Singlet oxygen treatment of algae-laden water: An elegant way of decontamination without cellular damage

Algae-laden water with high levels of dissolved organics and cyanotoxins adversely affects water treatment plants and drinking water safety. As an emergency treatment, oxidation-assisted coagulation improves the removal efficiency of algae cells by lowering their motility, but the applied oxidants cause cellular damages that lead to serious release of intracellular organic pollutants. Here, we unveiled that singlet oxygen (¹O₂) provides state-of-the-art pretreatment that destabilizes the algal cells to make them more and readily removed, but does not disrupt the cells and cause the release of intracellular materials. Meanwhile, the extracellular pollutants related to cyanotoxins and taste-and-odor compounds can be effectively eliminated by ¹O₂ from aqueous phase. In contrast to ¹O₂, other oxidant species such as ozone (O₃), hydroxyl radical (•OH), hypochlorite ion (ClO^-), peroxymonosulfate (PMS), or permanganate ion (MnO₄^-) damaged the algae cells and led to serious organic contamination. We gained insights how ¹O₂ induced the nonviability and surface modification of algae cells while keeping them undamaged, which facilitates the algae pollution control by coagulation. Finally, we successfully applied the ¹O₂ treatment to real algae-contaminated water from a nearby reservoir. Our findings support that ¹O₂ technology may serve as the next-generation emergency treatment to deal with algae-laden water.