LOCAL COULOMETRIC METHOD FOR THE DETERMINATION OF BIODEGRADABLE ORGANIC SUBSTANCES IN WATER

Abstract

The invention belongs to the field of chemical analysis of aquatic environments and specifically concerns a local coulometric method for the determination of biodegradable organic substances in water. The invention makes use of a dynamic determination of a cutoff or measurement point, in which the change of the physical quantity to be measured (such as voltage signals or derived current or charge) is monitored in real-time, and the point where the absolute value of the rate of change reaches the maximum is selected as the cutoff or measurement point for data collection, thereby optimizing the accuracy of data collection. By determining the dynamic cutoff or measurement point, the invention improves the precision of the data and reduces the detection time, suitable for efficient automated determination of biodegradable organic substances in water.

Description

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[0003] Although BOD5 is widely used, it has significant disadvantages: long detection time (5 days), not suitable for real-time monitoring; Major operational errors (such as variations in microbial activity and dilution errors); Sensitivity to toxicants, which can distort results. 5

[0004] In recent years, microbial fuel cell (MFC) technology has been introduced into the water quality monitoring field for its unique advantages. MFC converts the chemical energy of organic matter into electrical energy through the metabolic activity of electricity-producing microbes, with the following characteristics: 10

[0005] Self-sustaining: the anode biofilm can self-regenerate without frequent replacement; Direct electrical signal: no external power supply or complex signal conversion is required; Multi-indicator potential: can be expanded to detect toxicants, dissolved oxygen, and other parameters. 15

[0006] However, existing MFC-based BOM detection methods still have significant limitations:

[0007] Maximum Current (Voltage) Method: At high BOM concentrations, current output saturates, resulting in loss of linear correlation and environmental influence. Coulometric Method: The 20 coulomb quantity (CY) is strongly influenced by the coulomine efficiency (CE). Competition from non-electricity-producing microbes (such as fermentation bacteria) causes CE instability, especially in low-concentration samples where CE is abnormally high (>100%), seriously affecting accuracy. Open-Circuit Voltage Method: The relationship between BOM concentrations and open-circuit voltage (OCV) is unclear, and prolonged open-circuit operation can lead to inactivation of anode microbes, limiting practical applicability. BE2025 / 5607 3

[0008] The root of these problems lies in the shortcomings of the signal truncating strategy: traditional coulometric methods require waiting for the reaction to complete (up to 8.3 hours), while late in the reaction the activity of non-electricity producing microbes increases.increases, amplifying CE distortions and system errors.5 Therefore, in the field of chemical analysis techniques for aquatic environments, there is an urgent need for a method that utilizes MFCom to scientifically, rationally, and accurately detect biodegradable organic substances, and thus overcome existing technical limitations.10 SUMMARY OF THE INVENTION

[0009] In view of the above, the object of the invention is to provide a local coulometric method for the determination of biodegradable organic substances in water.15

[0010] To achieve the above-mentioned object, the invention offers the following technical solution:

[0011] The invention provides a dynamic determination of cut-off / measurement points for the coulometric method, where the change in the physical quantity to be measured is monitored in real time and the point with the maximum absolute change is selected as the data collection cut-off;

[0012] The physical quantity to be measured is a voltage signal or a derivative intermediate parameter calculated from the voltage signal, whereintermediate parameters current or charge;

[0013] The physical quantity to be measured is the output voltage of the electrochemical reaction system. BE2025 / 5607 4

[0014] Furthermore, the invention provides a method for the determination of biodegradable organic substances in water based on dynamic cut-off, in which a bio-electrochemical system is used for the local coulometric method: (a) Construction of a three-chamber reactor: consisting of an anode chamber with anode liquid, a cathode chamber with cathode liquid, an ion exchange membrane separating the anode and cathode chambers, and an external circuit connecting the anode and cathode; the external circuit includes an external resistor and a voltage recorder for real-time monitoring of the output voltage; (b) Microbial activation: inoculated the anode chamber with 10 electricity-producing microbial populations and activated the biofilm at a constant temperature; (c) Dynamic detection and calculation:

[0015] recorded time-series data of the continuous output voltage of the voltage recorder;

[0016] Choose the point of maximum absolute decay rate of the output voltage as the data collection cutoff;

[0017] Based on the output voltage data before the cutoff point, calculate the local coulometric gain (Q1) according to equation (1): Q=∫ () (1)

[0018] Where: E c l is the output voltage, R e x t is the value of the external resistance;

[0019] Calculate the equivalent oxygen consumption of the anode fluid (BOMQ1) according to equation (2): BOM × (2) BE2025 / 5607 5

[0020] Where: V is the effective volume of the anode electrolyte, F is the Faraday constant.

