Implementation of a Hyperbolic Vortex Plasma Reactor for the Removal of Micropollutants in Water

The focus of our research is to optimize plasma discharge for the degradation of micropollutants in water, which is a growing environmental concern nowadays. We discovered that by optimizing plasma discharge and carefully dosing cationic surfactants, we can reach nearly 100%PFAS degradation using only moderate energy input. Plasma treatment is typically an energy-intensive process.

However, by applying plasma pulses, energy consumption can be significantly reduced while improving performance. And in this study, we demonstrate how to achieve this optimization. After setting up the hyperbolic vortex plasma, use the electrical circuit designed for the direct current arc discharge setup.

Connect the positive and negative high voltage outputs from the bridge rectifier to the electrodes positioned above the surface of the water vortex. Plug the variac into a 230 volt alternating current power outlet and switch off the red safety switch to enable high voltage. Using the variac, gradually increase the voltage from zero to 250 volts to ignite the plasma discharge.

Next, use the electrical circuit configured for alternating current arc discharge. Then connect both high voltage outputs to the electrodes located above the surface of the water vortex. After connecting the variac and disengaging the safety switches shown earlier, gradually increase the voltage from zero volts to 250 volts to ignite the plasma discharge.

Next, to perform a glow discharge in a helium atmosphere, use the electrical circuit shown here. Connect the high voltage outputs of the electrical circuit to the electrodes positioned above the surface of the water vortex. Once the variac is connected and the safety switch is disengaged, open the gas valve to introduce helium at the desired flow rate.

Then using the variac, slowly increase the voltage to ignite the plasma discharge until electrical breakdown occurs between the electrodes and the plasma shifts from glow discharge to arc discharge. Next, to initiate the bipolar flashover pulse discharge, use the electrical circuit as shown in the schematic, connect the high voltage outputs to the electrodes, variac to a 230 volt alternating current power outlet and disengage the safety switch. Then gradually increase the voltage from zero to 250 volts to ignite the plasma discharge.

For monopolar pulsed streamer discharges, use the circuit shown in the schematic for positive or negative discharge as needed. Connect the opposite terminal to a visible spark gap and ground electrode. Attach the rest of the high voltage outputs to the electrodes situated above the water vortex surface.

Then open the gas valve and adjust the compressed airflow to 0.5 to one atmosphere to purge the spark gap. After connecting the variac and engaging the safety switch, ignite the plasma discharge as shown earlier. To terminate the experiment, reduce the variac voltage, switch off the power supply, and engage the safety switch.

Then close all gas valves for helium and compressed air if they were used during the experiment. Using a grounding stick, touch all metallic components to verify that they're properly grounded. Among the three discharges, flashover generated the highest concentrations of hydrogen peroxide at approximately 450 milligrams per liter, nitrite at around 90 milligrams per liter, and nitrate at about 340 milligrams per liter.

The flashover discharge caused the most pronounced drop in pH, reducing it from approximately 5.5 to 2.3. Electrical conductivity was highest in the flashover treated samples, reaching about 2, 300 microsiemens per centimeter. Oxidation-reduction potential increased most significantly in the flashover discharge, reaching approximately 600 millivolts.

Flashover discharge achieved the fastest and most complete PFOS degradation for both initial concentrations, reaching nearly 100%conversion by 60 minutes, outperforming the positive and negative discharges. In the PFAS matrix, without surfactant, long-chain compounds like PFDA, PFNA, PFOS, and PFOA exhibited degradation above 90%after 75 minutes. In contrast, short chain species, such as PFBS and PFBA, remained largely ungraded or increased in concentration due to byproduct formation.

With surfactant addition, all long-chain PFAS compounds were degraded above 95%and degradation of short-chain compounds, like PFBA, improved from minus 19%to approximately 53%and PFBS from 22%to about 95%The concentration of PFHxA started decreasing after 20 minutes and PFPeA dropped after 30 minutes of treatment with surfactant dosing, indicating progressive breakdown of PFAS byproducts.