Environmental fate and behavior of silver nanoparticles in natural estuarine systems

Silver nanoparticles (AgNPs) are widely used in many consumer products, whereas their environmental behaviors in natural aquatic systems remain unknown, especially in natural brackish media. Therefore, it is urgent to investigate the environmental fate of AgNPs in natural brackish waters. Here, we investigated the stability of citrate-coated AgNPs in natural brackish water collected from 6 different sites with distinct salinities in the Xinglinwan Reservoir, located in Xiamen City, southeast China. The obtained results showed that AgNP colloids remained stable in low-salinity waters, which was mainly determined by the effects of dissolved organic matter (DOM) promoting the stability of the nanoparticles. However, the environmental fate of AgNPs in high-salinity waters was dominated by the salinity or ionic strength, especially the free ion concentrations of Cl^?, SO₄^2?, or S^2?, resulting in rapid sedimentation and dissolution. In addition, both DOM and salinity contributed to the environmental behavior of AgNPs in moderate-salinity waters, ultimately resulting in either colloidal stability or sedimentation. Overall, these results may reveal that AgNPs remain relatively stable for a long period in low-salinity natural waters, and that the stability might gradually decrease as AgNPs are transferred from freshwaters through brackish waters and eventually end up in seawater along the bay. Our findings also further indicate that the toxicity and potential risks of AgNPs may present more serious threats to the environment and organisms in natural freshwaters than in natural estuarine systems or seawater.     

The dynamic development of bacterial community following long-term weathering of bauxite residue

Bauxite residue is the industrial waste generated from alumina production and commonly deposited in impoundments. These sites are bare of vegetation due to the extreme high salinity and alkalinity, as well as lack of nutrients. However, long term weathering processes could improve residue properties to support the plant establishment. Here we investigate the development of bacterial communities and the geochemical drivers in bauxite residue, using Illumina high-throughput sequencing technology. Long term weathering reduced the pH in bauxite residue and increased its nutrients content. The bacterial community also significantly developed during long term weathering processes. Taxonomic analysis revealed that natural weathering processes encouraged the populations of Proteobacteria, Chloroflexi, Acidobacteria and Planctomycetes, whereas reducing the populations of Firmicutes and Actinobacteria. Redundancy analysis (RDA) indicated that total organic carbon (TOC) was the dominant factors affecting microbial structure. The results have demonstrated that natural weathering processes improved the soil development on the abandoned bauxite residue disposal areas, which also increased our understanding of the correlation between microbial variation and residue properties during natural weathering processes in Bauxite residue disposal areas.     

Synthesis of novel adsorbent by intercalation of biopolymer in LDH for the removal of arsenic from synthetic and natural water

This study focuses on the synthesis of nanocomposites named CCA and CZA that were prepared by the incorporation of cellulose(CL) in the Ca/Al and Zn/Al layered double hydroxide(LDH),respectively.These materials were then used for the uptake of As(Ⅲ)and As(V) from aqueous medium.Characterization of both nanocomposites(CCA and CZA) was done using FTIR and Raman analysis to identify the functional groups, N_2 adsorption-desorption isotherms to determine the specific surface area and pore geometry and XPS analysis to obtain the surface atomic composition.Some other characters were investigated using simultaneous TGA and DTA and elemental chemical analysis(CHNS/O).The crystallinity of the prepared nanocomposites was displayed by XRD patterns.Furthermore,the sheet-like structure of the LDHs and the irregularity of surface morphology with porous structure were observed by TEM and SEM microphotographs.Optimization of maximum adsorption capacity was adjusted using different parameters including pH,contact time and adsorbent dosage.The pseudo-second-order model was in good fitting with kinetics results.The adsorption isotherm results showed that CZA exhibits better adsorption capacity for As(Ⅲ) than CCA and the Langmuir isotherm model described the data well for both nanocomposites.Thermodynamic studies illustrated the endothermic nature of CCA and exothermic nature on CZA,as well as the fact that the adsorption process is spontaneous.A real water sample collected from well located in Gabes(Tunisia),has also been treated.The obtained experimental results were confirmed that these sorbents are efficient for the treatment of hazardous toxic species such as.     

