Ultrasound-assisted plasma: a novel technique for inactivation of aquatic microorganisms.

Nonthermal plasma and ultrasound are two techniques capable of microorganism inactivation in a liquid phase. However, the interaction between the two techniques is not yet understood. In this study, an ultrasound-assisted plasma (USaP) technique by combining the two means is proposed. A lab-scale USaP system was designed and experimentally tested. The inactivation experiments were conducted with various conditions of two types of electrode layout (submerged and hybrid reactors), aeration or not, and two microorganism species E. coli and yeast. For a 30-min treatment, the inactivation efficiencies with no aeration were 2-, 2-, and 6-log reductions for ultrasound, plasma, and ultrasound-assisted plasma, respectively; and with aeration were 2-, 6-, and 6-log reductions, respectively. The aeration greatly enhanced the inactivation efficiency for the plasma but not for the ultrasound or the ultrasound-assisted plasma. The influences of electrode layout and microorganism species were insignificant on the inactivation efficiency. On the other hand, for a submerged reactor without aeration, the inactivation efficiency achieved with ultrasound-assisted plasma (eta(USaP)) was not only greater than eta(ultasound) or eta(plasma), but also greater than the summation of eta(ultrasound and eta(plasma). Namely, a synergistic effect of ultrasound-plasma combination on the inactivation was observed. No such synergistic effect was observed in a hybrid reactor or in aeration cases. The synergism is speculatively a virtue of the ultrasonic-generated bubbles that easily induce plasma discharges, and thus enhance microorganism inactivation in water.

Removal of volatile organic compounds by single-stage and two-stage plasma catalysis systems: a review of the performance enhancement mechanisms, current status, and suitable applications.

This paper provides a comprehensive review regarding the application of plasma catalysis, the integration of nonthermal plasma and catalysis, on VOC removal. This novel technique combinesthe advantages of fast ignition/response from nonthermal plasma and high selectivity from catalysis. It has been successfully demonstrated that plasma catalysis could serve as an effective solution to the major bottlenecks encountered by nonthermal plasma, i.e., the reduction of energy consumption and unwanted/hazardous byproducts. Instead of working independently, the combination could induce extra performance enhancement mechanisms either in a single-stage or a two-stage configuration, in which the catalyst is located inside and downstream from the nonthermal plasma reactor, respectively. These mechanisms are believed to be responsible for the higher energy efficiency and better CO2 selectivity achieved with plasma catalysis. A comprehensive discussion on the performance enhancement mechanisms is provided in this review paper. Moreover, the current status of the applications of two different plasma catalysis systems on VOC abatement are also given and compared. The catalyst plays an important role in both configurations. Especially for the single-stage type, depositing an inappropriate active component on catalytic support would decrease the VOC removal efficiency instead. To date, no definite conclusion on catalyst selection forthe single-stage plasma catalysis is available. However, MnO2 seems to be the best catalyst for two-stage configuration because it could effectively decompose ozone and generate active species toward VOC destruction. On the other hand, although the single-stage plasma catalysis has been proved to be superior to the two-stage configuration, it does not mean that the former is always the best choice. Considering the typical VOC concentrations from different sources and the characteristics of different plasma catalysis systems, the single-stage and two-stage configurations are suggested to be more suitable for industrial and indoor air applications, respectively.