Aquaculture wastewater treatment system based on pretreated magnesium anode and method for recovering nitrogen and phosphorus in aquaculture wastewater

Abstract

The present invention relates to an aquaculture wastewater treatment system based on a pretreated magnesium anode and a method for recovering nitrogen and phosphorus in aquaculture wastewater. The aquaculture wastewater treatment system based on a pretreated magnesium anode of the present invention comprises a reactor, an anode based on a pretreated magnesium, a cathode, an external resistor and a plurality of wires, etc. The anode based on the pretreated magnesium is prepared from magnesium slag solid waste, and the cathode is a titanium sheet; the pretreated aquaculture wastewater is placed in the aquaculture wastewater treatment system based on the pretreated magnesium anode, and after the circuit is closed, the Mg generated by the anode based on the pretreated magnesium is recovered. 2+ , and OH- produced in the system, provide a magnesium source for nitrogen and phosphorus recovery in aquaculture wastewater and adjust the pH value, which is conducive to the precipitation of struvite and magnesium phosphate precipitation to obtain nitrogen and phosphorus resources. The present invention uses an aquaculture wastewater treatment system composed of an anode based on pretreated magnesium to recover nitrogen and phosphorus in aquaculture wastewater, and realizes the renewal of aquaculture wastewater through a technical model of treating waste with waste.

Description

Technical Field

[0001] The invention belongs to the field of industrial solid waste resource utilization and nutrient resource recovery, and specifically relates to an aquaculture wastewater treatment system composed of a pretreated magnesium anode and a method for recovering nitrogen and phosphorus in aquaculture wastewater. Background Art

[0002] With the over-exploitation of fishery resources in natural water bodies such as rivers, lakes and reservoirs and the implementation of environmental protection measures, coupled with the rapid increase in people's demand for fish and aquatic products, the contradiction between supply and demand has continued to intensify, and land-based aquaculture has become one of the best ways to meet the development of fisheries and environmental protection at the same time. However, as a high-density and high-input artificial enclosure system, residual bait and excrement pollution has become one of the main problems that seriously restrict high-density land-based aquaculture. Studies have shown that less than 50% of the feed in aquaculture is retained in the bodies of farmed animals, and a large part of the rest remains in the aquaculture water, which increases the nitrogen and phosphorus content in the aquaculture water and causes the rapid deterioration of the environmental water quality in the aquaculture area. On the one hand, it affects the growth of the aquaculture objects and the product quality. On the other hand, the large amount of high-concentration pollutants discharged from aquaculture will seriously threaten the sustainable development of this industry.

[0003] At present, there have been many studies on the treatment of aquaculture wastewater by physical, chemical, biological and combined treatment methods, but there are still a series of problems such as high investment and operation costs, serious secondary pollution of sludge and difficulty in continuously meeting the standards of drainage water quality. Using nutrients such as N and P in aquaculture wastewater to produce fertilizers is a green and sustainable technical model. The production of struvite from aquaculture wastewater is carried out by adding magnesium salts for chemical precipitation, while adjusting the pH value or using aeration to strip carbon dioxide to remove high-content N, P and other substances in aquaculture wastewater. In the past, the most common source of Mg was Mg salts, such as MgCl2, MgSO4 and MgO. However, the solubility of Mg(OH)2 and MgCO3 in water is low, and the technical model cannot be used on a large scale. The electrochemical magnesium dissolution method seems to be suitable for the dissolution of active magnesium, promoting the combination of N, P and Mg in aquaculture wastewater to form struvite, but this process requires electrical energy. Metal-air fuel cells have attracted a lot of attention as electrochemical energy storage and conversion devices due to their high theoretical energy density and low cost. The reactions involved in the removal of N and P by magnesium-air batteries are as follows:

[0004] Mg→Mg 2+ +2e -

[0005] O2+2H2O+4e - →4OH -

[0006] 2Mg+O2+2H2O→2Mg(OH)2

[0007]

[0008] Therefore, the use of magnesium-air fuel cell technology to overcome the insolubility problem of Mg, recover N and P from aquaculture wastewater, and use them as fertilizers has potential prospects.

[0009] Prior art, such as the Chinese invention patent with publication number CN107814470A, discloses a device and method for electrochemical precipitation recovery of nitrogen and phosphorus in excess sludge, which specifically discloses the following content: the magnesium rod anode and the carbon rod cathode undergo electron transfer under the action of direct current to provide magnesium ions and hydroxides respectively, and the ammonium ions and phosphate ions provided by the excess sludge are converted into struvite precipitation. Although this method can achieve the recovery of phosphorus in excess sludge without the need for additional addition of magnesium salts, it also has some shortcomings. First, a large amount of NaOH needs to be added to improve the efficiency of decomposition of excess sludge, and the cost of the reagent is too high; in addition, the pH value of the sedimentation tank is maintained between 7-8, resulting in low purity of the recovered struvite; finally, applying direct current to promote electrochemical reactions will increase energy consumption costs. In addition, the Chinese invention patent with publication number CN111584980A discloses a method for recovering phosphorus resources and electrical energy in urine using a magnesium-air fuel cell. A magnesium-air fuel cell was constructed, including a battery cavity, an anode, a cathode, an external resistor and several wires. The anode was a metal magnesium anode, and the cathode was a platinum-carbon air cathode. Urine was added to the battery cavity, and the reaction started after connecting to the external circuit. The battery anode directly lost electrons to produce Mg 2+ , cathode oxygen reduction produces OH - , provide magnesium source and alkali source for precipitation reaction, generate struvite precipitate or magnesium phosphate precipitate, and recover electric energy through redox reaction at the same time. After disconnecting the external circuit to stop the reaction, filter the urine and recover the precipitate to obtain phosphorus resources. Although these methods can recover nitrogen and phosphorus in urine, the distance between the anode and cathode is too small, which makes the equipment unable to process a large amount of aquaculture wastewater, and the actual expansion application is relatively limited. In addition, the cost of the anode material used is relatively high. Therefore, it is necessary to further reduce the cost of electrode materials and expand their application to other aquaculture wastewaters to achieve the expansion and application of the equipment.