Vertical profiles of biogenic volatile organic compounds as observed online at a tower in Beijing

Vertical profiles of isoprene and monoterpenes were measured by a proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) at heights of 3, 15, 32, 64, and 102 m above the ground on the Institute of Atmospheric Physics (IAP) tower in central Beijing during the winter of 2016 and the summer of 2017. Isoprene mixing ratios were larger in summer due to much stronger local emissions whereas monoterpenes were lower in summer due largely to their consumption by much higher levels of ozone. Isoprene mixing ratios were the highest at the 32 m in summer (1.64 ± 0.66 ppbV) and at 15 m in winter (1.41 ± 0.64 ppbV) with decreasing concentrations to the ground and to the 102 m, indicating emission from the tree canopy of the surrounding parks. Monoterpene mixing ratios were the highest at the 3 m height in both the winter (0.71 ± 0.42 ppbV) and summer (0.16 ± 0.10 ppbV) with a gradual decreasing trend to 102 m, indicting an emission from near the ground level. The lowest isoprene and monoterpene mixing ratios all occurred at 102 m, which were 0.71 ± 0.42 ppbV (winter) and 1.35 ± 0.51 ppbV (summer) for isoprene, and 0.42 ± 0.22 ppbV (winter) and 0.07 ± 0.06 ppbV (summer) for monoterpenes. Isoprene in the summer and monoterpenes in the winter, as observed at the five heights, showed significant mutual correlations. In the winter monoterpenes were positively correlated with combustion tracers CO and acetonitrile at 3 m, suggesting possible anthropogenic sources.     

Simultaneous removal and oxidation of arsenic from water by δ-MnO2 modified activated carbon

The ubiquitous arsenic in groundwater poses a great risk to human health due to its environmental toxicity and carcinogenicity. In the present work, a new adsorbent, δ-MnO₂ modified activated carbon, was prepared, and its performance for the uptake of arsenate and arsenite species from aqueous solutions was investigated by batch experiments. Various techniques, including FESEM-EDX, p-XRD, XPS and BET surface area analysis, were employed to characterize the properties of the adsorbent and the arsenic adsorption mechanisms. The results showed that δ-MnO₂ covered on the surface and padded in the pores of the activated carbon. Adsorption kinetic studies revealed that approximately 90.1% and 76.8% of As(III) and As(V), respectively, were removed by the adsorbent in the first 9 hr, and adsorption achieved equilibrium within 48 hr. The maximum adsorption capacities of As(V) and As(III) at pH 4.0 calculated from Langmuir adsorption isotherms were 13.30 and 12.56 mg/g, respectively. The effect of pH on As(V) and As(III) removal was similar, and the removal efficiency significantly reduced with the increase of solution pH. Arsenite oxidation and adsorption kinetics showed that the As(V) concentration in solution due to As(III) oxidation and reductive dissolution of MnO₂ increased rapidly during the first 12 min, and then gradually decreased. Based on the XPS analysis, nearly 93.3% of As(III) had been oxidized to As(V) on the adsorbent surface and around 38.9% of Mn(IV) had been reduced to Mn(II) after As(III) adsorption. This approach provides a possible method for the purification of arsenic-contaminated groundwater.     

Effect of bioflocculants on the coagulation activity of alum for removal of trihalomethane precursors from low turbid water

Reactivity of chlorine towards hydrophobic groups present in natural organic matter(NOM)provokes the formation of carcinogenic disinfection byproducts such as trihalomethanes in chlorinated water. The present study aimed to investigate the variations in coagulant activity of alum using two different bioflocculants(coagulant aid) namely, Moringa oleifera and Cyamopsis tetragonoloba for the removal of hydrophobic fractions of NOM and subsequent chlorine consumption by treated water. Effect of dual coagulants on trihalomethane surrogate parameters such as total organic carbon, dissolved organic carbon, UV absorbing materials and prominent hydrophobic species such as phenolic groups along with aromatic chromophores, polyhydroxy aromatic moiety have also been studied. The concept of differential spectroscopy and absorbance slope index has been employed to understand the combined effects of alum-bioflocculants on the reactivity of NOM with chlorine. Our result shows that the combination of alum and C. tetragonoloba is more efficient for reducing trihalomethane surrogates from chlorinated water as compared to M. oleifera. C. tetragonoloba elicited synchronized effects of sweep coagulation and particle bridging-adsorption which eventually facilitated efficient removal of hydrophobic fractions of NOM. The variation in the mechanistic approach of bioflocculants was due to the presence of cationic charge on M. oleifera and adhesive property of C. tetragonoloba.     

