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The toxicity of 17 selected process e uents, 11 reactive dyestu s and 8 auxiliaries from a textile dyeing and ®nishing mill in Ayazaga, Istanbul, Turkey was evaluated by bioluminescence test using bacteria Vibrio ®scheri in LUMIStox 300. The EC 20 and EC 50 for auxiliaries, the EC 20 for dyestu s were determined. For selected process e uents GLvalues, the dilution level at which a wastewater sample causes less than 20% inhibition, were examined. Our results demonstrate that the toxicity assessment with luminescent bacteria is e ective and of practical use for chemicals applied in textile ®nishing industry with the limitation of the deep dark-colored dye bath samples and for the related e uents. Inhibition e ects of numerous dyestu s as well as auxiliaries to luminescent bacteria di ered considerably with a range 5±600 mg l À1 for EC 20 and 9±6930 mg l À1 for EC 50 , respectively. Among 17 e uents, 1 sample exhibited high toxicity (GL 100), 7 showed moderate toxicity (GL 12±32), and 9 had a GL-value <10 indicating a low or no toxicity. Ó

The effect of ozonation (20.5 mg l À1 ) on the degradation processes of an azo dye, Remazol Black 5 (RB5; CI) was studied. Conventional parameters such as chemical oxygen demand (COD), total organic carbon (TOC), pH, conductivity, colour removal, biodegradability (BOD 5=28 ), and toxic potential of the dye and its degradation products were monitored during the process. The results obtained indicated that ozonation is a highly effective way to remove the colour of a corresponding dye solution. However, a considerable organic load still remained as indicated by high COD and TOC residues. The COD, TOC reductions were about 40% and 25% for 6 h ozonation of 2 g l À1 RB5 aqueous solution. During the ozonation process the rapid decrease of pH and the sharp increase of conductivity indicated the formation of acidic by-products and small fragments and ions which were identified by high performance ion chromatography. The BOD 28 data revealed that first by-products after partial ozonation (10-150 min) of RB5 were more biodegradable than the parent compound and ozonation can enhance the biodegradability of azo dyes. During the first 150 min of total 360 min of oxidation, the formation of first by-products with high toxic potential took place as it could be confirmed by two acute toxicity-screening tests, the bioluminescence test (Vibrio fischerii) and the neutral red cytotoxicity assay (rat hepatoma cells). The significant enhancement of microbial biodegradability after long-term ozonation could also be seen as a decrease of toxic intermediates in correlation with the ozonation time as indicated in BOD 28 biological degradation test results.

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