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Textile industry is one of the most common and essential sectors in the world. On the other hand, high volume of water consumption and varying wastewater characteristics due to many products such as dyes, biocides, carriers, detergents, etc. used in the process are the factors that have caused a continuous effort to find appropriate technologies to treat textile industry wastewater. In the last decade, the use of advanced oxidation processes (AOPs) has gained importance to degrade, decolorise and detoxicify the textile wastewater. However, the main mechanisms for AOPs for removing toxicity, thus, any contribution by the reduction of decreased inert factions in the effluent of textile wastewater are still to be studied. This study aimed to investigate the relation between inert COD fractions (which are characteristics in part of the influent wastewater, and in part generated in the biological treatment as the common used treatment process for textile industry) and effluent toxicity in the presence/absence of pre-ozonation. 18.5 mg/ l of ozone dose was applied during 30 min oxidation on two wastewater samples taken from balancing tank of a textile industry localized in Istanbul, Turkey. A direct assessment method was used to determine inert COD fractions of the raw and ozonated wastewater samples. The toxicity of raw and treated was tested using newborn (<24 h) samples of Daphnia magna for 24 h exposure time. The soluble inert COD (SI) decreased significantly while soluble residual microbial product (SP) increased slightly due to preozonation. The sum of soluble inert fractions *Corresponding author. Presented at the 9th Environmental Science and Technology Symposium, September 1–3, 2005, Rhodes, Greece. Organized by the Global NEST organization and prepared with the editorial help of the University of Aegean, Mytilene, Greece and the University of Salerno, Fisciano (SA), Italy. 0011-9164/07/$– See front matter © 2007 Elsevier B.V. All rights reserved

This study aimed to evaluate the effect of ozonation on textile industry wastewater COD fractions and acute toxicity, and investigation of their relation which was the innovative approach of it. The main findings obtained can be outlined as follows: • The different transfer ozone (TrO3) doses for S1 and S2 can be explained by wastewater composition and the color intensity and also other varying ozone initiators, promoters and scavengers in textile industry wastewater. • Ozonation decreased the soluble inert COD fraction of wastewater, thus, the sum of soluble residual COD (sum of soluble inert and residual metabolic COD at the effluents) decreased below the discharge limits (250 mg/ L). • Ozone is effective for removing acute toxicity from the textile wastewater.