Aging of PVDF and PES ultrafiltration membranes by sodium hypochlorite: Effect of solution pH

Sodium hypochlorite (NaClO) is a commonly applied cleaning agent for ultrafiltration membranes in water and wastewater treatment. Long-term exposure to NaClO might change the properties and performance of polymeric membranes, and ultimately shorten membrane lifespan. Active species in NaClO solution vary with solution pH, and the aging effects can change depending on the membrane material. In this study, the aging of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) membranes by NaClO at pH 3–11 was investigated by examining variations in chemical composition, surface charge, surface morphology, mechanical strength, permeability, and retention ability. Polyvinyl pyrrolidone (PVP), which was blended in both membranes, was oxidized and dislodged due to NaClO aging at all investigated pH values, but the oxidation products and dislodgement ratio of PVP varied with solution pH. For the PVDF membrane, NaClO aging at pH 3–11 caused a moderate increase in permeability and decreased retention due to the oxidation and release of PVP. The tensile strength decreased only at pH 11 because of the defluorination of PVDF molecules. For the PES membrane, NaClO aging at all investigated pH resulted in chain scission of PES molecules, which was favored at pH 7 and 9, potentially due to the formation of free radicals. Therefore, a decrease in tensile strength and retention ability, as well as an increase in permeability, occurred in the PES membrane for NaClO aging at pH 3–11. Overall, the results can provide a basis for selecting chemical cleaning conditions for PVDF and PES membranes.     

Identification of close relationship between atmospheric oxidation and ozone formation regimes in a photochemically active region

Understanding ozone (O₃) formation regime is a prerequisite in formulating an effective O₃ pollution control strategy. Photochemical indicator is a simple and direct method in identifying O₃ formation regimes. Most used indicators are derived from observations, whereas the role of atmospheric oxidation is not in consideration, which is the core driver of O₃ formation. Thus, it may impact accuracy in signaling O₃ formation regimes. In this study, an advanced three-dimensional numerical modeling system was used to investigate the relationship between atmospheric oxidation and O₃ formation regimes during a long-lasting O₃ exceedance event in September 2017 over the Pearl River Delta (PRD) of China. We discovered a clear relationship between atmospheric oxidative capacity and O₃ formation regime. Over eastern PRD, O₃ formation was mainly in a NO_x-limited regime when HO₂/OH ratio was higher than 11, while in a VOC-limited regime when the ratio was lower than 9.5. Over central and western PRD, an HO₂/OH ratio higher than 5 and lower than 2 was indicative of NO_x-limited and VOC-limited regime, respectively. Physical contribution, including horizontal transport and vertical transport, may pose uncertainties on the indication of O₃ formation regime by HO₂/OH ratio. In comparison with other commonly used photochemical indicators, HO₂/OH ratio had the best performance in differentiating O₃ formation regimes. This study highlighted the necessities in using an atmospheric oxidative capacity-based indicator to infer O₃ formation regime, and underscored the importance of characterizing behaviors of radicals to gain insight in atmospheric processes leading to O₃ pollution over a photochemically active region.     

Removal of unburned carbon from municipal solid waste fly ash by column flotation

Unburned carbon (UC) is the major source of organic contaminants in municipal solid waste (MSW) fly ash. So most organic contaminants can be removed by the removal of the UC from the MSW fly ash. In this paper, we first used a technique of column flotation to remove UC from MSW fly ash. The influences of column flotation parameters on the recovery efficiency of UC were systematically studied. It was found that the UC recovery efficiency was greatly influenced by the gas flow rate, pH value, collector kerosene's concentration and the types of fly ash. By optimizing the above parameters, we have successfully removed 61.2% of the UC from MSW fly ash having 5.24% UC content. The removal mechanism was well accounted for the kinetic theory of column flotation and surface-chemistry theory. The results indicate that the column flotation technique is effective in removing the UC from MSW fly ash, and show that there is a strong possibility for practical application of this technique in removing the organic contaminants from MSW fly ash.     

湖泊富营养化模型的研究进展

湖泊的富营养化是全球普遍关注的环境问题之一.湖泊的富营养化模型是防治、修复和治理湖泊富营养化的重要决策工具.按研究的侧重点不同,将湖泊富营养化模型分为简单回归模型、水质模型、生态模型和生态-水动力水质模型,并分别回顾了四类模型的研究进展.最后指出湖泊富营养化模型的发展趋势,强调不确定理论、3S技术、耦合模型是今后湖泊富营养化模型研究的重点,应在此基础上建立通用的模拟、预测、评价和优化模型,为湖泊富营养化管理提供科学依据.     

Long-term estimation of plastic material resources from end-of-life vehicles in China: a scenario analysis considering multiple industry standards

Journal of Material Cycles and Waste Management - The recycling and treatment of plastic waste become an increasingly serious environmental degradation challenge. To promote the recycling of...     

Fabrication and characterization of lightweight aggregate prepared from steel mill sludge in one step

Journal of Material Cycles and Waste Management - The qualified green lightweight aggregate (LWA) was successfully prepared from steel mill sludge (SMS) and fly ash (FAS) in one step using the...     

The interception effect of heavy metals in different types of Chinese fir plantations

Environmental Geochemistry and Health - The aim of this research is to investigate the interception effect of heavy metals, such as zinc (Zn), copper (Cu), lead (Pb), arsenic (As), and cadmium (Cd)...     

Improving protected area effectiveness through consideration of different human-pressure baselines

Previous assessments of the effectiveness of protected areas (PAs) focused primarily on changes in human pressure over time and did not consider the different human-pressure baselines of PAs, thereby potentially over- or underestimating PA effectiveness. We developed a framework that considers both human-pressure baseline and change in human pressure over time and assessed the effectiveness of 338 PAs in China from 2010 to 2020. The initial state of human pressure on PAs was taken as the baseline, and changes in human pressure index (HPI) were further analyzed under different baselines. We used the random forest models to identify the management measures that most improved effectiveness in resisting human pressure for the PAs with different baselines. Finally, the relationships between the changes in the HPI and the changes in natural ecosystems in PAs were analyzed with different baselines. Of PAs with low HPI baselines, medium HPI baselines, and high HPI baselines, 76.92% (n=150), 11.11% (n=12), and 22.86% (n=8) , respectively, showed positive effects in resisting human pressure. Overall, ignoring human-pressure baselines somewhat underestimated the positive effects of PAs, especially for those with low initial human pressure. For PAs with different initial human pressures, different management measures should be taken to improve effectiveness and reduce threats to natural ecosystems. We believe our framework is useful for assessing the effectiveness of PAs globally, and we recommend it be included in the Convention on Biological Diversity Post-2020 Strategy.     

Effects of bedform migration on nutrient fluxes at the sediment–water interface: a theoretical analysis

Environmental Fluid Mechanics - Nutrient fluxes at the sediment–water interface are essential for water quality and aquatic ecosystems. In this study, a unified expression for the sediment...