A method for denitrification based on electrochemical coupling of carbon dioxide fixation by microorganisms

Abstract

The application discloses a wastewater denitrification method based on electrochemical coupling biological fixation of carbon dioxide, and the system comprises an MES sleeve-shaped double-cavity reactor, a sewage mixing pool and a denitrification reactor. The cathode chamber and the anode chamber of the MES sleeve-shaped double-cavity reactor are separated by a cation exchange membrane, the cathode chamber and the anode chamber are connected to the negative electrode and the positive electrode of a power supply respectively, and the cathode chamber is enriched with homoacetogenic bacteria. The denitrification reactor is a single-chamber denitrification reactor, and a carbon brush is used as a carrier to enrich heterotrophic denitrification bacteria. The method realizes efficient conversion of CO2 to acetic acid, reduces carbon emission, solves the problems of high energy consumption and difficulty in use of CO2 reduction products, and can realize biological treatment of nitrate-containing wastewater without adding an external carbon source.

Description

TECHNICAL FIELD

[0001] The application relates to a method and device for low-carbon treatment of nitrate wastewater based on a denitrification process of carbon dioxide fixed by electrochemical coupling and biological fixation. BACKGROUND

[0002] At present, excessive emission of CO2 by human beings causes greenhouse effect on the nature, aggravates global warming and other serious environmental problems. Traditional chemical methods often convert CO2 into chemicals by hydrogenation, which needs to consume a large amount of energy and hydrogen, and has high economic cost. Although some new technologies such as electrocatalytic reduction of CO2 are constantly emerging, catalysts are needed to solve the problems of long-term stability under high current density and product selectivity decay, and high energy consumption of separation and purification, so that the industrialization of the technology still faces many challenges, and it is essential and imperative to explore new paths of CO2 utilization and conversion.

[0003] Microbial electrosynthesis system (MES) is a new technology in which microorganisms use electrodes as electron donors to convert carbon dioxide into bio-chemicals and biofuels. Compared with electrocatalytic reduction, it has the advantages of good stability and low cost, and is considered as a promising green bio-manufacturing technology for carbon dioxide fixation.

[0004] In addition to the path of CO2 utilization and conversion, the application of the product is also a key problem. At present, the CO2 reduction technology faces the problems of low product selectivity, low concentration, high energy consumption of product separation and purification, and has not found a suitable application scenario that can overcome these problems. Exploring the organic combination of CO2 reduction and environmental pollution comprehensive treatment is expected to provide new ideas for technology landing and carbon neutralization in the environmental pollution control industry. Sewage treatment plants are major consumers of energy and carbon source chemicals, and produce and emit a large amount of CO2 in the process of pollutant degradation and conversion, which is a carbon emission source that cannot be ignored. We found a new application scenario of CO2 reduction technology, i.e. the combination of CO2 reduction technology and sewage denitrification. This application scenario can greatly reduce the threshold of CO2 reduction technology application, and can reduce carbon emissions in the process of sewage biological treatment.

[0005] The MES is combined with the sewage denitrification process, microorganisms in the MES absorb CO2 to convert into organic carbon source, and subsequent sewage treatment directly uses the organic matter generated by the MES as an additional carbon source for biological denitrification. The process has the following advantages: the sewage biological denitrification process has a wide range of carbon source requirements, and organic small molecules such as alcohol, aldehyde and acid can be utilized, overcoming the challenge of complex product separation in the CO2 reduction technology; the pH of the sewage denitrification process and the biological growth environment in the MES are neutral, and the two are consistent; the functional microorganisms for sewage denitrification have high diversity and strong adaptability, and can be self-adapted and domesticated according to the provided organic small molecules. The process not only realizes efficient reduction of CO2, but also solves the problems of difficult utilization of products and large carbon emission in the sewage denitrification process, and is a very promising low-carbon water treatment technology. SUMMARY

[0006] The application is to couple the CO2 efficient reduction technology (providing organic carbon source) of MES with the biological denitrification process (consuming organic carbon source) of sewage. First, homoacetogenic bacteria are used to reduce CO2 to acetic acid in the MES reactor, and the homoacetogenic bacteria liquid is separated from the acetic acid nutrient solution by a hollow fiber membrane. The acetic acid nutrient solution is mixed with nitrate wastewater in proportion and then flows into the denitrification reactor, and the denitrifying bacteria are used to remove nitrate from the sewage. The application realizes efficient conversion of CO2 to acetic acid, reduces carbon emission, solves the problems of high energy consumption and difficult use of CO2 reduction products, and can realize biological treatment of nitrate-containing wastewater without additional carbon source.

