Ecological Risk Assessment Of PFOS/PFOA Pollution In Hefei Wastewater Treatment Plant And Its Adsorption On Dehydrated Sludge

Perfluorooctanoic acid（PFOA）and Perfluorooctane Sulfonate（PFOS）,as perfluorinated compounds,are widely existed in the products of industry and consumption,including the materials of paper packaging and non-stick pan.With the improvement of human’s living environment,the urban sewage treatment factories have become the main pollution sources of perfluorinated compounds,such as PFOS and PFOA,being rich in the dehydrated sludge,which cause extensive concern for their ecological risk.In this study,the ecological risks of the sewage and sludge were evaluated by the risk quotient（RQ）,which was based on the contents of PFOS and PFOA in the influx,effluent and dehydrated sludge of the surrounding urban sewage treatment factories in Hefei.To further provide the support for the risk assessment and control of pollution,the adsorption-desorption behaviors of PFOS and PFOA in the activated sludge were analyzed.The main results were listed as follows:1.The main physical and chemical properties and heavy metal content of the dehydrated sludge from 5 sewage treatment factories were determined.Results showed that the pH values were 6.30-6.78,the water contents ranged from 74.3%to 82.5%,the percentage ranges of the organic matter were 22.8%-40.2%,and the percentages of the total content for nitrogen,phosphorus and potassium in the dehydrated sludge were2.8%-6.2%.Different heavy metal contents were in the range as follows:Pb:63.7-91.7mg/kg;As:33.1-67.1 mg/kg;Cd:3.1-15.5 mg/kg;Cr:41980.0-48800.0 mg/kg;Co:15.8-22.4 mg/kg;:89.9-294.6 mg/kg;Fe:79826.7-414533.3 mg/kg;Mn:1194.8-4114.0mg/kg;Ni:43.3-87.1 mg/kg;Zn:156.1-3874.0 mg/kg.2.The samples of inflow,effluent sewage and sludge were collected from 12 sewage treatment factories in Hefei,and their ecological risks were evaluated.It was detected that the content ranges of PFOS and PFOA in inflow sewage were 7.20-814.20 ng/mL and0.38-11.34 ng/mL,and those in effluent sewage were 7.15-1298.41 ng/mL and 0.33-25.96ng/mL,respectively,indicating that the sewage treatment could not remove PFOS and PFOA.The content ranges of PFOS and of PFOA in the sludge were 228.65-1635.65 ng/g,5.70-21.68 ng/g,respectively.The values of RQ were in a range of 0.0006-0.1141,showing that the concentrations of PFOA from the 12 factories did not satisfy the low ecological risk standard.For PFOS,all sampling points showed high potential risks to the environment with a RQ range of 0.29-32.57,except for CT point（RQ=51.94）which posed more risky.3.The adsorption-desorption characteristics of PFOS and PFOA on dehydrated sludge were analyzed using the batch equilibrium method:The adsorption density of PFOA and PFOS were 0.9471⁰.9527μg/g and 0.8345⁰.8353μg/g,respectively,with the different conditions of pH（5,7,9）,concentrations of CaCl₂（0.005,0.01,0.05 mol/L）and temperatures（10,20,40℃）.The effects of pH,temperature and ionic strength on the adsorption density of PFOS/PFOA were not significant.However,when the solution was acidic or alkaline and the ion concentration was close to 0.03 mol/L,it was positive for the adsorption of PFOA in the aqueous phase by the dehydrated sludge.The higher pH value and the ion concentration of 0.02 mol/L resulted in high distribution of PFOS to the dehydrated sludge.Moreover,the equilibration time of PFOS and PFOA on the dehydrated sludge was 3 h and 6h,and that of PFOA on the activate sludge biochar was 8h.4.The optimum conditions for the adsorption of PFOS/PFOA were presented at temperature of 25℃,pH value of 7.00,and the CaCl₂ concentration of 0.01 mol/L by response surface analysis.Under that condition,the adsorption density of PFOS and PFOA on the dehydrated sludge was 0.8898μg/g and 0.9311μg/g,and that of PFOA on the activated sludge was 0.9954μg/g.5.The best correlations of the adsorption kinetics of PFOS/PFOA on the dehydrated sludge were the double constant equation and Elovich equation,and that of the adsorption isotherm was the Langmuir equation.The adsorption of PFOS/PFOA on dehydrated sludge was irreversible.