Geomembrane Research Articles

Cost-Effective Salt Harvesting: Efficient and Sustainable Production through Technological Innovation

Maximizing the quantity, quality, and cost-efficiency of salt production requires innovative approaches. This study presents a novel geo-membrane (GM)-based salt production technique that significantly improves salt yield and quality for Indian salt producers. The GM method is simple to implement across various salt production facilities, requiring only basic equipment. Compared to traditional methods, statistical analyses demonstrate substantial improvements in both the quantity and quality of salt produced with the GM method. The process enhances salt purity by 12–15%, reduces production costs by 15-20%, and prevents brine leakage, optimizing solar energy utilization in crystallization ponds. Keywords: salt production, geo-membrane, salt crystallization pond, cost-efficiency,sustainability

Two-dimensional migration characteristics of contaminant through composite liner with arbitrarily distributed defects

Previous studies indicate that liner defects can significantly accelerate contaminant migration in landfill, shortening the migration time by orders of magnitude. Although the effect of defects upon contaminant migration and barrier capacity of liner system has been investigated based on several theoretical models, they are always limited to one-dimensional scopes. Here a two-dimensional (2-D) model was established for contaminant transport through composite liner to the soil layer, with geomembrane (GM) defects arbitrarily distributed along the horizontal direction, and then Laplace transform, Fourier transform, and boundary transform method were utilized to derive its semi-analytical solution, which was verified by experimental data and numerical results. The obtained solution can take nonuniformly distributed defects into account and demonstrates the 2-D contaminant concentration and flux profiles in the spatiotemporal domain. Computational results of the solution are employed to illustrate the roles of material coefficients and modeling sizes upon the variations of contaminant concentration and flux. Results support that contaminant migration is expedited by the GM defect in landfill, and geosynthetics clay liner can reduce the pollution level caused by GM failure. Moreover, the contaminant flux will not be significantly influenced by the defect positions, which, however, leads to non-negligible impact on concentration profiles.

Transport parameters for PFOA and PFOS migration through GCL's and composite liners used in landfills

The effect of applied stress (20, 60, and 150 kPa) on the diffusion of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) through a geosynthetic clay liner (GCL) is examined. The diffusion coefficients deduced from GCL diffusion tests for PFOA and PFOS decrease linearly with decreasing final bulk GCL void ratio (increasing applied stresses). The different components of the same GCL are also tested for PFOA and PFOS sorption. No statistically significant sorption of PFOA is observed for any of the components of the GCL. However, some sorption of PFOS onto the cover and carrier geotextiles of the GCL is observed with in an average distribution coefficient, Kd ∼2.22 ml/g for the GCL. Permeants containing different PFAS compounds are tested to assess their impact on the Geomembrane (GMB) - GCL interface transmissivity in composite liners. Results show PFAS concentrations up to 20 ppm had negligible impact on the GMB-GCL interface transmissivity. Lastly, the GCL specimens extracted from the diffusion tests are tested for hydraulic conductivity. No impact of PFAS is seen on the hydraulic conductivity of GCLs subjected to high applied loads, but a small increase is seen on the GCLs subjected to relatively low applied stresses.

Impact of differential settlement on leakage through geomembranes in waste covers

To quantify the effects of differential settlement on leakage through a geomembrane (GMB) hole in waste (landfill/mine tailings) covers, field experiments were conducted at Queen's University Experimental Liner Test Site on two sections, each with a 4H : 1V slope. Over 13 months, measurements showed that a 3 m × 2 m × 0.12–0.17 m depression in Section B led to a 51-fold increase in leakage when compared to Section A, which had no such depression (493 l vs 11.1 l). Notably, in Section B, 284 mm of precipitation between November and February resulted in 281 l of leakage, whereas 537 mm of precipitation between June and September led to a mere 142 l of leakage. A 3D numerical investigation provides encouraging agreement with the experimental measurements and confirms a counterintuitive 43% increase in leakage with a decrease in the temperature of cover sand from 21.9°C to 1°C, due to the influence of temperature-dependent viscosity on the hydraulic conductivity of the cover soil. This paper offers insights for optimizing waste cover design and inspection procedures to mitigate the challenges of contaminant control.

