Removal of PCBs in contaminated soils by means of chemical reduction and advanced oxidation processes

Abstract

Although the chemical reduction and advanced oxidation processes have been widely used individually, very few studies have assessed the combined reduction/oxidation approach for soil remediation. In the present study, experiments were performed in spiked sand and historically contaminated soil by using four synthetic nanoparticles (Fe(0), Fe/Ni, Fe3O4, Fe3 - x Ni x O4). These nanoparticles were tested firstly for reductive transformation of polychlorinated biphenyls (PCBs) and then employed as catalysts to promote chemical oxidation reactions (H2O2 or persulfate). Obtained results indicated that bimetallic nanoparticles Fe/Ni showed the highest efficiency in reduction of PCB28 and PCB118 in spiked sand (97 and 79 %, respectively), whereas magnetite (Fe3O4) exhibited a high catalytic stability during the combined reduction/oxidation approach. In chemical oxidation, persulfate showed higher PCB degradation extent than hydrogen peroxide. As expected, the degradation efficiency was found to be limited in historically contaminated soil, where only Fe(0) and Fe/Ni particles exhibited reductive capability towards PCBs (13 and 18 %). In oxidation step, the highest degradation extents were obtained in presence of Fe(0) and Fe/Ni (18-19 %). The increase in particle and oxidant doses improved the efficiency of treatment, but overall degradation extents did not exceed 30 %, suggesting that only a small part of PCBs in soil was available for reaction with catalyst and/or oxidant. The use of organic solvent or cyclodextrin to improve the PCB availability in soil did not enhance degradation efficiency, underscoring the strong impact of soil matrix. Moreover, a better PCB degradation was observed in sand spiked with extractable organic matter separated from contaminated soil. In contrast to fractions with higher particle size (250-500 and <500 μm), no PCB degradation was observed in the finest fraction (≤250 μm) having higher organic matter content. These findings may have important practical implications to promote successively reduction and oxidation reactions in soils and understand the impact of soil properties on remediation performance.

Unexpected bias of freeze-drying on the performance assessment of chemical oxidation of soils contaminated by polychlorinated biphenyls

“…In this case, the eutectic point is quickly reached and smaller ice crystals are expected to form (Choi 2018;. That also may stop the oxidation reaction in the soil containing oxidant during the kinetic assessment without adding a new chemical reagent in soil (Tang 2015;Rybnikova 2016). To check whether the higher degradation extents observed at the beginning of the reaction in Fig.…”

“…The low temperature dehydration process is a necessary step in the soil preparation (Monfort 2019;Tang 2015;Rybnikova 2016), thus allowing an efficient extraction of target molecules using organic solvent. Another reason is the preservation of all physical and chemical properties of the soil with no impact on the reaction performance.…”

“…Freeze-drying process, contrary to freeze-thaw cycles, increases the stability of soil aggregates (Dagesse 2011), thus preserving the soil integrity. Because a rapid freezing may be utilized to quench the reactions in aqueous media (Monfort 2019;Tang 2015;Rybnikova 2016), lyophilization followed by solvent extraction of batch samples is an adequate technique for kinetic studies.…”

“…Several studies have already highlighted the effect of freezing to explain the oxidation of nitrites into nitrate in the permafrost or in polar regions Sun 2017;Takenaka 1992), the dissolution of iron oxides in atmospheric mineral dust (Jeong 2012;Jeong 2015), the reduction of chromate and A c c e p t e d M a n u s c r i p t bromate in frozen solution by organic compound as electron donor Kim 2011;Min 2017), or the activation of periodate in frozen solution for enhanced degradation of organic contaminants (Choi 2018). However, the freezing effect has never been investigated in the context of soil remediation where freezedrying is commonly used in the preparation of soil samples (Monfort 2019;Tang 2015;Rybnikova 2016).…”

Remediation of an aged PCP-contaminated soil by chemical oxidation under flow-through conditions

“…Fe 0 and magnetite nanoparticles used in this study were synthesized according to the methods described elsewhere in Rybnikova et al [20] and Schwertmann and Cornell [21], respectively.…”