, the water in the feed liquid cell 4 is stretched, permeated through the forward osmosis membrane 3 and diffused into the liquid cell 5. , the forward osmosis drawn liquid in the drawn liquid cell 5 is discharged from the drawn liquid outlet 9 to the forward osmosis drawn liquid pool; in order to avoid the resulting decrease in osmotic pressure driving force, it is necessary to circulate the forward osmosis drawn liquid in the forward osmosis drawn liquid pool through the drawn liquid inlet and outlet 8 into the drawn liquid cell 5, maintain a stable osmotic pressure difference and thus ensure a higher water flux; due to the salinity gradient on both sides of the forward osmosis membrane 3, part of the salt in the forward osmosis drawn liquid in the drawn liquid cell 5 will infiltrate into the feed liquid cell 4 due to the reverse diffusion of the solute, resulting in a decrease in the forward osmosis drawn liquid concentration and salt accumulation, thereby resulting in a decrease in water flux, and ultimately resulting in the inability of water to be stretched into the drawn liquid cell 5 in time, so that the wastewater in the feed liquid cell 4 overflows through the overflow port 7 to flow back to the waste liquid pool;

[0058] In the above operation, since the wastewater continuously or indirectly enters the feed liquid cell 4 of the forward osmosis membrane bioreactor unit 1 from the water inlet 6, the inorganic, organic and biological pollutants in the wastewater will adhere to the membrane pollution layer formed on the surface of the forward osmosis membrane 3, which will cause the water flux to decrease and affect the system performance. Therefore, the cathode 11 with copper oxide nanowires grown on the surface is placed on the side of the feed liquid cell 4 on the surface of the forward osmosis membrane 3, and a low voltage (greater than 0 and less than or equal to 2V) is applied by a DC power supply 14. The low surface curvature of the copper oxide nanowires increases the charge density of the cathode 11. This "lightning rod effect" increases the electric field strength on the electrode surface by several orders of magnitude (greater than 100kV / cm), thereby utilizing the electrostatic repulsion of the local strong electric field to make the negatively charged pollutants move away from the membrane surface, thereby alleviating the formation of membrane pollution; the cathode 11 is placed on the surface of the forward osmosis membrane 3 in the form of a water inlet screen, and a low voltage (greater than 0 and less than or equal to 2V) is applied by a DC power supply 14. =0 is less than or equal to 2V), on the one hand, it can reduce the attachment of pollutants on the surface of the cathode 11 and the forward osmosis membrane 3 by hydraulic action, and on the other hand, it can remove the biofilm formed on the surface of the cathode 11 and the forward osmosis membrane 3 by the bactericidal effect of the local strong electric field, slow down the formation of biological composite pollution, and avoid the decrease of water flux and the reduction of system performance; a low voltage (greater than 0 and less than or equal to 2V) is applied to the cathode 11 by the DC power supply 14, and the microorganisms and organic matter in the feed liquid cell 4 are in a micro-electric field environment, which can promote the metabolism of microbial cells, enhance microbial activity, and promote the degradation of pollutants; at the same time, the micro-electric field environment will affect the structure of the microbial community, and further affect the utilization and metabolic behavior of the microorganisms on the substances, thereby affecting the formation of membrane pollution; in addition, the induced current will cause an oxidation reaction near the anode 10, which can cooperate with the microorganisms to oxidize and degrade organic pollutants, and can oxidize and break the difficult-to-biodegrade macromolecular pollutants into small molecular intermediates for microbial utilization.

