A system and method for synchronously degrading organic pollutants and synthesizing ammonia in wastewater

Abstract

The present invention provides a system and method for synchronously degrading organic pollutants and synthesizing ammonia in wastewater, which relates to the field of wastewater treatment. The system includes: a dielectric barrier discharge reaction unit for degrading organic pollutants in wastewater and generating nitrogen oxides; an electrocatalytic ammonia synthesis unit connected to the dielectric barrier discharge reaction unit for reducing the nitrogen oxides in wastewater to synthesize ammonia; and an ammonia extraction and collection unit connected to the electrocatalytic ammonia synthesis unit for extracting the synthesized ammonia from water and collecting it. The present invention also provides a method for synchronously degrading organic pollutants and synthesizing ammonia in wastewater based on this system. The present invention couples dielectric barrier discharge with electrocatalytic ammonia synthesis, which can effectively treat organic pollutant wastewater and efficiently synthesize ammonia synchronously, turning waste into treasure, enabling the high-efficiency recycling of wastewater, contributing to the achievement of the dual-carbon goal, and promoting green, low-carbon and high-quality development.

Description

Technical Field

[0001] The present invention relates to the field of wastewater treatment, and particularly to a system and method for simultaneously degrading organic pollutants and synthesizing ammonia in wastewater. Background Art

[0002] Among nitrogen compounds, ammonia is one of the most important compounds. Ammonia is widely used in the manufacture of fertilizers and as a reagent in industries such as pharmaceuticals, metallurgy, refrigeration, explosives, and textiles. Ammonia can be used as a fertilizer source, an energy carrier, and a chemical precursor. Ammonia has great potential as a next-generation carbon-free energy carrier, which means that their use does not cause the greenhouse effect.

[0003] The current industrial process for producing ammonia is the Haber-Bosch (H-B) process, which is an efficient thermal catalytic process based on an iron-based catalyst and involves the reaction of H2 and N2 at high pressure and high temperature. The extreme reaction conditions require high energy consumption, which comes from the combustion of fossil fuels and releases carbon dioxide into the atmosphere. Statistical data shows that the carbon dioxide released by H-B ammonia synthesis accounts for 11% of the global carbon dioxide emissions. Therefore, there is an urgent need for a clean, efficient, and environmentally friendly method for ammonia production.

[0004] The electrochemical reduction of nitrate is considered a promising method for synthesizing ammonia because it uses green electrons as reducing agents and has mild operating conditions. Anthropogenic emissions of nitrate in industrial or agricultural wastewater can seriously pollute water resources, leading to massive algal blooms and hypoxia of aquatic plants and animals. In addition, groundwater pollution containing high concentrations of nitrate, and the ingestion of these nitrates through drinking water can cause human methemoglobinemia, increased heart rate, and nausea, and increase the likelihood of blue baby syndrome. Therefore, the process of synthesizing ammonia by electrochemically reducing nitrate in wastewater is beneficial to convert nitrate into recyclable ammonia from the perspective of "turning waste into treasure". However, industrial or agricultural wastewater often contains refractory organic pollutants, and simple electrocatalysis limits the types of wastewater that can be utilized.

[0005] Plasma is a completely ionized gas that is electrically neutral, the fourth form of matter existence in addition to gas, liquid, and solid, a conducting fluid composed of excited atoms, positive and negative ions, electrons, free radicals, and neutral particles, and is affected and dominated by magnetic fields. At present, some researchers have tried to apply plasma technology to the field of ammonia synthesis. Patent document CN114540858A discloses an integrated ammonia synthesis device coupling jet plasma and multistage electrocatalysis, which includes a multi-inlet jet plasma reactor, a multistage electrocatalytic system based on a nitrogen and phosphorus doped molybdenum disulfide electrocatalyst, and a tail gas recirculation system. First, solar energy is used to drive jet plasma to convert air into NO x and improve the water solubility of NO through means such as a gas storage tank and tail gas recirculationx The concentration provides reaction raw materials for the electrocatalytic process; then, multiple H-type electrolytic cells are connected in series to achieve multi-stage catalysis. At the same time, the prepared highly catalytically active nitrogen and phosphorus doped molybdenum disulfide electrocatalyst is used to maximize the conversion efficiency of the electrocatalytic process. Finally, N2 in the air is continuously converted into NH3 in the electrolyte, realizing the efficient conversion of renewable solar energy into high-grade chemical energy, and at the same time solving the energy consumption problem in the plasma process.

[0006] However, the aforementioned device mainly activates air through plasma to achieve the conversion from N2 to NH3. This method not only requires a high input energy to break the nitrogen-nitrogen triple bond, but also a large amount of active oxygen generated by plasma discharge is not fully utilized, and there are still deficiencies in energy utilization. Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present invention is to overcome the defect in energy utilization existing in the synthesis of ammonia by applying plasma technology in the prior art, so as to provide a system and method for simultaneously degrading organic pollutants in wastewater and synthesizing ammonia.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a system for simultaneously degrading organic pollutants in wastewater and synthesizing ammonia, comprising:

[0010] A dielectric barrier discharge reaction unit for degrading organic pollutants in wastewater and generating nitrogen oxides;

[0011] An electrocatalytic ammonia synthesis unit connected to the dielectric barrier discharge reaction unit for reducing and synthesizing ammonia from nitrogen oxides in wastewater;

[0012] An ammonia extraction and collection unit connected to the electrocatalytic ammonia synthesis unit for extracting and collecting the synthesized ammonia from water.

