A MEC reactor and a rapid test method for organic wastewater BOD

Abstract

The present invention provides a MEC reactor and a rapid testing method for BOD of organic wastewater, and relates to the field of analysis and detection technology. Based on MEC sensing technology, the present invention constructs an efficient MEC reactor; at the same time, combined with a continuous short-cycle testing method and a supporting data calculation method, a rapid testing method that can be applied to various types of complex organic wastewater that does not contain biotoxic substances and has a concentration of >5mgBOD / L is obtained. After three cycles of testing, the present invention takes the last two stable cycles for calculation. At the same time, when calculating, the curve is divided into multiple segments according to the changes in the main components of degraded organic matter in different time periods, and a segmented weighted calculation is performed. Compared with the ordinary coulometric method, this calculation method can more accurately combine the coulometric charge with the five-day respiration method BOD from the perspective of actual microbial electrochemical metabolism, has good data reproducibility, a test time of <2h, and a test result error of <10% compared to the national standard BOD5.

Description

Technical Field

[0001] The present invention relates to the technical field of analysis and detection, in particular to a MEC reactor and a rapid testing method for BOD of organic wastewater. Background Art

[0002] Biochemical oxygen demand (BOD) refers to the level of organic matter in water that can be used by microorganisms, and plays an important role in sewage plant operation and maintenance, environmental monitoring and other fields.

[0003] The national standard dilution inoculation method for BOD5 testing requires five days, requiring water sample dilution and inoculation. The testing process is also susceptible to temperature, water sample properties, and inoculation effects, making it unsuitable for engineering applications. The differential pressure gauge BOD testing technique, which uses a differential pressure gauge as an auxiliary, also suffers from similar drawbacks.

[0004] Other existing indirect BOD testing methods, such as the microbial electrode method and the microbial fuel cell sensor method, cannot guarantee the long-term stability of the test. Especially when testing the BOD of organic wastewater containing complex material components, the test results have a large error compared with the national standard BOD5, and the data reproducibility is poor. Summary of the Invention

[0005] The purpose of the present invention is to provide a MEC reactor and a rapid testing method for BOD of organic wastewater, which is suitable for the rapid detection of various complex organic wastewaters that do not contain biotoxic substances, and has good data reproducibility and small error with the test results of the national standard BOD5.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides an MEC reactor, comprising a reactor body, a bioanode and a cathode; the bioanode is located at the center of a cavity of the reactor body; the cathode wraps around the bioanode but does not contact the bioanode, and the hollow cavity between the bioanode and the cathode constitutes an electrolysis chamber; the reactor body is provided with a water inlet and a water outlet;

[0008] The bioanode includes a bioaffinity material and functional microorganisms attached to the bioaffinity material; the functional microorganisms include electroactive microorganisms and mixed bacterial species; the electroactive microorganisms are purified sulfur-reducing bacteria; and the mixed bacterial species at least simultaneously include Methanobacterium, Methanogens, Propionibacterium and Klebsiella.

[0009] Preferably, the volume of the bioanode accounts for more than 60% of the volume of the reactor main cavity.

[0010] Preferably, the cathode is in close contact with the inner wall of the reactor body.

[0011] Preferably, the cathode is a titanium-based material; the mass content of titanium in the titanium-based material is greater than 80%.

[0012] Preferably, the cathode is a mesh structure, and the mesh number of the mesh structure is above 100 meshes.

[0013] Preferably, the biocompatible material is a carbon-based material.

[0014] The present invention provides a rapid testing method for BOD of organic wastewater, comprising the following steps:

[0015] The MEC reactor described in the above scheme is filled with a nutrient solution containing sodium acetate and free of dissolved oxygen. The nutrient solution is replaced every 1 to 3 days. The current change in each cycle is detected. When the difference between the current peaks of adjacent cycles is less than 5%, the MEC reactor is considered to be successfully started.

[0016] The organic wastewater to be tested is introduced into the electrolysis chamber of the successfully started MEC reactor through the water inlet, and the wastewater is discharged through the water outlet after staying for 10 to 40 minutes. This is repeated three times, and the current data generated during the operation is recorded. The time-current curves obtained from the last two tests are averaged to obtain an averaged time-current curve. The averaged time-current curve is fitted using an exponential decay curve to obtain a fitted time-current curve; the termination current of the fitted time-current curve is 0.01 to 0.1 mA; the curve is divided into n+1 characteristic decline stages according to the number n of inflection points of the fitted time-current curve, and the BOD is calculated according to Formula 1;

[0017]

[0018] In formula 1, Q0 is the reactor's reference charge, C. When the volume of the bioanode accounts for more than 80% of the reactor's main cavity volume, 3000 C is used. When the volume of the bioanode accounts for 60-80% of the reactor's main cavity volume, Q0 = 150 V + 4200, where V is the volume percentage, %.

