Insights into the characteristics of changes in dissolved organic matter fluorescence components on the natural attenuation process of toluene.

Natural attenuation (NA) is of great significance for the remediation of contaminated groundwater, and how to identify NA patterns of toluene in aquifers more quickly and effectively poses an urgent challenge. In this study, the NA of toluene in two typical soils was conducted by means of soil column experiment. Based on column experiments, dissolved organic matter (DOM) was rapidly identified using fluorescence spectroscopy, and the relationship between DOM and the NA of toluene was established through structural equation modeling analysis. The adsorption rates of toluene in clay and sandy soil were 39 % and 26 %, respectively. The adsorption capacity and total NA capacity of silty clay were large. The occurrence of fluorescence peaks of protein-like components and specific products indicated the occurrence of biodegradation. Arenimonas, Acidovorax and Brevundimonas were the main degrading bacteria identified in Column A, while Pseudomonas, Azotobacter and Mycobacterium were the main ones identified in Column B. The pH, ORP, and Fe(II) were the most important factors affecting the composition of microbial communities, which in turn affected the NA of toluene. These results provide a new way to quickly identify NA of toluene.

Insight into degradation mechanism of PCBs from thermal desorption off-gas over iron-based catalysts.

Iron-based catalysts were developed to achieve the hydrodechlorination (HDC)/oxidation of polychlorinated biphenyls (PCBs) from thermal desorption off-gas, and Fe3O4/γ-Al2O3 showed higher dechlorination efficiency than Fe2O3/γ-Al2O3. The optimal Fe loading resulted in 95.5% degradation efficiency and 76.9% toxicity reduction of gaseous PCBs, and the optimal Fe3O4/γ-Al2O3 exhibited excellent stability during a 60-h test. The gas chromatography-mass spectrometry analysis of intermediate products indicated the presence of two competitive degradation pathways, namely, hydrodechlorination and oxidation with Fe3O4/γ-Al2O3 as catalyst. During the first stage (reductive dechlorination), the reductive activity of iron-based catalysts was effectively enhanced in the presence of water, which was confirmed by density functional theory (DFT) calculations. The removal of chlorine atoms was found in the order of meta > para > ortho. During the second stage (oxidation), hydroxyl and superoxide anion radicals were found to attack PCBs on the surface of Fe3O4/γ-Al2O3. This study provides an insight into the HDC and oxidation mechanism of gaseous PCBs over iron-based catalysts.

Insights into the mechanism of low-temperature H2S oxidation over Zn-Cu/Al2O3 catalyst.

Odor pollution caused by toxic chemicals with low human olfactory thresholds, such as hydrogen sulfide (H2S), has become a major cause of environmental grievance world-wide. Although the low-temperature (<180 °C) catalytic oxidation of H2S using metal oxides has received widespread attention, desulfurization performance is not ideal. Herein, a series of Zn-Cu/Al2O3 catalysts were developed using an impregnation method based on the Al2O3 hydrophilicity and the effects of zinc loading on the catalyst physicochemical properties and performance were systematically studied. The catalysts were characterized using inductively coupled plasma-optical emission spectrometry (ICP-OES), N2 adsorption-desorption isotherms, scanning electron microscopy with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). It was found that optimization of zinc doping could improve the hydrophilicity of the catalyst, and hence its activity. Catalytic activity was also dependent on operational parameters such as temperature, humidity and space velocity. The Zn3Cu3 catalyst exhibited the highest breakthrough capacity of 353.91 mg/g at 50 °C and at a relative humidity of 50%. The excellent desulfurization performance was attributed to oxygen vacancies contributed by CuO, Cu2O and ZnO, which facilitated the conversion of H2O into hydroxyl radicals. Consequently, a hydroxyl radical-induced desulfurization mechanism over Zn-Cu/Al2O3 is proposed. This work provides a potential green and efficient catalyst for the selective oxidation of H2S.

In-situ degradation of polybrominated diphenyl ethers from thermal desorption off-gas over structured Fe-based/γ-Al2O3/Al plate-type catalyst.

Thermal desorption was an efficient method for removal of decabromodiphenyl ether (BDE-209) from contaminated soil, but some less brominated diphenyl ethers (tri- to hepta-BDEs) with high toxicity were detected in the effluent gas. Herein, a novel anodic alumina supported Fe-based catalyst was developed and applied for in-situ degradation of gaseous polybrominated diphenyl ethers (PBDEs). The produced Fe/γ-Al2O3/Al catalyst was able to degrade PBDEs in the effluent gas, while a low activity with degradation efficiency of 70.1% was observed. As such, Cu was added into the Fe-based catalyst, and the effects of Cu loading on gaseous PBDEs degradation were systematically examined. A proper copper loading was found to increase the active Fe3O4 sites, thus improving the catalytic activity. Meanwhile, the degradation of gaseous PBDEs by Fe-based catalysts follows a pseudo-first-order model. A 90.2% PBDEs degradation efficiency was achieved at 375 °C on the optimized Fe/Cu/γ-Al2O3/Al catalyst, which demonstrated that the anodic alumina supported Fe and Cu was an excellent catalyst for gaseous PBDEs degradation system. Thus, this study provides a promising method and catalyst to achieve in-situ degradation of gaseous PBDEs.