Development of a photocatalytic reactor for water disinfection with a consideration of the factors that promote bacterial resistance to photocatalytic treatment

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.<br><br>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.<br>