Removal Of NPs And PFCs From Surface Treated Wastewater By Coagulation Sedimentation And Biological Treatment Process

Silver Nanoparticles(NP-Ag),Zinc Oxide Nanoparticles(NP-Zn O),Perfluorooctanoic Acid(PFOA)and Perfluorooctane Sulfonate(PFOS)are four of the most typical nanoparticles and perfluorinated compounds.They are confirmed to have biotoxicity and bio-concentration when used in large doses,in the same time,they will bring potential threats to human health.Due to the unique physicochemical property,the four chemicals are widely utilized in surface treatment industry,and then are probably to enter into the wastewater and thereby will be released into the environment.In the treatment of wastewater from the surface treatment industry,coagulation sedimentation and biological treatment are two commonly used treatment methods.But at present,there is no systematic study about these two methods to control and remove these four pollutants,there is no explicit environmental threshold concentration as a reference for emission.Therefore,based on the investigation of a surface treatment Industrial Park in Huizhou,this paper systematically investigated the removal efficiency of the four substances by coagulation sedimentation and biological treatment process,and calculated the threshold concentration of water environment as a reference for emissions.The investigation was conducted and the results showed that,the key process and concentration range of the four material when entering into the surface treatment wastewater are clarified.The results showed that coarsening,palladium activation,coking copper,acid copper,semi gloss nickel,preparation of color paste,semi finished product modulation and coating process will cause the four substances to enter into the producing wastewater.The concentration range of NP-Ag,NP-Zn O,PFOA and PFOS in the producing wastewater is 400~1400 ?g/L,300~1800 ?g/L,100~1000 ?g/L and 400~1600 ?g/L respectively.Based on the existing aquatic toxicity data of these four substances,a threshold evaluation model was established and the water environment threshold of each material was calculated.The effect of coagulation sedimentation and activated sludge biological treatment on the removal of single pollutants was investigated.The results show that the removal rate of NP-Ag and NP-Zn O can reach more than 80% by coagulation and sedimentation,and the removal efficiency of PFOA and PFOS is less than 20%.The removal mechanism of coagulant precipitation may be that the pollutants adsorb on the hydrolysates of coagulant to form a huge floc and precipitate.The average removal rate of NP-Ag,NP-Zn O,PFOA and PFOS by activated sludge method is about 86%,94%,29% and 55%,and the removal efficiency is more stable.The removal of these four substances by activated sludge system depends mainly on the adsorption effect of sludge.The removal efficiency of four mixed pollutants in the comprehensive wastewater treatment process of the park was investigated.The results showed that: in the long-term stable operation,the average removal rates of the four hybrid target pollution are respectively 98.7%,99.8%,87.8% and 96.2% by treatment system consisting of SBR activated sludge treatment plant,coagulation sedimentation process and BAF biofilter system.The activated sludge system has the greatest contribution to the removal of two nanomaterials and activated sludge treatment with biofilter on two kinds of perfluorinated compounds play a major role in the removal.But the concentration of these four substances in the processing tail water is still higher than the threshold concentration,therefore this paper proposes taking a filter column with functional modified ceramsite which prepared in the early stage of the laboratory as the terminal security means.The results show that four substances in the water are stably below the calculated threshold concentration.