[0021] Preferences:

[0022] The ion exchange membrane is a proton exchange membrane; the air cathode comprises a carbon cloth structure with a diffusion layer and a Pt / C5 catalytic layer;

[0023] The external resistance is an adjustable resistance in the range of 800Ω to 1200Ω;

[0024] The anode fluid formulation per liter contains:

[0025] Carbon source components: glucose 0.15g, glutamic acid 0.15g; 10

[0026] Electrolyte: KCl 0.30g, NH4Cl 0.30g;

[0027] Buffer system: NaH2PO4 2H2O 5.08g, Na2HPO4 12H2O 20.85g;

[0028] Growth factors: trace mineral solution 10.5mL, vitamin solution 6mL;

[0029] Supplement: ultrapure water; 15

[0030] The cathode fluid formulation per liter contains: NaH2PO4 2H2O 3.1g, Na2HPO4 12H2O 10.1g, supplemented with ultrapure water;

[0031] The constant temperature at step (b) is 28±3℃;

[0032] The data collection frequency at step (c) is once every 5 minutes;

[0033] The method is applied in water quality monitoring.20

[0034] Advantages of the invention

[0035] The invention originally chooses the point of maximum absolute change as a cut-off point for voltage recording; this point is easy to find and can significantly reduce the measurement time, thus increasing the operational efficiency. In addition, the local coulometric method25 using this cut-off point shows a better linear correlation between oxygen consumption BOMQ1 and the concentration of the GGA standard solution of electricity-producing microbes. BE2025 / 5607 6 This offers a more scientific, rational and accurate method.for the determination of biodegradable organic substances in water using MFC and offers new insights and directions for scientific control of water pollution, with great promotional potential and wide application possibilities. 5

[0036] Other advantages, objects and features of the invention will be set forth to some extent in the following description and will be obvious or deducible to those skilled in the art based on study of the text below or by practice of the invention. The objects and other advantages of the invention may be realized 10 and obtained from the description below. EXPLANATION OF THE ACCOMPANYING DRAWINGS

[0037] In order to make the purposes, technical solutions and advantages of the invention clearer, the invention is described in detail below in conjunction with the attached drawings:

[0038] Figure 1 is a schematic representation of the principle of using a microbial fuel cell sensor for the detection of biodegradable organic substances;

[0039] Figure 2 is a graph of the relationship between output voltage and time when implementing the coulometric method and the local coulometric method according to the invention, respectively;

[0040] Figure 3 is a schematic representation of the linear relationship between BOM value and GGA standard solution concentration when implementing the coulometric method and the local coulometric method according to the invention, respectively; BE2025 / 5607 7

[0041] Figure 4 is a bar chart of the relationship between coulom efficiency and GGA standard solution concentration when implementing the coulometric method and the local coulometric method according to the invention. SPECIFIC EMBODIMENTS 5

[0042] The invention is explained in detail below in combination with Figures 1 through 4 and concrete embodiments.

[0043] A dynamic determination of cut-off / measurement points for the coulometric method, in which, by means of real-time monitoring of the change in the physical quantity to be measured, the point with a maximum absolute change of 10 is chosen as the data collection cut-off;The physical quantity to be measured is a voltage signal or an intermediate parameter calculated from the voltage signal, where the intermediate parameters include current or charge; the physical quantity to be measured is the output voltage of the electrochemical reaction system. 15

[0044] A method for the determination of biodegradable organic substances in water based on dynamic cut-off, using a bioelectrochemical system for the local coulometric method:

[0045] (a) Construction of the bioelectrochemical reaction system, as shown in Figure 1. The reaction system comprises an anode chamber, a cathode chamber, an exchange membrane separating the anode chamber and the cathode chamber; the anode chamber is equipped with a first electrode as an anode, the cathode chamber with a second electrode as a cathode; the first and second electrodes are connected to an external resistor and a voltage measuring device.

