Interpretation of out-diffusion experiments on crystalline rocks using random walk modeling

Matrix diffusion in saturated rocks with very low permeability is one of the major mechanisms of solute transport. Laboratory out-diffusion experiments on rock samples may provide an estimate of the bulk diffusion coefficient. However, numerous results have shown that this average parameter does not really depict the complex mechanism of diffusion as a function of the internal heterogeneity of crystalline rocks. Two-dimensional images of the porosity distribution in a granite sample were obtained by impregnation with a radioactive resin and autoradiography. Some examples based on these images and synthetic images were used to perform numerical simulations of out-diffusion using two different random walk methods. The simulated shapes of the out-diffusion curves depend on the spatial distribution of the porosity and on the pore connectivity with the border of the sample. Such relations might explain the multiple nested slopes or the convex shapes often observed on real experimental curves.     

Mathematical modeling of biofiltration in activated pine-bark charge of a biofilter

Aim, Scope and Background Human economic activities cause emissions of various pollutants of an organic nature: butanol, butyl acetate, methanol, formaldehyde, phenol, benzene, toluene, xylene, etc. These compounds are emitted to atmosphere by various enterprises of food, chemistry, wood processing industries, from transportation means, agricultural enterprises, etc. Therefore, when purifying air from these pollutants, it is necessary to apply efficient and inexpensive air purification methods. In this dimension, the biological air purification is chosen from all possible air cleaning methods. An experimental biofilter with the activated charge of pine bark was developed at the Department of Environment Protection of the Vilnius Gediminas Technical University. In the course of the experimental investigation, it was determined that this air purification method is efficient. Filter efficiency, when purifying air of volatile organic compounds (butanol, butyl acetate and xylene), to a great extent, depending on the nature and concentrations (up to 100 mg/m3) of pollutants injected, might go up to 70-98%. The mathematical model of the biofilter was developed based on the research results and fully taking into consideration physical, chemical, and biological processes going on during its operations. Main Features The aim of this article is to determine biodegradation constant , absorption capacity , and half empiric expressions of filter efficiency. Knowing this, it is possible to find out the dependence of the filter efficiency on the operational parameters of the filter (i.e. on the concentrations and the height of biocharge of the initial pollutants (butanol, butyl acetate, xylene) fed through it). Conclusions With the help of mathematical modeling, the biodegradation constants and absorption capability of volatile organic compounds (butanol, butyl acetate, and xylene) fed into the biofilter charged with the activated pine bark and used for the cleaning of volatile organic compounds, as well as the efficiency of the biofilter in half empiric expression, have been established. It has been discovered that the constant of pollutant biodegradation is a value inverse to the time during which the amount of pollutants in the filter becomes times higher. It is rather complicated to carry out theoretical calculation of the biodegradation constant at a molecular level, therefore this constant has been established based on the results obtained in the course of research. The equations describing pollutant dynamics in the filter charge and the air cleaning processes going on in it have been derived from diffusion equations in a mobile medium. The modeling helped to find out the absorption capacity of the examined pollutants, which by its numeric value is equal to the volume unit of the absorbed gas amount. The latter factor, the same as the biodegradation constant, was determined basing on the experimental results. Mathematical modeling brought a range of formulas expressing dependences of each pollutant's efficiency on its initial concentrations and filter charge height. Recommendation /Outlook. Based on the experimental data, a mathematical model has been developed which will allow the measuring of the filter efficiency not only with regard to the absorption and biodegradation of the pollutants under examination, but also with regard to other pollutants and their compounds, etc., having an impact on the filter performance. The results of the mathematical modeling have revealed that the modeling of processes going on in the filter is much simpler than isthe performance of long and costly experiments. The developed mathematical model makes it possible to measure the filter efficiency at the present moment.     

