Arab J Sci Eng DOI 10.1007/s13369-015-1666-1 RESEARCH ARTICLE - CHEMICAL ENGINEERING Adsorption of Reactive Blue Dye from Aqueous Solutions Using Sawdust as Adsorbent: Optimization, Kinetic, and Equilibrium Studies G. M. Ratnamala 1 · U. B. Deshannavar 1 · Sunil Munyal 1 · Kushal Tashildar 1 · Suraj Patil 1 · Amar Shinde 1 Received: 2 January 2015 / Accepted: 13 April 2015 © King Fahd University of Petroleum & Minerals 2015 Abstract Adsorption using sawdust from Malaysian teak wood as adsorbent has been studied in order to remove reactive blue dye from aqueous solutions (AS). The dye removal study comprised of investigation of parameters such as concentration of dye, pH, agitation time, and tempera- ture. Optimization was performed using response surface methodology. Kinetics of adsorption of reactive blue dye with activated sawdust was analyzed using Lagergren’s kinetic models, and it was found that the dye reduction efficiency by activated sawdust followed pseudo-second-order kinetic model. Langmuir and Freundlich’s isotherm models were used for the fitment of batch adsorption experimental data, and it was observed that Langmuir model was found to agree with the values obtained by experimentation based on regression analysis and RMSD values. The study showed that activated sawdust as a promising adsorbent for the reduction of reactive blue dye from AS. Keywords Reactive blue dye · Sawdust · Adsorption · Isotherm · Kinetic models List of symbols Q o Adsorption capacity (mg/g) k f Adsorption capacity (mg/g) t Agitation time (min) q Amount of adsorbate adsorbed (mg/g) B U. B. Deshannavar deshannavar@gmail.com 1 Department of Chemical Engineering, KLE DR. M.S. Sheshgiri College of Engineering and Technology, Udyambag, Belgaum 590008, Karnataka, India q e Amount adsorbed at equilibrium (mg/g) b Constant (L/mg) n Constant (–) R L Dimensionless constant (–) c e Equilibrium concentration of adsorbate (mg/L) K 1 Lagergren’s pseudo-first-order rate constant (min −1 ) K 2 Lagergren’s pseudo-second-order rate constant (g mg −1 min −1 ) 1 Introduction Freshwater—prominent utility of textile, paper, food, phar- maceutical, tannery and printing industries—finds it way as effluent into water bodies. This wastewater mainly con- tains unexhausted dyestuffs which are regarded as major water pollutants [1, 2]. The unexhausted dyestuffs are non- biodegradable, stable, and toxic in nature and affect the aquatic life, food chain, and human beings [2–5]. The treatment of wastewater containing unexhausted dyestuffs hence gains utmost priority prior to its discharge into water streams. Among various treatment methods for the treat- ment of effluents containing unexhausted dyestuffs and other organic/inorganic pollutants, adsorption has got highest pri- ority as the process is simple in operation and inexpensive [6]. Activated carbon is proved to be an effective adsorbent in effluent treatment process. However, there is a scope to find readily available inexpensive adsorbents from agro-industrial origin. Several researchers have used these wastes as adsor- bent materials and reported them as effectual adsorbents. Bhatti et al. [7], Lim et al. [8], and Khan et al. [9] tried Cit- rus sinensis (mosambi) bagasse, Lemna minor (duckweed), and pine needles biochar as adsorbent for the removal of methylene blue, methyl violet 2B, and reactive black-5 dyes, 123