[0019] n is the number of inflection points of the fitted time-current curve, which is set according to the actual situation and is 0 to 2. It is dimensionless.

[0020] ε i ——The weighting coefficient of each characteristic descending stage of the fitting time-current curve, dimensionless, when n=0, i=1, ε1=1; when n=1, i=1, 2, ε1=0.4, ε2=0.6; when n=2, i=1, 2, 3, ε1=0.2, ε2=0.2, ε3=0.6;

[0021] F——Faraday constant, 96500C / mol;

[0022] σ——total oxygen efficiency, mol·L / mg;

[0023] I F ——Fitting curve, mA;

[0024] t i-1 ——the starting time of the characteristic descent curve of the i-th segment, s;

[0025] t i ——the end point of the characteristic descent curve of the i-th segment, s;

[0026] BOD——calculated BOD value, mg / L;

[0027] The method for calculating σ - total oxygen efficiency includes: using a five-day respiration method to measure the BOD5 value of the organic wastewater, and then substituting the BOD5 value into Formula 1 to calculate σ - total oxygen efficiency.

[0028] Preferably, before introducing the organic wastewater, the process further includes draining the liquid in the MEC reactor and washing the chamber of the MEC reactor with deionized water.

[0029] Preferably, the pH value of the nutrient solution is 7.2; the concentration of sodium acetate in the nutrient solution is 0.1-0.5 mg / L.

[0030] Preferably, the BOD5 of the organic wastewater to be tested is greater than 5 mg / L and does not contain any biotoxic substances.

[0031] The present invention provides an MEC reactor, comprising a reactor body, a bioanode and a cathode; the bioanode is located at the center of a cavity of the reactor body; the cathode wraps around the bioanode but does not contact the bioanode, and the hollow cavity between the bioanode and the cathode constitutes an electrolysis chamber; the reactor body is provided with a water inlet and a water outlet; the bioanode comprises a bioaffinity material and functional microorganisms attached to the bioaffinity material; the functional microorganisms comprise electroactive microorganisms and mixed bacterial species; the electroactive microorganism is purified Geobacter sulfurreducens; and the mixed bacterial species at least simultaneously comprise Methanobacterium, Methanogens, Propionibacterium and Klebsiella.

[0032] In the process of testing BOD in a microbial electrolysis cell (MEC), electroactive microorganisms can consume BOD while generating electrons, and transfer the electrons to the electrode to generate an electrical signal. By analyzing the electrical signal, BOD information can be obtained. The present invention uses purified Geobacter sulfurreducens as one of the functional microorganisms attached to the bioanode, thereby ensuring that the electroactive microorganisms have a high relative abundance among the functional microorganisms; in addition, the present invention also adds mixed strains to the bioanode. These mixed strains have the functions of producing methanogens, producing acetic acid, and degrading propionic acid. They are rich in variety and can adapt to a variety of water characteristics. They can convert complex organic matter into substrates such as acetic acid that are easily utilized by electroactive microorganisms, thereby enabling the functional microbial film of the bioanode to consume more complex organic matter and generate a stronger electrical signal. Therefore, the MEC reactor of the present invention has a wide detection range and can test different organic wastewaters containing complex substances.

[0033] The present invention is based on MEC sensing technology to construct an efficient MEC reactor; at the same time, combined with a continuous short-cycle test method and a supporting data calculation method, a rapid testing method that can be applied to various types of complex organic wastewater that does not contain biotoxic substances with a BOD value of >5mg BOD / L is obtained. After three cycles of testing, the present invention takes the last two stable cycles for calculation. At the same time, when calculating, the curve is divided into multiple segments according to the changes in the main components of the degraded organic matter in different time periods, and a segmented weighted calculation is performed. Compared with the ordinary coulometric method, this calculation method can more accurately combine the coulometric charge with the five-day respiration method BOD from the perspective of actual microbial electrochemical metabolism. The data has good reproducibility, and the error with the test result of the national standard BOD5 is <10%.

