Evaluating the potential of wax impregnated reactive components for long-term acenaphthene removal

The catalytic oxidation of acenaphthene (ANA) was investigated using a controlled-release persulfate candle (PSC) and Fe(II) candle (Fe(II)C) to provide long-lasting oxidation conditions during groundwater remediation. To the best of our knowledge, this study is the first attempt to compare the pseudo-first-order rate constant (k_obs) and % removal of ANA oxidation using PSC/Fe(II)C, PS solution (PS_aq)/Fe(II) solution (Fe(II)_aq), PSC/Fe(II)_aq, and PS_aq/Fe(II)C systems. The k_obs and % removal of ANA in the PSC/Fe(II)C system exceeded those in the other systems. The optimal degradation conditions used were 0.1 mM ANA; 3.08 mM equilibrium concentration of PS (C_e,PS) released from PSC (controlled-release rate constant, k_cr = 7.731 day⁻¹); 5.673 mM equilibrium concentration of Fe(II) (C_e,Fe(II)) released from Fe(II)C (k_cr = 3.796 day⁻¹); unadjusted pH (~7.0); and 25 °C. Radical scavenger studies and electron spin resonance (ESR) spectra showed that sulfate (SO₄^•−) and hydroxyl (^•OH) radicals were involved in the ANA oxidation, but ^•OH was the dominant radical species in the PSC/Fe(II)C system. Cl⁻, SO₄²⁻, and HCO₃⁻ acted as radical scavengers. The introduction of hydroxylamine (HA) into the PSC/Fe(II)C system resulted in a notable enhancement of ANA removal efficiency, increasing it from 51.8 % to 82.6 % within 10 min. Additionally, the PSC/Fe(II)C + HA system exhibited a higher Fe(II) consumption efficiency of 96.6 %, surpassing that of the PSC/Fe(II)_aq + HA system, which registered an efficiency of 88.6 %. Intermediate byproducts after 24 h of reaction were detected as non-toxic byproducts by liquid chromatography-mass spectrometry (LC-MS). The PSC/Fe(II)C system would be beneficial for the remediation of polycyclic aromatic hydrocarbons in groundwater due to the continuous supply of Fe(II) and PS for a long time.