Method for enhancing organic wastewater degradation based on external magnetic field

Abstract

A method for enhancing organic wastewater degradation based on an external magnetic field is characterized in that a strip-shaped conductive carbon felt is fixed in a reactor, water flow in the reactor flows out from the upper part and the lower part, a rotating magnetic field of 5-30 mT is arranged at the lower part of the reactor, and the effective length of the conductive carbon felt is 12-13 cm. The conductive carbon felt with a specific length is used as an electrode, a rotating magnetic field is externally added, the activity of microorganisms is adjusted through the magnetic field, and meanwhile, the rotating magnetic field generates an electric field to act on the conductive carbon felt, so that directional enrichment of the microorganisms on the surface of the carbon felt is promoted; according to the present invention, the microbial fuel cell with the cathode and anode distribution formed on the same conductive carbon felt is formed, the cell structure is simple, the reaction is performed in the single-chamber reactor, the operation is simplified, the rapid degradation of the organic wastewater is achieved, the wastewater is deeply treated by using the primary cell, the COD removal rate in the wastewater reaches 90.13%, and the TN removal rate reaches 89.7%.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for enhancing the degradation of organic wastewater based on an external magnetic field. Background Art

[0002] Microbial fuel cell (MFC) is a device that uses microorganisms to convert chemical energy in organic matter into electrical energy. Its basic working principle is that in the anaerobic environment of the anode chamber, organic matter is decomposed by microorganisms and releases electrons and protons. Electrons are effectively transferred between the biological components and the anode through a suitable point value transfer medium, and are transferred to the cathode through an external circuit to form an electric current. Protons are transferred to the cathode through proton exchange, and the oxidant (O2) is reduced and combined with protons to form water at the cathode. Usually, microbial fuel cells require a cathode, cathode chamber, anode, anode chamber, anion and cation exchange membranes, external resistors, etc. The structure is complex, and the anode and cathode chambers require different nutritional conditions, dissolved oxygen, etc.

[0003] Electrochemical methods have been reported to increase anaerobic consumption, but continuous power supply and complex electrodes installed inside the digester limit their practical application. Electric field stimulated microbial fuel cells also require separate cathodes and anodes, and in order to achieve different processes, the anode and cathode are generally in different reactors. An ion exchange membrane is required between the anode and cathode, and an external resistor is required between the electrodes. The anode and cathode chambers need to supply different wastewaters and provide different reaction conditions. For example, the anode is mostly anaerobic, and the cathode is an aerobic reaction, which requires different dissolved oxygen conditions. Single-chamber reactors already exist in the prior art, but the cathode and anode are still separated, and there is a specific distance between the cathode and anode, etc. However, it is still necessary to load the nutrient environment and accurately control the dissolved oxygen, and an external resistor is also required. Summary of the invention

[0004] Based on the above technical problems, the purpose of the present invention is to provide a method for enhancing the degradation of organic wastewater based on an external magnetic field. This method realizes the gradient change of different dissolved oxygen in the same reactor by adding a rotating magnetic field on the carbon felt, and combines the effect of the dynamic magnetic field to realize the directional aggregation of electricity-producing microorganisms and electricity-consuming microorganisms, thereby realizing the deep treatment of organic wastewater.

[0005] The purpose of the present invention is achieved through the following technical solutions: A method for enhancing the degradation of organic wastewater based on an external magnetic field, characterized in that: a strip of conductive carbon felt is fixed inside a reactor, water flows in from top to bottom of the reactor, a rotating magnetic field of 5 to 30 mT is set at the bottom of the reactor, and the effective length of the conductive carbon felt is 12 to 13 cm.

[0006] The length of the conductive carbon felt is 15cm, ensuring that its effective length is 12~13cm. If the length is too long, the internal resistance of the carbon felt will increase, the movement of electrons will be hindered, and the wastewater treatment efficiency will be affected.

[0007] Furthermore, the conductive carbon felt is firstly subjected to enrichment treatment before being fixed in the reactor for wastewater treatment. Specifically, it is firstly immersed in the inoculated sludge for 5 to 7 days to allow the microorganisms in the sludge to adhere to the surface of the carbon felt, and then the nutrient solution is added for further immersion, and a rotating magnetic field of 5 to 30 mT is added for 5 to 7 days.