[0034] In addition, when testing the BOD of organic wastewater, the present invention only needs to filter out large-particle suspended solids without the need for other pre-treatments such as dilution, and the operation is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the structure of the MEC reactor; 1-water outlet, 2-bioanode, 3-cathode, 4-reactor body, 5-electrode lead opening, 6-water inlet;

[0036] Figure 2 The time-current error band curves for the last two times of the two water samples in Example 1 are shown;

[0037] Figure 3 The time-current error band curves for the last two times of Example 2;

[0038] Figure 4 Example 3 Three-cycle time-current curve of the glucose-glutamate standard sample test. DETAILED DESCRIPTION

[0039] The present invention provides an MEC reactor, comprising a reactor body, a bioanode and a cathode; the bioanode is located at the center of a cavity of the reactor body; the cathode wraps around the bioanode but does not contact the bioanode, and the hollow cavity between the bioanode and the cathode constitutes an electrolysis chamber; the reactor body is provided with a water inlet and a water outlet;

[0040] The bioanode includes a bioaffinity material and functional microorganisms attached to the bioaffinity material; the functional microorganisms include electroactive microorganisms and mixed bacterial species; the electroactive microorganisms are purified sulfur-reducing bacteria; and the mixed bacterial species at least simultaneously include Methanobacterium, Methanogens, Propionibacterium and Klebsiella.

[0041] The following combination Figure 1 The structure of the MEC reactor of the present invention will be described.

[0042] like Figure 1 As shown, the MEC reactor provided by the present invention includes a reactor body. In the present invention, the reactor body is preferably a hollow cylinder; the reactor body is provided with a water inlet and a water outlet. More specifically, the water inlet is provided on the lower side of the reactor body, and the water outlet is provided on the top surface of the reactor body. In the present invention, the inner diameter of the reactor body is preferably 20 to 40 mm, more preferably 25 to 30 mm; the height of the reactor body is preferably 40 to 60 mm, more preferably 50 mm. The present invention has no special requirements for the material of the reactor body. In the embodiment of the present invention, it is specifically made of engineering plastic.

[0043] The MEC reactor provided by the present invention includes a bioanode; the bioanode is located at the center of the cavity of the reactor body, that is, the vertical central axis of the bioanode coincides with the central axis of the reactor body. In the present invention, the bioanode is preferably cylindrical, but can also have other shapes, such as a rectangular parallelepiped, which can be freely adjusted by those skilled in the art. In the present invention, the height of the bioanode is preferably consistent with the height of the reactor body; the volume of the bioanode preferably accounts for more than 60% of the volume of the reactor body cavity, more preferably more than 80%, and even more preferably 80-90%. The present invention can adjust the volume percentage of the bioanode by adjusting its diameter. By controlling the volume percentage of the bioanode to above 80%, the present invention ensures a high inoculum of functional microorganisms, which in turn helps further improve the speed and accuracy of BOD testing. When the volume percentage is less than 80%, the error between the test results and the national standard five-day respiration method results will be significantly increased. When the volume percentage is less than 60%, the bioreactor is considered unsuitable for the rapid BOD testing of the present invention.

[0044] In the present invention, the bioanode includes a bioaffinity material and functional microorganisms attached to the bioaffinity material; the functional microorganisms include electroactive microorganisms and mixed bacterial species; the electroactive microorganisms are purified Geobacter sulfurreducens; and the mixed bacterial species at least simultaneously include Methanobacterium, Methanogens, Propionibacterium and Klebsiella.

[0045] On the one hand, the present invention uses purified Geobacter sulfurreducens as an electroactive microorganism, ensuring that the electroactive microorganisms in the functional microorganisms have a high relative abundance, which is conducive to the generation of a stronger electrical signal. On the other hand, the present invention also adds mixed strains to the bioanode. These mixed strains have the functions of producing methane, producing acetic acid and degrading propionic acid. They are rich in variety and can adapt to various water characteristics. They can convert complex organic matter into substrates such as acetic acid that can be easily utilized by electroactive microorganisms, thereby enabling the functional microbial membrane of the bioanode to consume more complex organic matter and generate a stronger electrical signal. Therefore, the MEC reactor of the present invention has a wide detection range and can test the BOD values ​​of different organic wastewaters containing complex substances.

[0046] In the present invention, the bioaffinity material is preferably a carbon-based material; the carbon-based material preferably comprises a cylinder formed by stacking carbon fiber filaments, a porous graphite column, or a millstone, more preferably a porous graphite column. In the present invention, the bioaffinity material serves to attach functional microorganisms. Prior to use, the bioaffinity material is preferably ultrasonically cleaned with acetone, ethanol, or ultrapure water and then air-dried at room temperature.

[0047] The present invention has no special requirements for the preparation process of the bioanode, and the bioanode is prepared by microbial inoculation methods well known in the art. In an embodiment of the present invention, the preparation method of the bioanode preferably includes the following steps:

[0048] 1. Pure bacterial inoculation: Purified Geobacter sulfurreducens stored in -80℃ refrigerator was revived and activated in nutrient broth medium for 12 hours. Under sterile conditions, 100mL of liquid bacterial solution was placed in a 30℃ incubator for activation. OD 600 =0.1 when connected to the reactor;

[0049] 2. After the pure bacteria are inoculated, culture until the current naturally rises and then drops to less than 0.1 mA;

[0050] 3. Pure bacterial culture: Replace the nutrient solution with pH = 7.2, containing 0.3 mg / L sodium acetate and DO < 0.1 mg / L into the MEC reactor. When the MEC current is less than 0.1 mA, replace the nutrient solution with new one. Repeat twice.

