Self-driven bio-electro-Fenton sewage treatment method based on granular sludge electroactivity domestication

Abstract

The invention discloses a self-driven bio-electro-Fenton sewage treatment method based on granular sludge electroactivity domestication. The sewage treatment method comprises the following steps: firstly, inoculating anaerobic granular sludge into an anode chamber of a microbial fuel cell, fixing a clustered carbon fiber electrode in a biological anode chamber as an electrode collector, taking a cathode as an oxygen reduction cathode, and performing electrochemical enrichment to obtain electroactive granular sludge; then, preparing an iron-cobalt diatomic catalyst from the nitrogen-doped graphene oxide, cobalt phthalocyanine and iron phthalocyanine; and finally, adding the iron-cobalt diatomic catalyst into the electroactive granular sludge to form a hybrid structure, controlling dissolved oxygen in a reaction system, and degrading organic pollutants by adopting an SBR (sequencing batch reactor). The biological electro-Fenton technology has a better effect of removing refractory organic pollutants, and compared with a traditional electro-Fenton method, the self-Fenton technology can achieve the activity of molecular oxygen without external electric energy input.

Description

Technical Field

[0001] The present invention belongs to the field of water pollution control, and particularly relates to a self-driven bioelectro-Fenton sewage treatment method based on electroactive domestication of granular sludge Background Art

[0002] Biological treatment technologies based on the activated sludge process are the main technical means in the current sewage treatment industry, especially for municipal sewage treatment. However, the rapid industrialization and urbanization in the past few decades have led to a rapid increase in the discharge of industrial sewage containing various refractory organic pollutants. These organic pollutants often have the characteristics of low concentration, environmental persistence, and biological recalcitrance, posing a continuous threat to environmental and ecological health. Since most of these refractory organic pollutants are synthetic after industrialization, microorganisms have not evolved functional proteins to effectively degrade these pollutants, and biological treatment technologies represented by the activated sludge process are difficult to effectively remove, which has become the main challenge in the current field of water pollution control

[0003] The Fenton reaction uses Fe 2+ to activate H 2 O 2 to generate strongly oxidizing hydroxyl radicals (OH · ) and other reactive species, which can effectively remove various refractory organic pollutants and is one of the main options for removing refractory organic pollutants in industrial sewage at present. However, due to the high cost of H 2 O 2 reagents and the problem of difficult-to-treat Fenton iron sludge in the Fenton reaction, various derivative Fenton technologies, namely, the Fenton-like reaction, have attracted wide interest in recent years. In particular, electro-Fenton combines cathodic reduction with the Fenton reaction, and through a specific three-electron oxygen reduction reaction, a series of reactions such as in-situ synthesis and activation of H 2 O 2 and regeneration of ferric iron can be achieved simultaneously in the cathode region, overcoming the problems of the traditional Fenton reaction and having great application potential. On the other hand, in the current mainstream electro-Fenton system, the anodic reaction is water electrolysis, which consumes a large amount of electric energy and greatly increases the water treatment cost

[0004] Microbial fuel cell is a new sewage biological treatment technology based on extracellular electron transfer of electroactive microorganisms. Different from traditional biological treatment technologies, although electroactive microorganisms in the bioanode region cannot effectively degrade refractory organic pollutants, the extracellular electrons they generate can reach the cathode through the external circuit and then reduce and activate molecular oxygen to occur electro-Fenton reaction, realizing the degradation of refractory pollutants. This Fenton-like technology combining microbial fuel cell and electro-Fenton reaction is defined as bioelectro-Fenton. Compared with the electro-Fenton technology of traditional anodic electrolyzed water, the bioanode greatly reduces the energy demand of the anodic reaction and can even directly drive the cathode electro-Fenton, with great advantages. On the other hand, however, the overall efficiency of the traditional bioelectro-Fenton reaction based on biofilm anode is not high due to the low anode biomass, and it is difficult to scale up the bioelectrochemical reactor, so it is still difficult to carry out large-scale applications. Summary of the Invention

[0005] Aiming at the limitations of the low overall efficiency of the bioelectro-Fenton system and the difficulty in scaling up the reactor in the prior art, the present invention proposes a self-driven bioelectro-Fenton sewage treatment method based on electroactive domestication of granular sludge. After electrochemically domesticating anaerobic granular sludge, iron-cobalt dual-atom catalysts are directly doped in the electroactive granular sludge to realize the technical idea of self-driven electro-Fenton for in-situ activation of molecular oxygen by biological electrons. The present invention mainly inoculates anaerobic granular sludge into the bioanode chamber, and after electrochemical enrichment, electroactive granular sludge with efficient extracellular electron transfer is obtained; at the same time, iron-cobalt dual-atom catalysts for efficiently reducing and activating molecular oxygen are prepared, and after co-incubating the two, a hybrid of granular sludge and dual-atom catalysts is obtained, and the dissolved oxygen concentration is controlled to enable the biological electrons generated by the granular sludge to be transferred to the iron-cobalt dual-atom catalysts to activate molecular oxygen and realize self-driven electro-Fenton.