[0010] Therefore, how to find a low-cost technology that can be applied on a large scale to prepare magnesium rod anodes and efficiently recover nitrogen and phosphorus from aquaculture wastewater is obviously of great significance to the aquaculture industry. Summary of the invention

[0011] Based on the above defects, the purpose of the present invention is to provide a method for recovering nitrogen and phosphorus from aquaculture wastewater, reduce the cost of preparing electrodes, chemical agent input and electricity consumption, and recover valuable resources in aquaculture wastewater to alleviate point source pollution caused by aquaculture wastewater.

[0012] An object of the present invention is to provide an anode based on pretreated magnesium, the anode based on pretreated magnesium comprising the following substances: pretreated magnesium powder, carbon powder and copper powder;

[0013] Wherein, the pretreated magnesium powder includes magnesium oxide and magnesium boride.

[0014] Furthermore, the shape of the pre-treated magnesium-based anode is selected from sheet, column or block.

[0015] Furthermore, in the anode based on pretreated magnesium, the mass ratio of pretreated magnesium powder, carbon powder and copper powder is (1.5-2.5):(0.2-0.8):1.

[0016] Another object of the present invention is to provide a method for preparing the above-mentioned pretreated magnesium anode, comprising the following steps:

[0017] S1, titanium powder, carbon powder, magnesium powder and boron powder are subjected to a self-propagating high temperature synthesis reaction in a mass ratio of 1:(2-3):1:1 to obtain pretreated magnesium powder;

[0018] S2, mixing the pretreated magnesium powder, carbon powder and copper powder by ball milling in a mass ratio of (1.5-2.5):(0.2-0.8):1 to obtain a mixed pretreated magnesium powder;

[0019] S3, mixing the mixed pretreated magnesium powder with chitosan and polyacrylamide and adding water, dropping epichlorohydrin and keeping warm in a water bath, washing, filtering and drying to obtain a solid powder;

[0020] S4, subjecting the solid powder to high-pressure torsional extrusion molding.

[0021] Furthermore, in step S1, the raw material of the magnesium powder is magnesium slag solid waste generated in the Pidgeon process for magnesium smelting, including filtered dust waste, high-temperature calcination residue and cutting waste.

[0022] Furthermore, in step S1, the magnesium powder is obtained by grinding and crushing the magnesium slag solid waste produced in the Pidgeon process of magnesium smelting by a ball mill.

[0023] Furthermore, in step S1, the temperature of the self-propagating high temperature synthesis reaction is 500-600°C.

[0024] Furthermore, in step S2, the particle size of the pretreated magnesium powder, carbon powder and copper powder is 300-400 mesh.

[0025] Furthermore, in step S2, the ball milling speed is 75-85% of the critical speed, and the ball milling time is 10-30 min.

[0026] Furthermore, in step S3, the mass ratio of the mixed pretreated magnesium powder, chitosan, polyacrylamide, and epichlorohydrin is 10:(0.1-0.2):(0.2-0.5):0.1.

[0027] Furthermore, in step S3, the water bath is kept at a temperature of 50-60°C.

[0028] Furthermore, in step S3, the washing solvent is anhydrous ethanol.

[0029] Furthermore, in step S3, the drying temperature is 40°C-50°C.

[0030] Furthermore, in step S4, the pressure of the high-pressure torsional extrusion molding is 20T and the number of revolutions is 5 revolutions.

[0031] Furthermore, in step S4, the dimensions of the anode based on the pretreated magnesium obtained by the high-pressure torsional extrusion molding are 10 cm in length, 2 cm in width, and 1.5 mm in thickness.

[0032] Another object of the present invention is to provide an aquaculture wastewater treatment system composed of the pretreated magnesium-based anode, comprising the following components:

[0033] An external power source (1), an anode (4) based on pretreated magnesium, a reactor (5), a cathode (6), a water inlet device (10), and a water outlet device (7);

[0034] wherein the anode (4) and cathode (6) based on pretreated magnesium are arranged in a reactor (5), and the anode (4) based on pretreated magnesium is arranged at a central position of the reactor (5);

[0035] The cathode (6) is in a thin layer shape and is arranged on the inner wall of the reactor (5) around the anode (4) based on the pretreated magnesium as the center of the circle;

[0036] The upper part of the reactor (5) is connected to a water inlet device (10) having a function of adjusting the pH value of aquaculture wastewater, and the lower part on the opposite side is connected to a water outlet device (7);

[0037] The external power source (1) electrically connects the anode (4) and cathode (6) based on the pretreated magnesium;

[0038] The relative area ratio of the anode (4) and cathode (6) based on pretreated magnesium is 1:(1.5-2), and the distance is 6.0-10.0 cm.

[0039] Furthermore, the aquaculture wastewater treatment system composed of the pretreated magnesium-based anode (4) further comprises a resistor (2), a conductor (3), a valve (8), a water pipe conduit (9), a water inlet (13), a water outlet (14), a bottom water outlet (15), a magnetic stirring system (11), a product collection filter (12), and an aquaculture wastewater nitrogen and phosphorus content monitor (16);

[0040] Specifically:

[0041] The external power source (1), the two ends of which are electrically connected to the anode (4) and cathode (6) based on the pretreated magnesium;

[0042] The resistor (2) is connected to the circuit between the external power source (1) and the anode (4) and cathode (6) based on the pretreated magnesium, and has a resistance value of 30-100Ω, and is used to adjust the current and voltage in the circuit;

[0043] The conductor (3) is used to form a loop;

[0044] The reactor (5) is provided with a magnetic stirring system (11) at the lower part of the container; a product collection filter (12) is provided at the bottom; and the product collection filter (12) covers the bottom water outlet (15); a water outlet (14) is provided at the side of the lower end of the container, and the water outlet (14) is connected to the lower half of the side of the water outlet device (7); the magnetic stirring system (11) is used to homogenize the pH value of the aquaculture wastewater, avoid the local pH value being too high, maintain it within the appropriate pH value range for the formation of struvite, and avoid concentration polarization near the electrode;

[0045] Specifically, the concentration polarization means that due to the change of ion concentration near the electrode, when the ion concentration decreases, the ion migration speed slows down, thereby generating polarization.