[0051] 4. Mixed bacteria inoculation: add 0.8 mg / L of sodium acetate to the sludge leachate of the cultured mixed bacteria, adjust the pH to 7.2 and the DO to < 0.1 mg / L to obtain the functional bacteria inoculation solution, replace the inoculation solution into the MEC reactor, and replace the new inoculation solution when the MEC current is less than 0.1 mA;

[0052] 5. Cultivation: Replace the nutrient solution with pH = 7.2, containing 0.3 mg / L sodium acetate and DO < 0.1 mg / L into the MEC reactor. When the MEC current is less than 0.1 mA, replace with new nutrient solution. Repeat until the difference in current peak value is less than 5%, indicating that the bioanode is successfully prepared.

[0053] The present invention has no particular requirements for the source of the purified Geobacter sulfurreducens; it can be obtained using purification methods well known in the art. Specifically, it is obtained by isolating and purifying a biofilm from a microbial electrolysis cell bioanode cultured for two years in the laboratory. The mixed bacterial strain is domesticated in the laboratory from domestic sewage and fermentation wastewater. Preferably, 16S rDNA sequencing of the bioanode membrane is performed to detect the presence of Methanobacterium, Methanogens, Propionicimonas, and Klebsiella (i.e., Methanobacterium, Methanocorpusculum, Propionicimonas, and Klebsiella).

[0054] The MEC reactor provided by the present invention includes a cathode; the cathode wraps around the bioanode but does not contact it, and the hollow cavity between the bioanode and the cathode constitutes an electrolysis chamber. In the present invention, the cathode is preferably close to the inner wall of the reactor body. In the present invention, the cathode is preferably a titanium-based material, and the mass content of titanium in the titanium-based material is preferably greater than 80%. The present invention uses a titanium substrate as a cathode, which has excellent electrical conductivity and catalytic properties. In the present invention, the cathode is preferably a mesh structure, and the mesh number of the mesh structure is preferably above 100 meshes. The mesh structure used in the present invention helps to remove the electrode reaction products near the metal mesh while hydraulic shearing, promotes the reaction in the positive direction, and the mesh structure is not easy to cause blockage and can save costs. In the present invention, the height of the cathode is preferably consistent with the reactor body.

[0055] As an embodiment of the present invention, an electrode lead opening is provided on the bottom surface of the MEC reactor, and the electrode lead opening is used to lead out the wires of the biological anode and cathode, and the led-out wires are connected to a power source.

[0056] In actual testing, the present invention assembled a complete BOD sensor using a MEC reactor, a microcurrent acquisition card, and a sampling pump. Specifically, the positive and negative electrodes of a 0.5-1.0V DC power supply were connected to the bioanode and cathode of the MEC reactor, respectively. The microcurrent acquisition card was connected in series in the circuit to collect the electrical signal. The sampling pump's water inlet was connected to the water sample to be tested, and its outlet was connected to the MEC reactor's water inlet.

[0057] The present invention provides a rapid testing method for BOD of organic wastewater, comprising the following steps:

[0058] The MEC reactor described in the above scheme is filled with a nutrient solution containing sodium acetate and free of dissolved oxygen. The nutrient solution is replaced every 1 to 3 days. The current change in each cycle is detected. When the difference between the current peaks of adjacent cycles is less than 5%, the MEC reactor is considered to be successfully started.

[0059] The organic wastewater to be tested is introduced into the electrolysis chamber of the successfully started MEC reactor through the water inlet, and the wastewater is discharged through the water outlet after staying for 10 to 30 minutes. This is repeated three times, and the current data generated during the operation is recorded. The time-current curves obtained from the last two tests are averaged to obtain an averaged time-current curve. The averaged time-current curve is fitted using an exponential decay curve to obtain a fitted time-current curve. The curve is divided into n+1 characteristic descending stages according to the number n of inflection points of the fitted time-current curve. The termination current of the fitted time-current curve is 0.01 to 0.1 mA. The BOD is calculated according to Formula 1.

[0060]

[0061] In formula 1, Q0 is the reactor's reference charge, C. When the volume of the bioanode accounts for more than 80% of the reactor's main cavity volume, 3000 C is used. When the volume of the bioanode accounts for 60-80% of the reactor's main cavity volume, Q0 = 150 V + 4200, where V is the volume percentage, %.

[0062] n is the number of inflection points of the fitted time-current curve, which is set according to the actual situation and is 0 to 2. It is dimensionless.