[0006] To achieve the above invention object, the present invention provides the following technical solutions:

[0007] A self-driven bioelectro-Fenton sewage treatment method based on electroactive domestication of granular sludge, comprising: First, inoculate anaerobic granular sludge into the anode chamber of the microbial fuel cell, fix a bundled carbon fiber electrode as the electrode collector in the bioanode chamber, the cathode is an oxygen reduction cathode, and after connecting the anode and cathode with a resistor, carry out the domestication of anaerobic granular sludge under the condition of discharging of the microbial fuel cell, and complete the electrochemical enrichment to obtain electroactive granular sludge; then, prepare iron-cobalt dual-atom catalysts with nitrogen-doped graphene oxide, cobalt phthalocyanine and iron phthalocyanine; finally, add the iron-cobalt dual-atom catalysts to the electroactive granular sludge to form a hybrid structure, control the dissolved oxygen in the reaction system, and use an SBR reactor to realize the generation of bioelectricity and the activity of molecular oxygen to degrade organic pollutants.

[0008] Furthermore, the self-driven bioelectro-Fenton sewage treatment method based on electroactive domestication of granular sludge of the present invention specifically comprises the following steps:

[0009] (1) Preparation of electroactive granular sludge: Anaerobic granular sludge was inoculated into the bioanode chamber of a dual-chamber microbial fuel cell reactor. The bioanode chamber was fixed with a bundled carbon fiber electrode as the electrode collector, and the cathode was an oxygen reduction cathode. After connecting the anode and cathode with a resistor, electroactive granular sludge was obtained through electrochemical enrichment; electroactive granular sludge was obtained by electrochemically acclimating anaerobic granular sludge, enabling the electroactive granular sludge to transfer extracellular electrons to an external catalyst at a relatively small anodic overpotential.

[0010] The anaerobic granular sludge inoculated in step (1) was cultivated in an anaerobic reactor using short-chain organic acids with C2-C5 as the main substrate, and the diameter of the anaerobic granular sludge was not less than 0.5 mm after passing through a sieve; the short-chain organic acid was acetic acid or citric acid.

[0011] In step (1), the anaerobic granular sludge was electrochemically enriched in a dual-chamber microbial fuel cell reactor, and there were no special requirements for the internal space shape of the reactor; among them, the bioanode chamber was fixed with a bundled carbon fiber electrode as the electrode collector, and an appropriate carbon fiber length was selected so that it could touch the entire reactor, enabling anaerobic granular sludge at different positions in the anode chamber to still effectively undergo electrochemical interactions with the carbon fiber. The anaerobic granular sludge was filled into the anode chamber, and only 10% of the space was left at the top of the anode chamber to maintain the aqueous phase.

[0012] In step (1), the cathode of the dual-chamber microbial fuel cell reactor was selected as an oxygen reduction cathode, specifically a carbon felt electrode modified with a platinum-carbon catalyst. Its preparation was as follows: Using the carbon felt electrode as the base electrode, the oxygen reduction active catalyst was dispersed in an organic solvent, mixed with a certain amount of 5% mass concentration Nafion solution, and then drop-coated onto the surface of the carbon felt electrode and dried in vacuum for later use; the oxygen reduction active catalyst in the cathode could be a commercial Pt / C catalyst. The principle for catalyst selection was that it could effectively reduce dissolved oxygen under the condition of stirring the catholyte and had good stability, with the performance decline less than 10% after continuous operation for 1 month; the organic solvent was ethanol.

[0013] In the electrochemical enrichment stage in step (1), artificial wastewater was used as the anolyte, with acetate as the carbon source, 1000 mg / L COD per day, 50 mM phosphate as the buffer, the initial pH was adjusted to 7, the C:N ratio was 10:1 - 20:1, and Wolfe mineral salts and Wolfe vitamins were also required to be added; the catholyte was 100 mM Na 2 SO 4 solution, and a magnetic stirrer was used to maintain the dissolved oxygen concentration > 4 mg / L; the electrochemical enrichment time was 7 - 14 days.

[0014] In step (1), the anode and cathode are connected by a resistor and enriched under the discharge mode of the microbial fuel cell. Among them, the resistance value of the resistor is determined by the effective volume of the anode chamber. When the volume of the anode chamber is larger, the resistance should be reduced. Generally, when the volume of the anode chamber is 100 mL, a resistor of 50 ohms or 100 ohms can be externally connected. Too large a resistance will result in a smaller enrichment current, and the overall electroactivity of the finally obtained electroactive granular sludge will be weak. When the microbial fuel cell operates, the anode chamber can operate in a sequential batch mode or a continuous flow mode, and the parameters such as sodium acetate concentration and hydraulic retention time are generally determined according to the amount of 1000 mg / L COD per day. Use a data acquisition system to record the piezoelectricity at both ends of the externally connected resistor, calculate the current using Ohm's law, and determine the current density (A / m 3 ) normalized to the volume of the anode chamber. In continuous discharge, it can be observed that the current density gradually increases. Generally, after 7-14 days of electrochemical enrichment, the current density reaches 10 A / m 3 or the maximum current density reaches 50 A / m in the polarization curve test 3 , which means the completion of electrochemical enrichment. At this time, the granular sludge has a high abundance of electroactive microorganisms, and the anaerobic granular sludge is transformed into electroactive granular sludge.