[0007] The specific technical solutions adopted are as follows:

[0008] A denitrification method based on electrochemical coupling biological fixation of carbon dioxide, comprising the following steps:

[0009] (1) adding nutrient solution and activated carbon into the cathode chamber of the MES sleeve-shaped double-chamber reactor, adding sodium sulfate solution into the anode chamber, and then adding homoacetogenic bacteria liquid into the cathode chamber, controlling the reactor to be in an oxygen-free condition and continuously stirring to culture the homoacetogenic bacteria; after the activity OD 600 of the homoacetogenic bacteria decreases by more than 30%, the nutrient solution is changed to continuous feeding, and the MES sleeve-shaped double-chamber reactor is continuously operated;

[0010] (2) using a hollow fiber membrane to separate the homoacetogenic bacteria liquid flowing out of the cathode of the MES sleeve-shaped double-chamber reactor from the acetic acid nutrient solution, and returning the separated homoacetogenic bacteria liquid to the cathode chamber of the MES sleeve-shaped double-chamber reactor;

[0011] (3) the acetic acid-containing nutrient solution separated by the hollow fiber membrane is mixed with the nitrate-containing wastewater in a sewage mixing tank at a carbon-nitrogen ratio of 2±0.1:1, and then is flowed into a denitrification reactor, the denitrification reactor containing heterotrophic denitrifying bacteria, and the denitrification reactor is controlled to be in an anaerobic condition to remove the nitrate in the wastewater.

[0012] Preferably, the MES sleeve-shaped double-chamber reactor uses a cation exchange membrane to separate the cathode chamber from the anode chamber; the anode chamber is located in the middle of the reactor, and the cathode chamber is arranged around the anode chamber, and the volume ratio of the anode chamber to the cathode chamber is 1:5-10; the pH in the MES sleeve-shaped double-chamber reactor is controlled to be 7.0±0.1, and the temperature is controlled to be 35±0.5℃.

[0013] Preferably, the concentration of the sodium sulfate solution is 0.2 mol / L; and the concentration of the activated carbon in the cathode solution is 1.5 g / L.

[0014] The preparation method of the activated carbon is as follows: taking rice husk as raw material, pyrolyzing the raw material at 600℃ under N2 atmosphere in a tubular furnace, then grinding and sieving the pyrolyzed product through a 100-mesh sieve; acidifying the sieved activated carbon in a mixed solution of H2SO4 and HNO3, then washing the acidified activated carbon particles with distilled water until the pH is 7, and drying to obtain the final activated carbon particles.

[0015] Preferably, the denitrification reactor is used to enrich heterotrophic denitrifying bacteria before the nitrate removal process, and glucose and acetic acid are used as organic carbon sources in the enrichment process; the temperature in the denitrification reactor is controlled to be 30±0.5℃.

[0016] Preferably, the MES sleeve-shaped double-chamber reactor and the denitrification reactor are both fully stirred, and the stirring speed is maintained at 300-500 rpm.

[0017] Preferably, the TOC concentration of the mixed wastewater in step (4) is ≤500±10 ppm, the nitrate concentration is ≤250±10 ppm, the carbon-nitrogen ratio is 2±0.1:1, and the pH value is 7-8.

[0018] Preferably, the method for controlling the denitrification reactor to be in an anaerobic or anoxic environment is to blow nitrogen, and to use a direct current power supply to provide a constant current of 200 mA-1 A to the MES sleeve-shaped double-chamber reactor to electrolyze water to generate H2 and continuously introduce CO2, so as to ensure anaerobic condition and provide H2 and inorganic carbon source for homoacetogenic bacteria, and the molar ratio of H2 to CO2 in the MES sleeve-shaped double-chamber reactor is 2:1.