[0063] ε i ——The weighting coefficient of each characteristic descending stage of the fitting time-current curve, dimensionless, when n=0, i=1, ε1=1; when n=1, i=1, 2, ε1=0.4, ε2=0.6; when n=2, i=1, 2, 3, ε1=0.2, ε2=0.2, ε3=0.6;

[0064] F——Faraday constant, 96500C / mol;

[0065] σ——total oxygen efficiency, mol·L / mg;

[0066] I F ——Fitting curve, mA;

[0067] t i-1 ——the starting time of the characteristic descent curve of the i-th segment, s;

[0068] t i ——the end point of the characteristic descent curve of the i-th segment, s;

[0069] BOD - calculated BOD value, mg / L.

[0070] The present invention fills the MEC reactor with a nutrient solution containing sodium acetate and free of dissolved oxygen. The nutrient solution is replaced every 1 to 3 days, preferably every 2 days. The current change in each cycle is detected. When the difference between the current peak values ​​of adjacent cycles is less than 5%, the MEC reactor is considered to be successfully started.

[0071] In the present invention, the pH value of the nutrient solution is preferably 7.2; the concentration of sodium acetate in the nutrient solution is preferably 0.1-0.5 mg / L, more preferably 0.2-0.3 mg / L. The functional microorganisms of the present invention are strictly anaerobic or facultative anaerobic. Oxygen interferes with the enrichment and colonization of functional bacteria in the initial stage of culture, so dissolved oxygen cannot be contained in the nutrient solution. However, after the culture matures, it is not necessary to ensure that the water sample is strictly anaerobic during actual testing.

[0072] The present invention preferably utilizes a micro-current acquisition card to detect the current change in each cycle.

[0073] After the MEC reactor is successfully started, the present invention preferably drains the liquid in the MEC reactor, cleans the chamber of the MEC reactor with deionized water, and then introduces organic wastewater for detection.

[0074] The present invention has no special requirements for the deionized water cleaning process. The deionized water is directly filled into the electrolysis chamber of the MEC reactor, left there for 5 minutes, and then discharged.

[0075] In the present invention, the BOD5 of the organic wastewater to be tested is preferably greater than 5 mg / L and does not contain biotoxic substances. The present invention has no special requirements for the composition of the organic wastewater to be tested and is applicable to organic wastewater with complex components. In the present invention, when the organic wastewater to be tested contains water containing large suspended particles, the present invention preferably filters it through a 20-mesh filter before sampling. The present invention does not require any pretreatment and is simpler to operate and has a shorter process than existing detection methods.

[0076] The present invention introduces the organic wastewater to be tested into the electrolysis chamber of the successfully started MEC reactor through the water inlet, and discharges it through the water outlet after staying for 10 to 40 minutes. The process is repeated three times, and the current data generated during the operation is recorded. The time-current curves obtained from the last two tests are averaged to obtain the averaged time-current curve.

[0077] In the present invention, the amount of organic wastewater to be tested is preferably sufficient to fill the electrolysis chamber. The last two time-current curves are stable and repeatable, reflecting the true state of the water sample test. The current curve of the first cycle has a large error, indicating that the bioanode is adapting to the water sample. Therefore, the present invention averages the time-current curves obtained from the last two tests to obtain an averaged time-current curve, ensuring data accuracy and good reproducibility.

[0078] After obtaining the averaged time-current curve, the present invention uses an exponential decay curve to fit the averaged time-current curve to obtain a fitted time-current curve; the termination current of the fitted time-current curve is 0.01 to 0.1 mA; and the BOD is calculated according to Formula 1.

[0079] In the present invention, since the current decays continuously over time during actual detection, the present invention adopts an exponential decay curve for fitting, which is more in line with actual conditions. The present invention has no special requirements for the fitting process, and fitting processes well known in the art can be used. In the present invention, the termination current of the fitting time-current curve is preferably 0.01 to 0.1 mA, and more preferably 0.01 to 0.05 mA.

[0080] After obtaining the fitting time-current curve, the present invention determines the number n of inflection points of current decline (zero points of the second-order derivative) based on the fitting time-current curve, divides the fitting time-current curve into n+1 characteristic decline stages, and calculates the BOD according to Formula 1.

[0081] In the present invention, the calculation method of σ - total oxygen efficiency in Formula 1 includes: using the five-day respiration method to measure the BOD5 value of the organic wastewater, and then substituting the BOD5 value into Formula 1 to calculate σ - total oxygen efficiency.

[0082] The present invention preferably measures the BOD5 values ​​of a plurality of organic wastewater samples, calculates a plurality of σ values, and then calculates the average σ value as the σ value for subsequent actual detection.

