Ozonation of textile wastewater: physicochemical and phytotoxic aspects.

The purpose of this work was to evaluate the performance of ozonation as a technique to treat textile effluents. This performance evaluation was made using physico-chemical parameters and phytotoxic endpoints (i.e. biomass growth enzyme activities - catalase and peroxidase). After ozonation, the color absorbance (523 nm) was reduced by 80.9% and the pH decreased from 10.9 to approximately 7.5 while COD reduction reached nearly 87%. Phytotoxicity tests carried out in solution with three plant species (i.e. soybean, rice and wheat) allowed us to compare toxicity data of both, raw and ozonated effluents. The biomass (fresh weight) of the 3 plant species clearly decreases as a function of the increase in raw effluent concentration with LOEC values of 100% for rice and wheat, and 50% for soybean. Activities of catalase and peroxidase in the 3 plant species exposed to the raw textile effluent were significantly different from plant controls. The LOEC values for catalase were 6.2% (in wheat and soybean plants), and 25% (in rice plants), while for peroxidase the LOEC values were 6.2% (in rice plants), 25% (in soybean plants), and 50% (in wheat plants). Reduction in the phytotoxicity of textile effluent samples after ozonation is likely due to the elimination of the toxic organic fraction oxidized during this process. Regarding endpoint sensitivity, our results showed that biomass endpoint was less sensitive than biochemical endpoint. In conclusion, ozonation was relatively effective in reducing physico-chemical parameters and phytotoxic effects of textile effluents. Plant enzyme assays used in this study proved to be a sensitive tool in order to determine the toxicity of industrial effluents and may be used to evaluate efficiency of established (or emergent) wastewater treatment technology.

Toxicity-based criteria for the evaluation of textile wastewater treatment efficiency.

Brazilian textile mills import wastewater treatment technologies, performances of which are generally evaluated only on a physicochemical basis. Thus, a battery of bioassays was used to evaluate the performance of an ozonation system to treat textile effluents. Comparative toxicological profiles for bacteria (Vibrio fischeri), algae (Scenedesmus subspicatus), daphnia (Daphnia magna), fish (Poecilia reticulata), and plants (soybean--Glycine max, rice--Oryza sativa, and wheat--Triticum aestivum), as well as genotoxic effects (Vicia faba micronucleus assay), are presented for both raw and ozonated textile effluents. The relative sensitivity of bioassays (or end points) to textile effluents found in this study in decreasing order was plant enzymes > bacteria > algae daphnids approximately = plant biomass approximately = germination rate > fish. No significant genotoxic effect was found. We have concluded that ozonation was relatively effective in reducing toxicity of textile effluents. Bioassays used in this study proved to be sensitive and reliable tools for determining the toxicity of industrial effluents, and thus they can be used to evaluate emerging technology efficiency.