The aggregation of common manganese dioxide (MnO2) colloids has great impact on their surface reactivity and therefore on their fates as well as associated natural and synthetic contaminants in engineered (e.g. water treatment) and natural aquatic environments. Nevertheless, little is known about the aggregation kinetics of MnO2 colloids and the effect of humic acid (HA) and surfactants on these. In this study, the early stage aggregation kinetics of MnO2 nanoparticles in NaNO3 and Ca(NO3)2 solutions in the presence of HA and surfactants (i.e., sodium dodecyl sulfate (SDS), and polyvinylpyrrolidone (PVP)) were modeled through time-resolved dynamic light scattering. In the presence of HA, MnO2 colloids were significantly stabilized with a critical coagulation concentration (CCC) of ~300 mmol·L-1 NaNO3 and 4 mmol·L-1 Ca(NO3)2. Electrophoretic mobility (EPM) measurements confirmed that steric hindrance may be primarily responsible for increasing colloidal stability in the presence of HA. Moreover, the molecular and/or chemical properties of HA might impact its stabilizing efficiency. In the case of PVP, only a slight increase of aggregation kinetics was observed, due to steric reactions originating from adsorbed layers of PVP on the MnO2 surface. Consequently, higher CCC values were obtained in the presence of PVP. However, there was a negligible reduction in MnO2 colloidal stability in the presence of 20 mg·L-1SDS. 相似文献
Changes in solution chemistry and transport conditions can lead to the release of deposited MnO2 nanoparticles from a solid interface, allowing them to re-enter the aqueous environment. Understanding the release behavior of MnO2 nanoparticles from naturally occurring surfaces is critical for better prediction of the transport potential and environmental fate of MnO2 nanoparticles. In this study, the release of MnO2 nanoparticles was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D), and different environmental surface types, solution pH values and representative macromolecular organics were considered. MnO2 nanoparticles were first deposited on crystal sensors at elevated NaNO3 concentrations before being rinsed with double-deionized water to induce their remobilization. The results reveal that the release rate of MnO2 depends on the surface type, in the decreasing order: SiO2 > Fe3O4 > Al2O3, resulting from electrostatic interactions between the surface and particles. Moreover, differences in solution pH can lead to variance in the release behavior of MnO2 nanoparticles. The release rate from surfaces was significantly higher at pH 9.8 that at 4.5, indicating that alkaline conditions were more favorable for the mobilization of MnO2 in the aquatic environment. In the presence of macromolecular organics, bovine serum albumin (BSA) can inhibit the release of MnO2 from the surfaces due to attractive forces. In presence of humic acid (HA) and sodium alginate (SA), the MnO2 nanoparticles were more likely to be mobile, which may be associated with a large repulsive barrier imparted by steric effects. 相似文献
Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and microelectrode technology were employed to evaluate the Nitrous oxide (N2O) production in biological aerated filters (BAFs) under varied dissolved oxygen (DO) concentrations during treating wastewater under laboratory scale. The average yield of gasous N2O showed more than 4-fold increase when the DO levels were reduced from 6.0 to 2.0 mg?L–1, indicating that low DO may drive N2O generation. PCR-DGGE results revealed that Nitratifractor salsuginis were dominant and may be responsible for N2O emission from the BAFs system. While at a low DO concentration (2.0 mg?L–1), Flavobacterium urocaniciphilum might play a role. When DO concentration was the limiting factor (reduced from 6.0 to 2.0 mg?L–1) for nitrification, it reduced NO2--N oxidation as well as the total nitrification. The data from this study contribute to explain how N2O production changes in response to DO concentration, and may be helpful for reduction of N2O through regulation of DO levels.
This paper compares legal systems for water management in France and China, with a focus on integrated water resources management and regarding in particular the formulation of policies and their implementation. The research shows that China has committed itself to the efficient management of water resources through the development of various policy tools during the current period. This commitment, however, has often been interrupted and distorted by politics, resulting in the neglect of socioeconomic and environmental priorities. France has developed a legislative framework and practical instruments to apply integrated water resources management at the river basin level since the 1960s. This experience and the current implementation of the European Water Framework Directive brings elements that can contribute to Chinese society meeting its water challenges. 相似文献
The characteristics of wintertime volatile organic compounds (VOCs) in the North China Plain (NCP) region are complicated and remain obscure. VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a rural site in the NCP from November to December 2018. Uncalibrated ions measured by PTR-ToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector (GC-MS/FID). The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions, the secondary formation of oxygenated VOCs (OVOCs) is non-negligible in the wintertime, i.e., OVOCs accounts for 42% ± 7% in the total VOCs (151.3 ± 75.6 ppbV). We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes. The chemical changes of organic carbon in a pollution accumulation period were investigated, which suggests an essential role of fragmentation reactions for large, chemically reduced compounds during the heavy-polluted stage in wintertime pollution. The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of “coal to gas” strategies in curbing air pollutants. The high abundances of some key species (e.g. oxygenated aromatics) indicate the strong emissions of coal combustion in wintertime of NCP. The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs. 相似文献
In this study, an approach integrating digital land use/cover change (LUCC) analysis, hydraulic modeling and statistical methods was applied to quantify the effect of LUCC on floods in terms of inundation extent, flood arrival time and maximum water depth. The study took Beijing as an example and analyzed five specific floods with return periods of 20-year, 50-year, 100-year, 1000-year and 10000-year on the basis of LUCC over a nine-year period from 1996 to 2004. The analysis reveals that 1) during the period of analysis Beijing experienced unprecedented LUCC; 2) LUCC can affect inundation extent and flood arrival time, and floods with longer return periods are more influenced; 3) LUCC can affect maximum water depth and floods with shorter return periods are more influenced; and 4) LUCC is a major flood security stressor for Beijing. It warns that those cities having experienced rapid expansion during recent decades in China are in danger of more serious floods and recommends that their actual land use patterns should be carefully assessed considering flood security. This integrated approach is demonstrated to be a useful tool for joint assessment, planning and management of land and water. 相似文献