Clarification is one of the main steps in producing glycerin from glycerin–rich solution (namely sweetwater) in oleo-chemical industry. In this study, ZnO nanoparticles (9–12 nm in diameter) were incorporated into polysulfone (PSf) membranes to improve the membrane antifouling properties toward the fatty acids in sweetwater. The hybrid membranes were fabricated through wet phase inversion method. The modified membranes exhibited better water permeability, membrane surface hydrophilicity (improvement from 82° to 62.1°) and resistance toward fouling by fatty acids. In this study, the best membrane was obtained in the presence of 3% of ZnO nanoparticles, which showed good fouling resistance, high solution flux and a very high rejection of fatty acids (≥80%) in comparison with the pure PSf membranes, at the same experimental conditions. The enhanced membrane performances during the clarification of sweetwater were attributed to the unique properties of ZnO nanoparticles that were uniformly dispersed in the PSf structures. 相似文献
Landslides - In the design of multiple rigid barriers, the height of the first barrier governs the impact dynamics of debris flow on the next barrier in a channel. However, current design... 相似文献
Landslides - Natural terrain landslides are mainly triggered by rainstorms in Hong Kong, which pose great threats to life and property. To mitigate landslide risk, building a prediction model which... 相似文献
Ocean Dynamics - In this paper, a two-phase coastal liquid-sediment system and a wave breaker were numerically simulated using a particle-based smooth particle hydrodynamics (SPH). To verify the... 相似文献
Understanding the interaction between complex geophysical flows and barriers remains a critical challenge for protecting infrastructure in mountainous regions. The scientific challenge lies in understanding how grain stresses in complex geophysical flows become manifested in the dynamic response of a rigid barrier. A series of physical flume tests were conducted to investigate the influence of varying the particle diameter of mono-dispersed flows on the impact kinematics of a model rigid barrier. Particle sizes of 3, 10, 23 and 38 mm were investigated. Physical tests results were then used to calibrate a discrete element model for carrying out numerical back-analyses. Results reveal that aside from considering bulk characteristics of the flow, such as the average velocity and bulk density, the impact load strongly depends on the particle size. The particle size influences the degree of grain inertial stresses which become manifested as sharp impulses in the dynamic response of a rigid barrier. Impact models that only consider a single impulse using the equation of elastic collision warrant caution as a cluster of coarse grains induce numerous impulses that can exceed current design recommendations by several orders of magnitude. Although these impulses are transient, they may induce local strucutral damage. Furthermore, the equation of elastic collision should be adopted when the normalized particle size with the flow depth, δ/h, is larger than 0.9 for Froude numbers less than 3.5. 相似文献
Lateritic clay is well recognized to contain significant amount of iron and aluminium oxides (sesquioxide). These oxides enhance the formation of soil aggregates which would greatly affect soil structure. So far, no study has been carried out purposely to investigate the influence of aggregate-dependent structure on the mechanical behaviour of the lateritic clay. In this study, structure effects on the compression and shear behaviour of a saturated lateritic clay were studied. Intact, recompacted and reconstituted specimens were studied through oedometer, isotropic compression and consolidated undrained shear tests. Microstructure of these specimens was determined using the mercury intrusion porosimetry and scanning electron microscopy (SEM) techniques and then used to explain the observed behaviour. It was found that the compressibility of recompacted/reconstituted specimens was about 90% larger than intact specimen. Different from soft clay, the influence of microstructure does not show an obvious reduction in compressibility after yielding. The peak shear strength of intact specimen was about 100% higher than those of reconstituted/recompacted specimens. The significant difference in compression and shear behaviour is mainly because the aggregates of intact specimen were about 90% larger than those of reconstituted/recompacted specimens, as revealed by the SEM results. As a result, particle contacts forming the force chain were therefore larger in the intact specimen. The intact specimen therefore became less compressible and more dilative.