[0059] Example 2

[0060] The device and method for alleviating membrane contamination of a forward osmosis membrane bioreactor shown in Example 1 are used to treat water, and the steps are as follows:

[0061] In this example, different simulated wastewaters to be treated (1, 500 mg / L humic acid solution; 2, 500 mg / L sodium alginate solution) and forward osmosis extract (1 mol·L -1CaCl2) condition, the device alleviates membrane pollution and controls the pollutant removal effect. Among them, the forward osmosis membrane 3 is fixed between the feed liquid cell 4 and the draw liquid cell 5. The feed liquid cell 4 and the draw liquid cell 5 on both sides of the forward osmosis membrane 3 are 50mm long, 50mm wide and 35mm deep. Two rubber gaskets are used to clamp the forward osmosis membrane 3 to fix it. The forward osmosis membrane 3 is a cellulose triacetate membrane (CTA), the conductive metal wire 12 is a titanium wire with good conductivity; the resistance of the resistance wire 13 is 1000Ω; the DC power supply 14 is an adjustable DC power supply, and the load voltage is 0.6~4V. The distance between the anode 10 and the nano cathode 11 is 1.5cm. The batch filtration experiment is run with the active layer facing the raw liquid (AL-FS mode). The initial volume of the three simulated wastewaters to be treated and the forward osmosis draw liquid is 1000mL. The DC power supply 14 provides a DC voltage of 2V. The feed liquid cell 4 contains 3 g of activated sludge; the speed of circulating solution into the feed liquid cell 4 and the draw liquid cell 5 is 96 mL / min.

[0062] At the same time, ordinary metal mesh electrodes were used instead of copper oxide nanowire electrodes for comparison. The results after treatment are as follows:

[0063] Compared with ordinary metal mesh electrodes, the copper oxide nanowire electrode has significantly improved system permeability, reduced salt reverse osmosis, and alleviated membrane pollution. The electrode is connected to an external DC voltage of 2V, and the humic acid solution is pumped into the feed liquid cell 4 of the reactor through the water inlet 6, and at the same time, 1 mol·L is pumped into the draw liquid cell 5 through the draw liquid inlet 8. -1 Calcium chloride is used as the forward osmosis drawing liquid to draw water from the feed liquid cell 4. The cathode 11 reduces the adhesion of pollutants on the surface of the cathode 11 and the forward osmosis membrane 3 through hydraulic action on the one hand, and can repel pollutants with the same charge through the electrophoresis and dielectrophoresis of the local strong electric field on the other hand, thereby slowing down the formation of membrane pollution and avoiding the decrease of water flux and system performance. After running for 24 hours, the water recovery amount of the copper oxide nanowire electrode system was 115.3±4.2g, while the water recovery amount of the ordinary metal mesh electrode system was 63.9±3.7g. The effect of the copper oxide nanowire electrode was improved by more than 70% compared with the ordinary metal mesh electrode; in the ordinary metal mesh electrode system, the system water flux dropped to 3.77±0.22LMH, and dropped to 6.76±0.08LMH in the copper oxide nanowire electrode system of the present invention; in the ordinary metal mesh electrode system, the system conductivity was 1165.5±256.7us / cm, while in the copper oxide nanowire electrode system of the present invention, the conductivity was 733±130.1us / cm, and the salt reverse osmosis situation was improved; the membrane pollution situation after the operation of the copper oxide nanowire electrode system of the present invention was significantly alleviated compared with the ordinary electrode system.

[0064] Sodium alginate was compared with humic acid to simulate the effect of the type of wastewater to be treated on the system performance. The electrodes were connected to a DC voltage of 2V, and the sodium alginate solution was pumped into the feed liquid cell 4 of the reactor through the water inlet 6. At the same time, 1 mol·L of sodium alginate was pumped into the draw liquid cell 5 through the draw liquid inlet 8. -1 Calcium chloride is used as the forward osmosis extraction liquid to extract the simulated wastewater to be treated in the feed liquid cell 4. After 24 hours of operation, the water recovery of the ordinary metal mesh electrode system is 53.3±1.5g, which is significantly lower than the case without power (74.3±1.2g), while the water recovery of the copper oxide nanowire electrode system is 78.9±0.4g, which is better than the case without power (75.4±0.9g); in the ordinary metal mesh electrode system, the system water flux drops to 3.14±0.09LMH, and in the copper oxide nanowire electrode system of the present invention, it drops to 4.65±0.03LMH. The permeability of the copper oxide nanowire electrode is significantly improved compared with the ordinary metal mesh electrode. In the ordinary metal mesh electrode system, the system conductivity is 459.5±10.6us / cm, while in the copper oxide nanowire electrode system of the present invention, the system conductivity is 382.0±42.4us / cm, and the salt reverse osmosis situation is improved. The membrane pollution of the copper oxide nanowire electrode system after operation of the present invention is significantly alleviated compared with the ordinary electrode system. However, compared with the treatment of humic acid solution, the system permeability and membrane pollution are limited when used to treat sodium alginate.

