Typical Landfill Research Articles

Translational failure analysis of landfill with retaining wall along the underlying liner system

The scope of this paper is to develop a new three-part wedge analysis method, introducing the effects of solid waste shear strength and retaining wall on the translational failure of landfills. A typical landfill can be divided into three parts: an active wedge lying on the back slope that tends to cause failure, a passive wedge, and a retaining wall resting on the foundation or liner system that helps to resist any movements. Using this method, the amount and direction of the interwedge force can be calculated, and the upper and lower bound solutions for the landfill stability, i.e., FSmax and FSmin, can be easily determined. When an average factor of safety, FSave, is used as a solution replacing the true factor of safety, FStrue, the upper bound of difference between FSave and FStrue is not more than 5% for all considered cases in this study. The retaining wall of the landfill seriously affects the value of the factor of safety; simply ignoring the retaining wall will lead to serious underestimation of the factor of safety. The factor of safety at the interface between active and passive wedges is defined as FSV. The values of FSV/FSave vary between 1.95 and 2.05 and are concentrated around 2.0. The approximate solutions of FS with adequate accuracy can be obtained by assuming FSV = 2FS.

Atmospheric emissions and attenuation of non-methane organic compounds in cover soils at a French landfill

In addition to methane (CH(4)) and carbon dioxide (CO(2)), landfill gas may contain more than 200 non-methane organic compounds (NMOCs) including C(2+)-alkanes, aromatics, and halogenated hydrocarbons. Although the trace components make up less than 1% v/v of typical landfill gas, they may exert a disproportionate environmental burden. The objective of this work was to study the dynamics of CH(4) and NMOCs in the landfill cover soils overlying two types of gas collection systems: a conventional gas collection system with vertical wells and an innovative horizontal gas collection layer consisting of permeable gravel with a geomembrane above it. The 47 NMOCs quantified in the landfill gas samples included primarily alkanes (C(2)-C(10)), alkenes (C(2)-C(4)), halogenated hydrocarbons (including (hydro)chlorofluorocarbons ((H)CFCs)), and aromatic hydrocarbons (BTEXs). In general, both CH(4) and NMOC fluxes were all very small with positive and negative fluxes. The highest percentages of positive fluxes in this study (considering all quantified species) were observed at the hotspots, located mainly along cell perimeters of the conventional cell. The capacity of the cover soil for NMOC oxidation was investigated in microcosms incubated with CH(4) and oxygen (O(2)). The cover soil showed a relatively high capacity for CH(4) oxidation and simultaneous co-oxidation of the halogenated aliphatic compounds, especially at the conventional cell. Fully substituted carbons (TeCM, PCE, CFC-11, CFC-12, CFC-113, HFC-134a, and HCFC-141b) were not degraded in the presence of CH(4) and O(2). Benzene and toluene were also degraded with relative high rates. This study demonstrates that landfill soil covers show a significant potential for CH(4) oxidation and co-oxidation of NMOCs.

Inertial distress of waste landfills

The seismic response of municipal solid waste landfills has recently drawn much attention due to the environmental, socio-economical, and public-health issues that could be raised in the case of a failure. However, there are certain technical issues that have not been fully addressed, such as the impact of local site conditions on the seismic response of a landfill. This study presents the results of a parametric numerical simulation that has been performed in order to examine the inertial distress of a typical solid waste landfill. Emphasis is given on the special characteristics of the ground motion, while the nonlinearity of both soil and waste materials is taken into account by an iterative equivalent linear procedure. Results indicate that soil conditions as well as the seismic excitation and the landfill characteristics play a significant and unquantifiable role on the inertial accelerations developed on the landfill.

