Method for recycling nitrate radicals by treating high-salinity wastewater through electroactive microorganisms

Abstract

The invention belongs to the technical field of sewage treatment, and particularly discloses a method for recycling nitrate radicals by treating high-salinity wastewater through electroactive microorganisms, a microbial electrolysis cell three-electrode single-chamber system is adopted, high-salinity wastewater is used for domesticating and culturing a biological membrane, and the biological membrane has a good nitrate removal effect on nitrate wastewater with the salinity of 1%-3% and can be used for recycling nitrate radicals. For nitrate wastewater with the salinity of 1%-2%, nitrogen can be partially recovered in the form of ammonia, the defect that energy consumption is high when ammonia nitrogen resources are recovered from nitrate wastewater is overcome, the high nitrate removal rate is guaranteed, and meanwhile the defect that nitrate is difficult to recover from high-salinity wastewater is overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a method for treating high-salt wastewater by electroactive microorganisms to recover nitrate ions. Background Art

[0002] In China, a large amount of nitrate waste liquid is generated every year in industries such as electroplating, chips, and circuit boards. It has characteristics such as high salinity, strong toxicity, and complex composition. If these wastewaters are directly discharged into the water environment, it will have an adverse impact on the water ecological environment, and its efficient treatment has become a difficult problem that has attracted much attention in the environmental field. Traditional physicochemical treatment technologies such as reverse osmosis and ion exchange, although widely used, face inherent defects such as high treatment costs and easy generation of secondary pollution. In contrast, biological denitrification technology has attracted much attention due to its excellent selectivity and environmental friendliness. However, conventional biological denitrification processes (including anaerobic ammonium oxidation and aerobic-anoxic denitrification) have significant energy consumption problems.

[0003] Microbial electrochemical technology (MET) combines the advantages of electrochemical reduction and biocatalytic denitrification, and has advantages such as low energy consumption, high efficiency, and environmental friendliness. MET generally can achieve a 100% nitrate removal rate and a maximum nitrate removal rate of 200 mg / L / d. Denitrifying microorganisms use electroactive microorganisms to oxidize organic matter to release electrons and directly or indirectly reduce nitrate. In addition, electroactive biofilms can selectively convert NO3 - to NH4 + , combined with the in-situ generated OH - at the cathode and the bioelectromigration process, to achieve the recovery of high-value ammonia. Compared with traditional metal / inorganic non-metal catalysts, the biocatalyst (NrfA enzyme) used by electroactive biofilms has high specificity, mild conditions, and low cost, and has been proven to achieve high yield and high selectivity in ammonia synthesis. Therefore, the "pollution treatment-resource recovery" dual effect of MET provides great potential for the treatment and resource recovery of nitrate waste liquid.

[0004] However, current research mostly focuses on the denitrification and ammonia recovery efficiency of MET under ideal conditions, ignoring the complexity of the nitrate wastewater matrix, especially the high-concentration coexisting ions (such as Cl - , Na + , SO4 2-etc.). On the one hand, an appropriate amount of salt ions can increase the conductivity and reduce the internal resistance of the solution, thereby improving the electrochemical performance of MET. However, excessive salinity will inhibit the electron transfer of microorganisms and change the community structure through multiple mechanisms such as osmotic pressure imbalance, ion-specific toxicity, and oxidative stress, thereby restricting the denitrification or ammonia recovery efficiency. Therefore, it is still unknown whether MET can achieve nitrate removal and ammonia recovery under high salinity. Summary of the Invention

[0005] The object of the present invention is to provide a method for recovering nitrate from high-salt wastewater by electroactive microorganisms, which solves the problem of high energy consumption in recovering ammonia nitrogen resources from nitrate wastewater, ensures a high nitrate removal rate, and at the same time overcomes the disadvantage of difficult recovery of nitrate from high-salt wastewater.

