Sunshine and a pinch of tropical soils: A natural, low-cost photo-Fenton variation for safer water, assisted by H2O2 or percabonate

Clean water is essential for human survival, but access to safe drinking water remains a challenge in resource -limited regions. Herein, we explored a low-cost but effective solution for water potabilization using natural iron sources from soils along with sunlight to remove coliforms from water. We evaluated 30 soil samples from tropical regions and among them, we found that soils from Colombia and Cameroon with high clay content and low carbon levels were the most effective catalysts. Their combination with H2O2 enhanced the solar disinfection (SODIS) yield and induced a heterogeneous photo-Fenton process with secondary homogeneous contribution and/or photocatalytic action. We also found that storing soils in acidic conditions increased the concentration of soluble iron species, leading to enhanced E. coli removal due to homogeneous Fenton and Fenton-like processes. The addition of citrate as a ligand further improved the performance of the system, by facilitating the regen-eration of dissolved iron, through metal chelation, thanks to the formation of photo-active complexes. Moreover, we explored the possibility of using sodium percarbonate as a substitute for H2O2 and found it to be a successful alternative, even over alkaline lake water samples. We discuss the mechanism behind the improved activity of sodium percarbonate and suggest that ferruginous soils, when combined with any form of H2O2, can induce the photo-Fenton process over a wide pH range and at low mg/L concentrations. Our study provides valuable in-sights into the potential of using natural iron sources to enhance solar disinfection, making clean water more accessible to communities in need.