Selective removal of phenanthrene for the recovery of sodium dodecyl sulfate by UV-C and UV-C/PDS processes: Performance, mechanism and soil washing recycling

Abstract

Soil washing is commonly used to remediate PAHs contaminated sites. However, the effluent after washing containing PAHs and surfactant may cause secondary pollution and remediation cost is still high, unless PAHs are selectively removed from the effluent and the surfactant is recovered and recycled. Herein, ultraviolet irradiation (254 nm, UV-C) and its combination with peroxydisulfate (UV-C/PDS) were applied to selectively degrade PHE in the synthetic soil washing effluent. At natural pH of 8.6, 98.2 % of PHE was removed within 30 min under 6 W UV-C irradiation. After adding 2 mM PDS, the time was shortened to 8 min but still achieving 98.7 % PHE removal and less toxic treated effluent than UV-C alone. The 1O2 was the main oxidizing species in UV-C alone system, while 1O2 as well OH and SO4− were responsible for PHE removal in the UV-C/PDS system. The possible intermediates of PHE degradation were recognized using liquid chromatography-mass spectrometry technique and the degradation pathways in both systems were proposed. Soil washing recycling experiments verified the recovered SDS could be reused directly without surfactant supplement and the soil washing efficiency changed insignificantly during three cycles. It indicates UV-C/PDS coupled with soil washing is a promising remediation technology.