[0015] (2) Preparation of iron-cobalt dual-atom catalyst: Using nitrogen-doped graphene as the substrate, iron phthalocyanine and cobalt phthalocyanine as precursors, a highly efficient molecular oxygen-activating and biocompatible iron-cobalt dual-atom catalyst is prepared by pyrolysis after adsorption through the π-π interaction between nitrogen-doped graphene and cobalt phthalocyanine and iron phthalocyanine;

[0016] The pyrolysis described in step (2) is divided into two-step pyrolysis, which are carried out at 500 °C and 700 °C respectively, and each step of pyrolysis lasts for 1 hour;

[0017] The nitrogen-doped graphene described in step (2) is prepared by carbonization after the reaction of purchased graphene oxide with dicyandiamide; among them, the graphene oxide is required to be single-layer or double-layer, and the mass ratio of graphene oxide to dicyandiamide is 2:1. After the two are mixed and stirred in the aqueous phase for 2 hours, they are vacuum dried and pyrolyzed in a tube furnace under a nitrogen atmosphere to obtain nitrogen-doped graphene with a nitrogen content of 7-8%; the pyrolysis is divided into two-step pyrolysis, which are carried out at 500 °C and 700 °C respectively, and each step of pyrolysis lasts for 1 hour;

[0018] The specific preparation steps of step (2) are as follows: first, grinding nitrogen-doped graphene and then ultrasonically dispersing it in an ethanol solution at a concentration of 1 mg / mL; then, dispersing cobalt phthalocyanine and iron phthalocyanine in an ethanol solution in turn, both at a concentration of 0.5-2 mg / L; finally, mixing the nitrogen-doped graphene dispersion with the cobalt phthalocyanine and iron phthalocyanine dispersions, stirring at room temperature for 2 hours, and then centrifuging and collecting the sample, washing the sample three times with deionized water, and then vacuum drying to obtain an iron-cobalt diatomic catalyst. In the iron-cobalt diatomic catalyst prepared by this method, cobalt and iron should each account for 1.4-1.8% of the total mass of the catalyst;

[0019] (3) Hybridization of electroactive granular sludge and iron-cobalt diatomic catalyst: First, the iron-cobalt diatomic catalyst prepared in step (2) is dispersed in an ethanol solution by ultrasonication to prepare a catalyst dispersion stock solution with a concentration of 1 mg / mL. Then, the catalyst is diluted by artificial water distribution to a final concentration of 200 μg / mL. Finally, the electroactive granular sludge prepared in step (1) is placed in the diluted catalyst solution and incubated under anaerobic conditions for 12 hours to allow the iron-cobalt diatomic catalyst to fully react with the anaerobic granular sludge microorganisms and be adsorbed to form a hybrid of the electroactive granular sludge and the iron-cobalt diatomic catalyst;

[0020] The concentration of the electroactive granular sludge in the catalyst solution in step (3) is 200 g MLSS / L;

[0021] (4) Self-driven bio-electro-Fenton degradation of pollutants: the electroactive granular sludge prepared in step (3) and the iron-cobalt diatomic catalyst hybrid are transferred to a SBR reactor for wastewater treatment;

[0022] The volume of the electroactive granular sludge should account for 10-20% of the total effective volume of the SBR reactor.

[0023] The SBR reactor described in step (4) is provided with a water inlet and a reflux water inlet at the bottom, and a water outlet and a reflux water outlet are respectively provided on both sides of the top; the water inlet is connected to the water inlet pump, and the reflux water outlet is connected to the reflux water inlet at the bottom through the reflux pump; a sampling port is provided between the water inlet and the water outlet, and a dissolved oxygen probe and an adjustable aeration pump are configured on the top.

[0024] The SBR reactor used in the present invention should generally have a structure of bottom water inlet and top aeration reflux, and be equipped with a dissolved oxygen probe and an adjustable aeration pump to ensure that the dissolved oxygen level can be accurately controlled during operation. In order to effectively cause the electro-Fenton reaction, the inlet water should contain a carbon source that can be utilized by microorganisms such as BOD. After the bottom water is inlet, self-Fenton degradation is carried out in a continuous flow mode, and the dissolved oxygen concentration of the reaction system is regulated by adjusting the aeration rate and the reflux ratio. Samples are collected from the outlet, and conventional indicators such as COD, ammonia nitrogen, and the removal of difficult-to-degrade pollutants are analyzed, and then parameters such as hydraulic retention time are optimized in a targeted manner to achieve effective removal.

[0025] The dissolved oxygen level in the reaction environment is crucial for determining the removal level of pollutants in the reaction system, especially for recalcitrant organic pollutants. Therefore, the reactor design should fully consider dissolved oxygen regulation. The SBR strategy adopted in this invention is bottom feeding, top aeration, and reflux. Ideally, the dissolved oxygen level is regulated by a dissolved oxygen electrode and an aeration pump, such that the dissolved oxygen concentration in the region filled with electroactive granular sludge should be between 2 - 4 mg / L. When the dissolved oxygen concentration is lower than this level, although electroactive microorganisms in the electroactive granular sludge can generate extracellular electrons, due to insufficient dissolved oxygen, it is difficult to effectively generate reactive species such as hydroxyl radicals on the surface of the iron-cobalt dual-atom catalyst, and the removal of pollutants mainly relies on biodegradation, and the removal of organic pollutants that cannot be biodegraded is insufficient. When the dissolved oxygen concentration is higher than 4 mg / L, with the increase in the dissolved oxygen concentration, the extracellular electron transfer efficiency of the electroactive granular sludge rapidly decreases, and reactive species such as hydroxyl radicals cannot be generated on the surface of the iron-cobalt dual-atom catalyst either. Within the optimal dissolved oxygen concentration range of 2 - 4 mg / L, this system can remove conventional organic pollutants through microbial degradation and also remove various recalcitrant organic pollutants through the electro-Fenton reaction.