[0046] The anode (4) based on pretreated magnesium and the cathode (6) are arranged in a reactor (5), and the anode (4) based on pretreated magnesium is arranged at a central position of the reactor (5);

[0047] The cathode (6) is in the form of a thin layer, and is arranged around the inner wall of the reactor (5) with the pretreated magnesium-based anode (4) as the center of the circle; and is used for generating OH by oxidation-reduction reaction. - ;

[0048] The valve (8) is arranged between the water pipe conduit (9) and the water inlet (13);

[0049] The opening in the upper part of the side of the reactor (5) is connected to a monitor (16) for nitrogen and phosphorus content in aquaculture wastewater, and is used to monitor the pH value of the aquaculture wastewater;

[0050] The water inlet device (10), the upper half of the side surface of which is in communication with the upper half of the side surface of the reactor;

[0051] The lower half of the side surface of the water outlet device (7) is connected to the lower half of the side surface of the reactor;

[0052] Furthermore, a method for recovering nitrogen and phosphorus resources in aquaculture wastewater based on an aquaculture wastewater treatment system composed of a pretreated magnesium anode (4) comprises the following steps:

[0053] L1, the aquaculture wastewater in the water inlet device (10) enters the reactor (5) through the water inlet (13), connects the circuit and turns on the magnetic stirring system (11) to react; the anode (4) based on the pretreated magnesium directly loses electrons to generate Mg 2+ , a redox reaction occurs at the cathode (6) to produce OH - , providing magnesium source and alkali source for precipitation reaction, generating struvite precipitation or magnesium phosphate precipitation;

[0054] L2. According to the online monitoring data of the nitrogen and phosphorus content monitor (16) of the aquaculture wastewater, and compared with the limit values ​​specified in the Level A standard of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (DB32 / 4440-2022) (the ammonia nitrogen, total nitrogen and total phosphorus limits are 1.5 mg / L, 10 mg / L and 0.3 mg / L respectively), the optimal hydraulic retention time is determined, the magnetic stirring system (11) is turned off to stop stirring, and the aquaculture wastewater is allowed to stand and the reacted aquaculture wastewater enters the water outlet device (7) through the outlet (14), and the precipitate is filtered through the product collection filter (12), collected and dried to constant weight.

[0055] Furthermore, in step L1, the rotation speed of the magnetic stirring system (11) during the stirring process is 80-150 rpm, and the pH value of the aquaculture wastewater is maintained at 8.5-9.2 to maintain the formation of high-purity struvite and the efficient removal of nitrogen and phosphorus;

[0056] Furthermore, in step L2, the precipitate is filtered through a product collection filter (12), and the product collection filter (12) is a microporous filter of 300-500 mesh;

[0057] Furthermore, in step L2, the drying temperature is 60°C.

[0058] The present invention has the following beneficial effects:

[0059] 1. The technical solution of the present invention utilizes the magnesium slag solid waste generated in the Pijiang process of magnesium smelting, including filtered dust waste, high-temperature calcination residues and cutting waste, as the source of magnesium raw materials for the anode based on pretreated magnesium, which has the advantage of low cost.

[0060] 2. The technical solution proposed in the present invention is to dope copper powder and carbon powder into the pretreated magnesium powder. The copper powder has a higher conductivity, which is beneficial to the transfer of electrons and to increasing the reaction rate between the active substance and the ions in the aquaculture wastewater. The incorporation of carbon powder is beneficial to the formation of the porous structure of the anode during the preparation process, which can improve the recovery efficiency of nitrogen and phosphorus resources and achieve the effect of efficiently recovering nitrogen and phosphorus in aquaculture wastewater.

[0061] 3. The technical solution proposed by the present invention is to mix the pre-treated magnesium powder with chitosan and polyacrylamide and add water, drop epichlorohydrin and keep warm in a water bath, wash, filter and dry to obtain a solid powder. The added chitosan, polyacrylamide and epichlorohydrin play a role in powder plasticity and consolidation, while reducing concentration polarization as much as possible to slow down the Mg 2+ The release of oxygen achieves the effect of protecting the anode and achieving a steady state in the water treatment system. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 A diagram of an aquaculture wastewater treatment system based on a pretreated magnesium anode according to an embodiment of the present invention is shown.

[0063] Figure numerals: 1-external power supply, 2-resistance, 3-conductor, 4-anode based on pretreated magnesium, 5-reactor, 6-cathode, 7-water outlet, 8-valve, 9-water pipe conduit, 10-water inlet, 11-magnetic stirring system, 12-product collection filter, 13-water inlet, 14-water outlet, 15-bottom water outlet, 16-aquaculture wastewater nitrogen and phosphorus content monitor, 17-switch, 18-precipitation.

[0064] Figure 2 The X-ray diffraction pattern of the pretreated magnesium powder prepared in Example 1 of the present invention is shown.

[0065] Figure 3 The graph shows the change of nitrogen and phosphorus content over time during the treatment of aquaculture wastewater by the aquaculture wastewater treatment system composed of the anode based on pretreated magnesium in Example 1 of the present invention.

[0066] Figure 4 The X-ray diffraction diagram of the precipitate produced during the recovery of nitrogen and phosphorus in the aquaculture wastewater treatment system composed of the anode based on pretreated magnesium in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0067] In order to more clearly illustrate the technical solution of the present invention, the following examples are listed. Unless otherwise stated, the raw materials, reactions and post-treatment methods shown in the examples are common raw materials on the market and technical methods well known to those skilled in the art.

