Short communication Methylene blue (cationic dye) adsorption onto sugar beet pulp: Equilibrium isotherm and kinetic studies Vesna M. Vuc ˇurovic ´ *, Radojka N. Razmovski, Miodrag N. Tekic ´ University of Novi Sad, Faculty of Technology, Boulevard Cara Lazara 1, 21000 Novi Sad, Serbia 1. Introduction The plastic, textile, dye, dyestuffs, leather, cosmetics, pharma- ceuticals, food, paper-making industries produce large volumes of highly colored waste water from different steps in the dyeing and finishing processes [1]. Discharge of such highly colored effluents can cause serious environmental impacts in the neighboring receptor water bodies because color impedes light penetration, retards photosynthetic activity, inhibits the growth of biota etc. Methylene blue (MB) is the most commonly used substance for dying cotton, wood and silk. On inhalation it can cause difficult breathing, while on the direct contact it may cause permanent injury of the eyes of human and animals, burning sensations, neusea, worming, profuse sweating, mental confusion and methemoglobinemia. Adsorption is considered to be superior to other physico-chemical or biological techniques for treatment of dye effluents [2,3]. Highly efficient adsorbent material for the removal of dyes is activated carbon. However, high cost of commercially available activated carbons, high operating cost and problems with regeneration hamper the use of activated carbon for large-scale application [2]. This has lead many researchers to search for low-cost adsorbents such as natural agro-industrial or plant waste materials for the removal of dyes and other contaminants from waste water, as a replacement for costly commercially adsorbents [3]. Sugar beet (Beta vulgaris L.) pulp (SBP) is an important and very cheap (100 US$ per metric tone) byproduct from the beet sugar industry, produced annually in large quantities. On a dry weight basis, SBP contains 65–80% polysaccharides, consisting roughly of 40% cellulose, 30% hemicelluloses, and 30% pectin [4]. Due to the carboxyl functions of galacturonic acid, pectic substances are known to strongly bind cations in solution. Sugar beet pulp (SBP) has been previously used as an adsorbent for the removal of methal ions such as cadmium and led [5], and Gemazol turquoise blue-G (anionic dye) [6]. The present study would be the first report describing the effect of initial dye concentration, contact time and solution pH on the rate and mechanism of MB adsorption on SBP. 2. Materials and methods 2.1. Adsorbate and adsorbent Methylene blue (3,7-bis(Dimethylamino)-phenazathionium chloride tetramethylthionine chloride) is cationic dye with molecular weight of 373.9 g/mol, and maximum wavelength of 668 nm. The MB used in this work was the analytical grade (Merck, Germany). Experimental solutions of MB were prepared by diluting the stock solution (50 mg/L) with distilled water. The SBP obtained from the TE-TO Senta Sugar Factory, Serbia, was extensively washed and boiled (10 min) with distilled water to Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 108–111 A R T I C L E I N F O Article history: Received 1 February 2011 Received in revised form 12 May 2011 Accepted 5 June 2011 Available online 29 July 2011 Keywords: Sugar beet pulp Adsorption Isotherm Methylene blue Kinetics A B S T R A C T Sugar beet pulp (SBP) is a well known adsorbent, however the use of sugar beet pulp as an adsorbent for removal of cationic dyes was not reported in the literature, so far. Batch adsorption experiments were conducted to study the effects of contact time, initial concentration (20–50 mg/L) and pH (2–8) on the removal of methylene blue (MB) from aqueous solution by SBP. Freundlich and Langmuir isotherm models were found to be suitable for description of MB adsorption on SBP. The SBP was found to have a Langmuir monolayers adsorption capacity of 714.29 mg/g at pH 8 and 25 8C. The results showed that the pseudo-second-order kinetic model best described the absorption process (R 2  0.9999). The extent of MB adsorption on SBP increased along with an increase of initial pH of the solution and initial MB concentration. The results demonstrated that the SBP is a promising adsorbent for removal of MB from aqueous solutions. ß 2011 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +381 214853676; fax: +381 21450413. E-mail address: vvvesna@uns.ac.rs (V.M. Vuc ˇurovic ´). Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers jou r nal h o mep age: w ww.els evier .co m/lo c ate/jtic e 1876-1070/$ – see front matter ß 2011 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jtice.2011.06.008