[0008] Furthermore, the concentrations of the components in the nutrient solution are as follows: FeCl3·6H2O, 1.5 g·L -1 ; H3BO3, 0.15 g·L -1 ; MnSO4.7H2O, 0.102 g L -1 ; CoCl2·6H2O, 0.15 g·L -1 ; ZnSO4·7H2O, 0.12 g·L -1 ;CuSO4·5H2O, 0.03g·L -1 ;Na2MoO4·2H2O, 0.06g·L -1 ; KI, 0.18 g·L -1 ;MgSO4·7H2O, 0.1g·L -1 ;CaCl2·7H2O, 0.015g·L -1 .

[0009] Before being fixed, the conductive carbon felt was first placed in an acetone solution for ultrasonic treatment for 30 min, then immersed in a 10% HCl solution for acid pickling for 5 min, and finally ultrasonically cleaned with deionized water until neutral, and then dried.

[0010] After enrichment, the reactor was left to stand for 2 h. After the nutrient solution was slowly discharged from the bottom by gravity, the reactor was sealed, the sewage was pumped into the reactor by a peristaltic pump, and a rotating magnetic field of 5-30 mT was applied.

[0011] Furthermore, the seeding sludge was taken from an aerobic tank in the AAO process of a certain urban sewage treatment plant in Wanzhou. The aerobic tank sludge was settled for 30 minutes and the supernatant was removed before being used as the seeding sludge. The sludge concentration was 4500 mg / L.

[0012] Furthermore, the rotating magnetic field has a rotation speed of 50-400 rpm, and the magnetic cutting conductive carbon felt has a frequency of 100-800 Hz.

[0013] Furthermore, the water inlet rate at the reactor inlet was 2~17mL / min, the dissolved oxygen in the inlet was 2~5mg / L, and the hydraulic retention time (HRT) was controlled to be 6~24h.

[0014] The biofilm is a catalyst for the electricity-generating reaction. The better the biofilm is, the more conducive it is to the conduction of electrons, and the smaller the planned internal resistance of the anode. The present invention does not use a biofilm, but relies on an external rotating magnetic field. The magnetic field of a specific rotation speed and a specific field strength cuts the conductive carbon felt at a specific cutting frequency, thereby promoting the directional movement of electrons in the conductive carbon felt. During the enrichment process, the rotating magnetic field also regulates the activity of microorganisms, promoting the enrichment of microorganisms at both ends of the conductive carbon felt, enriching electron-gaining microorganisms at the upper end of the conductive carbon felt to form a cathode, and enriching electron-losing microorganisms at the lower end to form an anode.

[0015] In the process of sewage treatment, if the regulation is not appropriate, the electrode composite structure formed during enrichment cannot be maintained stably, resulting in the inability to effectively form the microbial battery and sewage treatment. In the process of sewage treatment, by adjusting the initial dissolved oxygen of the influent and the hydraulic retention time, and cooperating with the action of the rotating electric field, a difference is formed in the reactor, where there is oxygen at the top, and the dissolved oxygen gradually decreases in a step-by-step manner until the bottom is anoxic, so that aerobic microorganisms and anoxic microorganisms can be stably enriched at both ends of the carbon felt, stabilizing the stable composite structure of the electrodes formed at both ends of the conductive carbon felt.

