Method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater by electrodialysis

Abstract

The application discloses a method for synchronously recovering ammonia nitrogen and removing heavy metals from wastewater by electrodialysis, which comprises the following steps: preparing an electrodialysis system, and then feeding wastewater containing ammonia nitrogen and heavy metals into an anode chamber of the electrodialysis system to perform electrodialysis treatment; ammonium ions and metal ions pass through a proton exchange membrane into a cathode chamber, and through reaction, the heavy metals are removed and the ammonia nitrogen is recovered. According to the method, high-concentration ammonia nitrogen can be recovered while the heavy metals are removed from the wastewater without adding chemical reagents, the recovered high-concentration ammonia nitrogen can be used as a fertilizer, so that the purpose of waste utilization is achieved, and the scientific concept of economic and environmental protection is met.

Description

Technical Field

[0001] This invention belongs to the field of ecological environment governance technology, specifically relating to a method for simultaneously recovering ammonia nitrogen and removing heavy metals using electrodialysis. Background Technology

[0002] Ammonia nitrogen and heavy metal pollution in water resources have long been major environmental problems that urgently need to be addressed. During metal mining and smelting processes, heavy metals, either in their elemental form or as metal ions, migrate with surface runoff into surrounding water and soil environments, causing widespread water and soil pollution. The harmful effects of heavy metals are self-evident; once they enter the human body, they directly damage the liver and can even affect the nervous system, causing irreversible damage. Therefore, surface water discharge standards have consistently imposed strict limits on heavy metal concentrations. Furthermore, although ammonia nitrogen is a nutrient required by plants, and there have been no reports of ammonia nitrogen in drinking water posing a health hazard to humans, excessive ammonia nitrogen still poses a significant threat to aquatic life. It is well known that eutrophication in water bodies leads to rampant algae growth, depriving other plants and animals of their habitat; simultaneously, algal toxins and ammonia nitrogen themselves have certain biotoxicity to fish and shrimp, and the resulting foul odors from eutrophication severely impact normal human activities. Therefore, ammonia nitrogen and heavy metal pollution are important research directions in the environmental field.

[0003] In actual production processes, water bodies often contain both ammonia nitrogen and heavy metal pollutants, such as manganese slag leachate, landfill leachate, and biogas slurry. Taking manganese slag leachate as an example, as an indispensable raw material for the steel industry, manganese ore has a long history of mining and a large demand; before 2018, China was the world's largest producer of manganese ore. However, electrolytic manganese slag, the most significant pollutant in manganese production, is not listed in the "National Hazardous Waste List." Manganese slag has long been stored using stockpiling methods, which not only puts enormous pressure on the storage space but also seriously endangers the surrounding ecological environment. Especially after rainwater runoff, large amounts of ammonia nitrogen, heavy metals, and other toxic and harmful substances in the manganese slag enter surrounding surface water bodies through leachate runoff, or migrate into surrounding soil and even groundwater, causing large-scale water and soil pollution.

