Influence of Bacterial, Environmental and Physical Factors in Design of Photocatalytic Reactors for Water Disinfection

The design of photocatalytic reactors for use in bacterial disinfection studies is often based on defined laboratory conditions, which are not a true representation of the harsh and ever-changing environment that bacteria encounter in nature. In this study four parameters (growth phase, biofilm production, pH and irradiation source) subject to continuous flux in nature, which could affect the efficacy of photocatalytic disinfection studies, were examined and their importance in process design was considered. The results produced a number of key findings which should be taken into consideration when designing photocatalytic reactors for biological processes. Using Escherichia coli as a model organism, studies of effects of pH and bacterial growth phase showed that cells in the stationary phase and at a pH of 8 were more resistant to photocatalytic breakdown. Only at a pH of 4 and while in the logarithmic growth phase, was complete photocatalytic destruction achieved. This process was further enhanced by replacing six 8 W black lamps with a single high-power UV-LED operated at 1.05 W. The impact of virulence was investigated by comparing photocatalytic destruction of a biofilm producing and non-producing strain of Staphylococcus epidermidis. The results indicated that there were no differences in susceptibility to disinfection suggesting that the capacity alone to express a virulence factor may not generate greater resistance to photocatalytic destruction.