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ABSTRACT: 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.
Environmental Science and Technology 07/2009; 43(12):4493-7. · 5.23 Impact Factor
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ABSTRACT: Hybrid gas-liquid electrical discharge has been investigated in recent years as an innovative technology for contaminated water treatment. A high-voltage pulsed-power supply is commonly needed for the generation of electrical discharges. This paper aims, in lieu of cost effectiveness, to evaluate the degradation efficiency of electrical discharges with an alternating-current (ac) power since it is generally cheaper than a pulsed one. An ac power supply with a fixed voltage of 13 kV and a fixed frequency of 60 Hz is therefore adopted in this paper for the inactivation of aquatic microorganism. The energies required for one log order of reduction of E. coli, S. aureus, and Yeast were 23, 34, and 31 J/ml, respectively. The energy efficiencies achieved with an ac power in this paper are comparable with other studies that achieved with a pulsed-power.
IEEE Transactions on Plasma Science 03/2008; · 1.17 Impact Factor
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ABSTRACT: Perfluorocompounds (PFCs) are widely used in the semiconductor manufacturing industry as etching gases and chamber cleaning gases. However, PFCs intensely absorb infrared radiation and aggravates global warming consequently. This study applies nonthermal plasma technologies to destroy PFCs including CF4, C2F6, SF6, and NF3. Four kinds of nonthermal plasma reactors including dielectric barrier discharge (DBD), packed-bed plasma (PBP), tandem packed-bed plasma (TPBP), and combined plasma catalysis (CPC) were constructed and tested. Experimental results indicated that higher oxygen and argon contents in the gas streams were beneficial to PFC abatement. For a single CPC reactor, the maximum removal efficiency achieved was 34%. The reduction requirement for semiconductor manufacturing (PFC abatement efficiency > 95%) could be accomplished by combining three CPC reactors in series. The maximum removal efficiency achieved and corresponding energy efficiency were both in the order of CPC > DBD > PBP > TPBP. Endproduct analysis indicated that CF4 was mainly converted into CO2, COF2, and CO. The selectivity of CO2 was in the trend of CPC > PBP > TPBP > DBD, being just reverse to the trend of COF2 selectivity. In general, CPC reactor performs with greater destruction efficiency, better energy utilization, and less hazardous products than the rest three reactors for PFC abatement.
Journal of Advanced Oxidation Technologies 12/2004; 8(1):33-40. · 0.81 Impact Factor
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ABSTRACT: Inactivation of Escherichia coli in water was experimentally studied, with pulsed electrical discharges in a hybrid gas–liquid reactor. The pH was dramatically decreased from 7 to ∼3 within 60 min, accompanying with a 6-log reduction. To evaluate the contribution of pH on inactivation, a set of experiments were designed and tested. Results indicate that the contribution of low pH to the inactivation could be neglected compared to that of electrical discharges. On the other hand, the decrease of pH could be eased as carbonate or phosphate buffer was added to the treated water. However, the inactivation efficiency was greatly reduced because the buffers could deplete the active species formed in electrical discharges. Besides, a new finding is addressed in this paper that the water after plasma treatment still owns a certain extent of inactivation ability, functioning like the free chlorine residual. The environmental adaptation ability of E. coli to electrical discharges was also investigated.
Journal of Electrostatics.