[0026] Due to the direct aerobic metabolism of microorganisms and the selectivity of the oxygen reduction reaction on the surface of the iron-cobalt catalyst, the yield of converting COD into reactive species such as hydroxyl radicals is affected, and the estimated electron utilization rate is not higher than 5%. Therefore, the total amount of recalcitrant organic pollutants degraded by the electro-Fenton reaction is relatively low, and it can only be effectively degraded when the COD proportion of recalcitrant organic pollutants is not higher than 1%, mainly used for the removal of low-concentration recalcitrant organic pollutants.

[0027] Compared with traditional bioelectro-Fenton technology, this invention has the following beneficial effects:

[0028] (1) This invention adopts the construction idea of hybridizing microorganisms and electro-Fenton catalysts, avoiding many limitations in the scale-up of electro-chemical reactors;

[0029] (2) This invention uses granular sludge as the carrier for electroactive microorganisms. Its millimeter-scale size can form a dissolved oxygen gradient inside, such that when the dissolved oxygen requirement for electro-Fenton is met on the outside of the granular sludge, an anaerobic environment is maintained inside the sludge, and electroactive microorganisms can perform extracellular electron transfer instead of direct aerobic respiration.

[0030] (3) This invention adopts a self-Fenton system that can utilize bioelectricity to generate reactive species such as hydroxyl radicals, which has a better effect on the removal of recalcitrant organic pollutants. Compared with traditional electro-Fenton methods, this self-Fenton technology can activate molecular oxygen without external electrical energy input, providing a new idea for overcoming the limitation of high energy consumption in electro-Fenton treatment technology and having important significance. Description of the Drawings

[0031] Figure 1The physical photo and scanning electron microscope image of the anaerobic granular sludge inoculated for the present invention.

[0032] Figure 2 The physical photo of the dual-chamber microbial fuel cell reactor described in the present invention.

[0033] Figure 3 The aberration-corrected high-resolution scanning transmission electron microscope image of the iron-cobalt dual-atom catalyst prepared in the example of the present invention.

[0034] Figure 4 The schematic diagram of the SBR reactor for self-driven bioelectro-Fenton to remove low-concentration refractory organic pollutants in the present invention.

[0035] Figure 4 In the figure, each label is: 1 water outlet, 2 sampling port, 3 water inlet, 4 water inlet pump, 5 reflux pump, 6 reflux water outlet, 7 reflux water inlet, 8 dissolved oxygen probe, 9 adjustable aeration pump. Detailed implementation manners

[0036] The present invention will be further described and explained below in conjunction with the accompanying drawings and specific implementation manners. The technical features of each implementation manner in the present invention can be combined correspondingly without conflict.

[0037] Example

[0038] A self-driven bioelectro-Fenton sewage treatment method based on electroactive domestication of granular sludge specifically includes the following steps:

[0039] (1) Preparation of electroactive granular sludge: Inoculate anaerobic granular sludge into the biological anode chamber of a dual-chamber microbial fuel cell reactor. The biological anode chamber is fixed with a bundled carbon fiber electrode as the electrode collector, and the cathode is an oxygen reduction cathode. After connecting the anode and cathode with a resistor, electroactive granular sludge is obtained through electrochemical enrichment; electroactive granular sludge is obtained by electrochemically domesticating anaerobic granular sludge, enabling the electroactive granular sludge to transfer extracellular electrons to an external catalyst under a small anodic overpotential.

[0040] The inoculated anaerobic granular sludge in step (1) is cultivated through an anaerobic reactor using short-chain organic acids with C2-C5 as the main substrate, and the diameter of the anaerobic granular sludge is not less than 0.5 mm after passing through a sieve; the short-chain organic acid is acetic acid or citric acid.

[0041] The anaerobic granular sludge described in step (1) is electrochemically enriched in a dual-chamber microbial fuel cell reactor, and there are no special requirements for the internal space shape of the reactor. Among them, a bundled carbon fiber electrode is fixed in the bioanode chamber as an electrode collector, and an appropriate carbon fiber length is selected so that it can reach the entire reactor, enabling the anaerobic granular sludge at different positions in the anode chamber to still effectively undergo electrochemical reactions with the carbon fiber. The anaerobic granular sludge is filled into the anode chamber, and only 10% of the space at the top of the anode chamber is left for maintaining the aqueous phase.

[0042] For the cathode of the dual-chamber microbial fuel cell reactor described in step (1), an oxygen reduction cathode is selected, specifically a carbon felt electrode modified with a platinum-carbon catalyst. Its preparation method is as follows: using the carbon felt electrode as the base electrode, after dispersing the oxygen reduction active catalyst into an organic solvent, it is mixed with a certain amount of Nafion solution with a mass concentration of 5% and then drop-coated onto the surface of the carbon felt electrode, and dried in vacuum for later use. The oxygen reduction active catalyst in the cathode can be a commercial Pt / C catalyst. The principle for catalyst selection is that it can effectively reduce dissolved oxygen under the condition of stirring the catholyte and has good stability, with a performance decline of less than 10% after continuous operation for 1 month. The organic solvent is ethanol.