[0013] Further, the dielectric barrier discharge reaction unit includes: an inner dielectric tube, an outer dielectric tube, a high-voltage power supply, a high-voltage electrode, a grounded electrode and an air pump,

[0014] wherein, the inner dielectric tube is nested inside the outer dielectric tube, a liquid phase space is formed between the two, the outer dielectric tube is connected to the grounded electrode, the water outlet of the outer dielectric tube is connected to the electrocatalytic ammonia synthesis unit, the high-voltage electrode is connected to the high-voltage power supply, the high-voltage electrode is arranged inside the inner dielectric tube, and the air pump is communicated with the inner dielectric tube so that gas is blown into the inner dielectric tube by the air pump and discharged from the bottom of the inner dielectric tube.

[0015] Further, the electrocatalytic ammonia synthesis unit includes: an electrolytic cell, an anode, a cathode, and an electrochemical workstation.

[0016] Wherein, the water inlet of the electrolytic cell is connected to the dielectric barrier discharge reaction unit, the water outlet of the electrolytic cell is connected to the ammonia extraction and collection unit, the anode and the cathode are arranged in the electrolytic cell, and the electrochemical workstation is respectively connected to the anode and the cathode.

[0017] Further, the anode is a platinum sheet, the cathode is modified copper foam, and the modified copper foam is obtained by treating copper foam with radio frequency plasma in an argon or oxygen atmosphere. Preferably, the power of the radio frequency plasma treatment is 190 - 220 W, and the time is 20 - 30 min.

[0018] Further, the system for synchronously degrading organic pollutants in wastewater and synthesizing ammonia further includes:

[0019] A material modification unit, including a radio frequency power supply and a radio frequency reactor connected thereto, for preparing the modified copper foam.

[0020] Further, the ammonia extraction and collection unit includes: a gas cylinder, an ammonia stripping device, and a condenser.

[0021] Wherein, one end of the inlet pipe of the ammonia stripping device extends into the ammonia stripping device, and the other end is connected to the gas cylinder, for extracting ammonia from the wastewater; the outlet pipe of the ammonia stripping device is connected to the condenser, for condensing and liquefying the extracted ammonia to obtain liquid ammonia.

[0022] Further, the ammonia extraction and collection unit further includes: an ammonia absorption tank, and the inlet pipe of the ammonia absorption tank is connected to the outlet pipe of the ammonia stripping device, for reacting the ammonia extracted with the hydrochloric acid solution contained in the ammonia absorption tank to generate ammonium chloride.

[0023] Further, the ammonia extraction and collection unit further includes: a sedimentation chamber, and the sedimentation chamber is connected to the outlet pipe of the ammonia stripping device, for sedimenting the treated wastewater.

[0024] Further, the power supplies in the dielectric barrier discharge reaction unit and the electrocatalytic ammonia synthesis unit are both powered by renewable energy.

[0025] In a second aspect, the present invention provides a method for synchronously degrading organic pollutants in wastewater and synthesizing ammonia, which is carried out based on the system for synchronously degrading organic pollutants in wastewater and synthesizing ammonia, and the method includes:

[0026] (1) Wastewater is introduced into the dielectric barrier discharge reaction unit, and organic pollutants in the wastewater are degraded by dielectric barrier discharge reaction to generate nitrogen oxides.

[0027] (2) The wastewater treated by the dielectric barrier discharge reaction unit is introduced into the electrocatalytic ammonia synthesis unit, and the nitrogen oxides in the wastewater are reduced and synthesized into ammonia through electrocatalytic ammonia synthesis reaction.

[0028] (3) The wastewater treated by the electrocatalytic ammonia synthesis unit is introduced into the ammonia extraction and collection unit, and the synthesized ammonia is extracted from the water and collected.

[0029] Further, in step (1), the conditions of the dielectric barrier discharge reaction are: power 20 - 40 W, time 15 - 30 min, air is introduced as the gas source, and preferably, the air flow rate is 25 L / min.

[0030] Further, in step (2), the conditions of the electrocatalytic ammonia synthesis reaction are: platinum sheet anode, modified foam copper cathode, input voltage -0.4 V to -0.7 V vs. RHE, time 100 - 180 min, and preferably, the electrode spacing is 20 mm.

[0031] Among them, the modified foam copper is obtained by treating foam copper with radio frequency plasma in an argon or oxygen atmosphere, and the power of the radio frequency plasma treatment is 190 - 220 W, and the time is 20 - 30 min.

[0032] Further, in step (3), ammonia is extracted from the water by introducing argon into the wastewater treated by the electrocatalytic ammonia synthesis unit, the gas velocity is 5 - 10 L / min, and the time is 3 - 5 min.

[0033] The technical solution of the present invention has the following advantages:

[0034] The system for synchronously degrading organic pollutants in wastewater and synthesizing ammonia provided by the present invention includes a dielectric barrier discharge reaction unit, an electrocatalytic ammonia synthesis unit, and an ammonia extraction and collection unit. Among them, the dielectric barrier discharge reaction unit synchronously degrades organic pollutants in wastewater and generates nitrogen oxides; the electrocatalytic ammonia synthesis unit reduces and synthesizes ammonia from the nitrogen oxides in the wastewater; the ammonia extraction and collection unit extracts and collects the synthesized ammonia from the water.

