| With the rapid development of the textile-dyeing industry in China,the discharge of textile-dyeing wastewater has increased dramatically.It has a complex composition and is rich in toxic and hazardous substances.This kind of wastewater is discharged into natural water body directly after reaching the standard through biochemical treatment.However,the current process used in the textile-dyeing wastewater treatment plants(TDPs)can't completely eliminate the toxic and harmful substances in the wastewater,resulting in residual pollutants entering the receiving water body along with the drainage,which has a potential impact on the ecological environment of nearby water bodies.This research aims to study the characteristics and bio-toxic effects of dissolved organic matter(DOM)in the textile-dyeing effluents(TDEs)in the Pearl River Delta region of China.The main findings are as follows:(1)The quality of these four TDEs all reached the wastewater discharge standards.The ultraviolet absorption spectrum curve of DOM has a similar trend,mainly between 240?450nm,which is not enough to explain the difference in the composition of DOM components in TDEs.The parallel factor analysis(PARAFAC)model identified 3 typical fluorescence components from three-dimensional excitation-emission matrix(3D-EEM)of DOM,which are the humic-like fluorescence component(C1,?Ex/Em=250,300/460 nm),tryptophan-like fluorescent component(C2,?Ex/Em=240,280/350 nm)and tyrosine-like fluorescent component(C3,?Ex/Em=275/310 nm).The results of fluorescence regional integration(FRI)showed that the tryptophan-like protein regions accounted for the main contribution(47.44%?51.62%)in these TDEs,followed by the tyrosine-like fluorescence region,and the humic-like areas had the lowest contribution rate(9.50%?29.66%),showing a certain degree of weak humic.(2)Scenedemus obliquus(S.obliquus)was selected as the test organism.According to the changes at biomass level(cell density),biochemical level(superoxide dismutase(SOD)activity and chlorophyll a(Chl-a)synthesis)and structural level(cell membrane integrity and biological macromolecules)to comprehensively evaluate the bio-toxic effects of TDEs.The SOD activity of the experimental group increased from day 3(0.51±0.14?0.59±0.15 U/m L)to day 12(0.69±0.1?1.03±0.04 U/m L),and then decreased(0.6±0.06?0.78±0.06 U/m L).The SOD activity of the control group gradually increased,reaching 0.58±0.07?0.68±0.09U/m L at the end of exposure.The synthesis of Chl-a in the experimental group increased slowly with the increase of exposure time,and showed a downward trend,which was significantly lower than that of the control group(P<0.05).The results showed that DOM had a"low promotion and high inhibition"effect on the growth of S.obliquus.The low concentration of DOM stimulated the biomass and SOD activity of algae in a short time,and the algal cell membrane began to rupture,but without any significant effect on Chl-a synthesis.With the increase of TDEs concentration and exposure time,the growth of algae was inhibited,and its SOD activity began to decline,and Chl-a synthesis was severely inhibited.In summary,the DOM of TDEs was weakly humic and had two-sides effect on the growth of S.obliquus.Low concentration of TDEs exerts a certain stress on algae cells in a short time to stimulate their growth.With the increase of exposure time and concentration,the effect of external stress began to inhibit the activity of SOD,which in turn affects its removal capacity.The membrane lipid peroxidation of alga cells was strengthened,which in turn affected the photosynthetic system and inhibited the metabolism and reproduction of algae.This study is helpful for understanding the DOM characteristics of TDEs and their toxic effects on algae. |
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