Solar-assisted bacterial disinfection and removal of contaminants of emerging concern by Fe2+-activated HSO5- vs. S2O82- in drinking water

Abstract

This research demonstrates the feasibility to enhance solar disinfection (SODIS) treatment by addition of peroxymonosulfate (PMS) and peroxydisulfate (PDS) by the generation of sulfate (and hydroxyl) radicals through different activation routes. The different promoters were i) sunlight irradiation, ii) mild heat (40 °C), and iii) μM amounts of Fe2+, all present during actual field SODIS experiments, or voluntarily added alongside PMS/PDS. In a first approach, the promoters were studied separately, in pairs and finally all together in a combined process (CP). In all the cases, PMS showed a higher efficiency than PDS in E. coli removal, requiring lower concentration and a faster reaction time towards total bacterial inactivation. Therefore, the combined process (Oxidant/Fe2+/Sunlight/40 °C) reached total bacterial inactivation (6-logU) in 30 min when PMS was used, while it took twice as long with the PDS. These effects can be further enhanced when PMS with H2O2 is used, and barely 20 min are needed for complete bacterial removal. Besides total disinfection, the combined processes were suitable to eliminate micropollutants in μg/L concentration (drugs, pesticides, etc.) during solar treatment. Finally, the efficiency of the treatment methods was successfully tested in a lake water matrix, in a feasibility assay as a potential drinking water treatment method. The economic analysis highly supports the use of these oxidants. Although the use of PMS or PDS increases the cost of treatment, it is not mandatory to add other reagents or external activators; iron is ubiquitous in natural water and can act as activator, while during SODIS sunlight irradiation can provide UV and mild water heating, hence act as an effective disinfection method. Finally, a mechanistic proposal for the combined processes is given, as an overview of the occurring reactions leading to bacterial inactivation.