Transport of per-polyfluoroalkyl substances (PFAS) in high-density polyethylene (HDPE) geomembrane liners

The objective of this study is to investigate the fate and transport of per-polyfluoroalkyl substances (PFAS) through a high-density polyethylene (HDPE) geomembrane (GM) that is commonly used in landfill composite liner systems. Tests were conducted to measure the sorption and diffusion of four per-polyfluoroalkyl substances (PFAS) with varying numbers of carbons in chain and functional groups on HDPE GM. Perfluoroalkyl carboxyl acids (PFCAs), and perfluoroalkyl sulphonic acids (PFSAs) were investigated in this study. The partition coefficients (Kd) on HDPE GM ranged from 5 to 12 L/Kg. Kd showed an increasing trend with chain length and were found to be sensitive to functional groups of PFAS. Molecular weight directly affected the Kd. The diffusion coefficients (Dg) of PFCAs and PFSAs through 0.1-mm HDPE GM were found to be in the orders of 10-18 to 10-17 m2/s. The Dg decreased with increasing molar mass and were also observed to be dependent on the functional group. Dg of PFSAs was lower than that of PFCAs for a similar number of carbons in the chain.

Experimental study on the effect of temperature on HDPE geomembrane/geotextile interface shear characteristics

Geomembranes (GMBs) and geotextiles (GTXs) are the most widely used geosynthetics in landfills and other barrier systems. While various temperature environments may be encountered in practice, the interface shear characteristics of geosynthetics under different temperatures are still not clear. Shear tests of the interface between a high-density polyethylene GMB and nonwoven GTX are performed using a temperature-controlled submerged direct shear apparatus. The testing temperatures range from 10 °C to 70 °C, which covers most of the situations commonly encountered in engineering. The shear behaviors of the textured GMB/GTX interface and smooth GMB/GTX interface are presented, and the mechanism of the temperature influence is analyzed according to the test results and phenomena. Temperature has a significant impact on the GMB/GTX interface peak strength and post-peak strength, and maximum interface shear strength could be obtained when the temperature is approximately 30–40 °C. The influencing mechanisms of temperature on the GMB/GTX interface shear strength are thoroughly discussed. The shear characteristics of the GMB/GTX interface under different temperatures are critical to the stability analysis of geosynthetic slopes in special condition, and this study can also provide a reference for the effect of temperature on the shear behavior of other geosynthetics.

A Semi-Analytical Model of Contaminant Transport in Barrier Systems with Arbitrary Numbers of Layers

In regions with sanitary landfills, unsuitable liner designs can result in significant soil and groundwater contamination, leading to substantial environmental remediation costs. Addressing this challenge, we propose a semi-analytical model for solute transport that uses the advection–dispersion–reaction equation in a multi-layered liner system. A distinctive feature of our model is its ability to account for infiltration velocity, arbitrary numbers of layers, thin layers such as geomembranes, and mass flow. We validated our model against existing published models and applied it to a case study of a real sanitary landfill in the capital of Brazil. Through parametric analyses, we simulated contaminant transport across various layers, including the geomembrane (GM), geosynthetic clay liner (GCL), soil liner (SL), and compacted clay liner (CCL). The analyses showed the importance of choosing the most appropriate construction system based on the location and availability of materials. Considering toluene contamination, a GM molecular diffusion coefficient (DGM) greater than 10−13 m2 s−1 exhibited similar efficiency when compared with CCL (60 cm thick). In addition, the results showed that the liner system may have the same efficiency in changing SL (60 cm thick) for a GCL (1 cm thick).

