Unlocking high-efficiency decontamination by building a novel heterogeneous catalytic reduction system of thiourea dioxide/biochar

Herein, we reported a new contaminant purification paradigm, which enabled highly efficient reductive denitration and dechlorination using a green, stable reducing agent thiourea dioxide (TDO) coupled with biochar (BC) over a wide pH range under anoxic conditions. Specifically, BC acted as both activators and electron shuttles for TDO decomposition to achieve complete anoxic degradation of p-nitrophenol (PNP), p-nitroaniline, 4-chlorophenol and 2,4-dichlorophenol within 2 h. During this process, multiple strongly reducing species (i.e., SO22-, SO2•- and e-/H•) were generated in BC/TDO systems, accounting for 13.3%, 9.7% and 75.5% of PNP removal, respectively. While electron transfer between TDO and H+ or contaminants mediated by BC led to H• generation and contaminant reduction. These processes depended on the electron-accepting capacity and electron-conducting domains of biochar. Significantly, the BC/TDO systems were highly efficient at a pH of 2.0-8.0, especially under acidic conditions, which performed robustly in common natural water constituents.

NanoFe3O4 accelerates anoxic biodegradation of 3, 5, 6-trichloro-2-pyridinol

3, 5, 6-trichloro-2-pyridinol (TCP) is a widespread organic pollutant with persistent, mobile and high antimicrobial effects. Here, nanoFe₃O₄ was firstly introduced into the anoxic biodegradation of TCP. It was found that nanoFe₃O₄ significantly accelerated TCP biodegradation. The removal rate of TCP (100 mg L^-1) increased from 83.03% to 98.74% within 12 h in the presence of nanoFe₃O₄, and the addition of nanoFe₃O₄ also promoted the accumulation of CO₂. Reductive dechlorination mechanism was involved in anoxic biodegradation of TCP. Molecular approaches further revealed that nanoFe₃O₄ distinctly induced the shifts of bacterial community. The dominant genus Ochrobactrum was converted to genus Delftia in nanoFe₃O₄ treatment, and the relative abundance of Delftia increased from 10.26% to 44.62%. Meanwhile, the total relative abundance of bacteria related to TCP dechlorination and degradation significantly increased in the presence of nanoFe₃O₄. These results indicated that nanoFe₃O₄ induced the enrichment of TCP-degrading bacteria to promote the anoxic biodegradation of TCP.

Studies on the anoxic dissipation and metabolism of pyribambenz propyl (ZJ0273) in soils using position-specific radiolabeling

Pyribambenz propyl (ZJ0273) is a polycyclic herbicide with increasing use, although studies show that it tends to be persistent in soil and pose phytotoxicity to rotational crops. This study employed an improved ring-specific (14)C labeling method to characterize its anoxic metabolism, with (14)C positioned on the benzoate, pyrimidyl or benzyl rings. Separation and identification of the metabolites were achieved by liquid chromatography (LC), ultralow-level liquid scintillation spectrometry, and LC-mass spectrometry (MS). Results show that the anoxic degradation follows first-order kinetics and the half-lives are approximately 38.7, 50.2 and 70.7d for loamy, saline and clayey soils, respectively. A total of five radioactive intermediates (M1-M5) were detected, and due to the loss of radiolabels, different radiochromatograms were obtained from different labels, i.e., radioactive M5 was only detected for pyrimidinyl-(14)C; M3 and M4 were only detected for pyrimidinyl-(14)C and benzyl-(14)C, while M1 and M2 were detected for all labels. Based on their appearance pattern and fragmentations from LC-MS, the structures of M1-M5 were identified, and they were proposed to form by reactions such as de-estering, hydrolysis, acylation, CN cleavage, and demethylation. All metabolites have been previously detected in aerobic soils except M4, which is a demethylation product from M3, and identified as 2-(4-hydroxy-6-methoxypyrimidin-2-yloxy)benzoic acid. The results show that ZJ0273 is more persistent in anoxic soils, and its degradation pathways and intermediates are different from aerobic metabolism and differ with the soil types, suggesting that soil-specific and farming practices may be important considerations in the use of this herbicide. The ring-specific labeling provides full molecular information about the referred compound and guarantees the reliability of the results, and can be used as an effective tool for metabolite profiling of polycyclic compounds.