Discipline: Technology and Engineering
Subcategory: Civil/Mechanical/Manufacturing Engineering
Andre Luna Magdaleno - Arizona State University
Co-Author(s): Gabriel Antonio Cerrón-Calle, Arizona State University, Tempe, AZ; John C. Graf, NASA Johnson Space Center, Houston, TX; Onur G. Apul, University of Maine, ME; Sergi Garcia-Segura, Arizona State University, Tempe, AZ
All human spaceflight missions have the critical requirement for environmental control and life support systems (ECLSS). Recovery of oxygen (O2) and effective sequestration of carbon dioxide (CO2) is essential for long-duration crewed space exploration. The current Sabatier system has poor O2 recovery efficiency, with an approximate 50% return from supplied CO2. Algal bioreactors may increase return yields by providing a multifunctional approach for closed loop CO2 reclamation, including (i) biofuel production, (ii) biomass for nutritional supplementation, and (iii) O2 production. Performance of current algal systems is limited by availability and low mass transfer efficiency of CO2 in an aqueous solution. Nanobubbles (NBs) are nano-sized cavities of gas ranging between 50 to 1000 nm in diameter. NBs have little to no buoyancy, providing gravity-independent means for gas supply and remain suspended for extended periods, up to months, in aqueous solution. The nanometric size of these gas interfaces, along with their long-term stability, can become a paradigm shift that drastically increases the efficiency of gas delivery and maximizes volumetric mass transfer coefficients (KLa). Quantification of NBs is possible, but very little is known about their promising applications in bioreactor systems. Experimental results suggest that NBs in solution behave as uncompressible liquids and produce homogeneous solutions with available gas content above saturated dissolved concentrations. The use of NBs can be a game changer for gas-starved systems. This work focuses on the initial studies understanding first the fundamentals of CO2 nanobubbles and their capability to impact water chemistry due to their unique gas-liquid interface interactions. It was hypothesized that carbon dioxide nanobubbles could increase buffering capacity and effective gas transfer within water solution.CO2 nanobubbles were generated using a nanobubble generator membrane pump system with CO2 gas intake. The analysis was done by recording CO2 nanobubbles characteristics and the physiochemical response to the introduction of the nanobubbles to the water at different generation times (10, 30, 50, and 70 min) and benchmarked against traditional macrobubbles of CO2 for the same amount of delivered gas. Additional analysis was done on the effect of pH on the nanobubbles due to the carbonate system increasing the pH. The system had both CO2 in the gas phase as nanobubbles and liquid as dissolved solvents therefore the effective concentration of CO2 was evaluated by measuring the buffer capacity (β). The size distribution of nanobubbles during the experiments was measured by Nanoparticle Track Analysis (NTA) where this also determined the concentration of gas as nanobubbles. Findings reported were that the mass transfer coefficient (KLa) showed a dramatically increase by 11-fold for the same volume of gas delivered when using nanobubbles. The β values obtained for nanobubbles were 7 times higher than that of traditional bubbles which can lead to significant source of CO2 availability by using the nanobubble method. Nanobubbles, consequently, undergo mass loss at higher pH corresponding to mass transfer process due to concentration gradient at the surrounding nanobubbles.
Funder Acknowledgement(s): This research is supported by the Western Alliance to Expand Student Opportunities (WAESO) Louis Stokes Alliance for Minority Participation (LSAMP) National Science Foundation (NSF) Cooperative Agreement No. HRD-1619524
Faculty Advisor: Sergi Garcia-Segura, email@example.com
Role: I lead the project focusing on generation of the nanobubbles and the analytical techniques used in particular Nanoparticle Track Analysis