Disinfection of spring water and secondary treated municipal wastewater by TiO2 photocatalysis

The photocatalytic disinfection of spring water and secondary treated municipal wastewater by means of UV-A irradiation over TiO₂ suspensions was investigated. Water samples were taken from a spring supplying water to the city of Chania, Western Crete, Greece, while wastewater samples were collected from the outlet of the secondary treatment of Chania municipal wastewater treatment plant. The effect of various operating parameters such as photocatalyst type (rutile, anatase, mixture of anatase and rutile) and concentration (0.5-1 g/L), contact time (up to 60 min) and sample pH (6-8) on the disinfection as assessed in terms of faecal indicator microorganisms (total coliforms and enterococci) inactivation was examined. A commercially available Degussa P25 TiO₂ powder, consisting of 75% anatase and 25% rutile, was found substantially more active than pure anatase or rutile for both groups of bacteria inactivation which increased with increasing contact time and catalyst concentration, whereas small pH changes had little effect on destruction. For both groups of bacteria tested, inactivation followed a first order kinetic expression with the gram positive Enterococcus sp. being considerably more resistant to photocatalytic disinfection than total coliforms.