Sorption and diffusion of per-polyfluoroalkyl substances (PFAS) in high-density polyethylene geomembranes

The objective of this study is to investigate the fate and transport of per-polyfluoroalkyl substances (PFAS) through a high-density polyethylene (HDPE) geomembrane (GM) that is commonly used in landfill composite liner systems. Tests were conducted to measure the sorption and diffusion of per-polyfluoroalkyl substances (PFAS) with varying number of carbons in chain and functional groups on HDPE GM. Perfluoroalkyl carboxyl acids (PFCAs), perfluoroalkyl sulphonic acids (PFSAs), alkyl-sulfonamidoacetic acids (FOSAAs), fluorotelomer sulfonic acids (FtSAs), alkane sulfonamides (FOSA) and ether carboxylic acids (Gen X) were investigated in this study. The partition coefficients (Kd) on HDPE GM ranged from 3.8 to 98.3 L/kg. PFAS with amide and sulfonic functional groups showed stronger sorption than that of PFAS with carboxylic acid functional groups. Molecular weight directly affected the Kd for long-chained PFAS whereas the Kd of short-chained PFAS was not sensitive to molecular weight. The diffusion coefficients (Dg) of PFCAs and PFSAs through 0.1-mm HDPE GM were found to be in the orders of 10-18 to 10-17 m2/s. The Dg decreased with increasing molar mass and were also observed to be dependent on the functional group. Dg of PFSAs was lower than that of PFCAs for similar number of carbons in the chain. The estimated mass flux for PFAS in an intact 1.5-mm HDPE GM varied from 38.7 to 2080.8 ng/m2/year whereas the estimated diffusive breakthrough time for PFAS in intact 1.5-mm HDPE was 1526 years or longer.

A comparative numerical evaluation of linear anode arrangements for enhancing above ground storage tank cathodic protection via mesh grid and concentric ring designs

Cathodic protection as a complementary method is one of the most effective ways to prevent corrosion, along with coating and choosing the suitable material. There are different ways to protect the storage tank bottom. Due to the presence of the geo membrane layer and its effective and pivotal role, the use of mixed metal oxide (MMO) anodes is highly recommended. In the current study, the protection process of the above-ground storage tank bottom is simulated using MMO backfilled wire (concentric rings) and ribbon anodes (mesh grid system). In this regard, several parameters must be considered in reaching the protection criteria. The simulation results show that the effect of the limiting oxygen current density, soil resistivity and the anodic current have the greatest role. Anode depth and the spacing between the anodes are also critical factors if they have large values. Due to the importance of the number of conductor bars and feeding cables, two configurations have been presented for ribbon anodes. These configurations have a direct impact on grid resistance, rectifier size, and related costs. Finally, an economic comparison has been made regarding the use of sacrificial and MMO anodes in the form of ribbon next to wire anodes. The results show that, in the use of ribbon anodes, MMO anodes have better performance than magnesium and zinc sacrificial anodes, and the cost required for MMO linear anodes is far lower than the method of sacrificial ribbon anodes. In the present study, the cost of the MMO linear anode system is approximately 20% of zinc and magnesium sacrificial ribbon anode system cost.

Shear strength of HDPE smooth geomembrane/bentonite-polymer geosynthetic clay liner interface

This study investigated the impact of polymer elution on the interface shear strength between a smooth geomembrane (GMB) and two types of bentonite-polymer (B–P) geosynthetic clay liners (GCLs) containing linear and crosslinked polymers. Tests were also conducted with sodium bentonite (Na–B) GCLs as a control. Interface shear tests were conducted with dry, two-stage, and free hydration conditions with varying normal stresses. The results showed that under dry conditions, the displacement at peak strength and shear strength envelops of GMB/Na–B GCL and GMB/B–P GCLs were similar. However, the displacement at peak strength of GMB/B–P GCLs was higher than that of GMB/Na–B GCL under two-stage and free hydration. Meanwhile, the peak shear strength of the GMB/B–P GCLs showed a greater reduction than that of GMB/Na–B GCLs when transitioning from a dry condition to a free hydration condition at the same normal stress, particularly at higher normal stress. Loss on ignition (LOI) tests confirmed that there was a decrease in polymer loading of B–P GCLs after the shearing test, indicating polymer elution occurred during the shearing test. The result suggests that polymer elution had a significant effect on the GMB/B–P GCL interface shear strength, especially at higher normal stress.