[0035] There is a synergistic effect between the dielectric barrier discharge reaction unit and the electrocatalytic ammonia synthesis unit, and the specific analysis is as follows:

[0036] First, from the perspective of the nitrogen source for electrocatalytic ammonia synthesis:

[0037] During the dielectric barrier discharge process, the degradation of organic pollutants and nitrogen fixation proceed simultaneously. On the one hand, wastewater usually contains a large amount of nitrogen-containing organic pollutants and nitrogen-containing microorganisms, such as eutrophic cyanobacteria water and wastewater with a high COD containing a heterocyclic azo ring. The free radicals generated by dielectric barrier discharge attack organic substances, playing a good role in degrading the organic pollutants in the wastewater. At the same time, nitrate and nitrite are produced, which can be used as the nitrogen source for electrocatalytic ammonia synthesis. On the other hand, a large amount of reactive oxygen is generated during the dielectric barrier discharge process, reacting with nitrogen in the air to produce a large amount of NO x , further increasing the concentration of nitrate and nitrite in the wastewater, which also serves as the nitrogen source for electrocatalytic ammonia synthesis. That is, the dielectric barrier discharge reaction unit produces a high content of nitrate and nitrite while effectively degrading organic pollutants. Part of this is provided by the nitrogen in the organic matter, and the other part is obtained by fixing the nitrogen in the air. Compared with the nitrogen source generated by dielectric barrier discharge of ordinary water, the nitrogen sources generated in these two aspects of the present invention can significantly improve the effect and efficiency of subsequent electrocatalytic ammonia synthesis. The present invention effectively solves the problem of high energy consumption for the cleavage of the nitrogen-nitrogen triple bond in the prior art, provides a new nitrogen source, and greatly improves the reaction rate of ammonia synthesis.

[0038] Second, from the perspective of the liquid environment for electrocatalytic ammonia synthesis:

[0039] During the dielectric barrier discharge process, organic pollutants undergo macromolecular cleavage, generating a series of small molecule compounds. Some of them hydrolyze into ions, generating conductive polarity. Coupled with the nitrate and nitrite produced by the degradation of organic pollutants, and the many ions that already exist in the wastewater itself, all can increase the conductivity of the system during the electrocatalytic ammonia synthesis process, reduce the resistance of the system, thereby increasing the current density generated by electrocatalysis and reducing energy consumption.

[0040] In summary, after the dielectric barrier discharge degrades the organic pollutants in the wastewater, it will lead to an increase in the content of nitrate and nitrite in the wastewater. Therefore, it is difficult to recycle and resourcefully circulate the wastewater after treatment by this means. However, the high content of nitrate and nitrite can just be used as the raw materials for electrocatalytic ammonia synthesis. Therefore, the present invention couples dielectric barrier discharge with electrocatalytic ammonia synthesis, which can simultaneously achieve the effective treatment of organic pollutant wastewater and the efficient synthesis of ammonia, turning waste into treasure, enabling the wastewater to be efficiently recycled, contributing to the achievement of the dual-carbon goal, and promoting green and low-carbon high-quality development. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 is a schematic diagram of the system for synchronously degrading organic pollutants and synthesizing ammonia provided in Embodiment 1 of the present invention;

[0043] Figure 2 is a schematic diagram showing the change of the degradation rate of Rh 6G with time during the dielectric barrier discharge in Experimental Example 1 of the present invention;

[0044] Figure 3 is the ammonia production rate and Faraday efficiency when different cathode materials are used in Experimental Example 1 and Experimental Example 2 of the present invention;

[0045] Figure 4 is a schematic diagram showing the change of conductivity with time during the dielectric barrier discharge in Experimental Example 3 of the present invention;

[0046] Figure 5 is in Experimental Example 3 of the present invention during the dielectric barrier discharge, NO3 - and NO2 - schematic diagram of the change of concentration with time.

[0047] Reference numerals:

[0048] 1 - inner dielectric tube; 2 - outer dielectric tube; 3 - high - voltage power supply; 4 - high - voltage electrode; 5 - ground electrode; 6 - air pump; 7 - electrolytic cell; 8 - anode; 9 - cathode; 10 - electrochemical workstation; 11 - first peristaltic pump; 12 - radio - frequency power supply; 13 - radio - frequency reactor; 14 - gas cylinder; 15 - ammonia stripping device; 16 - condenser; 17 - second peristaltic pump; 18 - ammonia absorption tank; 19 - precipitation chamber; 20 - renewable energy. Specific Embodiments

[0049] The following will clearly and completely describe the technical solutions of the present invention with reference to the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0050] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "inner" and "outer" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0051] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "connected" and "connected to" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0052] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0053] For those not specified with specific experimental steps or conditions in the examples, the operations or conditions of the conventional experimental steps described in the literature in the art can be followed. The raw materials or instruments used are all conventional products that can be obtained through commercial purchase, including but not limited to the raw materials or instruments used in the examples of the present application.