[0043] In the electrochemically enrichment stage described in step (1), artificial wastewater is used as the anolyte, with acetate as the carbon source, 1000 mg / L COD per day, 50 mM phosphate as the buffer, the initial pH is adjusted to 7, the C:N ratio is 10:1 - 20:1, and Wolfe mineral salts and Wolfe vitamins need to be added. The catholyte is a 100 mM Na 2 SO 4 solution, and a magnetic stirrer is used to maintain the dissolved oxygen concentration > 4 mg / L. The electrochemically enrichment time is 7 - 14 days.

[0044] In step (1), the anode and cathode are connected by a resistor and enriched in the discharge mode of the microbial fuel cell. Among them, the resistance value of the resistor is determined by the effective volume of the anode chamber. When the volume of the anode chamber is larger, the resistance should be reduced. Usually, when the volume of the anode chamber is 100 mL, a 50-ohm or 100-ohm resistor can be externally connected. Too large a resistance will result in a smaller enrichment current, and the overall electroactivity of the finally obtained electroactive granular sludge will be weak. When the microbial fuel cell is operating, the anode chamber can operate in a batch or continuous flow mode. Generally, parameters such as the concentration of sodium acetate and the hydraulic retention time are determined according to the amount of 1000 mg / L COD per day. Use a data acquisition system to record the piezoelectricity at both ends of the externally connected resistor, calculate the current using Ohm's law, and determine the current density (A / m 3 ) normalized to the volume of the anode chamber. During continuous discharge, it can be observed that the current density gradually increases. Usually, after 7 - 14 days of electrochemical enrichment, the current density reaches 10 A / m 3Or the maximum current density reaches 50 A / m² during the polarization curve test 3 , which means the completion of electrochemical enrichment. At this time, the granular sludge has a high abundance of electroactive microorganisms, and the anaerobic granular sludge is transformed into electroactive granular sludge.

[0045] (2) Preparation of iron-cobalt dual-atom catalyst: Using nitrogen-doped graphene as the substrate and iron phthalocyanine and cobalt phthalocyanine as precursors, a highly efficient molecular oxygen-activating and biocompatible iron-cobalt dual-atom catalyst is prepared by pyrolysis after adsorption through the π-π interaction between nitrogen-doped graphene and cobalt phthalocyanine and iron phthalocyanine;

[0046] The pyrolysis in step (2) is divided into two-step pyrolysis, which are carried out at 500 °C and 700 °C respectively, and each step of pyrolysis lasts for 1 hour;

[0047] The nitrogen-doped graphene in step (2) is prepared by carbonization after the reaction of purchased graphene oxide with dicyandiamide; among them, the graphene oxide is required to be monolayer or bilayer, and the mass ratio of graphene oxide to dicyandiamide is 2:1. After the two are mixed and stirred in the aqueous phase for 2 hours, they are vacuum dried and pyrolyzed in a tube furnace under a nitrogen atmosphere to obtain nitrogen-doped graphene with a nitrogen content of 7-8%; the pyrolysis is divided into two-step pyrolysis, which are carried out at 500 °C and 700 °C respectively, and each step of pyrolysis lasts for 1 hour;

[0048] The specific preparation steps of step (2) are as follows: First, grind the nitrogen-doped graphene and then ultrasonically disperse it in an ethanol solution with a concentration of 1 mg / mL; then, disperse cobalt phthalocyanine and iron phthalocyanine in the ethanol solution in turn, and the concentrations of both are 0.5-2 mg / L; finally, mix the nitrogen-doped graphene dispersion with the cobalt phthalocyanine and iron phthalocyanine dispersions, stir at room temperature for 2 hours, then centrifuge to collect the sample, wash the sample three times with deionized water, and then vacuum dry to obtain the iron-cobalt dual-atom catalyst. For the iron-cobalt dual-atom catalyst prepared by this method, cobalt and iron should each account for 1.4-1.8% of the total mass of the catalyst;

[0049] (3) Hybridization of electroactive granular sludge and iron-cobalt dual-atom catalyst: First, ultrasonically disperse the iron-cobalt dual-atom catalyst prepared in step (2) in an ethanol solution to prepare a catalyst dispersion mother liquor with a concentration of 1 mg / mL, and then dilute the catalyst with artificial water to make its final concentration 50-200 μg / mL. Finally, place the electroactive granular sludge prepared in step (1) into the diluted catalyst solution and incubate it under anaerobic conditions for 12-18 hours to allow the iron-cobalt dual-atom catalyst to fully interact with the anaerobic granular sludge microorganisms and be adsorbed to form a hybrid of electroactive granular sludge and iron-cobalt dual-atom catalyst;

[0050] The concentration of the electroactive granular sludge in the catalyst solution in step (3) is 200 g MLSS / L;

[0051] (4) Self-driven bioelectrochemical Fenton degradation of pollutants: Transfer the electroactive granular sludge and iron-cobalt dual-atom catalyst hybrid prepared in step (3) to an SBR reactor for sewage treatment;

[0052] Among them, the volume of the electroactive granular sludge should account for 10-20% of the total effective volume of the SBR reactor.

