Inactivation of Heterosigma akashiwo under UV/peroxydisulfate advanced disinfection system in marine waters

Heterosigma akashiwo (H. akashiwo) is recognized as a harmful algal bloom (HABs) species with a global distribution, capable of posing significant threats to marine ecosystems, particularly when spread through ship ballast water. This investigation focused on elucidating the inactivation kinetics and underlying mechanism of H. akashiwo through a combined ultraviolet irradiation and peroxydisulfate (UV/PDS) process. The results demonstrated a strong synergistic effect within the UV/PDS system, resulting in an inactivation of 0.78-ln and 2.67-ln within 40 min of UV and UV/PDS processes. The principal agents accountable for inactivation were identified as sulfate radicals (•SO₄^-) and hydroxyl radical (•OH), which exhibited a synergistic effect in the UV/PDS process. Furthermore, the study observed a negatively impact of seawater pH and salinity on the efficiency of inactivation. UV/PDS caused oxidative stress on algal cells, initially involving the participation of antioxidant enzymes in counteracting cellular damage, but this protective mechanism diminished as the reaction duration extended. The UV/PDS treatment not only inflicted damage upon H. akashiwo's photosynthetic system but also caused the extracellular release of DNA and algal organic matter (AOM) due to damaged cell membranes. Transcriptome analysis provided a molecular biology perspective on the cellular inactivation process. Upregulation of genes linked to photosynthesis and oxidative phosphorylation suggested a potential elevation in energy metabolism. In contrast, genes associated with cellular and metabolic processes, including glycolysis and the tricarboxylic acid cycle (TCA cycle), exhibited downregulation. Moreover, this treatment exerted an inhibitory influence on RNA polymerase and protein synthesis, resulting in the reduced expression of genetic information.