[0054] As Figure 1 shown, the present invention provides a system for synchronously degrading organic pollutants in wastewater and synthesizing ammonia, including:

[0055] A dielectric barrier discharge reaction unit for degrading organic pollutants in wastewater and generating nitrogen oxides;

[0056] An electrocatalytic ammonia synthesis unit connected to the dielectric barrier discharge reaction unit for reducing and synthesizing ammonia from the nitrogen oxides in the wastewater;

[0057] An ammonia extraction and collection unit connected to the electrocatalytic ammonia synthesis unit for extracting the synthesized ammonia from the water and collecting it.

[0058] The type of wastewater source processed by the system provided by the present invention is not limited, and it can be applied to different types of industrial wastewater, agricultural wastewater, etc., such as eutrophic blue-green algae water, wastewater with a high COD containing heterocyclic azo rings, etc.

[0059] In the system provided by the present invention, the dielectric barrier discharge reaction unit can select the dielectric barrier discharge reactor provided in the prior art, as long as it can achieve the function of treating wastewater by dielectric barrier discharge, and the present invention does not limit its specific structure.

[0060] As an optional embodiment of the present invention, the dielectric barrier discharge reaction unit includes: an inner dielectric tube 1, an outer dielectric tube 2, a high-voltage power supply 3, a high-voltage electrode 4, a grounding electrode 5, and an air pump 6. Among them, the inner dielectric tube 1 is nested inside the outer dielectric tube 2, and a liquid phase space is formed between the two. The outer dielectric tube 2 is connected to the grounding electrode 5, and the water outlet of the outer dielectric tube 2 is connected to the electrocatalytic ammonia synthesis unit. The high-voltage electrode 4 is connected to the high-voltage power supply 3, and the high-voltage electrode 4 is arranged inside the inner dielectric tube 1. The air pump 6 is communicated with the inner dielectric tube 1. Both the inner dielectric tube 1 and the outer dielectric tube 2 are made of quartz glass. The wastewater to be treated is introduced into the liquid phase space between the inner dielectric tube 1 and the outer dielectric tube 2, and the gas is pumped into the inner dielectric tube 1 by the air pump 6 and discharged from its bottom into the liquid phase space to carry out gas-liquid discharge.

[0061] In the system provided by the present invention, the electrocatalytic ammonia synthesis unit can select the electrocatalytic ammonia synthesis reaction device provided in the prior art, as long as it can achieve the function of electrocatalytic ammonia synthesis, and the present invention does not limit its specific structure, electrode type, etc.

[0062] As an optional embodiment of the present invention, the electrocatalytic ammonia synthesis unit includes: an electrolytic cell 7, an anode 8, a cathode 9, and an electrochemical workstation 10. Among them, the water inlet of the electrolytic cell 7 is connected to the dielectric barrier discharge reaction unit, and the water outlet of the electrolytic cell 7 is connected to the ammonia extraction and collection unit. The anode 8 and the cathode 9 are arranged inside the electrolytic cell 7, and the electrochemical workstation 10 is respectively connected to the anode 8 and the cathode 9.

[0063] Specifically, the water inlet of the electrolytic cell 7 is connected to the water outlet of the outer dielectric tube 2 in the dielectric barrier discharge reaction unit, and the two are connected by a pipeline. A first peristaltic pump 11 is arranged on the pipeline to pump the wastewater in the outer dielectric tube 2 into the electrolytic cell 7.

[0064] Nitrate and nitrite in the wastewater undergo an electrocatalytic ammonia synthesis reaction to generate ammonia under the action of the anode 8 and the cathode 9. The mechanism is well-known in the art and will not be elaborated here. The cathode 9 and the anode 8 can select the electrodes used in electrocatalytic ammonia synthesis in the art.

[0065] As an optional embodiment of the present invention, the anode 8 is a platinum sheet, and the cathode 9 is a modified copper foam. The modified copper foam is obtained by treating the copper foam with radio frequency plasma in an atmosphere of argon or oxygen. Preferably, the power of the radio frequency plasma treatment is 190 to 220 W, and the time is 20 to 30 minutes. More preferably, the copper foam needs to be cut, cleaned and dried before the radio frequency plasma treatment. For example, the commercially available copper foam can be cut into a size of 2 cm × 2 cm, ultrasonically cleaned by ethanol, hydrochloric acid solution and deionized water, and dried in an oven at 65 ° C for 10 hours. The copper foam material after radio frequency plasma treatment has considerable ammonia production and Faraday efficiency.

[0066] As an optional embodiment of the present invention, the system for simultaneously degrading organic pollutants in wastewater and synthesizing ammonia provided by the present invention also includes: a material modification unit, including a radio frequency power supply 12 and a radio frequency reactor 13 connected thereto, for preparing modified foam copper. Specifically, the air in the radio frequency reactor 13 is first exhausted with argon or oxygen, and then the radio frequency power supply 12 is used for discharge, and the resulting material is a foam copper material rich in oxygen vacancies.

[0067] The ammonia extraction and collection unit in the system provided by the present invention can select a device provided in the prior art that can extract and collect ammonia in liquid, as long as it can achieve the function of ammonia extraction and collection. The present invention does not limit its specific structure, connection relationship, etc.