Permeability mechanism of PVC-P geomembranes based on low-field NMR technology

The permeability of plasticized polyvinyl chloride (PVC-P) geomembranes (GMBs) is of significant importance to the safe operation of the impermeable structures and even the project. To avoid the drawbacks of adopting the permeability coefficient to characterize permeability traditionally, this paper presents a mathematical model of porosity and seepage discharge based on the results of the vertical permeability test and porosity obtained from low-field nuclear magnetic resonance (NMR) test, and the applicability of porosity to evaluate the permeability was explored combined with the dynamic distribution of pores and pore radius. The results show that the low-field NMR technology with 1H atoms as the probe can accurately measure the distribution of pores and pore radius in the PVC-P GMB. The proportion of micropores (Mic), mesopores (Mes) and macropores (Mac) and the shrinkage or development of pore radius are primarily responsible for the variation of the porosity. The porosity is closely correlated with the seepage discharge, and the constructed model can accurately predict the seepage discharge. Furthermore, the porosity can provide technical support for the evaluation of the permeability of PVC-P GMBs and the selection of appropriate GMBs for engineering design.

A solution for calculating the leakage rate through GMB/CCL composite liners with long defects

Geomembranes (GMBs) of the landfill composite liners frequently contain long defects, which will form the dominant flow path in the composite liner. The significant differences between the geosynthetic clay liner (GCL) and the compacted clay liner (CCL) lead to distinct flow patterns in the defective composite liners. For GMB/CCL composite liners, the induced flow in the CCL is two-dimensional, thus the existing solution with the assumption of one-dimensional flow significantly underestimates the leakage rate with a maximum relative error of 87% when compared to the results of a 2D finite element model. A new solution for predicting the leakage rate through GMB/CCL composite liners with a long defect is proposed with a consideration of two-dimensional flow in the CCL, with relative errors of leakage rate less than 29% for the cases investigated. The proposed solution also shows a lower relative error for the wetted distance (6–23%) compared to the existing solution (49–77%) for GMB/CCL composite liner cases. The comparisons with numerical results show that the proposed analytical solution significantly reduces the underestimation of leakage rate through the defective GMB/CCL composite liner, thus can help to improve the composite liner design for landfills.

Analytical solutions for contaminant transport through a GMB/CCL composite liner system considering effective porosity and thermodiffusion

This study presents analytical solutions for one-dimensional contaminant transport through a saturated double-layer composite liner system consisting of a geomembrane (GMB) and a compacted clay liner (CCL), considering the effects of CCL effective porosity, GMB defects, and thermodiffusion. The solutions provide temperature distribution at steady state and contaminant concentration distribution and total contaminant mass flux for transient-state condition. The heat transfer algorithm of the solutions accounts for advection, conduction, and thermal mechanical dispersion, while the solute transport algorithm of the solutions accounts for molecular diffusion, advection, mechanical dispersion, sorption, and thermodiffusion. The proposed solutions are validated against experimental data and verified against numerical solution. Using the proposed solutions, a series of parametric studies is conducted and the results indicate that neglecting the effect of thermodiffusion can underestimate the contaminant outflow rate at the bottom of the GMB/CCL liner by 6.9%∼130%. Depending on conditions, the effect of thermodiffusion on contaminant transport through the GMB/CCL liner decreases with increasing leachate head, increasing length of GMB wrinkle, and increasing number of GMB defects. CCL effective porosity also has a significant impact on contaminant transport through the GMB/CCL liner system, and neglecting this effect can substantially overestimate the contaminant outflow rate.