[0016] Most specifically, a method for enhancing the degradation of organic wastewater based on an external magnetic field is characterized by comprising the following steps: (1) Pretreatment of conductive carbon felt A conductive carbon felt with a length of 15 cm was first placed in an acetone solution for ultrasonic treatment for 30 min, then immersed in a 10% HCl solution for acid washing for 5 min, and finally ultrasonically cleaned with deionized water until neutral, and then dried; (2) Enrichment treatment; The pretreated conductive carbon felt is fixed to the reactor, and the inoculated sludge is first added to soak for 5 to 7 days to allow the microorganisms in the sludge to adhere to the surface of the carbon felt. After the inoculated sludge is discharged, the nutrient solution is added to continue soaking. A rotating magnetic field with a magnetic field strength of 5-30 mT is set at the bottom of the reactor (the magnetic field is strong at the conductive carbon felt in the center of the reactor). The magnets are placed in parallel on both sides of the reactor. The magnets remain parallel during the rotation process. The magnetic field strength is controlled by adjusting the distance between the parallel magnets. The rotating magnetic field speed is 50-400rpm and lasts for 5 to 7 days. The components of the simulated sewage are NaAc·3H2O, 0.250~0.30 g·L -1 ; KH2PO4, 0.0015~0.0020g·L -1 ; NH4Cl, 0.035~0.040 g·L -1 ; KH2PO4, 2.5~3.5 g·L -1 ; 0.8~1.2mL·L -1Nutrient solution, simulated wastewater COD about 100 mg / L, prepared with NaAc·3H2O, the prepared simulated wastewater was sterilized by ultraviolet light; The components of the nutrient solution are FeCl3·6H2O, 1.6~2.4 g·L -1 ; H3BO3, 0.12~0.18 g·L -1 ; MnSO4.7H2O, 0.08~0.12 g L -1 ;CoCl2·6H2O, 0.12~0.16 g·L -1 ;ZnSO4·7H2O, 0.10~0.15g·L -1 ;CuSO4·5H2O, 0.01~0.04 g·L -1 ;Na2MoO4·2H2O, 0.05~0.07 g·L -1 ; KI, 0.15~0.20g·L -1 ;MgSO4·7H2O, 0.08~0.12 g·L -1 ;CaCl2·7H2O, 0.012~0.018 g·L -1 ; (3) Wastewater treatment Sewage is pumped into the reactor through a peristaltic pump at the water inlet at the upper end. At the same time, a rotating magnetic field of 5~30 mT is applied, the rotating magnetic field speed is 50~400 rpm, the frequency of the magnetically cut conductive carbon felt is 100~800 Hz, the peristaltic pump water inlet rate is 2~17 mL / min, the dissolved oxygen in the inlet is 2~5 mg / L, and the hydraulic retention time (HRT) is controlled to be 6~24 h.

[0017] The present invention has the following technical effects: The present invention uses a conductive carbon felt of a specific length as an electrode, and regulates the activity of microorganisms through the magnetic field itself by applying an external rotating magnetic field. At the same time, the rotating magnetic field generates an electric field acting on the conductive carbon felt, thereby promoting the directional enrichment of microorganisms on the surface of the carbon felt, forming a microbial fuel cell with anode and cathode distribution on the same conductive carbon felt. The battery has a simple structure, reacts in a single-chamber reactor, simplifies the operation, and realizes the rapid degradation of organic wastewater. The primary battery is used to deeply treat wastewater, and the COD removal rate in the wastewater reaches 90.13%, and the TN removal rate reaches 89.7%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : Schematic diagram of the reactor structure principle used in the present invention.

[0019] Figure 2 : SEM image of conductive carbon felt before enrichment treatment in the present invention.

[0020] Figure 3 : SEM image of the conductive carbon felt after enrichment treatment in the present invention.

[0021] Figure 4 : The COD removal rate curve and voltage change curve of the three stages tested in the present invention.

[0022] Figure 5 : The present invention tests the effect of short-term magnetic field on wastewater degradation COD removal rate curve and voltage change curve. DETAILED DESCRIPTION

[0023] The present invention is described in detail below through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-mentioned contents of the present invention.

