Increased Rhamnolipid Concentration and Productivity Achieved with Advanced Process Design

Rhamnolipids are biosurfactants having several applications. A major limitation in rhamnolipid production is low productivity, which decreases significantly during stationary-phase production. In this study, fermentations were first made with nitrogen-limited stationary phase. Long-term rhamnolipid production (up to 505 h) could be maintained with low-rate N-source addition but the intermittent cell growth led to lower productivity (q(p)), particularly apparent at the highest addition rate. Four fermentations were next made under non-N-limited stationary phase without and with N-source supplementation; q(p)could be much higher at 24-26 mg g(-1)h(-1). Three final fermentations were designed to build the maximum cell concentration to 30 g L(-1)in two growth phases where the growth rate in the second phase was regulated by N-addition to control foaming. Cultures then entered non-N-limited stationary phase and were N-supplemented. At an optimal rate of 15% growth-N per 24 h to maintain cell activity, a highest rhamnolipid concentration of 120 g L(-1)was obtained after 144 h with overall productivity of 839 mg L(-1)h(-1).