Degradation of bacteria for water purification in a TiO2-coated photocatalytic reactor illuminated by solar light

In this study, the inactivation of various bacterial strains in a solar illuminated photocatalysis reactor with a titania photocatalyst dispersed in a geopolymer coating is studied. The modular reactor design consists of connected catalyst-coated open water carrying chutes. The cleaning efficiency of the process against chemical and biological water contaminants was evaluated by means of test series with methylene blue as a reference for chemical contamination and by studying the inactivation of the strains Escherichia coli, Bacillus subtilis, Pseudomonas fluorescens and an undefined mixed culture from the effluent of the secondary clarifier of a wastewater treatment plant as biological contaminants. Test series with methylene blue showed reduction efficiencies of 17–63% for non-catalyst-coated reference reactors and 55–99% for catalyst-coated reactors within 120–300 min of exposure to natural sunlight. Disinfection test series showed reduction efficiencies of 0.0–2.8 log units (without catalyst) and 0.0–4.4 log units (with catalyst) for mentioned bacteria and the mixed culture within 40–180 min of light exposure. Hence, the catalyst-coated system consistently showed a significantly higher degradation efficiency than the non-coated reference. A comparison of methylene blue degradation under natural solar irradiation and artificial UVA irradiation conditions showed that this simple reactor concept is suitable for the combined elimination of trace substances and disinfection of water even at moderate flux rates of 1000 W/m².