Imagine an aquarium with fine air bubbles constantly rising. In a photobioreactor, these bubbles do more than create an atmosphere; they introduce carbon dioxide into the water and remove oxygen. An Indonesian research team shows that smarter bubbling can significantly accelerate the growth of microalgae. The study was published in Scientific Reports on September 1, 2025.
Smarter drinking
The research group built a rectangular airlift reactor with baffles and used a mushroom-shaped air distributor that produces many small bubbles. Baffles keep the bubbles inside the column longer and break larger bubbles into smaller ones. This increases the contact surface between gas and water, precisely what algae need to quickly absorb carbon dioxide and grow.
Reactor in picture
The Synechococcus HS 9 species was cultivated in a 25-liter setup. Aeration was set at two liters per minute with air containing 0,04 percent carbon dioxide. The researchers monitored pH, dissolved gases, and optical density, filmed bubble behavior, and calculated how bubble size and rise rate relate to mixing and mass transport. They explicitly state that this was a single, continuous, and unrepeatable experiment.
Numbers that count
The bubbles remained small, around 0,114 micrometers, and rose moderately quickly. The measured mass transfer coefficients were high for oxygen and carbon dioxide, approximately 0,099 and 3,226 per second, respectively. Around day thirteen, the culture reached the peak of the growth phase with a total of XNUMX grams of dry biomass. In this type of reactor, the contact between gas and liquid is often the limiting factor, making these values relevant.
Return from aeration
This is a practical tip for anyone working on biofuels or bio-based chemicals. Productivity depends not only on the algae species or the medium, but also on the bubbles themselves. With a different distributor and baffle geometry, you can dissolve more carbon dioxide and therefore produce more cell material per liter per day. Furthermore, airlift systems have few moving parts and are energy-efficient, which helps with scale-up.
The results are promising, but this is just one trial. Repetition and larger-scale testing, with variations in light, nutrients, and aeration, should reveal whether the gains from small bubbles can be maintained outside the lab. All formulas, data series, and video footage are available in the open-access publication.
Source: Nature.com
