Core-Shell MnFe Nanocatalyst Derived from Prussian Blue Analogs for Peroxymonosulfate Activation: Nonradical Mechanism and Bimetallic Valence Cycle.

Sulfamethazine (SAT) is widely present in sediment, soil, rivers, and groundwater. Unfortunately, traditional water treatment technologies are inefficient at eliminating SAT from contaminated water. Therefore, developing an effective and ecologically friendly treatment procedure to effectively remove SAT is critical. This has raised concerns about its potential impact on the environment and human health. In this study, metal-organic-inorganic composites consisting of graphene-encapsulated Fe-Mn metal catalyst (Mn3Fe1-NC) were synthesized by calcining MnFe Prussian blue analogs (PBA) under a nitrogen atmosphere. The composites were applied to activate peroxymonosulfate (PMS) and facilitate the degradation of SAT in aquatic environments. The Mn3Fe1-NC, dosed with 5 mg, in combination with PMS, dosed with 1.5 mmol L-1, achieved a 91.8% degradation efficiency of SAT. The transformation of the CN skeleton led to the formation of a carbon shell structure, which consequently reduced metal ion leaching from the material. At various pH levels, the iron and manganese ions were observed to leach out at levels lower than 0.1392 and 0.0580 mg L-1, respectively. In contrast, the Mn3Fe1-NC was found to be minimally impacted by pH levels and coexisting ions present in the aqueous environment. Radical burst experiments and electrochemical analysis tests verified that degradation primarily occurs through the nonradical pathway of electron transfer. The active sites responsible for this process were identified as the Mn (IV) and graphitic-N atoms on the material, which facilitate direct electron transfer. Additionally, the presence of Fe atoms promotes the valence cycling of Mn atoms. This study introduces new insights into the reaction mechanism and the constitutive relationship of catalytic centers in nonradical oxidation reactions.

Multiphase migration and transformation of BTEX on groundwater table fluctuation in riparian petrochemical sites.

Light non-aqueous phase liquids (LNAPL) are considered to be a composition-based risk, containing multiple chemical ingredients that release dissolved- and vapor-phase plumes. In dissolved form, there is a saturation-based risk as the water source expands, affecting groundwater aquifers on a larger scale in the aquifer. As a typical pollutant found in petrochemical contaminated sites, the migration and transformation of benzene, toluene, ethylbenzene, and o-xylene (BTEX) between gas, aqueous, and NAPL phases are distinctly affected by groundwater table fluctuation (GTF). BTEX multiphase migration and transformation pattern in a petrochemical factory at the riverside was simulated based on the TMVOC model in differentiating pollution distribution and interphase transformation under stable or fluctuating groundwater tables conditions. TMVOC model performed an excellent simulation effect on the migration and transformation of BTEX in GTF circumstances. In comparison with the stable groundwater table condition, the BTEX pollution depth under GTF increased by 0.5 m, the pollution area increased by 25%, and the total mass increased by 0.12 × 102 kg. In both cases, the mass reduction of NAPL-phase pollutants was more significant than the total mass reduction of pollutants, and GTF further promoted the mass conversion of NAPL-phase pollutants to water pollutants. Prominently, as the groundwater table rises, the GTF can correct for evacuation, and the transport flux of gaseous pollutants at the atmospheric boundary decreases with increasing transport distance. Furthermore, descended groundwater table will intensify the transmission flux of gaseous pollutants at the atmospheric boundary with the transmission range expanding, which can be harmful to human health on the surface due to gaseous pollutants entering into the air.

Cadmium tolerance and accumulation characteristics of wetland emergent plants under hydroponic conditions.

For the purpose of screening a potential Cd-hyperaccumulator for Cd-contaminated soil in paddy fields, four kinds of wetland emergent plants (Iris sibirica L., Acorus calamus L., Typha orientalis Presl and Cyperus alternifolius L.) were investigated for their cadmium tolerance and accumulation characteristics under hydroponic conditions. The physiological responses of plants, Cd concentration in tissues, Cd accumulation, bioaccumulation factor (BCF) and translocation factor (TCF) were investigated to evaluate the abilities of wetland emergent plants to absorb and accumulate Cd. In comparison with the other selected emergent plants, Iris sibirica L. has the strongest Cd-tolerance for the absence of Cd toxic symptoms and a Cd concentration as high as 127.3 mg kg-1 in shoots. Due to its large biomass, the Cd accumulation could reach up to 9.4 mg per plant in roots and 5.7 mg per plant in shoots, respectively. Iris sibirica L. possesses the highest TCF, and its BCF for Cd increased with increasing concentration of spiked Cd in the hydroponic solutions. The results indicate that Iris sibirica L. is a potential Cd-hyperaccumulator that may have a strong capacity for extracting Cd from Cd-contaminated paddy soils.

Identification of dominating factors affecting vadose zone vulnerability by a simulation method.

The characteristics of vadose zone vulnerability dominating factors (VDFs) are closely related to the migration and transformation mechanisms of contaminants in the vadose zone, which directly affect the state of the contaminants percolating to the groundwater. This study analyzes the hydrogeological profile of the pore water regions in the vadose zone, and conceptualizes the vadose zone as single lithologic, double lithologic, or multi lithologic. To accurately determine how the location of the pollution source influences the groundwater, we classify the permeabilities (thicknesses) of different media into clay-layer and non-clay-layer permeabilities (thicknesses), and introduce the maximum pollution thickness. Meanwhile, the physicochemical reactions of the contaminants in the vadose zone are represented by the soil adsorption and soil degradability. The VDFs are determined from the factors and parameters in groundwater vulnerability assessment. The VDFs are identified and sequenced in simulations and a sensitivity analysis. When applied to three polluted sites in China, the method improved the weighting of factors in groundwater vulnerability assessment, and increased the reliability of predicting groundwater vulnerability to contaminants.

Method for screening prevention and control measures and technologies based on groundwater pollution intensity assessment.

This paper presents a system for determining the evaluation and gradation indices of groundwater pollution intensity (GPI). Considering the characteristics of the vadose zone and pollution sources, the system decides which anti-seepage measures should be implemented at the contaminated site. The pollution sources hazards (PSH) and groundwater intrinsic vulnerability (GIV) are graded by the revised Nemerow Pollution Index and an improved DRTAS model, respectively. GPI is evaluated and graded by a double-sided multi-factor coupling model, which is constructed by the matrix method. The contaminated sites are categorized as prior, ordinary, or common sites. From the GPI results, we develop guiding principles for preventing and removing pollution sources, procedural interruption and remediation, and end treatment and monitoring. Thus, we can select appropriate prevention and control technologies (PCT). To screen the technological schemes and optimize the traditional analytical hierarchy process (AHP), we adopt the technique for order preference by the similarity to ideal solution (TOPSIS) method. Our GPI approach and PCT screening are applied to three types of pollution sites: the refuse dump of a rare earth mine development project (a potential pollution source), a chromium slag dump, and a landfill (existing pollution sources). These three sites are identified as ordinary, prior, and ordinary sites, respectively. The anti-seepage materials at the refuse dump should perform as effectively as a 1.5-m-thick clay bed. The chromium slag dump should be preferentially treated by soil flushing and in situ chemical remediation. The landfill should be treated by natural attenuation technology. The proposed PCT screening approach was compared with conventional screening methods results at the three sites and proved feasible and effective. The proposed method can provide technical support for the monitoring and management of groundwater pollution in China.