Diffusive Transport of VOCs through LLDPE and Two Coextruded Geomembranes

The diffusive properties of two coextruded geomembranes, one with a polyamide inner core and the other with an ethylene vinyl-alcohol (EVOH) inner core, and a standard 0.53-mm (20-mil) linear low-density polyethylene (LLDPE) geomembrane were examined. Diffusion and sorption laboratory tests were performed to estimate the parameters controlling diffusive migration, including the partitioning, diffusion, and permeation coefficients of the geomembrane in both the aqueous and vapor phases. Results indicate a significant reduction in mass flux through the coextruded geomembranes compared to conventional LLDPE. The EVOH coextruded geomembrane had the lowest permeation coefficients (Pg) with a range of (2–6)×10?12?m2?s?1 for diffusion from the aqueous phase. These values for EVOH are upper bounds and the actual values may be lower than as stated. The polyamide (nylon) coextruded geomembrane had higher values than for EVOH, with a Pg range of (0.7–2.2)×10?11?m2?s?1 from the aqueous phase. The highest permeation coefficients were for the standard 20-mil LLDPE, which ranged from (0.6–1.1)×10?10?m2?s?1. Thus the permeation coefficient for LLDPE was about one order of magnitude greater than for the nylon coextruded and at least two orders of magnitudes higher than for the EVOH coextruded geomembrane. Both coextruded geomembranes showed decreased Pg values and therefore improved diffusive resistance to volatile organic compounds over traditional 0.56-mm PVC geomembranes. The EVOH geomembrane showed a 5–12-fold decrease in Pg in comparison to a 2.0-mm high density polyethylene geomembrane.     

Permeation of Organics through Linear Low Density Polyethylene Geomembranes under Mechanical Deformation

The effect of mechanical deformation on the permeation of methylene chloride (MEC), trichloroethylene (TCE) as well as mixtures thereof through linear low-density polyethylene (LLDPE) geomembranes was studied using a new experimental technique. A total of fifty experimental conditions involving five different deformations, five different concentrations and two types of LLDPE geomembranes were evaluated following a full factorial experimental design. Mixtures of TCE and MEC (0.66, 0.50, and 0.34 volumetric fraction) were tested through geomembranes elongated uniaxially (10% and 20%) as well as in the biaxial mode (10%×10%?and?20%×20%). The breakthrough times for the permeation of TCE and MEC decreased with elongation for both types of geomembranes. A reduction in breakthrough times between 38 and 45% was observed for the permeation of MEC and TCE though geomembranes elongated 20%×20% in the biaxial mode compared to the nonelongated specimens. Evidence of stress-enhanced transport was also observed as the steady-state permeation rates of MEC increased between 200 and 300% where geomembranes were elongated 20%×20% in the biaxial mode compared to the nonelongated samples. Enhanced transport of MEC was also noted during the permeation of the MEC–TCE mixtures.     

Applying a One-Dimensional Mass Transport Model Using Groundwater Concentration Data

One-dimensional analytical mass transport models are familiar to environmental professionals because they are typically used as learning devices in undergraduate groundwater courses. The application of the models requires relatively certain knowledge of contaminant release to the saturated zone. However, release data are typically not reliably known at sites with uncontrolled contaminant releases. A mass balance approach has been developed to calculate contaminant release parameters based on site-specific groundwater concentration data. Standard numerical calibration and sensitivity analysis techniques were modified for use with the one-dimensional spreadsheet model. A groundwater concentration dataset from a Superfund site was used to evaluate three schemes for calculating the model initial concentration. The site application demonstrates how the spreadsheet model could be used for preliminary remediation system comparisons including restoration time estimating. The use of the spreadsheet model may reduce the effort associated with subsequent numerical modeling typically required for remedial design. The spreadsheet application highlights the importance of collecting physical data with groundwater concentration data.     

