Solar photocatalytic disinfection of E. coli and bacteriophages MS2, ΦX174 and PR772 using TiO2, ZnO and ruthenium based complexes in a continuous flow system

The performance of photocatalytic treatment processes were assessed using different photocatalysts against E. coli and bacteriophages MS2, ΦX174 and PR772, in a recirculating continuous flow compound parabolic collector system under real sunlight conditions. Suspended TiO2 and ZnO nanoparticle powders and Tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate in solution were tested separately, as well as in combination, using E. coli. For a 3-log reduction of E. coli in distilled water, inactivation rates in terms of cumulative dose were in the order Ru(bpy)3Cl2>(TiO2 & Ru(bpy)3Cl2)>(ZnO & Ru(bpy)3Cl2)>ZnO>TiO2>photolysis. Reactivation of E. coli was observed following all trials despite the detection limit being reached, although the reactivated colonies were observed to be under stress and much slower growing when compared to original colonies. Treatment with Ru(bpy)3Cl2 was also compared against standard photolysis of bacteriophages MS2, ΦX174 and PR772 with the order of photolytic inactivation for a 3-log reduction in terms of cumulative UV-A dose being ΦX174>PR772>MS2. However, MS2 was found to be the most susceptible bacteriophage to treatment with Ru(bpy)3Cl2, with complete removal of the phage observed within the first 15min of exposure. Ru(bpy)3Cl2 also significantly improved inactivation rates for PR772 and ΦX174. •Photocatalysis with TiO2, ZnO and Ru(bpy)3Cl2 showed significant improvement on photolysis of E. coli.•The presence of Ru(bpy)3Cl2 significantly improved the performance of both ZnO and TiO2.•Reactivation of E. coli was observed following all photocatalytic trials despite the detection limit being reached.•Ru(bpy)3Cl2 dramatically improved inactivation of MS2, PR772 and ΦX174 phages compared to photolysis.•Singlet oxygen can be more aggressive as a disinfecting agent than ROS produced with standard TiO2 photocatalysis.