Combined effect of acoustic cavitation and pulsed discharge plasma on wastewater treatment efficiency in a circulating reactor: A case study of Rhodamine B.

• Combination of acoustic cavitation and plasma results in an enhancement of degradation efficiency. • Acoustic cavitation assisted plasma can be created in wide ranges of pH and electrical conductivity. • Higher flow rates of circulating solutions cause a further enhancement in the degradation efficiency. • The process proposed has the potential to extend the application area of underwater plasma. The present study investigates the wastewater treatment performance of an acoustic cavitation assisted plasma (ACAP) process in a circulating reactor using Rhodamine B (RhB) as a model water pollution. The concept of this process was proposed by the authors recently for a batch type rector. The measurements revealed that combining the ultrasound irradiation with pulsed discharge plasma allows the RhB degradation efficiency to be drastically increased as compared with the plasma-alone case. This effect is especially significant at higher values of solution electrical conductivity examined in a range of 20 ~ 400 μS/cm. Acidic conditions and larger flow rates of solution were found to be favorable for the degradation efficiency. The effect of flow rate was also analyzed through numerical simulation. The results indicated that the mass transfer of RhB to the plasma-cavitation zone is one of the controlling parameters influencing the degradation performance. Behavior of bubbles and pulse discharge frequency were examined using a high-speed video camera. Relatively large bubbles were found to favor the plasma pulse generation and propagation when move near the high-voltage electrode. On the whole, the results of this study suggest that the ACAP process has the potential to synergistically extend the application area of underwater plasma in both research and industry. [ABSTRACT FROM AUTHOR]