Fenton sludge generated in the flocculation stage of the Fenton oxidation process contains significant amounts of ferric iron and organic pollutants , which require proper treatment. Previous studies have demonstrated that adding Fenton sludge to an anaerobic digester can decompose some of the organic pollutants in the Fenton sludge to lower its environmental risk, but iron gradually accumulates in the reactor, which weakens the sustainability of the method. In this study, Fenton sludge was introduced into a hydrolytic acidification reactor with a weak acid environment to relieve the iron accumulation as well as improve the degradation of organic matter. The results showed that the added Fenton sludge acted as an extracellular electron acceptor to induce dissimilatory iron reduction, which increased chemical oxygen demand (COD) removal and acidification efficiency by 16.1% and 19.8%, respectively, compared to the group without Fenton sludge. Along with the operation, more than 90% of the Fe(III) in Fenton sludge was reduced to Fe(II), and part of them was released to the effluent. Moreover, the Fe(II) in the effluent could be used as flocculants and Fenton reagents to further decrease the effluent COD by 29.8% and 44.5%, respectively. It provided a sustainable strategy to reuse Fenton sludge to enhance organic degradation based on the iron cycle.
The efficient and eco-friendly remediation of polycyclic aromatic hydrocarbons (PAHs) in soil and groundwater through advanced oxidation remains a critical challenge. In this study, nano zero-valent iron (nZVI) and sulfurized nano zero-valent iron (S-nZVI) were utilized to activate peroxymonosulfate (PMS), demonstrating significant potential for fluoranthene (FLT) degradation. PMS/S-nZVI system outperformed PMS/nZVI system, achieving higher efficiency with lower reagent dosages. Dissolved Fe(II) analysis indicated enhanced Fe(III)/Fe(II) cycling in PMS/S-nZVI system, driven by the synergistic role of elemental sulfur. Both systems generated reactive species (SO 4 − •, O 2 − •, and HO•), with SO 4 − • identified as the dominant contributor to FLT degradation. Water quality variations significantly impacted FLT removal, with PMS/S-nZVI system exhibiting greater adaptability to diverse conditions compared to PMS/nZVI system. FLT degradation was more effective under acidic conditions. The high concentrations of HCO 3 − , Br − , and HA, and the presence of surfactants such as Tween-80 significantly hindered degradation. In contrast, low concentrations of Cl − and HA enhanced the process. Simulated real groundwater experiments revealed that pre-conditioning the solution pH to 5.0 achieved FLT removal efficiencies of 89.9 % and 91.8 % for PMS/nZVI and PMS/S-nZVI systems, respectively, with oxidant dosages increased by fivefold. In water-soil coupled slurry experiments, a water-soil ratio of 15:1, a reaction time of 6 h, and neutral post-reaction pH resulted in FLT degradation exceeding 90 %. This study highlights the potential of PMS-based advanced oxidation processes, particularly PMS/S-nZVI system, as an effective and adaptable approach for the remediation of PAHs-contaminated soil and groundwater.
Fengyue Zhao,Juan Xiao,Shipeng Geng,Yi Wang,Panagiotis Tsiakaras,Shuqin Song
Fe 3+ /Fe 2+ interconversion is one of the key factors for heterogeneous electro-Fenton degradation of organic pollutants. In this study, MIL-101Fe-derived carbon wrapping Fe 7 S 8 nanocomposite (Fe 7 S 8 /C-1-600) exhibits outstanding rhodamine B (RhB) degradation ability with extremely low iron leaching and high recyclable degradability within 60 min in a wide pH range. Moreover, Fe 7 S 8 /C-1-600 presents a much higher activity for RhB degradation than Fe 3 O 4 counterpart without sulfidation, which could be mainly attributed to the accelerated Fe 3+ /Fe 2+ cycling by iron with both multiple valences (Fe 0 , Fe 2+ , and Fe 3+ ) and sulfur species (S 2− and S 2 2− ) of the catalyst. The enhancement of H 2 O 2 adsorption and activation into OH on Fe 7 S 8 surface is confirmed by density functional theory calculations with respect to that on Fe 3 O 4 . Interestingly, SO 4 · − can be generated by reacting S 2 2− with dissolved O 2 and subsequently converted into ·OH, which further facilitates RhB degradation. These findings may shed a new insight into the potential application of metal sulfides for wastewater treatment.
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