Convex sieve plate airlift bioreactor for enhanced oxygen transfer and refined soybean oil wastewater valorization

Regulating oxygen transfer is critical for improving wastewater valorization based on aerobic bioprocesses. In this study, a convex sieve plate (CSP) was designed to enhance gas-liquid dispersion in an airlift loop reactor (ALR), and its geometric parameters were optimized using a computational fluid dynamics (CFD)-population balance model (PBM) approach combined with response surface methodology. The effects of perforation rate, aperture diameter, arch height, and hole angle on gas holdup, liquid velocity, bubble-size distribution, and volumetric oxygen mass transfer coefficient were systematically investigated. The optimal CSP parameters were 23% perforation rate, 0.005 m aperture diameter, 0.03 m arch height, and 50° hole angle. The CFD-PBM results revealed that the convex geometry and inclined apertures redistributed radial momentum, promoted bubble breakup, suppressed premature recoalescence, and extended the effective axial mass-transfer domain. During refined soybean oil wastewater valorization by Trichosporon fermentans, the ALR-CSP increased biomass by approximately 1 g/L and chemical oxygen demand removal by 5 percentage points compared with the conventional ALR. A microbial lipid concentration of 2.1 g/L with a 49.5% (w/w) lipid content was obtained. The established relationship between geometric parameters and gas-liquid flow redistribution may guide targeted structural regulation for enhancing aerobic wastewater valorization.