Remediation of poly-and perfluoroalkyl substances (PFAS) contaminated soil using gas fractionation enhanced technology

Abstract

This study investigated a gas fractionation enhanced soil washing method for poly-and perfluoroalkyl substances (PFAS) removal from contaminated soil. With the assistance of gas fractionation, PFAS removal was increased by a factor of 9, compared to the conventional soil washing method. Pre-extraction (pre-treatment) of the soil with water before gas fractionation enhanced PFAS removal from soil. The optimum extraction time varied based on the soil particle size, since it will change the swelling time of the soil. The influence of various operational conditions such as water to soil mass ratio (W:S ratio), gas type in fractionation, gas flowrate, fractionation time and soil pre-treatment condition have been studied to identify the critical influencing factors. Among various W:S ratios (2, 4, 5, 6, 8, and 10) studied, higher W:S ratio resulted in better PFAS removals, but PFAS removal began to plateau as the W:S ratio increased. PFAS removal could be improved by repeated treatment with low water consumption. Air, oxygen, and ozone generated by air and oxygen were used, in which ozone generated by oxygen achieved the highest PFAS removals of 55.9%. Among different fractionation times (10 min, 20 min and 30 min), a fractionation time of 20 min achieved better total PFAS removal for studied soil, because PFOS was the dominant species in the total PFAS. However, the removal of some PFAS species, such as PFHxS, would be increased with extended fractionation time. With constant fractionation time (10 min), PFAS removal performance improved with the increasing gas flowrate.