Structural characteristic and ammonium and manganese catalytic activity of two types of filter media in groundwater treatment

Two types of filter media in groundwater treatment were conducted for a comparative study of surface structure and catalytic performance. Natural filter media was adopted from a conventional aeration–filtration groundwater treatment plant, and active filter media as a novel and promising filter media was also adopted. The physicochemical properties of these two kinds of filter media were characterized using numerous analytical techniques,such as X-Ray diffraction(XRD), scanning electron microscope(SEM), energy dispersive X-ray(EDX), X-ray photoelectron spectroscopy(XPS) and Zeta potential. The catalytic activities of these filter media were evaluated for ammonium and manganese oxidation.XRD data showed that both active filter media and natural filter media belonged to birnessite family. A new manganese dioxide(Mn O2) phase(PDF#72-1982) was found in the structure of natural filter media. The SEM micrograph of natural filter media showed honeycomb structures and the active filter media presented plate structures and consisted of stacked particle. These natural filter media presented lower level of some trace elements such as calcium and magnesium, lower degree of crystallinity, lower Mn(III) content and lattice oxygen content than that of active filter media, which were associated with its poor ammonium and manganese catalytic activities. In addition, some γ-Fe2 O3 and Mn CO3 were found in the coating which may hinder the ammonium and manganese catalytic oxidation. This study provides a thorough and comprehensive understanding about the most commonly used filter media in water treatment, which can provide a theoretical guide to practical applications.     

轮南地区奥陶系天然裂缝的发育机理及其对流体活动的控制

地下天然裂缝是导致地质灾害的主要原因之一 ,其机理研究是防灾的基础。轮南地区奥陶系天然裂缝的埋深在 5 0 0 0m以下 ,其发育受多种因素控制 ,且在地质演化过程中经历了多期发育而成 ,发育机理非常典型、复杂。笔者通过观察、描述岩心的裂缝发育特征 ,分析了深度、温度、围压等的变化以及剥蚀、裂缝充填对地下岩体力学性质的影响 ;进而建立综合数学模型 ,对裂缝发育概率分布和发育特点做出预测 ;根据计算结果 ,分析了轮南地区奥陶系天然裂缝的发育机理 ;通过天然裂缝分布与井内流体测试结果的对比分析 ,探讨了裂缝分布对地下流体活动的控制作用。     

天然气输送管道泄漏事故危害定量分析

针对某市天然气利用工程中高压输送管道可能发生的天然气泄漏的危险性进行分析 ,求出了其最大的泄漏流量。通过高斯扩散模式定量计算在大气为中性条件下 ,天然气在大气中的轴向、径向和切向的扩散距离 ,从而计算出该天然气 -空气混合云团的体积。对该体积预混云团的火灾危害进行评估 ,计算形成火球的参数 ,用热辐射剂量准则计算其伤害半径。对该预混云团可能产生的爆轰后果 ,采用超压准则计算其对人员和建筑物的伤害半径。并用热辐射强度准则对可能产生稳态燃烧进行了危害半径的计算     

Using environmental accounts to promote sustainable development: Experience in southern Africa

Environmental accounts bring together economic and environmental information in a common framework to measure the contribution of the environment to the economy and the impact of the economy on the environment. They enable governments to set priorities, monitor economic policies more precisely, enact more effective environmental regulations and resource management strategies, and design more efficient market instruments for environmental policies. This article uses examples from the regional environmental accounting programme in southern Africa to demonstrate the usefulness of environmental accounts to policy-making and natural resource management. The examples address the contribution of natural capital endowments (minerals and fisheries) to sustainable development in Botswana and Namibia; the economic importance of non-market forest goods and services in South Africa; and the socio-economic impact of current water allocation and pricing policies in Botswana, Namibia and South Africa. While there are many additional policy applications, these few provide a powerful argument for the use of environmental accounts in all countries.