[0024] Example 1 A method for enhancing the degradation of organic wastewater based on an external magnetic field comprises the following steps: (1) Pretreatment of conductive carbon felt A conductive carbon felt with a length of 15 cm was first placed in an acetone solution for ultrasonic treatment for 30 min, then immersed in a 10% HCl solution for acid washing for 5 min, and finally ultrasonically cleaned with deionized water until neutral, and then dried; (2) Enrichment treatment; The pretreated conductive carbon felt was fixed to the reactor, and the inoculated sludge was first added to soak for 5-7 days to allow the microorganisms in the sludge to adhere to the surface of the carbon felt. After the inoculated sludge was discharged, simulated wastewater and nutrient solution were added to continue soaking. A rotating magnetic field with a magnetic field strength of 5-30 mT was set at the bottom of the reactor (the magnetic field was strong at the conductive carbon felt in the center of the reactor). Magnets were placed in parallel on both sides of the reactor. The magnets remained parallel during the rotation process. The magnetic field strength was controlled by adjusting the distance between the parallel magnets. The rotating magnetic field speed was 200rpm and lasted for 6 days. The components of the simulated sewage are NaAc·3H2O, 0.286 g·L -1 ; KH2PO4, 0.0019 g·L -1 ; NH4Cl, 0.0382 g·L -1 ; KH2PO4, 3 g·L -1 ; 1 mL·L -1 Nutrient solution, simulated wastewater COD about 100mg / L, prepared with NaAc·3H2O. The influent pH was adjusted to 7 with 1M HCl / NaOH standard solution. The prepared simulated wastewater was sterilized with ultraviolet light; The components of the nutrient solution are FeCl3·6H2O, 1.5g·L-1 ; H3BO3, 0.15 g·L -1 ; MnSO4.7H2O, 0.102 g L -1 ; CoCl2·6H2O, 0.15 g·L -1 ; ZnSO4·7H2O, 0.12 g·L -1 ;CuSO4·5H2O, 0.03g·L -1 ;Na2MoO4·2H2O, 0.06g·L -1 ; KI, 0.18 g·L -1 ;MgSO4·7H2O, 0.1g·L -1 ;CaCl2·7H2O, 0.015g·L -1 ; (3) Wastewater treatment Sewage was pumped into the reactor through a peristaltic pump at the upper water inlet. At the same time, a rotating magnetic field of 20 mT was applied. The rotating magnetic field speed was 200 rpm, the frequency of the magnetically cut conductive carbon felt was 400 Hz, the peristaltic pump water inlet rate was 10 mL / min, the dissolved oxygen in the inlet was 5 mg / L, and the hydraulic retention time (HRT) was controlled to be 6 h.

[0025] Figure 1 Schematic diagram of the structure of the single-chamber reactor used in the present invention.

[0026] Figure 2 The conductive carbon felt is not enriched. It can be seen that it is smooth and has no material attached. The microbial attachment on the anode and cathode of the reactor is observed using a scanning electron microscope (SEM). The specific operation steps are as follows: s1. Sampling: Use scissors to cut carbon felt electrode samples of approximately 0.5 cm × 0.5 cm in size.

[0027] s2. Biofixation: Soak the bioelectrode sample in a 2.5% glutaraldehyde solution at 4°C for 12 h.

[0028] s3. Washing: Rinse the bioelectrode sample with 0.1M (phosphate buffered saline) PBS three times, 20 min each time, to remove residual glutaraldehyde in the sample.

[0029] s4. Dehydration: Soak the bioelectrode samples in ethanol solutions with concentrations of 25%, 50%, 70%, 90%, and 100% in turn for 15 minutes each time.

[0030] s5. Freeze drying: Place the bioelectrode sample in a vacuum freeze dryer (10N / A, Ningbo Xinzhi Biotechnology Co., Ltd.) and dry for 24 hours.

[0031] s6. Microscopic examination: The dried bioelectrode samples were pasted on the scanning electron microscope aluminum plate with conductive glue. After pretreatment, the surface morphology of the samples was imaged using a SEM5000 scanning electron microscope (Guoyi Quantum Technology Co., Ltd.).

[0032] The results are as follows Figure 3 As shown, Figure 3 A and B are SEM images at different magnifications. It can be seen that after microbial inoculation, a large number of microorganisms are enriched on the carbon felt under the action of the magnetic field. The microbial mass is large, the surface of the carbon felt fiber is rough, and a more obvious gradient change is formed from the bottom to the top of the carbon felt. The amount of microbial attachment is greater at the lower end of the carbon felt (the end where the magnetic field acts). One possible reason is that the static magnetic field causes the selective enrichment of microorganisms. As the intensity of the static magnetic field decreases, this enrichment effect gradually weakens. Another reason may be the directional movement of electrons caused by the rotating magnetic field, which leads to the selective enrichment of electron-donating microorganisms in the lower part of the carbon felt, while the upper part of the carbon felt forms an electron-requiring microbial enrichment area. Due to the increase in the electron transfer path from bottom to top, the internal resistance increases, and the electrons are gradually lost during the upward transfer process, so that the microbial load in the middle and upper ends of the carbon felt gradually decreases compared with the lower part, thus forming a gradient enrichment of microorganisms on the surface of the carbon felt. This shows that the rotating magnetic field accelerates the rapid selective enrichment of microorganisms on the carbon felt, and it is a dual enrichment of the static magnetic field and the rotating magnetic field.

