Injecting nanobubbles into culture media can significantly improve microalgae cultivation by enhancing gas transfer, mixing, and process stability. Nanobubbles are ultra-fine gas bubbles (approximately 50–200 nm). Because of their extremely small size, they provide a very high gas–liquid interfacial area and long residence time, which can substantially increase CO₂ and O₂ mass transfer
coefficients (kLa) compared with conventional coarse aeration. They also tend to carry a negative surface charge, which helps prevent coalescence and can support flotation-based harvesting. In some systems, nanobubble collapse or dissolution may also generate reactive oxygen species (ROS), including hydroxyl radicals (•OH), which can influence cellular metabolism under controlled conditions.
These effects have been associated in the literature with improved algal growth rates and biomass yields. Reported gains vary by species, reactor design, gas type, and operating conditions, but studies have shown biomass improvements
in the range of roughly 10–40% or more in selected systems when nanobubbles are used for CO₂ or air delivery instead of conventional aeration. Reported additional benefits include higher lipid or pigment accumulation in some species and improved biomass recovery through nanobubble flotation.
1.0 Nanobubble Mechanisms and Algal Physiology:
High Interfacial Area and Gas Transfer: Nanobubbles’ nanoscale size gives them an extremely high gas–liquid interfacial area per unit volume, which sharply increases the volumetric mass-transfer coefficient (kLa) for sparged gases. For a given gas flow, reducing bubble size from millimeter scale to nanometer scale can increase the specific interfacial area by 10–100×. The resulting increase in kLa enables faster saturation of CO₂ and O₂. In practice, nanobubbles can sustain dissolved CO₂ for longer periods and support higher cell densities. Improved CO₂ availability accelerates photosynthesis and carbon fixation, thereby boosting growth.
Long Residence and Stability: Unlike coarse bubbles that rise rapidly and burst, nanobubbles are often neutrally buoyant and can remain suspended for days to weeks. This extended lifetime maintains a large dissolved-gas reservoir in the medium. Their small size also creates very high internal pressure, as described by the Young–Laplace relationship, which further drives gas dissolution. In effect, nanobubbles act as a “gas battery” that slowly delivers CO₂ or O₂ over time
Surface Charge and Flotation: Nanobubbles typically carry a net negative zeta potential of several tens of millivolts. This charge helps prevent bubble coalescence and stabilizes the colloidal suspension. In cultivation systems, this property can be exploited for harvesting: adding a cationic (positively charged) polymer or coagulant can bridge algal cells to bubbles, causing flocculation or flotation. Nanobubble flotation has achieved very high biomass recovery efficiencies in a short time in some studies
Figure: Schematic illustrating nanobubble-assisted algal harvesting through cationic polymer bridging, floc formation, and flotation for efficient biomass recovery.
ROS and Cavitation Effects: When nanobubbles collapse, either spontaneously or under pressure, they can generate localized high temperatures and pressures and produce ROS, especially hydroxyl radicals (•OH). While violent collapse, such as in sonication, is not typically used in cultivation, even mild bubble dissolution may generate some ROS. At low to moderate concentrations, ROS act as cell signaling molecules rather than harmful oxidants. They stimulate stress-response pathways, increase antioxidant enzyme activity, and can slightly loosen
cell walls, making nutrient transport more efficient. This controlled oxidative stress often enhances photosynthetic activity, promotes cell growth, and stimulates the production of valuable secondary metabolites. As a result, nanobubble-treated cultures often show improved biomass productivity and higher concentrations of commercially valuable compounds. Overall, the controlled generation of ROS is considered one of the key mechanisms through which nanobubbles enhance algal growth and metabolite production.
2.0 Biological Effects of Nanobubbles:
- Growth Rate & Biomass: Numerous studies report higher algal growth rates or final biomass under nanobubble aeration compared with conventional aeration. Overall, gains in growth and biomass reported in the literature range from about 10% to 50%, depending on species, nanobubble system, and operating conditions. These gains are generally attributed to improved CO₂ uptake and reduced CO₂ stripping.
- Biochemical Composition: Enhanced nutrient and gas transfer can alter cellular composition. Several studies note that nanobubbling, especially with CO₂, may stimulate lipid or pigment accumulation. For instance, Chlorella cultures operated under optimized microbubble regimes showed increased lipid content and productivity. In Haematococcus, nanobubble aeration increased astaxanthin content along with growth.
- Carbon Utilization and Photosynthetic Performance: CO₂ nanobubbles can improve carbon availability and gas–liquid mass transfer in algal cultivation. A recent study using Scenedesmus obliquus reported a carbon utilization efficiency of 27.86 ± 0.63% with CO₂ nanobubbles, along with a 10.11 ± 0.01% increase in biomass over 14 days compared with macrobubble CO₂ delivery. The improved performance was attributed to enhanced CO₂ mass transfer and carbon utilization.
- Nutrient Uptake and Stress: Enhanced mixing by nanobubbles leads to more uniform nutrient distribution in the reactor, including nitrogen and phosphorus. In wastewater-fed algal systems, micro-/nanobubbles have accelerated the breakdown of organics and increased nutrient bioavailability, indirectly improving algal nutrient uptake. Some studies report higher N and P removal rates in nanobubble-enhanced systems than in controls. The mild oxidative environment created by nanobubble dissolution may also oxidize recalcitrant organic compounds into simpler forms, benefiting mixotrophic (photosynthesis + organic carbon uptake) or heterotrophic (organic carbon uptake only) uptake.