[0068] As an optional embodiment of the present invention, the ammonia extraction and collection unit includes: a gas cylinder 14, an ammonia stripping device 15 and a condenser 16, wherein one end of the air inlet pipe of the ammonia stripping device 15 extends into the interior of the ammonia stripping device 15, and the other end is connected to the gas cylinder 14, which is used to extract ammonia from the wastewater; the air outlet pipe of the ammonia stripping device 15 is connected to the condenser 16, which is used to collect the extracted ammonia by condensation and liquefaction to obtain liquid ammonia.

[0069] Specifically, the water inlet of the ammonia stripping device 15 is connected to the water outlet of the electrolytic cell 7 in the electrocatalytic ammonia synthesis unit, and the two are connected by a pipeline. A second peristaltic pump 17 is provided on the pipeline to pump the wastewater in the electrolytic cell 7 into the ammonia stripping device 15.

[0070] By introducing argon into the waste water in the ammonia stripping device 15, the ammonia dissolved in the water can be released, and the temperature of the gaseous ammonia is reduced in the condenser 16 to liquefy it into liquid ammonia, thereby realizing the collection of the product.

[0071] As an optional embodiment of the present invention, the ammonia extraction and collection unit also includes: an ammonia absorption tank 18, the air inlet pipe of the ammonia absorption tank 18 is connected to the air outlet pipe of the ammonia stripping device 15, and is used to utilize the hydrochloric acid solution contained in the ammonia absorption tank 18 to react with the extracted ammonia to generate ammonium chloride.

[0072] The ammonia absorption tank 18 is an optional ammonia collection method. The hydrochloric acid solution contained in the ammonia absorption tank 18 can be used to capture ammonia. Ammonia reacts with hydrochloric acid to form ammonium chloride. Evaporating the solution can obtain ammonium chloride solid, that is, the preparation of nitrogen fertilizer is realized. Preferably, the concentration of the hydrochloric acid solution is 0.5M.

[0073] As an optional implementation manner of the present invention, the ammonia extraction and collection unit further includes: a precipitation chamber 19, and the precipitation chamber 19 is connected to the water outlet pipe of the ammonia stripping device 15 for precipitating the treated wastewater. The treated low-nitrogen wastewater enters the precipitation chamber 19 and can be recycled after passing the detection.

[0074] As an optional implementation manner of the present invention, the power supplies in the dielectric barrier discharge reaction unit and the electrocatalytic ammonia synthesis unit are both powered by renewable energy 20. For example, wind energy or solar energy is used to supply power to the high-voltage power supply 3 in the dielectric barrier discharge reaction unit and the electrochemical workstation 10 in the electrocatalytic ammonia synthesis unit respectively.

[0075] The present invention also provides a method for synchronously degrading organic pollutants in wastewater and synthesizing ammonia, which is carried out based on the system for synchronously degrading organic pollutants in wastewater and synthesizing ammonia. The method includes:

[0076] (1) Pass wastewater into the dielectric barrier discharge reaction unit, and degrade the organic pollutants in the wastewater through dielectric barrier discharge reaction to generate nitrogen oxides;

[0077] (2) Pass the wastewater treated by the dielectric barrier discharge reaction unit into the electrocatalytic ammonia synthesis unit, and reduce the nitrogen oxides in the wastewater to synthesize ammonia through electrocatalytic ammonia synthesis reaction;

[0078] (3) Pass the wastewater treated by the electrocatalytic ammonia synthesis unit into the ammonia extraction and collection unit, and extract and collect the synthesized ammonia from the water.

[0079] As an optional implementation manner of the present invention, in step (1), the conditions of the dielectric barrier discharge reaction are: power 20 - 40W, time 15 - 30min, air is introduced as the gas source, and the air flow rate is 25L / min.

[0080] As an optional implementation manner of the present invention, in step (2), the conditions of the electrocatalytic ammonia synthesis reaction are: platinum sheet anode 8, modified foam copper cathode 9, electrode spacing 20mm, input voltage -0.4V to -0.7V vs. RHE, time 100 - 180min.

[0081] As an alternative embodiment of the present invention, in step (3), argon is introduced into the wastewater treated by the electrocatalytic ammonia synthesis unit to extract the synthesized ammonia from the water.

[0082] The technical solutions provided by the present invention will be further described in detail below with reference to specific embodiments.

[0083] As Figure 1 shown, this embodiment provides a system for synchronously degrading organic pollutants and synthesizing ammonia in wastewater, which consists of the following units:

[0084] The dielectric barrier discharge reaction unit is composed of an inner dielectric tube 1, an outer dielectric tube 2, a high-voltage power supply 3, a high-voltage electrode 4, a grounding electrode 5 and an air pump 6. Among them, the inner dielectric tube 1 is nested inside the outer dielectric tube 2, and a liquid phase space is formed between them. The outer dielectric tube 2 is connected to the grounding electrode 5, and the water outlet of the outer dielectric tube 2 is connected to the electrocatalytic ammonia synthesis unit. The high-voltage electrode 4 is connected to the high-voltage power supply 3, the high-voltage electrode 4 is arranged inside the inner dielectric tube 1, the air pump 6 is communicated with the inner dielectric tube 1, and the high-voltage electrode 4 is powered by the renewable energy source 20;

