Radial basis function method for 1-D and 2-D groundwater contaminant transport modeling

In this paper we develop a meshless method for modeling groundwater contaminant transport. The algorithm uses collocation method with radial basis functions. Numerical results are presented for several cases: pure diffusion; advection and dispersion for continuous source; advection and dispersion for instantaneous source; advection and dispersion for patch-source. The results show that the method is very simple and accurate.Jichun Li likes to thank the UNLV Research Office for the NIA grant support for this project. This work is also partially supported by Nevada EPSCoR. The authors are very grateful to the reviewers for their valuable comments on improving this paper.     

Pollutant dispersion in a large indoor space: Part 1 -- Scaled experiments using a water-filled model with occupants and furniture

Scale modeling is a useful tool for analyzing complex indoor spaces. Scale model experiments can reduce experimental costs, improve control of flow and temperature conditions, and provide a practical method for pretesting full-scale system modifications. However, changes in physical scale and working fluid (air or water) can complicate interpretation of the equivalent effects in the full-scale structure. This paper presents a detailed scaling analysis of a water tank experiment designed to model a large indoor space, and experimental results obtained with this model to assess the influence of furniture and people in the pollutant concentration field at breathing height. Theoretical calculations are derived for predicting the effects from losses of molecular diffusion, small scale eddies, turbulent kinetic energy, and turbulent mass diffusivity in a scale model, even without Reynolds number matching. Pollutant dispersion experiments were performed in a water-filled 30:1 scale model of a large room, using uranine dye injected continuously from a small point source. Pollutant concentrations were measured in a plane, using laser-induced fluorescence techniques, for three interior configurations: unobstructed, table-like obstructions, and table-like and figure-like obstructions. Concentrations within the measurement plane varied by more than an order of magnitude, even after the concentration field was fully developed. Objects in the model interior had a significant effect on both the concentration field and fluctuation intensity in the measurement plane. PRACTICAL IMPLICATION: This scale model study demonstrates both the utility of scale models for investigating dispersion in indoor environments and the significant impact of turbulence created by furnishings and people on pollutant transport from floor level sources. In a room with no furniture or occupants, the average concentration can vary by about a factor of 3 across the room. Adding furniture and occupants can increase this spatial variation by another factor of 3.     

Coupling spatially distributed river and groundwater transport models to investigate contaminant dynamics at river corridor scales

Rivers and aquifers are mutually dependent components of the hydrological cycle, typically characterised by temporal dynamics that are a few orders of magnitude apart. This characteristic is often advocated to justify the use of independent single-system models to maximise the outcome for the available computational resources. However, the rapid increase in computational power presently provides means to explore new and more complex modelling schemes, which better reflect the complex physical reality. We present a new modelling framework, FLUXOS, developed from the full coupling of modified versions of state-of-the-art standalone river and groundwater flow and transport models. The model is validated against analytical solutions and applied to real world scenarios in the complex urban corridor of the Ciliwung River in Jakarta to show its flexibility for practical applications and its capabilities as an exploratory tool for realistic investigation of contamination sources and pathways determining non-linear behaviours of river-aquifer interactions.     

Binding of a perfluorinated surfactant to β-lactoglobulin in aqueous solutions

Perfluorooctanoate (PFOA) is one of the perfluorinated contaminants detected in food. Its binding to proteins seems to be the vector of its transfer in food products. We combined several approaches as isothermal titration calorimetry (ITC), fluorescence spectroscopy, infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) in order to elucidate how PFOA binds to β-lactoglobulin, the major whey protein component. Our results show that the binding of PFOA to β-lactoglobulin is not driven by hydrophobic interactions. Similar to its hydrogenated analogue, PFOA does not insert into the hydrophobic pocket of β-lactoglobulin, despite its higher hydrophobicity. Rather, the binding is electrostatically driven. PFOA binding has a denaturizing effect on the protein, decreases its thermal stability and prevents β-lactoglobulin to aggregate during heat treatment.     

Challenges in hydrogen fuel sampling due to contaminant behaviour in different gas cylinders

Increasing deployment of fuel cell electric vehicles (FCEVs) has led to implementation of hydrogen quality regulations (ISO 14687:2019) to prevent FCEV loss of performance. Hydrogen refuelling stations operators must be able to send representative samples of hydrogen fuel for analysis. Stability of contaminants in sampling vessels needs to be known at ISO 14687:2019 thresholds. A 4-month stability study was carried out on mixtures of ISO 14687 contaminants at amount fractions close to the thresholds in two types of sampling cylinders (SPECTRA-SEAL® and SGS? aluminium cylinders). SPECTRA-SEAL® cylinder allowed representative sampling of CO, CO₂, CH₄, C₂H₆, N₂, Ar, He, Cl₂CH₂, H₂O, O₂, CH₂O₂ in hydrogen fuel for 2 months. SGS? cylinder allowed representative sampling of CO, CO₂, CH4, C₂H₆, N₂, Ar, He, Cl₂CH₂, H₂O, O₂, H₂S for 4 months. Further work is needed to allow representative sampling of ammonia and formaldehyde.     