[0033] In the sewage treatment process of step (3) of Example 1, the treatment data was detected. The first stage started from 5 days, and after 3 days of stability, the data was stabilized on the 7th day and entered the second stage, which lasted for 5 days. The second stage ended on the 12th day, and then the magnetic field was removed, and the reactor entered the third stage. The data of the third stage was collected for 5 days: According to the Rapid Digestion Spectrophotometric Method for Determination of Chemical Oxygen Demand in Water (HJ / T399-2007), COD was measured using a chemical oxygen demand (COD) rapid tester 5B-3C (V8) (Lianhua Technology). 1 mL of water was sampled each time for water quality analysis, and the water was filtered through a 0.45 μm filter before analysis. The dissolved oxygen at the inlet and outlet of the reactor was measured using a rapid dissolved oxygen tester, and the voltage at both ends of the reactor was measured using a multimeter.

[0034] The results are as follows Figure 4 As shown in the figure, from the COD content change curve, it can be seen that the rotating magnetic field promotes the enrichment of microorganisms on the conductive carbon felt. Under the action of 20 mT rotating magnetic field, the average COD of the effluent in the second stage is about 14.69 mg / L, and the COD removal rate reaches 85.32%. After the third stage of de-electrostatic rotating magnetic field, the average COD of the treated effluent is about 40.79 mg / L, and the COD removal rate is 59.21%, which is a decrease of about 26 percentage points.

[0035] It can be seen from the voltage change curve that voltage is generated during the reaction process. The most special thing is that under the action of the rotating magnetic field, the reactor voltage is relatively stable, while the voltage in the reactor fluctuates greatly after the rotating magnetic field is removed. Another special phenomenon is that the voltage corresponding to the stage with higher COD removal rate in the reactor is relatively small, while the voltage is higher when the COD removal rate is lower. This may be because the introduction of the rotating magnetic field reduces the internal resistance of the reactor, thereby promoting the rapid movement of electrons. The relatively stable voltage in the second stage also shows that the rotating magnetic field forms a relatively stable potential difference between the upper and lower parts of the reactor, indicating that the upper and lower parts of the conductive carbon felt in the reactor form a relatively stable selective aggregation of power-producing microorganisms and power-consuming microorganisms, so that different electrodes are formed at both ends of the conductive carbon felt, and the rotating magnetic field prompts the reactor to form a magnetoelectric fuel cell.

[0036] At the end of the experiment, we monitored the total nitrogen (TN) content in the effluent at the end of each reaction stage. The results showed that under the action of a 20 mT rotating magnetic field, the TN content in the effluent of the second stage was about 1.8 mg / L, and the TN removal rate reached 82%. After removing the rotating magnetic field in the third stage, the TN content in the treated effluent was about 4.2 mg / L, and the TN removal rate was 58%, a decrease of about 24 percentage points.

[0037] Comparative Example 1 Compared with Example 1, the difference is that, under the action of the 20 mT rotating magnetic field, after the water quality of the reactor effluent is stable, the rotating magnetic field is directly removed, specifically, the 20 mT rotating magnetic field is applied for the first 6 hours, and the rotating magnetic field is removed for the next 6 hours. Figure 5 As shown in the figure, it can be seen that after removing the rotating magnetic field, the effluent COD increased significantly, the 6-hour effluent COD average increased from 40.22 mg / L to 49.06 mg / L, and the removal rate decreased from 59.78% to 50.94%. Before and after the 20 mT magnetic field was removed, the voltage of the reactor did not change significantly, indicating that short-term magnetic field changes would not cause a rapid response of early microorganisms. However, the significant increase in effluent COD after removing the magnetic field also shows that the rotating magnetic field accelerates the life activities of microorganisms, accelerates the electron transfer efficiency of the reactor, and reduces the internal resistance of the reactor.

