Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aza Aoba, Aramaki, Aoba-Ku, Sendai 980-8579, Japan.
Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aza Aoba, Aramaki, Aoba-Ku, Sendai 980-8579, Japan.
Ultrason Sonochem. 2019 Apr;52:318-325. doi: 10.1016/j.ultsonch.2018.12.003. Epub 2018 Dec 4.
A novel wastewater treatment process, acoustic cavitation assisted plasma (ACAP) is proposed in this study aiming at expanding the treatable range of water pollutants due to a synergetic effect of ultrasound irradiation and high voltage plasma discharge. In this process, the role of acoustic cavitation is not only to provide generation of chemically active OH radicals, as for example in conventional ultrasonic wastewater treatment techniques, but also to ensure conditions for stable plasma generation in wastewater and, thus, to extend the treatable range of water pollutants. Rhodamine B (RhB) was used as a model pollutant in experiments examining effects of ultrasound amplitude, RhB initial concentration, output voltage, solution pH and electrical conductivity on the RhB degradation efficiency. The results revealed that the ultrasound-assisted plasma generation requires lower output voltages and allows to increase the acceptable range of electrical conductivity of treatable solutions up to 1000 μS/cm, that is about 24 times higher than in the case of conventional plasma discharge treatment. The alkaline and acid medium were found to be favorable for higher degradation efficiency. Additional measurements and results of recent investigations concerning underwater plasma showed that microbubbles presented in cavitation zone could serve as "bridges" making the pulse discharge propagation between the electrodes easier than in the conventional case. Besides, acoustic cavitation assists a faster transition of plasma discharge from ineffective streamer type to more effective spark type that further contributes to the improvement of the treatment performance.
本研究提出了一种新型的废水处理工艺，即声空化辅助等离子体（ACAP），旨在通过超声辐射和高压等离子体放电的协同作用，扩大水污染物的处理范围。在该工艺中，声空化的作用不仅在于提供化学活性 OH 自由基的生成，如在传统的超声废水处理技术中，而且还在于确保在废水中稳定产生等离子体的条件，从而扩展水污染物的处理范围。实验中以罗丹明 B（RhB）为模型污染物，考察了超声幅度、RhB 初始浓度、输出电压、溶液 pH 值和电导率对 RhB 降解效率的影响。结果表明，超声辅助等离子体的产生需要较低的输出电压，并允许将可处理溶液的电导率接受范围提高到 1000 μS/cm，这大约是传统等离子体放电处理的 24 倍。研究发现，碱性和酸性介质有利于更高的降解效率。最近有关水下等离子体的附加测量和研究结果表明，在空化区存在的微气泡可以作为“桥梁”，使脉冲放电在电极之间的传播比在常规情况下更容易。此外，声空化有助于更快地将等离子体放电从无效的流光型转变为更有效的火花型，从而进一步提高处理性能。