[0019] Preferably, the hydraulic retention time of the MES sleeve-shaped double-chamber reactor is 300-500 hours during continuous flow operation, and the hydraulic retention time of the denitrification reactor is 24-36 hours.

[0020] Preferably, the nutrient solution in step (1) comprises phosphate, sodium chloride, ammonium chloride, vitamins and minerals; the phosphate comprises hydrogen phosphate and dihydrogen phosphate; the vitamins comprise vitamin H, vitamin B1, vitamin B2, vitamin B3, vitamin B5, vitamin B6, vitamin B9, vitamin B12, vitamin Bx, thioctic acid; the minerals comprise iron chloride hexahydrate, boric acid, copper sulfate pentahydrate, potassium iodide, manganese chloride tetrahydrate, sodium molybdate dihydrate, zinc sulfate heptahydrate, cobalt chloride hexahydrate, nickel chloride hexahydrate.

[0021] Preferably, the hollow fiber membrane adopts modified polypropylene as the membrane material, the inner diameter is 200-300 microns, the outer diameter is 300-400 microns, the pore size is less than 0.1 micron, the porosity is less than 50%, and the filtration efficiency is greater than 5.0 ml / (cm 2 ·min).

[0022] In the method, the homoacetogenic bacteria efficiently convert CO2 into acetic acid, the heterotrophic denitrifying bacteria utilize acetic acid as an electron donor and carbon source for denitrification and nitrogen removal treatment of wastewater, and the hydrogen autotrophic acetic acid production and heterotrophic denitrification coupling system realizes simultaneous efficient nitrogen removal of the wastewater.

[0023] 2CO2+4H2→CH3COOH+2H2O

[0024] CH3COO - +1.18NO3 - +2.18H + →0.12C5H7O2N+1.4CO2+2.5H2O+0.53N2

[0025] Compared with the prior art, the method has the beneficial effects that:

[0026] (1) The method couples the CO2 efficient reduction technology (provides organic carbon source) of MES with the biological nitrogen removal process (consumes organic carbon source) of wastewater, the homoacetogenic bacteria efficiently convert CO2 into acetic acid, and the heterotrophic denitrifying bacteria utilize acetic acid as an electron donor and carbon source for denitrification and nitrogen removal treatment of wastewater. The efficient reduction of CO2 solves the problems of high energy consumption and difficulty in separation of CO2 reduction products.

[0027] (2) The method has high efficiency in treating nitrate wastewater, good effluent water quality, and realizes CO2 fixation and reduces carbon emissions. The denitrification rate reaches 90-95%, the nitrate content of the discharged wastewater is ≤10 ppm, and the emission standard is met.

[0028] (3) The present application adds activated carbon in the cathode solution, promotes the formation of biofilm on the stainless steel cathode of acetic acid bacteria, reduces the loss of bacteria when the continuous flow is changed after the homoacetogenic bacteria culture is completed, has higher acetic acid production every day, and is convenient for subsequent separation of bacteria and bacterial liquid. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the OD of homoacetogenic bacteria of Example 1 without adding activated carbon 600 Growth activity and acetic acid production graph.

[0030] Figure 2 is the OD of homoacetogenic bacteria of Example 1 with activated carbon 600 Growth activity and acetic acid production graph.

[0031] Figure 3 is the device graph of Example 2 based on the method of electrochemically coupling biological fixation of carbon dioxide and denitrification.

[0032] Figure 4 is the TOC and NO3 - -N consumption graph of the heterotrophic denitrification reactor of Example 2.

[0033] Figure 5 is the mixed wastewater TOC inflow and outflow change graph of the heterotrophic denitrification reactor of Example 2.

[0034] Figure 6 is the mixed wastewater NO3 - -N inflow and outflow change graph of the heterotrophic denitrification reactor of Example 2.

[0035] Figure 7 is the device graph of the hydrogen autotrophic denitrification reactor of Example 3.

