Synergistic Effect of Atmospheric-pressure Plasma and TiO2 Photocatalysis on Inactivation of Escherichia coli Cells in Aqueous Media.

Renwu Zhou,Jiangwei Li,Xianhui Zhang,Zhong Chen,Size Yang,Kateryna Bazaka,Kostya Ostrikov,Qiang Chen,Rusen Zhou,Xingquan Wang

doi:10.1038/srep39552

Abstract

Atmospheric-pressure plasma and TiO2 photocatalysis have been widely investigated separately for the management and reduction of microorganisms in aqueous solutions. In this paper, the two methods were combined in order to achieve a more profound understanding of their interactions in disinfection of water contaminated by Escherichia coli. Under water discharges carried out by microplasma jet arrays can result in a rapid inactivation of E. coli cells. The inactivation efficiency is largely dependent on the feed gases used, the plasma treatment time, and the discharge power. Compared to atmospheric-pressure N2, He and air microplasma arrays, O2 microplasma had the highest activity against E. coli cells in aqueous solution, and showed >99.9% bacterial inactivation efficiency within 4 min. Addition of TiO2 photocatalytic film to the plasma discharge reactor significantly enhanced the inactivation efficiency of the O2 microplasma system, decreasing the time required to achieve 99.9% killing of E. coli cells to 1 min. This may be attributed to the enhancement of ROS generation due to high catalytic activity and stability of the TiO2 photocatalyst in the combined plasma-TiO2 systems. Present work demonstrated the synergistic effect of the two agents, which can be correlated in order to maximize treatment efficiency.

Highlights

Non-equilibrium low temperature plasma inactivation of microorganisms has attracted increased attention in recent years due to its efficacy against a wide range of bacteria and fungi[1,2]
Given that the kinetic rate is widely applied to evaluate different disinfection processes, the process of E. coli disinfection in this study was fitted with CW model expressed by Eq 1 23,27,28: ln Ct = −kt where C0 and Ct are the respective concentration of live E. coli cells at the start (t = 0) and the end of treatment (t), respectively, and k is the kinetic rate
The plasma inactivation of E. coli cells suspended in water was performed by using atmospheric-pressure N2, He, air, and O2 microplasma arrays

Summary

Introduction

Non-equilibrium low temperature plasma inactivation of microorganisms has attracted increased attention in recent years due to its efficacy against a wide range of bacteria and fungi[1,2]. High reactivity and short lifetime means that only a fraction of the species generated during plasma treatment are able to penetrate the gas−liquid interface to reach the intended target[4], potentially limiting the efficiency of gas phase plasma inactivation against microorganisms in a moist environment or in bulk liquids. Higher chemical reaction rates of -generated species translate to significantly improved killing efficacy, as demonstrated by efficient inactivation of Bacillus subtilis spores using a direct-current, cold atmospheric-pressure air plasma microjet generated in water[6]. As well as promoting chemical reactions, these effects may directly contribute to the killing of the microorganisms, e.g. by changing the transport across the cell membrane, or declumping the cells, their individual contributions to the overall biological activity of plasma have received relatively little attention[10]. In view of this, developing a combined technology to utilize both chemical and physical effects derived from plasma would be imperative and meaningful

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Discussion

Conclusion