The Retardation And Transport Of Typical PFAS In Porous Media Under Co-contaminated Conditions

Per and polyfluoroalkyl substances are a group of surfactants with high thermal,chemical,and biological stability,and have been widely used in many industrial,commercial,and military applications.The transport behavior of PFAS in porous media has become a recent focus of research.Considering the co-exist of multi-PFAS in the environment media,it is critical to figure out the transport behavior of PFAS under co-exist condition when characterizing and evaluation the multi-PFAS co-cotaminanted sites.Due to being employed in electroplating and leather tanning industries,the hexavalent chromium(Cr(?))and perfluorooctane sulfonate(PFOS)can cause co-contaminated system.It is highly necessary to understand the transport behavior of PFOS in porous media under co-exist condition with Cr(?).Based on those different co-contaminanted PFAS sites,multiple-PFAS co-transport,single-PFAS and Cr(?)co-transport miscible displacement experiments and the numerical simulation study were conducted.The main results are shown below:1)PFOS and three PFCAs(perfluoroalkyl carboxylic acids),PFOA(perfluorooctanoic acid),PFBA(perfluorobutanoic acid)and PFTr DA(perfluorotridecanoic acid)were employed to conduct the saturated and un-saturated miscible-displacement experiments to investigate the effects of PFCAs on the transport of PFOS in porous media Accu Sand(quartz sand).The experiments results indicate that the presence of PFCA shows no measurable impact on the solid-phase adsorption of PFOS under saturated condition.For unsaturated experiment,the air-water interfacial adsorption of PFOS is decreased by PFCA through the competitive adsorption between the PFOS and PFCA at the air-water interface.The chain length of PFCA shows no influence on the air-water interfacial adsorption of PFOS during transport under this experiment condition.2)Three porous media,Eustis,Vinton and Borden,with different geochemical properties were employed to conduct the PFOS/PFOA and Cr(?)co-transport miscible-displacement experiments under saturated condition.The object of this work is to investigate the co-transport behavior of PFAS and Cr(?)in porous media and its influence factors.The results indicate that,under saturated condition,the presenc of Cr(?)can decrease the adsorption and retardation of PFOS in the porous media and lead to a larger PFOS contaminant plume.This process is affected by the geochemical properties of porous media(e.g.clay minerals,metal oxides and organic carbon contents).The retardation and transport of PFOA in the porous media is not affected by the presence of Cr(?).3)The breakthrough curves of the co-transport of PFAS under un-saturated condition and the breakthrough curves of the transport of PFOS/PFOA with Cr(?)under saturated condition were chose to do the mathematical modeling separately.The simulation results demonstrate that the transport of PFOS in quartz sand is not measurably impacted by surfactant-induced flow,and the adsorption of PFOS at the air-water interfacial area is nonlinear.The multiple-component Langmuir model could not predict the competitive sorption between PFCA and PFOS at the air-water interface during transport.The presence of Cr(?)could decrease the instantaneous sorption of PFOS in the porous media.