[0036] Figure 8 is the mixed wastewater NO3 - -N inflow and outflow change and consumption graph of the hydrogen autotrophic denitrification reactor of Example 3. DETAILED DESCRIPTION

[0037] The present application will be further illustrated below in conjunction with the embodiments and drawings. It should be understood that these embodiments are only used to illustrate the present application, and are not used to limit the scope of the present application.

[0038] The homoacetogen, heterotrophic denitrifying bacteria and hydrogen autotrophic denitrifying bacteria are all industrial commonly used strains, and commercially available products can be directly selected. The homoacetogen can convert carbon dioxide and hydrogen into acetic acid in the anaerobic acid production process, and its effect is enhanced when the hydrogen partial pressure is high. The heterotrophic denitrifying bacteria can utilize nitrate and nitrite as electron acceptors, thereby oxidizing organic matter into nitrogen and releasing a large amount of nitrogen, thereby promoting the nitrogen cycle of the ecological system. The hydrogen autotrophic denitrifying bacteria can utilize hydrogen as an electron donor and nitrate and nitrite as electron acceptors to reduce nitrate into gaseous nitrogen.

[0039] The hollow fiber membrane of the present application adopts modified polypropylene as the membrane material, the inner diameter is 200-300 microns, the outer diameter is 300-400 microns, the pore size is less than 0.1 micron, the porosity is less than 50%, and the filtration efficiency is greater than 5.0 ml / (cm 2 ·min).

[0040] The homoacetogen of the present application uses a microbial nutrient solution (i.e. the nutrient solution of the present application), and the solvent is deionized water, and the composition includes: sodium hydrogen phosphate 6g / L, potassium dihydrogen phosphate 3g / L, sodium chloride 0.5g / L, ammonium sulfide 0.5g / L, trace elements 1ml / L, and vitamins 1ml / L; the vitamins include vitamin H 0.002g / L, vitamin B1 0.05g / L, vitamin B2 0.05g / L, vitamin B3 0.05g / L, vitamin B5 0.05g / L, vitamin B6 0.01g / L, vitamin B9 0.002g / L, vitamin B12 0.0001g / L, vitamin Bx 0.05g / L, and thioctic acid 0.05g / L; the minerals include iron chloride hexahydrate 1.5g / L, boric acid 0.15g / L, copper sulfate pentahydrate 0.03g / L, potassium iodide 0.18g / L, manganese chloride tetrahydrate 0.12g / L, sodium molybdate dihydrate 0.06g / L, zinc sulfate heptahydrate 0.12g / L, cobalt chloride hexahydrate 0.15g / L, and nickel chloride hexahydrate 0.023g / L.

[0041] The heterotrophic denitrifying bacteria of the embodiment of the present application are enriched from anaerobic sludge, 225ml of anaerobic sludge taken from the anaerobic biological filter of the Juhua Group sewage plant is inoculated into 900ml of a denitrification reactor, a carbon brush is used as a carrier for bacterial enrichment, and microbial nutrient solution and sodium nitrate (the microbial nutrient solution is the same as the homoacetogen nutrient solution of the present application, and the sodium nitrate is used to simulate nitrated wastewater) are added. The temperature is controlled at 30±0.5℃, the rotation speed is 300rpm, and the hydraulic retention time is 24-36 hours. In the initial stage of domestication, the heterotrophic denitrifying bacteria are additionally added with glucose as an external carbon source to activate the bacteria, and then acetic acid is used to replace glucose as a carbon source to make the bacteria gradually adapt, until the enrichment and domestication of the heterotrophic denitrifying bacteria in the denitrification reactor are completed.

[0042] When the acetic acid bacteria reactor is converted to a continuous flow reactor and the heterotrophic denitrifying bacteria in the denitrification reactor adapt to acetic acid as a carbon source (i.e., after the heterotrophic denitrifying bacteria have completed enrichment and acclimatization), the acetic acid bacteria reactor and the denitrification reactor are coupled. At this time, the denitrification reactor directly uses 2... # The acetic acid-containing nutrient solution filtered by hollow fiber membranes is used as the nutrient source, and sodium nitrate is still used to simulate nitrification wastewater.