[0006] To achieve the above object, the present invention provides a method for recovering nitrate from high-salt wastewater by electroactive microorganisms, which uses a three-electrode single chamber, a multi-channel potentiostat, and a programmable logic master control system to recover nitrate, including the following steps: S1. The high-salt wastewater is added to the three-electrode single chamber for biodegradation. The electroactive microorganisms decompose the organic substrate through their own life activities and generate electrons and protons. The electrons are transferred from the electroactive microorganisms through extracellular electrons and then through the external circuit. S2. Denitrifying microorganisms or electroactive microorganisms use nitrate as an electron acceptor to carry out denitrification or dissimilatory reduction to ammonium, which is oxidized to ammonium nitrogen for further recovery and utilization. A reduction reaction of water to hydroxide and hydrogen occurs in the three-electrode single chamber. S3. The multi-channel potentiostat detects the current and displays it through the programmable logic master control system, reflecting the growth status of electroactive microorganisms and the consumption degree of organic matter and nitrate from the current aspect. When the current appears at a peak and drops to 0, it proves that the organic matter and nitrate in the reactor have been removed and consumed, and the next round of influent treatment can be carried out. The entire treatment system is connected to the programmable logic master control system for data acquisition and system control. [[ID=1�]]

[0007] Preferably, in step S1, the three-electrode single chamber includes a working electrode, a counter electrode, and a reference electrode. A platinum sheet is provided on the counter electrode. The three-electrode single chamber is connected to the working electrode, the counter electrode, and the reference electrode through wires and is connected to the multi-channel potentiostat. High-salt wastewater is provided inside the three-electrode single chamber. The multi-channel potentiostat is electrically connected to the programmable logic master control system, and the programmable logic master control system controls the three-electrode single chamber and the multi-channel potentiostat.

[0008] Preferably, in step S1, the three-electrode single chamber operates at a set temperature of 30°C.

[0009] Preferably, in step S1, before the high-salt wastewater is added to the three-electrode single chamber, it is aerated with nitrogen for 10-20 minutes to remove oxygen.

[0010] The advantages and beneficial effects of the present invention using the above method for treating high-salt wastewater with electroactive microorganisms to recover nitrate are as follows: 1. Compared with other nitrate removal and recovery processes such as nitrification-denitrification and anaerobic ammonium oxidation, the present invention reduces energy consumption, does not require the addition of chemical agents, and nitrogen is no longer released into the atmosphere in the form of gaseous nitrogen, but exists in the form of ammonium nitrogen, waiting for the next step of recovery and utilization, significantly reducing the pollution load and treatment energy consumption of nitrate wastewater, and promoting the resource utilization of nitrogen in wastewater.

[0011] 2. The present invention can achieve a high nitrate removal rate, ensure the safety standard of the effluent, the nitrate removal rate can reach more than 99%, the equipment is simple, occupies a small area, is easy to operate, and has a low cost.

[0012] 3. The present invention can achieve the conversion and recovery of nitrate in wastewater with a relatively high salinity, avoiding the situation where the microorganisms lose their activity due to the too high salinity of the nitrate wastewater, resulting in the inability of the system to remove and recover nitrate.

[0013] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0014] Figure 1 is the overall structural schematic diagram of the device for treating high-salt wastewater with electroactive microorganisms to recover nitrate of the present invention; Figure 2 is the line graph of the COD removal rate of the present invention; Figure 3 is the bar graph of the nitrate nitrogen concentration measured at different salinities of the present invention; Figure 4 is the bar graph of the ammonium nitrogen concentration measured at different salinities of the present invention.

[0015] Reference Signs 1. Three-electrode single chamber; 2. Multi-channel potentiostat; 3. Programmable logic master control system; 4. Working electrode; 5. Counter electrode; 6. Reference electrode; 7. Electric wire; 8. Conducting wire; 9. High-salt wastewater. Detailed Embodiments

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention belongs.

[0018] Unless otherwise defined, the reagents, equipment and other materials used in the present invention are all obtained from regular commercial sources.

