Enzyme and Microbial Technology 35 (2004) 399–404 Efficiency of simulated textile wastewater decolorization process based on the methanogenic activity of upflow anaerobic sludge blanket reactor in salt inhibition condition Mustafa Is ¸ik ∗ Environmental Engineering Department, Engineering Faculty, Dokuz Eylul University, Buca Kaynaklar Campus, 35160 Izmir, Turkey Accepted 23 April 2004 Abstract The performance of a plot scale upflow anaerobic sludge blanket reactor treating simulated cotton textile wastewater was examined to understand the effect of salt concentration in the color and COD removal efficiencies. The salt (NaCl) concentration increased from 0 to 128 g l -1 while HRT, and the organic loadings were kept constant giving a HRT of 20h and a 3.86 of volumetric organic loading rates. COD removal efficiencies decreased up to 18 from 80% as methanogenic bacteria inhibited by increasing salt concentration in the feed. High volatile fatty acid concentrations, low pH and high volatile fatty acids/bicarbonate alkalinity ratios in the effluent of reactor show the inhibition of methanogenic bacteria. A salt concentration of 128 g l -1 cause to reduce methane percentage and methane production rates to 30% and 180 ml/day from 70% and 2260 ml/day. Although COD removal efficiencies decreased, However, the color removals was not effected (decolorization efficiency = 100%) with increasing NaCl concentration as high as 128 g l -1 in the feed. © 2004 Elsevier Inc. All rights reserved. Keywords: Salt inhibition; Azo dyes; Simulated textile wastewater; UASB 1. Introduction Textile processes industries produce high quantities of ef- fluent with wastes containing dyes, sizing agents, salts and dyeing auxiliaries. Textile effluents contributes significantly to pollution load on receiving waters in converting natural and man made fibres into fabrics and their products [1]. Different type of pollutants in textile wastewater can arise from differ- ent sources of the textile manufacturing process which are mainly scouring, desizing, bleaching, mercerising, washing, dyeing and finishing. Process wastewater compositions vary Abbreviations: UASB, upflow anaerobic sludge blanket reactor; SS, suspended solids; VSS, volatile suspended solids; CMC, carboxymethyl cellulose; VFA, volatile fatty acids; COD, chemical oxygen demand; HRT, hydraulic retention time; B.Alk., bicarbonate alkalinity ∗ Present address: Environmental Engineering Department, Aksaray En- gineering Faculty, Ni˘ gde University, 68100 Aksaray, Turkey. Tel.: +90 382 21509 53/132; fax: +90 382 21509 52. E-mail address: mustafa.isik@deu.edu.tr (M. Is ¸ik). widely due the variety of recipes, techniques, machinery raw materials, and fabrics. The organic load results from scouring and desizing process in textile effluents. Organic load cause high demand on aeration systems and activated sludge bulk- ing problems in the conventional treatment [2]. Possibly, the problematic waste flow of textile processing come from the dye house as the removal of water soluble, residual azo dyes which, cause colored effluent are difficult in conventional treatment. Azo dyes constitutes about 60–70% of commer- cial dyes used in dyeing processes. They have electron with- drawing characteristics due to azo bond (N N) in structure. Therefore, their biodegradation are impossible under aerobic conditions in which, oxygen are used the electron acceptor in stead of azo dye. However under anaerobic conditions, azo dyes are used a terminal electron acceptor in electron transport chains and breakdown of azo bond with including electrons results in decolorization of wastewater [3]. Vari- ous physicochemical (coagulation, membrane filtration, and adsorption) advanced oxidation processes (fenton, Ultra Vio- let, and H 2 O 2 oxidation), biological processes (conventional 0141-0229/$ – see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.enzmictec.2004.04.018