[0043] Example 1: Construction of an acetic acid bacteria reactor

[0044] First, add 900ml of nutrient solution and 1.5g of activated carbon to the 1000ml cathode chamber of the #1 MES sleeve-shaped double-chamber reactor. Then, add 100ml of 0.2mol / L sodium sulfate solution to the 100ml anode chamber of the same reactor. Next, add 100ml of homologous acetic acid-producing bacteria solution to the cathode. Control the temperature at 35.5±0.5℃, current at 500mA, CO2 flow rate at 77.78μmol / min, rotation speed at 500rpm, and pH at 7.0±0.1. The activity OD of the homologous acetic acid-producing bacteria is then measured. 600 After the drop exceeded 30%, switch to continuous flow (nutrient solution continuously enters), and replace the liquid 70ml daily; complete the construction of the acetic acid bacteria reactor.

[0045] This invention adds 1.5 g / L of activated carbon to the cathode solution to promote the formation of a biofilm by acetic acid bacteria on the stainless steel cathode. This reduces bacterial loss when switching to continuous flow after the homologous acetic acid-producing bacteria culture is complete, resulting in higher daily acetic acid production and facilitating subsequent separation of bacteria from the bacterial solution. In this embodiment, the activated carbon is prepared as follows: rice husks are used as raw material. The raw material is pyrolyzed in a tube furnace under a N2 atmosphere at 600°C for 60 min, with a heating rate of 5°C / min. Afterward, it is ground and sieved through a 100-mesh filter. 10 g of activated carbon is placed in 1 mol / L H2SO4 (75 ml) and 1 mol / L HNO3 (25 ml) and mixed at 70°C for 4 hours. The acidified activated carbon particles are washed with distilled water until the pH reaches 7 and then placed in an oven at 100°C for 24 hours to obtain the final activated carbon particles (AC).

[0046] To verify the effectiveness of biochar addition, a control group acetic acid bacteria reactor was constructed under the same experimental conditions. The difference in the control group was that no activated carbon particles were added initially. The reaction time was determined by the OD (Organic Demand) period. 600 When the price drop exceeded 30%, the reactor was switched to continuous flow and operated for a total of 80 days. The results of the control group and the experimental group are as follows: Figure 1 and Figure 2 As shown. According to Figure 1The blank control group without adding activated carbon reached 18.40 g / L of acetic acid content on the 24th day. The reactor was changed to continuous flow operation for 56 days, and 60 ml of cathode nutrient solution was replaced daily. The average daily acetic acid production during the continuous flow period was 1.08 g / day. According to the formula: (1.08 g / day) / (18.40 g / L) = 0.059, the acetic acid production was increased by 5.9%. Figure 2 The acetic acid content of the activated carbon group reached 20.32 g / L on the 20th day. The reactor was changed to continuous flow operation for 60 days, and 70 ml of cathode nutrient solution was replaced daily. The average daily acetic acid production during the continuous flow period was 1.46 g / day, with a 35.19% increase in acetic acid production.

[0047] Example 2: Construction of an electrochemically coupled biological fixed carbon dioxide denitrification device

[0048] The wastewater treatment object was NO3 - The wastewater with a -N concentration of 120-300 mg / L, a TOC concentration controlled at 240-500 mg / L, and an initial pH of 7.0±1.0.

[0049] The acetic acid bacteria reactor was a sleeve-shaped double-chamber, with an anode chamber capacity of 100 ml and a cathode chamber capacity of 1000 ml. The acetic acid bacteria reactor was constructed according to the method of Example 1, with the first 0-20 days as a closed sequencing batch, the pH controlled at 7.0±0.1, the temperature at 35±0.5℃, the current at 500 mA, and the CO2 supply flow rate at 77.78 μmol / min; the 21st-80th days were changed to continuous flow, coupled with the denitrification reactor, and 70 ml of cathode nutrient solution was replaced daily.

[0050] The denitrification reactor had a volume of 900 ml and used carbon brush to enrich denitrifying bacteria. The denitrification reactor was constructed, the coupling between the two reactors was tested, and the denitrification effect was tested according to the following flow:

[0051] Stage I (1-4 days): The denitrification reactor used glucose as an additional carbon source component to add nutrient solution (same as the nutrient solution for homoacetogenic bacteria of the present application), with an inflow TOC concentration of 500±10 ppm, a NO3 - -N concentration of 250±10 ppm, and a hydraulic retention time of 24 h.