[0046] The exchange membrane is a proton exchange membrane. BE2025 / 5607 8 The second electrode is an air cathode consisting of a carbon cloth,where the carbon cloth comprises a diffusion layer and a Pt / C catalytic layer. The external resistance is between 800 and 1200 Ω.

[0047] (b) Microbial activation: inoculate the anode chamber with electricity-producing microbial populations and activate the biofilm under constant temperature.

[0048] The composition of the anode fluid per liter contains: glucose 0.15g, glutamic acid 0.15g; KCl 0.30g, NH4Cl 0.30g; NaH2PO4 2H2O 5.08g, Na2HPO4 12H2O 20.85g; trace mineral solution 12.5ml, vitamin solution 5ml; the rest is ultrapure water.

[0049] The composition of the cathode fluid per liter contains: NaH2PO4 2H2O 3.1g, Na2HPO4 12H2O 10.1g, supplemented with ultrapure water. The constant temperature is 28±3°C.

[0050] (c) Dynamic detection and calculation:

[0051] Record continuous time series data of the output voltage with the voltage recorder;

[0052] Choose the point of maximum absolute decay rate of the output voltage as data collection cutoff.

[0053] Coulometric gain(Q1) according to equation(1): Q=∫ () (1)20

[0054] Where: E cell is the output voltage, R x t is the value of the external resistance;

[0055] Calculated oxygen consumption equivalent of the anode fluid (BOMQ1) according to equation (2): BOM × (2)25

[0056] Where: V is the effective volume of the anode electrolyte, F is the Faraday constant.

[0057] Data were collected at a rate of one measurement of the output voltage every 5 minutes. BE2025 / 5607 9

[0058] As shown in Figure 2, the test used GGA standard solutions of different concentrations as per equation. The results show that the response time of the local coulometric yield (T1) is shorter than that of the conventional coulometric yield (T2). As shown in Table 1 with comparative test results of five different GGA concentrations, it is clear that compared to the traditional coulometric method, the local coulometric method provides a measured content of biodegradable organic matter that is closer to the theoretically calculated value.is located, while the required test time is significantly reduced. For example, at a 10 GGA concentration of 37.5 mg / L, the response time of the local coulometric yield was only 0.99 hours, or only 12% of the time required by the conventional coulometric method. As shown in Figure 3, it appears that, compared with the conventional coulometric method (BOMQ shown above), the local coulometric method obtained by the new 15 cut-off method (L-BOMQ shown below) shows a better linear correlation between the calculated BOM value and the concentration of the GGA standard solution. Within the concentration range of 37.5–375 mg / L of the samples examined, the linear equation was determined to be sy = 1.16 x– for the 20 coulometric method, based on the data in the comparative test table. 3.0251with correlation coefficient R=0.9958; while for the local coulometric method according to the invention the equation y=1.11x–32.85 was found with correlation coefficient R=0.9992. It is clear that the results of the local coulometric method are better25exhibit linearity. The test results are more scientific, more rational and accurate, and—most importantly—offer new insights and directions for the scientific control of water pollution. BE2025 / 5607 10 Table 1 of comparative test results GGA Concentration (mgL-1) Theoretical BO D5 Value (mgL-1) BOMQ (mgL-1) BOMQl (mgL-1) BOM Ql / BO MQ T(h)T1(h) T1 / T 37.550 36.68+4.15 11.9+0.47 0.32 8.29+0.54 0.99+0.18 0.12 75100 80.81±3.55 45.08±2.55 88 0.56 10.14± 0.39 2.44±0. 19 0.2 4 150200 186.67±4 .98 136.3±2. 71 0.73 21.53± 0.38 6.19±0. 84 0.2 9 225300 251.68±7 .54 213.73± 6.45 0.85 25.22± 0.29 8.92±0. 72 0.3 5 375500 432.53±1 0.01 382.97± 8.61 0.89 33.56± 0.25 18.08± 0.58 0.5 4

[0059] As shown