[0065] Example 3 Comparison of the effects of different extraction solutions

[0066] The experimental process is the same as that of Example 2, except that the forward osmosis draw solution CaCl2 is replaced by commonly used NaCl and NH4Cl. The sodium alginate solution is pumped into the feed liquid cell 4 of the reactor through the water inlet 6 and operated for 24 hours at 1 mol·L -1 Under the same concentration of forward osmosis draw solution, the initial water flux of the three draw solutions in the non-electric system was similar, and the water flux gradually decreased during the 24-hour operation, and after 24 hours, the water flux was 1 mol·L -1 The final water flux of CaCl2 draw solution was the lowest at 4.44±0.05LMH, the final water flux of NaCl draw solution was 5.23±0.02LMH, and the final water flux of NH4Cl was the highest at 5.60±0.12LMH.

[0067] In the powered system (taking 2 V voltage as an example), the initial water flux of the three extracting solutions was similar to that of the non-powered system. The water flux gradually decreased during the 24-hour operation and reached 1 mol·L after 24 hours. -1The final water flux of CaCl2 draw solution was the lowest at 4.65±0.03LMH, which was only 60% of that of NaCl and NH4Cl. The final water flux distribution of NaCl and NH4Cl was 7.34±0.16LMH and 7.16±0.11LMH respectively. After 24 hours, the water recovery of CaCl2 draw solution in the powered system (taking 2V voltage as an example) was not significantly improved compared with that without power supply, while the water recovery of NaCl and NH4Cl increased by 40% and 27% respectively compared with that of the non-power supply system. After 24 hours, the system conductivity of the powered system (taking 2V voltage as an example) was 382.0±42. 4us / cm, sodium chloride is 1029.5±17.7us / cm, ammonium chloride is 2117.0±70.7us / cm, the conductivity of the three forward osmosis draw solutions is increased by 37%, 17% and 22% respectively compared with the uncharged system (calcium chloride is 277.0±7.2us / cm, sodium chloride is 880.5±119.5us / cm, ammonium chloride is 1729.8±189.9us / cm), among which the reverse osmosis amount of calcium chloride is the smallest, and the reverse osmosis of ammonium chloride is the most serious. Under the conditions of the three forward osmosis draw solutions, the reaction type between reverse osmosis ions and pollutants has an important influence on the system permeability and membrane fouling.

[0068] Example 4 Comparison of the effects of different applied voltage intensities

[0069] The experimental process is the same as that of Example 2, except that 0V, 0.6V, 2V, and 4V voltages are used to compare the effects of different voltage strengths on system performance. The humic acid solution is pumped into the feed liquid cell 4 of the reactor through the water inlet 6, and 1 mol·L is pumped into the draw liquid cell 5 through the draw liquid inlet 8. -1 Calcium chloride is used as the extraction liquid to extract water from the feed liquid cell 4. After running for 24 hours, the water recovery of the system under the four voltage intensities is 70.0±2.1g, 100.3±2.4g, 115.3±4.2g, and 93.0±0.9g, respectively, and the water flux of the system decreases to 4.20±0.07LMH, 5.85±0.07LMH, 6.76±0.08LMH, and 5.45±0.06LMH, respectively; the conductivity under the four voltage intensities is 386.0±25.5us / cm, 419.5±33.2us / cm, 733.0±130.1us / cm, and 1836.5±77.1us / cm, respectively. The improvement effect of the four voltage intensities on the system performance shows a trend of 2V>0.6V>4V>0V.

