Development of a microfluidic atmospheric - pressure plasma reactor for water treatment

Conventional water treatment methodologies are often incapable of eliminating chemical and biological pollutants from water sources leaving residual contaminants in treated water. These contaminants are of growing concern due to their potential for adverse health effects from chronic exposure. Non-thermal plasma generated in a dielectric barrier microfluidic plasma reactor, operated at atmospheric pressure, was studied for its potential to treat organic contaminants and pathogenic microorganisms in water. In this thesis, non-thermal plasma generated in a microfluidic reactor was investigated for the degradation of contaminants in water. The overall aim of this thesis is to optimize treatment efficiency of an organic contaminant, i.e. methylene blue, and biological contaminants, i.e. E. coli and P. aeruginosa, in non-thermal plasma by investigating the key process parameters. The microfluidic device in this work incorporated a dielectric barrier discharge generated in a continuous gas flow stream of a two-phase annular flow regime generated in the microchannel of the device. Using air as the carrier gas, low concentrations of long-lived chemicals generated in plasma such as nitrates were detected in plasma treated water. The relative degradation rates of MB were influenced by the residence time of the sample solution in the discharge zone, type of gas applied, channel depth and flow rate. Increasing the residence time inside the plasma region led to higher levels of degradation. Using a 100 μm deep device, oxygen was found to be the most effective gas for promoting MB degradation and by reducing the channel depth to 50 μm, the highest results were obtained, achieving more than a 97% level of degradation with air as the applied gas at a flow rate of 4 ml/min. Effective disinfection of water was achieved using air as the carrier gas. Full inactivation of both bacteria (108 CFU/mL maximum number of each bacteria treated) as monocultures and mixed cultures in water was achieved after 5 seconds of residence time in the plasma zone. The microfluidic system presented here demonstrates proof–of-concept that plasma technology can be utilised as an advanced oxidation process for water treatment, with the potential to achieve total mineralization of organics and hence eliminate water treatment consumables such as filters and disinfectants. A summary of the findings of this work is presented in Chapter 7 including further works

A microfluidic atmospheric-pressure plasma reactor for water treatment

A dielectric barrier discharge microfluidic plasma reactor, operated at atmospheric pressure, was studied for its potential to treat organic contaminants in water. Microfluidic technology represents a compelling approach for plasma-based water treatment due to inherent characteristics such as a large surface-area-to-volume ratio and flow control, in inexpensive and portable devices. The microfluidic device in this work incorporated a dielectric barrier discharge generated in a continuous gas flow stream of a two-phase annular flow regime in the microchannels of the device. Methylene blue in solution was used to investigate plasma induced degradation of dissolved organic compounds within the microfluidic device. The relative degradation rates of methylene blue were influenced by the residence time of the sample solution in the discharge zone, type of gas applied, channel depth and flow rate. Increasing the residence time inside the plasma region led to higher levels of degradation. Oxygen was found to be the most effective gas, with the spectra obtained using Liquid Chromatography-Mass Spectroscopy indicating the most significant degradation. By reducing the channel depth from 100 to 50 µm, the best results were obtained, achieving a greater than 97% level of methylene blue degradation. The microfluidic system presented here demonstrates proof-of-concept that plasma technology can be utilised as an advanced oxidation process for water treatment, with the potential to eliminate water treatment consumables such as filters and disinfectants

Evaluation of a microfluidic atmospheric-pressure plasma reactor for water treatment

A dielectric barrier discharge (DBD) microfluidic plasma reactor, operated at atmospheric pressure, was studied for its potential to treat organic contaminants in water. The proposed microfluidic plasma reactor (MPR) allows in situ production of plasma in a continuous flow, operated under atmospheric pressure, for plasma-based water treatment. The MPR operates with glass as the dielectric barrier, where plasma is generated in the continuous gas flow stream of a gas-liquid two-phase annular flow regime in the microchannels. The microchannels have dimensions of 100 µm depth, 250 µm width and the plasma is generated in an approximately 21 cm length of microchannel arranged in a serpentine pattern. Methylene blue (MB) in solution was used as a model organic to investigate its degradation by plasma generated in the microchannels. The influence of discharge time, residence time and gas sources, i.e. air, argon and oxygen, on MB degradation was studied. The percentage degradation increased with lower liquid flow rates, with maximum degradation of MB achieved at a liquid flow rate of 35 µL/min and inlet gas pressure of 1 bar using oxygen as the working gas. Liquid chromatography/mass spectrometry analysis of the MB solution after treatment suggests degradation through fragmentation of MB. It is intended that the device will be used as proof of concept to introduce plasma technology as an advanced oxidation process for water treatment, with the potential to achieve total mineralization of dissolved organic materials and microbial inactivation, replacing water treatment chemicals and consumables

On-chip electrochemical detection of glucose towards the miniaturised quality control of carbohydrate-based radiotracers

The miniaturisation of positron emission tomography (PET) radiotracer production is facilitating a move towards a dose-on-demand strategy that would enable a stratified approach to patient diagnostics, but while the on-chip synthesis steps have been demonstrated, the subsequent quality control (QC) testing steps have received much less attention. As part of the development of an integrated QC platform for PET tracers, we have developed two microfluidic electrochemical detectors for the pulsed amperometric detection (PAD) of carbohydrate-based radiotracers, with a particular view to the QC testing of the most important tracer, [18F]2-fluoro-2-deoxy-d-glucose ([18F]FDG). The first device employed a commercial screen-printed electrode (SPE) to enable a single-use format, while the second device incorporated wire electrodes for use as a more permanent fixture in a QC instrument. A flow-injection analysis (FIA)-style setup was used to inject boluses of d-glucose into the chips in a proxy for intended chromatographic separations prior to PAD. In proof-of-concept testing of the devices, the chips featuring the SPE and the wire electrodes yielded limits of detection of 0.1 ppm and 9 ppm, respectively, each below the required limits for [18F]FDG, and thus making both methodologies viable for the QC testing of PET radiotracers in a dose-on-demand format