Cadmium concentration and water body flow velocity synchronous detection method for dispersed drain outlet

Abstract

The invention belongs to the technical field of water environment detection, and particularly relates to a heavy metal concentration and water body flow velocity synchronous detection method for a dispersed drain outlet, which is used for synchronously detecting the heavy metal cadmium concentration and the water body flow velocity. The core of the method comprises a three-electrode sensing system consisting of a working electrode coated with a tungsten oxide film, a reference electrode and a counter electrode, and is assisted by an electrochemical workstation, a peristaltic pump, a flow cell and a signal processing module. The cadmium concentration is accurately measured through the square wave anodic stripping voltammetry, the flow velocity is synchronously detected through the open circuit potentiometry, dual-function detection is achieved through integration of the square wave anodic stripping voltammetry and the open circuit potentiometry, synchronous in-situ detection of the cadmium concentration and the water body flow velocity is achieved, and errors caused by measurement position differences are effectively eliminated. The result shows that the cadmium concentration and the dissolution peak current are in a linear relationship, and the water flow velocity logarithm and the open-circuit potential are in a linear relationship. The method designed by the invention is suitable for scattered and small sewage draining exit scenes, and effectively solves the problems of time consumption and equipment redundancy of traditional step-by-step detection. In an actual water sample test, the cadmium recovery rate is 80%-120%, the flow velocity measurement RSD is smaller than or equal to 5.0%, high reproducibility, stability and anti-interference performance are achieved, technical support is provided for real-time online evaluation of the total heavy metal emission amount, and the method has remarkable environmental monitoring application potential.

Description

Technical Field

[0001] This invention belongs to the technical field of water environment monitoring, and particularly relates to a method for simultaneously detecting heavy metal concentration and water flow velocity at decentralized sewage outlets. Background Technology

[0002] With rapid industrialization and urbanization, heavy metal pollution has become a key focus of environmental regulation due to its high toxicity, persistent degradation, and bioaccumulation. Cadmium, in particular, is a typical toxic heavy metal. Especially in some urban and industrial areas, the numerous and widely distributed small-scale sewage outlets are difficult to monitor effectively, making their pollutant emissions a major challenge for water environment management. Accurate assessment of cadmium's total emissions, as a typical toxic heavy metal, is crucial for water environment protection. Simultaneous monitoring of water concentration and flow rate is key to accurately capturing the dynamics of cadmium ion pollution and avoiding misjudgments.

[0003] Simultaneous monitoring of water concentration and flow velocity essentially reflects a dynamic monitoring approach. Water concentration reflects the amount of cadmium ions present, while flow velocity determines their diffusion rate and residence time: at high flow rates, pollutants diffuse over a wide area, but the concentration per unit volume may decrease; at slow flow rates, pollutants tend to accumulate in localized areas, increasing the risk of elevated concentrations. By simultaneously monitoring both, not only can the flux of cadmium ions be calculated, but also, combined with hydrological models, the pollution diffusion pathways and impact range can be predicted.

[0004] In existing technologies, the detection of cadmium concentration and water flow velocity typically employs separate sensors, leading to cumbersome operation, high costs, and difficulty in achieving simultaneous monitoring. While electrochemical methods offer advantages in portability and high sensitivity, their simultaneous application in cadmium detection and water flow velocity measurement remains a technological bottleneck. For example, while square-wave anodic stripping voltammetry is suitable for trace heavy metal detection, it requires optimization with specific electrode materials; and flow velocity measurement often relies on complex optical or mechanical sensors, making it difficult to integrate with electrochemical systems. For aquatic environments with small-scale sewage outlets, there is an urgent need for a method that can simultaneously, on-site, and pollution-free detect heavy metal concentration and water flow velocity to address the technical challenges of total discharge assessment.

