Disinfection of urban wastewater by solar driven and UV lamp - TiO2 photocatalysis: Effect on a multi drug resistant Escherichia coli strain

The effect of TiO2 photocatalysis on the inactivation of an antibiotic resistant Escherichia coli strain selected from an urban wastewater treatment plant (UWWTP) effluent was investigated. Different light sources including a 250 W wide spectrum lamp, a 125 W UV-A lamp and solar radiation, as well as, photocatalysts loadings (TiO2 Degussa P25) in the range from 0.05 to 2.00 g TiO2 L-1 were evaluated. The higher efficiency (total bacterial inactivation after 10 min of irradiation) was observed in the absence of TiO2 when the wastewater was irradiated using the 250 W lamp. In the presence of TiO2 a decreasing inactivation trend was observed (99.76% and 72.22% inactivation after 10 min irradiation at 0.10 and 2.00 g TiO2 L-1 respectively). Under solar simulated conditions the highest inactivation efficiency (93.17%) after 10 min of irradiation was achieved at the lower photocatalyst loading (0.05 g TiO2 L-1). The concept of "reactor optical thickness" was introduced to explain the rates of disinfection observed. The optimum photocatalyst loading estimated by radiation absorption-scattering modeling was found to be 0.1 g TiO2 L-1 for all lamps. The difference between experimental tests and modeling may be due to TiO2 particles aggregation. Comparative kinetic tests between solar and solar simulated photocatalytic (SSP) processes using 0.05 g TiO2 L-1 in suspension showed a quite similar inactivation behavior up to 30 mm of irradiation, but only the SSP process resulted in a total inactivation of bacteria after 60 min of exposure. Antibiotic resistant test (Kirby Bauer) on survived colonies showed that the SSP and SP processes affected in different ways the resistance of E. coli strain to the target antibiotics. (C) 2014 Elsevier Ltd. All rights reserved.