[0052] Stage II (5-10 days): The denitrification reactor used acetic acid as an additional carbon source component to add nutrient solution, with an inflow TOC concentration of 500±10 ppm, a NO3 - -N concentration of 250±10 ppm, and a hydraulic retention time of 24 h.

[0053] Phase III (days 11-26) involves coupling the denitrification reactor with the acetic acid bacteria reactor. Acetic acid solution filtered through a hollow fiber membrane is directly used as the nutrient source for the heterotrophic denitrifying bacteria. The mixing of the acetic acid solution with the denitrifying wastewater is controlled to maintain an influent TOC concentration of 480 ± 10 ppm and NO3- concentration of 480 ± 10 ppm. - The -N concentration was 240±10ppm, and the hydraulic retention time was 24h.

[0054] Phase IV (days 27-36): The mixing ratio of acetic acid solution and denitrification wastewater was adjusted to control the inflow TOC concentration at 245±5 ppm, and NO3-. - The -N concentration was 125±5ppm, and the hydraulic retention time was 24h.

[0055] Phase V (days 37-67): The hydraulic retention time was changed to 36 hours, and the inflow TOC concentration was controlled at 245±5 ppm, NO3- - -N concentration is 125±5ppm.

[0056] The results are as follows: Figure 2 The acetic acid bacteria reactor shown was switched to continuous flow on day 21, and the bacterial OD... 600 It can maintain a concentration of 0.95±0.05 g / L, and the acetic acid concentration can be maintained at 20.5±0.5 g / L, operating stably for 60 days; Figure 4 Daily TOC and NO3 consumption of the denitrification reactor - The concentration of -N; Figure 5 and Figure 6 TOC and NO3 flowing in and out respectively - Changes in the concentration of -N.

[0057] In this embodiment, the two systems were coupled on day 21 of the acetic acid bacteria reactor construction and day 11 of the denitrification reactor construction. The coupled system operated for a total of 57 days, divided into three parts: the first part corresponds to the coupling adaptation period. Figures 4-6 In Phase III (days 11 to 26), acetic acid-containing nutrient solution was mixed with nitrate-nitrogen wastewater, and heterotrophic denitrifying bacteria gradually adapted to the coupled system. The hydraulic retention time was 24 hours. The inflow TOC of the wastewater was 480–490 ppm, and the outflow was 177–316 ppm; the inflow NO3... - -N was 235–245 ppm, and the effluent was 78–168 ppm; the nitrate and nitrogen treatment efficiency stabilized at 3.93 ± 0.05 ppm / (L·h); the second part corresponds to Figures 4-6 In Phase IV (days 27 to 36), to optimize effluent quality, the TOC and NO3 levels of the wastewater inflow were changed. - -N, by changing the mixing ratio of acetic acid nutrient solution and nitrate wastewater to achieve an inflow TOC of 240–245 ppm and NO3. -- N is 120-130 ppm, effluent TOC is 60-70 ppm, effluent NO3 - - N is 35-47 ppm, the nitrate treatment efficiency is 3.94±0.1 ppm / (L·h), and stable operation is maintained for 10 days; the third part corresponds to Figures 4-6 the V stage (37th to 67th day) in Table 1, in order to make the effluent wastewater reach the discharge index, the hydraulic retention time of the denitrification reactor is further optimized to be 36 hours, the TOC of the influent wastewater is still 240-245 ppm, and the NO3 - - N is still 120-130 ppm, the TOC and NO3 - - N concentration is all lower than 10 ppm to reach the discharge standard, and the NO3 - - N treatment efficiency reaches 3.64±0.1 ppm / (L·h), and can be stably operated for 31 days.

[0058] Comparison of denitrification performance between Example 3 and hydrogen autotrophic system

[0059] The hydrogen autotrophic system and the electrochemical coupling biological fixed carbon dioxide system constructed by the application are used to compare the denitrification efficiency.