[0038] Comparative Example 2 Compared with Example 1, the difference is that when the external magnetic field is applied, the magnetic field used is a fixed magnetic field, that is, the rotation rate is 0, and the other step parameters are the same as those in Example 1.

[0039] The results show that the microorganisms on the surface of the carbon felt did not form obvious enrichment at both ends during the enrichment process in Comparative Example 2. In the wastewater treatment process, the microbial enrichment did not enrich to both ends of the carbon felt as we expected, resulting in a slow electron movement rate in the reactor and unsatisfactory sewage treatment effect. During the wastewater treatment monitoring process, the voltage changes irregularly, and the COD and total nitrogen (TN) removal rates after wastewater treatment are sometimes high and sometimes low, and have never reached a balance state. The highest COD removal rate only reached 44.75%. When the magnetic field is removed, the COD removal rate shows a certain downward trend.

[0040] The sewage with an original COD of 210.54 mg / g was treated according to the method of Example 1, and the COD removal rate of the final stable effluent reached 91.13%, and the TN removal rate reached 89.7%.

[0041] Example 2 A method for enhancing the degradation of organic wastewater based on an external magnetic field comprises the following steps: (1) Pretreatment of conductive carbon felt A conductive carbon felt with a length of 15 cm was first placed in an acetone solution for ultrasonic treatment for 30 min, then immersed in a 10% HCl solution for acid washing for 5 min, and finally ultrasonically cleaned with deionized water until neutral, and then dried; (2) Enrichment treatment; The pretreated conductive carbon felt was fixed to the reactor, and the inoculated sludge was first added and soaked for 7 days to allow the microorganisms in the sludge to adhere to the surface of the carbon felt. After the inoculated sludge was discharged, simulated wastewater and nutrient solution were added to continue soaking. A rotating magnetic field with a magnetic field strength of 5 mT was set at the bottom of the reactor (the magnetic field was strong at the conductive carbon felt in the center of the reactor). The magnets were placed in parallel on both sides of the reactor. The magnets remained parallel during the rotation process. The magnetic field strength was controlled by adjusting the distance between the parallel magnets. The rotating magnetic field speed was 50 rpm and lasted for 7 days. The components of the simulated sewage were NaAc·3H2O, 0.250 g·L -1 ; KH2PO4, 0.0015 g·L -1 ; NH4Cl, 0.035 g·L -1 ; KH2PO4, 2.5 g·L -1 ; 0.8 mL·L -1 Nutrient solution, simulated wastewater COD about 100mg / L, prepared with NaAc·3H2O, the prepared simulated wastewater is sterilized by ultraviolet light; The components of the nutrient solution are FeCl3·6H2O, 1.6 g·L -1 ; H3BO3, 0.12 g·L -1 ; MnSO4.7H2O, 0.08 g L -1; CoCl2·6H2O, 0.12 g·L -1 ; ZnSO4·7H2O, 0.10 g·L -1 ;CuSO4·5H2O, 0.01 g·L -1 ;Na2MoO4·2H2O, 0.05 g·L -1 ; KI, 0.15 g·L -1 ;MgSO4·7H2O, 0.08 g·L -1 ;CaCl2·7H2O, 0.012 g·L -1 ; (3) Wastewater treatment Sewage was pumped into the reactor through a peristaltic pump at the water inlet at the upper end. At the same time, a rotating magnetic field of 5 mT was applied. The rotating magnetic field speed was 400 rpm, the frequency of the magnetically cut conductive carbon felt was 100 Hz, the peristaltic pump water inlet rate was 2 mL / min, the dissolved oxygen in the inlet was 2 mg / L, and the hydraulic retention time (HRT) was controlled to be 24 h.

