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.