3.0 Our Results:
Nanokriti conducted laboratory-scale experiments at the IIT Ropar laboratories to evaluate the effect of nanobubble-containing water on the cultivation of the freshwater microalga Chlorella sorokiniana. The growth of C. sorokiniana was monitored over a 14-day cultivation period using direct cell counting and optical density measurements. Overall, media prepared with nanobubble-containing water supported greater algal growth than the corresponding control media.
Both Air-NBs and O₂-NBs enhanced cell proliferation throughout the cultivation period, with growth differences becoming more pronounced during the later stages. Visual observation further supported these findings, as nanobubble-treated cultures exhibited a darker green coloration, indicating increased biomass accumulation. Among the two treatments, Air-NBs produced slightly greater growth than O₂-NBs under the experimental conditions. Since the dissolved gas concentrations were maintained at comparable levels in both the control and nanobubble-treated media, the enhanced growth was attributed primarily to the presence of nanobubbles rather than differences in dissolved gas concentration.
Biochemical analyses performed at the end of cultivation further confirmed the beneficial effects of nanobubbles on C. sorokiniana. Cultures grown in nanobubble-containing media exhibited greater biomass accumulation together with higher protein, chlorophyll, and carotenoid contents than the control cultures. These improvements in biochemical composition were consistent with the enhanced growth performance, indicating that nanobubbles not only promoted cell proliferation but also stimulated photosynthetic activity and overall cellular metabolism.
Collectively, the results demonstrate that nanobubble-containing media can significantly improve both biomass production and the biochemical productivity of C. sorokiniana, highlighting the potential of nanobubble technology for enhancing sustainable microalgal cultivation.
4.0 Industrial Applications:
Nanobubble aeration could enhance any large-scale algal process where gas transfer is limited:
- Biofuel Production: For phototrophic biofuels, improving CO₂ use efficiency directly lowers footprint and cost. NB systems could raise productivity in raceways or PBRs, improving yields per land/volume. They also facilitate low-energy harvesting (foam flotation), reducing downstream costs.
- High-Value Algal Products: In nutraceuticals or aquafeed algae (e.g. Spirulina, Chlorella, Haematococcus), the modest size scale and high product value justify NB systems. Enhanced pigment or lipid yields (as hinted for Haematococcus astaxanthin) could increase revenue.
- Wastewater Treatment & Algal Bioremediation: In integrated systems, NBs serve dual roles: aeration for nitrification and flotation-based harvesting.
- Aquaculture: Although not direct algae cultivation, many fish farms use NB for water quality and plankton growth. Enhancing algae feed in hatcheries (bioflocs) could be an application.
- Carbon Capture: By boosting algal CO₂ uptake, NB-enabled cultivation could be paired with flue gas feed (e.g. from fermentation) for carbon capture.
5.0 Conclusions and Recommendations:
Nanobubble technology offers a practical route to overcome key bottlenecks in algal cultivation by improving gas transfer, mixing, and biomass recovery. Empirical studies consistently show faster CO₂ and O₂ delivery and higher biomass yields when nanobubbles are used. In some cases, nanobubble aeration also supports higher pigment or lipid accumulation.
For algae cultivation projects, nanobubbles should be evaluated through pilot trials to optimize gas type, bubble concentration, residence time, hydraulic configuration, and species-specific operating conditions. Site-specific validation is important because performance depends on reactor geometry, light regime, nutrient status, and gas dosing strategy.
Nanokriti systems are well suited for such trials and for scale-up where improved gas utilization, lower maintenance, and process integration are required. Overall, nanobubble aeration is a promising frontier technique for algal biotechnology and a strong candidate for industrial deployment where productivity and process efficiency are priorities.
6.0 References:
- Nirmalkar, N., Pacek, A. W., & Barigou, M. (2018). On the existence and stability of bulk nanobubbles. Langmuir, 34(37), 10964–10973.
- Nirmalkar, N., Pacek, A. W., & Barigou, M. (2018). Interpreting the interfacial and colloidal stability of bulk nanobubbles. Soft Matter, 14, 9643–9656.
- Agarwal, A., Ng, W. J., & Liu, Y. (2011). Principle and applications of microbubble and nanobubble technology for water treatment. Chemosphere, 84(9), 1175–1180.
- Temesgen, T., Bui, T. T., Han, M., Kim, T. I., & Park, H. (2017). Micro and nanobubble technologies as a new horizon for water treatment techniques: A review. Advances in Colloid and Interface Science, 246, 40–51.
- Li, L., Wei, J., Lee, Y.-Y., Zhang, Y., Xue, S., Atukuri, S., Li, Y., Marhaba, T., Zhang, X., & Zhang, W. (2026). “Comparative study of CO₂ nanobubbles and macrobubbles: Effects on water chemistry, microalgal growth, and carbon utilization.” Water Research, 288, 124714. DOI: 10.1016/j.watres.2025.124714.