Experiments On Minimizing Algae In Ballast Water By Combination Of Micro-pore Filtration And UV Radiation

Most of world trade is completed by shipping,the exchange of ship's ballast water results in the damage to the local marine environment and human health.Ballast water has become the most important way of the harmful organisms spreading in oceans and one of the most serious marine pollution.The problem of marine environment caused by ship's ballast water has been paid a significant attention to.During the past 30 years,the IMO and the United Nations have adopted a series of conventions,guidance documents and general assembly resolutions to guide the control of ship's ballast water.There are more than 27 methods for ship's ballast water treatment. Comparing with the income/cost,it is obvious that filtration and UV are better than other methods. Relatively,both methods have lower cost and environmental cost,but also higher validity, reliability and security. So a combination of filtration and UV radiation must be a main research trend of removing algae in ballast water in future.This thesis wanted to utilize a combination of micro-pore filter and UV radiation to remove algae in ballast water.The method is not only efficiency and low cost but also can make up for their respective shortages.According to the provisions of D-2 in the Convention (G8),the sizes of tested algae are less than 50 microns but greater than or equal to 10 microns.Three kinds of simulated ballast water were prepared by mixing natural seawater with Chlorella,Nitzschia closterium and Platymonas subcordiformis respectively. With the changes of initial algae concentration and flow rate,the removal rates of algae were tested and analyzed when the simulated ballast water was treated by the micro-pore filter,the UV radiation,and the combination of micro-pore filter and UV radiation.The combination way is the best,and the sequence of the removal rates is as follows:Platymonas subcordiformis>Nitzschia Closterium>Chlorella.Using the combination of micro-pore filtration and UV radiation,the removal rate of Platymonas subcordiformis is 100%,so the larger the size of algal,the higher the removal rate is.