Diffusion of volatile organic compounds (VOCs) through elastomeric bituminous geomembranes (BGMs)

Diffusion of volatile organic compounds (VOCs) through a 4.1 mm elastomeric bituminous geomembrane (BGM) is investigated using a dilute aqueous solution of four aromatic hydrocarbons: benzene, toluene, ethylbenzene, and xylenes (BTEX). Due to the very different diffusion characteristics of the BGM components, double-compartment diffusion experiments are separately conducted on the bituminous and non-bituminous components of the BGM to assess their diffusion parameters. A two-layer computer model is developed to obtain the diffusion parameters of the BGM that correlates with the 890-day laboratory diffusion test data obtained for the multicomponent BGM and allows the modelling of transient diffusion. Using contaminant transport modelling, the BGMs performance as a diffusive barrier for different applications is evaluated and compared to different polymeric geomembranes (GMBs). It is shown that using BGM as part of the cover system for a hydrocarbon-contaminated soil landfill or as a vapour barrier below concrete building foundations can decrease the BTEX mass flux through the cover system and the peak concentration of contaminant in the indoor air compared to monolayer polymeric GMBs. It is also predicted to reduce the impact on the aquifer when modelled as a part of the composite liner without holes for a hypothetical solid waste landfill.

Geomembrane leaks detection and leakage correlation factor analysis of composite liner systems for fifty-five (55) solid waste landfills in China

In composite liner system (CLS), there are little field data on the number, size, and shape of geomembrane (GMB) holes, which are the key parameters to identify and evaluate the volume of leachate leakage from landfills. In this paper, in-situ detection of GMB holes in composite liner systems of 55 solid waste landfills in China was conducted by electrical leak location (ELL) method, and the following conclusions were drawn. The holes frequency, equivalent radius, and theoretical leakage volume of double-layer systems are lower than those of single-layer systems under the same geotextile (GT) density by 28.2%, 51.4%, and more than 60%, respectively. As the thickness of GMB increases, the holes frequency, equivalent radius and theoretical leakage volume reduce observably. Regarding protecting GMB, the density of geotextiles should not be less than 600 g/m2. Through the analysis of various correlation factors, the thickness of geomembrane is an important parameter affecting the amount of leakage. This study will provide a reference for analyzing the data of field investigation, which would provide constructive suggestions for the composite liner system.

Longevity of multilayered textured HDPE geomembranes in low-level waste applications

The degradation behaviour of five multilayered textured white geomembranes (GMBs) is investigated when immersed in two synthetic low-level waste (LLW) leachates with pH 7 and 9 at a range of temperatures (40–85 °C) for 48–55 months. Results are compared to the performance of the GMBs in synthetic municipal solid waste (MSW) leachate. Increasing pH from 7 to 9 gives slightly faster antioxidant depletion in LLW leachate. The estimated time to nominal failure for the GMBs is at least 20% longer in LLW leachate than in MSW leachate containing surfactant that accelerates both antioxidant depletion and stress cracking. Thus, MSW leachate can be used as a conservative proxy to estimate the service life of a GMB in contact with LLW leachate. Two GMBs are considered very highly likely to meet the required 550 year design life of the near-surface disposal facilities even based on the most conservative prediction of the time to nominal failure for the GMBs.

Transport of Organic Contaminants in Composite Vertical Cut-Off Wall with Defective HDPE Geomembrane.

Soil-bentonite vertical cut-off wall is an emergency technique used for contaminant control in geo-environmental engineering, high-density polyethylene (HDPE) geomembrane (GM) with an extremely low-permeability coefficient is expected to enhance the contaminant barrier effect of the vertical cut-off wall. To evaluate the barrier performance of the composite barrier composed of GM and soil-bentonite mixture towards organic contaminant, while also quantitively revealing the impact of GM defects and placement, a one-dimensional transport model for organic contaminants in composite barrier is solved under semi-infinite boundary conditions. The proposed transport model is validated by numerical simulations using COMSOL Multiphysics 5.4, and the effects of GM defect rate, placement within the composite isolation wall, and contact level with soil-bentonite on contaminant transport behavior are further studied. The results show that as the average frequency of GM defects increases from 2.5 to 50 holes per hectare, the breakthrough time of organic contaminants through composite barrier decreases by almost 70%. Poor contact level between GM and soil-bentonite mixture may reduce the breakthrough time of the composite cut-off wall by 65%. Although the selection of GM placement has limited impact on the transient flux of contaminants, it does affect the total flux of contaminants over a certain period of time. The effects of permeability coefficient, effective diffusion coefficient, distribution coefficient, and hydraulic head of the composite cut-off wall can be considered by the proposed analytical solution, which would provide guidance and reference for the design and service performance evaluation of the composite cut-off wall.