[0019] Example 1 As Figure 1 shown, in the method for recovering nitrate from high-salt wastewater by electroactive microorganisms, a three-electrode single chamber 1, a multi-channel potentiostat 2 and a programmable logic master control system 3 are used to recover nitrate. The three-electrode single chamber 1 includes a working electrode 4, a counter electrode 5 and a reference electrode 6. A platinum sheet is provided on the counter electrode 5. Jacks for inserting the working electrode 4, the counter electrode 5 and the reference electrode 6 are provided on the cover of the three-electrode single chamber 1. The three-electrode single chamber 1 is connected to the working electrode 4, the counter electrode 5 and the reference electrode 6 through a wire 7 and is connected to the multi-channel potentiostat 2. High-salt wastewater 9 is provided inside the three-electrode single chamber 1. The multi-channel potentiostat 2 and the programmable logic master control system 3 are electrically connected through a wire 8 of the multi-channel potentiostat 2 itself. The programmable logic master control system 3 controls the whole device.

[0020] The working electrode 4, the reference electrode 6 and the counter electrode 5 all extend below the liquid level of the high-salt wastewater 9 in the three-electrode single chamber 1. The working electrode 4 controls an immersion length of 4.5 cm. The platinum sheet of the counter electrode 5 is parallel to the working electrode 4, and the immersion depth of the platinum sheet is the same as that of the working electrode 4.

[0021] The three-electrode single chamber 1 reaches an anoxic or anaerobic state by sealing the periphery of the single chamber lid with a sealing film and evenly applying glue to the jacks of the single chamber lid.

[0022] The multi-channel potentiostat 2 contains eight channels, and each channel contains three wires 7 connected to the three-electrode single chamber 1.

[0023] The three-electrode single chamber 1 operates at a set temperature of 30 °C.

[0024] A method for recovering nitrate from high-salt wastewater by electroactive microorganisms includes the following steps: S1. The high-salt wastewater 9 enters the three-electrode single chamber 1 for biodegradation. The electroactive microorganisms on the working electrode 4 decompose the organic substrate through their own life activities and generate electrons and protons. Subsequently, the electrons are transferred from the electroactive microorganisms to the working electrode 4 through extracellular electron transfer, and then transferred to the counter electrode 5 through an external circuit. Before the high-salt wastewater 9 is added to the three-electrode single chamber 1, the high-salt wastewater 9 is aerated with nitrogen for 10 - 20 minutes to remove oxygen.

[0025] S2. The denitrifying microorganisms or electroactive microorganisms near the working electrode 4 use nitrate as an electron acceptor to carry out denitrification or dissimilatory reduction to ammonium, and are oxidized to ammonium nitrogen for further recovery and utilization. A reduction reaction of water to hydroxide ions and hydrogen gas occurs on the counter electrode 5.

[0026] S3. The working electrode 4, counter electrode 5, and reference electrode 6 in the three-electrode single chamber 1 are connected to the multi-channel potentiostat 2 through wires 7. The multi-channel potentiostat 2 can detect the current and display it through the programmable logic master control system 3. From the current aspect, it can reflect the growth status of electroactive microorganisms and the consumption degree of organic matter and nitrate, etc. When the current appears at a peak and drops to 0, it proves that the organic matter and nitrate in the reactor have been removed and consumed, and the next round of influent treatment can be carried out; the entire treatment system is connected by the programmable logic master control system to collect data and control the system.

[0027] A high-salt wastewater 9 treatment experiment was carried out on the method of recovering nitrate by treating high-salt wastewater 9 with electroactive microorganisms. The water quality parameters of the influent sewage were as follows: the chemical oxygen demand concentration (COD) was 1015.95 mg / L, and the nitrate nitrogen concentration was 3.344 mM. Several salinity wastewaters with salinities of 1%, 1.25%, 1.5%, 1.75%, 2%, 2.5%, and 3% NaCl were set. In this way, the water quality of electroplating wastewater was simulated. The test results are as Figure 2 , Figure 3 and Figure 4 shown.