[0085] The electrocatalytic ammonia synthesis unit is composed of an electrolytic cell 7, an anode 8, a cathode 9 and an electrochemical workstation 10. Among them, the water inlet of the electrolytic cell 7 is connected to the water outlet of the outer dielectric tube 2 through a pipeline, and a first peristaltic pump 11 is arranged on the pipeline. The anode 8 and the cathode 9 are arranged inside the electrolytic cell 7 and fixed by a glassy carbon electrode clamp. The electrochemical workstation 10 is respectively connected to the anode 8 and the cathode 9. The anode 8 is a platinum sheet, and the cathode 9 is modified foam copper. The modified foam copper is obtained by treating foam copper with radio frequency plasma in an argon or oxygen atmosphere. The electrochemical workstation 10 is powered by the renewable energy source 20;

[0086] The ammonia extraction and collection unit is composed of a gas cylinder 14, an ammonia stripping device 15, a condenser 16, an ammonia absorption tank 18 and a precipitation chamber 19. Among them, the water inlet of the ammonia stripping device 15 is connected to the water outlet of the electrolytic cell 7 through a pipeline, and a second peristaltic pump 17 is arranged on the pipeline. One end of the inlet pipe of the ammonia stripping device 15 extends into the ammonia stripping device 15, and the other end is connected to the gas cylinder 14. The outlet pipe of the ammonia stripping device 15 is respectively connected to the condenser 16 and the ammonia absorption tank 18. Hydrochloric acid solution is contained in the ammonia absorption tank 18, and the precipitation chamber 19 is connected to the outlet pipe of the ammonia stripping device 15;

[0087] The material modification unit is composed of a radio frequency power supply 12 and a radio frequency reactor 13 connected thereto.

[0088] This embodiment also provides a method for synchronously degrading organic pollutants and synthesizing ammonia based on the system of Embodiment 1. The steps of this method are as follows:

[0089] (1) Feed the wastewater to be treated into the outer medium tube 2, feed air into the inner medium tube 1, turn on the high-voltage power supply 3, and degrade the organic pollutants in the wastewater and generate nitrogen oxides through dielectric barrier discharge reaction;

[0090] (2) Turn on the first peristaltic pump 11, feed the wastewater in the outer medium tube 2 into the electrolytic cell 7, turn on the electrochemical workstation 10, and reduce and synthesize ammonia from the nitrogen oxides in the wastewater through electrocatalytic ammonia synthesis reaction under the action of the anode 8 and the cathode 9. Among them, the cathode 9 is prepared in advance through the material modification unit: cut the commercially available foam copper material into appropriate sizes, ultrasonically clean it successively with ethanol, hydrochloric acid solution and deionized water, dry it in an oven, place it in the radio frequency reactor 13, evacuate the air in the radio frequency reactor 13 with argon or oxygen, and turn on the radio frequency power supply 12 for radio frequency plasma treatment to obtain it;

[0091] (3) Turn on the second peristaltic pump 17, feed the wastewater in the electrolytic cell 7 into the ammonia stripping device 15, feed argon into the wastewater in the ammonia stripping device 15, extract the synthesized ammonia from the water. On the one hand, condense and collect liquid ammonia through the condenser 16, on the other hand, generate ammonium chloride through the ammonia absorption tank 18, evaporate and collect solid ammonium chloride, and discharge the wastewater in the ammonia stripping device 15 into the precipitation chamber 19 for precipitation to obtain low-nitrogen wastewater.

[0092] Experimental Example 1

[0093] This experimental example aims to verify the degradation effect of organic pollutants and the ammonia synthesis effect provided by the foregoing embodiment. In the experiment, the cathode used in electrocatalysis was obtained by radio frequency plasma treatment of foam copper in an argon atmosphere, and the dielectric barrier discharge reaction unit used a commercially available dielectric barrier discharge reactor. The specific experimental method is as follows:

[0094] Prepare the modified foam copper electrode: Cut the commercially available foam copper into a size of 2 cm × 2 cm, ultrasonically clean it successively with ethanol, hydrochloric acid solution and deionized water, dry it in an oven at 65 °C for 10 h, place it in the radio frequency reactor, evacuate the air in the radio frequency reactor with argon, turn on the radio frequency power supply, and discharge at a power of 200 W for 30 min to obtain the modified foam copper electrode.

[0095] Prepare 200 mL of simulated dye wastewater with an initial concentration of 100 mg / L of rhodamine 6G (Rh 6G) using KOH solution (0.1 M) as the solvent. Feed the simulated polluted wastewater into the outer medium tube (250 mL), discharge at a power of 40 W for 15 min. During the discharge process, use an air pump to blow air into the inner medium tube as the gas source, and the air flow rate is 25 L / min. Sampling and detection are carried out at 5 min, 10 min, and 15 min after discharge respectively, and the degradation rate of Rh 6G is calculated as Figure 2As shown. Sampling results after 15 minutes of discharging: The concentration of Rh 6G decreased from the initial concentration of 100 mg / L to 9.0 mg / L (the degradation rate reached 94.0% in 15 minutes), and the NO3 - content was 231 mg / L, and the NO2 - content was 397 mg / L.