[0060] The hydrogen autotrophic denitrification system uses hydrogen autotrophic denitrification bacteria, and the same specification denitrification reactor as in Example 2 is used, and the specific structure is shown in Table 2. Figure 7 225 ml of hydrogen autotrophic denitrification bacteria liquid enriched in the laboratory is inoculated into a 900 ml denitrification reactor, a carbon brush is used as a carrier, the temperature is controlled at 30±0.5℃, the rotation speed is 300 rpm, the hydraulic retention time is 24 hours, the same nutrient solution as the homoacetogenic bacteria is added, and 0.73-1.52 g / L of sodium nitrate is additionally added to simulate the nitrification wastewater for denitrification treatment. The above experimental conditions are the same as those when the heterotrophic denitrification reactor in the electrochemical coupling biological fixed carbon dioxide system is built, the difference is that the hydrogen autotrophic denitrification bacteria does not need to add any organic carbon source, but needs to supply CO2 at a flow rate of 77.78 μmol / min and H2 at a flow rate of 155.56 μmol / min (the same as the CO2 and H2 parameters required by the homoacetogenic bacteria in the electrochemical coupling biological fixed carbon dioxide system).

[0061] The hydrogen autotrophic denitrification reactor is operated for 30 days, and the denitrification effect is shown in Table 3. Figure 8 When the temperature is controlled at 30±0.5℃, the rotation speed is 300 rpm, and the hydraulic retention time is 24 hours, the denitrification efficiency is: when the influent nitrate content is 235-250 ppm, the nitrate treatment efficiency is 1.35±0.05 ppm / (L·h); when the influent nitrate content is 120-130 ppm, the nitrate treatment efficiency is 1.55±0.1 ppm / (L·h).

[0062] The denitrification efficiency of the electrochemical coupling biological fixed carbon dioxide denitrification system constructed by the application is as follows: when the temperature is controlled at 30±0.5 ℃, the rotation speed is 300 rpm, and the hydraulic retention time is 24 hours, the nitrate nitrogen treatment efficiency is 3.93±0.05 ppm / (L·h) when the inflow nitrate nitrogen content is 235-250 ppm; and the nitrate nitrogen treatment efficiency is 3.94±0.1 ppm / (L·h) when the inflow nitrate nitrogen content is 120-130 ppm. It can be seen that the denitrification performance of the electrochemical coupling biological fixed carbon dioxide system constructed by the application is superior to that of the hydrogen autotrophic system.

[0063] The above examples have described the technical solutions of the application in detail, and it should be understood that the above description is only a specific embodiment of the application and is not used to limit the application, and any modification, supplement or similar replacement within the principle range of the application should be included in the protection range of the application.

Claims

1. A method for denitrification based on electrochemically coupled biofixation of carbon dioxide, characterized in that, Comprising the following steps: (1) Add nutrient solution and activated carbon to the cathode chamber of the MES sleeve-shaped double-chamber reactor, add sodium sulfate solution to the anode chamber, and then add homologous acetic acid-producing bacteria solution to the cathode chamber. Control the reactor under anaerobic conditions and continuously stir to cultivate homologous acetic acid-producing bacteria; wait for the activity OD of homologous acetic acid-producing bacteria to reach a certain level. 600 After the decrease exceeded 30%, the nutrient solution was switched to continuous feeding, and the MES sleeve-shaped dual-chamber reactor was operated continuously. The activated carbon was added to the cathode solution at a rate of 1.5 g / L. The activated carbon was prepared by using rice husks as raw material, which was pyrolyzed at 600℃ in a tube furnace under a N2 atmosphere, then ground and sieved through a 100-mesh screen. The sieved activated carbon was acidified in a mixed solution of H2SO4 and HNO3, then washed with distilled water until the pH reached 7, and dried to obtain the final activated carbon particles. (2) using a hollow fiber membrane to separate the homoacetogenic bacteria solution flowing out of the cathode of the MES sleeve-shaped double-chamber reactor from the acetic acid-containing nutrient solution, and returning the separated homoacetogenic bacteria solution to the cathode chamber of the MES sleeve-shaped double-chamber reactor; (3) mixing the acetic acid-containing nutrient solution separated by the hollow fiber membrane with the nitrate-containing wastewater in a sewage mixing tank according to a carbon-nitrogen ratio of 2±0.1:1, and then flowing into the denitrification reactor, which contains heterotrophic denitrifying bacteria and is controlled to be in an anaerobic condition for nitrate removal of the wastewater; the hydraulic retention time of the MES sleeve-shaped double-chamber reactor is 300-500 hours; and the hydraulic retention time of the denitrification reactor is 24-36 hours. 2.The method of claim 1, wherein the method is characterized by, The MES sleeve-shaped double-chamber reactor uses a cation exchange membrane to separate the cathode chamber from the anode chamber; the anode chamber is located in the middle of the reactor, and the cathode chamber surrounds the anode chamber, with a volume ratio of the anode chamber to the cathode chamber being 1:5-10; the pH in the cathode chamber is controlled to be 7.0±0.1, and the temperature is controlled to be 35±0.5℃.

