Microalgal-luffa sponge immobilized disc: a new efficient biosorbent for the removal of Ni(II) from aqueous solution N. Akhtar 1 , J. Iqbal 2 and M. Iqbal 3 1 Department of Biology, Government Islamia College for Women, 2 Department of Botany, University of Punjab, Quaid-e-Azam Campus, and 3 Environment Biotechnology Group, Biotechnology and Food Research Center, PCSIR Laboratories Complex, Lahore, Pakistan 2002/384: received 11 December 2002, revised 8 April 2003 and accepted 24 April 2003 ABSTRACT N. AKHTAR, J. IQBAL AND M. IQBAL. 2003. Aims: The aim was to develop a new, efficient and cost-effective biosorbent for the removal of heavy metals from aqueous solution. Methods and Results: A new biosorbent was developed by immobilizing a unicellular green microalga Chlorella sorokiniana within luffa sponge discs and used for the removal of metal ions from aqueous solution. Microalgal-luffa sponge immobilized discs (MLIDs) removed Ni(II) very rapidly, with 97% of equilibrium loading being reached in 5 min. MLIDs were tested for their potential to remove Ni(II) from aqueous solution in fixed-bed column bioreactor. The regenerated MLIDs retained 92®9% of the initial binding capacity for Ni(II) up to five cycles of reuse. Conclusions: In this study for the first time, C. sorokiniana biomass immobilized within luffa sponge disc was successfully used as a metal biosorbent for the removal of Ni(II). It appears that MLIDs can be used as an effective biosorbent for efficient removal of Ni(II) or other metals from aqueous solution. Significance and Impact of the Study: MLIDs biosorption system was shown to have good biosorption properties with respect to Ni(II). Efficient metal removal ability of MLIDs, low cost and simplicity of the technique used for the preparation of MILDs could provide an attractive strategy for developing high-affinity biosorption system for heavy metal removal. Keywords: biosorption, Chlorella sorokiniana, Luffa cylindrica, luffa sponge, microalgae, nickel(II). INTRODUCTION Industrial effluents, particularly those containing heavy metals, are a cause of serious hazard to human health and other forms of life. Environmental protection laws demand that industrial discharges are duly treated to minimum acceptable limits of various toxic metals. Conventional methods are either cost-prohibitive or not practicable on account of operational shortcomings (Atkinson et al. 1998). Biosorption by algal biomass has been recently projected as an alternative for the remediation of wastewaters containing toxic metals (Robinson 1998). However, the fragile nature of algal biomass is not suitable for robust wastewater treatment operations (Chu et al. 1997). This has led to the interest in the use of entrapped biomass as immobilized preparations. Several immobilization media, such as alginates, carrageen- ans and polacrylamide gel have been used for this purpose (Robinson 1998). Immobilization based on these polymeric matrices, however, result in restrictive diffusion because of closed embedding structures with low mechanical strength. The purpose of the present study, therefore, is to provide a new immobilized microalgal biosorption process using a low cost, physically strong, ridged and highly porous immobil- ization matrix; luffa sponge. The use of luffa sponge for immobilization of algal, fungal and yeast cells has long been reported (Iqbal and Zafar 1993; Ogbonna et al. 1997). Correspondence to: Dr Muhammed Iqbal, Department of Chemical and Process Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK (e-mail: m.iqbal@sheffield.ac.uk). ª 2003 The Society for Applied Microbiology Letters in Applied Microbiology 2003, 37, 149–153