[0068] The following raw materials are used in the embodiments of the present invention:

[0069] Magnesium slag solid waste refers to the magnesium slag solid waste generated in the Pijiang process of magnesium smelting, including filter dust waste, high-temperature calcination residue and cutting waste;

[0070] Titanium powder, purity 99.99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0071] Carbon powder, which is biochar from biomass, was prepared by thermal pyrolysis at 600 °C for 1 h and ground;

[0072] Boron powder, amorphous powder, purity ≥95%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0073] Copper powder, purity 99.9%, ≥325 mesh, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0074] Chitosan, medium viscosity, 200-400 mPa.s, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0075] Polyacrylamide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0076] Example 1

[0077] Step 1: Preparation of pretreated magnesium-based anode

[0078] An anode based on pretreated magnesium comprises the following substances: pretreated magnesium powder, carbon powder and copper powder, wherein the pretreated magnesium powder comprises magnesium oxide and magnesium boride.

[0079] The pre-treated magnesium based anode is in the shape of a sheet.

[0080] The method for preparing the anode based on pretreated magnesium comprises the following steps:

[0081] S1. Grind the magnesium slag solid waste with a ball mill to obtain magnesium powder, and carry out a self-propagating high temperature synthesis reaction of titanium powder, carbon powder, magnesium powder and boron powder at a mass ratio of 1:2:1:1 at 500° C. under argon protection for 2 hours to obtain pretreated magnesium powder;

[0082] S2, pretreated magnesium powder, carbon powder and copper powder with a particle size of 300 mesh were mixed in a mass ratio of 1.5:0.2:1, and ball milled for 10 min at 85% critical speed in a ball mill to obtain mixed pretreated magnesium powder;

[0083] S3, adding the mixed pretreated magnesium powder, chitosan and polyacrylamide into water, then dropping epichlorohydrin and keeping warm in a water bath at 50°C for 24h (mixed pretreated magnesium powder: chitosan: polyacrylamide: water: epichlorohydrin = 10:0.2:0.2:5:0.1, m / m / m / m / m), washing with anhydrous ethanol, filtering, and drying at 40°C to obtain a solid powder;

[0084] S4. The solid powder is subjected to high-pressure twisting extrusion molding at a pressure of 20T and a rotation number of 5 to obtain a sheet-shaped pretreated magnesium-based anode having a length of 10 cm, a width of 2 cm and a thickness of 1.5 mm.

[0085] Step 2: Forming an aquaculture wastewater treatment system based on the pretreated magnesium anode (4)

[0086] The aquaculture wastewater treatment system based on the pre-treated magnesium anode (4) comprises the following components:

[0087] An external power source (1), an anode (4) based on pretreated magnesium, a reactor (5), a cathode (6), a water inlet device (10), and a water outlet device (7);

[0088] wherein the anode (4) and cathode (6) based on pretreated magnesium are arranged in a reactor (5), and the anode (4) based on pretreated magnesium is arranged at a central position of the reactor (5);

[0089] The cathode (6) is in a thin layer shape and is arranged on the inner wall of the reactor (5) around the anode (4) based on the pretreated magnesium as the center of the circle;

[0090] The upper part of the reactor (5) is connected to a water inlet device (10) having a function of adjusting the pH value of aquaculture wastewater, and the lower part on the opposite side is connected to a water outlet device (7);

[0091] The external power source (1) electrically connects the anode (4) and cathode (6) based on the pretreated magnesium;

[0092] The aquaculture wastewater treatment system composed of the pretreated magnesium anode (4) also includes a resistor (2) with a resistance value of 30Ω, a wire (3), a reactor (5), a valve (8), a water pipe (9), a water inlet (13), a water outlet (14), a bottom water outlet (15), a magnetic stirring system (11), a product collection filter (12), and a monitor for nitrogen and phosphorus content in aquaculture wastewater (16);

[0093] Specifically:

[0094] The external power source (1), the two ends of which are electrically connected to the anode (4) and cathode (6) based on the pretreated magnesium;

[0095] The resistor (2) is connected to the circuit between the external power source and the anode (4) and cathode (6) based on the pretreated magnesium, and has a resistance of 30Ω, and is used to adjust the current and voltage in the circuit;

[0096] The conductor (3) is used to form a loop;

[0097] The reactor (5) is provided with a magnetic stirring system (11) at the lower part of the container; a product collection filter (12) is provided at the bottom; and the product collection filter (12) covers the bottom water outlet (15); a water outlet (14) is provided at the side of the lower end of the container, and the water outlet (14) is connected to the lower half of the side of the water outlet device (7); the magnetic stirring system (11) is used to homogenize the pH value of the aquaculture wastewater, avoid the local pH value being too high, maintain it within the appropriate pH value range for the formation of struvite, and avoid concentration polarization near the electrode;

[0098] The anode (4) based on pretreated magnesium and the cathode (6) are arranged in a reactor (5), and the anode (4) based on pretreated magnesium is arranged at a central position of the reactor (5);

[0099] The cathode (6) is in the form of a thin layer, and is arranged around the inner wall of the reactor (5) with the pretreated magnesium-based anode (4) as the center of the circle; it is used for generating OH by oxidation-reduction reaction. - ;

[0100] The valve (8) is arranged between the water pipe conduit (9) and the water inlet (13);

[0101] The opening in the upper part of the side of the reactor (5) is connected to a monitor (16) for nitrogen and phosphorus content in aquaculture wastewater, and is used to monitor the pH value of the aquaculture wastewater;

[0102] The upper half of the side surface of the water inlet device (10) is connected to the upper half of the side surface of the reactor;

[0103] The lower half of the side surface of the water outlet device (7) is connected to the lower half of the side surface of the reactor;

[0104] The relative area ratio (surface area ratio) of the pretreated magnesium anode (4) and cathode (6) is 1:1.5, and the lateral distance between the electrodes is 6.0 cm.

[0105] Step 3: operate the aquaculture wastewater treatment system composed of the pretreated magnesium anode (4) to recover nitrogen and phosphorus in the aquaculture wastewater.

