Colloidal Ozone Aphrons For In Situ And Targeting Removal Of Phenanthrene From Simulated Aquifer Sediments

The hydrophobic polycyclic aromatic hydrocarbons(PAHs)are apt to adhere tightly to the sediments in aquifer and thus pose great threats to the aquatic environment of groundwater and surface water as well as human health.The present study constructed functionalized microbubbles,named colloidal ozone aphrons(COAs),by dissolving ozone-contained air into the nonionic surfactant(Tween-20)solution at the pressure of 300 k Pa for the in situ remediation of phenanthrene(PHE)-contaminated sediments.The basic proper ties of COAs stability,gas content and diameter were characterized.The interfacial behavior characteristics of COAs were studied,including surface adsorption characteristics,migration and diffusion characteristics in aqueous sediments and desorption kinetics of PHE on sediments.The focus was on the desorption and oxidation efficiency of COAs on sediments.In addition,considered the effects of salinity and aging on the above three aspects.The main results and conclusions of the paper are as follows:(1)When the initial concentration of Tween-20 was below and above CMC,the stability of COAs was slightly weaken compared with that of CGAs in the absence of ozone,but the half-life time of COAs still remained to be greater than 200 s.The properties of COAs were greatly affected by salinity.With the increase of salinity in water,the half-life of COAs was obviously reduced from 220 s to 160 s.The gas content increased with the increase of salinity.(2)Generally,the removal efficiency from sediments and the oxidation degradation efficiency of PHE by COAs followed the order of “hydrophobic surface with highPHE concentration” > “hydrophilic surface with low PHE concentration” > “hydrophobic surface with low PHE concentration”.When the initial PHE concentration was 240.0 ?g/kg,approximately 96.9% of PHE was removed from the sediments and 84.9% of the overall PHE was oxidized at the high ozone concentration of 0.6 mg/L.(3)The desorption of PHE on the hydrophilic sediments decreased with increasing salinity,but the desorption of PHE on hydrophobic sediments was not affected by salinity;The desorption and oxidative degradation rate of PHE on COAs compared with ozone microbubble(OMs)removed “ high-level PHE of hydrophobic sediments ” was better,the desorption rate was up to 87.5%,and the oxidative degradation rate could reach about 75%.The effect of removing in actual river water would decrease,but repeated treatment could effectively remove the PHE on the sediment.(4)The preferred concentration of removal aging PHE on sediments by COAs was 2 CMC.The effect of using COAs to remove aging PHE from hydrophilic sediments could reach 51.7% better than the hydrophobic sediments,but slightly worse than 67.5% of the ozone microbubbles,and the oxidative degradation rate was 41.9%.COAs achieved the in situ and targeted removal of hydrophobic organic pollutants from aquifer sediments,and had certain effects on aging hydrophobic organic pollutants in sediments.This study provides experimental and theoretical basis for the implementation of COA-involved technology in the remediation of PAH-contaminated aquifer sediments.