| The frequent outbreak of red tides is a serious threat to the ecological safety,economy and public health.One of the most important reasons for the frequent outbreak of red tides is the resting cysts stored in the sediment and ballast water,which will germinate and lead to a rapid reproduction in algae density under suitable environmental conditions.However,the resting cysts are resistant to normal algaecides because of their thick cyst walls.Therefore,how to inactivate the resting cysts quickly and efficiently is one of the biggest challenges in handling red tides and preventing from invasive species.Hydroxyl radical(·OH)is a strong oxidant with high reaction rate and friendly to the environment when applied to the inactivation of red tide algae cysts.So,advanced oxidant technology(AOT)based on ·OH is a perfect way to reach a quick and efficient inactivation of resting cysts.In this paper,a*OH treatment system based on a strong ionization discharge is established and applied to inactivate the resting cysts of a typical red tide algae Scrippsiella trochoidea.Also,the effect of ·OH on the morphology and germination potential of cysts is studied.In addition,this paper compares the effect of ·OH and three typical algaecides.Here are the main conclusions:(1)An atmospheric strong ionization discharge is used to achieve the production of ·OH which is applied to inactivate the two types of S.trochoidea resting cysts.The dose-effect and time-effect of ·OH on the inactivation of cysts are studied,results are as follows.When the total reactive oxidant(TRO)is 1.46 mg/L and the treatment time is 3.1 s,the concentration of naked-type cysts reduce to zero from 531 cells/mL.In addition,when TRO is 1.90 mg/L and treatment time is 4.1 s,the spiny-type cyst reach 0 when the beginning concentration is 634 cells/mL.The TRO decay kinetics is studied and used to calculate the CT value of ·OH on the inactivation of spiny-type and naked-type cysts.The CT value of ·OH on the naked-type cysts is 0.24 mg·min/L when the inactivation rate is 100%while the CT value on the spiny-type is 0.28 mg·min/L.In general,·OH can achieve a quick and efficient inactivation of S.trochoidea resting cysts.In addition,the ·OH treatment can improve the water quality to a certain extent.Moreover,bromate is not detected.(2)This paper investigates the change of germination potential of S.trochoidea resting cysts before and after ·OH treatment.And the result show that the germination rate of spiny-type and naked-type cysts is reduced to zero under the killing dose which means the cysts lose the potential to become a vegetative cell.The change in germination potential means that-OH achieves the complete inactivation of the "seed"of rea tide.(3)The effect of ·OH on the cell morphology,photosynthesis activity,damage on DNA and ultrastructure of the cysts is also investigated.SEM results show that under the killing dose 1.90 mg/L,the structure remains intact while ·OH can cause slight damage on the cyst wall and get in the cyst cell.When ·OH enters the cyst cell,·OH can destroy the cell membrane permeability,degrade the intracellular organic matter and oxidize biological macromolecules including the chlorophyll,oil droplets and nucleus.However,when the TRO reaches 4.12 mg/L,the cysts get ruptured leading to the leakage of DOC that is the precursor of disinfection by-products(DBPs).(4)CuSO4,H2O2 and ClO2 are typical algaecides that are widely used worldwide.The comparison of ·OH and the three algaecides on the inactivation of S.trochoidea resting cysts is investigated.When the CT value of CuSO4 is 30000 mg·min/L,the inactivation rate of S.trochoidea resting cysts is 12.9%.Also,the inactivation rate of S.trochoidea resting cysts reaches 24.1%when the CT value of H2O2 is 120000 mg ·min/L.CIO2 can achieve 100%inactivation rate when the CT value is 7200 mg·min/L.However,the CT value of ·OH is 0.28 mg min/L which is much lower than the three typical algaecides.The reason why ·OH has a much lower CT value is that·OH is a strong oxidant and has much higher reaction rate which enables it to cause damage on the cyst wall,enter the cyst cell and oxidize biological macromolecules.In general,this paper establishes the ·OH treatment system based on an atmospheric strong ionization discharge and achieves the inactivation of resting cysts of typical red tide algae S.trochoidea.Also,the mechanism of ·OH on the inactivation of S.trochoidea cysts is explored and the comparison of three typical algaecides and·OH is clarified.In a word,the ·OH treatment system offers new method to prevent the sea away from red tide and invasion species. |
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