Residual Micro Organic Pollutants And Their Biotoxicity Of The Effluent From The Textile Wastewater Treatment Plants At Pearl River Delta

In the past thirty years,so many textile industries were built and developed in Pearl River Delta at a surprising speed,which discharged millions tons of textile wastewater into Pearl River.However,textile wastewater,characterized by high color,high organics,and high toxicity,caused a severe negative impact on the ecosystem of the Pearl River.The purpose of this study was to explore the residual micro organic pollutants and their biotoxicity of effluent from the typical textile wastewater treatment plants at Pearl River Delta.In this study,water samples were collected from nine typical textile wastewater treatment plants located at Pearl River Delta.By the methods of three dimensional excitation emission matrix（3DEEM）and Fourier transform infrared spectroscopy（FTIR）,biotoxicity test and combined to conventional water quality parameters,such as the specific UV absorbance at254nm(UV₂₅₄),chemical oxygen demand（COD）,total organic carbon（TOC）,the residual micro organic pollutants,and toxic effect of textile effluents were studied.The main results of this study are as following:（1）The overall residual organic content of nine typical textile plants were analyzed.Results showed that most textile effluents discharged by textile wastewater treatment plants met the requirement of the national discharge standard.The COD values ranged from 21.30mg·L^-1 to 117.34 mg·L^-1,the TOC values ranged from 5.31 mg·L^-11 to 46.24 mg·L^-1,and the UV₂₅₄54 values ranged from 0.081 cm^-11 to 2.054 cm^-1.The residual dissolved organic matter（DOM）of textile effluents were evaluated by the 3DEEM and FTIR.Peak-picking results showed that five fluorescence peaks（Peak A,Peak B,Peak C,Peak D,and Peak E）and two fluorescence peaks（Peak A and Peak B）were found in textile effluents.FRI results showed that the tryptophan-like（II）,fulvic acid-like substances（III）,and soluble microbial product-like（IV）were the dominant compounds in the effluent DOM.FTIR results indicated that the benzene-derived products and aromatic amines were main residual organics in the textile effluents.（2）The biotoxicity effect of textile effluents were evaluated by the toxicity test.The toxic results showed that the toxic values of the effluents from the nine plants ranged from 0.02mg·L^-11 to 0.24 mg·L^-1.The obvious toxic effect were observed in most textile effluents,only the effluent of A,B,and F were nontoxic.（3）The advantages and disadvantages of two tertiary treatments including ozone oxidation and membrane filtration were compared by using the conventional water quality parameters(COD,TOC,and UV₂₅₄),DOM and toxicity effect as indicators.（i）Ozone oxidation and membrane filtration both removed residual organics(COD,TOC,and UV₂₅₄)of textile secondary effluent effectively.（ii）By comparison with ozone oxidation,membrane process was more effective to reducing tryptophan-like（Ⅱ）,soluble microbial product-like（Ⅳ）and fulvic acid-like substances（Ⅲ）（DOM main compositions）.（iii）Membrane filtration removed toxic matters more efficiently,while the toxicity of textile effluent was increased after ozonization.In conclusion,residual DOM and toxic matters still remained in the textile effluents.Membrane filtration seemed as a more suitable tertiary treatment process in an actual application to decrease the residual DOM and toxicity effect of textile effluents.