[0004] Currently, commonly used technologies for ammonia nitrogen treatment include biochemical methods, catalytic oxidation, ion exchange, and precipitation. Biochemical methods, such as the optimized combined process for treating urban domestic wastewater disclosed in Chinese patent document CN109354335A, suffer from drawbacks such as excessively long reaction times, incomplete degradation, and the presence of nitrates as degradation products, which can easily cause secondary pollution. Catalytic oxidation methods, such as the total nitrogen removal method for nitrogen-containing organic wastewater disclosed in Chinese patent document CN112607924A, have shorter reaction times than biochemical methods and can completely convert ammonia nitrogen into other nitrogen-containing substances. However, the reaction process easily produces more toxic nitrates and nitrites. More importantly, ammonia nitrogen is an inorganic nitrogen salt that can be directly absorbed by plants, making purification of ammonia nitrogen more valuable than direct oxidation. Precipitation is the simplest to operate and the fastest to react, simultaneously precipitating heavy metals and recovering ammonia nitrogen. However, the reaction process requires the addition of large amounts of chemical reagents, which does not meet the requirements of green environmental protection. Ion exchange and adsorption methods, such as the ion exchange device disclosed in Chinese patent document CN105271468A for removing ammonia nitrogen, are relatively mild and economical methods for recovering ammonia nitrogen. They are suitable for pure ammonia nitrogen wastewater or heavy metal wastewater, but not for mixed wastewater containing ammonia nitrogen and heavy metals, because simple ion exchange cannot simultaneously separate ammonia nitrogen and heavy metals. Furthermore, the driving force for ion exchange is generally the concentration gradient; while the effect is significant in the initial stage of treating high-concentration pollutants, the lower the pollutant concentration, the more difficult the ion exchange becomes as the reaction time progresses. Therefore, there is an urgent need to find a method that can simultaneously remove heavy metals and recover ammonia nitrogen from wastewater, which is of great significance for environmental pollution control and the realization of "waste utilization." Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for simultaneous removal of heavy metals and recovery of ammonia nitrogen in wastewater by electrodialysis.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0007] A method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis includes the following steps: preparing an electrodialysis system, the electrodialysis system including an anode chamber with an anode and a cathode chamber with a cathode, a proton exchange membrane being provided between the anode chamber and the cathode chamber, the anode being a self-supporting titanium dioxide nanomesh electrode; passing wastewater containing ammonia nitrogen and heavy metals into the anode chamber of the electrodialysis system for electrodialysis treatment, ammonium ions and metal ions passing through the proton exchange membrane into the cathode chamber, and through reaction, achieving heavy metal removal and ammonia nitrogen recovery; the preparation method of the self-supporting titanium dioxide nanomesh electrode includes the following steps: mixing a mixed solution of sodium hydroxide with foamed titanium, the solvent in the mixed solution of sodium hydroxide being water and alcohol, carrying out a hydrothermal reaction at 100℃~200℃, washing and drying, and calcining at 400℃~600℃ to obtain the self-supporting titanium dioxide nanomesh electrode.

[0008] In the above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals by wastewater electrodialysis, preferably, the initial pH value of the wastewater containing ammonia nitrogen and heavy metals is 3-12, the concentration of ammonia nitrogen in the wastewater containing ammonia nitrogen and heavy metals is 25 mgN / L-200 mgN / L, the concentration of heavy metals in the wastewater containing ammonia nitrogen and heavy metals is 0.5 mg / L-3.0 mg / L, and the heavy metals in the wastewater containing ammonia nitrogen and heavy metals include at least one of cadmium, chromium, lead, cobalt and manganese.

[0009] In the above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals by wastewater electrodialysis, preferably, the electrolyte in the electrodialysis system is a sodium sulfate solution, and the initial concentration of the sodium sulfate solution is 50 mmol / L to 100 mmol / L.

[0010] In the above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals via wastewater electrodialysis, preferably, the current density in the electrodialysis system is 2 mA / cm². 2 ~6mA / cm 2 .

[0011] In the above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals by wastewater electrodialysis, preferably, the foamed titanium is pretreated as follows before mixing: the foamed titanium is polished with 50-200 mesh sandpaper, soaked in sodium hydroxide aqueous solution for 1-2 hours, then soaked in boiling oxalic acid solution for 1-2 hours, and washed with water until neutral; the mass fraction of the sodium hydroxide aqueous solution is 1%-10%, and the mass fraction of the oxalic acid solution is 1%-10%.

[0012] In the above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals by wastewater electrodialysis, preferably, the hydrothermal reaction time is 10h to 20h, the calcination time is 1h to 2h, and the calcination atmosphere is an inert gas.

[0013] The above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals by wastewater electrodialysis preferably includes the following steps in the preparation of the sodium hydroxide mixed solution: mixing sodium hydroxide aqueous solution with ethanol and stirring for 10 min to 30 min to obtain a sodium hydroxide mixed solution; the volume ratio of the sodium hydroxide aqueous solution to ethanol is 1 to 10:1, and the concentration of the sodium hydroxide aqueous solution is 0.5 mol / L to 5 mol / L.

[0014] In the above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals by wastewater electrodialysis, preferably, the drying temperature is 40℃~60℃ and the drying time is 8h~16h.

[0015] Preferably, in the above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals by wastewater electrodialysis, the electrodialysis treatment is carried out under normal pressure, the temperature of the electrodialysis treatment is 10℃~40℃, and the time of the electrodialysis treatment is 8h~12h.

[0016] In the above-mentioned method for simultaneous recovery of ammonia nitrogen and removal of heavy metals via wastewater electrodialysis, preferably, the cathode is a carbon felt cathode, the distance between the cathode and the anode is 8cm to 12cm, and the facing area of ​​the cathode and anode is 8cm². 2 ~12cm 2 .

