Eliminating bacterial endotoxins and associated inhalation hazards in reclaimed water via ultraviolet/ferrate combination disinfection

Sewage effluent and reclaimed water usually contain elevated concentrations of bacteria-derived endotoxins, which may have serious public health implications upon exposure. Both conventional disinfection methods, such as chlorine, ultraviolet, and ozone disinfection, and the new potassium ferrate disinfection process have limited endotoxin removal capacity. Therefore, it is necessary to find new methods of removing endotoxins. In this study, we investigated the effects of ultraviolet/ferrate (UV/Fe(VI)) combination treatment on endotoxin elimination and inhalation hazard control. Our results indicate that UV or Fe(VI) alone cannot sufficiently eliminate endotoxins but can instead exacerbate endotoxin release during bacterial inactivation. However, the UV/Fe(VI) combination rapidly eliminated approximately 85.6 % of both pure and bacteria-derived endotoxins. The optimal conditions for this disinfection process were determined to be 10 mg/L of Fe(VI) and 160 μW/cm 2 of UV exposure for 15 min. Furthermore, the pH value, bicarbonate (HCO 3 – ), humic acid, and turbidity were determined as potential factors that may affect UV/Fe(VI)-mediated endotoxin removal in reclaimed water. The potential mechanism underlying UV/Fe(VI)-induced endotoxin degradation involves several strongly oxidizing species, among which Fe(IV)/Fe(V) is regarded as the primary contributor, followed by the superoxide anion ( • O 2 – ) and hydroxyl ( • OH) radicals. These active substances induce the breakdown of the endotoxin molecular structure into smaller, non-toxic fragments. Furthermore, pure endotoxins, Escherichia coli , and Pseudomonas aeruginosa were disinfected with UV/Fe(VI), and then these aerosolized samples were inhaled exposed to mice. Our results demonstrated that combined use of UV and Fe(VI), rather than administration alone, remarkably blunted bacterial- and endotoxin-induced lung injury. In conclusion, these results demonstrate that the UV/Fe(VI) approach successfully eliminates endotoxins and related inhalation hazards from reclaimed water.