[0083] The present invention utilizes the five-day breathing method to calibrate the σ value, thereby ensuring the accuracy of the detection data.

[0084] The present invention is based on the coulometric method. The time-current curves generated after the last two sample injections are averaged, and the BOD value is calculated through fitting prediction, segmented integration, and weighted summation. Compared with the ordinary coulometric method, this calculation method can more accurately combine the coulometric charge with the five-day respiration method BOD from the perspective of actual microbial electrochemical metabolism. The data has good reproducibility, and the error with the national standard BOD5 test result is less than 10%.

[0085] In the present invention, the above calculation method and formula are preferably built into a microcurrent acquisition card, and the microcurrent acquisition card automatically outputs the BOD value.

[0086] In this invention, when the MEC reactor is not used for an extended period, a nutrient solution with a pH of 7.2 and 2 mg / L of sodium acetate is introduced into the MEC chamber to maintain the device. The nutrient solution is replaced monthly. The next time the MEC reactor is used, it can be tested without restarting.

[0087] The MEC reactor and the rapid testing method for BOD of organic wastewater provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0088] The structure of the MEC reactor used in the following examples is as follows: Figure 1 As shown, the reactor body is a hollow cylinder with an inner diameter of 30 mm and a height of 60 mm, and is made of engineering plastic; the bioanode is located in the center of the cavity of the reactor body, and its height is consistent with that of the reactor body. The bioanode includes a bioaffinity material, which is a porous graphite column; functional microorganisms are attached to the porous graphite column, and the functional microorganisms include purified sulfur-reducing bacteria and mixed strains, and the mixed strains include at least Methanobacterium, Methanogens, Propionibacterium and Klebsiella. The specific preparation method of the bioanode has been discussed above and will not be repeated here. The volume of the bioanode is 90% of the volume of the reactor body cavity; the cathode is a pure titanium mesh, which is close to the inner wall of the reactor body, the cathode height is consistent with the reactor body height, and the mesh size of the cathode mesh is 100 mesh.

[0089] The MEC reactor, a microcurrent acquisition card, and a sampling pump are assembled into a complete BOD sensor for use. Specifically, the positive and negative electrodes of a 1.0V DC power supply are connected to the bioanode and cathode of the MEC reactor. The microcurrent acquisition card is connected in series with the bioanode and cathode of the MEC reactor in a circuit to collect electrical signals. The sampling pump's water inlet is connected to the water sample to be tested, and its outlet is connected to the MEC reactor's water inlet.

[0090] Example 1

[0091] Test fermentation wastewater with BOD5 of about 6000 mg / L

[0092] ① Parameter solution

[0093] Prepare a BOD sensor, take samples and collect time-current curves according to the above process, average the last two time-current curves to obtain an averaged time-current curve; fit the averaged time-current curve to obtain a fitted time-current curve. Since there are two inflection points in the fitted time-current curve when testing the fermentation wastewater, the curve is divided into three sections according to the time points corresponding to the two inflection points, and ε1, ε2 = 0.2, and ε3 = 0.6 are taken. Within 1 hour, a total of three groups of fermentation wastewater samples at different times are taken for testing respectively, and the five-day respiration method BOD5 values ​​of the three groups of water samples are tested at the same time. The relevant data are substituted into formula 1, and the σ values ​​are calculated respectively. The average is then taken to obtain σ = 0.052, which is substituted into formula 1 for subsequent calculations.

[0094] ②Sample testing

[0095] Fermentation wastewater samples were taken on March 13, 2023 and March 16, 2023, respectively. The fermentation wastewater was introduced into the electrolysis chamber of the successfully started MEC reactor through the water inlet, and then discharged through the water outlet after staying for 40 minutes. This was repeated three times. The current data generated during the operation was recorded using a microcurrent acquisition card. The time-current curves obtained from the last two tests were averaged, and the standard deviation was calculated to obtain the averaged time-current curve. An error band diagram was drawn, see Figure 2. Figure 2 , the averaged time-current curve is fitted using the exponential decay curve to obtain the fitted time-current curve; the fitting curve formula on March 16 is:

[0096]

[0097]

[0098]

[0099] The termination current of the fitting time-current curve is 0.1 mA; substituting it into the BOD calculation formula, the BOD values ​​can be obtained to be 5980 mg / L and 5000 mg / L, which have errors of 4.5% and 2.2% compared with the national standard dilution inoculation method BOD5 (5720 mg / L, 4890 mg / L), respectively.

[0100] also, Figure 2 The results show that: during the two water sample tests, the error between the time-current curves of the last two cycles is small, the original curve of the test process is stable, and the test results of fermentation wastewater containing complex organic matter at different time periods are fully reliable. The total test time is 40 minutes, indicating that the test time of the present invention is short.