[0017] Compared with the prior art, the advantages of the present invention are as follows:

[0018] This invention provides a method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis. Wastewater containing ammonia nitrogen and heavy metals is introduced into the anode chamber of an electrodialysis system. Under the influence of an electric field, the ammonia nitrogen and heavy metals gradually transfer from the anode chamber to the cathode chamber, at which point the water in the anode chamber meets discharge standards. Simultaneously, due to the unavoidable electrolysis reaction during electrodialysis, the pH value in the anode chamber decreases while the pH value in the cathode chamber increases, creating a naturally high-pH environment in the cathode chamber. Consequently, heavy metals entering the cathode chamber are converted into precipitates, thus separating from the ammonia nitrogen. Compared to commonly used anodes such as Pt and BDD, the self-supporting titanium dioxide nanomesh electrode used in this invention can rapidly and efficiently drive the transfer of ammonia nitrogen to the cathode chamber, significantly improving the ammonia nitrogen permeability and making ammonia nitrogen recovery easier. This method also offers advantages such as good stability, corrosion resistance, and good reusability. The method of this invention can efficiently remove heavy metals from wastewater while recovering high-concentration ammonia nitrogen without adding external chemical reagents. The recovered high-concentration ammonia nitrogen can be used as fertilizer, thereby achieving the purpose of "waste utilization" and conforming to the scientific concept of economic and environmental protection. Attached Figure Description

[0019] Figure 1This is a schematic diagram of the method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis in Embodiment 1 of the present invention.

[0020] Figure 2 This is a diagram showing the effect of heavy metal removal during electrodialysis treatment in Embodiment 1 of the present invention.

[0021] Figure 3 This is a graph showing the permeation rate of ammonia nitrogen in wastewater under different initial electrolyte concentrations in Example 2 of the present invention.

[0022] Figure 4 This is a graph showing the permeation rate of ammonia nitrogen in wastewater under different pH conditions in Example 3 of the present invention.

[0023] Figure 5 This is a graph showing the permeation rate of ammonia nitrogen in wastewater at different initial ammonia nitrogen concentrations in Example 4 of the present invention.

[0024] Figure 6 This is a graph showing the permeation rate of ammonia nitrogen in wastewater under different current densities in Example 5 of the present invention.

[0025] Figure 7 This is a diagram showing the effect of heavy metal removal during electrodialysis treatment in Embodiment 6 of the present invention.

[0026] Figure 8 This is a graph showing the permeation rate of ammonia nitrogen in wastewater under different anode conditions in Example 7 of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0028] Example 1:

[0029] A method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis according to the present invention, comprising the following steps: (The method utilizes an electrodialysis system to treat wastewater containing ammonia nitrogen and heavy metals via electrodialysis.)

[0030] (1) Establishment of the electrodialysis system:

[0031] The electrodialysis system includes an anode chamber with an anode and a cathode chamber with a cathode. A proton exchange membrane is installed between the anode and cathode chambers. The anode is a self-supporting titanium dioxide nanomesh electrode, and the cathode is a carbon felt cathode. The distance between the cathode and anode is 8 cm, and the area of ​​their facing surfaces is 10 cm². 2 The electrolyte is a sodium sulfate solution, placed in the cathode and anode chambers, with an initial concentration of 50 mmol / L and a current density of 5 mA / cm². 2 .

[0032] The preparation method of the self-supporting titanium dioxide nanomesh electrode is as follows:

[0033] (1.1) Cut the foamed titanium into medium-sized rectangles, polish them with 100-grit sandpaper, soak them in 5wt% NaOH solution for 1 hour, then soak them in 10wt% oxalic acid solution for 2 hours, and then rinse them with deionized water until neutral to obtain pretreated foamed titanium, which is then stored in anhydrous ethanol for later use.

[0034] (1.2) With an anhydrous ethanol to NaOH solution volume ratio of 1:8 and NaOH solution concentration of 0.5 mol / L, anhydrous ethanol was added to NaOH solution and stirred for 10 min to mix the solution evenly, thus obtaining a mixed solution of sodium hydroxide.

[0035] (1.3) Pour the sodium hydroxide mixture obtained in step (1.2) into the liner of the polytetrafluoroethylene reactor, and put the pretreated foam titanium obtained in step (1.1) into it for hydrothermal reaction, that is, keep it at 180℃ for 16h to obtain titanium dioxide nanomesh electrode.