[0042] The initial COD of the treated sewage in this embodiment was 204.6 mg / L, the average COD of the treated effluent was about 18.54 mg / L, the COD removal rate reached 90.94%, the effluent TN was about 3.1 mg / L, and the TN removal rate reached 89.4%. After removing the rotating magnetic field, the COD removal rate of the treated effluent was 62.13%, a decrease of about 29 percentage points, and the TN removal rate of the treated effluent was 59.8%, a decrease of about 30 percentage points.

[0043] Example 3 A method for enhancing the degradation of organic wastewater based on an external magnetic field comprises the following steps: (1) Pretreatment of conductive carbon felt A conductive carbon felt with a length of 15 cm was first placed in an acetone solution for ultrasonic treatment for 30 min, then immersed in a 10% HCl solution for acid washing for 5 min, and finally ultrasonically cleaned with deionized water until neutral, and then dried; (2) Enrichment treatment; The pretreated conductive carbon felt was fixed to the reactor, and the inoculated sludge was first added and soaked for 5 days to allow the microorganisms in the sludge to adhere to the surface of the carbon felt. After the inoculated sludge was discharged, the nutrient solution was added and continued to soak. A rotating magnetic field with a magnetic field strength of 30 mT was set at the bottom of the reactor (the magnetic field was strong at the conductive carbon felt in the center of the reactor). The magnets were placed in parallel on both sides of the reactor. The magnets remained parallel during the rotation process. The magnetic field strength was controlled by adjusting the distance between the parallel magnets. The rotating magnetic field speed was 400 rpm and lasted for 5 days. The components of the simulated sewage were NaAc·3H2O, 0.30 g·L -1 ; KH2PO4, 0.0020 g·L-1 ; NH4Cl, 0.040 g·L -1 ; KH2PO4, 3.5 g·L -1 ; 1.2 mL·L -1 Nutrient solution, simulated wastewater COD about 100mg / L, prepared with NaAc·3H2O, the prepared simulated wastewater is sterilized by ultraviolet light; The components of the nutrient solution are FeCl3·6H2O, 2.4 g·L -1 ; H3BO3, 0.18 g·L -1 ; MnSO4.7H2O, 0.12 g L -1 ; CoCl2·6H2O, 0.16 g·L -1 ; ZnSO4·7H2O, 0.15 g·L -1 ;CuSO4·5H2O, 0.04 g·L -1 ;Na2MoO4·2H2O, 0.07 g·L -1 ; KI, 0.20 g·L -1 ;MgSO4·7H2O, 0.12 g·L -1 ;CaCl2·7H2O, 0.018 g·L -1 ; (3) Wastewater treatment Sewage was pumped into the reactor through a peristaltic pump at the water inlet at the upper end. At the same time, a rotating magnetic field of 30 mT was applied. The rotating magnetic field speed was 50 rpm, the frequency of the magnetically cut conductive carbon felt was 800 Hz, the peristaltic pump water inlet rate was 17 mL / min, the dissolved oxygen in the inlet was 4 mg / L, and the hydraulic retention time (HRT) was controlled to be 10 h.

[0044] We have also tried to increase the strength of the rotating magnetic field or increase the rotation rate of the magnetic field, but found that both would lead to a decrease in the directional enrichment of microorganisms on the carbon felt surface, thereby reducing the sewage treatment effect.

[0045] In this embodiment, the initial COD of the treated sewage was 192.8 mg / L, the average COD of the treated effluent was about 17.6 mg / L, the COD removal rate reached 90.89%, the effluent TN was about 2.9 mg / L, the TN removal rate reached 88.4%, and after removing the rotating magnetic field, the COD removal rate of the treated effluent was 61.50%, and the removal rate decreased by about 28 percentage points. The TN removal rate of the treated effluent was 59.2%, and the removal rate decreased by about 29 percentage points.

Claims

1. A method for enhancing the degradation of organic wastewater based on an external magnetic field, characterized in that: A strip of conductive carbon felt is fixed inside the reactor, water flows in from top to bottom and out from the reactor, a rotating magnetic field of 5-30 mT is set at the bottom of the reactor, and the effective length of the conductive carbon felt is 12-13 cm.

