Enhanced remediation of Cr(VI)-contaminated groundwater by coupling electrokinetics with ZVI/Fe3O4/AC-based permeable reactive barrier.

Although widely used in permeation reaction barrier (PRB) for strengthening the removal of various heavy metals, zero-valent iron (ZVI) is limited by various inherent drawbacks, such as easy passivation and poor electron transfer. As a solution, a synergistic system with PRB and electrokinetics (PRB-EK) was established and applied for the efficient removal of Cr(VI)-contaminated groundwater. As the filling material of PRB, ZVI/Fe3O4/activated carbon (ZVI/Fe3O4/AC) composites were synthesized by ball milling and thermal treatment. A series of continuous flow column experiments and batch tests was conducted to evaluate the removal efficiency of Cr(VI). Results showed that the removal efficiency of Cr(VI) remained above 93% even when the bed volume (BV) reached 2000 under the operational parameters (iron/AC mass ratio, 2:1; current, 5 mA). The mechanism of Cr(VI) removal by the PRB-EK system was revealed through field emission scanning electron microscopy images, X-ray diffraction, X-ray photoelectron spectroscopy, Fe2+ concentration, and redox potential (Eh) values. The key in Cr(VI) reduction was the Fe2+/Fe3+ cycle driven by the surface microelectrolysis of the composites. The application of an externally supplied weak direct current maintained the redox process by enhancing the electron transfer capability of the system, thereby prolonging the column lifetime. Cr(VI) chemical speciation was determined through sequential extraction, verifying the stability and safety of the system. These findings provide a scientific basis for PRB design and the in-situ remediation of Cr(VI)-contaminated groundwater.

Facile green synthetic graphene-based Co-Fe Prussian blue analogues as an activator of peroxymonosulfate for the degradation of levofloxacin hydrochloride.

A kind of Co-Fe Prussian blue analogues (Co-Fe PBAs), cobalt hexacyanoferrate Co3[Fe(CN)6]2, and graphene oxide (GO) were combined to synthesize magnetically separable Co-Fe PBAs@rGO nanocomposites through a simple two-step hydrothermal method. The crystalline structure, morphology and textural properties of the Co-Fe PBAs@rGO nanocomposites were characterized. The catalytic performance of the nanocomposites was evaluated by PMS activation, with Levofloxacin Hydrochloride (LVF) as the target contaminant. Synergistic interactions between the Co-Fe PBAs and rGO prevented the aggregation of the Co-Fe PBAs nanoparticles, which resulted in enhanced degradation efficiencies. The influence of several critical parameters was investigated, including the reaction temperature, PMS and Co-Fe PBAs@rGO catalyst concentrations, solution pH and salt content. LVF degradation was favored at higher catalyst and PMS concentrations, high temperatures, and in neutral or weak acidic solutions. Sulphate radicals were the dominant active species in the Co-Fe PBAs@rGO/PMS system. In addition, the Co-Fe PBAs@rGO exhibited no significant decrease in LVF degradation efficiency following five catalytic cycles. Thus, the as-prepared Co-Fe PBAs@rGO nanocomposite catalyst might be applied to the removal of hard-to-degrade organics owing to its high catalytic ability to activate PMS, as well as its good reusability and recyclability.

Preliminary assessment on exposure of four typical populations to potentially toxic metals by means of skin wipes under the influence of haze pollution.