[0005] Therefore, addressing the shortcomings of existing technologies, this patent presents a method for simultaneously detecting cadmium concentration and water flow velocity at decentralized sewage outlets. By electrochemically oxidizing a tungsten electrode and utilizing the deprotonation properties of the hydrated tungsten oxide layer, flow velocity detection is achieved simultaneously. This technological approach not only solves the problem of the limited functionality of traditional electrochemical sensors but also, through material optimization and innovative detection methods, achieves simultaneous and high-precision measurement of cadmium ion concentration and water flow velocity, providing a new approach for assessing the total amount of water pollutants discharged from small sewage outlets. It enables on-site, pollution-free, simultaneous, and highly sensitive hydrological and water quality monitoring. Summary of the Invention

[0006] This invention addresses the challenge of cadmium pollution detection at dispersed sewage outlets by providing a simultaneous detection method. This method solves the problems of traditional detection methods, which require separate measurements of heavy metal concentration and water flow velocity, and involve complex and inconvenient equipment. The sensor, based on a tungsten oxide thin-film electrode, simultaneously and accurately detects the concentration and flow velocity of divalent cadmium in water, providing a reliable means for real-time assessment of total cadmium emissions. Its core lies in significantly enhancing the adsorption capacity of cadmium ions on the tungsten electrode surface through electrochemical oxidation treatment; combining this with square-wave anodic stripping voltammetry for precise determination of divalent chromium concentration; and utilizing open-circuit potential method to capture changes in flow potential to calculate flow velocity. No additional reagents are required, secondary pollution is avoided, and the method combines high sensitivity with portability, making it suitable for complex environments.

[0007] The problem to be solved by this invention is achieved through the following techniques:

[0008] This invention provides a method for simultaneous detection of cadmium concentration and flow rate at decentralized sewage outlets, wherein the manufacturing process of the tungsten oxide working electrode of the sensor includes the following steps;

[0009] Step 1: Pre-treatment of tungsten oxide electrode preparation. First, polish the tungsten metal electrode on sandpaper, then place the electrode on a polishing cloth with alumina particles and polish until smooth and unobstructed, then ultrasonically treat it in ultrapure water.

[0010] In the sanding process, the sandpaper grit is 1000-1500 grit, and the sanding path is a figure-eight sanding motion.

[0011] The alumina polishing process uses alumina particles of 0.3–0.8 μmol / L.

[0012] The ultrasound duration is 20–40 seconds.

[0013] Step 2: Oxidize the working electrode. A three-electrode system is formed with a pure tungsten electrode as the working electrode, a platinum wire electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. Oxidation is performed by cyclic voltammetry scan in H2SO4 solution. After electrochemical oxidation treatment, the electrode is continuously immersed in H2SO4 solution.

[0014] The concentration of the H2SO4 solution is 0.05–0.3 mol / L, preferably 0.08–0.15 mol / L;

[0015] The scanning range of the cyclic voltammetry oxidation is 0.5–2.5 V, preferably 1.0–2.0 V; the scanning rate is 0.01–0.1 V / s, preferably 0.02–0.05 V / s; and the number of cycles is 10–50, preferably 15–25.

[0016] The soaking time for the post-oxidation treatment is 6h to 24h, preferably 10h to 14h.

[0017] Step 3: Activate the electrode. After soaking in H2SO4 solution, remove the electrode and wash it with deionized water. Then place it in mixed phosphate buffer solution to activate the electrode surface.

[0018] The pH range of the mixed phosphate buffer solution is 6.5–7.2, preferably 6.8–7.0, and the buffer concentration is 0.01–0.1 mol / L, preferably 0.02–0.05 mol / L.

[0019] This invention provides a method for simultaneously detecting cadmium concentration and water flow velocity at decentralized sewage outlets. It utilizes square wave anodic stripping voltammetry and open-circuit potential method for simultaneous detection. The square wave anodic stripping voltammetry is used to detect divalent chromium concentration. The specific process includes the following:

[0020] The enrichment process uses the current-time curve method, in which the working electrode is placed in an electrolytic cell containing divalent cadmium and a constant negative potential is applied.