N ϵ-(carboxymethyl)lysine: A Review on Analytical Methods,Formation, and Occurrence in Processed Food,and Health Impact

Foods are often heat processed and may contain advanced glycation end products (AGE). One of the most widely studied AGE is N ^?-(carboxymethyl)lysine (CML); nevertheless, knowledge on dietary CML is fragmentary. This study aimed to review current scientific knowledge on analytical methods to determine CML contents in food, chemical pathways of CML formation in food, occurrence of CML in food, and health implications of dietary exposure to CML. Chemical analyses of CML in food products are carried out by immunochemical assays and instrumental methods, but the former method may interfere with the food matrix. CML is formed in food through various chemical pathways, depending on food ingredients and processing conditions. The compound is present in many cooked foods, with relatively high concentrations in carbohydrate-rich foods and dairy products. Dietary CML is very likely to impair human health, but full cause-effect evidence is not available yet. More studies on metabolic effects and impact of food-derived CML on human health should be performed. Food production should be optimized to minimize CML concentrations, while maintaining acceptable microbiological safety and organoleptic properties of the final food product. To this end, more insights into effects of food composition and processing conditions on CML formation are necessary.     

Determination of polydimethylsiloxanes by 1H-NMR in wine and edible oils

Fourier transform ¹H-nuclear magnetic resonance (NMR) spectroscopy was suitable for the quantitative determination of polydimethylsiloxanes (PDMS) in wine and edible oil samples. This approach offers highly specific qualitative and quantitative analysis due to silicone-specific location of proton signals linked to carbon atoms located directly next to silicon atoms (0-0.5 ppm), as well as a different location of signals in the range for different organosilicon structures. The method can be used for the control of PDMS at regulatory limits in foodstuffs (10 mg kg^-1) using hexamethyldisiloxane (HDMS) as an internal standard. Samples were prepared by extraction under suitable conditions to separate the analyte, and with analyte enrichment before ¹H-NMR analysis. Analytical procedures were developed to permit the determination of PDMS at 0.06 mg kg^-1 in wine and at 6 mg kg^-1 in edible oils samples using readily available NMR instrumentation. It was, however, possible to lower the limit of detection to 6 μg kg^-1 for wine and to 60 μg kg^-1 for edible oils using a higher field instrument (500 MHz). Relative standard deviations (S_r) were obtained for wine (0.028) and for oil samples (0.043), which when compared with values obtained for samples spiked with PDMS (0.021) indicated that the sample preparation was the main factor determining the precision of the method. The average recovery rates for PDMS were 97 and 95% for wine and edible oils, respectively. PDMS was detected in four brands of Italian wine, with Chianti-Rafaello containing the highest concentration (0.35 mg kg^-1), and in four types of edible oils, highest concentration (11.9 mg kg^-1) being found in Italian corn oil. None of the levels of PDMS found in the food samples exceeded the permissible standards laid down by the Codex Alimentarius Commission (10 mg kg^-1), with the exception of the one corn oil sample.     

Residual crude oil concentrations and ecotoxicity of polluted tropical soils after phytoremediation

Changes in residual crude oil concentrations and soil ecotoxicity during the phytoremediation assessment of tropical plants growing on crude oil-polluted soils were evaluated in a greenhouse study. The plants (Panicum maximum, Zea mays, Centrosema spp. and Pueraria spp.) were grown in weathered polluted soil samples in microcosms for 10?weeks. Residual crude oil in soil was quantified colorimetrically, while the ecotoxicity of the vegetated and control soil samples were evaluated using earthworms’ percentage survival and crop seeds’ germination bioassays. It was observed that planting of 1% (w/w) polluted soil samples reduced crude oil in the rhizosphere soils of P. maximum and Centrosema spp. by 71.6?±?1.4 and 55.3?±?4.3%, respectively. These are in contrast with 37.5?±?2.5% reduction in non-vegetated control soil samples. The ecotoxicity assays indicated that planting also effected reduction of crude oils’ toxicity positively. There were 100, 40?±?28.3 and 50?±?21.1% survival of test earthworms, respectively, after 24?h in 1% w/w polluted soil samples phytoremediated with P. maximum, Centrosema spp. and Pueraria spp. as against 0% survival in non-vegetated control samples. The observed sensitivity of the test organisms to chemical stress bodes well for providing rapid information on effectiveness of remediation programmes.     

Diffusion and wetting on contaminated solids

The wetting dynamics of a drop of liquid (1) deposited on a solid on which there is already a thin layer of liquid (2) (contaminant, or maybe a wetting agent) is considered. Diffusion of liquid 2 into liquid 1 by Fickian diffusion leads to evolving effective solid/drop interfacial free energy, occurring during spreading, and modifying wetting kinetics. Spreading rate is increased. Strange behaviour is predicted near equilibrium conditions. The wetting line may “overshoot”, before receding asymptotically. The motion of a two‐dimensional drop is modelled, assuming it is given a slight push to one side after deposition. We expect a regime of spontaneous translational drop motion due to asymmetry in capillary conditions at the two triple lines. Diffusional wetting is compared to reactive wetting.