Single pass saltwater disinfection using low voltage electrolysis: Potential implications for aquaculture systems

Abstract

Open net pen saltwater aquaculture faces criticism due to the potential transmission of pathogens between fish farms and to wild stocks. To address this issue and improve the sustainability and growth of net pen farming, closed containment farms have been suggested, but the cost and feasibility of disinfecting large volumes of water in these types of farms is problematic. We explored the potential for using electrolysis to disinfect saltwater in a flow-through system with water flow velocities between 47 and 105 cm/s. This was the first step to investigating whether this technology could be applied to saltwater flow-through closed containment systems. Various voltage levels (3.3–9.0 V) were applied to generate chlorine from saltwater. We found the disinfection properties of the system varied with wattage (i.e., voltage × ampere), velocity of water flow over the electrodes, salinity of water, and residual chlorine contact time. Wattage was highly correlated with the production of chlorine, and this relationship was dependent on water flow (p = 0.0398). A slower flow velocity led to higher chlorine concentration, and the effect was more pronounced at higher wattages. Using a zero-inflated negative binomial regression model, we found the probability of full disinfection was increased by increasing wattage (p < 0.001) and the residual chlorine contact time (p < 0.001). The level of disinfection (count model) suggested the number of bacteria in the treated samples was determined by the interaction between wattage and flow (p = 0.0056) and the interaction between wattage and salinity (p < 0.001). The bacterial count was also associated with residual chlorine contact time (p < 0.001). The results of this study, although preliminary and limited in their scale, offering a potential solution for disinfecting large volumes of seawater, which could make closed containment fish farming in the ocean viable for reducing bacterial transmission within a farm and to wild fish stocks.