[0021] During the enrichment process, a magnetic stirrer is used to stir the mixture, thereby improving the enrichment efficiency.

[0022] Once the enrichment reaches the predetermined time, the negative potential is stopped, and the electrode potential is changed to scan to the positive potential region, generating an anodic dissolution peak.

[0023] By measuring the peak current of the anodic dissolution peak, and based on the linear relationship between the peak current and the concentration of divalent cadmium, a quantitative analysis of the concentration of divalent cadmium can be achieved.

[0024] Furthermore, the open-circuit potential method is used to detect water flow velocity. It measures the potential difference between the electrode and the solution without an external current. The specific process includes the following:

[0025] By connecting a peristaltic pump to a flow cell, the flow rate of the liquid in the flow cell can be adjusted by changing the speed of the peristaltic pump.

[0026] By simulating the electrode's response to potential under different flow velocities, the velocity measurement performance of the electrode under flow conditions is analyzed, providing a basis for the accurate measurement of water flow velocity.

[0027] Furthermore, under optimal experimental conditions, divalent cadmium and water flow velocity were detected, and the relationship between the peak dissolution current and divalent cadmium, as well as the relationship between the open-circuit voltage and water flow velocity, were analyzed. Based on this, a method for detecting divalent cadmium concentration and water flow velocity was established.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention enables simultaneous in-situ detection of divalent cadmium concentration and water flow velocity, effectively eliminating errors introduced by differences in measurement location;

[0030] This invention utilizes tungsten oxide thin-film electrodes, which possess both high sensitivity and anti-contamination properties, thus avoiding secondary pollution;

[0031] This invention, based on the flow potential, eliminates the need for complex mechanical structures, making it suitable for portable applications.

[0032] This invention achieves a low detection limit and a low flow rate range, meeting practical detection needs;

[0033] The present invention achieves an actual water sample recovery rate of 80% to 120% and a flow velocity measurement RSD of ≤5%, making it valuable for engineering applications. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the device system for detecting Cd(II) and flow rate in this invention;

[0035] Figure 2 This is a schematic diagram of the electrochemical detection principle of heavy metals in this invention;

[0036] Figure 3 This is a schematic diagram of the electrochemical flow rate detection principle in this invention;

[0037] Figure 4 This is a curve for detecting different concentrations of Cd(II) in this invention, as well as a linear relationship between peak current value and Cd(II);

[0038] Figure 5 These are curves for detecting different flow rates in this invention, as well as a linear relationship between open-circuit voltage and the logarithm of flow rate;

[0039] Figure 6 This is an actual water sample detection diagram of the dual-function sensor in this invention.

[0040] Table 1 shows the results of detecting divalent cadmium in actual water samples in this invention.

[0041] Table 2 shows the results of the actual water sample flow rate. Specific implementation steps

[0042] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0045] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0046] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0047] This invention provides a dual-function detection method for divalent chromium concentration and flow velocity in water bodies, with specific embodiments as follows:

[0048] Example 1

[0049] A sensor for simultaneously detecting cadmium concentration and flow rate at decentralized sewage outlets is used. A schematic diagram of the specific device system is shown below. Figure 1 As shown. The sensor includes a tungsten oxide working electrode, a silver-silver chloride reference electrode, and a platinum wire counter electrode, which together form a three-electrode system. The tungsten oxide electrode undergoes electrochemical oxidation treatment to form a porous thin film structure. The specific fabrication process includes the following steps:

[0050] Step 1: Pre-treatment of tungsten oxide electrode preparation. First, the tungsten metal electrode is polished by drawing an "8" on 1200-grit sandpaper. Then, the electrode is placed on a polishing cloth with 0.5 μmol / L alumina particles and polished until smooth and unobstructed. After that, it is ultrasonically treated in ultrapure water for 30 seconds.

