Biosorption the Possible Alternative to Existing Conventional Technologies for Sequestering Heavy Metal Ions from Aqueous Streams: A Review

Transition metal ions in industrial effluent discharge are of great threat to the environment. Several conventional treatment technologies viz., ion exchange, membrane separation, ultra-filtration, ion flotation, electro-coagulation, electrodialysis, sedimentation and reverse osmosis have been employed. However these methods involve high operating cost and produce large volume of toxic chemical sludge. In this context, biosorption process could be helpful and is emerging as a potential alternative to the existing technologies for the removal and recovery of metal ions from aqueous solutions. The major advantages of biosorption over conventional treatment methods include high efficiency, minimization of chemical sludge, low cost in regeneration of biosorbents and possibility of metal recovery. Agricultural waste materials being cellulosic are an excellent source for metal biosorption. They have different functional groups viz. hydroxyl, carboxyl, phenolic, amino, acetamido etc. having affinity for metal ions to form chelates and metal complexes. The mechanism of biosorption process includes chemisorption, complexation, diffusion, ion exchange, micro precipitation and surface adsorption. The aim of this review article is to provide the information on biosorption as a possible alternative to other conventional technologies and to highlight the chemical composition of agricultural waste material along with adsorption models and mechanism for metal biosorption.