[0053] In step (4), the bottom of the SBR reactor is provided with a water inlet and a reflux water inlet, and the two sides of the top are respectively provided with a water outlet and a reflux water outlet; the water inlet is connected to a water inlet pump, and the reflux water outlet is connected to the bottom reflux water inlet through a reflux pump; a sampling port is provided between the water inlet and the water outlet, and at the same time, a dissolved oxygen probe and an adjustable aeration pump are configured at the top.

[0054] The SBR reactor used in the present invention usually should have a structure of bottom water inlet, top aeration and reflux, and be equipped with a dissolved oxygen probe and an adjustable aeration pump to ensure accurate control of the dissolved oxygen level during operation. To effectively occur the electro-Fenton reaction, the influent water should contain biodegradable carbon sources such as BOD. After bottom water inlet, self-Fenton degradation is carried out in the continuous flow mode, and the dissolved oxygen concentration in the reaction system is regulated by adjusting the aeration rate and reflux ratio. Samples are collected from the water outlet to analyze conventional indicators such as COD and ammonia nitrogen and the removal of refractory pollutants, and then parameters such as hydraulic retention time are optimized accordingly to achieve effective removal.

[0055] The dissolved oxygen level in the reaction environment is the key to determining the pollutant removal level in the reaction system, especially for refractory organic pollutants. Therefore, the reactor design should fully consider the regulation of dissolved oxygen. The SBR strategy adopted in the present invention is bottom water inlet, top aeration and reflux. Ideally, the dissolved oxygen level is regulated by a dissolved oxygen electrode and an aeration pump, so that the dissolved oxygen concentration in the area filled with electroactive granular sludge should be between 2-4 mg / L. When the dissolved oxygen concentration is lower than this level, although the electroactive microorganisms in the electroactive granular sludge can generate extracellular electrons, due to insufficient dissolved oxygen, it is difficult to effectively generate active species such as hydroxyl radicals on the surface of the iron-cobalt dual-atom catalyst, and the pollutant removal is mainly biodegradation, and the removal of organic pollutants that cannot be biodegraded is insufficient. When the dissolved oxygen concentration is higher than 4 mg / L, with the increase of the dissolved oxygen concentration, the extracellular electron transfer efficiency of the electroactive granular sludge decreases rapidly, and the surface of the iron-cobalt dual-atom catalyst also cannot generate active species such as hydroxyl radicals. Within the optimal dissolved oxygen concentration range of 2-4 mg / L, this system can remove conventional organic pollutants through microbial degradation and also remove various refractory organic pollutants through the electro-Fenton reaction.

[0056] Use the above sewage treatment device to treat COD, ammonia nitrogen and refractory organic pollutant tetracycline in sewage.

[0057] Configure simulated sewage, where sodium acetate simulates COD (200 mg / L), ammonia nitrogen is 20 mg / L, the concentration of tetracycline is 2 mg / L, and 10 mL / L of Wolfe mineral salts and sodium chloride are added to make the total salinity reach 0.8%.

[0058] Water enters from the water inlet 3, and the effluent-to-reflux ratio is set to 1:3. The total hydraulic retention time is 6 hours. After 1 day of trial operation, adjust the aeration pump to maintain the dissolved oxygen concentration at 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, and 5 mg / L respectively. Detect the COD, ammonia nitrogen, and tetracycline concentrations in the effluent, and use the salicylic acid method to detect the hydroxyl radicals in the reaction system.

[0059] As shown in Table 1 below, at different dissolved oxygen concentrations, the COD removal rate can reach a relatively high level, and the ammonia nitrogen removal rate increases significantly when the dissolved oxygen concentration is relatively high. For the refractory pollutant tetracycline, there is obvious removal only at 2 - 4 mg / L. At lower or higher dissolved oxygen levels, the removal rate is only about 20%, and no hydroxyl radicals are detected in the reaction system using the salicylic acid method, indicating that the biological Fenton reaction does not occur.

[0060] Table 1 Pollutant removal rates at different dissolved oxygen levels

[0061] COD (mg / L) <![CDATA[NH 4 + (mg / L)]]> Tetracycline (mg / L) Influent 217±9.0 20±1.5 2.1±0.2 Effluent with 1 mg / L DO 23±2.0 14.8±0.5 1.7±0.2 Effluent with 2 mg / L DO 22±0.8 11.2±0.9 1.1±0.1 Effluent with 3 mg / L DO 18±2.3 4.3±0.5 0.7±0.1 Effluent with 4 mg / L DO 19.0±2.3 3.8±0.2 0.6±0.2 Effluent with 5 mg / L DO 14.3±2.7 3.7±0.3 1.6±0.2

[0062] Figure 1 These are the physical photos and scanning electron microscope pictures of the anaerobic granular sludge used in the present invention. The granular sludge is taken from the anaerobic bioreactor for treating citric acid wastewater, and particles with a diameter less than 0.5 mm are removed after sieving. Under a high-power scanning electron microscope, the porous structure and microbial cells of the anaerobic granular sludge are clearly visible, which can ensure mass transfer and the growth metabolism of microorganisms inside the granular sludge and the transformation of pollutants.

