Biosequestration of chromium(iii) in an aqueous solution using cationic and anionic biosurfactants produced from two different Bacillus sp. – a comparative study

Abstract

Tannery wastewater discharged from chrome tanning section contains Cr(III) in the range of 2100–2300 ppm, and a viable technique for its removal remains a great concern for the leather industry. The ability of a biosurfactant to chelate toxic heavy metal ions and form an insoluble precipitate may be exploited in the treatment of Cr(III) containing wastewater. In the present study, a biosurfactant producing microorganisms, Bacillus subtilis and Bacillus cereus, were isolated from tannery wastewater-contaminated soil using palm oil and coconut oil as the substrates. The biosurfactants produced from palm oil (palm oil BS) and coconut oil (coconut oil BS) were characterized as anionic and cationic biosurfactants, respectively, using the blue agar plate method, agar double diffusion technique and zeta potential measurement. The biosurfactants were characterized for their amino acid composition and elemental (CHNS) composition. The thermal behavior of the biosurfactant was characterized by TGA and DSC. The surface tension of the anionic and cationic biosurfactants were 28.16 ± 0.2 mN m⁻¹ and 23.02 ± 0.2 mN m⁻¹, respectively. The SDS-PAGE and FT-IR analyses confirmed that both the biosurfactants were lipoproteins in nature. The binding ability of the lipoprotein anionic and lipoprotein cationic BS with chromium (Cr(III)) ions in an aqueous solution was then determined. The interaction of Cr(III) with BS was confirmed using FT-IR, SEM-EDX analysis and atomic absorption spectrophotometry (AAS).