Comparison of the photocatalytic disinfection of E. coli suspensions in slurry, wall and fixed-bed reactors

The performances of different configurations of photoreactors were compared for the photocatalytic disinfection of Escherichia coli aqueous suspensions and methylene blue photodegradation. Titania was immobilized in an annular reactor in two different ways: on the inner reactor wall and on the packing of a fixed-bed. The influence of the increase in the TiO2 layer thickness has been studied, and the results have been compared with those obtained with TiO2 slurries of increasing concentration. Experimental results for methylene blue degradation were in agreement with those expected from the characterization data of the immobilized systems, but they did not fit with the variation of the activity for microorganisms inactivation. The increase in the density of the TiO2 film caused by the heat treatment carried out after every coating cycle reduce the TiO2 surface available for the interaction with bacteria, although it remains accessible for the dye molecules. Although immobilized systems show a lower disinfection activity in deionized water than TiO2 slurries, they show a lower inhibition by the presence of organic matter, leading to comparable irradiation times to reach bacterial concentrations below the detection limit in the treatment of wastewater treatment plant effluents. Moreover, immobilized systems have shown that they are stable and do not present deactivation after several cycles of reuse, being readily applicable for continuous water treatment systems.