Effect of Long Retention Time in the Settler on Phosphorus Removal from Communal Wastewater (4 pp)

- Goals. The objective of the paper is to illustrate the solution of a chronic problem occurring in a wastewater treatment facility with a capacity of 12,000 inhabitant equivalent. A drastic phosphorus concentration increase (two or three times higher than the Hungarian limit of 1 mg/l) was observed in the wastewater treatment facility for a long time (12–24 h) with changing time periods indicating malfunctioning in the operation of the facility. Methods Computer-aided simulation technique was used to develop a solution for the treatment of the problem using a software developed by the Department of Environmental and Chemical Engineering, University of Veszprém, Hungary. Results and Discussion The simulation studies show that if the nightly inflow is less than 200 m3/h at least for two hours, the system doesn't then receive enough fresh nutrients which can cause a deficiency in the nutrient uptake of the PAOs in the anaerobic zones. This can result in the fact that the PAOs accumulate less phosphorus into the aerobic zones. Conclusion Long retention time (10 h) is the reason for the problem, namely – under special conditions – the phosphorus in the sludge of the settling tank of the wastewater treatment plant. The problem was caused by phosphorus dissolution from the sludge of the settling tank during the undesirably long retention time.     

Sources of organic aerosol: Positive matrix factorization of molecular marker data and comparison of results from different source apportionment models

This paper presents results from positive matrix factorization (PMF) of organic molecular marker data to investigate the sources of organic carbon (OC) in Pittsburgh, Pennsylvania. PMF analysis of 21 different combinations of input species found essentially the same seven factors with distinctive source-class-specific groupings of molecular markers. To link factors with source classes we directly compare PMF factor profiles with actual source profiles. Six of the PMF factors appear related to primary emissions from sources such as motor vehicles, biomass combustion, and food cooking. Each primary factor contributed between 5% and 10% of the annual-average OC with the exception of the cooking related factor which contributed 20% of the OC. However, the contribution of the cooking factor was sensitive to the specific combinations of input species. PMF could not differentiate between gasoline and diesel emissions, but the aggregate contribution of primary emissions from these two source classes is estimated to be less than 10% of the annual-average OC. One factor appears related to secondary organic aerosol based on its substantial contribution to biogenic oxidation products. This secondary factor contributed more than 50% of the summertime average OC. Reasonable agreement was observed between the PMF results and those of a previously published chemical mass balance (CMB) analysis of the same molecular marker dataset. Individual PMF factors are correlated with specific CMB sources, but systematic biases exist between the two estimates. These biases were generally within the uncertainty of the two estimates, but there is also evidence that PMF is not cleanly differentiating between source classes.     

Uptake and Modeling of Pesticides by Roots and Shoots of Parrotfeather (Myriophyllum aquaticum) (5 pp)

Intention, Goal, Scope, Background Aquatic plants have a great potential to function as in situ, on-site biosinks and biofilters of pollutants. They are used for phytoremediation and phytotoxicity studies. Pesticide uptake studies are very important to predict contaminant accumulation, translocation, and transformation. There are a lot of models which have been developed for emergent plants, but there are not any existing models for submerged aquatic plants for assessing pesticide uptake. Objective In this study, uptake of selected pesticides in parrotfeather (Myriophyllum aquaticum) were studied and the results were modeled with the aid of Log Kow and the concentration of pesticides. At the end, the developed model was compared to other existing models. Methods The test was conducted with parrotfeather as a model plant. The bioassay and cultivation of this plant were examined. Pesticide uptake by roots and shoots was determined using 14C-radiolabeled materials. Results and Discussion The results were fitted with an equation that showed a relationship between uptake and lipophilicity of pesticides. The model was compared with other pesticide uptake models developed for other plants. Atrazine and cycloxidim were taken up more by roots than by shoots in comparison to other pesticides used. The total uptake, both in shoots and roots, was lower than for terbutryn and trifluralin. The best appropriate model was developed from the results against the other models seen in the literature. The concentration factors (Root Concentration Factor (RCF) and Submerged Shoot Concentration Factor (SSCF)) increased with a higher Kow of the substances. The Submerged Shoot Concentration Factor (SSCF) revealed a better relationship of the chemicals than did the Root Concentration Factor (RCF). Conclusions In this study, an uptake model was developed for rooted, submerged aquatic plants. Further studies are necessary to develop and compare models with different plants and pesticides. Recommendation and Outlook Such studies as this one may be extended to other environmental pollutants in the aquatic ecosystem and may be employed to evaluate the possibility of using different plants in phytoremediation studies.     