[0101] Example 2

[0102] Test the deep treated effluent with BOD5 of about 10mg / L

[0103] ① Parameter solution

[0104] Prepare a BOD sensor. According to the characteristic of the small BOD of the tested water sample, shorten the single cycle to 10 minutes. Sampling and collecting time-current curves are carried out according to the above process. The last two time-current curves are averaged to obtain the averaged time-current curve. The averaged time-current curve is fitted to obtain a fitted time-current curve. There is one inflection point of the fitted time-current curve. The curve is divided into two sections according to the time corresponding to the inflection point, and ε1 = 0.4 and ε2 = 0.6 are taken. Within 1 hour, 3 groups of fermentation wastewater samples at different times are taken and tested separately. At the same time, the five-day respiration method BOD5 values ​​of the 3 groups of water samples are tested. The relevant data are substituted into the formula, and the σ values ​​are calculated respectively. Then, the average is σ = 0.75, which is substituted into the formula for subsequent calculations.

[0105] ②Sample testing

[0106] Take 100 mL of deep-treated effluent sample and pass it into the electrolysis chamber of the successfully started MEC reactor through the water inlet. After staying for 10 minutes, discharge it through the water outlet. Repeat three times. Use a microcurrent acquisition card to record the current data generated during the operation. Average the time-current curves obtained from the last two tests, calculate the standard deviation, and obtain the averaged time-current curve. Make an error band diagram, see Figure 3 , the averaged time-current curve is fitted using the exponential decay curve to obtain the fitted time-current curve. The fitting time-current curve formula is:

[0107]

[0108]

[0109] Substituting the BOD calculation formula into the test result, the test result is 12 mg / L. Compared with the national standard dilution inoculation method BOD5=13 mg / L, the test result error of this method is 7.7%, and the total test time is 30 minutes, making the test efficient and reliable.

[0110] Example 3

[0111] Laboratory test of glucose-glutamate standard sample with BOD5=250mg / L

[0112] ① Parameter solution

[0113] Prepare the BOD sensor as described in the method plan, start the automatic periodic sampling and data processing program, introduce the glucose-glutamate standard sample with BOD5=250 mg / L into the electrolysis chamber, and obtain 0 inflection points of the fitted time-current curve. Then divide the curve into 1 section according to the time corresponding to 0 inflection point, and take ε1=1. Take 3 groups of fermentation wastewater samples at different times within 1 hour for testing respectively, and test the BOD5 values ​​of the 3 groups of water samples by the five-day respiration method at the same time. Substitute the relevant data into the formula, calculate the σ value respectively, and then take the average to obtain σ=0.8, which is substituted into the formula for subsequent calculations.

[0114] ②Sample testing

[0115] Take 100mL of glucose-glutamic acid standard sample with BOD5=250mg / L and inject it into the sample according to the above method. The time-current curve of three cycles is as follows: Figure 4 As shown, the last two time-current curves obtained are averaged to obtain an averaged time-current curve, and the averaged time-current curve is fitted using an exponential decay curve to obtain a fitted time-current curve. The test result is 240 mg / L when substituted into the BOD calculation formula, with an error of 4%.

[0116] It can be seen from the results of the above examples that the test results of different water samples using the method of the present invention are stable and reliable, and no pre-treatment of the water samples is required.

[0117] Comparative Example 1:

[0118] Comparison with differential pressure meter BOD tester

[0119] For fermentation wastewater with BOD5>5000mg / L, when using the conventional differential pressure meter BOD tester on the market, it is necessary to go through steps such as dilution inoculation, addition of nitrification inhibitors, and addition of carbon dioxide absorbents. Due to the complex composition of organic matter in the wastewater, it is not easy to accurately determine the range of BOD5 by COD, so it is usually necessary to prepare multiple dilution concentrations for testing. Each test process takes five days. At the same time, the test results are easily affected by the ambient temperature and the sealing of the differential pressure test system.

[0120] In contrast, the solution of the present invention uses mature bioelectrodes as sensing elements. For organic wastewater with different compositions, there is no need for complex pretreatment operations such as dilution and inoculation of water samples. The entire testing process only requires starting the sampling program, updating the water sample into the electrolytic cell at a cycle of 10 to 20 minutes, and reading the data at the end.

[0121] Comparative Example 2

[0122] Comparison with microbial electrode rapid detection instrument

[0123] For water samples from the biochemical pool of a sewage treatment plant with BOD5 < 5000 mg / L, the BOD5 test is performed using a microbial electrode method BOD rapid tester based on immobilized Escherichia coli. The error between the results and the BOD5 results obtained by the national standard dilution inoculation method can easily be > 10%. Especially when the instrument is used for more than 1 month, the error will continue to increase.