Effects of earthworm cast and powdered activated carbon on methane removal capacity of landfill cover soils

Landfill gases could be vented through a layer of landfill cover soil that could serve as a biofilter to oxidize methane to carbon dioxide and water. Properly managed landfill cover soil layers may reduce atmospheric CH 4 emissions from landfills. In the present study, the effects of earthworm cast and powdered activated carbon (PAC) on the CH 4 removal capacity of the landfill cover soil was investigated. For this purpose, column and batch tests were conducted using three different materials: typical landfill cover soil, landfill cover soil amended with earthworm cast, and landfill cover soil amended with PAC. The maximum CH 4 removal rate of the columns filled with landfill cover soil amended with earthworm cast was 14.6 mol m −2 d −1, whereas that of the columns filled with typical landfill cover soil was 7.4 mol m −2 d −1. This result shows that amendment with earthworm cast could stimulate the CH 4-oxidizing capacity of landfill cover soil. The CH 4 removal rate of the columns filled with landfill cover soil amended with PAC also showed the same removal rate, but the vertical profile of gas concentrations in the columns and the methanotrophic population measured in the microbial assay suggested that the decrease of CH 4 concentration in the columns is mainly due to sorption. Based on the results from this study, amendment of landfill cover soil with earthworm cast and PAC could improve its CH 4 removal capacity and thus achieve a major reduction in atmospheric CH 4 emission as compared with the same landfill cover soil without any amendment.

Methane oxidation in landfill cover soil; the combined effects of moisture content, nutrient addition, and cover thickness

Oxidation of methane by methanotrophs in the landfill cover soil provides a source reduction for methane. Full factorial 23 experimental design using heterogeneous batch reactors was conducted to investigate statistically the individual and combined effects of soil moisture content, nutrient addition, and cover thickness on the CH4 oxidation process, during the migration through a landfill cover soil. Adding fertilizer as nutrient source to the 200 mm layer thickness of the landfill cover soil that contained 30% moisture content increased the CH4 oxidation efficiency from 38% to 81%. While, adding nutrients to the soil with less moisture content (15%) affected negatively the bacterial performance of methane oxidation, possibly as a result of toxicity or microbial water stress. Kinetic constants were reported and statistical design model was developed to describe the expected methane oxidation efficiencies under different levels of moisture content and nutrient addition that occur in a typical landfill cover soil.Key words: methane oxidation, landfill cover soil, moisture content, nutrients, soil thickness.

Review of the use of paper clay in the solid waste industry: physical and chemical properties

The purpose of the paper is to give an overview of utilisation of paper clay, or paper sludge, in Northeastern USA. This paper will outline typical landfill cover practices, overview the paper-making process, discuss the waste generated by the paper industry, and discuss the beneficial uses of paper clays.

Effects of local site conditions on the seismic response of municipal solid waste landfills

Over the last decade, the seismic response of landfills made of municipal solid waste has drawn attention mainly due to the environmental and public-health issues that could be raised in the event of a failure. Nevertheless, there are several associated technical issues that have not been adequately investigated. One of these is the impact of local site conditions on the earthquake-induced accelerations and, thereby, on the seismic design of a landfill. This study presents the results of a parametric numerical simulation that has been performed in order to examine the effects of local site conditions on the dynamic response of a typical landfill. Emphasis is given on the special characteristics of ground motion, while the material nonlinearity of both soil and waste is taken into account by an equivalent-linear procedure. Results indicate that local site conditions may play a significant role in the seismic response of a landfill. However, this role cannot be judged a priori as beneficial or detrimental, as it depends not only on soil conditions and seismic excitation, but also on the material and geometric characteristics of the landfill.

Assessment of long-term pH developments in leachate from waste incineration residues