[0063] Figure 2 This is the microbial fuel cell reactor used for electrochemically domesticating anaerobic granular sludge. The reactor is made of acrylic, with a two-chamber structure. The internal dimensions of both the anode and cathode chambers are 4 cm × 6 cm × 6 cm, separated by a Nafion 117 proton exchange membrane with a diameter of 3.5 cm. The oxygen reduction cathode is on the left, using a modified carbon felt electrode of 2 cm × 4 cm. The biological anode is on the right, filled with 2 g of wet-weight anaerobic granular sludge, with a corresponding MLSS of 200 g / L. A bundled carbon fiber electrode is additionally inserted on the right as an electron collector. This electrode is cylindrical, with a diameter of 5 cm and a height of 6 cm. A 100-ohm resistor is connected between the anode and cathode.

[0064] During the enrichment stage, the influent of the bioanode was artificial wastewater, with sodium acetate as the organic substrate. The reactor loading was 1000 mg / L COD per day. To ensure the renewal of the microbial community in the anaerobic granular sludge, 10 mL Wolfe / L mineral salts and 10 mL / L vitamin stock solution were added to the wastewater. Meanwhile, to improve the electricity generation efficiency, 50 mM PBS buffer solution was used with an initial pH of 7. The bioanode in the enrichment stage was operated in a sequential batch mode, with sodium acetate supplemented once a day, and 20 mL of the supernatant replaced every three days to prevent acidification of the anode chamber. The terminal voltage across the resistor was collected using a data acquisition card, and the corresponding current density was calculated using Ohm's law. After the reactor was started, the terminal voltage gradually increased, and the current density converted in the anode chamber reached 22 A / m 3 , indicating that the anaerobic granular sludge had been transformed into electroactive granular sludge.

[0065] Figure 3 This is the aberration-corrected high-resolution scanning transmission electron microscopy image of the iron-cobalt dual-atom catalyst prepared in the embodiment of the present invention. The preparation of the iron-cobalt dual-atom catalyst refers to the invention content, and finally the aberration-corrected high-resolution scanning transmission electron microscopy of the catalyst is as Figure 3 shown. The bright spots on the dark substrate indicate the successful loading of iron atoms and cobalt atoms, and the size conforms to the characteristics of a single-atom catalyst. When hybridizing the electroactive granular sludge with the iron-cobalt dual-atom catalyst, the catalyst dosage was 200 mg / L, and the co-incubation time was 12 hours.

[0066] Figure 4 This is the SBR reactor used in the sewage treatment experiment. The reactor is designed with bottom influent and top reflux aeration. The inner diameter of the reactor is 5 cm and the height is 1 m. The hybrid electroactive granular sludge fills about 20% of the volume. Each part of the reactor is shown in the figure, and the most core parts are the dissolved oxygen probe and the aeration pump for regulating the dissolved oxygen.

Claims

1. A self-driven bio-electric Fenton wastewater treatment method based on the electroactive domestication of granular sludge, characterized in that: include: Firstly, anaerobic granular sludge is inoculated in the anode chamber of the microbial fuel cell, a bundled carbon fiber electrode is fixed in the biological anode chamber as an electrode collector, and the cathode is an oxygen reduction cathode. After connecting the anode and cathode with a resistor, the anaerobic granular sludge is domesticated under the condition of discharge of the microbial fuel cell, and the electroactive granular sludge is obtained through electrochemical enrichment. Afterwards, the iron-cobalt diatomic catalyst was prepared by using nitrogen-doped graphene oxide, cobalt phthalocyanine and iron phthalocyanine; Finally, the iron-cobalt diatomic catalyst was added to the electroactive granular sludge to form a hybrid structure, and the dissolved oxygen in the reaction system was controlled. The SBR reactor was used to achieve the generation of bioelectricity and the activity of molecular oxygen to degrade organic pollutants.

2. The self-driven bio-electric Fenton sewage treatment method based on the electroactive domestication of granular sludge according to claim 1 is characterized in that: The specific steps include: (1) Preparation of electroactive granular sludge: Anaerobic granular sludge is inoculated into the bioanode chamber of a dual-chamber microbial fuel cell reactor. The bioanode chamber is fixed with a bundled carbon fiber electrode as an electrode collector, and the cathode is an oxygen reduction cathode. After connecting the anode and cathode with a resistor, electroactive granular sludge is obtained after electrochemical enrichment. (2) Preparation of iron-cobalt diatomic catalysts: Using nitrogen-doped graphene as a substrate and iron phthalocyanine and cobalt phthalocyanine as precursors, the nitrogen-doped graphene was adsorbed on cobalt phthalocyanine and iron phthalocyanine via π-π interactions followed by thermal decomposition to prepare an iron-cobalt diatomic catalyst that efficiently activated molecular oxygen and was biocompatible; (3) Hybridization of electroactive granular sludge and iron-cobalt diatomic catalyst: First, the iron-cobalt diatomic catalyst prepared in step (2) is dispersed in an ethanol solution by ultrasonication to prepare a catalyst dispersion stock solution with a concentration of 1 mg / mL. Then, the catalyst is diluted by artificial water distribution to a final concentration of 200 μg / mL. Finally, the electroactive granular sludge prepared in step (1) is placed in the diluted catalyst solution and incubated under anaerobic conditions for 12 hours to allow the iron-cobalt diatomic catalyst to fully react with the anaerobic granular sludge microorganisms and be adsorbed to form a hybrid of the electroactive granular sludge and the iron-cobalt diatomic catalyst; The concentration of the electroactive granular sludge in the catalyst solution in step (3) is 200 g MLSS / L; (4) Self-driven bio-electro-Fenton degradation of pollutants: the electroactive granular sludge prepared in step (3) and the iron-cobalt diatomic catalyst hybrid are transferred to a SBR reactor for wastewater treatment; The volume of the electroactive granular sludge should account for 10-20% of the total effective volume of the SBR reactor.

