Improving CO2 concentration and retention via nanobubble generation in aqueous solutions

• Saturation with carbon dioxide nanobubbles increases concentration and stability • Salt content influences carbon dioxide concentration and stability in dispersions • Nanobubble saturation of growth media results in higher concentration and stability The application of nanobubbles (NBs) in materials research, water treatment, and chemical reactions is well documented, primarily due to their high stability, longevity, and enhanced mass transfer rates. Recently, oxygen and air nanobubbles have been employed in enhancing algal and plant growth. However, data on carbon dioxide nanobubbles remain scarce, particularly regarding their effects on concentration and retention. In this work, carbon dioxide was dissolved into aqueous solutions with varying salt concentrations, and the flow was depressurized through a needle valve to generate NBs dispersions. Particle number and carbon dioxide concentration were analyzed over a 10-day period and compared with a control solution generated via bubbling. The dispersions exhibited significant NBs concentrations and, more importantly, higher carbon dioxide levels than the bubbling solution. The highest concentrations were observed in 1 mM NaCl and distilled water, corresponding to increases of 136% and 97%, respectively. All dispersions maintained superior concentrations compared to the control. Furthermore, the dispersions retained elevated carbon dioxide levels for an average of five additional days relative to the bubbling solution. Finally, the experimental data were used to fit exponential models describing the evolution of the dispersions. These models revealed both the influence of the saturation methodology and the trade-off between salinity, particle size, and carbon dioxide retention. Overall, the results demonstrate that this methodology provides advantages over conventional carbon dioxide delivery strategies and may contribute to process optimization in algal biomass production.