3. The method of claim 1, wherein the electrochemically coupled biofixation of carbon dioxide is denitrification. The concentration of the sodium sulfate solution is 0.2 mol / L. 4.The method of claim 1, wherein the method is characterized by, The denitrification reactor is pre-enriched with heterotrophic denitrifying bacteria before the nitrate removal process of the wastewater, and glucose and acetic acid are used as organic carbon sources in succession during the enrichment process; the temperature in the denitrification reactor is controlled to be 30±0.5℃. 5.The method of claim 1, wherein the method is characterized by, Both the MES sleeve-shaped double-chamber reactor and the denitrification reactor are fully stirred, with the stirring speed being maintained at 300-500 rpm. 6.The method of claim 1, wherein the method is characterized by, The TOC concentration of the mixed wastewater in step (4) is ≤500±10 ppm, the nitrate concentration is ≤250±10 ppm, the carbon-nitrogen ratio is 2±0.1, and the pH value is 7-8. 7.The method of claim 1, wherein the method is characterized by, The method for controlling the denitrification reactor to be in an anaerobic or anoxic environment is to blow nitrogen gas, use a direct current power supply to provide a constant current of 200 mA-1 A for the MES sleeve-shaped double-chamber reactor to electrolyze water to generate H2, and continuously introduce CO2, to ensure anaerobic conditions while providing H2 and inorganic carbon sources for homoacetogenic bacteria, with a molar ratio of H2 to CO2 in the MES sleeve-shaped double-chamber reactor being 2:

1.

8. The method for denitrification based on electrochemically coupled biofixation of carbon dioxide according to claim 1, wherein, The solvent of the nutrient solution in step (1) is water, and the composition comprises: sodium hydrogen phosphate 6 g / L, potassium dihydrogen phosphate 3 g / L, sodium chloride 0.5 g / L, ammonium chloride 0.5 g / L, mineral substance 1 ml / L, and vitamin 1 ml / L; the vitamin comprises vitamin H 0.002 g / L, vitamin B1 0.05 g / L, vitamin B2 0.05 g / L, vitamin B3 0.05 g / L, vitamin B5 0.05 g / L, vitamin B6 0.01 g / L, vitamin B9 0.002 g / L, vitamin B12 0.0001 g / L, vitamin Bx 0.05 g / L, and thioctic acid 0.05 g / L; and the mineral substance comprises iron chloride hexahydrate 1.5 g / L, boric acid 0.15 g / L, copper sulfate pentahydrate 0.03 g / L, potassium iodide 0.18 g / L, manganese chloride tetrahydrate 0.12 g / L, sodium molybdate dihydrate 0.06 g / L, zinc sulfate heptahydrate 0.12 g / L, cobalt chloride hexahydrate 0.15 g / L, and nickel chloride hexahydrate 0.023 g / L. 9.The method of claim 1, wherein the method is characterized by, The hollow fiber membrane adopts modified polypropylene as the membrane material, the inner diameter is 200-300 microns, the outer diameter is 300-400 microns, the pore size is less than 0.1 micron, the porosity is less than 50%, and the filtration efficiency is greater than 5.0 ml / (cm 2 · min).

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