Inactivation effect and mechanisms of combined ultraviolet and metal-doped nano-TiO(2) on treating Escherichia coli and Enterococci in ballast water

Wang, Xixi; Huang, Yanli; Zhang, Kun; Shi, Yue; Lu, Zheng; Wang, Yinhao

The discharge of ship ballast water (containing large amounts of alien organisms) has caused severe ecological hazards to marine environments. In this study, three metal elements (Ag, Fe, and Gd) were doped to nano-TiO(2) material respectively (content: 0.4%, 0.7%, and 1.0%) to improve inactivation effect of Escherichia coli and Enterococci in ballast water. Experimental results indicate that compared with the sole ultraviolet (UV) and the UV and original nano-TiO(2), the UV and metal-doped nano-TiO(2) increased the bacterial inactivation rate to different extents. For each metal element, high external metal content (1.0%) corresponded to high inactivation effort. The doping of Ag resulted in optimal inactivation effort, and the addition of Fe and Gd caused unobvious effort. At the end of the inactivation process (20 s), the UV and 1% Ag-doped nano-TiO(2) reached the highest logarithmic sterilization rates (0.915 for Escherichia coli and 0.805 for Enterococcus). The doping of Ag, Fe, and Gd did not change the anatase phase TiO(2) crystal form, and 1% Ag-doped nano-TiO(2) had the smallest particle diameter and the evenest distribution of nanoparticles. Compared with the sole UV, the UV and Ag-doped nano-TiO(2) treatment resulted in higher malondialdehyde contents (0.0646 μmol/L for Escherichia coli and 0.0529 μmol/L for Enterococci) and lower superoxide dismutase activities (0.672 U/mL for Escherichia coli and 0.792 U/mL for Enterococci), which were in accordance with high inactivation rates in these cases.