Removal of polycyclic aromatic hydrocarbons (PAHs) from contaminated soil using polymeric nanoparticles

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds of great concern due to their potential risk to human health and the environment as they are likely bound to soils and difficult to remove. In this study, the amphiphilic polyurethane (APU) nanoparticles made of poly(ethylene glycol)-modified urethane acrylate (PMUA) precursor chains (80-110 nm) were synthesized to use in remediation of PAHs contaminated soil-packed column. Through batch and column tests, the sorption ability of APU nanoparticles under various phenanthrene (PHEN) and benzo(a)pyrene (BaP) concentrations are investigated. The test results supported that the application of APU nanoparticles could be applied to remove PAHs that have he logK[subscript ow] ranges between 4.6 and 6.5, thereby promoted the application of APU nanoparticles to other hydrophobic organic compounds having similar physicochemical properties. The experiment on steady state attainment revealed that sorption kinetic of test compounds onto APU was more rapid than onto soil (24 and 48 hours, respectively). The partition coefficient between soil and water, K[subscript s,w], of PHEN was lower than that of BaP (PHEN=1776+-88 L/kg; BaP=3162+-363 L/kg). By Normalizing K[subscript s,w] using organic carbon content in the soil, logK[subscript oc] of PHEN and BaP obtained from arithmetic equation (PHEN=4.88; (BaP=5.13) yielded parallel results compared to logK[subscript oc] from other studies. The partition coefficient between soil and APU, K[subscript s,APU], suggested that both PHEN and BaP were likely to sorb onto APU nanoparticles rather than sorbed onto soil. The results revealed that K [subscript s,APU] of PHEN was slightly higher than that of BaP (PHEN=0.55+-0.03 L/kg; BaP=0.36+-0.02 L/kg). Mass balance on APU nanoparticles mobility in soil demonstrated that 94% of the particles was recovered from the soil column. The removal of PHEN and BaP from pre-contaiminated soil column evidently supported that greatest recovery of test compounds were obtained regarding 24-hours flow interruption. In low contamination soil column (0.35 mg/kg), approximately 90% and 50% of initially sorbed PHEN and BaP were recovered over the duration of the experiment. In contrast, approximately 29% and 15% of initially sorbed PHEN and BaP were recovered in high contamination soil column (1.75 mg/kg). These results showed that increase in concentration of PAHs in the soil column reduced APU nanoparticles effectiveness and longer duration of the flow interruption should be considered in APU nanoparticles-assisted remediation. The column tests demonstrated that APU nanoparticles could effectively flush PHEN from soil contaminated with low concentration. However, the significant factor that decreased the efficiency of BaP remediation may be due to the sorption of BaP onto APU in column reached its equilibrium slower than that in batch experiment. Therefore, longer duration of flow interruption than 24 hours would tentatively increase the removal efficiency of BaP from the soil.