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%.