Integrated valorization of rice-stubble and waste cooking oil for rhamnolipid production with process optimization, techno-economic and life-cycle assessment

The present study employed central composite design to optimize fermentation parameters for rhamnolipid production. Reducing sugar rich fermentable hydrolysate was generated by dilute acid hydrolysis of rice stubble under the optimized conditions with subsequent activated carbon treatment. Detoxified hydrolysate was further combined with crude glycerol from waste cooking oil. Fermentation by Pseudomonas aeruginosa 2297 on these integrated substrates produced the highest titer of 5,220 ± 285.9 mg/L with an emulsification index of 67.13% under optimized concentrations of rice stubble hydrolysate of 12.21 g/L, crude glycerol of 30.52 g/L, NaNO 3 of 5.19 g/L and fermentation time of about 120 h. Rhamnolipid production was confirmed by FTIR and LC-MS. It demonstrated concentration-dependent antibacterial properties towards Gram-positive bacteria up to a 12.17 mm zone of inhibition, although activity may vary with degree of purification and congener composition. A minimum selling price of USD 1.30/g was estimated through techno-economic analysis considering zero net present value which serves as a reference to assess further economic potential. A life cycle assessment showed a climate change impact of 1.25 kg CO₂ eq /g, with fermentation electricity accounting for most emissions. Both assessments are design-stage estimates extrapolated from shake-flask data. These results identify energy demand as the dominant sustainability constraint.