Combination of steam-enhanced extraction and electrical resistance heating for efficient remediation of perchloroethylene-contaminated soil:Coupling merits and energy consumption

In situ thermal desorption(ISTD)technology effectively remediates soil contaminated by dense nonaqueous phase liquids(DNAPLs).However,more efforts are required to minimize the energy consumption of ISTD technology.This study developed a laboratory-scale experimental device to explore the coupling merits of two traditional desorption technologies:steam-enhanced extraction(SEE)and electrical resistance heating(ERH).The results showed that injecting high-density steam(>1 g/min)into loam or clay with relatively high moisture content(>13.3%)could fracture the soil matrix and lead to the occurrence of the preferential flow of steam.For ERH alone,the electrical resistance and soil moisture loss were critical factors influencing heating power.When ERH and SEE were combined,preheating soil by ERH could increase soil permeability,effectively alleviating the problem of preferential flow of SEE.Meanwhile,steam injection heated the soil and provided moisture for maintaining soil electrical conductivity,thereby ensuring power stability in the ERH process.Compared with ERH alone(8 V/cm)and SEE alone(1 g/min steam),the energy consumption of combined method in remediating perchloroethylene-contaminated soil was reduced by 39.3%and 52.9%,respectively.These findings indicate that the combined method is more favorable than ERH or SEE alone for remediating DNAPL-contaminated subsurfaces when considering ISTD technology.