The Effect Of Ozonation Treatment On Physico-Chemical Properties And Biotoxicity Of Reserve Osmosis Concentration Fractions From Industrial Park

To improve the water quality evaluation of reverse osmosis concentrate(ROC)by ozonation,we selected the ROC from wastewater reuse system of wastewater treatment plant in industrial park as the object,selected the ozonation as the treatment method,and then fractionated the raw and ozonated ROC into hydrophobic acid(HOA),hydrophobic base(HOB),hydrophobic neutral(HON)and hydrophilic fraction(HI)by XAD-8 resin.The combination of physico-chemical analysis and biotoxicity evaluation including a battery of bioassays and developmental toxicity was employed to investigate the effect of ozonation on physico-chemical properties and biotoxicities of ROC fractions.We systematically evaluated the water quality safety,identified the key toxic fraction,and established the correlation between chemical and toxicity in this way.We expected to show new lights on the effec of ozonation on toxicity reduction of ROC and identification of key toxic fraction.The effect of ozonation on organic matter degradation,molecular weight distribution(MWD),fluorescent response characteristic and functional groups of ROC fractions was measured by TOC,UV254,high performance liquid chromatography-size exclusion chromatography(HPLC-SEC),three-dimensional excitation-emission matrix fluorescence spectroscopy(3D-EEM)and fourier transform infrared spectrometer(FT-IR),evaluating the basic water quality of ROC and its four fractions before and after ozonation.The organic matter concentration of ROC fractions in order was HI>HOA>HON>HOB.The organic matter of HO A,HON and HI in ROC was significantly degraded by ozonation,especially for the organic matter rich in unsaturated carbon bond.However,the content of HOB was no significant change and the HI proportion increased.There were differences in MWD,fluorescent response characteristic and functional groups of ROC fractions.The organic matters in ROC fractions could be degraded to low molecular weight by ozonation,while low molecular weight acid and neutral matter of protein-like substance in HI was difficult to be degraded by ozonation.In HOB,carboxyl vibration and C=O stretching of amide-1 weakened,N-H bending vibration of amide-2 and C-N stretching enhanced,and C=O stretching of-COOH appeared.Consequently,the amino acid in HOB was oxidized into disinfection by-products(DBPs)such as aniline and acetic acid derivative by ozonation.The effect of ozonation on toxicity reduction of ROC and its four fractions was evaluated by a battery of biotoxicity assays with heterotrophic level,including bioluminescence inhibition assay using photobacterium T3,euglena gracilis assay and cytotoxicity assay.We identified the key toxic fraction and established the correlation between chemical and toxicity.The biotoxicity of ROC could be effectively reduced by ozonation,while that of HOB and HI could not be effectively reduced,and even the toxicities measured in bioluminescence inhibition assay of HOB and cytotoxicity assay of HOB and HI increased.Moreover,the chemical data(TOC and UV254)of HO A and HON demonstrated a well correlation with their toxicities,yielding the correlation coefficients of 0.915 and 0.886,respectively.However,poor correlations were obtained for HOB and HI between their chemical and toxicological data,yielding the lowest correlation coefficients of 0.230 and 0.060,respectively.The individual-level measurement(e.g.,mortality,hatching rate,heart rate,pericardial area,body length,malformation rate and enzyme activity)was performed to identify the developmental toxicity characteristics of zebrafish embryos exposed to ROC and its four fractions before and after ozonation and the effect of ozonation on developmental toxicity of ROC fractions.Subsequently,we measured the mRNA expression level of gene related to cardiac development,skeletal development and enzymatic acticity of zebrafish embryos to explosure the molecular mechanism of bitoxicity.As for the zebrafish embryos exposed to ozonated ROC,their morality and malformation rate decreased,heart rate and hatching rate increased.In addition,pericardial area decreased to and body length increased to approximate that of blank control group after ozonation.Moreover,after ozonation,pericardial edema percentages of zebrafish embryos exposed to HOA and HON decreased,while that exposed to HOB and HI was opposite.There was the similar change of expression level of amhc gene related to cardiac development.ROC fractions synergistically influenced skeletal development of zebrafish embryos,and the order of magnitude was HI>HOA>HOB>HON.After ozonation,the body length of zebrafish embryos exposed to ROC fractions had no significant change,spine curvature percentage of zebrafish embryos exposed to HOA increased,while that exposed to HON decreased.There was the similar change of expression level of bmp2 and bmp4 gene related to skeleton development.After ozonation,the oxidative damage of zebrafish embryos induced by ROC decreased,and oxidative stress toxicity of ROC decreased.Then the expression of sodl and cat gene was promoted,and the SOD acticity and CAT activity decreased.The organic matters in ROC was significantly degraded from high molecular wight to low molecular wight by ozonation.The protein-like substance in HI was difficult to be degraded by ozonation,and the amino acid in HOB was oxidized into toxic substances such as aniline and acetic acid derivative by ozonation.After ozonation,the biotoxicity of ROC and the oxidative damage of zebrafish embryos induced by ROC were effectively decreased,and the developmental features of zebrafish embryos were related to the mRNA expression level of corresponding genes.The toxicity of HOB andHI did not effectively decrease by ozonation,and even the correlations between their chemical and toxicological data were poor.The analysis of ROC fractions could provide more information for ozonation effect,while physico-chemical analysis or biotoxicity evaluation based on one species could not fully indicate the environmental risk of ozonated ROC.Therefore,it's quite necessary to evaluate the water quality safety of ozonated ROC fractions by combination method of physico-chemical analysis and biotoxicity evaluation.