Landfill Gas Control Research Articles

Axisymmetric gas flow model for bioreactor landfills incorporating MSW compression and leachate recirculation

To control the landfill gas (LFG) emission, LFG collection systems with vertical wells are extensively used in municipal solid waste (MSW) landfills. When investigating the LFG flow behavior, the solid–liquid–gas interactions cannot be neglected, especially in bioreactor landfills. In this study, an axisymmetric numerical model incorporating MSW compression and leachate recirculation was developed to describe the transient gas flow in bioreactor landfills. In the model, the porosity distribution was evaluated through circular computations, and the temporal and spatial changes in moisture were determined using the unsaturated–saturated seepage flow model. Based on these calculations, the governing equations of gas migration were solved using the finite element method. The influences of MSW properties, recirculation rate and well vacuum pressure were then investigated. The results show that the MSW compression and leachate recirculation have a significant impact on the distributions of gas generation, permeability and pressure. As the recirculation rate increases from 1 to 9 mm day−1, the gas permeability can decrease about 1 order of magnitude and thus the radius of influence decreases from 39 to 31 m. It is important to keep a balance between the acceleration of landfill stability and the recovery efficiency of LFG. These results provide helpful guidelines for the design of leachate recirculation and LFG control systems.

From a Literature Review to an Alternative Treatment System for Landfill Gas and Leachate

This paper provides an alternative treatment system for landfill gas and leachate control in order to reduce the energy consumption and disposal cost, using the recycled landfill gas as the combustion promoter for incineration of the leachate. This study starts by providing a literature review to summarize and analyze different approaches being applied to landfill leachate treatment. Subsequently, a conceptual prototype is proposed, which can be built using existing technology by means of technical possibility analysis, whilst economic benefits could be returned through preliminary comparison. With the proposed introduction of a “waste treatment park”, this alternative treatment system could provide a template for leachate and landfill gas control. This study may provide an insight for landfill operators and engineers to promote the transformation from the conceptual framework to the real achievement. Finally, the limitations of the conceptual model and analysis are discussed, laying a foundation for further work.

Third Indian Geotechnical Society: Ferroco Terzaghi Oration Design and Construction of Barrier Systems to Minimize Environmental Impacts Due to Municipal Solid Waste Leachate and Gas

Based on case histories and the latest research, this paper examines municipal solid waste landfills as a system comprised of three primary subsystems (the hydrogeology and barrier system below the waste; the waste and landfill operations; and the landfill cover and landfill gas control system) that exists in a broader social/regulatory/administrative/economic system. Issues discussed include the effects of waste type and waste management risks, landfill leachate and leachate collection, landfill gas and gas collection, the hydrogeology and barrier subsystem required to contain contaminants in leachate and landfill gas from escape by both advection and diffusion, the dependence of a landfill design on the type and amount of waste and the operational model, materials specifications, and construction issues. Lessons to be learnt from the past problems are discussed together with the implications for modern waste management. The success of modern systems are noted together with the need to maintain vigilance and avoid complacency with respect to landfill siting, design, approval, construction, operations, after-use, and in approving subsequent surrounding land use. The importance of considering the interactions between the different components of the landfill system is discussed in the context of the need to ensure that changes in terms of waste stream or modes of landfill operations are carefully researched and considered in developing designs to provide long-term environmental protection.

Effect of biogas generation on radon emissions from landfills receiving radium-bearing waste from shale gas development

Dramatic increases in the development of oil and natural gas from shale formations will result in large quantities of drill cuttings, flowback water, and produced water. These organic-rich shale gas formations often contain elevated concentrations of naturally occurring radioactive materials (NORM), such as uranium, thorium, and radium. Production of oil and gas from these formations will also lead to the development of technologically enhanced NORM (TENORM) in production equipment. Disposal of these potentially radium-bearing materials in municipal solid waste (MSW) landfills could release radon to the atmosphere. Risk analyses of disposal of radium-bearing TENORM in MSW landfills sponsored by the Department of Energy did not consider the effect of landfill gas (LFG) generation or LFG control systems on radon emissions. Simulation of radon emissions from landfills with LFG generation indicates that LFG generation can significantly increase radon emissions relative to emissions without LFG generation, where the radon emissions are largely controlled by vapor-phase diffusion. Although the operation of LFG control systems at landfills with radon source materials can result in point-source atmospheric radon plumes, the LFG control systems tend to reduce overall radon emissions by reducing advective gas flow through the landfill surface, and increasing the radon residence time in the subsurface, thus allowing more time for radon to decay. In some of the disposal scenarios considered, the radon flux from the landfill and off-site atmospheric activities exceed levels that would be allowed for radon emissions from uranium mill tailings. Implications: Increased development of hydrocarbons from organic-rich shale formations has raised public concern that wastes from these activities containing naturally occurring radioactive materials, particularly radium, may be disposed in municipal solid waste landfills and endanger public health by releasing radon to the atmosphere. This paper analyses the processes by which radon may be emitted from a landfill to the atmosphere. The analyses indicate that landfill gas generation can significantly increase radon emissions, but that the actual level of radon emissions depend on the place of the waste, construction of the landfill cover, and nature of the landfill gas control system.

