Waterborne pathogens threaten public health and are particularly problematic for the aquaculture industry, where water is a critical element in maintaining the health and growth of aquatic animals. Water treatment strategies are crucial in preventing waterborne diseases. However, traditional water disinfection methods, such as ozonation, ultraviolet radiation, and chlorination/dichlorination, are limited due to difficulty in transportation and storage, short duration of efficacy, and safety issues. Recently, nanomaterials have emerged as potential materials with high efficiency at removing a wide range of pathogens due to their large surface area and specific reactivity. These materials have broad applications, from electronics to biotechnology, and they have attracted attention as an alternative to traditional water treatment technologies. However, there is little information about applying nanomaterials to mitigate microbial infections in water, especially in the aquaculture sector. Therefore, searching for and evaluating promising nanomaterials which have potential in public health and aquaculture applications to combat waterborne diseases is necessary.

In the first part of my research, I evaluated the ability of the CCCSNs to control fungus (i.e., Saprolegnia parasitica). The CCCSNs are a type of copper-based nanoparticles coated with a thin protective carbon shell, which may be suitable for large-scale water disinfection with low cost because copper is cost-effective relative to other metals such as silver, and copper-based nanoparticles are reported to have a wide range of antimicrobial activity. Our results indicated that the CCCSNs and its commercial filter product (COPPERWARE^®) could inhibit the growth of Saprolegnia parasitica (S. parasitica) with a low concentration of CCCSNs and a small quantity of COPPERWARE^®. However, copper leaching and water turbidity were observed when using COPPERWARE^®. In addition, we did not find that COPPERWARE^® was efficient in controlling fish bacteria such as Streptococcus agalactiae (S. agalactiae) and Vibrio parahemolyticus (V. parahaemolyticus). To inactivate waterborne bacteria, we evaluated a different nanomaterial: laser-induced graphene (LIG), which was reported to have excellent antibacterial effects after photo radiation or applying electricity.

In my study, LIG electrodes effectively disinfected bacteria and viruses. We demonstrated that LIG electrodes with low electricity inactivated both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Bacillus subtilis) in seawater without a noticeable change in water parameters (pH, dissolved oxygen (DO), and temperature) and high levels of oxidants (chlorine, ozone (O₃), and hydrogen peroxide (H₂O₂)) during water treatment. In addition, rapid disinfection towards the enveloped (feline infectious peritonitis virus) and non-enveloped (coxsackievirus B3 virus) viruses could also be achieved by LIG electrodes in seawater. The LIG technology rapidly inactivated different types of bacteria and viruses without high energy consumption in our lab-scale research, indicating its promising applications to eliminate waterborne pathogens in larger-scale saltwater systems.

The last component of my project investigated the LIG electrodes' antibacterial mechanism and health impact on a model fish species Japanese medaka. My studies suggested an array of mechanisms working synergistically to inactivate E.coli, including adsorption of bacteria to the anode surface, high pH near the cathode, and generation of different oxidant species. Reactive chlorine species (RCS) were likely responsible for the primary antibacterial mechanism. Despite the RCS and other oxidants, Japanese medaka showed no mortality, no abnormal behavior, and no significant damage on the gill after exposure to the LIG electrodes activated by 3 V for eight days. However, when we used 6 V to activate the LIG over a 10-day treatment, we observed 11% mortality. In this latter case, abnormal fish behaviors were observed starting on day 2, including reduced feeding response, reduced shadow response, and sitting at the bottom of the tank. In summary, the LIG electrochemical system effectively disinfected different types of bacteria and viruses in salt water with only 3 V electricity. Although the system needs to be scaled to commercial applications, which will take more research, it shows great promise for controlling waterborne diseases.