[0036] (1.4) The titanium dioxide nanomesh electrode obtained in step (1.3) is repeatedly rinsed with water until the eluent is neutral, dried at 40°C for 10 h, and then placed in a tube furnace under an inert gas atmosphere at 4°C·min. -1 The temperature was increased to 500℃ and kept constant for 2 hours. After cooling to room temperature in the furnace, the electrode was removed to obtain a self-supporting titanium dioxide nanomesh electrode.

[0037] (2) Electrodialysis treatment:

[0038] Wastewater containing ammonia nitrogen and heavy metals is passed into the anode chamber of an electrodialysis system and held at 25°C under normal pressure for 8 hours. The treated water that meets the standards is then discharged, while ammonium ions and metal ions enter the cathode chamber, achieving metal precipitation and ammonia nitrogen recovery. The next batch of wastewater containing ammonia nitrogen and heavy metals is then fed into the anode chamber of the electrodialysis system for further electrodialysis treatment, and this process is repeated. The solution in the cathode chamber is not replaced throughout the entire cycle, thus achieving the goal of concentrating ammonia nitrogen.

[0039] In this embodiment, the initial concentrations of ammonia nitrogen, Cd, Cr, and Pb in the wastewater containing ammonia nitrogen and heavy metals are 50 mg N / L, 0.5 mg / L, 0.5 mg / L, and 7, respectively.

[0040] Figure 1 This is a schematic diagram of the method for simultaneous recovery of ammonia nitrogen and removal of heavy metals via wastewater electrodialysis in Embodiment 1 of the present invention. Figure 1It is known that under the influence of the electric field, positively charged ammonium ions and metal ions pass through the proton exchange membrane into the cathode chamber. Furthermore, due to the unavoidable side reaction of water electrolysis during electrodialysis, the cathode chamber remains in an alkaline environment. After entering the cathode chamber, the metal ions react with a large number of hydroxide ions, producing a precipitate that recovers ammonia nitrogen while removing heavy metals. Therefore, the effluent from the anode chamber meets discharge standards, and the ammonia nitrogen concentrate from the cathode chamber contains almost no heavy metals.

[0041] Figure 2 This image shows the effect of heavy metal removal during electrodialysis treatment in Example 1 of the present invention. Figure 2 It can be seen that as the electrodialysis process proceeds, most of the heavy metal ions in the anode chamber can be transferred to the cathode chamber; at the same time, no excessive heavy metal ions can be detected after 8 hours of electrodialysis treatment, indicating that the heavy metal ions are immediately converted into precipitates upon entering the cathode chamber. Therefore, the ammonia nitrogen concentrate in the cathode chamber can be safely recycled.

[0042] Example 2:

[0043] The present invention discloses a method for simultaneous recovery of ammonia nitrogen and removal of heavy metals from wastewater by electrodialysis. The effect of different initial electrolyte concentrations on the electrodialysis treatment results was investigated. The method is basically the same as that in Example 1, except that the initial concentrations of sodium sulfate solution are 60 mmol / L, 75 mmol / L, and 100 mmol / L.

[0044] Figure 3 This is a graph showing the permeation rate of ammonia nitrogen in wastewater at different initial electrolyte concentrations in Example 2 of the present invention. Figure 3 It can be seen that the permeability of ammonia nitrogen is significantly negatively correlated with the initial electrolyte concentration. We attribute this to the driving effect of the electric field force. Specifically, as the electrolyte concentration increases, the number of charges in the electrodialysis treatment system increases, that is, the conductivity of the electrodialysis treatment system increases, the resistance decreases, the voltage decreases, the effect of the electric field force weakens, and the electrodialysis rate of ammonia nitrogen decreases accordingly.

[0045] Example 3:

[0046] The present invention discloses a method for simultaneous recovery of ammonia nitrogen and removal of heavy metals from wastewater by electrodialysis. The influence of different pH conditions on the electrodialysis treatment results was investigated. The method is basically the same as that in Example 1, except that the initial pH values ​​of the wastewater containing ammonia nitrogen and heavy metals are 3, 5 and 9, respectively.

[0047] Figure 4 This is a graph showing the permeation rate of ammonia nitrogen in wastewater under different pH conditions in Example 3 of the present invention. Figure 4It can be observed that the electrodialysis rate of ammonia nitrogen does not change significantly under different pH levels, but the overall trend shows a slight increase in effectiveness under a slightly acidic to neutral environment. This suggests that due to the recurrent side reactions during water electrolysis, the pH in the anode chamber will always drop below 2, thus pH has little effect on electrodialysis. However, excessively high or low pH values ​​will lead to increased ion concentration in the solution and decreased voltage, thereby affecting the electrodialysis rate, with its effectiveness decreasing compared to a neutral environment.

