A pilot airlift reactor integrated a low-shear swirl microbubble generator for yeast production using straw as substrate.

A pilot-scale airlift loop reactor (ALR) coupled with a low-shear swirl microbubble generator was first successfully designed and verified to improve mass transfer, mixing, and yeast production using straw. The hydrodynamics was explored in an air-straw-liquid system. With enhanced external circulation and microbubbles less than 150 μm, mass transfer was promoted by 11.5 times. The impacts of the low-shear microbubble generator on solid substrates and cell activity were also investigated. After long-term operation, the straw d50 decreased by about 3 μm, and Candida utilis (C. utilis) cells continued to exhibit good activity. It produced 40.8 % more viable cells than traditional ALR when C. utilis was cultivated. This integrated dual-cycle bioreactor has excellent mixing and mass transfer capabilities, resistance to blockage, and relatively low shear, favoring biological fermentation. This work demonstrates the effectiveness of the novel microbubble ALR design, improving yeast productivity and offering an effective solution for solid substrate utilization.