Sodium citrate and biochar synergistic improvement of nanoscale zero-valent iron composite for the removal of chromium (Ⅵ) in aqueous solutions

Sodium citrate (SC) is a widely-used food and industrial additive with the properties of complexation and microbial degradation. In the present study, nano-zero-valent iron reaction system ([email protected]) was successfully established by modifying nanoscale zero-valent iron (nZVI) with SC and biochar (BC), and was employed to remove Cr(Ⅵ) from aqueous solutions. The nZVI, SC-nZVI and [email protected] were characterized and compared using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses (TGA), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that nZVI was successfully loaded on the biochar, and both the agglomeration and surface passivation problems of nanoparticles were well resolved. The dosage of SC, C:Fe, initial pH and Cr(Ⅵ) concentration demonstrated direct effects on the removal efficiency. The maximum Cr(Ⅵ) removal rate and the removal capacity within 60 min were 99.7% and 199.46 mg/g, respectively (C:Fe was 1:1, SC dosage was 1.12 mol.%, temperature was 25°C, pH = 7, and the original concentration of Cr(Ⅵ) was 20 mg/L). The reaction confirmed to follow the pseudo-second-order reaction kinetics, and the order of the reaction rate constant k was as follows: [email protected] > [email protected] > SC-nZVI > nZVI. In addition, the mechanism of Cr(Ⅵ) removal by [email protected] mainly involved adsorption, reduction and co-precipitation, and the reduction of Cr(Ⅵ) to Cr(Ⅲ) by nano Fe⁰ played a vital role. Findings from the present study demonstrated that the [email protected] exhibited excellent removal efficiency toward Cr(Ⅵ) with an improved synergistic characteristic by SC and BC.     

论环境刑事诉讼上诉期间生态修复行为的法律定性

环境刑事诉讼上诉期间的生态环境修复行为逐渐被一些地方法院在二审程序中作为从宽减刑的情节考察。虽然此举有益于激励环境刑事被告人积极履行环境恢复义务,然则在未有明文规定的先决条件下贸然将其纳入从宽量刑考量,也许会打破传统二审救济纠错的应然功能设计,使得环境刑事诉讼二审功能的实现存在矛盾偏差。由是对于上诉期间发生的生态修复行为的法律定性,应明确归属于判决后刑罚执行阶段的减刑情节予以考量,并且为配合化解此类矛盾,我国须及时制定相应的专门法规、适用原则和配套制度措施,从而最大限度发挥生态修复行为在环境刑事诉讼中的效用。     

Patterns and drivers of CH4 concentration and diffusive flux from a temperate river–reservoir system in North China

Freshwater reservoirs are regarded as an important anthropogenic source of methane (CH₄) emissions. The temporal and spatial variability of CH₄ emissions from different reservoirs results in uncertainty in the estimation of the global CH₄ budget. In this study, surface water CH₄ concentrations were measured and diffusive CH₄ fluxes were estimated via a thin boundary layer model in a temperate river–reservoir system in North China, using spatial (33 sites) and temporal (four seasons) monitoring; the system has experienced intensive aquaculture disturbance. Our results indicated that the dissolved CH₄ concentration in the reservoir ranged from 0.07 to 0.58 µmol/L, with an annual average of 0.13 ± 0.10 µmol/L, and the diffusive CH₄ flux across the water–air interface ranged from 0.66 to 3.61 μmol/(m²•hr), with an annual average of 1.67 ± 0.75 μmol/(m²•hr). During the study period, the dissolved CH₄ concentration was supersaturated and was a net source of atmospheric CH₄. Notably, CH₄ concentration and diffusive flux portrayed large temporal and spatial heterogeneity. The river inflow zone was determined to be a hotspot for CH₄ emissions, and its flux was significantly higher than that of the tributary and main basin; the CH₄ flux in autumn was greater than that in other seasons. We also deduced that the CH₄ concentration/diffusive flux was co-regulated mainly by water temperature, water depth, and water productivity (Chla, trophic status). Our results highlight the importance of considering the spatiotemporal variability of diffusive CH₄ flux from temperate reservoirs to estimate the CH₄ budget at regional and global scales.