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

Patinglag, Laila (2019) Development of a microfluidic atmospheric - pressure plasma reactor for water treatment. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

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.