[0070] The electrodes were connected to external DC voltages of 0V, 0.6V, 2V, and 4V. The sodium alginate solution was pumped into the feed liquid cell 4 of the reactor through the water inlet 6. At the same time, 1 mol·L sodium alginate was pumped into the draw liquid cell 5 through the draw liquid inlet 8. -1Calcium chloride is used as the extraction liquid to extract water from the feed liquid cell 4. After 24 hours of operation, the water recovery of the system under the four voltage intensities is 75.4±0.9g, 73.2±1.5g, 78.9±0.4g, and 42.6±2.1g, respectively, and the water flux of the system decreases by 4.44±0.05LMH, 4.34±0.04LMH, 4.65±0.03LMH, and 2.51±0.12LMH, respectively; the conductivity under the four voltage intensities is 277.0±7.2us / cm, 277.0±8.5us / cm, 382.0±42.4us / cm, and 534.0±62.2us / cm, respectively. The improvement effect of the four voltage intensities on the system performance shows a trend of 2V>0V>0.6V>4V.

[0071] Example 5 Simulation of the effect of treating urban sewage

[0072] The experimental process is the same as in Example 2. The simulated wastewater to be treated is: biological composite wastewater (simulated municipal wastewater is inoculated with aerobic sludge. The specific formula of simulated municipal wastewater contains: 500 mg·L -1 Sodium acetate (390mg·L -1 COD), 22mg·L -1 KH2PO4, 75mg·L -1 NH4Cl (i.e. 20 mg·L -1 NH4 + -N)、20mg·L -1 CaCl2, 100mg·L -1 MgCl2 and 1mL·L -1 Trace elements (1 liter of distilled water contains 50g FeCl2·4H2O, 1.25g ZnCl2, 12.5g MnCl2·4H2O, 1.25g (NH4)6Mo9O 24 ·4H2O, 3.75gCoCl·6H2O, 2.5gNiCl2·6H2O, 0.75gCuCl2·2H2O and 1.25g H3BO3), and the sludge concentration of the mixed liquid of sludge and water in the biological composite wastewater is guaranteed to be between 2000 and 3000mg·L -1 The electrodes were connected to external DC voltages of 0V, 0.6V, 2V, and 4V, and the biocomposite wastewater was pumped into the feed liquid cell 4 of the reactor through the water inlet 6, and 1 mol·L was pumped into the draw liquid cell 5 through the draw liquid inlet 8. -1Sodium chloride was used as the draw liquid to draw water from the feed liquid cell 4. After 5 days of operation, the water recovery of the system under the four voltage intensities of 0 to 4V was 306.6±31.9g, 394.4±12.7g, 286.0±5.7g, and 232.1±15.6g, respectively, and the water flux of the system decreased to 3.62±0.28LMH, 4.65±0.15LMH, 3.37±0.07LMH, and 3.48±0.05LMH, respectively; the conductivity under the four voltage intensities was 1798.6±125.4us / cm, 2096.7±148.4us / cm, 5008.2±253.3us / cm, and 101296.4±12824.4us / cm, respectively. The improvement effect of the four voltage intensities on the system performance showed a trend of 0.6V>0V>2V>4V.

Claims

1. A device for alleviating membrane fouling in a forward osmosis membrane bioreactor, comprising a forward osmosis membrane bioreactor unit (1) and an electrode unit (2), characterized in that: The forward osmosis membrane bioreactor unit (1) comprises a feed liquid cell (4) and an extraction liquid cell (5) separated by a forward osmosis membrane (3), wherein the feed liquid cell (4) contains activated sludge; the extraction liquid cell (5) is a forward osmosis extraction liquid that is pumped in a cycle; the electrode unit (2) comprises an anode (10) and a nano cathode (11), wherein the anode (10) is placed in the feed liquid cell (4), and the nano cathode (11) is placed on the surface of the forward osmosis membrane (3) at one side of the feed liquid cell (4); a voltage greater than 0 and less than or equal to 2V is applied to the electrode unit (2), so that a local strong electric field can be formed on the surface of the forward osmosis membrane (3), thereby generating a "lightning rod effect".

