Inactivation of Scrippsiella trochoidea cysts by different physical and chemical methods: Application to the treatment of ballast water

Highlights: • Inactivation of dinocysts by different physical and chemical methods were studied. • Cysts were completely inactivated after treatment by 38 °C for 5 h. • UV, US and freshwater inhibited but did not completely inactivate cyst germination. • H₂O₂ completely inactivated cyst germination at high concentration for long duration. • The combined treatments were more effective, especially those of heating and UV. - Abstract: Effects of heating, ultraviolet (UV), ultrasound (US), hydrogen peroxide (H₂O₂) and freshwater, and the combined treatments on inactivation of cysts of Scrippsiella trochoidea and cysts in sediment suspension were studied. Heating was the most efficient way to inactivate cyst germination, and cysts were completely inactivated at 38 °C for 5 h. UV, US, and freshwater efficiently inhibited but could not completely inactivate cyst germination. Effects of heating, UV, and US on cyst germination decreased for cysts in sediment, and germination rates increased by 6.7–48% compared to the same treatment for cysts without sediment. H₂O₂ significantly inhibited cyst germination, but complete inactivation occurred at high concentration for long duration (100 mg/L, 6d). The combined treatments were more effective, especially the combinations of heating and UV. The results suggested that heating might be a feasible way for ballast water treatment especially after combined with filtration and UV.