[0051] Step 2: Oxidize the working electrode. A three-electrode system is formed using a pure tungsten electrode as the working electrode, a platinum wire electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. Cyclic voltammetry is performed in a 0.1 mol / L H2SO4 solution with a scanning voltage range of 1.0 V-2.0 V and a scanning rate of 0.02 V / s for a total of 20 cycles. After electrochemical oxidation, the electrode is immersed in a 0.1 mol / L H2SO4 solution for 12 hours.

[0052] Step 3: Activate the electrode. After soaking in 0.1 mol / L H2SO4 solution for 12 hours, remove the electrode and wash it with deionized water. Then place it in a mixed phosphate buffer solution with pH=6.86 and a concentration of 0.025 mol / L to activate the electrode surface.

[0053] The method of this invention utilizes square wave anodic stripping voltammetry and open circuit potential method to simultaneously detect divalent cadmium concentration and water flow velocity.

[0054] The principle of the anodic stripping voltammetry for detecting divalent cadmium concentration is as follows: Figure 2 As shown.

[0055] The open-circuit potential method is used to detect water flow velocity, and its principle is as follows: Figure 3 As shown.

[0056] Furthermore, under optimal experimental conditions, divalent cadmium and water flow velocity were detected, and the relationship between the peak dissolution current and divalent cadmium, as well as the relationship between the open-circuit voltage and water flow velocity, were analyzed. Based on this, a method for detecting divalent cadmium concentration and water flow velocity was established.

[0057] To evaluate the electrochemical performance of the bifunctional sensor for divalent cadmium, a square wave stripping voltammetry experiment was performed in 0.1 mol / L PBS solution at pH 4.8 under optimized conditions.

[0058] Figure 4 The illustration shows square-wave dissolution voltammetry curves of divalent cadmium at different concentrations. It is clearly visible from the graph that the dissolution peak of divalent cadmium stably appears around -0.8V, and the peak current exhibits a regular increasing trend with increasing concentration of divalent cadmium in the solution. This indicates that the sensor can effectively detect divalent cadmium in a concentration range of 1 μmol / L to 20 μmol / L.

[0059] Further analysis Figure 4 The data shows that the concentration of divalent cadmium does indeed exhibit a good linear relationship with its dissolution peak current. The linear regression equation obtained through fitting is:

[0060] I = -9.088C - 51.329

[0061] Where: I is the peak current value, μA; C is the concentration of divalent cadmium, μmol / L. Experimental data show a significant linear relationship between concentration and peak current value, with a linear correlation coefficient R0. 2 =0.9796. Furthermore, to determine the sensor's detection limit, a three-times signal-to-noise ratio method was used to calculate the detection limit for divalent cadmium, which was found to be 5 × 10⁻⁶. -7 μmol / L.

[0062] In the determination of water flow velocity, the optimal conditions of pH 4.8 and 0.1 mol / L PBS buffer solution were selected as the electrolyte solution.

[0063] The experimental setup consisted of a specially designed flow cell to simulate the flow state of water at different flow velocities and to investigate the response characteristics of a dual-function sensor to water flow velocity. During the experiment, the sensor was placed in the flow cell, and the water flow velocity was set. At each flow velocity, the open-circuit voltage was measured using a tungsten oxide thin-film electrode. Once the flow velocity reached a steady state, the sensor's open-circuit voltage reading also tended to stabilize. To ensure data reliability, multiple stable measurement points were selected for each flow velocity condition, and their average value was taken as the final experimental data. Finally, a linear fit was performed. Figure 5 As shown.

