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.