Environmental assessment of residue disposal needs to account for long-term changes in leaching conditions. Leaching of heavy metals from incineration residues are highly affected by the leachate pH; the overall environmental consequences of disposing of these residues are therefore greatly influenced by changes in pH over time. The paper presents an approach for assessing pH changes in leachate from municipal solid waste incineration (MSWI) air-pollution-control (APC) residues. Residue samples were subjected to a stepwise batch extraction method in order to obtain residue samples at a range of pH values (similar to common pH-dependence tests), and then on these samples to determine leaching of alkalinity as well as remaining solid phase alkalinity. On a range of APC residues covering various pretreatment and disposal options, this procedure was used to determine leachable and residual alkalinity as a function of pH. Mass balance calculations for typical disposal scenarios were used to provide data on pH as a function of the liquid-to-solid (L/S) ratio in the leaching system. Regardless of residue type and pretreatment, pH was found to stay above 7 for L/S ratios up to about 2000 L kg(-1) corresponding to about 100,000 years in typical landfill scenarios. It was found that pH changes were mainly governed by alkalinity decreases from leaching processes rather than neutralization reactions. The results suggest that leaching testing for assessment purposes should be carried out in the alkaline range, for example, at pH 9. The paper offers a thorough basis for further modelling of incineration residue leaching and for modelling the environmental consequences of landfilling and utilization of these residues.

Experimental Study of Factors Controlling Sorption of Heavy Metals on Ariake Clay and Implication for Practice

A series of batch tests have been presented to investigate the effects of solid-solution contact time, solid:solution ratio, and pH of solution on sorption of Cd2+ and Pb2+ on Ariake clay from Kyushu region of Japan. The results show that, among the three investigated factors, solid:solution ratio (SD/SN) seems to be the crucial controlling factor. The Freundlich sorption parameters determined from the batch tests were applied to a typical field landfill in which the Ariake clay was used as soil barrier. The impacts of the landfill were assessed by numerical analysis. Based on the analysis result, the significance of selecting proper solid:solution ratio for determining sorption parameters from batch test has been discussed.

A study on sorption properties of Cd 2+ on Ariake clay for evaluating its potential use as a landfill barrier material

To assess the potential use of Ariake clay from Kyushu region of Japan as a landfill barrier material, the results of a series of batch tests are presented to investigate on the effects of solid–solution contact time, solid : solution ratio and pH of solution on sorption of Cd 2+ and Pb 2+ on the Ariake clay. The results show that in addition to the three investigated factors, solid : solution ratio seems to be the crucial controlling factor. The Freundlich sorption parameters determined from the batch tests are applied to a typical landfill site in which the Ariake clay is used as a soil barrier. The impacts of the landfill on the underlying aquifer are assessed through numerical analysis. Based on the analysis results, the significance of selecting proper solid : solution ratio for determining sorption parameters from batch tests is discussed.

Landfill lining stability and integrity: the role of waste settlement

Design of landfills must consider stability both within and between elements of the lining system, within the waste and involving the sub-grade. However, the design must also consider the long-term integrity of the lining system. Stresses, and hence deformations, in both mineral and geosynthetic lining materials must be controlled to ensure preferential flow paths are not formed. An assessment of integrity requires knowledge of the interaction between components of the lining system and the waste body as it settles. This paper considers assessment of both global stability and local failure that could result in loss of lining integrity. Results are presented that demonstrate traditional limit equilibrium techniques cannot be used to assess local failure. Factors of safety relate to global stability failure (i.e. development of a continuous failure surface) and not local failure that can lead to loss of integrity. Numerical analysis techniques can be used to assess local instability. Example results are presented for typical landfill cell geometries. These demonstrate the mechanism of local failure and sensitivity of behaviour to waste properties. Local factors of safety are introduced to illustrate the likelihood of integrity failure due to loss of geomembrane protection.