[0028] It can be seen from Figure 2 that the COD removal rate of the wastewater remains at a relatively high level when the salinity is 1% - 1.75%, reaching more than 92%, and the highest can reach 97%. When the salinity is as high as 2% NaCl, the removal rate can still be more than 60%.

[0029] It can be seen from Figure 3 that at different salinities, the nitrate nitrogen concentrations measured at 0 h, 6 h, [12 h, 24 h, 36 h, and 48 h] can show that with the increase of salinity, the nitrate nitrogen in the wastewater can maintain a very high removal rate, remaining above 99%.

[0030] It can be seen from Figure 4 that at different salinities, the ammonium nitrogen concentrations measured at 0 h, 6 h, [12 h, 24 h, 36 h, and 48 h] can show that with the increase of salinity, the ability of nitrate nitrogen in the wastewater to be converted into ammonium nitrogen becomes stronger and stronger. When the salinity is 1.75%, the ability of dissimilatory reduction to ammonium is the strongest. When the salinity is 2%, it is slightly weaker, but still maintains a good DNRA (dissimilatory nitrate reduction to ammonium) ability.

[0031] Therefore, the method of recovering nitrate by treating high-salt wastewater with electroactive microorganisms according to the present invention solves the deficiency of high energy consumption in recovering ammonia nitrogen resources from nitrate wastewater, ensures a relatively high removal rate of nitrate, and at the same time overcomes the disadvantage of difficulty in recovering nitrate from high-salt wastewater.

[0032] **Note**: There seems to be a formatting issue in the original text where some time points like "12h" are not separated clearly in the numbered list. I have added commas in the translation for better readability where appropriate. Also, the text in brackets in the translation is added to make the sentence more complete and clear in English.Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent replacements, and these modifications or equivalent replacements do not enable the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for recovering nitrate from high-salt wastewater by electroactive microorganisms, which uses a three-electrode single-chamber, multi-channel potentiostat and a programmable logic master control system to recover nitrate, is characterized in that The steps are as follows: S1. High-salt wastewater is added to a three-electrode single chamber for biodegradation. Electroactive microorganisms decompose organic substrates through their own life activities and generate electrons and protons. The electrons are transferred from the electroactive microorganisms through extracellular electrons and then through an external circuit. S2. Denitrifying microorganisms or electroactive microorganisms use nitrate as an electron acceptor to carry out denitrification or dissimilatory reduction to ammonium, which is oxidized to ammonium nitrogen for further recycling. A reduction reaction of water to hydroxide ions and hydrogen occurs in the three-electrode single chamber. S3. The multi-channel potentiostat detects the current and displays it through an editable logic master control system, reflecting the growth status of electroactive microorganisms and the consumption degrees of organic matter and nitrate from the current aspect. When the current appears at a peak and drops to 0, it proves that the organic matter and nitrate in the reactor have been removed and consumed, and the next round of influent treatment can be carried out. The entire treatment system is connected to the programmable logic master control system for data acquisition and system control.

2. The method for recovering nitrate from high-salt wastewater by electroactive microorganisms according to claim 1, characterized in that: In step S1, the three-electrode single chamber includes a working electrode, a counter electrode, and a reference electrode. A platinum sheet is provided on the counter electrode. The three-electrode single chamber is connected to the working electrode, the counter electrode, and the reference electrode through wires and is connected to the multi-channel potentiostat. High-salt wastewater is provided inside the three-electrode single chamber. The multi-channel potentiostat is electrically connected to the programmable logic master control system, and the programmable logic master control system controls the three-electrode single chamber and the multi-channel potentiostat.

3. The method for recovering nitrate from high-salt wastewater by electroactive microorganisms according to claim 1, characterized in that: In step S1, the three-electrode single chamber operates under the condition that the set temperature is 30 °C.

4. The method for recovering nitrate from high-salt wastewater by electroactive microorganisms according to claim 1, characterized in that: In step S1, before the high-salt wastewater is added to the three-electrode single chamber, it is aerated with nitrogen for 10 - 20 minutes to remove oxygen.

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