Colloid and heavy metal transport at landfill sites in direct contact with groundwater

Colloids are ubiquitous in aquatic systems and are suspected of facilitating contaminant transport. At sites where the disposed waste is in direct contact with ground water, two main prerequisites for colloidal transport are fulfilled: these two prerequisites are a high concentration of colloids and many different contaminants, some that are very unlikely to be transported in an aqueous solution. In our investigation, three landfill sites with different historical background and hydrogeological conditions were examined. The colloids upstream, downstream, and inside the waste disposal sites were characterized with respect to their size distribution and chemical composition. The particle concentration upgradient and downgradient of the sites were 2-23 and 8-80 mg/L, respectively. Inside the waste disposal sites the particle concentration was 160-870 mg/L. The particles upgradient reflected the mineral composition of the aquifer, with calcareous colloids and silicates dominating the composition. Downgradient of the sites, we saw an increase of iron-precipitates and salt colloids, together with organic colloids. However, the downgradient colloids were significantly different from the colloids and particles inside of the disposal sites with respect to their size and chemical composition. Colloids inside the disposal sites reflected the waste composition and degradation. The association of heavy metal ions to colloids and particles showed a surprisingly high fraction of dissolved metal ions. We determined that the lowest metal ion concentrations (less than 20% of the total concentration) were associated with the colloid size class between 10 nm and 1 microm, which is considered most mobile in porous systems. The association of Fe and Mn to colloids was dominated by the redox conditions inside the disposal sites, where there was a reducing environment, Fe and Mn were dissolved. Outside the disposal sites, where there was an oxidizing environment, these metals formed colloids and particles >1 microm. Together with these particles, As was precipitating. For other metal ions (Cd, Co, Cu, Ni, Pb, Zn), we determined an association to colloids coinciding roughly with the colloid size distribution. The results suggest that the change of hydrochemical conditions at the interface, from a reducing, high ionic strength environment inside of the disposal sites to an oxidizing, low ionic strength environment in the groundwater together with physical filtration effects for the larger particles, is an effective chemical barrier for colloids. Field observations suggest, that the colloids form a rather persistent coating around the aquifer matrix that reduces the hydraulic conductivity and enhances the sorption capacity of the aquifer close to the waste disposal sites. In every case, there was an increase of the contaminant concentrations downstream of the waste disposal sites, but the increase was less than expected from the initial transport calculations, which were under the assumption that there was a direct contact between the waste disposal site and the groundwater. It seems more than likely, that under the given conditions, colloids are contributing to a self sealing layer at the landfill bottom. The results of this study are relevant for the assessment of many landfills without appropriate landfill sealing systems.     

社区行动规划方法在扬州老城保护中的应用

公众参与近年来在我国已引起越来越多的关注,但居民和社区参与的实践操作还很少.社区行动规划是发动居民参与社区规划和建设的一种方法,国际上已有较为成功的运用.德国技术合作公司(GTZ)和扬州市政府引入社区行动规划方法,鼓励居民参与历史街区的保护并改善自身的居住条件,在实践中尝试了老城保护中的公众参与方法.     

Concrete corrosion in wastewater systems: Prediction and sensitivity analysis using advanced extreme learning machine

The implementation of novel machine learning models can contribute remarkably to simulating the degradation of concrete due to environmental factors. This study considers the sulfuric acid corrosive factor in wastewater systems to simulate concrete mass loss using five machine learning models. The models include three different types of extreme learning machines, including the standard, online sequential, and kernel extreme learning machines, in addition to the artificial neural network, classification and regression tree model, and statistical multiple linear regression model. The reported values of concrete mass loss for six different types of concrete are the target values of the machine learning models. The input variability was assessed based on two scenarios prior to the application of the predictive models. For the first assessment, the machine learning models were developed using all the available cement and concrete mixture input variables; the second assessment was conducted based on the gamma test approach, which is a sensitivity analysis technique. Subsequently, the sensitivity analysis of the most effective parameters for concrete corrosion was tested using three different approaches. The adopted methodology attained optimistic and reliable modeling results. The online sequential extreme learning machine model demonstrated superior performance over the other investigated models in predicting the concrete mass loss of different types of concrete.     

Impacts of emerging organic contaminants on freshwater resources: review of recent occurrences, sources, fate and effects

Rapid urbanization and frequent disposal of wastewater to surface water cause widespread contamination of freshwater supplies with emerging contaminants, such as pharmaceuticals, insecticides, surfactants, endocrine disruptors, including hormones. Although these organic contaminants may be present at trace levels, their adverse effects on aquatic life, animals and even humans are a growing concern. Numerous studies have been published on the occurrence and fate of emerging organic contaminants in different parts of the world, spanning a wide range of sources and aquatic environments including freshwater catchments, effluent wastewater streams, lakes, rivers, reservoirs, estuaries and marine waters. This paper reviews recent studies on the occurrence and fate of frequently detected pharmaceuticals and hormones and identifies areas that merit further research.     

Optimierung der thermischen Behaglichkeit im Bestand

In der modernen Welt ist der Mensch es z. B. vom Auto her gewohnt, das Innenraumklima selbst einzustellen, und zwar individuell für Fahrer und Beifahrer. Schwieriger wird dies in unseren Gebäuden, die im Normalfall nur beheizt werden können. Für den Sommer ist die Klimaanlage eine Ausnahme, auch wenn die Verbreitung immer weiter voranschreitet. Kommen mehrere Personen in einem Raum zusammen, ist ein individuelles Wohlfühlklima nicht möglich. Hier kommt es darauf an, den Anteil der unzufriedenen Nutzer möglichst gering zu halten. Im nachfolgenden Beitrag werden die Ursachen für die Beschwerden zweier Großraumbüros untersucht und Vorschläge zur Verbesserung vorgestellt. Optimisation of thermal comfort in existing buildings. In the modern world people are used to being able to adjust the interior climate, for example with individual settings for car drivers and passengers. The situation is more difficult in buildings which normally only have a heating system without provision for cooling. In moderate climates air‐conditioning systems are an exception, although they are becoming increasingly popular. If several people come together in a room, it is impossible to adjust the conditions to the satisfaction of all occupants. The key is to keep the ratio of dissatisfied users to a minimum. This paper examines the reasons for complaints in two open‐plan offices and offers suggestions for improvements.     

