Application Cases

Experiment Name: Research on Electrically Enhanced Sludge Remediation Technology

Research Direction:In recent years, although wastewater becomes clearer after treatment at sewage treatment plants, the pollutants in the water are enriched and precipitated in the remaining sludge, rather than being completely eliminated. The increasing annual production of sludge is bound to become a ticking time bomb for environmental crises. Academician Hou Lian'an of the Chinese Academy of Engineering pointed out that, influenced by the "heavy water, light sludge" mindset, and constrained by regulatory loopholes, high treatment costs, and poor sales of end products, about 80% of the sludge produced by existing sewage treatment plants in China has not been properly treated. The increasing annual production of sludge, in line with the increasing treatment volumes of municipal and industrial wastewater, is bound to become a ticking time bomb for environmental crises. Currently, more than 150 components, including heavy metal salts such as Pb, Cd, Cr, Zn, and Cu, hard-to-degrade toxic substances, and persistent organic pollutants, have been confirmed to exist in sludge. If not properly treated and discharged indiscriminately, secondary pollution is highly likely to occur.

Therefore, researching reasonable ways to dispose of and fully utilize sludge is one of the urgent issues in the environmental field with significant practical significance. When using inert electrodes, applying an external electric field will cause the electrolysis of water at the electrodes. At the same time, O₂ and H⁺ are produced at the anode, while OH⁻ and H₂ are produced at the cathode. The generated gases escape into the air, while the produced hydrogen ions and hydroxide ions move towards the cathode and anode areas, respectively, under the influence of the electric field through electroosmosis, electrophoresis, and diffusion until they meet and neutralize each other, causing a pH jump.

Replacing the traditional steady-state DC electric field with a high-frequency sine wave electric field for the electrokinetic remediation experiment of copper tailings, the neutralization effect produced during the polarity alternation of the sine wave electric field can effectively consume the OH⁻ that accumulates at the cathode, preventing OH⁻ from combining with Cu²⁺ dissolved and migrated from the tailings to the cathode to form precipitates, which would otherwise hinder the reaction from continuing and reduce the removal efficiency of Cu²⁺. Studies have shown that, under the condition of controlling other factors constant, sine wave electric field remediation can increase the removal rate of Cu²⁺ by 72%. Compared with traditional continuous power supply methods, periodic power supply can significantly reduce the overall energy consumption of the device while ensuring the removal rate of the pollutant As. Ming Zhou et al. used the method of exchanging electrodes to electrically remediate Cr-contaminated soil. The study showed that exchanging electrodes can effectively reduce the focusing effect that occurs in traditional electrokinetic remediation technology, increase the current in the reaction system, and remove 91.88% of hexavalent chromium from the soil. Peng Zhang et al. used a two-dimensional cross-electric field to remediate soil near a chromium slag site, that is, a longitudinal electric field was added to the horizontal DC electric field to prevent the downward migration trend of hexavalent chromium in the medium, significantly improving the remediation efficiency of hexavalent chromium-contaminated soil.

Experiment Purpose:To achieve the migration, capture, and release of heavy metals in sludge, laying the foundation for subsequent experiments.

Testing Equipment:Signal generator, ATA-3040 power amplifier, high-precision oscilloscope, automatic titrator, magnetic stirrer, peristaltic pump, acrylic reactor, anode and cathode, magnetic stirrer, electric stirrer.

Experimental Process:To output a square wave power supply with specific frequency and amplitude, a function signal generator and power amplifier were assembled as the power source, equipped with a high-precision oscilloscope to verify the accuracy of the output waveform. The power supply output square wave frequency was controlled at 600 Hz. Three groups of experiments (three parallel experiments) were set up: EK-1, EK-2, and EK-3. According to the voltage gradients of 1 V/cm, 1.5 V/cm, and 2 V/cm, the corresponding power supply output square wave amplitude was adjusted to -4.5-0 V, -6.75-0 V, and -9-0 V (taking the cathode as an example). 100 mL of NaNO₃ (0.01 mol/L) solution was added to the cathode chamber as the electrolyte. The pH control system was adjusted to maintain the pH value of the electrolyte in the cathode chamber around 5.5 during the operation. The components of the acrylic reactor were assembled, and 1 L of the sludge to be treated was added to the anode chamber/sludge chamber of the reactor using a peristaltic pump. The power supply was connected, and continuous electrification was maintained for 36 hours. To prevent sludge sedimentation in the anode chamber and maintain the homogeneity of the solute in the cathode chamber, during the remediation process, the sludge in the anode chamber and the electrolyte in the cathode chamber were slowly stirred at room temperature at speeds of 40 r/min and 300 r/min, respectively, using a magnetic stirrer and an electric stirrer. Samples were taken at 0 h, 6 h, 12 h, 24 h, and 36 h to determine the pH value and heavy metal content of the sludge. After the remediation was completed, the cathode carbon felt was removed. To determine the amount of heavy metals recovered at the cathode, the cathode was air-dried at room temperature and then placed in 20 mL of 0.1 mol/L HNO₃ solution for 12 hours. After the deposited heavy metals on the cathode were completely dissolved, the resulting solution was filtered through a 0.45 μm filter membrane. The obtained sample was diluted by a certain factor and then analyzed by ICP-MS to determine the total amount of heavy metals in the solution. The experimental flowchart is shown in Figure 1-1.

Figure 1-1 Experimental Flowchart

Experimental Results:SEM tests on self-doped polyaniline materials showed that the obtained self-doped polyaniline materials are aggregates of porous hollow spheres and particles, characterized by low density and high specific surface area, which can achieve a larger π-conjugated structure. Adsorption performance experiments of the material on different metal ion solutions verified the material's excellent recognition performance for Pb²⁺. Further FT-IR tests indicated that the presence of -SO₃⁻, -NH₂, -N=, and N-H groups in the material shows a stronger complexation effect for Pb²⁺. Impedance tests on carbon felt electrodes showed that the addition of carbon powder increased the conductivity of the electrode. When Nafion solution was added as a binder, although the insulating nature of Nafion would hinder the transfer of electrons on the electrode surface, the presence of Nafion significantly improved the mechanical stability of the working electrode, which is beneficial for the subsequent enrichment of Pb²⁺. Cyclic voltammetry tests on carbon felt electrodes showed that after self-doped polyaniline material was loaded as an electroactive substance onto the carbon felt electrode, Pb²⁺ began to accumulate on the electrode surface and undergo redox reactions. The peak current and shape of the modified carbon felt electrode determined the optimal doping amount of Nafion solution.

Figure 1-2 Effects of Different Nafion Doping Amounts on the Electrochemical Activity of Self-Doped Polyaniline/Carbon Powder/Nafion-Modified Carbon Felt Electrode

Figure 1-3 Cyclic Voltammograms of Carbon Felt Electrode and Self-Doped Polyaniline/Carbon Powder/Nafion-Modified Carbon Felt Electrode

Power Amplifier Recommendation: ATA-3040C Power Amplifier

Figure: Performance Parameters of the ATA-3040C Power Amplifier

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