Plasma generated in contact with water has been extensively investigated in various electrode geometries and various discharge types for water treatment, of which the applications have been employed industrially on different scales. The reactive species such as OH radicals, O3, H2O2 and HO2 can be generated from the reactions that occur at the plasma-water interface. For discharges above water, the effect of positive gas ions, which lead to the formation of positive water ions, is considered the main pathway for OH radical formation; while for the discharge under water, the water dissociation by electron collisions is considered as the main pathway.However, the reaction zone for the production of reactive species (gas or liquid phase) is still controversial. This thesis presents a study of the plasma generated in the gas phase in contact with water by various discharge types for water treatment. The discharge characteristics, OH radical and H2O2 production, and solution conductivity and pH variation were investigated and compared under different experimental conditions. The degradation of methylene blue dye was investigated under DBD.The transition of impulsive current discharges into impulsive-diffuse discharges was recorded by increasing the solution conductivity; a further transition of the discharge type into a spark was recorded when the solution conductivity was increased to >2.4 mS/cm. The H2O2 energy efficiency of 1.1 g/kWh was recorded under positive impulsive current discharges in N2 and helium.The highest charge/H2O2 ratio of 1:1.26 was recorded under positive impulsive current discharges in O2 and N2. Under positive DC glow discharges, the H2O2 energy efficiency of 1.9 g/kWh was recorded in air discharges, and was slightly increased to 1.95 g/kWh when using a flow liquid electrode. Increased solution acidity and basicity from neutral solution have negative effects on H2O2 production. A significant amount of water vapour was observed under DC glow discharges, resulting in a negative effect on H2O2 production.Under negative discharges, no H2O2 production was detected in water after O2, N2, air and helium discharge treatments. In DBD, a threshold voltage is required to initiate electrical discharges between the glass plate and the water, through the micro-pores. The H2O2 production yield of 1.1 g/kWh was recorded in O2 discharge treatment. The degradation yield of methylene blue dye of 310 g/kWh was achieved within the first minute of O2 discharge treatment.
|Date of Award||28 Aug 2017|
- University Of Strathclyde
|Sponsors||University of Strathclyde|
|Supervisor||Tao Wang (Supervisor) & Scott MacGregor (Supervisor)|