Abstract
Contaminated drinking water is a growing global problem and it is predicted that half of the world's population will be living in water-stressed areas in the near future. Therefore, the deployment of suitable technology that is capable of treating a broad range of contaminants is essential. Photocatalysis is capable of removing harmful pollutants from water in order to achieve a high standard of effluent quality. This research project describes the development of photocatalytic reactor technology for the disinfection of wastewater to provide safe drinking water. OH radicals are highly reactive species produced during photocatalysis. Their ability to oxidise harmful contaminants has been widely studied as it is believed that OH radicals are the primary cause of bacterial disinfection. OH radical production was investigated using coumarin as a chemical probe and P25 TÌO2 over a large range of coumarin concentrations and photocatalyst loadings which have not been previously investigated. The optimum conditions for OH radical production were found to be a 250 nM starting concentration of coumarin and 0.5 g L 1 TÌO2. The role of bacterial factors was considered in conjunction with the microbial sensitivity to photocatalytic treatment. Factors which appeared to be important for photocatalytic disinfection were bacterial phase of growth, pH, catalyst loading and the efficiency of the UV light source. Differences in cell wall structure between gram positive and gram negative bacteria and the expression of bacterial virulence factors did not appear to affect the efficacy of photocatalytic disinfection. A spinning disc reactor (SDR) was designed with consideration of these important factors, in order to enhance the overall process. The SDR successfully degraded coumarin and completely destroyed E. coli K12 within a 2.5 - 3 hr period.Complete disinfection is not usually achieved in immobilised photocatalytic reactor systems used for microbial disinfection. This suggests that the SDR design provided the perfect environment for bacterial disinfection. It could also be noted that the ability of immobilised photocatalytic reactor technology has reportedly been much more successful in the degradation of chemicals than microorganisms as living organisms are more complex pollutants. A more advanced SDR was developed and investigated to find the optimal reaction conditions such as ideal disc rotation speed and inlet flowrate, most viable LED light source, reaction pH and best mass transfer conditions. An interesting issue regarding the adhesion between the bacteria and the surface hydrophobicity of the Ti02 surface of the disc was uncovered which had a direct effect on the level of disinfection achieved by the SDR.
| Date of Award | 2019 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Northern Ireland Department for the Economy |
| Supervisor | Peter Robertson (Supervisor) & Jeanette Robertson (Supervisor) |