Journal of Hazardous Materials B134 (2006) 190–196 The reuse of dried activated sludge for adsorption of reactive dye Osman Gulnaz ∗ , Aysenur Kaya, Sadik Dincer Department of Biology, Faculty of Arts and Sciences, Cukurova University, 01330 Balcali, Adana, Turkey Received 17 May 2004; received in revised form 26 October 2005; accepted 26 October 2005 Available online 15 December 2005 Abstract Adsorption processes are alternative effective methods for removal of textile dyes from aqueous solutions. The adsorption ability of adsorbent affects by physico-chemical environment for this reason in this paper effect of initial pH, dye concentrations, temperature and dye hydrolyzation were determined in a batch system for removal of reactive dye by dried activated sludge. The Langmuir isotherm model was well described of adsorption reactive dye and maximum monolayer adsorption capacity (at pH 2) of activated sludge was determined as 116, 93 and 71 mg g -1 for 20 ◦ , 35 ◦ and 50 ◦ C, respectively. Initial pH 2, 20 ◦ C and 30 min contact time are suitable for removal of reactive dyes from aqueous solutions. Activated sludge was characterized by FT-IR analysis and results showed that active sludge has different functional groups and functional groups of activated sludge are able to react with dye molecules in aqueous solution. The pseudo first-order, second-order and intraparticle diffusion kinetics were used to describe the kinetic data. The pseudo second-order kinetic model was fit well over the range of contact times and also an intra particle diffusion kinetic model was fit well but in the first 30 min. The dye hydrolyzation was affected adsorption capacity of biomass and adsorption capacity of biomass decreased with dye hydrolyzation from 74 to 38 mg g -1 . © 2005 Elsevier B.V. All rights reserved. Keywords: Activated sludge; Reactive dyes; Kinetic modelling; Adsorption; Reactive Black 5 1. Introduction Environmental pollution increases with increasing industrial developments. Most of pollutant and or their degradation prod- ucts are become toxic for aquatic and terrestrial environment. For this reason treatment of wastewaters is one of the most important environmental issues. Dyes are widely used in different industrial area for colouring the final products in textile, leather, paper, and plastics indus- tries. Disposal of dyes into receiving waters causes damage to the environment. In textile processing, a significant proportion of synthetic organic dyestuffs are released annually to waste streams, which eventually enter the environment [1]. Elimina- tion of dyes in the textile dying process is very difficult by conventional wastewater treatment methods. These dyes are stable under the environmental effects, such as light, pH and microbial attack. Dye wastewaters are usually treated by phys- ∗ Corresponding author. Tel.: +90 322 3386081; fax: +90 322 3386070. E-mail addresses: ogulnaz@cu.edu.tr, ogulnaz@mail.yahoo.com (O. Gulnaz). ical or chemical processes including coagulation, flocculation, biosorption, ultrafiltration, oxidation and ozonation, etc. [2–6]. Degradation products of textile dyes may be toxic [7] and these degradation products are resistant to further biodegradation in environment. Activated carbon is widely used adsorbent material for removal of pollutants from wastewaters. The use of activated carbon can be expensive, loses in the application and regenera- tion processes, this is increased the cost of the activated carbon, so that many investigators have been studying the feasibility of less expensive materials, such as algae, peat, chitin, saw dust, tree barks, clays, fly ash and biomass [8–12] etc. Reactive dyestuffs are mostly used dyestuffs in textile indus- try. Reactive dyes require alkaline conditions in dying process and it was hydrolyzed in alkaline environment. The hydrolyzed dyes in textile wastewaters were predominant form according to non hydrolyzed dye [13]. The textile effluents cause environmental problems. Turkey is among countries which have world wide range of textile indus- tries. For this reason textile wastewaters are important prob- lem for Turkey. In this paper, reuse of dried activated sludge and effect of physico-chemical environment; initial pH, dye 0304-3894/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2005.10.050