BACKGROUND: This article proposes a new methodology for calculating k(L)a in airlift reactors (ALRs) based on a digital imaging technique and Higbie's model. Four ARLs with different internal diameters (28, 37.4, 45, and 55 mm) were used to determine the aeration patterns, velocities, and size distributions of the bubbles. Video recordings lasting 10 s were recorded using a 1080p slow-motion camera at 240 frames per second (fps). In 100 frames per video, between 500 and 599 frames, the characteristics of the bubbles were captured and then processed using the sci-kit-image Python package. RESULTS: The Higbie model coupled with image analysis was used to determine k(L), and was then compared with the experimental values and k(L)a correlations. As a result, bubble velocities between 0.2 and 0.8 m s(-1) were determined. CONCLUSIONS: The k(L)a values (20-28 h(-1)) calculated using the new methodology were close to the experimental values and were compared with the correlations for ALRs. (c) 2025 Society of Chemical Industry (SCI).