2. The method for enhancing the degradation of organic wastewater based on an external magnetic field as claimed in claim 1, characterized in that: The conductive carbon felt is firstly enriched before being fixed in the reactor for wastewater treatment. Specifically, it is firstly immersed in the inoculated sludge for 5 to 7 days to allow the microorganisms in the sludge to adhere to the surface of the carbon felt. Then, a nutrient solution is added for further immersion, and a rotating magnetic field of 5 to 30 mT is added for 5 to 7 days.

3. A method for enhancing the degradation of organic wastewater based on an external magnetic field as claimed in claim 1 or 2, characterized in that: After enrichment, the reactor was left to stand for 2 h. After the nutrient solution was slowly discharged from the bottom by gravity, the reactor was sealed, the sewage was pumped into the reactor by a peristaltic pump, and a rotating magnetic field of 5-30 mT was applied.

4. A method for enhancing the degradation of organic wastewater based on an external magnetic field according to any one of claims 1 to 3, characterized in that: The rotating magnetic field has a rotation speed of 50-400 rpm, and the magnetic cutting conductive carbon felt has a frequency of 100-800 Hz.

5. A method for enhancing the degradation of organic wastewater based on an external magnetic field according to any one of claims 1 to 4, characterized in that: The water inlet rate at the reactor inlet is 2~17mL / min, the dissolved oxygen in the inlet is 2~5mg / L, and the hydraulic retention time (HRT) is controlled to be 6~24h.

6. A method for enhancing the degradation of organic wastewater based on an external magnetic field, characterized in that: The steps include: (1) Pretreatment of conductive carbon felt A conductive carbon felt with a length of 15 cm was first placed in an acetone solution for ultrasonic treatment for 30 min, then immersed in a 10% HCl solution for acid washing for 5 min, and finally ultrasonically cleaned with deionized water until neutral, and then dried; (2) Enrichment treatment; The pretreated conductive carbon felt is fixed into the reactor, and the inoculated sludge is first added and soaked for 5 to 7 days to allow the microorganisms in the sludge to adhere to the surface of the carbon felt. After the inoculated sludge is discharged, the external simulated wastewater and nutrient solution are added to continue soaking. A rotating magnetic field with a magnetic field strength of 5-30 mT is set at the bottom of the reactor (the magnetic field is strong at the conductive carbon felt in the center of the reactor), and magnets are placed in parallel on both sides of the reactor. The magnets remain parallel during rotation, and the magnetic field strength is controlled by adjusting the distance between the parallel magnets. The rotating magnetic field speed is 50-400rpm and lasts for 5 to 7 days. The components of the simulated sewage are NaAc·3H2O, 0.250~0.30 g·L -1 ;KH2PO4, 0.0015~0.0020 g·L -1 ; NH4Cl, 0.035~0.040 g·L -1 ; KH2PO4, 2.5~3.5 g·L -1 ; 0.8~1.2mL·L -1 Nutrient solution, simulated wastewater COD about 100 mg / L, prepared with NaAc·3H2O, the prepared simulated wastewater was sterilized by ultraviolet light; The components of the nutrient solution are FeCl3·6H2O, 1.6~2.4 g·L -1 ; H3BO3, 0.12~0.18 g·L -1 ; MnSO4.7H2O, 0.08~0.12 g L -1 ;CoCl2·6H2O, 0.12~0.16 g·L -1 ;ZnSO4·7H2O, 0.10~0.15g·L -1 ;CuSO4·5H2O, 0.01~0.04 g·L -1 ;Na2MoO4·2H2O, 0.05~0.07 g·L -1 ; KI, 0.15~0.20g·L -1 ;MgSO4·7H2O, 0.08~0.12 g·L -1 ;CaCl2·7H2O, 0.012~0.018 g·L -1 ; (3) Wastewater treatment Sewage is pumped into the reactor through a peristaltic pump at the water inlet at the upper end. At the same time, a rotating magnetic field of 5~30 mT is applied, the rotating magnetic field speed is 50~400 rpm, the frequency of the magnetically cut conductive carbon felt is 100~800 Hz, the peristaltic pump water inlet rate is 2~17 mL / min, the dissolved oxygen in the inlet is 2~5 mg / L, and the hydraulic retention time (HRT) is controlled to be 6~24 h.

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