Measured gas emissions from four landfills in South Africa and some implications for landfill design and methane recovery in semi-arid climates

The magnitude of annual global emissions of methane from municipal solid waste landfills without landfill gas control systems implies that these landfills are significant contributors to the atmospheric load of greenhouse gases. There have been a number of field studies undertaken internationally to measure actual fluxes of methane and carbon dioxide from landfills, with a view to corroborating modelled predictions of the contribution of landfills to the global greenhouse gas budget. The vast majority of these studies have been undertaken in more temperate climates and in developed countries. This paper reports a study of landfill gas emissions from four large landfills located in the semi-arid interior of South Africa. A static accumulation chamber was used and measurements were made at each site over a period of two to three days. The results were analysed by three different methods, all of them leading to the same general conclusion that landfill gas emission rates were lower than expected. A common conclusion based on results from all four sites was that capping of landfills in semi-arid climates with low permeability covers would probably significantly retard the already low rate of waste degradation and thus gas generation. While this may be regarded as advantageous in the short term, it cannot be relied upon in perpetuity as clayey landfill covers will inevitably desiccate and crack in a semiarid environment. In addition, reasonable after-care periods for such landfills are likely to extend well beyond the currently stipulated 30-year period, and efforts to encourage energy recovery from landfills may be hampered because gas generation rates decrease as the waste dries out under conditions of minimal recharge from precipitation. A landfill cover that allows small amounts of percolation of rainfall into the waste may therefore in fact be beneficial in semiarid climates, although care would need to be taken to carefully regulate this infiltration.

Methane generation from UK landfill sites and its use as an energy resource

Emissions of methane from UK landfill sites are estimated to be about 46% of the country's total releases of methane to atmosphere. Combusting landfill gas offers an effective way of reducing emissions from this source. Using landfill gas as an energy resource also reduces dependence on fossil fuel sources of energy. There are currently over 60 landfill sites in the UK where landfill gas is used either directly or in power generation schemes, combusting about 190 kt of methane per year. This figure is predicted to exceed 550 kt per year by 2000 as a result of market incentive schemes for power generation from non-fossil sources and of increased environmental legislation to encourage landfill gas control and use.

Landfill Gas: From Environment to Energy

A survey was recently achieved, on behalf of the Commission of the European Communities, to scrutinise the state-of-the-art of landfill gas control and exploitation. The survey is divided into 8 parts After an Executive Summary, part I deals with the environmental impact of landfill gas and details 166 reported cases of landfill gas damages in uncontrolled landfills. The second one details the process of landfill gas generation and the technology of landfill gas control by its exploitation. The third part surveys the methodologies for monitoring landfill gas emissions for landfill gas potential evaluation and for safety. The fourth part deals with policies and legal aspects of landfill gas in the European Community and in the World. The fifth part estimates landfill gas potentials and overviews the economics of landfill gas control and exploitation, notably by the exhaustive assessment of 6 case studies. The sixth part gives the status of landfill gas exploitation in the European Community and in the World. The two final parts list utilities and references.

Safe and effective gas recovery by means of a low-technology, integrated site design approach

The benefits of landfill gas control are two-fold: hazard or nuisance elimination and revenue generation by energy sales. A large number of schemes has been established, mainly in the U.S.A., but also in Western Europe. For the majority of these projects the aim has been to maximise gas recovery at already completed sites, or sections of sites. Gas recovery plant design has been almost purely “retro-fit” in concept. This approach can be costly both in terms of capital-overspend as well as possible ineffectiveness of gas leakage (or migration) control. Moreover, the “Western” methodology is generally inappropriate to landfills in Eastern European countries owing to the differing characteristics of landfill design such as surface cover placement, division of the site into cells, leachate and surface water collection. However, by considering carefully the special characteristics of these sites and, most significantly, adopting an “integrated design” approach, then energy recovery from landfill gas can be both profitable and environmentally beneficial. The aim of this paper is to identify the key factors which influence landfill gas collection effectiveness and to incorporate these in an overall site design strategy. In this way, the gas collection plant is optimised and linked directly to a specification for the site final cover contour. Simple design procedures are employed and the modelling and analysis aspects are short, concise and readily verifiable. This new methodology is discussed in detail and the design techniques are applied to a “national” Eastern European site.

Utilization of landfills as building sites

Landfill gas (LFG) control measures and operating experience are described for two landfill sites which have been developed in the City of Carson, California. Investigations began in 1975 to develop a completed 10.5-ha Class II landfill site (household and commercial wastes) as a six-screen drive-in theatre including projection and concession facilities. LFG control facilities include 30 extraction wells for on-site protection, 19 perimeter extraction wells for migration control, blower/flare facilities and a subslab membrane and automatic gas detection system for backup protection during active system downtime. Investigations for the second site began in 1977 to develop 3.8 ha of a 7.2-ha Class II landfill site as a truck sales and service centre. LFG control facilities include 14 extraction wells, blower/flare facilities and a subslab membrane. Ongoing operation and maintenance of LFG control facilities is required at both sites to permit continued site occupancy. Activities include blower/flare maintenance, well field monitoring and adjustment, site settlement inspection and repair, monitoring system calibration and maintenance, etc. Buildings at both locations are supported on foundation piles driven through the former landfilled materials.

Utilization of Landfills as Building Sites

Landfill gas (LFG) control measures and operating experience are described for two landfill sites which have been developed in the City of Carson, California. Investigations began in 1975 to develop a completed 10.5-ha Class II landfill site (household and commercial wastes) as a six-screen drive-in theatre including projection and concession facilities. LFG control facilities include 30 extraction wells for on-site protection, 19 perimeter extraction wells for migration control, blower/flare facilities and a subslab membrane and automatic gas detection system for backup protection during active system downtime. Investigations for the second site began in 1977 to develop 3.8 ha of a 7.2-ha Class II landfill site as a truck sales and service centre. LFG control facilities include 14 extraction wells, blower/flare facilities and a subslab membrane. Ongoing operation and maintenance of LFG control facilities is required at both sites to permit continued site occupancy. Activities include blower/flare maintenance, well field monitoring and adjustment, site settlement inspection and repair, monitoring system calibration and maintenance, etc. Buildings at both locations are supported on foundation piles driven through the former landfilied materials.