To investigate the exposure risk of human beings to nine potentially toxic metals (PTMs), namely, Cu, Cr, Zn, As, Cd, Pb, Ni, Mn, and Co, skin wipe samples were collected from four types of populations, namely, children, undergraduates, security guards, and professional drivers, under different haze pollution levels in Xinxiang, China by using Ghost wipes. The Ghost wipes were quantitatively analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after microwave digestion. Generally, Zn (ND-1350µg/m2 for undergraduates, ND-2660µg/m2 for security guards, ND-2460µg/m2 for children, and ND-2530µg/m2 for professional drivers) showed the highest concentration among the four populations, followed by Cu (0.02-83.4µg/m2 for undergraduates, ND-70.2µg/m2 for security guards, 23.2-487µg/m2 for children, and ND-116µg/m2 for professional drivers). As (ND-5.7µg/m2 for undergraduates, ND-2.3µg/m2 for security guards, ND-21.1µg/m2 for children, and ND-11.0µg/m2 for professional drivers) and Co (ND-6.0µg/m2 for undergraduates, ND-7.9µg/m2 for security guards, ND-13.4µg/m2 for children, and ND-2.1µg/m2 for professional drivers) showed the lowest concentrations in all populations. Remarkable differences were found among the four populations and PTM levels decreased in the following order: children, professional drivers, security guards, and undergraduates. Gender variation was discovered for undergraduates and children. Generally, PTM contamination in skin wipes collected during a light haze pollution level was generally higher than that during a heavy haze pollution level, but PTM contamination was comparable between the two haze pollution levels for children. Non-carcinogenic exposure risks to As, Cd, and Pb for all populations were higher than those for the other six elements but all of them were within the acceptable safety threshold, indicating no apparent non-carcinogenic risk.

Oxidation of ofloxacin by Oxone/Co(2+): identification of reaction products and pathways.

Oxidative degradation of ofloxacin (OFX) by sulfate free radicals (SO4 (-•)) in the UV/Oxone/Co(2+)oxidation process was investigated for the first time, with a special focus upon identifying the transformation products as well as understanding the reaction pathways. Thirteen main compounds were identified after the initial transformation of OFX; the detailed structural information of which were characterized by high-performance liquid chromatography-high resolution mass spectrometry and MS fragmentation analysis. The degradation pathways mainly encompassed ring openings at both the piperazinyl substituent and the quinolone moiety, indicating that the usage of SO4 (-•) aided the oxidative degradation of OFX to undergo more facile routes compared to those in previous reports by using OH(•)/h(+) as the oxidant, where the initial transformation attacks were mainly confined to the piperazine moiety. Moreover, in this study, smart control over the pH conditions of the oxidation system via different modes of Oxone dosage resulted in the selective degradation of the functional sites of OFX molecule, where it was shown that the SO4 (-•)-driven destruction of the quinolone moiety of OFX molecule favored the neutral pH conditions. This would be beneficial for the reduction of bacterial resistance against quinolones in the aqueous environment.

Facile, effective, and environment-friendly degradation of sulfamonomethoxine in aqueous solution with the aid of a UV/Oxone oxidative process.

The degradation of sulfamonomethoxine (SMM) in the aqueous environment by the combination of UV illumination and Oxone has been studied. Experimental results indicated that the UV illumination can effectively activate Oxone to produce sulfate-free radicals (SO4 (-•)). When 10 mmol L(-1) Oxone was added, 96.78 % removal of SMM (5 mg L(-1)) was achieved within 90 min. Mineralization of SMM was investigated by measuring the total organic carbon, which decreased by 89.01 % after 90 min reaction. Six intermediate compounds generated during the SMM degradation were identified with the aid of liquid chromatography and mass spectroscopy, combined with proton nuclear magnetic resonance spectroscopy. A general reaction pathway for the degradation of SMM was proposed, where the presence of SO4 (-•) remained crucial during the degradation process.

Highly efficient degradation of ofloxacin by UV/Oxone/Co2+ oxidation process.

INTRODUCTION: In this study, UV/Oxone/Co(2+) oxidation process was applied to degradation of ofloxacin (OFL) in the presence of Co(2+) as the catalytic and Oxone as the oxidant. The operation parameters including pH, temperature, dosages of reagents, and reaction time were studied in detail. RESULTS: The results showed that the optimum conditions for the UV/Oxone/Co(2+) processes were determined as follows: temperature = 25°C, pH = 5.0, [Oxone] = 0.6 mmol/L, [Oxone]/[Co(2+)] = 1,000, and reaction time = 60 min. Under these conditions, 100% of the OFL degraded. The kinetics was also studied, and degradation of OFL by the UV/Oxone/Co(2+) process could be described by first-order kinetics. CONCLUSIONS: Mineralization of the process was investigated by measuring the total organic carbon (TOC), and the TOC decreased by 87.0% after 60 min. This process could be used as a pretreatment method for wastewater containing ofloxacin.