[0048] Example 4:

[0049] The present invention discloses a method for simultaneous recovery of ammonia nitrogen and removal of heavy metals from wastewater via electrodialysis. The method investigates the effect of different initial ammonia nitrogen concentrations in wastewater containing ammonia nitrogen and heavy metals on the electrodialysis treatment results. The method is basically the same as that in Example 1, except that the initial concentrations of ammonia nitrogen in the wastewater containing ammonia nitrogen and heavy metals are 25 mg N / L, 100 mg N / L, and 200 mg N / L, respectively.

[0050] Figure 5 This is a graph showing the permeation rate of ammonia nitrogen in wastewater under different initial ammonia nitrogen concentrations in Example 4 of the present invention. Figure 5 It can be seen that the lower the initial ammonia nitrogen concentration, the higher the ammonia nitrogen permeability. The permeation rate curve also shows that the lower the initial ammonia nitrogen concentration, the faster the permeation rate. At the same time, we found that the rate in the later stages of permeation is slightly lower than in the initial stages. This may be because the anions and cations generated by water electrolysis increase the ion concentration in the system in the later stages of electrodialysis, leading to a decrease in voltage and thus a decrease in the electrodialysis rate. This is consistent with the principle that the permeability is slightly higher under neutral conditions.

[0051] Example 5:

[0052] This invention discloses a method for simultaneous recovery of ammonia nitrogen and removal of heavy metals from wastewater via electrodialysis. The effect of different current densities on the electrodialysis treatment results was investigated. The method is essentially the same as that in Example 1, except that the current density is 2 mA / cm². 2 3mA / cm 2 4mA / cm 2 6mA / cm 2 .

[0053] The energy consumption at different current densities can be calculated using the following formula:

[0054]

[0055] Figure 6 This is a graph showing the permeation rate of ammonia nitrogen in wastewater under different current densities in Example 5 of the present invention. Figure 6It can be seen that, under the same initial ammonia nitrogen concentration and pH value, the ammonia nitrogen permeability is significantly positively correlated with the current density, which further verifies the hypothesis of the driving effect of the electric field force during electrodialysis. With the increase of current density, the voltage in the system increases, the electric field force strengthens, and the electrodialysis rate of ammonia nitrogen increases accordingly. Furthermore, although a higher current density results in a higher ammonia nitrogen permeability, it also increases the energy consumption per 1 kg N treated.

[0056] Example 6:

[0057] This invention discloses a method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis. The impact of complex water body conditions on the electrodialysis treatment results was investigated. The method is essentially the same as that in Example 1, except that the wastewater containing ammonia nitrogen and heavy metals is replaced with manganese slag leachate. In this manganese slag leachate, the initial concentration of ammonia nitrogen (NH3-N) is 70.25 mgN / L, and the concentration of magnesium... 2+ Ca 2 + Mn 2+ Co 2+ Pb 2+ The initial concentrations were 17.1501 mg / L, 0.6641 mg / L, 44.4531 mg / L, 0.04695 mg / L, and 0.089 mg / L, respectively.

[0058] Figure 7 This is a diagram illustrating the removal effect of heavy metals during electrodialysis treatment in Example 6 of the present invention. Figure 7 As the reaction proceeds, most of the ammonia nitrogen and metal ions in the anode chamber are transferred to the cathode chamber. After the reaction, the concentration of heavy metal ions in the effluent from the anode chamber is below the national standard concentration, meeting the discharge requirements. Furthermore, no excessive heavy metal content was detected in the solution in the cathode chamber after the reaction, indicating that most of the metal ions are converted into precipitates after entering the cathode chamber. Therefore, the concentrated ammonia nitrogen solution from the cathode chamber is safe to use.

[0059] Example 7:

[0060] The present invention discloses a method for simultaneous recovery of ammonia nitrogen and removal of heavy metals from wastewater by electrodialysis. The method investigates the effect of different electrode materials as anodes on the electrodialysis treatment effect. The method is basically the same as that in Example 1, except that platinum electrode, BDD, nickel foam, and titanium foam are used instead of self-supporting titanium dioxide nanomesh electrode as anode.

