Clean 2009, 37 (11), 901 – 907 S. Renganathan et al. 901 Sahadevan Renganathan 1 Jayabalan Kalpana 1 Mahendradas Dharmendira Kumar 1 Manickam Velan 1 1 Department of Chemical Engineering, Alagappa College of Technology, Anna University Chennai, India. Research Article Equilibrium and Kinetic Studies on the Removal of Reactive Red 2 Dye from an Aqueous Solution Using a Positively Charged Functional Group of the Nymphaea rubra Biosorbent Nymphaea rubra stem was used as a low cost and easily available biosorbent for the removal of Reactive Red 2 dye from an aqueous solution. Initially, the effects of bio- sorbent dosage (0.2 – 1.0 g L –1 ), pH (1 – 6), and dye concentration (30 – 110 mg L –1 ) on dye removal were studied. Batch experiments were carried out for biosorption kinetics and isotherm studies. The results showed that dye uptake capacity was found to increase with a decrease in biosorbent dosage. Equilibrium uptake capacity was found to be greatest at a pH value of 2.0, when compared to all other pH values studied. The equilibrium biosorption isotherms were analyzed by the Freundlich and Langmuir models. The equilibrium data was found to fit very well with the Freund- lich isotherm model when compared to the Langmuir isotherm model. The kinetic data was analyzed using pseudo-first order and pseudo-second order kinetic models. From the results, it was observed that the kinetic data was found to fit the pseudo- second order kinetic model very well. The surface morphology of the stem of the N. rubra biosorbent was exemplified by scanning electron microscopy. Fourier transform infrared analysis was employed to confirm the existence of an amine group in the stem of N. rubra. Keywords: Biosorption; Dyes; Kinetics; Nymphaea rubra; Reactive dye; Received: June 18, 2009; revised: September 20, 2009; accepted: October 2, 2009 DOI: 10.1002/clen.200900133 1 Introduction Dyes are synthetic organic aromatic water-soluble dispersible colo- rants. They have potential applications in various industries, such as textile, leather, paper, plastic, etc., to color the final products [1]. Generally, dyes are stable to light, heat, and oxidizing agents. They are biologically non-degradable. The extensive use of dyes often poses pollution problems in the form of colored waste water. Environmental pollution caused by industrial wastewater has become a common problem in many countries. Although dye concentrations are very low in aquatic envi- ronments, the effluents from these industries are highly visible and undesirable [2]. Moreover, the disposal of these wastes into receiving water can cause damage to the environment, as they may signifi- cantly affect the photosynthetic activity of aquatic life, due to reduced light penetration. The dye molecules may also be toxic to some aquatic life [3]. Reactive dyes usually have a synthetic origin and complex aro- matic molecular structures, which make them stable and difficult to biodegrade [4]. Reactive dyes differ from all other dyes since they bind to textile fibers, such as cellulose and cotton, through covalent bonds [5]. Reactive dyes are typically azo-based chromophores combined with various types of reactive groups, which show different reactiv- ity. They are extensively used in many textile industries due to their favorable characteristics, such as bright color, water-fastness, and simple application techniques [6]. However, nearly 50% of reactive dyes may be lost in the effluent after dyeing with cellulose fibers, and are highly recalcitrant to conventional wastewater treatment processes [7]. The methods used for the removal of color from indus- trial effluents include biological treatment, coagulation, flotation, adsorption, oxidation, hyper filtration, etc. [8, 9]. Biosorption is a conventional wastewater treatment method. It reduces, to a large extent, the pollutant levels of wastewater and it is a process that is economically feasible [10]. Consequently, biosorption techniques seem to have the most potential for future use in industrial wastewater treatment [11] because of their proven efficiency in the removal of organic and metal pollutants [12–14]. The most widely used adsorbent for this purpose is activated carbon, but its overlying cost [8, 15] has led to the search for cheaper alternative materials, such as orange and banana peel [16], neem leaf [17], rice husk ash [18], and peanut hull [19]. N. rubra is an aquatic plant, commonly referred to as “Water Lil- ies”, these plants have adapted to living in a total water environ- Correspondence: Dr. S. Renganathan, Department of Chemical Engi- neering, Alagappa College of Technology, Anna University Chennai, Chennai-600025, India. E-mail: rengsah@rediffmail.com i 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com