An unsaturated soil is a three-phase material that is ubiquitous on the earth’s surface. The fully saturated and completely dry states are just two limiting conditions of an unsaturated soil. The state and properties of unsaturated soils can change significantly with external loads, weather conditions and groundwater level. Proper modelling of the state-dependent behaviour of unsaturated soils is crucial for analysing the performance of almost all civil engineering structures. So far, there are many unsaturated soil models and several relevant review papers in the literature. None of the existing review papers, however, focused on the state dependency of unsaturated soil behaviour. Moreover, some aspects of soil behaviour have not been reviewed, including small strain stiffness, dilatancy and stress-dependence of water retention curve. In the current review paper, the state dependency of unsaturated soil behaviour is reviewed, with a particular attention to the three missing parts. The review is carried out in a unified and relatively simple constitutive framework, which adopts a three-by-three compliance matrix to link incremental volumetric strain, deviator strain and degree of saturation to incremental mean net stress, deviator stress and suction. All of the nine variables in the proposed three-by-three compliance matrix have clear physical meanings and can be measured through compression, shearing and water retention tests. Theoretical models based on other constitutive stress variables can be also converted to this framework by matrix transformation.
Composting is one of the waste disposal methods adopted for disposal of livestock waste in Hong Kong. The composting livestock waste normally undergoes 6-8 weeks fermentation, followed by 16-20 weeks maturation. The matured compost is sold as soil conditioner in the local market. In 2006, feedstock material and a time-series of compost samples were collected throughout the fermentation and maturation process from the Sha Ling Composting Plant in the New Territories. The feedstock material and compost samples were analyzed for contents of three unintentional persistent organic pollutants (POPs), i.e. dioxins/furans, dioxin-like PCBs and total PCBs. These POPs are unintentionally produced by-products of chemical industrial processes and combustion processes. Selected heavy metals were also analyzed, which served as conservative tracers to determine potential mass loss during the composting process. Levels of contamination by these POPs were found to be low in the matured compost for sale. The mean concentrations (lower-upper bound) of total dioxins/furans, total dioxin-like PCBs and total PCBs were 2.01-2.05 ng I-TEQ/kg dw, 0.04-0.05 ng WHO-TEQ/kg dw and 1.55-1.55 microg/kg dw, respectively. Progressively elevated levels of these POPs were observed in the compost samples during the fermentation process. Analysis of the congener profiles revealed that the heptaCDD and octaCDD were the main contributors to the observed increase in dioxin/furan content. The possible sources of dioxins/furans in the compost were discussed. The study results established a local dioxins/furans emission factor specific to the trade and provided a better estimate of the annual dioxins/furans emission for the livestock waste composting activity in Hong Kong. 相似文献
Environmental factors in estuaries are highly variable in terms of both spatial and temporal dimensions and hence phytoplankton biomass, as well as community structure, is dynamic. Two cruises were carried out in the Changjiang (Yangtze River) Estuary and adjacent area in spring and summer. The result of CHEMTAX calculation suggests that in spring diatoms and chlorophytes contribute equally to phytoplankton biomass, while phytoplankton community structure is mainly composed of diatoms in summer. We encountered blooms in summer with chlorophyll a (CHLa) over 10 μg l−1 off the Changjiang Estuary and they were mainly caused by diatoms (>90%). Based on the HPLC analysis of samples collected, phytoplankton pigments mainly concentrated beyond the front between 122.5°E and 123°E where nutrients and turbidity were best balanced. Euphotic depth (Zeu, calculated from Secchi disk depth) to surface mixed layer depth (Zmix) ratio (i.e. Zeu/Zmix) were comparable in spring (average value 1.2) and the ratio increased to 5.2 in summer. Variation of the ratio indicates an apparent shift of light and physical conditions from spring to summer. Correspondingly, CHLa was positively related to Zeu/Zmix ratio (r2 = 0.83) in spring, indicating the light limitation over the whole investigation area. On the other hand, the relationship of CHLa and Zeu/Zmix ratio became unclear when Zeu/Zmix ratio >3 in summer. This is probably due to the combination of both light limitation before the front and nutrient limitation beyond the front. In addition, evidence was found that light condition can impact the diagnostic pigments in the Changjiang Estuary. 相似文献
