Enhanced in-situ remediation of VOCs-contaminated soil using alkaline activated persulfate with co-solvent assistance for improved removal efficiency

The development of efficient and sustainable remediation strategies is critical for treating volatile organic compound (VOCs)-contaminated soil. This study investigated the removal of methylbenzene (MB) and ethylbenzene (EB) from contaminated soil through co-solvent-assisted alkaline activation of persulfate (PS) system, The effect of the co-solvent in enhancing the desorption and solubilization of MB and EB was also evaluated. Under optimal conditions (C_PS = 382 mmol L⁻¹, pH 12, 40 % (v/v) acetonitrile (ACN) as co-solvent), the removal rates of MB and EB reached 41.5 % and 50.9 % on the 1st day, significantly higher than those without ACN (11.4 % and 16.2 %, respectively). Moreover, the removal rates further increased to 91.7 % for MB and 94.5 % for EB on the 21st day. The higher degradation rate of EB was attributed to the relatively weak benzylic C–C bond (76.4 kcal mol⁻¹) and C–H bonds (85.4 kcal mol⁻¹) at the ethyl site. Electron spin resonance (ESR) and quenching experiments confirmed that •OH and ${\text{SO}}_4^{·-}$ were the dominant reactive oxygen species, contributing 52.0 % and 35.2 % to MB degradation, respectively. The degradation of MB and EB proceeded via hydrogen abstraction, hydroxylation, electron transfer, and dealkylation, culminating in complete mineralization. Toxicity assessments using T.E.S.T. and bioluminescent bacteria assays indicated a significant reduction in ecological risk, with bioluminescence inhibition for MB and EB decreasing from 70.7 % (very toxic) and 98.3 % (very toxic) to 8.2 % (low toxicity) and 5.6 % (low toxicity), respectively. In summary, this study presents a promising strategy for the remediation of VOCs-contaminated soils.