[0064] The results show that the open-circuit voltage of the tungsten oxide thin film electrode increases with the increase of water flow velocity, and the open-circuit voltage can quickly reach a stable state at the same flow velocity. Figure 5 As shown in the illustration, the logarithm of the flow velocity exhibits a good linear relationship with its open-circuit potential. The regression equation obtained through linear fitting is:

[0065] V = 1.39ln(v) - 121.87

[0066] Where: V is the open-circuit voltage, mV; v is the water flow velocity, mm / s. The linear correlation coefficient R0 2 =0.9828, indicating a good linear relationship between the logarithm of the flow velocity and the open-circuit potential value. This demonstrates that under the same optimized conditions, the sensor can not only effectively detect cadmium ions but also accurately detect water flow velocity. By detecting cadmium ion concentration on-site and combining it with simultaneously measured water flow velocity data, a more accurate estimation of the total heavy metal content in a specific area can be made.

[0067] Example 2

[0068] The actual samples were natural water samples from an inland river in Hangzhou. The sampling method was followed according to the Technical Specifications for Groundwater Environmental Monitoring, and simultaneous detection experiments were conducted on the concentration of divalent cadmium and the water flow velocity.

[0069] The collected water sample was mixed with PBS buffer solution at a 1:1 volume ratio, and the pH of the mixture was adjusted to 4.8 to suit the optimal operating conditions of the sensor.

[0070] Since the concentration of divalent chromium in natural water samples is low and difficult to detect, a mother liquor containing divalent cadmium was added to the treated sample to achieve a concentration of 5.0 μmol / L, in order to simulate the divalent cadmium content in actual polluted water bodies.

[0071] The prepared solution was placed into an electrochemical detection system with a flow rate of 5.0 mm / s. The results obtained from the actual water sample were compared with the values ​​after adding heavy metal ions. The measured water flow rate was also compared with the results of the peristaltic pump flow rate. The results are as follows: Figure 6 As shown.

[0072] The recovery rate of divalent cadmium concentration and the measured values ​​of water flow velocity are shown in Tables 1 and 2. The recovery rate is between 80% and 120%, indicating that its performance is excellent and meets the requirements of practical applications. At the same time, the RSD of the water flow velocity measurement does not exceed 5.0%, indicating that this dual-function sensor has good application potential in actual water sample detection.

[0073] Table 1. Results of Detection of Divalent Cadmium in Actual Water Samples:

[0074] Table 2 shows the results of actual water sample flow velocity detection:

[0075] This invention provides a method for simultaneously detecting cadmium concentration and water flow velocity at dispersed sewage outlets. This method not only overcomes the limitations of traditional methods, the inconvenience of carrying detection instruments, and the high cost of detection, but also effectively addresses the challenge of detecting the total amount of pollution discharged from dispersed and small sewage outlets.

[0076] The embodiments listed above are typical and preferred embodiments of the present invention, and are only used to describe and explain the technical solutions of the present invention in detail so as to facilitate the reader's understanding. They are not intended to limit the scope of protection or application of the present invention.

Claims

1. A method for simultaneously detecting cadmium concentration and water flow velocity at decentralized sewage outlets, characterized in that, Includes the following: A tungsten oxide working electrode is prepared, wherein a porous tungsten oxide thin film structure is formed on the surface of a metallic tungsten electrode by electrochemical oxidation treatment. A square wave anodic stripping voltammetry method was used to enrich and dissolve divalent cadmium ions in water. The concentration of divalent cadmium was quantitatively detected by detecting the peak current of the stripping peak and the linear relationship between the peak current and the concentration of divalent cadmium. Simultaneously, the open-circuit potential method is used to measure the potential difference between the tungsten oxide working electrode and the solution under the condition of no external current, and the relationship between the potential difference and the water flow velocity is analyzed to achieve synchronous detection of the water flow velocity. Based on synchronously obtained data on divalent cadmium concentration and water flow velocity, the total amount of cadmium pollutants discharged into the water body is assessed.