[0106] The experiment was conducted using simulated aquaculture wastewater, which was prepared as follows: 0.02M CaCl2, 0.01M MgCl2·6H2O, 0.1M NaCl, 0.1M Na2SO4, 0.01M KCl, and NO3 - -N, NO2 - -N、NH4 + The average mass concentrations of -N, TN, and TP were 6.5, 0.8, 4.5, 13, and 6.0 mg L -1.

[0107] The switch (17) is closed, the external power supply (1) is powered on at a voltage of 12V, and the resistor (2) is powered on at a voltage of 30Ω to operate the aquaculture wastewater treatment system composed of the pretreated magnesium anode (4), and the simulated aquaculture wastewater enters the reactor (5) with a volume of 20L through the water inlet device (10), and the water inlet volume is 0.15L / min. The magnetic stirring system (11) is turned on and the stirring speed is 80rpm; the nitrogen and phosphorus content in the reaction tank is monitored by the aquaculture wastewater nitrogen and phosphorus content monitor (16); the pH value of the simulated aquaculture wastewater in the reactor (5) is adjusted by the aquaculture wastewater pH value adjustment function of the water inlet device (10), and the pH value of the simulated aquaculture wastewater is homogenized by the magnetic stirring system (11), and the simulated aquaculture wastewater is maintained at 8.5-9.2 during the stirring process to improve the formation efficiency of high-purity magnesium phosphate;

[0108] The nitrogen and phosphorus concentrations of the simulated aquaculture wastewater are monitored online by the aquaculture wastewater nitrogen and phosphorus content monitor (16). When the nitrogen and phosphorus contents in the reactor (5) are lower than the limit values ​​specified in the Level A standard of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (DB32 / 4440-2022), the magnetic stirring system (11) can be turned off. The simulated aquaculture wastewater after the reaction is precipitated and flows out through the outlet (14), with an outlet volume of 0.15 L / min. The bottom suspension is filtered through a 300-mesh product collection filter (12) to collect the precipitate, and then the remaining simulated aquaculture wastewater is discharged through the bottom outlet (15). The precipitate is dried in an oven at 60° C. to a constant weight.

[0109] Figure 1 A diagram of an aquaculture wastewater treatment system based on a pretreated magnesium anode according to an embodiment of the present invention is shown.

[0110] Figure numerals: 1-external power supply, 2-resistance, 3-conductor, 4-anode based on pretreated magnesium, 5-reactor, 6-cathode, 7-water outlet, 8-valve, 9-water pipe conduit, 10-water inlet, 11-magnetic stirring system, 12-product collection filter, 13-water inlet, 14-water outlet, 15-bottom water outlet, 16-aquaculture wastewater nitrogen and phosphorus content monitor, 17-switch, 18-precipitation.

[0111] Example 2

[0112] Step 1: Preparation of pretreated magnesium-based anode

[0113] An anode based on pretreated magnesium comprises the following substances: pretreated magnesium powder, carbon powder and copper powder, wherein the pretreated magnesium powder comprises magnesium oxide and magnesium boride.

[0114] The pre-treated magnesium based anode is in the shape of a sheet.

[0115] The method for preparing the anode based on pretreated magnesium comprises the following steps:

[0116] S1. Grind the magnesium slag solid waste with a ball mill to obtain magnesium powder, and carry out a self-propagating high temperature synthesis reaction of titanium powder, carbon powder, magnesium powder and boron powder at a mass ratio of 1:3:1:1 at 600° C. under argon protection for 2 h to obtain pretreated magnesium powder;

[0117] S2, pretreated magnesium powder, carbon powder and copper powder with a particle size of 400 mesh were mixed in a mass ratio of 1.5:0.5:1, and ball milled for 10 min at 85% critical speed in a ball mill to obtain mixed pretreated magnesium powder;

[0118] S3, adding the mixed pretreated magnesium powder, chitosan and polyacrylamide into water, then dropping epichlorohydrin and keeping warm in a water bath at 60°C for 18h (mixed pretreated magnesium powder: chitosan: polyacrylamide: water: epichlorohydrin = 10:0.1:0.2:5:0.1, m / m / m / m / m), washing with anhydrous ethanol, filtering, and drying at 40°C to obtain a solid powder;

[0119] S4. The solid powder is subjected to high-pressure twisting extrusion molding at a pressure of 20T and a rotation number of 5 to obtain a sheet-shaped pretreated magnesium-based anode having a length of 10 cm, a width of 2 cm and a thickness of 1.5 mm.

[0120] Step 2: Forming an aquaculture wastewater treatment system based on pretreated magnesium anodes

[0121] The aquaculture wastewater treatment system based on pre-treated magnesium anodes includes the following components:

[0122] An external power source (1), an anode (4) based on pretreated magnesium, a reactor (5), a cathode (6), a water inlet device (10), and a water outlet device (7);

[0123] wherein the anode (4) and cathode (6) based on pretreated magnesium are arranged in a reactor (5), and the anode (4) based on pretreated magnesium is arranged at a central position of the reactor (5);

[0124] The cathode (6) is in a thin layer shape and is arranged on the inner wall of the reactor (5) around the anode (4) based on the pretreated magnesium as the center of the circle;

[0125] The upper part of the reactor (5) is connected to a water inlet device (10) having a function of adjusting the pH value of aquaculture wastewater, and the lower part on the opposite side is connected to a water outlet device (7);

[0126] The external power source (1) electrically connects the anode (4) and cathode (6) based on the pretreated magnesium;

[0127] The aquaculture wastewater treatment system composed of the pretreated magnesium anode (4) also includes a resistor (2) with a resistance value of 100Ω, a wire (3), a reactor (5), a valve (8), a water pipe (9), a water inlet (13), a water outlet (14), a bottom water outlet (15), a magnetic stirring system (11), a product collection filter (12), and a monitor for nitrogen and phosphorus content in aquaculture wastewater (16);

[0128] Specifically:

