Killing Efficiency Research Of Low Pressure UV On Organisms In Ballast Water

The introduction of aquatic invasive species via ships’ ballast water becomesworse and worse as a result of rapid of world ship industry development. To reducethe risk of introducing non-native species into foreign ecosystems, the InternationalMaritime Organization (IMO) in2004passed the―International Convention for theControl and Management of Ships’ Ballast Water and Sediments‖. This conventionsets standards for the maximum number of viable organisms, which must be metbefore the release of ballast water into the environment. One way to meet therequirements of the Ballast Water Convention is ballast water treatment. In this study,artificial ballast water was treated by5-day darkness treatment alone, UV radiationalone and UV radiation combined with darkness treatment, respectively. Waterqualities and changes of biological community and/or biological efficacy aftertreatment using three methods mentioned above were investigated.For salinity of15PSU, after5-day darkness treatment alone, the averagemortalities of organisms in artificial ballast water in≥50μm and≥10μm to <50μmgroups were85.1%and99.96%, respectively. Mortality of organisms in≥10μm to<50μm group changed significantly with dissolve oxygen and dissolve oxygensaturation (p <0.05). The density of organisms in≥10μm to <50μm group was metthe D-2standard of the IMO, whereas the density of organisms in≥50μm group wasnot. Mortality of organisms in≥10μm to <50μm group was higher than those in≥50μm group. For salinity of2PSU, after5-day darkness treatment alone, the averagemortalities of organisms in artificial ballast water in≥50μm and≥10μm to <50μmgroups were97.64%and99.91%, respectively. Density of organisms in≥10μm to<50μm group (0.34cell/mL) was met the D-2standard of the IMO, whereas thedensity of organisms in≥50μm group was not.For salinity of both15and2PSU, after UV radiation treatment alone, the averagemortalities of organisms in artificial ballast water in≥50μm and≥10μm to <50μmgroups were99.5%and94%, respectively. The effectiveness of UV radiation for disinfecting tiny organisms was significant. Mortality increases with reducing flowrate due to longer UV radiation time. Mortalities of organisms in≥50μm and≥10μmto <50μm groups with the flow rate of25m3/h were higher than those with the flowrate of40m3/h. Mortality of organisms in≥10μm to <50μm group was98.78%,meeting the D-2standard of the IMO. Mortality of organism in≥50μm group wassignificantly negative correlation with initial plankton densities (r=-0.86). Density oforganism was not met the D-2standard of the IMO when initial density was largerthan105individuals/m3.Mortality of organisms in≥10μm to <50μm group after combination of UVradiation with darkness treatment was significantly higher than that after UV radiationalone, having a mortality of99.8%. After combination, density of organisms in≥10μm to <50μm group in each test cycle was lower than10cell/mL, which met the D-2standard of the IMO. Density of organisms in≥10μm to <50μm group wassignificantly lower after UV radiation plus darkness than before treatment (p <0.05).After combination, density of organisms in≥50μm group in each test cycle decreasedsignificantly, and the results met the D-2standard of the IMO. Density of organismsin≥50μm group was significantly lower after UV radiation plus darkness than beforetreatment (p <0.05). UV radiation plus darkness had a good effectiveness onorganisms in≥50μm group.