Photocatalytic activity of a visible light active structured photocatalyst developed for municipal wastewater treatment

A visible light active structured photocatalyst consisting of Nitrogen-doped TiO2 particles immobilized on polystyrene spheres by solvent cast method was developed for possible application as tertiary treatment in small municipal wastewater treatment plants. The structured catalyst was characterized by spectroscopic and morphological techniques evidencing that the preparation method was able to disperse evenly anatase Nitrogen-doped TiO2 particles on polystyrene spheres and that the structured catalyst can be activated by visible light. The photocatalytic tests were driven first in a laboratory scale reactor configuration irradiated through visible light emitted by light emitting diodes and then using a solar compound triangular collector based reactor for outdoor experiments. The results from laboratory scale experiments did not show any photocatalyst deactivation after several treatment cycles; the photocatalytic process was effective in methylene blue degradation experiments and real wastewater disinfection (92.6% indigenous Escherichia coli inactivation after 120 min of irradiation time). In outdoor experiments under direct solar light, the structured photocatalyst confirmed its efficiency in the inactivation of indigenous Escherichia coli present in a municipal wastewater (87% inactivation after 120 min treatment and 2 kJ/L of cumulative energy per unit of volume) because the residual bacterial count met the limit (50 CFU/mL) established by Italian law for wastewater disposal in surface water.