[0129] The external power source (1), the two ends of which are electrically connected to the anode (4) and cathode (6) based on the pretreated magnesium;

[0130] The resistor (2) is connected to the circuit between the external power source (1) and the anode (4) and cathode (6) based on the pretreated magnesium, has a resistance of 100Ω, and is used to adjust the current and voltage in the circuit;

[0131] The conductor (3) is used to form a loop;

[0132] The reactor (5) is provided with a magnetic stirring system (11) at the lower part of the container; a product collection filter (12) is provided at the bottom; and the product collection filter (12) covers the bottom water outlet (15); a water outlet (14) is provided at the side of the lower end of the container, and the water outlet (14) is connected to the lower half of the side of the water outlet device (7); the magnetic stirring system (11) is used to homogenize the pH value of the aquaculture wastewater, avoid the local pH value being too high, maintain it within the appropriate pH value range for the formation of struvite, and avoid concentration polarization near the electrode;

[0133] The anode (4) based on pretreated magnesium and the cathode (6) are arranged in a reactor (5), and the anode (4) based on pretreated magnesium is arranged at a central position of the reactor (5);

[0134] The cathode (6) is in the form of a thin layer, and is arranged around the inner wall of the reactor (5) with the pretreated magnesium-based anode (4) as the center of the circle; and is used for generating OH by oxidation-reduction reaction. - ;

[0135] The valve (8) is arranged between the water pipe conduit (9) and the water inlet (13);

[0136] The opening in the upper part of the side of the reactor (5) is connected to a monitor (16) for nitrogen and phosphorus content in aquaculture wastewater, and is used to monitor the pH value of the aquaculture wastewater;

[0137] The upper part of the side surface of the water inlet device (10) is connected to the upper part of the side surface of the reactor;

[0138] The lower half of the side surface of the water outlet device (7) is connected to the lower half of the side surface of the reactor;

[0139] The relative area ratio of the anode (4) and cathode (6) based on pretreated magnesium is 1:2, and the distance between them is 10.0 cm.

[0140] Step 3: operate the aquaculture wastewater treatment system composed of the pretreated magnesium anode (4) to recover nitrogen and phosphorus in the aquaculture wastewater.

[0141] The actual aquaculture wastewater was collected from a certain aquaculture base in Foshan. - -N, NO2 - -N、NH4 + The average mass concentrations of -N, TN, and TP were 8.2, 0.4, 6.0, 14.8, and 6.4 mg·L, respectively. -1 .

[0142] The switch (17) is closed, the external power supply (1) is powered at 12V, the resistor (2) is powered at 100Ω, and the aquaculture wastewater treatment system composed of the pretreated magnesium anode (4) is operated. The aquaculture wastewater enters the reactor (5) with a volume of 20L through the water inlet device (10), and the water inlet volume is 0.15L / min. The magnetic stirring system (11) is turned on and the stirring speed is 150rpm; the nitrogen and phosphorus content in the reaction tank is monitored by the aquaculture wastewater nitrogen and phosphorus content monitor (16); the pH value of the aquaculture wastewater in the reactor (5) is adjusted by the pH value adjustment function of the water inlet device (10), and the pH value of the aquaculture wastewater is homogenized by the magnetic stirring system (11). During the stirring process, the aquaculture wastewater is maintained at 8.5-9.2 to improve the formation efficiency of high-purity magnesium ammonium phosphate;

[0143] The nitrogen and phosphorus concentrations of the aquaculture wastewater are monitored online by the aquaculture wastewater nitrogen and phosphorus content monitor (16). When the nitrogen and phosphorus contents in the reactor (5) are lower than the limit values ​​specified in the Level A standard of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (DB32 / 4440-2022), the magnetic stirring system (11) can be turned off. The aquaculture wastewater after the reaction is precipitated and flows out through the outlet (14), with an outlet volume of 0.15 L / min. The bottom suspension is filtered through a 500-mesh product collection filter (12) to collect the precipitate, and then the remaining aquaculture wastewater is discharged through the bottom outlet (15). The precipitate is dried in an oven at 60° C. to a constant weight.

[0144] Comparative Example 1

[0145] The difference between this comparative example and Example 1 is:

[0146] Step 1: Preparation of pretreated magnesium-based anode

[0147] An anode based on pretreated magnesium comprises the following substances: pretreated magnesium powder, carbon powder and copper powder, wherein the pretreated magnesium powder comprises magnesium oxide and magnesium boride.

[0148] The pre-treated magnesium based anode is in the shape of a sheet.

[0149] The method for preparing the anode based on pretreated magnesium comprises the following steps:

[0150] S1. Grind the magnesium slag solid waste with a ball mill to obtain magnesium powder, and carry out a self-propagating high temperature synthesis reaction of titanium powder, carbon powder, magnesium powder and boron powder at a mass ratio of 1:2:1:1 at 500° C. under argon protection for 2 hours to obtain pretreated magnesium powder;

[0151] S2, pretreated magnesium powder and copper powder with a particle size of 300 mesh were mixed in a mass ratio of 1:1, and ball milled for 10 min at 85% of the critical speed of a ball mill to obtain mixed pretreated magnesium powder;

[0152] S3, adding the mixed pretreated magnesium powder, chitosan and polyacrylamide into water, then dropping epichlorohydrin and keeping warm in a water bath at 50°C for 24h (mixed pretreated magnesium powder: chitosan: polyacrylamide: water: epichlorohydrin = 10:0.2:0.2:5:0.1, m / m / m / m / m), washing with anhydrous ethanol, filtering, and drying at 40°C to obtain a solid powder;

[0153] S4. The solid powder is subjected to high-pressure twisting extrusion molding at a pressure of 20T and a rotation number of 5 to obtain a sheet-shaped pretreated magnesium-based anode having a length of 10 cm, a width of 2 cm and a thickness of 1.5 mm.

[0154] The other steps are the same as those in Example 1.