[0124] In contrast, the solution of the present invention utilizes functional microbial communities for testing, which can maintain the stability of the sensor element for a longer period of time. A single element can maintain a repeat deviation of <10% for 3 to 6 months (for example, the BOD of the 0.5 g / L sodium acetate sample tested on December 11, 2022 by the present invention is 260 mg / L, and the BOD value of the 0.5 g / L sodium acetate sample tested on June 1, 2023 is 250 mg / L, and there is no significant difference between the two). At the same time, the calculation method of the segmented integral can ensure that the test results have an error of <10% with the national standard dilution inoculation method BOD5.

[0125] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A rapid test method for BOD of organic wastewater, characterized in that: The following steps are involved: The MEC reactor was filled with a nutrient solution containing sodium acetate and no dissolved oxygen. The nutrient solution was replaced every 1 to 3 days. The current change in each cycle was detected. When the difference between the current peaks of adjacent cycles was less than 5%, the MEC reactor was considered to have been successfully started. The organic wastewater to be tested is introduced into the electrolysis chamber of the successfully started MEC reactor through the water inlet, and the wastewater is discharged through the water outlet after staying for 10 to 40 minutes. This is repeated three times, and the current data generated during the operation is recorded. The time-current curves obtained from the last two tests are averaged to obtain an averaged time-current curve. The averaged time-current curve is fitted using an exponential decay curve to obtain a fitted time-current curve; the termination current of the fitted time-current curve is 0.01 to 0.1 mA; the curve is divided into n+1 characteristic decline stages according to the number n of inflection points of the fitted time-current curve, and the BOD is calculated according to Formula 1; In formula 1, Q0 is the reactor's reference charge, C. When the volume of the bioanode accounts for more than 80% of the reactor's main cavity volume, 3000 C is used. When the volume of the bioanode accounts for 60-80% of the reactor's main cavity volume, Q0 = 150 V + 4200, where V is the volume percentage, %. n is the number of inflection points of the fitted time-current curve, which is set according to the actual situation and is 0 to 2. It is dimensionless. ε i ——The weighting coefficient of each characteristic descending stage of the fitting time-current curve, dimensionless, when n=0, i=1, ε1=1; when n=1, i=1, 2, ε1=0.4, ε2=0.6; when n=2, i=1, 2, 3, ε1=0.2, ε2=0.2, ε3=0.6; F——Faraday constant, 96500C / mol; σ——total oxygen efficiency, mol·L / mg; I F ——Fitting curve, mA; t i-1 ——the starting time of the characteristic descent curve of the i-th segment, s; t i ——the end point of the characteristic descent curve of the i-th segment, s; BOD——calculated BOD value, mg / L; The method for calculating the σ-total oxygen efficiency includes: measuring the BOD5 value of the organic wastewater using a five-day respiration method, and then substituting the BOD5 value into Formula 1 to calculate the σ-total oxygen efficiency; The MEC reactor comprises a reactor body, a bioanode and a cathode; the bioanode is located in the center of the cavity of the reactor body; the cathode wraps around the bioanode but does not contact it, and the hollow cavity between the bioanode and the cathode constitutes an electrolysis chamber; the reactor body is provided with a water inlet and a water outlet; The bioanode includes a bioaffinity material and functional microorganisms attached to the bioaffinity material; the functional microorganisms include electroactive microorganisms and mixed bacterial species; the electroactive microorganisms are purified sulfur-reducing bacteria; and the mixed bacterial species at least simultaneously include Methanobacterium, Methanogens, Propionibacterium and Klebsiella.

2. The rapid testing method according to claim 1, characterized in that Before the organic wastewater is introduced, the liquid in the MEC reactor is drained and the chamber of the MEC reactor is cleaned with deionized water.

3. The rapid testing method according to claim 1, characterized in that The pH value of the nutrient solution is 7.2; the concentration of sodium acetate in the nutrient solution is 0.1-0.5 mg / L.

4. The rapid testing method according to claim 1, characterized in that The organic wastewater to be tested has a BOD5>5 mg / L and does not contain any biotoxic substances.

5. The rapid testing method according to claim 1, characterized in that: The volume of the bioanode accounts for more than 60% of the volume of the reactor main cavity.

6. The rapid testing method according to claim 1 or 5, characterized in that: The cathode is closely attached to the inner wall of the reactor body.

7. The rapid testing method according to claim 1, characterized in that: The cathode is made of titanium-based material; the mass content of titanium in the titanium-based material is greater than 80%.

8. The rapid testing method according to claim 1 or 7, characterized in that: The cathode is a mesh structure, and the mesh number of the mesh structure is above 100 meshes.

9. The rapid testing method according to claim 1, characterized in that: The bioaffinity material is a carbon-based material.

Images