Production of surfactin from rice mill polishing residue by submerged fermentation using Bacillus subtilis MTCC 2423

•Surfactin was produced from rice mill processing residue (RMPR).•Growth of B. subtilis MTCC 2423 was solely due to inherent nutrients present in residue.•Multi stage foam fractionation and acid precipitation was used to recover the product.•4.17 g surfactin/kg RMPR with molecular weight 1076 Da was obtained.•Foam separation of copper using surfactin resulted in 72.5% removal of copper.

Rice mill polishing residue (RMPR), an abundant and cheap agro residue, was used as substrate for microbial growth of Bacillus subtilis MTCC 2423 by submerged fermentation process to produce surfactin. Nutrients present in the residue were sufficient to sustain the growth of the microorganism. Multi stage foam fractionation followed by acid precipitation was used to concentrate and recover the product. Recoverable yield of surfactin was 4.17 g/kg residue. Product recovered in the foamate accounted for 69% of the total yield. The residual broth containing ∼30% surfactin exhibited biological oxygen demand and chemical oxygen demand values of 23 and 69 mg/L respectively. The microbial growth data was correlated using three parameter sigmoid models. Surfactin synthesized had a predominance of molecular weight 1076 Da. Foam separation of copper using surfactin resulted in a maximum removal of 72.5%.