Optimization of hydrodynamics for enhanced co-cultivation in bubble column reactors: Investigating flow dynamics and biomass productivity

• Scenedesmus – Lemna sp co-cultivation stabilized DO and pH, reducing algal stress • Co-cultivation nearly doubled productivity compared to monoculture systems • Optimized bubble column hydrodynamics enhanced algal biomass productivity by 11% • 10 cm diameter bubble column achieved optimal gas holdup and light distribution • Findings provide scale-up guidance for wastewater-fed biofuel production Hydrodynamic effects on algal cultivation have been studied, but limited work has addressed how bubble column diameter influences the co-cultivation of microalgae and duckweed in sewage wastewater systems and biofuel production. This is the first empirical study that fills the gap by experimentally evaluating the co-cultivation of Scenedesmus sp. and Lemna sp . (Duckweed) in wastewater fed reactors. This study evaluated how bubble column diameter and co-cultivation with Lemna sp. influence the biomass productivity and hydrodynamics of Scenedesmus-Lemna regimes. Three bubble columns with internal diameters of 5, 10, and 15 cm were operated under identical aeration (3 – 9 L/hr) and illumination conditions in both monoculture and co-culture configurations. The 10 cm column (C2) achieved the highest performance in co-culture, with a specific growth rate of 0,74 ± 0,05 mg d⁻¹ and biomass productivity of 93,85 ± 4,12 mg L⁻¹ d⁻¹, representing almost 90 % increase compared with monoculture. Additionally, co-culturing Scenedesmus sp. with Duckweed led to an 11 % increase in growth rates. Increased biomass suggests potential for increased biomolecules, including lipids and hydrocarbons. Co-cultivation also stabilized pH and dissolved oxygen and promoted attached growth on Lemna roots, offering a low-cost and novel attached harvesting pathway. These results highlight that reactor geometry and co-cultivation strategies are critical determinants of algal productivity and can substantially influence productivity and harvesting efficiency in large scale algal phycoremediation systems and enhance 3stability in wastewater treatment systems.