Hydrated area of a bentonite layer encapsulated between two geomembranes

Hydrated bentonite has a low shear strength, which may adversely impact the stability of structures incorporating geosynthetic clay liners (GCLs). Accordingly, in a growing number of GCL applications, the configuration is such that the bentonite layer is encapsulated between two geomembranes in order to reduce the potential for bentonite hydration. This paper considers an encapsulated bentonite layer formed using GM-GCL panels (i.e. panels consisting of a bentonite layer adhered to a carrier geomembrane). The panels are joined by overlapping at the edges and are overlain by a welded geomembrane. Water can migrate from the underlying soil into the bentonite of the overlaps, flow in the bentonite, and migrate laterally in the bentonite between the two geomembranes. Water is driven from the soil to the bentonite by a head difference that results in great part from the suction at the hydration front. This paper presents an analytical method to evaluate the extent of the hydrated area of the bentonite layer as a function of: time, the initial and hydrated moisture content of the bentonite, the hydraulic conductivity of the bentonite, the overlap width, the distance between overlaps, and the head difference. It is important to know the hydrated area for stability calculations. Numerical applications show that, for typical values of the parameters, it takes many decades to hydrate a significant fraction of the bentonite layer area. The analyses presented in this paper also show that, for typical landfill applications, the hydrated area due to leakage through defects in the upper geomembrane is negligible with respect to the hydrated area resulting from water migrating through the overlaps, assuming that the upper geomembrane is installed using good construction quality assurance practices. Uncertainties associated with the methodology presented herein are discussed, and guidance is provided on evaluation of the shear strength of the encapsulated bentonite layer as a function of the shear strength of the unhydrated bentonite, the shear strength of the hydrated bentonite, and the hydrated area.

Hydrated area of a bentonite layer encapsulated between two geomembranes

Hydrated bentonite has a low shear strength, which may adversely impact the stability of structures incorporating geosynthetic clay liners (GCLs). Accordingly, in a growing number of GCL applications, the configuration is such that the bentonite layer is encapsulated between two geomembranes in order to reduce the potential for bentonite hydration. This paper considers an encapsulated bentonite layer formed using GM-GCL panels (i.e. panels consisting of a bentonite layer adhered to a carrier geomembrane). The panels are joined by overlapping at the edges and are overlain by a welded geomembrane. Water can migrate from the underlying soil into the bentonite of the overlaps, flow in the bentonite, and migrate laterally in the bentonite between the two geomembranes. Water is driven from the soil to the bentonite by a head difference that results in great part from the suction at the hydration front. This paper presents an analytical method to evaluate the extent of the hydrated area of the bentonite layer as a function of: time, the initial and hydrated moisture content of the bentonite, the hydraulic conductivity of the bentonite, the overlap width, the distance between overlaps, and the head difference. It is important to know the hydrated area for stability calculations. Numerical applications show that, for typical values of the parameters, it takes many decades to hydrate a significant fraction of the bentonite layer area. The analyses presented in this paper also show that, for typical landfill applications, the hydrated area due to leakage through defects in the upper geomembrane is negligible with respect to the hydrated area resulting from water migrating through the overlaps, assuming that the upper geomembrane is installed using good construction quality assurance practices. Uncertainties associated with the methodology presented herein are discussed, and guidance is provided on evaluation of the shear strength of the encapsulated bentonite layer as a function of the shear strength of the unhydrated bentonite, the shear strength of the hydrated bentonite, and the hydrated area.

Site-dependent fate assessment in LCA: transport of heavy metals in soil

In spite of many recent advances in the impact assessment of emissions to air, surface water, and upper-soil layers, methods for emissions to deep soil layers and the groundwater are still missing for assessment tools such as life-cycle assessment (LCA). The goal of this paper is to provide such a method for assessing the fate of heavy metals in soils. The method was developed for the emissions from slag landfills but could, in principle, also be used in other applications. Our guidelines serve to estimate the transport time needed for a heavy metal to reach the groundwater as a function of spatial parameters such as infiltration rate, macropore flow, pH value, content of organic material, and distance to the groundwater. Default values for these parameters are suggested for typical landfill sites in Switzerland. The application of the method is illustrated in three case studies of actual landfill sites in Switzerland. The results of these case studies indicate that the retardation of heavy metals varies greatly depending on the local properties of the soil considered. Moreover, it is illustrated how the suggested procedure can be integrated into existing multimedia-fate models used in LCA.

Leaching of lead from computer printed wire boards and cathode ray tubes by municipal solid waste landfill leachates.

