Rhamnolipids (RL) are microbial glycolipid biosurfactants that have gained increasing attention due to their eco-friendly nature, with promising applications in environmental remediation and oil recovery. Despite their efficacy, industrial-scale RL production remains limited due to challenges in reproducibility and scalability. One of the reasons is that bioprocess scale-up from bench to pilot-scale systems often represents a major bottleneck in fermentation technology. An improper scale-up process can lead to microbial activity and product formation inconsistencies, affecting overall process yield and reproducibility. This study investigates the scale-up of RL production by Pseudomonas aeruginosa RS6 using biodiesel side stream waste glycerol as substrate, transitioning from a 1.5 to a 5 L bioreactor under a controlled constant impeller tip speed (Vtip) of 0.882 ms−1. Enhanced gas–liquid mass transfer was achieved in the 5 L system, reflected by a higher volumetric oxygen transfer coefficient (kLa) of 0.032 ± 0.00067 s−1 compared to 0.025 ± 0.00087 s−1 in the 1.5 L bioreactor. Correspondingly, the oxygen transfer rate (OTR) increased from 98.8 to 127.35 mmol L−1h−1. Both RL yield and productivity increased by approximately 22% and 45%, reaching a final RL concentration of 16.48 ± 0.02 gL−1 and productivity of 0.22 ± 0.11 g L−1h−1, respectively, in the 5 L bioreactor. Biomass of P. aeruginosa RS6 concentrations remained satisfactory across scales, indicating that shear forces did not compromise cell integrity. An opposite trend was observed in the oxygen uptake rate (OUR), suggesting prolonged oxygen availability and sustained microbial respiration in the 5 L bioreactor, likely driven by effective hydrodynamic control. Notably, produced RL maintained its high quality across both scales, exhibiting emulsification activity, EI24% of 62.38 ± 0.53 and 60.10 ± 0.34 on hydrophobic liquid kerosene and palm cooking oil, respectively. These findings validate constant Vtip as a robust scale-up strategy for RL production, effectively enhancing yield while maintaining microbial cell viability and physiological performance. By demonstrating consistent process behavior between bioreactor scales, this study provides experimental evidence that addresses common scale-up limitations, specifically poor scalability and reproducibility in RL biosurfactant production.   Keywords: Rhamnolipid, Bioreactor, Scale-up, Volumetric oxygen transfer coefficient, Oxygen transfer rate, Impeller tip speed
Figure 1: Schematic diagram of rhamnolipid production
Figure 2: Measured dimension of the Rushton-type impeller configuration; A 0.038 m of diameter of the impeller in the 1.5 L bioreactor, and B 0.064 m of diameter of the impeller in the 5 L bioreactor
Figure 3. Emulsification layer formed by RL produced in a 5 L bioreactor after 24 h, showing activity against kerosene (left) and palm cooking oil (right)
Source: Siti Syazwani Mahamad, Mohd Shamzi Mohamed,Mohd Nazren Radzuan, James Winterburn, Mohd Rafein Zakaria (2026). Bioreactor scale-up on rhamnolipid production by Pseudomonas aeruginosa RS6 based on constant impeller tip speed. Systems Microbiology and Biomanufacturing 6:20

Date of Input: 29/01/2026 | Updated: 29/01/2026 | ainzubaidah