Response surface methodology for cadmium biosorption on Pseudomonas aeruginosa Salman Ahmady-Asbchin ABSTRACT In this research the effects of various physicochemical factors on Cd 2þ biosorption such as initial metal concentration, pH and contact exposure time were studied. This study has shown a Cd 2þ biosorption, equilibrium time of about 5 min for Pseudomonas aeruginosa and the adsorption equilibrium data were well described by Langmuir equation. The maximum capacity for biosorption has been extrapolated to 0.56 mmol.g À1 for P. aeruginosa. The thermodynamic properties ΔG 0 , ΔH 0 , and ΔS 0 of Cd 2þ for biosorption were analyzed by the equilibrium constant value obtained from experimented data at different temperatures. The results show that biosorption of Cd 2þ by P. aeruginosa are endothermic and spontaneous with ΔH value of 36.35 J.mol À1 . By response surface methodology, the quadratic model has adequately described the experimental data based on the adjusted determination coefficient (R 2 ¼ 0.98). The optimum conditions for maximum uptake onto the biosorbent were established at 0.5 g.l À1 biosorbent concentration, pH 6 for the aqueous solution, and a temperature of 30 W C. Salman Ahmady-Asbchin Department of Molecular and Cell Biology, Faculty of Basic Science, University of Mazandaran, P.O. Box 47416-95447, Babolsar, Iran E-mail: sahmadyas@yahoo.fr; sa.ahmadi@umz.ac.ir Key words | biosorption, cadmium (II), Pseudomonas aeruginosa, response surface methodology INTRODUCTION Toxic heavy metals are frequently released in wastewaters produced by various industrial processes, such as those employed in the electroplating, metal finishing polishing, metallurgical, tannery, chemical manufacturing, mining, and battery manufacturing industries (Polprasert & Liya- nage ). The presence of metal ions in final industrial effluents is extremely undesirable, since they are toxic to both lower and higher organisms even at low doses (Schro- der et al. ; Doshi et al. ; Rehman & Anjum ; Ema et al. ; Pierron et al. ). Under certain environ- mental conditions, metals may accumulate in biological systems and reach toxic levels and then cause ecological issues, which damages health. Cadmium is one of the most toxic heavy metals in the ecosystem (Lagadic et al.  Koedrith & Seo ). Tox- icity of Cd 2þ is mediated by either carcinogenic or endocrine disturber effects via both genetic and epigenetic molecular mechanisms (Silva et al. ; Wang et al. ). In recent years, biological material has been widely used in Cd 2þ removal from aqueous solution. Bacteria are present in all areas of our environment and they are routinely used in Cd 2þ removal from aqueous solution; these may include, Pseudomonas putida (Pardo et al. ), Pseudomonas sp., Staphylococcus xylosus (Ziagova et al. ) and Pseudomo- nas aeruginosa (Mullen et al. ; Wang et al. ; Juwarkar et al. ; Singh et al. , ). Alongside bac- teria, there are several chemical methods and technologies that can be used to remove Cd 2þ . These include chemical precipitation, oxidation or reduction, filtration, ion exchange, electrochemical treatment, reverse osmosis, mem- brane technology and evaporation recovery. However, most of these methods and technologies are ineffective or highly expensive when metal concentrations are less than 100 mg.l À1 (Ahluwalia & Goyal ). Alternative methods of metal removal and recovery based on biological materials have also been considered. Certain types of microbial bio- mass can retain relatively high quantities of metals on their cell wall due to their structure. This metabolism-inde- pendent mechanism is called biosorption (Alexander ). In terms of biosorption, polysaccharides, proteins and lipids on bacterial cell walls offer many functional groups, such as carboxylate, hydroxyl, phosphate, amine and sul- phate groups which can bind to the metal ions. This natural affinity of biological structures for metallic elements 2608 © IWA Publishing 2016 Water Science & Technology | 73.11 | 2016 doi: 10.2166/wst.2016.061 Downloaded from https://iwaponline.com/wst/article-pdf/73/11/2608/460391/wst073112608.pdf by guest on 27 November 2018