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Title: Non-thermal air plasma discharges for food and water security applications
Author: Ni, Y.
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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The use of cold atmospheric pressure plasma for applications related to microbial decontamination has grown enormously over the last decade. Non-thermal plasmas generated in ambient air contain a wide variety of reactive oxygen and nitrogen species, or RONS. When such species interact with microorganisms they induce a number of biological changes, ultimately resulting in inactivation of the organism. This thesis focuses on the design, development, optimisation and application of air plasma systems for microbial decontamination. The aim of the work is to gain a better understanding of how RONS are produced in air plasma and how they are transported through different phases of matter, including gases and liquids. It is shown that RONS generation is highly dependent on the discharge conditions and two distinct modes of operation are observed. Downstream of the discharge, the transport of RONS to the sample region is of paramount importance as many highly-reactive species are lost. To address this challenge, the structure of the plasma generating electrodes was systematically studied to optimise the plasma generated air flow and therefore the transport of species downstream. Optimised electrode structures were shown to generate flow velocities in excess of 1m/s which is an order of magnitude improvement over transport by diffusion alone. Using the optimised plasma system, the impact of RONS in real decontamination scenarios linked to food and water security were considered. This included investigation of plasma decontamination of liquid samples, solid surfaces and tissues. It was shown that plasma decontamination can be extremely effective but many factors influence the efficacy of the approach. Microorganisms shielded within a liquid layer or by a complex surface morphology were shown to be particularly difficult to inactivate. Overall, this work has demonstrated that plasma can be a highly effective tool for microbial decontamination but careful consideration of both the discharge parameters and the sample properties is required to achieve the highest level of decontamination.
Supervisor: Walsh, J. L. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral