| With the increasingly close international trade,the global shipping industry is booming,and the problems of biological invasion caused by ship's ballast water are becoming more and more serious.The annual economic losses caused by ballast water to the marine ecological environment,human economic development and even health have been more than one billion dollars.In response to the ballast water problems,more than 50 countries around the world signed the International Convention for the Control and Management of Ballast Water and Sediments in Ships to ensure the clean treatment of ballast water.China also officially contracted in January 2019,so many shipping vessels,including our own,will need to install ballast water treatment facilities in accordance with the requirement of the Convention.However,the new"Binder Water Management System Approval Rules"came out at the end of 2016,and the requirements for regenerative evaluation of ballast water were put forward,which made the existing ballast water treatment equipment face a new test.At present,the ultraviolet ballast water treatment system accounts for about 40%of the global ballast water treatment market,and accounts for 70%of the market in China.In the ultraviolet ballast water treatment system,the combination of filtration and simple ultraviolet radiation/ultraviolet-photocatalysis technology is adopted,but in the actual ship applications and laboratory experiments,it is found that the microorganisms in the ballast water a single ultraviolet irradiation are especially Microalgae can perform photoremediation or dark repair in the light and dark environment through the repair its own DNA repair enzyme,and cut off or remove the pyrimidine dimer on the microalgae DNA strand after UV irradiation,thus invalidating the UV treatment.In order to verify the risk of microalgae regeneration in the current typical UV ballast water treatment system,this paper use the typical UVC irradiation method,secondary UVC irradiation method and UVC-photocatalysis method to treat three kinds of UV ballast water treatment system.The treatment experiments on the cell-free microalgae-Dicrateriain and the cell wall microalgae-Nitzschia closteriumthe in the simulated ballast water,through the absorbance value,chlorophyll value,algae celltreatment efficiency,regeneration rate and regeneration rate,etc.The characterization of the indicators was carried out to compare the treatment effects of two representative microalgae under different treatment conditions with the regeneration levels in light ang dark environment,and to analyze the difference in photosynthetic activity and reproductive capacity before and after regeneration.The experimental results show that for typical microalgae without cell wall,although UVC-photocatalysis and single UVC irradiation can significantly inhibit the photosynthetic activity of Dicrateriain and have higher processing efficiency.However,during 30-day light culture process,the microalgae have a regeneration phenomenon,and the regenerated microalgae have normal reproductive ability and photosynthetic activity.The secondary UVC irradiation method can completely destroy the activity of algae cells,and can achieve effective regeneration inhibition for typical microalgae without cell walls,avoiding the occurrence of light repair and dark repair;For the microalgae with cell walls,the transmission ability of UVC irradiation is significantly affected by the resistance of the cell wall,so that the three methods can restore the regenration and restore the reproductive capacity and photosynthetic activity.The experimental of this thesis show that UV accumulation irradiation and photocatalysis can inhibit the regeneration of microalgae to a certain extent,but for microalgae with cell wall protection,it is very close to the dose and frequency of enhanced UV irradiation or auxiliary means.It is difficult to completely suppress its regenration. |
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