Study On Offshore Environmental Safety Of Hydroxyl Radical Killing Microscopic Marine Pests

The coastal water zones account for 13%of China’s total territory,which are not only the pillar area of economic development,but also the"golden zone"of regional social and economic development.However,the coastal microscopic marine pests occur frequently due to the rapid development of coastal economy,such as invasive marine organisms and mariculture animal diseases,which seriously destroy marine biodiversity and threaten the coastal environment security.Therefore,how to quickly and efficiently kill microscopic marine pests and protect the environment safety of the coastal water has become a major national demand.In this thesis,hydroxyl radical（·OH）efficiently generated by atmospheric pressure ionization discharge,is used to kill invasive marine organisms in ballast water and parasites of cultured fish.Meanwhile,the marine environmental risk assessment is carried out in Dalian Port and Sanduao sea areas of Ningde respectively.The main research contents are as follows:（1）·OH efficiently generated by atmospheric pressure electric field ionization discharge,is used to kill invasive organisms in ballast water and parasites of cultured fish.The results showed that the concentration of algae cells is less than 10 cells/m L,and no bacteria were detected in treated ballast water when the concentration of·OH radicals solution is 2.49 mg/L,which comply with the performance standard in Regulation D-2 of the Ballast Water Convention.Besides,there is no regeneration of algae and bacteria after 5 days of treatment.In addition,all the Cryptocaryon irritans is killed after 6s of pipeline treatment when the concentration of·OH solution is 0.56 mg/L.Therefore,·OH can quickly and efficiently kill invasive marine organisms in ballast water and parasites of cultured fish.（2）The correlation between the concentration of·OH solution,water quality parameters such as seawater temperature,chlorophyll,turbidity and THMs is analyzed,then the variables with high correlation are selected and combined.Multiple regression models are developed for predicting the trichloromethane,bromodichloromethane,dibromochloromethane and bromoform concentrations produced in treated ballast water by using social science statistical software（SPSS）.The linear regression model R² of trichloromethane is 0.935,and the nonlinear regression model R² of bromomethane,chlorodibromomethane and bromodichloromethane are0.970,0.850 and 0.929 respectively.Subsequently,the validation of multiple regression models is carried out using additional data.There is no significant statistical difference between the predicted values and the measured values of the models in the range of experimental conditions（P>0.05）,which show that the models are reasonable and the prediction accuracy is high.Therefore,the prediction of the concentration of THMs in treated ballast water during·OH treatment is realized.（3）Based on the effective concentration of killing cultured fish parasites by·OH（0.5mg/L）,and meteorological hydrology data of Sanduao,the diffusion model of·OH solution concentration injection is established using EFDC-Explorer software.The diffusion of·OH solution with the change of injection time was determined as follows:1)The concentration of·OH solution in the fishing drainage area is 0.54 mg/L after injection for 15 min;2)·OH solution concentration attenuates to 0 mg/L when·OH injection is terminated and diffused for1 min.Furthermore,the prediction model of the effective sea area of·OH killing cultured fish parasites is established using one-dimensional water quality migration and transformation equation:（?）.After calculation,the effective area of·OH killing cultured fish parasites is 28.71 m² when the injection concentration of·OH solution is 10.15mg/L and injection time is 20 min.The relative error between·OH and the actual effective area is 10.3%,indicating strong applicability of the prediction model.（4）According to the requirement of the IMO G9,risk assessment of dalian port marine environment based on the discharge of 33,351 m³/d of ballast water is conducted after killing by·OH treatment.The aquatic toxicity tests for the treated water are carried out under internationally recognized guidelines.The ecotoxicity tests results indicate that·OH treated water has no growth inhibition on algae(I_rC₅₀,I_yC₅₀>100%)and no detectable toxic effects on Ctenogobius gymnauchen（NOAEC and NOEC>100%treated ballast water）.In addition,MAMPEC model is used to calculate the predicted environmental concentration（PEC）of disinfection by-products in treated ballast water during·OH treatment,combined with the the information of environment and characteristics of disinfection by-products.Predicted no effect concentration（PNEC）is estimated from acute and/or chronic toxicity data for aquatic organisms by dividing the appropriate assessment factors（AF）of disinfection by-products.The ratio between PEC and PNEC of the measured disinfection by-products are all less than 1,indicating that treated ballast water during·OH treatment has no potential risk to marine environment of Dalian Port（PEC/PNEC<1）.（5）The risk assessment of Sanduao mariculture environment is conducted during the injection of high·OH concentration,and the aquatic toxicity tests for the treated watert are carried out.The ecotoxicity tests results indicate that treated water has no growth inhibition on Skeletonema costatum(I_rC₅₀,I_yC₅₀>100%);no acute toxicity effects（NOAEC>100%）and no chronic toxicity effects（NOEC>100%）on Larimichthys crocea.Furthermore,EFDC-Explorer software is used to calculate the predicted environmental concentration（PEC）of disinfection by-products in treated water during·OH treatment,combined with the predicted no influence concentration（PNEC）.It shows that treated water had no potential risk to the sea environment of Sanduao（PEC/PNEC<1）.In conclusion,high concentration of·OH generated by atmospheric pressure ionization discharge is used to kill invasive organisms in ballast water and parasites of cultured fish efficiently.It can serve as a beneficial and useful tool for the coastal microscopic marine pests preventing-controlling,protecting the biological diversity of coastal waters to ensure the marine environment security.