[0155] Comparative Example 2

[0156] The difference between this comparative example and Example 2 is:

[0157] An anode based on pretreated magnesium comprises the following substances: pretreated magnesium powder, carbon powder and copper powder, wherein the pretreated magnesium powder comprises magnesium oxide and magnesium boride.

[0158] The pre-treated magnesium based anode is in the shape of a sheet.

[0159] The method for preparing the anode based on pretreated magnesium comprises the following steps:

[0160] S1. Grinding and crushing magnesium slag solid waste by ball mill to obtain magnesium powder, and subjecting titanium powder, magnesium powder and boron powder to a self-propagating high temperature synthesis reaction at a mass ratio of 1:1:1 at 600° C. under argon protection for 2 h to obtain pretreated magnesium powder;

[0161] S2, pretreated magnesium powder and copper powder with a particle size of 400 mesh are mixed in a mass ratio of 1.5:1, and ball milled for 10 min at 85% critical speed of a ball mill to obtain mixed pretreated magnesium powder;

[0162] S3, adding the mixed pretreated magnesium powder, chitosan and polyacrylamide into water, then dropping epichlorohydrin and keeping warm in a water bath at 60°C for 18h (mixed pretreated magnesium powder: chitosan: polyacrylamide: water: epichlorohydrin = 10:0.1:0.2:5:0.1, m / m / m / m / m), washing with anhydrous ethanol, filtering, and drying at 40°C to obtain a solid powder;

[0163] S4. The solid powder is subjected to high-pressure twisting extrusion molding at a pressure of 20T and a rotation number of 5 to obtain a sheet-shaped pretreated magnesium-based anode having a length of 10 cm, a width of 2 cm and a thickness of 1.5 mm.

[0164] The other steps are the same as those in Example 2.

[0165] Test Example 1

[0166] Test content: Composition of the pretreated magnesium powder obtained in step S1 of Example 1.

[0167] Test method: The XRD pattern of the pretreated magnesium powder obtained in step S1 of Example 1 was measured using an X-ray diffraction device.

[0168] Test results:

[0169] Figure 2 The X-ray diffraction pattern of the pretreated magnesium powder prepared in Example 1 of the present invention is shown. It can be seen that characteristic diffraction represented by MgO and MgB2 appears in the spectrum, so the components of the pretreated magnesium powder include substances such as MgO and MgB2.

[0170] Test Example 2

[0171] Test content: Nitrogen and phosphorus concentrations in the simulated aquaculture wastewater of Example 1.

[0172] Test method: Close the switch, connect the external power supply (1) at 12V voltage, and the resistor (2) at 30Ω to operate the aquaculture wastewater treatment system composed of the pretreated magnesium anode (4), and monitor the nitrogen and phosphorus content of the aquaculture wastewater online through the aquaculture wastewater nitrogen and phosphorus content monitor (16). Record the nitrogen and phosphorus concentrations displayed in the simulated aquaculture wastewater nitrogen and phosphorus content monitor (16) at 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110 and 120 minutes.

[0173] Test results:

[0174] Figure 3The graph shows the change of nitrogen and phosphorus content over time during the treatment of aquaculture wastewater by the aquaculture wastewater treatment system composed of the anode based on pretreated magnesium in Example 1 of the present invention.

[0175] It can be seen that: 1. The nitrogen and phosphorus content of the simulated aquaculture wastewater decreases over time. At 0 min, the nitrogen content in the simulated aquaculture wastewater is about 4.5 mg / L, and the phosphorus content is about 6.1 mg / L. At 120 min, the nitrogen and phosphorus content in the simulated aquaculture wastewater are both about 0.3 mg / L, almost completely turning into precipitation products; 2. After 50 min, NH4 + -N can meet the limit value of 1.5mg / L specified in the Class A standard of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (DB32 / 4440-2022). After 90 minutes, PO4 3- -P can meet the limit value of 0.3mg / L specified in the Level A standard of the "Pollutant Emission Standard for Urban Wastewater Treatment Plants" (DB32 / 4440-2022).

[0176] Test Example 3

[0177] Test content: The composition of the precipitate obtained from the nitrogen and phosphorus recovery process in Example 1.

[0178] Test method: X-ray diffraction equipment was used to measure the XRD pattern of the precipitate obtained in the nitrogen and phosphorus recovery process at the end of step 3 of Example 1.

[0179] Test results: Figure 4 As shown, the obtained precipitate has characteristic peaks of struvite, etc., and it can be obtained that the mineral phase of struvite Mg(NH4)PO4·6H2O exists in the recovered precipitate.

[0180] Test Example 4

[0181] Test content: The precipitate obtained from the nitrogen and phosphorus recovery process was dissolved in 10 mL of 0.2 M HCl acid and the nitrogen and phosphorus concentrations were determined.

[0182] Test method: Take 0.2g of dry precipitate, dissolve it in 10mL of 0.2M HCl acid and measure its PO4 3- -P、NH4 + -N concentration. Phosphate content was determined by molybdenum antimony spectrophotometry, and ammonia nitrogen content was determined by Nessler's reagent spectrophotometry: Shimadzu UV spectrophotometer UV2600.

[0183] Test results: As shown in Table 1, through the invented technical method, the purity of struvite in the precipitate recovered in Example 1 and Example 2 can reach 87.35% and 85.13%, while in Comparative Examples 1 and 2, the purity of struvite recovery is lower, which may be related to the release of Mg in the anode material and the generation of other precipitates. The analysis results of the P and N content in the precipitate also show that other impurities are generated in the precipitate generated by the reaction.

[0184] Table 1 Components in the precipitate

[0185]

[0186] Test Example 5

[0187] Test content: Verify the effect of treated simulated aquaculture wastewater on the growth of crucian carp.

[0188] Test method: Take crucian carp cultured in conventional fish ponds as the control group, and crucian carp cultured in treated simulated aquaculture wastewater as the treatment group. Monitor the growth indicators of fish at 30, 60, 120 and 180 days: weight.