Degradation of HDPE, LLDPE, and blended polyethylene geomembranes in extremely low and high pH mining solutions at 85 °C

The durability of five 1.5-mm thick geomembranes (GMBs) is investigated in pH 0.5 and 13.5 synthetic mining solutions using immersion tests. Two high density polyethylene (HDPE), two linear low density polyethylene (LLDPE), and one blended polyethylene (BPO) GMBs are investigated at 85 °C for incubation durations of 4.5–6.5 years. It is shown that the degradation of all five GMBs in the high pH solution is faster than in the low pH solution. In the pH 0.5 solution, one of the HDPEs and the BPO GMBs exhibited polymer degradation before or at the time of the depletion of their antioxidants. In pH 13.5, four out of the five GMBs exhibited degradation and followed the conceptual three-stage degradation model until nominal failure. However, there is no correlation between the long-term performance of these GMBs and their resin type or their initial properties since one of the examined LLDPEs outperformed all the higher density/crystallinity GMBs with higher initial properties while the other LLDPE did not perform well. Thus, when selecting a GMB for a desired application, the relative performance of different candidate GMBs can be only assessed using immersion tests using the solutions expected in the field.

Long-term Performance of Conductive-backed multilayered HDPE Geomembranes

The long-term performance of three multilayered textured white conductive-backed geomembranes (GMBs) is compared to the comparable textured nonconductive GMBs and their smooth edge/equivalent to investigate the effect of the conductive layer on their longevity. Oven immersion in synthetic municipal solid waste leachate is used at a range of temperatures to accelerate the ageing during an incubation period of 50 months. It is shown that the conductive layer can antagonistically or synergistically affect the antioxidant depletion of conductive-backed GMBs relative to nonconductive GMBs produced by the same GMB manufacturer and formulated using the same nominal resin and antioxidant package. However, their relative degradation at 85 °C does not necessarily follow their relative antioxidant depletion times implying that the manufacturing process and the interaction between the additive packages of these GMBs can affect their relative degradation beyond the antioxidant depletion stage. Arrhenius modelling predicts the antioxidant depletion stage at field temperatures ranging between 180 and 1400 years at 20 °C for two different conductive-backed GMBs produced by two different manufacturers. With such variation in the long-term performance of conductive-backed GMBs currently available in the market, their durability should be investigated before their use in barrier systems to ensure they can meet the required design life of the desired geoenvironmental application.

Machine-learning modelling of tensile force in anchored geomembrane liners

Geomembrane (GM) liners anchored in the trenches of municipal solid waste (MSW) landfills undergo pull-out failure when the applied tensile stresses exceed the ultimate strength of the liner. The present study estimates the tensile strength of GM liner against pull-out failure from anchorage with the help of machine-learning (ML) techniques. Five ML models, namely multilayer perceptron (MLP), extreme gradient boosting (XGB), support vector regression (SVR), random forest (RF) and locally weighted regression (LWR) were employed in this work. The effect of anchorage geometry, soil density and interface friction were studied with regards to the tensile strength of the GM. In this study, 1520 samples of soil–GM interface friction were used. The ML models were trained and tested with 90% and 10% of data, respectively. The performance of ML models was statistically examined using the coefficients of determination (R2, R2adj) and mean square errors (MSE, RMSE). In addition, an external validation model and K-fold cross-validation techniques were used to check the models’ performance and accuracy. Among the chosen ML models, MLP was found to be superior in accurately predicting the tensile strength of GM liner. The developed methodology is useful for tensile strength estimation and can be beneficially employed in landfill design.