Removal of chromium by mucilaginous seeds of Ocimum basilicum

Polysaccharides bound to bacteria or in isolated form have been shown to bind heavy metals. A limitation of this technology can be overcome by immobilization. In view of this Ocimum basilicum seeds which swell upon wetting could serve as natural immobilized source of agriculturally-based polysaccharides. The seeds consist of an inner hard core and a pectinous fibrillar outer layer. Pretreating the seeds with acid, alkali, periodate or boiling in water was found to alter the metal binding capacity. Of the various treatments given, seeds boiled in water were found to be superior in terms of mechanical stability and exhibited fairly optimal Cr(VI) uptake kinetics. The maximum adsorption capacity as calculated from the Langmuir isotherm was 205 mg Cr/g dry seeds. Biosorption of Cr(VI) was found to be pH dependent with maximum uptake at pH 1.5 wherein sorption was not affected by the presence of other metal ions such as Cd(2+), Cu(2+), Ca(2+) and Na(+). Seeds were used in a packed bed reactor for the continuous removal of Cr(VI). Thus O. basilicum seeds may have application as a potential bioresource in tropical countries such as India where they are widely available.