[0189] Test results: As shown in Table 2, it can be obtained that within 180 days, the weight of crucian carp in conventional fish ponds is basically equal to the weight of crucian carp cultured with the simulated aquaculture wastewater treated with Example 1 and Example 2, indicating that the simulated aquaculture wastewater treated with Example 1 and Example 2 can be used to culture crucian carp and the effect is basically the same as that of conventional fish ponds.

[0190] Table 2 Effects of different water sources on the growth weight of crucian carp (unit: g / carp)

[0191]

[0192]

[0193] Test Example 6

[0194] Test content: Verify the effect of nitrogen and phosphorus precipitation recovered from simulated aquaculture wastewater on lettuce growth.

[0195] Test method: A pot experiment was conducted to verify whether the recovered nitrogen and phosphorus precipitate can replace fertilizers. 14 treatments were set up and the same mass of soil was added. Three lettuces with uniform growth were planted in pots. The 14 treatments were as follows: no fertilizer, conventional fertilizer application treatment following agricultural operations, and 0.1wt%, 0.3wt% and 0.5wt% of the soil mass were added to the reaction system precipitates of Example 1, Example 2, Comparative Example 1 and Comparative Example 2, respectively. After 30 days of planting, the lettuces were taken out and the weight was tested. During this period, the management of the lettuces followed the agricultural operation.

[0196] Test results: As shown in Table 3, it can be obtained that after 30 days, the mass of the unfertilized lettuce is the smallest. When the addition amount of the nitrogen and phosphorus precipitate in Example 1 is 0.1wt%, the weight of the lettuce is significantly less than that of adding conventional fertilizers. When the addition amount is 0.3wt% and 0.5wt%, the weight of the lettuce is significantly greater than that of adding conventional fertilizers. This shows that when the addition amount is 0.3wt% and 0.5wt%, the nitrogen and phosphorus precipitate recovered from the simulated aquaculture wastewater can be used as an excellent fertilizer and applied to the cultivation of crops such as lettuce, which can promote the growth of lettuce.

[0197] Table 3 Effects of nitrogen and phosphorus precipitates recovered from simulated aquaculture wastewater on the growth weight of lettuce (unit: g / plant)

[0198]

[0199] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0200] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An anode based on pretreated magnesium, characterized in that The anode based on pretreated magnesium comprises the following substances: pretreated magnesium powder, carbon powder and copper powder; Wherein, the pretreated magnesium powder includes magnesium oxide and magnesium boride; The mass ratio of the pretreated magnesium powder, carbon powder and copper powder is (1.5-2.5):(0.2-0.8):1; The method for preparing the anode based on pretreated magnesium comprises the following steps: S1, titanium powder, carbon powder, magnesium powder and boron powder are subjected to a self-propagating high temperature synthesis reaction in a mass ratio of 1:(2-3):1:1 to obtain pretreated magnesium powder; S2, mixing the pretreated magnesium powder, carbon powder and copper powder by ball milling in a mass ratio of (1.5-2.5):(0.2-0.8):1 to obtain a mixed pretreated magnesium powder; S3, mixing the mixed pretreated magnesium powder with chitosan and polyacrylamide and adding water, dropping epichlorohydrin and keeping warm in a water bath, washing, filtering and drying to obtain a solid powder; S4, subjecting the solid powder to high-pressure torsional extrusion molding.

2. The pretreated magnesium-based anode according to claim 1, characterized in that The shape of the pre-treated magnesium-based anode is selected from a sheet, a column or a block.

3. The pretreated magnesium-based anode according to claim 1, characterized in that In step S1, the reaction temperature of the self-propagating high temperature synthesis reaction is 500-600°C.

4. The pretreated magnesium-based anode according to claim 1, characterized in that In step S3, the mass ratio of the mixed pretreated magnesium powder, chitosan, polyacrylamide and epichlorohydrin is 10:(0.1-0.2):(0.2-0.5):0.

1.

5. Aquaculture wastewater treatment system comprising an anode based on pretreated magnesium according to any one of claims 1 to 4, characterized in that: The aquaculture wastewater treatment system based on the pretreated magnesium anode comprises the following components: An external power source (1), an anode (4) based on pretreated magnesium, a reactor (5), a cathode (6), a water inlet device (10), and a water outlet device (7); wherein an anode (4) based on pretreated magnesium and a cathode (6) are arranged in a reactor (5), and the anode (4) based on pretreated magnesium is arranged at a central position of the reactor (5); The cathode (6) is in a thin layer shape and is arranged on the inner wall of the reactor (5) around the anode (4) based on the pretreated magnesium as the center of the circle; The upper part of the reactor (5) is connected to a water inlet device (10) having a function of adjusting the pH value of aquaculture wastewater, and the lower part on the opposite side is connected to a water outlet device (7); The external power source (1) electrically connects the pre-treated magnesium-based anode (4) and cathode (6).

6. The aquaculture wastewater treatment system based on the pretreated magnesium anode according to claim 5, characterized in that: The aquaculture wastewater treatment system based on the pretreated magnesium anode also includes a resistor (2), a magnetic stirring system (11), a product collection filter (12), and an aquaculture wastewater nitrogen and phosphorus content monitor (16); wherein the resistor (2) is connected to a circuit between the external power source (1) and the anode (4) and cathode (6) based on pretreated magnesium; The aquaculture wastewater nitrogen and phosphorus content monitor (16) is arranged on the side wall of the reactor (5); The magnetic stirring system (11), the product collecting filter (12), and the bottom water outlet (15) are arranged at the lower part of the reactor (5).

7. The aquaculture wastewater treatment system based on the pretreated magnesium anode according to claim 5, characterized in that: The relative area ratio of the anode (4) and cathode (6) based on pretreated magnesium is 1:(1.5-2), and the distance is 6.0-10.0 cm.

8. Use of the aquaculture wastewater treatment system composed of the pretreated magnesium anode according to claim 5 in recovering nitrogen and phosphorus from aquaculture wastewater.

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