2. The method for synchronously detecting cadmium concentration and water flow velocity at decentralized sewage outlets as described in claim 1, characterized in that, The method for preparing the tungsten oxide working electrode includes: The tungsten electrode was pretreated by sanding, polishing with alumina particles, and ultrasonic cleaning with ultrapure water. The pretreated tungsten electrode was used as the working electrode and cyclic voltammetric scanning oxidation was performed in sulfuric acid solution to form a tungsten oxide film. The electrode was then immersed in sulfuric acid solution for post-treatment. After soaking, the electrodes were cleaned and then activated in a mixed phosphate buffer solution.

3. The method for preparing the tungsten oxide working electrode as described in claim 2, characterized in that, In the sandpaper polishing process, the sandpaper grit is 1000-1500 grit, and the polishing trajectory is a figure-eight shape; the concentration of the alumina particles is 0.3-0.8 μmol / L; and the ultrasonic cleaning time is 20-40 s.

4. The method for preparing the tungsten oxide working electrode as described in claim 2, characterized in that, The conditions for the cyclic voltammetric oxidation are as follows: The concentration of the sulfuric acid solution is 0.05–0.3 mol / L; The scanning voltage range is 0.5–2.5V, preferably 1.0–2.0V; The scan rate is 0.01–0.1 V / s, preferably 0.02–0.05 V / s; The number of cycles is 10 to 50, preferably 15 to 25. The immersion time of the oxidized electrode in sulfuric acid solution is 6 to 24 hours, preferably 10 to 14 hours.

5. The method for preparing a tungsten oxide working electrode as described in claim 2, characterized in that, The pH range of the mixed phosphate buffer solution used in the activation treatment is 6.5–7.2, preferably 6.8–7.0, and the concentration is 0.01–0.1 mol / L, preferably 0.02–0.05 mol / L.

6. The method for synchronously detecting cadmium concentration and water flow velocity at decentralized sewage outlets as described in claim 1, characterized in that, The specific process of enriching and dissolving divalent cadmium ions in water using the square wave anodic stripping voltammetry method includes: The tungsten oxide working electrode was placed in an electrolytic cell containing divalent cadmium and enriched by applying a constant negative potential. During the process, the electrode was stirred with a magnetic stirrer to improve the enrichment efficiency. After enrichment, the applied potential is stopped and the scan is performed to the positive potential region, generating an anodic dissolution peak; The peak current of the dissolution peak was measured, and quantitative analysis was performed based on the linear relationship between the peak current and the concentration of divalent cadmium.

7. The method for simultaneous detection of cadmium concentration and water flow velocity at decentralized sewage outlets as described in claim 1, characterized in that, The process of detecting water flow velocity using the open-circuit potential method includes: The sensor is placed in a flow cell, and the liquid flow rate is adjusted by a peristaltic pump. The open-circuit potential of the tungsten oxide working electrode was measured under conditions of no applied current. The linear relationship between open circuit potential and the logarithm of water flow velocity was analyzed to achieve quantitative detection of flow velocity.

8. The method according to any one of claims 1 to 8, characterized in that, The tungsten oxide working electrode has the function of simultaneous detection of cadmium ion adsorption and flow potential response during the detection process, realizing synchronous, reagent-free, and pollution-free detection of heavy metal concentration and water flow rate.

9. The method according to any one of claims 1 to 9, characterized in that, The method is suitable for low-flow-rate environments, with a flow rate detection range covering 1–10 mm / s and a cadmium concentration detection limit of 5 × 10⁻⁶. -7 μmol / L.

10. A synchronous detection system for implementing the method according to any one of claims 1 to 10, characterized in that, include: A three-electrode system consisting of a tungsten oxide working electrode, a platinum wire counter electrode, and a silver-silver chloride or saturated calomel reference electrode; An electrochemical workstation is used for signal acquisition and control in performing square wave anodic stripping voltammetry and open circuit potential methods. A fluid control system consisting of a flow-through tank and a peristaltic pump is used to regulate and simulate water flow velocity; The data processing module is used to calculate the concentration of divalent cadmium and the water flow velocity based on the peak current and open circuit potential, and output the total pollutant discharge assessment results.

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