Elimination and ecotoxicity evaluation of phthalic acid esters from textile-dyeing wastewater

Phthalic acid esters (PAEs), presented in fabrics, surfactants and detergents, were discharged into the ecosystem during textile-dyeing wastewater treatment and might have adverse effects on water ecosystems. In this study, comprehensive investigations of the content and component distributions of 12 PAEs across different units of four textile-dyeing wastewater plants were carried out in Guangdong Province, China. Ecotoxicity assessments were also conducted based on risk quotients (RQs). On average, 93.54% TOC and 80.14% COD_Cr were removed following treatment at the four plants. The average concentration of Σ₁₂PAEs in effluent was 11.78 μg/L. PAEs with highest concentrations were dimethylphthalate (6.58 μg/L), bis(2-ethylhexyl)phthalate (2.23 μg/L), and dibutylphthalate (1.98 μg/L). The concentrations of the main toxic PAEs were 2.23 μg/L (bis(2-ethylhexyl)phthalate), 0.19 μg/L (diisononylphthalate) and 0.67 μg/L (dinoctylphthalate); corresponding RQs were 1.4, 0.55, and 0.54 for green algae, respectively. The RQs of Σ₁₂PAEs in effluent of the four plants were >0.1, indicating that Σ₁₂PAEs posed medium or higher ecological risk to fish, Daphnia and green algae. Physicochemical-biochemical system was found to be more effective than biochemical-physicochemical system for TOC and COD_Cr removal, because pre-physicochemical treatment helped to remove macromolecular organic substances, and reduced the competition with other pollutants during biochemical treatment. However, biochemical-physicochemical system was more effective than physicochemical-biochemical system for elimination of PAEs and for detoxification, since the biochemical treatment might produce the toxic PAEs that could helpfully be settled by post-physicochemical treatment. Moreover, ecotoxicity evaluation was recommended for current textile-dyeing wastewater treatment plants.