Biosorption of Procion Red MX 5B by Bacillus subtilis and Its Extracellular Polysaccharide: Effect of Immobilization

Abstract

Research Article Biosorption of Procion Red MX 5B by Bacillus subtilis and Its Extracellular Polysaccharide: Effect of ImmobilizationBacillus subtilis and its extracellular polysaccharide (EPS) were used in free form as well as immobilized form as biosorbent for the removal of an anionic dye Procion Red MX 5B. Low pH was favourable for biosorption. Immobilization resulted in reduced biosorption of the dye. The presence of functional groups responsible for the high adsorption capacity in free cells (FC) and EPS was confirmed by FTIR analysis. High Q max and b values were noted in the case of FC and free EPS in contrast to immobilized cells and EPS. The kinetics data showed that the adsorption system followed pseudo-first-order reaction at low dye concentration. Desorption of the dye was found to be 100% in 1 N NaOH. In the case of immobilized biomass and EPS the alginate was found to be unstable under high alkaline conditions of NaOH. IntroductionTextiles industries consume large amounts of water, particularly for bleaching and dyeing purposes. Textile industries contribute considerable amount of effluent of varying characteristics such as color, dissolved solids and various organic and inorganic substances. Treatment of the textile effluent normally involves neutralization, coagulation followed by biological treatment. This treatment involves large amount of acid, coagulants and energy. Attempts have been made to substitute microorganisms for chemicals. While most textile dyes have low aquatic toxicity, the discharge of highly colored untreated or partially treated textile mill effluents can impair the aesthetic value of receiving waters while also affecting water transparency and gas solubility, which may in turn negatively affect aquatic biota. The majority of technologies presently employed for color removal are based on physicochemical processes such as dilution, adsorption, coagulation and flocculation, chemical precipitation, oxidation, ion-exchange, reverse osmosis and ultra filtration [1]. Although adsorption on to activated carbon gained prominence as a treatment technology, its high cost and associated problems of regeneration have led to the constant search for alternate efficient low cost adsorbents [2]. Apart from agricultural and industrial wastes that have formed the bulk of low cost adsorbents, microbial adsorbents also form a major group of biosorbents which are being studied for their application in dye and metal removal technologies. Dye adsorption studies using microorganisms has been carried out by many researchers [3]. Several researchers have worked on microbial adsorbents such as Corynebacterium glutamicum [4], Trametes versicolor [5], Penicillium chrysogenum [6], Rhizopus arrhizus [7]and Aspergillus fumigatus [8] for dye adsorption. Very minimal works have been done with bacteria and their exopolysaccharides with regard to metal removal but not on dye removal [9]. EPS are heterogeneous mixture composed mainly of polysaccharides and proteins, with nucleic acids and lipids as minor constit...

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