2. The device for alleviating membrane pollution of a forward osmosis membrane bioreactor according to claim 1, characterized in that: A water inlet (6) is provided at the lower part of one side of the feed liquid cell (4), and an overflow port (7) is provided at the upper part of the other side of the feed liquid cell (4) corresponding to the water inlet (6). A draw liquid water inlet (8) is provided at the lower part of the draw liquid cell (5), and a draw liquid water outlet (9) is provided at the upper part of the other side of the draw liquid cell (5) corresponding to the draw liquid water inlet (8). The water inlet (6) and the overflow port (7) are respectively connected to a wastewater pool outside the device, and the draw liquid water inlet (8) and the draw liquid water outlet (9) are respectively connected to a forward osmosis draw liquid pool outside the device.

3. The device for alleviating membrane pollution of a forward osmosis membrane bioreactor according to claim 1, characterized in that: The anode (10) and the nano cathode (11) are connected to a DC power source (14) via a conductive metal wire (12) and a resistance wire (13); the anode (10) comprises activated carbon particles applied to a conductive carbon cloth, and the nano cathode (11) is a copper oxide nano electrode.

4. The device for alleviating membrane pollution of a forward osmosis membrane bioreactor according to claim 3, characterized in that: The conductive metal wire (12) is a titanium wire or a metal wire; the resistance of the resistance wire (13) is 1 to 1000Ω; the DC power supply (14) is an adjustable DC power supply, and the load voltage range is 0.6 to 4V.

5. The device for alleviating membrane fouling of a forward osmosis membrane bioreactor according to claim 3, characterized in that: The nano cathode (11) comprises a copper mesh as a substrate, and copper oxide nanowires are grown on the surface of the copper mesh through oxidation treatment.

6. The device for alleviating membrane fouling of a forward osmosis membrane bioreactor according to claim 1, characterized in that: The forward osmosis membrane bioreactor unit (1) is a box-type or columnar structure.

7. The device for alleviating membrane fouling of a forward osmosis membrane bioreactor according to claim 1, characterized in that: The forward osmosis membrane (3) is a triacetate cellulose membrane, a thin layer composite polyamide membrane or a modified membrane thereof.

8. The device for alleviating membrane fouling of a forward osmosis membrane bioreactor according to claim 1, characterized in that: The distance between the anode (10) and the nano cathode (11) is 1 to 2 cm.

9. The device for alleviating membrane fouling of a forward osmosis membrane bioreactor according to claim 3, characterized in that: The preparation method of the nano cathode (11), i.e., the copper oxide nano electrode, comprises the following steps: (A1) Cleaning: Rinse the copper mesh with acid and then with deionized water; (A2) Reaction: calcining the cleaned copper mesh in step (A1), cooling and oxidizing, and vertically growing copper oxide nanowires on the surface of the copper mesh; (A3) Coating: The copper mesh with copper oxide nanowires grown in step (A2) is transferred to a hydrochloric acid methyl acid buffer solution in which dopamine is dissolved, and the reaction is heated in a water bath so that dopamine is coated on the surface of the copper oxide nanowires to form a protective layer.

10. A method for treating wastewater using the device for alleviating membrane fouling of a forward osmosis membrane bioreactor according to any one of claims 1 to 9, characterized in that: The following steps are involved: (B1) wastewater enters the feed liquid cell (4) of the forward osmosis membrane bioreactor unit (1), a low voltage is applied to the electrode unit (2), the wastewater is intercepted by the forward osmosis membrane (3), and contacts and reacts with the microorganisms in the activated sludge in the feed liquid cell (4); (B2) The wastewater in the feed liquid cell (4) is stretched, permeates through the forward osmosis membrane (3), diffuses into the draw liquid cell (5), and mixes with the forward osmosis draw liquid pumped into the draw liquid cell (5). The wastewater overflowing from the feed liquid cell (4) flows back to the wastewater pool outside the device, and the treated wastewater in the draw liquid cell (5) returns to the forward osmosis draw liquid pool outside the device.

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