Removal of bacteria from coastal seawater by foam separation using dispersed bubbles and surface-active substances

The removal of bacteria from rearing water and washing water in aquaculture systems, aquariums and fishing port facilities is the most important means of diminishing the risk of fish diseases, improving public health and ensuring high food quality. However, there are few methods of bacterial elimination, e.g., disinfection. Thus, it is necessary to develop a technology for bacterial removal from coastal seawater. In this study, the removal efficiency for several groups of bacteria by foam separation using dispersed bubbles and surface-active substances was determined using both batch equipment and a continuous-flow unit. By batch processing with only 1 mg/l milk casein added as a surface-active substance and by supplying bubbles, viable bacteria, enterococci, Vibrio, and Salmonella-like bacteria were removed effectively at removal efficiencies of 80% or greater. In addition, suspended solids were also removed from coastal seawater. However, fecal coliforms were difficult to remove by foam separation. The removal efficiency for viable bacteria was greater than 70% using a continuous system. Bacteria were concentrated in a very small amount of generated foam and removed from the water. The foam separation using dispersed bubbles and surface-active substances is a feasible convenient technology for seawater purification as a treatment prior to membrane filtration or ultraviolet irradiation.