Monitoring the transport of biomass burning emissions in South America

The atmospheric transport of biomass burning emissions in the South American and African continents is being monitored annually using a numerical simulation of air mass motions; we use a tracer transport capability developed within RAMS (Regional Atmospheric Modeling System) coupled to an emission model. Mass conservation equations are solved for carbon monoxide (CO) and particulate material (PM2.5). Source emissions of trace gases and particles associated with biomass burning activities in tropical forest, savanna and pasture have been parameterized and introduced into the model. The sources are distributed spatially and temporally and assimilated daily using the biomass burning locations detected by remote sensing. Advection effects (at grid scale) and turbulent transport (at sub-grid scale) are provided by the RAMS parameterizations. A sub-grid transport parameterization associated with moist deep and shallow convection, not explicitly resolved by the model due to its low spatial resolution, has also been introduced. Sinks associated with the process of wet and dry removal of aerosol particles and chemical transformation of gases are parameterized and introduced in the mass conservation equation. An operational system has been implemented which produces daily 48-h numerical simulations (including 24-h forecasts) of CO and PM2.5, in addition to traditional meteorological fields. The good prediction skills of the model are demonstrated by comparisons with time series of PM2.5 measured at the surface.     

河流水体中重金属形态模型研究

本文提出了一种重金属形态模型,用于模拟水体中的水溶态、颗粒态和底泥、悬浮物的活动态和非活动态。以乐安江水体中铜污染为背景,计算结果与现场调查分析的数据比较表明,两者基本吻台,说明模型基本上是合理的,概括了重金属污染的重要过程,参数的选择反映了河流的实际情况。     

基于感知失衡的外卖配送交通安全研究*

为降低外卖配送交通事故发生概率,通过有序多分类Logistic回归分析个体属性与交通事故关联性,构建交通安全风险感知与配送效率感知失衡模型,分析外卖配送交通安全影响因素及路径关系。结果表明:配送员年龄、入行渠道对交通事故影响显著;COVID-19健康成本感知对交通安全风险感知和配送效率感知的失衡有显著中介调节作用。要实现交通感知平衡状态,互联网平台企业有必要按配送员年龄段、就业渠道实施差异化管理,树立良好交通安全意识。研究结果可为破解外卖配送“交通文明洼地”提供启示。     

Driver glare exposure with different vehicle frontlighting systems

Introduction: Highway safety performance at night has received less attention in research than daytime, despite the higher accident rates occurring under night-time conditions. This study presents a procedure to assess the potential hazard for drivers created by headlight glare and its interaction with the geometric design of highways. Method: The proposed procedure consists of a line-of-sight analysis performed by a geoprocessing model in geographic information systems to determine whether the rays of light that connect headlights and oncoming drivers are obstructed by either the roadway or its roadsides. Then, the procedure checks whether the non-obstructed rays of light are enclosed by a given headlight beam. Different hypotheses were set concerning the headlight beam features, including the horizontal spread angle and whether the headlights are fixed or swiveling. A highway section was selected to test and validate the procedure proposed. A 3D recreation of the highway and its environment derived from a LiDAR point cloud was used for this purpose. Results: The findings disclose how glare is produced on tangents, horizontal curves, transitions between them and sequences of curves. The effect of visual obstructions conveniently placed is also discussed. Conclusions: A greater glare incidence is produced as the horizontal headlights spread angle increases. Swiveling headlights increase glare on highways left curves and reduce it on right curves. Practical Applications: The procedure and conclusions of this study can contribute to develop more effective glare avoidance technologies as well as identify and assess glare-prone sections. The glare evaluation assists in evaluating glare countermeasures such as deciding whether to place a vegetation barrier and where.     

边界元法在填埋场气体运移数值模拟中的应用

基于多孔介质流体动力学理论和边界元法原理,构建了填埋气运移边界元数值模型,进行填埋场内部填理气的运动规律研究;通过与理想条件下的解析解对比分析,检验了该边界元数值模型方法本身;进行了垂直抽气井设施的填埋场实例气体运动数值模拟,得到了填埋场内部填埋气体的压力分布情况,由此确定了集气井的影响范围.模型精度分析和模型验证结果表明,该模型与解析解的平均相对误差在3%以下,与实测数据的平均相对误差均在10%左右,具有较高的精度;抽气井模拟结果表明,该模型可应用于填埋场气体运移的模拟预测和现场分析,能够为填埋场释放气体控制系统设计和优化提供理论依据.