The proper management of discarded electronic devices (E-waste) is an important issue for solid waste professionals because of the magnitude of the waste stream and because these devices often contain a variety of toxic metals (e.g., lead). While recycling of E-waste is developing, much of this waste stream is disposed in landfills. Leaching tests are frequently used to characterize the potential of a solid waste to leach when disposed in a landfill. In the United States, the Toxicity Characteristic Leaching Procedure (TCLP) is used to determine whether a solid waste is a hazardous waste by the toxicity characteristic. The TCLP is designed to simulate worse-case leaching in a landfill environment where the waste is co-disposed with municipal solid waste (MSW). While the TCLP is a required analysis from a regulatory perspective, the leachate concentrations measured may not accurately reflect the concentrations observed under typical landfill conditions. Another method that can be performed to assess the degree a pollutant might leach from a waste in a landfill is to use actual landfill leachate as the leaching solution. In this study, two lead-containing components found in electronic devices (printed wire boards from computers and cathode ray tubes from computers and televisions) were leached using the TCLP and leachates from 11 Florida landfills. California's Waste Extraction Test (WET) and the Synthetic Precipitation Leaching Procedure were also performed. The results indicated that the extractions using MSW landfill leachates resulted in lower lead concentrations than those by the TCLP. The pH of the leaching solution and the ability of the organic acids in the TCLP and WET to complex with the lead are factors that regulate the amount of lead leached.

Reaction Mechanisms in Solid-State Anaerobic Digestion: 1. The Reaction Front Hypothesis

The proposed mechanism applies to the solid-state anaerobic digestion of a bed of organic wastes or other substrates. It is initiated by a seed body above a minimum viable size, around which a multi-zoned, mobile, reaction front develops. Acetate is formed in the leading zone, then diffuses back to a separate methanogenic zone, which is protected from acid in hibition by an intervening, passive buffer zone. This front gradually advances until the whole waste mass has been stabilized. The front cannot cross voids, so good inter-particle contact accelerates the process. The number of seed bodies determines the number of fronts and thus the rate of stabilization. Moreover, seeding patterns largely determine the mean distance the fronts must cover in order to complete the stabilization process, so they have a major effect on process kinetics. In packed-bed digesters densely seeded with previously digested waste, viable seed bodies are plentiful and closely spaced. Consequently, numerous fronts are formed and the mean distance they must cover is short, so the process is quick. However, in a typical landfill, inadequate seeding greatly extends the distances the few fronts must travel and thus greatly prolongs the stabilization process. This solid-phase mechanism would be dominant in well-seeded, rich, organic wastes. However, in lean wastes or in the absence of viable seed bodies, conventional, liquid-phase mechanisms would be dominant instead. In some circumstances, the two mechanisms might also co-exist. In others, neither might be effective, so the raw waste could be preserved indefinitely. This hypothesis is proposed for evaluation and testing. No such mechanism seems to have been considered in process modelling, in the design of experimental studies or in the operation of packed-bed waste digesters and bioreactor landfills. How ever, it could have a major impact in all these applications.

ASSESSING SANITARY LANDFILL STABILIZATION USING WINTER AND SUMMER WASTE STREAMS IN SIMULATED LANDFILL CELLS

ABSTRACT This study was undertaken to provide a better understanding and to further define the stabilization processes involved in a typical municipal landfill representative of the city of Calgary, Canada, area. The objectives of this study were: (1) to characterize the composition of the solid waste constituents entering the landfill site, (2) to assess the relative decomposition of various waste components in the simulated test cells, (3) to parametize selected chemical and physical changes occurring during the stabilization process and (4) to determine water absorptive capacity of the different waste constituents. The results of the long term landfill stabilization using simulated landfill cell systems filled with winter and summer waste streams, respectively, have illustrated the potential changes that may occur with time with such systems. Based on the results, it can be inferred that the seasonal variation in waste composition deposited in a landfill will likely effect the rate of decomposition and settlement, chemical and physical characteristics of the leachate, moisture sorbing capacity of the site as well as variation in seasonal contaminants. Assuming that the results from the simulated landfills used during this study can be extrapolated to larger-scale landfill operations, it seems that summer waste streams pose a higher pollution threat to the environment than winter waste streams. The several trends observed in this study and the conclusions reported herein would have wide applications in landfill management.