Transport of Colloids and Associated Hydrophobic Organic Chemicals through a Natural Media Filter

In this project, the ability of natural media filtration (NMF) to remove colloidal particles and associated hydrophobic organic compounds from the aqueous phase was evaluated by performing sorption and transport experiments with leaf compost media. Phenanthrene sorption isotherm experiments for compost and model colloidal (latex) particles found that phenanthrene has a greater affinity for the colloidal particles than for the compost materials. In column experiments, the transport of phenanthrene through the NMF in the presence and absence of two colloidal particles with different hydrophobicities [sulfate (more hydrophobic) and carboxylate (less hydrophobic)] showed that the effluent phenanthrene concentration in the presence of colloids, particularly sulfate latex particles, is much higher than that in the absence of colloids. The results from a mathematical model used to evaluate data from the column experiments suggest that enhancement of contaminant transport can be significant under the following conditions: high colloidal concentrations, high partition coefficient between contaminant and colloids, or a slow desorption rate of contaminant from colloids.     

Estimation of Diffusion Coefficients and Solubilities for Organic Solvents Permeation through High-Density Polyethylene Geomembrane

Experiments on the permeation of several chlorinated and aromatic hydrocarbons through high-density polyethylene (HDPE) geomembranes were conducted using the ASTM F-739 standard test method. The diffusion coefficients were estimated by a one-dimensional diffusion equation based on Fick’s second law, and the solubilities of the solvents in HDPE were determined by the steady state permeation rates. The one-dimensional transient model was able to simulate the permeation concentrations and implied that equilibrium partition between organic solvent and HDPE geomembrane was not achieved during the initial permeation. The solubilities of organic solvents in the HDPE geomembranes obtained by immersion tests or weight gain methods of permeation experiments were not an appropriate boundary condition for the model simulation of permeation. It was found that the diffusion coefficients and solubilities of organic solvents correlated well with their molecular weights and dipole moment, respectively. The present work provides information on the extent of organic compounds permeations through HDPE geomembranes as applied in hazardous waste landfills.     

Removal of Refractory Organic Compounds in Liquid Swine Manure Obtained from a Biofiltration Process Using an Electrochemical Treatment

Swine wastewaters contain varied and high amounts of organic matter (proteins, antibiotic compounds, organic acids) which are difficult to oxidize biologically or chemically. The discharge of such effluents is undesirable and can cause excessive oxygen demand in the receiving water. In order to produce an effluent suitable for stream discharge, electrochemical techniques have been explored at the laboratory pilot scale, for refractory residual organic compound removal in liquid swine manure (LSM) following a biofiltration process. Two types of electrolytic cells (monopolar and bipolar electrode cells) using aluminum and mild steel electrodes were studied. Effectiveness was measured in terms of chemical oxygen demand (COD) and biological oxygen demand (BOD) reduction. The amount of residue sludge produced and energy consumed have been also considered. Results showed that the best performances of COD and BOD removal from LSM were obtained using either aluminum bipolar (Al-BP) electrodes or mild steel monopolar (Fe-MP) electrodes operated at current intensities of 0.5 and 2.0?A, respectively, through 30?min of treatment. The COD removal yields varied from 65 to 68%, whereas BOD removal reached 87%. The optimal conditions determined for organic compound removal, including energy consumption and metallic sludge disposal, involved a total cost of only $0.24?and?$0.29?United?States/m3 of treated LSM. The treatment using the Fe-MP system was found to be more economical and practical than the chemical treatment using FeCl3 as a coagulating agent.     

一个新的拓扑指数用于复杂化合物热容的预测

首先通过对分子图的顶点和边着色得到染色分子图，借助于相对键长和点价来分别代替拓扑距离和顶点度并结合分子图的邻接和距离矩阵提出了一个用于表征含多重键，杂原子化合物的拓扑指数Ｘｕ。将该拓扑指数用于烷烃、不饱和链烃、芳烃及含硫化合物的热容的预测，得到了良好的结果，计算值与实验值相当一致。该指数可望在ＱＳＰＲ／ＱＳＡＲ研究中作为一个有用的分子参数而得到推广应用。