Solar disinfection of drinking water at alkaline pH, assisted by ashes of spices and herbs containing catalytic metals, in a novel ?phyto-Fenton? process

In this manuscript, the improvement of solar disinfection (SODIS) for water treatment through the photo-Fenton reaction using iron replacements, namely calcined herbs and spices (thyme, cumin, cinnamon, ginger, and cocoa), naturally containing high content of metals. The bactericidal performance of SODIS, H2O2/light and solar photo-Fenton (light/H2O2/Fe2+) were assessed in pure and Lake Leman water. Sodium percarbonate (SPC) and ashes were successfully employed as substitutes of H2O2 and Fe2+, respectively. Low spices'/herbs' addition improved the H2O2/light process, especially when ginger, cumin, thyme, or cocoa were used, inducing effective heterogeneous photo-Fenton process even at alkaline pH. In ultrapure water, solar photo-Fenton with ashes was only slightly slower than the corresponding Fe2+-driven reaction, while in lake water total bacterial inactivation was achieved by cumin, thyme or ginger ashes. SPC enhanced SODIS performance, while the addition of ashes resulted in faster kinetics than light/SPC only. Overall, this work succeeded in converting the classic photo-Fenton process into a low-cost variant, the "phyto-Fenton" process, driven by the metals contained in the organic-free ashes and the H2O2 content of SPC.