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Abstract: In this study, a novel two-stage process, i.e. first stage for hydrogen species generation at 150°C and second stage for PCB dechlorination at 330°C, was developed for efficient PCB degradation in subcritical water with nanoscale Ni/Fe particles. The obtained results showed that over 92% of PCBs was completely converted into 1-alkyl-benzenes during this process. The addition of hydrogen donors could greatly enhance PCB dechlorination in descending order: oxalic acid≈HAc>NaH2PO4 ≈KH2PO4. The anion introduced along with H+ played the crucial role in overall dechlorination process due to the undesired reaction between anion and reactive nanoscale Ni/Fe. Oxalic acid was quite effective for the generation of hydrogen species by supply more available H+ without undesired side reaction. In contrast, phosphate could react with Ni/Fe rapidly to form complex precipitates on particle surface and thereby block the reactive sites of particle following suspension of dechlorination. In addition, low 150°C at first stage as compared to 330°C at second stage favored the dissolution and adsorption of hydrogen on Ni surface for catalyzing to form more reactive hydrogen species used for rapid dechlorination. [Copyright &y& Elsevier]

Abstract: Polychlorinated biphenyls (PCBs) are environmentally persistent, toxic, bioaccumulative and recalcitrant. In this study, aged PCBs from e-waste contaminated site were respectively subjected to Soxhlet and solvothermal treatments. The results indicated that solvothermal method was much more predominant for PCBs removal than traditional Soxhlet method. Sequential Soxhlet–solvothermal experiment demonstrated that Soxhlet unextractable (bound) PCBs were efficiently removed by solvothermal procedure due to enhanced solvating effects of organic solvents. The key point was that bound PCBs in the aged soil were partitioned in different components of soil organic matter, e.g., the solvothermal removal amounts of ∑I-VPCBs (sum of PCB8, PCB18, PCB28, PCB44, PCB66) from fulvic acid (FA), humic acid (HA), bound humic acid (bound HA), bound lipids and mineral fraction were 0.4, 40.8, 28.4, 19.8, and 10.6%, respectively. It was found that isopropanol was the most effective solvent for PCBs removal. The optimum performing temperature, time and liquid to solid ratio for PCB8, PCB18, PCB28, PCB44, and PCB66 were 170°C, 8h and 10:1, respectively. As for higher molecular weight PCB congeners, these conditions were 150°C, 10h and 15:1. Soil organic matter content was unchanged after solvothermal treatment indicating that soil fertility remained after the removal process. This work provides a more clean process for effective treatment of soils contaminated by persistent organic pollutants (POPs) in comparison to traditional methods. [Copyright &y& Elsevier]

Abstract: The present study was carried out to better understand the reactivity of nanoscale Ni/Fe particles towards the dechlorination of polychlorinated biphenyls (PCBs) contained in waste capacitor oil and the corresponding dechlorination mechanism in subcritical water. Batch experiments showed that nanoscale Ni/Fe particles could more quickly and effectively dechlorinate PCBs stepwise as compared to nanoscale zerovalent iron (n-ZVI) and nano-Ni0. The dechlorination products were much more centralized in the presence of Ni/Fe than other particles, and biphenyl, cyclohexyl-benzene and 1-alkyl-benzenes were the main products which can be used as raw chemicals. Moreover, catalytic hydrogenation by virtue of introduction of Ni0 as catalyst can not only result in rapid dechlorination but also avoid formation of toxic chlorinated hydrocarbons. The reactivity of nanoscale Ni/Fe can retain in subcritical water for rapid catalytic hydrodechlorination. This process poses the prospect of recovery of valuable chemicals in the course of disposal of hazardous PCB-containing capacitor oil or transformer oil. [Copyright &y& Elsevier]