The Site of Reaction in Solid-State Digestion: A New Hypothesis

The literature on solid-state digestion (SSD) reveals no convincing physical model of the process. Most of the reported reaction models implicitly assume homogeneity: the heterogeneous nature of the waste substrate may be noted but is rarely modelled. In contrast, this paper proposes an essential role for heterogeneity. A multi-zoned physical model and a localized reaction site are consistent with many characteristics of SSD. The fundamental hypothesis is that methanogenesis requires sites protected from the rapid acidogenesis occurring in the richer elements of the waste. If this protection is provided by mass-transfer resistances within pockets of leaner material, it is essential that their identity is not destroyed by excessive mixing or size reduction. A possible mechanism for such an effect is furnished by the proposed model, with a central role for mass transfer. Reaction is envisaged as occurring only in a thin layer, at an interface between rich and lean material. Acetogenesis and methanogenesis take place in distinct zones, with the latter protected from acid inhibition by mass-transfer resistances in an intervening buffer zone. The rate of waste stabilization is determined by the rate of advance of this multi-zoned reaction front. Several of the mass transfer processes occurring between these zones could be rate-limiting. This model suggests that methanogenesis in a typical landfill gradually spreads from discrete initiation points, with the reaction zones forming an expanding set of concentric shells. Process optimization may thus require maximizing the number of initiation points, subject to a constraint: only the larger seed fragments can develop. Reported failures to replicate the process at laboratory scale might thus be due to the use of homogenized feedstock. The implications of the model for commercial practice are discussed, as are potential methods of experimental verification.

Bottom ash from sludge cake as a barrier material to pollutant migration in landfills

Treated urban sewage sludge, which had been dewatered and dried in an open bed, was locally burnt in an open drum and bottom ashes were formed. This work investigated whether these bottom ashes of dried sludge cakes (SCbash)' produced by local labour and equipment, could be used as landfill covers or liners, a function normally served by clay. Laboratory tests were performed to determine the particle size distribution, Atterberg limits, compaction characteristics, hydraulic conductivity and shear strength parameters of the sludge cake. The effects of desiccation and freeze-thaw processes on the hydraulic conductivity of SCbash were also examined. It was found that properly compacted and stabilized SCbash has the requisite properties for use as landfill covers or liners. The SCbash can be compacted into a dense mass with a low hydraulic conductivity of the order of 1.15 X 10 -7 m s-1 (as a comparison, the hydraulic conductivity of compacted clay is around 10-9 m s-1). The compacted SCbash also showed good defence against the increases in hydraulic conductivity caused by desiccation and freeze-thaw processes compared with the data reported for compacted clays. The compacted SCbash also has a greater shear strength than is typically expected of compacted clay and therefore is likely to remain stable on a typical landfill slope design based on the shear strength of clay.

Landfill sealing potentials of bottom ashes of sludge cakes

The main objective of this study is to determine if bottom ashes of dried sludge cakes (SC bash) could be used as landfill cover or liner, a function which is normally performed with clay. Laboratory tests were performed to determine its particle size distribution, Atterberg limits, compaction characteristics, hydraulic conductivity, and shear strength parameters. The effects of desiccation and freeze–thaw on the hydraulic conductivity of SC bash were also examined. The results of this investigation proved that properly compacted and stabilized SC bash has the required properties to be used in landfill covers or liners. The SC bash can be compacted into a dense mass with a low hydraulic conductivity of the order of 1.15×10 −7 m/s. The compacted SC bash showed also a good resistance to the increase in hydraulic conductivity caused by desiccation and freeze–thaw as compared to other compacted clays. The results also indicated that the compacted SC bash has greater shear strength as typically expected for compacted clay, and therefore is likely to remain stable on a typical landfill slope designed and based on clay shear strength.