CHROMIUM (VI) BIOSORPTION BY IMMOBILIZED BIOMASS OF Bacillus cereus

Toxic heavy metal contamination of industrial wastewater is an important environmental problem. Many industries such as electroplating, pigments, metallurgical processes, and mining and leather industries release various concentrations of heavy metals like chromium. Chromium generally exists in different forms, mostly as trivalent and hexavalent forms. Trivalent chromium is nontoxic and relatively immobile in nature; whereas hexavalent chromium is soluble in water, mobile, and is known to be highly toxic with potential carcinogenic effects (Zouboulis et al., 2004). Tannery waste contains 80250 mg/L chromium (CIDS, 1992). Safe value in water for drinking purposes is 0.05 mg/L (U.S. EPA), and recommended value for discharge is less than 5 mg/L (Directive-98/83/EC). Conventional methods such as chemical precipitation, membrane filtration, ion exchange, and adsorption for removing heavy metals (Patterson, 1977; Sung and Ji, 1997) from wastewater have significant disadvantages including incomplete metal removal, need for expensive equipment and monitoring systems, high reagents, and energy requirements (Wilde and Benemann, 1993). Adsorption is an alternative technique for heavy metal removal. The search for alternative and innovative treatment techniques has focused attention on use of biological materials such as algae, fungi, yeast, and bacteria for removal and recovery technologies and has gained importance during recent years because of the better performance and low ABSTRACT Biosorption is potentially an attractive technology for treatment of wastewater for retaining heavy metals from dilute solutions. This study investigated the feasibility of Bacillus cereus M16 immobilized in different carriers as a biosorbent for chromium removal from aqueous solutions in batch mode; optimum conditions were determined. Experimental results showed the bacterial strain immobilized in calcium alginate gel matrix was most effective in removing Cr(VI) ion from solution. The uptake of metal was very fast initially, and equilibrium was attained within 80 mins. The overall biosorption process was best described by the pseudo second-order kinetics. Intraparticle diffusion was not the only rate-determining step. The sorption data conformed well to the Fruendlich isotherm model. The highest value of Cr(VI) uptake by Bacillus cereus M16 (6.0g/L ,dry basis) immobilized in 3% calcium alginate was 92.5% at 25 0C, when initial chromium concentration was 50 mg /L.