Sickerwassertransport von Kolloiden und Schwermetallen in Bergbaufolgelandschaften – Felduntersuchungen und Laborversuche

The influence of colloids on the transport of heavy metals at a former lignite mining site investigated. A three-dimensional hydrochemical mapping allows a view into the disposal revealing the stratigraphy within the water body. A SEM/EDX based single-particle method for the characterization of aquatic colloids was developed. Within a size range from 30 nm to 1 μm mostly inorganic silica and salt colloids were be detected, whereas the size fraction below 30 nm was predominated by organic colloids. Although some heavy metals, mainly Co and Cu, were associated to colloids, the total amount of heavy metal colloids was neglectable. Silica colloids were chosen for batch and column investigations. Though the sorption coefficients suggested that the colloids should be a sink for heavy metals, no significant changes of the transport behaviour due to the presence of colloids was observed. Instead, the colloids were filtered by the sediment. The results of teh field and laboratory work indicate clearly that there is no significant enhancement of heavy metal transport at the Kanena landfill site by inorganic colloids.     

Molecular modeling approach to the prediction of mechanical properties of silica‐reinforced rubbers

Recently, we have suggested a nanomechanical model for dissipative loss in filled elastomer networks in the context of the Payne effect. The mechanism is based on a total interfiller particle force exhibiting an intermittent loop, due to the combination of short‐range repulsion and dispersion forces with a long‐range elastic attraction. The sum of these forces leads, under external strain, to a spontaneous instability of “bonds” between the aggregates in a filler network and attendant energy dissipation. Here, we use molecular dynamics simulations to obtain chemically realistic forces between surface modified silica particles. The latter are combined with the above model to estimate the loss modulus and the low strain storage modulus in elastomers containing the aforementioned filler‐compatibilizer systems. The model is compared to experimental dynamic moduli of silica filled rubbers. We find good agreement between the model predictions and the experiments as function of the compatibilizer's molecular structure and its bulk concentration. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40806.     

Improvement of the high temperature properties of the LiYO2–Si3N4 system by removing residual Li

Effects of the vaporization of residual Li on the microstructure, oxidation behavior and high temperature properties of a low-temperature pressureless sintered Si₃N₄ using LiYO₂ additive were investigated. The oxidation and creep resistance of the Si₃N₄ was improved after an annealing at 1650 °C because residual Li, which deteriorated the high temperature properties of the Si₃N₄, could be mostly removed. The high temperature deformation of the Si₃N₄ was strongly suppressed after the annealing treatment. The annealed specimens retained 64% of the room temperature strength at 1300 °C in air. The present investigation reports a method to improve the high temperature properties of Si₃N₄.     

Effect of fiber length on processing and properties of extruded wood‐fiber/HDPE composites

Fiber length and distribution play important roles in the processing and mechanical performance of fiber‐based products such as paper and fiberboard. In the case of wood–plastic composites (WPC), the production of WPC with long fibers has been neglected, because they are difficult to handle with current production equipment. This study provides a better understanding of the effect of fiber length on WPC processing and properties. The objectives of this study were therefore to determine the role of fiber length in the formation process and property development of WPC. Three chemithermomechanical pulps (CTMP) with different lengths, distributions, and length‐to‐diameter ratios (L/D) were obtained by mechanical refining. Length, shape, and distribution were characterized using a fiber quality analyzer (FQA). The rheometer torque properties of high‐density polyethylene (HDPE) filled with the pulps at different loads were studied. Variations in fiber load and length distribution resulted in significant variations in melting properties and torque characteristics. Composites from the three length distributions were successfully processed using extrusion. Physical and mechanical properties of the obtained composites varied with both length distribution and additive type. Mechanical properties increased with increasing fiber length, whereas performance in water immersion tests decreased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Oil‐Fat Mixtures with Low Solid Fat Concentration: Influence of Fat Concentration and Cooling Conditions

Uniform suspension of particulates (salt or spices) in oil‐based marinades requires a gel behavior of the matrix. This can be achieved by adding a solid fat to the liquid oil. Besides rheology, appearance and thermal stability are important for the utilization as marinades. The influence of solid fat concentration (c_fat = 2.5–5.5 wt%) and average cooling speed (1.4, 2.6, and 4.7 °C/min) on the functional properties of oil‐fat gels from palm fat and canola oil was investigated. Oil‐fat mixtures showed complex physiochemical behavior depending on the solid fat concentration and cooling rate. All samples had a shear‐thinning behavior. Yield stresses and apparent viscosities increased at a constant cooling rate with increasing solid fat concentration. Frequency dependence of storage and loss modulus showed a transition from a viscous solution to a weak gel at c_fat > 3.5 wt%. Samples at increasing cooling rates transitioned to weak gels at lower fat concentration (2.5 wt%). Mixtures became turbid and increasingly whiter as both solid fat concentration and cooling rates increased, which was explained by increased light‐scattering by fat crystal aggregates. Results show the critical importance of proper formulation and preparation conditions on the functionality of oil‐based marinades.