3. The self-driven bio-electric Fenton sewage treatment method based on the electroactive domestication of granular sludge according to claim 2 is characterized in that: The anaerobic granular sludge inoculated in step (1) is obtained by cultivating an anaerobic reactor using C2-C5 short-chain organic acids as the main substrate, and the diameter of the anaerobic granular sludge after passing through the sieve is not less than 0.5 mm.

4. The self-driven bio-electric Fenton sewage treatment method based on the electroactive domestication of granular sludge according to claim 3 is characterized in that: The bundled carbon fibers used in the bioanode chamber in step (1) are long enough to reach the entire reactor, and the anaerobic granular sludge is filled into the bioanode chamber, leaving only 10% of the space at the top of the bioanode chamber for maintaining the water phase.

5. The self-driven bio-electric Fenton sewage treatment method based on the electroactive domestication of granular sludge according to claim 2 is characterized in that: The cathode of the dual-chamber microbial fuel cell reactor in step (1) is a carbon felt electrode modified with a platinum-carbon catalyst, wherein the carbon felt electrode is used as a base electrode, the oxygen reduction active catalyst is dispersed in an organic solvent, mixed with a Nafion solution having a mass concentration of 5%, and then dripped onto the surface of the carbon felt electrode, and then vacuum dried to obtain the obtained product; The catalyst is a Pt / C catalyst; The organic solvent is ethanol.

6. The self-driven bio-electric Fenton sewage treatment method based on the electroactive domestication of granular sludge according to claim 2 is characterized in that: In the electrochemical enrichment stage in step (1), the anolyte uses artificial water, acetate as the carbon source, 1000 mg / L COD / day, 50 mM phosphate as the buffer, the initial pH is adjusted to 7, the C:N ratio is 10:1 to 20:1, and Wolfe mineral salts and Wolfe vitamins are added; The cathodic solution was 100 mM Na2SO4 solution, and a magnetic stirrer was used to maintain the dissolved oxygen concentration > 4 mg / L; The electrochemical enrichment time is 7-14 days.

7. The self-driven bio-electric Fenton wastewater treatment method based on the electroactive domestication of granular sludge according to claim 2 is characterized in that: The pyrolysis in step (2) is divided into two steps, pyrolysis is performed at 500° C. and 700° C. respectively, and each step of pyrolysis lasts for 1 hour; 8. The self-driven bio-electric Fenton sewage treatment method based on the electroactive domestication of granular sludge according to claim 7 is characterized in that: The nitrogen-doped graphene in step (2) is prepared by carbonizing graphene oxide after reacting with dicyandiamide; wherein the graphene oxide is required to be a single layer or a double layer, the mass ratio of graphene oxide to dicyandiamide is 2:1, the two are mixed and stirred in an aqueous phase for reaction for 2 hours, vacuum dried, and pyrolyzed in a tubular furnace under a nitrogen environment to obtain nitrogen-doped graphene with a nitrogen content of 7-8%; the pyrolysis is divided into two steps, pyrolysis is performed at 500° C. and 700° C. respectively, and each step of pyrolysis lasts for 1 hour.

9. The self-driven bio-electric Fenton wastewater treatment method based on the electroactive domestication of granular sludge according to claim 8 is characterized in that: The specific preparation steps of step (2) are: First, nitrogen-doped graphene was ground and ultrasonically dispersed in an ethanol solution at a concentration of 1 mg / mL; Afterwards, cobalt phthalocyanine and iron phthalocyanine were also dispersed in the ethanol solution in sequence, and the concentration of both was 0.5-2 mg / L; Finally, the nitrogen-doped graphene dispersion was mixed with cobalt phthalocyanine and iron phthalocyanine dispersions, stirred at room temperature for 2 hours, and then centrifuged to collect the sample. The sample was washed three times with deionized water and then vacuum dried to obtain the iron-cobalt diatomic catalyst. In the iron-cobalt diatomic catalyst, cobalt and iron should each account for 1.4-1.8% of the total mass of the catalyst; 10. The self-driven bio-electric Fenton wastewater treatment method based on the electroactive domestication of granular sludge according to claim 2, characterized in that: The SBR reactor described in step (4) has a structure of bottom water inlet and top aeration and reflux. Specifically, a water inlet and a reflux inlet are provided at the bottom, and a water outlet and a reflux outlet are provided on both sides of the top respectively; the water inlet is connected to an inlet pump, and the reflux outlet is connected to the reflux inlet at the bottom through a reflux pump; a sampling port is provided between the water inlet and the water outlet, and at the same time, the dissolved oxygen level is regulated by configuring a dissolved oxygen probe and an adjustable aeration pump at the top, so that the dissolved oxygen concentration in the electroactive granular sludge filling area is between 2-4 mg / L.

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