Inactivation effect and kinetic analysis of multi-band ultraviolet LED combined with Ag/N modified magnetic TiO2 on microorganisms in ballast water

The invasion of harmful aquatic organisms from ship ballast water is a serious threat to the marine ecosystem. However, the existing treatment technology has the defects of high energy consumption, secondary pollution and easy revival of organisms, etc. How to inactivate the microorganisms in ballast water efficiently is always a difficult challenge. In this study, the inactivation of Karenia mikimotoi and Escherichia coli under UVA/UVCLED photocatalytic system (UVA/UVCLED + Ag/N-Fe3O4-SiO2-TiO2) was investigated using Ag-modified and Nmodified magnetic TiO2 nanomaterials. The results showed that the ability of 1.5 % Ag with 3 % N dual-modified TiO2 to enhance the system's biologically logarithmic inactivation rate was 4-5 times higher than that of conventional unmodified TiO2. The Ag/N-modified magnetic TiO2 had the best photocatalytic activity at a dosage of 500 mg/L. After 6 cycles of use, the inactivation efficiency in combination with UVA/UVCLED only decreased by 8.76 % compared with the initial use, and the recycling rate was still up to 95.75 %. Meanwhile, the scanning electron microscope showed that the photocatalyst itself only had some minor changes after 6 cycles, which confirmed the fact that the photocatalytic removal rate (higher than 91.24 %) could still be maintained at a high level. The UVA/UVCLED photocatalytic system significantly inhibited the scavenging ability of superoxide dismutase (SOD) on reactive oxygen species (ROS), enhanced the toxic effect of ROS on cells, and ultimately accelerated the process of apoptosis and inhibited biological resurrection. In addition, this study verified the inactivation kinetics of the target microorganisms using Chick-Watson, Hom and Biphasic models, and found that all individuals in the same population differed in their tolerance to UV radiation, and some of them absorbed more than a threshold dose of UV radiation before showing inactivation responses. The Biphasic model (R2: 0.99571-0.99926) can better simulate the nonlinear changes exhibited during the inactivation process and is more applicable to the actual disinfection situation of UVA/UVCLED photocatalytic systems. The UVA/UVCLED + Ag/N-Fe3O4-SiO2-TiO2 photocatalytic technology developed in this study, as a novel oxidation process, reduces energy consumption while effectively inhibiting the reanimation of organisms, and exhibits a strong potential for application in the fields of restoring the environment of water bodies and blocking the spread of pathogens.