Separation and Purification Technology 45 (2005) 25–31 Removal and recovery of heavy metals from aqueous solution using papaya wood as a new biosorbent Asma Saeed a , M. Waheed Akhter b , Muhammed Iqbal a,∗ a Environment Biotechnology Group, Biotechnology and Food Research Centre, PCSIR Laboratories Complex Ferozepur Road, Lahore 54600, Pakistan b Institute of Biochemistry and Biotechnology, University of Punjab, Lahore, Pakistan Received 4 October 2004; received in revised form 3 February 2005; accepted 10 February 2005 Abstract Papaya wood was evaluated as a new biosorbent of heavy metals. On contacting 10 mg l −l copper(II), cadmium(II) and zinc(II) solutions with 5gl −1 papaya wood, during shake flask contact time of 60 min, the respective metal removal was noted to be 97.8, 94.9 and 66.8%. Sorption was most efficient at pH 5. Metal ion biosorption increased as the ratio of metal solution to the biomass quantity decreased. Conversely, biosorption/g biosorbent decreased as the quantity of biomass increased. The increase in initial metal ion concentration was associated with steep increase in biosorption at lower concentrations, progressively reaching towards plateau at higher metal concentrations. At equilibrium, the affinity of papaya wood to biosorb metals was in the order of copper(II) > cadmium(II) > zinc(II), which remained the same during the testing of variables of different factors. The biosorption data perfectly fit the Langmuir adsorption isotherms model with 0.99 regression coefficient (r 2 ) for all the metals. The fit on Freundlich adsorption isotherms model was acceptable but not as good. The biosorption kinetics studies indicated that the data followed the second-order reaction with r 2 of 0.99. The first-order reaction was not applicable to the data. The metal-loaded papaya wood was completely desorbed with 0.1N HCl. During repeated biosorption–desorption for five cycles, no loss in the efficiency of copper(II) and cadmium(II) removal from their respective solutions and the metal-loaded biomass was noted. The study points to the potential of a novel use of papaya wood, itself a cause of environmental degradation and otherwise of no utility, for the treatment of wastewaters contaminated with heavy metals. © 2005 Elsevier B.V. All rights reserved. Keywords: Carica papaya; Biosorption; Heavy metal removal; Sorption isotherm; Biosorption kinetics; Desorption 1. Introduction Enhanced industrial activity during recent decades has led to the discharge of unprecedented volumes of wastewater, which is a serious cause of environmental degradation. Heavy metals, due to their high toxicity, pose a serious threat to biota and the environment [1]. Therefore, it is necessary to alleviate these metals from industrial effluents, before their discharge into water bodies. Several methods have been sug- gested for the removal of toxic metals from wastewaters [2]. Techno-economic considerations, however, limit their wide- scale application. During the last decade, biomass of diverse ∗ Corresponding author. Tel.: +92 42 9230688x291; fax: +92 42 9230705. E-mail address: iqbalmdr@brain.net.pk (M. Iqbal). origin has been reported to efficiently remove heavy metals. Successful metal biosorption has been reported by a variety of biological materials including, microalgae and seaweeds, bacteria, fungi and crop residues [3,4]. One category of biowastes on which little attention has been paid as metal biosorbents is the woody plant wastes. The few reported cases include pine bark and needles [5], sawdust [6], and petiolar felt-sheath of palm [7]. In this paper, accordingly, a new wood waste material is reported as a metal biosorbent. The work relates to biosorption properties of papaya wood, which is generated as a waste in papaya plantations and has otherwise no commercial worth. The purpose was to explore the potential of papaya wood waste to treat wastewaters contaminated with heavy metals. 1383-5866/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2005.02.004