[0096] Turn on the first peristaltic pump to introduce the simulated wastewater in the outer medium tube into a single-chamber (220 mL) electrolytic cell. Use modified foam copper as the working electrode (2 cm × 2 cm), a platinum sheet electrode as the counter electrode (1 cm × 2 cm), and a Hg / HgO electrode as the reference electrode (a commercially available cylindrical electrode with a front-end glass diameter of 6 mm). The electrodes are fixed by a glassy carbon electrode clamp, and the electrode spacing is 20 mm. Turn on the electrochemical workstation (Chenhua 660E type) and operate it at -0.6 V vs. RHE for 2 h. The ammonia production rate was calculated to be 0.46 mg h - 1 cm -2 (ammonia concentration determined by ultraviolet-visible spectrophotometry), and the Faraday efficiency was 83%.

[0097] Experimental Example 2

[0098] This experimental example aims to verify the degradation effect of organic pollutants and the ammonia synthesis effect of the system provided in the foregoing embodiment. The cathode used in the electrocatalysis in the experiment was obtained by treating foam copper with radio frequency plasma in an oxygen atmosphere. The dielectric barrier discharge reaction unit used a commercially available dielectric barrier discharge reactor. The specific experimental method is as follows:

[0099] Prepare the modified foam copper electrode: Cut the commercially available foam copper into a size of 2 cm × 2 cm, ultrasonically clean it successively with ethanol, hydrochloric acid solution, and deionized water, dry it in an oven at 65 °C for 10 h, place it in a radio frequency reactor, evacuate the air in the radio frequency reactor with oxygen, turn on the radio frequency power supply, and discharge at a power of 200 W for 30 min to obtain the modified foam copper electrode.

[0100] Prepare 200 mL of simulated dye wastewater with an initial concentration of 100 mg / L of rhodamine 6G (Rh 6G) using a KOH solution (0.1 M) as the solvent. Pass the simulated polluted wastewater into the outer medium tube (250 mL) and discharge it at a power of 40 W for 15 min. During the discharging process, use an air pump to blow air into the inner medium tube as the gas source, and the air flow rate is 25 L / min. Sample and detect after 15 minutes of discharging. The results: The concentration of Rh 6G decreased from the initial concentration of 100 mg / L to 8.6 mg / L (the degradation rate reached 94.3% in 15 minutes), and the NO3 - content was 233 mg / L, and the NO2 - content was 406 mg / L.

[0101] Turn on the first peristaltic pump to introduce the simulated wastewater in the external medium pipe into a single-chamber (220 mL) electrolytic cell. Use the modified foam copper as the working electrode (2 cm × 2 cm), a platinum sheet electrode as the counter electrode (1 cm × 2 cm), and a Hg / HgO electrode as the reference electrode (commercially available cylindrical electrode, with a 6-mm-diameter glass at the front end). The electrodes are fixed by a glassy carbon electrode clip, and the electrode spacing is 20 mm. Turn on the electrochemical workstation (Chenhua 660E type) and operate it for 2 h under the condition of -0.6 V vs. RHE. Calculate the ammonia production rate to be 0.91 mg h - 1 cm -2 , and the Faraday efficiency is 90%.

[0102] As a comparison, under the same experimental conditions as in Experimental Example 1 and Experimental Example 2, replace the cathode with commercially available foam copper without modification treatment. The comparison of its ammonia production rate and Faraday efficiency is as Figure 3 shown. It can be seen that under the oxygen / argon condition, the foam copper material treated by radio frequency plasma has considerable ammonia production and Faraday efficiency.

[0103] Experimental Example 3

[0104] This experimental example aims to study the influence of wastewater on the conductivity and nitrogen source content of the electrocatalytic ammonia synthesis system. Experiments are carried out based on a commercially available dielectric barrier discharge reactor. The specific experimental method is as follows:

[0105] Prepare 200 mL of simulated dye wastewater with an initial concentration of 100 mg / L of rhodamine 6G (Rh 6G) using a KOH solution (0.1 M) as the solvent (denoted as the Rh 6G solution). At the same time, use 200 mL of a KOH solution (0.1 M) as a control (denoted as the KOH solution). Pass the Rh 6G solution / KOH solution into the external medium pipe (250 mL) and discharge it at a power of 40 W for 15 min. During the discharge process, use an air pump to inject air into the internal medium pipe as the gas source, with an air flow rate of 25 L / min. Sampling and detection are carried out respectively after 5 min, 10 min, and 15 min of discharge. The detection indexes are: conductivity, NO3 - concentration and NO2 - concentration. The results are respectively as Figure 4 and Figure 5 shown.

[0106] As Figure 4 shown, the conductivity of the solution increases after dielectric barrier discharge, and the internal resistance of the solution decreases, which is beneficial to the subsequent electrocatalytic process. During the discharge process, rhodamine 6G will be cracked by macromolecules to produce a series of organic acids, alcohols, etc. Some of them will hydrolyze to produce ions, generating conductive polarity. In addition, nitrate, nitrite, etc. formed in the reaction will also dissolve in water and increase its conductivity.

[0107] As Figure 5As shown, nitrate and nitrite will be generated in the solution after dielectric barrier discharge. After adding nitrogen-containing organic matter (i.e., rhodamine 6G) to the system, the amounts of nitrate and nitrite generated will further increase, indicating that dielectric barrier discharge can produce high contents of nitrate and nitrite while effectively degrading refractory organic pollutants, and a part of which is provided by the nitrogen in the organic matter. The increase in the nitrogen source is more conducive to subsequent electrocatalytic ammonia production.

