An inexpensive strategy for facilitated recovery of metals and fermentation products by foam fractionation process

Microbial biosurfactants produce foam during aerobic-fermentation processes. The degree of foaminess and foam stability of the lipopeptide-biosurfactant produced by a marine Bacillus megaterium strain were investigated using simulated biosurfactant solution (SBS), biosurfactant broth without cells (BBWOC) and biosurfactant broth with cells (BBWC) in bubble column experiments. The experimental data for foam collapse were fitted using a first-order foam decay model. The first-order rate constant (k), a measure of foam stability, was maximum (k = 0.0003 S−1) for BBWOC in the pH range 6–9. However, maximum foam stability (k = 0.0006 S−1) was restricted to pH 7 for BBWC. Foam-based metal removal studies revealed that the metal removal followed a saturation model. The relative binding capacity of each divalent metal was greatly affected by the presence of other divalent metals. The order of lipopeptide binding capacity of the metals was Fe2+ > Ca2+ > Mg2+, with Fe2+ significantly influencing the foam stability. In case of Fe2+, Ca2+ and Mg2+, maximum metal recovery of 64.7 ± 4.3%, 52 ± 3.1% and 41.4 ± 3.6% respectively was observed at pH 7. The enrichment (E) of the other media components, including cells, was comparatively insignificant. The results of this study have implications in designing and optimizing biosurfactant or protein recovery in situ by foam fractionation as an inexpensive strategy, and also in facilitated metal recovery from industrial effluents and ores.