Air-nanobubbles ineffective to reduce pathogenic bacteria in fresh and brackish waters

Nanobubble (NB) technology has been hailed as a novel way to disinfect water. Previous studies suggested that when NBs collapse, they create shock waves that result in OH- free radicals, which can damage cells, including bacteria. In this study, we investigated, through a series of 11 experiments, the potential use of air nanobubbles (128 {+/-} 44 nm, mean {+/-} SD) to reduce the concentration of various pathogenic bacteria including Aeromonas hydrophila, A. veronii, Vibrio parahaemolyticus, and Streptococcus agalactiae under controlled, tank-based laboratory conditions. Despite the high number of nanobubbles continuously added to a relatively small volume of water in experimental tanks (50-100 L), we did not observe a consistent or significant decrease in bacteria that would control disease outbreaks. Although most of the experiments were conducted in fresh water on A. hydrophila, results were consistent across fresh and brackish water experiments, Gram-negative and Gram-positive bacteria, and a range of nanobubble concentrations. This study suggests air nanobubbles on their own are inadequate to significantly reduce high levels of pathogenic bacteria in water. We propose to explore other gases for improving the disinfection properties of this technology. SIGNIFICANCE STATEMENTAir nanobubbles did not sufficiently reduce the level of bacteria in laboratory experiments.