Application Cases

Experiment Name: Application of Power Amplifier in Research on Electrokinetic Migration of Municipal Sludge

Research Direction: Resource and Environmental Science

Test Objective:
In sludge treatment and disposal, resource recovery and utilization are key. When finalizing sludge treatment and disposal technologies, local governments should prioritize technologies related to sludge resource utilization to extend the lifespan of primary energy sources. Urban sludge, as the main component of "urban mines," holds significant development potential regarding its heavy metal resources. Under increasingly stringent environmental regulations, environmental protection investments will inevitably continue to rise. The effective recovery and recycling of heavy metal elements from excess sludge can potentially provide economic compensation for the high costs of sludge disposal. Therefore, it is of great practical significance to study effective ways to properly dispose of, treat, and fully utilize sludge.

To address these issues, this experiment designed a novel electrokinetic removal and recovery device for sludge. It replaced the conventional direct current (DC) power supply with a square wave power source having adjustable frequency and amplitude. The device utilizes the electrical double-layer structure on the electrode surface, combined with a replaceable self-assembled carbon felt electrode modified with a self-doped polyaniline/carbon powder/Nafion mixture that exhibits excellent Pb²⁺ selective adsorption. This setup targets and induces the capture of lead ions on the cathode surface, enabling the one-step removal and recovery of Pb from municipal sludge, aiming for the selective removal and targeted recovery of heavy metals from contaminated urban sludge.

Testing Equipment: ATA-3040 power amplifier, power signal generator, oscilloscope, electric stirrer, magnetic stirrer, constant temperature oscillator, etc.

Experimental Procedure:

Figure: Schematic Diagram of the Reaction Device

The design of the electrokinetic remediation device is crucial for improving the removal efficiency of heavy metals from the treated sludge and achieving resource utilization. Considering the advantages and disadvantages of existing typical sludge electrokinetic remediation devices, to achieve the one-step migration, capture, and release of heavy metals from sludge, a novel electrokinetic remediation device was constructed in this experiment, as shown in the figure above.

Based on the centripetal nature of the electric field in a circular configuration, a new sludge electrokinetic remediation device was designed. This device builds upon traditional fourth-generation devices and consists of a power supply system, a reaction device system, and a pH control system, as shown in Figure a. The pH control system comprises an automatic titrator, a magnetic stirrer, and a peristaltic pump. The power supply system consists of a function signal generator, a power amplifier, and a high-precision oscilloscope. Traditional electrolysis devices mostly use DC regulated power supplies. In this experiment, to output a square wave power source with specific frequency and amplitude, a function signal generator and a power amplifier were used as the power supply, equipped with a high-precision oscilloscope to verify the accuracy of the output waveform. The reaction device system consists of a plexiglass reactor, a cathode, an anode, a magnetic stirrer, and an electric stirrer. The structure of the plexiglass reactor is shown in Figure b. The device comprises an outer cylindrical wall and an inner cylindrical column from the outside to the inside. The outer wall is a hollow cylinder open at the top. The inner column is a hollow cylinder open at the top with a perforated (lattice) wall. The two parts are fixed by fitting the depression at the bottom of the inner column with the raised annular ring at the bottom of the outer wall, allowing for easy disassembly and assembly. Furthermore, to prevent leakage of the electrolyte from the cathode chamber, 316 stainless steel locks are used to secure the cation exchange membrane on the top and bottom of the inner column. To prevent sludge deposition in the anode zone during electrolysis and maintain the homogeneity of the solute in the cathode zone, the reaction device system is also equipped with an electric stirrer and a magnetic stirrer to slowly stir the sludge in the anode zone and the electrolyte in the cathode zone, respectively, during the reaction process. A ruthenium-platinum-titanium alloy was used as the anode material, formed into a cylinder with an outer diameter equal to the inner diameter of the outer wall, and placed tightly against the inner wall of the outer cylinder. The replaceable self-assembled carbon felt electrode modified with the self-doped polyaniline/carbon powder/Nafion mixture served as the cathode, suspended in the center of the inner column. After energizing, the direction of the electric field inside the plexiglass reactor is shown in Figure c.

The power supply system of the device was adjusted to output a square wave with an amplitude of -9 V to 0 V (using the cathode as an example). Six sets of experiments (EF-1, EF-2, EF-3, EF-4, EF-5, EF-6) were set up, with corresponding output square wave frequencies of 100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, and 600 Hz, respectively. 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 of the cathode chamber electrolyte at approximately 5.5 during operation. The components of the plexiglass reactor were assembled. 1 L of the sludge to be treated was added to the anode/sludge chamber of the reactor using a peristaltic pump. The power supply was turned on, and the system was run continuously for 36 hours. To prevent settling of the sludge in the anode chamber and maintain homogeneity of the solutes 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 using a magnetic stirrer (40 r/min) and an electric stirrer (300 r/min), respectively. After the remediation was completed, the cathode carbon felt was removed and allowed to air dry at room temperature. The deposition of heavy metal ions on the cathode surface was observed.

Experimental Results:

Figure: Removal of Heavy Metals from Sludge After Electrokinetic Treatment

As shown in the figure, the removal efficiency of different heavy metals from the sludge varied with the voltage gradient. The removal efficiency increased with higher voltage gradients. When the voltage gradient increased from 1 V/cm to 2 V/cm, the removal rate of Pb²⁺ increased from 44.67% to 64.78%. This is because a higher voltage gradient leads to a more pronounced acidification effect at the anode, causing a faster decrease in the pH of the sludge chamber. This favors the dissociation and extraction of heavy metal ions from the sludge, converting them into ionic forms that can migrate under the influence of the electric field. Additionally, the driving force on the heavy metal ions increases with the applied voltage gradient, resulting in higher removal efficiency.

Figure: Recovery Rate of Cathode Heavy Metals After Electrokinetic Treatment

As shown in the figure, the recovery rate of Pb is the highest. After removal from the sludge chamber, nearly all of the Pb was transferred to the cathode surface. This is attributed to the excellent electrochemical response between the active material and Pb. However, in addition to Pb, some Cu and Zn were also deposited on the electrode surface. This is due to the relatively high original content of Zn and Cu in the sludge and the inherent adsorption affinity of the active material for Zn and Cu.

Aigtek ATA-3040C Power Amplifier:

Figure: Specifications of the ATA-3040C Power Amplifier