[0061] Figure 8 This is a graph showing the permeation rate of ammonia nitrogen in wastewater under different anode conditions in Example 7 of the present invention. Figure 8It is evident that, under the same wastewater conditions, the self-supporting titanium dioxide nanoelectrode of this invention exhibits significantly higher electrodialysis efficiency than pure titanium foam. The permeability of ammonia nitrogen in the wastewater can reach 76% within 8 hours, while commonly used platinum and BDD electrodes, both domestically and internationally, can only achieve permeability rates of 58% and 63%, respectively. Although nickel foam electrodes can achieve similar electrodialysis effects to titanium dioxide nanomembranes, they are unstable, easily corroded, and cannot be reused.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis, characterized in that, The process includes the following steps: preparing an electrodialysis system, which includes an anode chamber with an anode and a cathode chamber with a cathode, with a proton exchange membrane between the anode and cathode chambers, and the anode being a self-supporting titanium dioxide nanomesh electrode; passing wastewater containing ammonia nitrogen and heavy metals into the anode chamber of the electrodialysis system for electrodialysis treatment, where ammonium ions and metal ions permeate through the proton exchange membrane into the cathode chamber, where a reaction occurs to remove heavy metals and recover ammonia nitrogen; the electrolyte in the electrodialysis system is a sodium sulfate solution with an initial concentration of 50 mmol / L to 100 mmol / L; and the current density in the electrodialysis system is 5 mA / cm². 2 ~6mA / cm 2 The concentration of ammonia nitrogen in the wastewater containing ammonia nitrogen and heavy metals is 25 mgN / L to 200 mgN / L, and the concentration of heavy metals in the wastewater containing ammonia nitrogen and heavy metals is 0.5 mg / L to 3.0 mg / L. The preparation method of the self-supporting titanium dioxide nanomesh electrode includes the following steps: mixing a mixed solution of sodium hydroxide with foamed titanium, wherein the solvent in the mixed solution of sodium hydroxide is water and alcohol, carrying out a hydrothermal reaction at 100℃ to 200℃, washing and drying, and calcining at 400℃ to 600℃ to obtain a self-supporting titanium dioxide nanomesh electrode; the calcination atmosphere is an inert gas.

2. The method for simultaneous recovery of ammonia nitrogen and removal of heavy metals from wastewater via electrodialysis according to claim 1, characterized in that, The initial pH value of the wastewater containing ammonia nitrogen and heavy metals is 3 to 12, and the heavy metals in the wastewater containing ammonia nitrogen and heavy metals include at least one of cadmium, chromium, lead, cobalt and manganese.

3. The method for simultaneous recovery of ammonia nitrogen and removal of heavy metals from wastewater via electrodialysis according to claim 1, characterized in that, Before mixing, the foamed titanium is pretreated as follows: the foamed titanium is polished with 50-200 mesh sandpaper, soaked in sodium hydroxide aqueous solution for 1-2 hours, then soaked in boiling oxalic acid solution for 1-2 hours, and washed with water until neutral; the mass fraction of the sodium hydroxide aqueous solution is 1%-10%, and the mass fraction of the oxalic acid solution is 1%-10%.

4. The method for simultaneous recovery of ammonia nitrogen and removal of heavy metals from wastewater via electrodialysis according to claim 1, characterized in that, The hydrothermal reaction takes 10 to 20 hours, and the calcination takes 1 to 2 hours.

5. The method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis according to any one of claims 1 to 4, characterized in that, The method for preparing the sodium hydroxide mixed solution includes the following steps: mixing an aqueous sodium hydroxide solution with ethanol and stirring for 10 min to 30 min to obtain a sodium hydroxide mixed solution; the volume ratio of the aqueous sodium hydroxide solution to ethanol is 1 to 10:1, and the concentration of the aqueous sodium hydroxide solution is 0.5 mol / L to 5 mol / L.

6. The method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis according to any one of claims 1 to 4, characterized in that, The drying temperature is 40℃~60℃, and the drying time is 8h~16h.

7. The method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis according to any one of claims 1 to 4, characterized in that, The electrodialysis treatment is carried out under normal pressure, the temperature of the electrodialysis treatment is 10℃~40℃, and the time of the electrodialysis treatment is 8h~12h.

8. The method for simultaneously recovering ammonia nitrogen and removing heavy metals from wastewater via electrodialysis according to any one of claims 1 to 4, characterized in that, The cathode is a carbon felt cathode, and the distance between the cathode and the anode is 8cm to 12cm. The area of ​​the cathode and the anode facing each other is 8cm². 2 ~12cm 2 .

Images