[0108] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A system for synchronously degrading organic pollutants and synthesizing ammonia in wastewater, characterized in that, Comprising: A dielectric barrier discharge reaction unit for degrading organic pollutants in wastewater and generating nitrogen oxides; An electrocatalytic ammonia synthesis unit connected to the dielectric barrier discharge reaction unit for reducing nitrogen oxides in wastewater to synthesize ammonia. The electrocatalytic ammonia synthesis unit includes: an electrolytic cell, an anode, a cathode, and an electrochemical workstation. Wherein, the water inlet of the electrolytic cell is connected to the dielectric barrier discharge reaction unit, the water outlet of the electrolytic cell is connected to the ammonia extraction and collection unit, the anode and the cathode are arranged in the electrolytic cell, the electrochemical workstation is respectively connected to the anode and the cathode, the anode is a platinum sheet, the cathode is modified foam copper, and the modified foam copper is obtained by treating foam copper with radio frequency plasma in an argon or oxygen atmosphere. The power of the radio frequency plasma treatment is 190 - 220W, and the time is 20 - 30min; An ammonia extraction and collection unit connected to the electrocatalytic ammonia synthesis unit for extracting and collecting the synthesized ammonia from water.

2. The system for synchronously degrading organic pollutants and synthesizing ammonia in wastewater according to claim 1, wherein The dielectric barrier discharge reaction unit includes: an inner dielectric tube, an outer dielectric tube, a high-voltage power supply, a high-voltage electrode, a grounding electrode, and an air pump. Wherein, the inner dielectric tube is nested inside the outer dielectric tube, forming a liquid phase space therebetween. The outer dielectric tube is connected to the grounding electrode, the water outlet of the outer dielectric tube is connected to the electrocatalytic ammonia synthesis unit, the high-voltage electrode is connected to the high-voltage power supply, the high-voltage electrode is arranged inside the inner dielectric tube, and the air pump is communicated with the inner dielectric tube so that gas is blown into the inner dielectric tube by the air pump and discharged from the bottom of the inner dielectric tube.

3. The system for synchronously degrading organic pollutants and synthesizing ammonia in wastewater according to claim 1, characterized in that, It further includes: A material modification unit including a radio frequency power supply and a radio frequency reactor connected thereto for preparing the modified foam copper.

4. The system for synchronously degrading organic pollutants and synthesizing ammonia in wastewater according to claim 1, characterized in that, The ammonia extraction and collection unit includes: a gas cylinder, an ammonia stripping device, and a condenser. Wherein, one end of the inlet pipe of the ammonia stripping device extends into the ammonia stripping device and the other end is connected to the gas cylinder for extracting ammonia from the wastewater; the outlet pipe of the ammonia stripping device is connected to the condenser for condensing and liquefying the extracted ammonia to collect liquid ammonia.

5. The system for synchronously degrading organic pollutants and synthesizing ammonia in wastewater according to claim 4, wherein, The ammonia extraction and collection unit further includes: an ammonia absorption tank. The inlet pipe of the ammonia absorption tank is connected to the outlet pipe of the ammonia stripping device for reacting the ammonia extracted with the hydrochloric acid solution contained in the ammonia absorption tank to generate ammonium chloride.

6. The system for synchronously degrading organic pollutants and synthesizing ammonia in wastewater according to claim 1, characterized in that, The power supplies in the dielectric barrier discharge reaction unit and the electrocatalytic ammonia synthesis unit are both powered by renewable energy.

7. A method for synchronously degrading organic pollutants and synthesizing ammonia in wastewater, characterized in that, Based on the system for synchronously degrading organic pollutants in wastewater and synthesizing ammonia according to any one of claims 1 - 6, the method includes: (1) Introduce wastewater into the dielectric barrier discharge reaction unit, and degrade the organic pollutants in the wastewater and generate nitrogen oxides through dielectric barrier discharge reaction; (2) Introduce the wastewater treated by the dielectric barrier discharge reaction unit into the electrocatalytic ammonia synthesis unit, and reduce the nitrogen oxides in the wastewater to synthesize ammonia through electrocatalytic ammonia synthesis reaction. (3) Feed the wastewater treated by the electrocatalytic ammonia synthesis unit into the ammonia extraction and collection unit to extract and collect the synthesized ammonia from the water.

8. The method for synchronously degrading organic pollutants in wastewater and synthesizing ammonia according to claim 7, characterized in that In step (1), the conditions of the dielectric barrier discharge reaction are: power 20-40 W, time 15-30 min, air is introduced as the gas source, and the air flow rate is 25 L / min; In step (2), the conditions of the electrocatalytic ammonia synthesis reaction are: platinum sheet anode, modified copper foam cathode, input voltage -0.4 V to -0.7 V vs. RHE, time 100-180 min, electrode spacing 20 mm, wherein the modified copper foam is obtained by treating copper foam with radio frequency plasma in an argon or oxygen atmosphere, and the power of the radio frequency plasma treatment is 190-220 W and the time is 20-30 min; In step (3), ammonia is extracted from the water by introducing argon into the wastewater treated by the electrocatalytic ammonia synthesis unit, with a gas velocity of 5-10 L / min and a time of 3-5 min.

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