Gas Collection Systems Research Articles

Assessing the performance of gas collection systems in select Chinese landfills according to the LandGEM model: drawbacks and potential direction

In China, municipal solid waste (MSW) is primarily treated by landfilling. Landfill gas (LFG) collection effectively reduces methane emission from MSW landfills. An accurate system of LFG collection is important in landfill planning, design, and operation. However, China has not developed such systems. In this study, the efficiency of methane collection is calculated in three Chinese landfills with different collection systems (A: vertical wells for MSW before 2010; combined horizontal trenches and under-membrane pipes for MSW from 2011 onwards; B: combined horizontal trenches and vertical wells; C: vertical wells only). This efficiency was computed by dividing the quantity of methane obtained from landfill operation records by the quantity estimated based on the LandGEM model. Results show that the collection efficiencies of landfills with vertical wells and/or horizontal pipes ranged from 8.3% to 27.9%, whereas those of a system equipped with geomembrane reached 65.3%. The poor performance of the landfills was attributed to the open burning of early-stage LFG, LFG release from cracks in high-density polyethylene covers, and high levels of leachate within a landfill site. Therefore, this study proposes an integrated LFG collection system that can remove leachate and collect gas from landfills that accept waste with high moisture content.

Comparison of municipal solid waste treatment technologies from a life cycle perspective in China

China has endured the increasing generation of municipal solid waste; hence, environmental analysis of current waste management systems is of crucial importance. This article presents a comprehensive life cycle assessment of three waste treatment technologies practiced in Hangzhou, China: landfill with and without energy recovery, and incineration with waste-to-energy. Adopting region-specific data, the study covers various environmental impacts, such as global warming, acidification, nutrient enrichment, photochemical ozone formation, human toxicity and ecotoxicity. The results show that energy recovery poses a positive effect in environmental savings. Environmental impacts decrease significantly in landfill with the utilization of biogas owing to combined effects by emission reduction and electricity generation. Incineration is preferable to landfill, but toxicity-related impacts also need to be improved. Furthermore, sensitivity analysis shows that the benefit of carbon sequestration will noticeably decrease global warming potential of both landfill scenarios. Gas collection efficiency is also a key parameter influencing the performance of landfill. Based on the results, improvement methods are proposed. Energy recovery is recommended both in landfill and incineration. For landfill, gas collection systems should be upgraded effectively; for incineration, great efforts should be made to reduce heavy metals and dioxin emissions.

ChemInform Abstract: Aluminum Waste Reaction Indicators in a Municipal Solid Waste Landfill

AbstractReview: 34 refs.

A Comparison of Performance of Landfill Gas Collection Wells with Varying Configurations

An investigation to compare the efficiency of landfill gas collection systems with different well numbers (one, two or four) and configurations (vertical or horizontal) has been conducted. The study has shown that with an increasing number of wells, the gas collection rate and efficiency are enhanced and the gas flux at the surface also becomes more uniform. In addition, the study has also suggested that for wells with the same screen length, a vertical well works better than a horizontal well in terms of gas extraction rate; however, it may result in a less uniform gas flux through the surface.

Gas Pressure Model for Layered Municipal Solid Waste Landfills

AbstractA mathematical model for calculating gas pressure profiles in layered landfill systems is presented. Solutions to scenarios considering a zero-pressure top boundary condition and a zero gas flux or fixed gas pressure bottom boundary condition are presented. Two cases, specified gas pressure and specified inward gas flux, are addressed for scenarios involving horizontal gas collection systems. A series of application examples demonstrate how the proposed model can be used to investigate the influences of (1) variation of gas generation rate with respect to depth and time, (2) soil covers, (3) horizontal collection layers, and (4) geomembrane and geosynthetic clay liner covers on gas pressure distribution in landfills. The proposed model provides a useful tool to landfill engineers in designing landfill gas management systems and in particular when selecting and specifying gas collection system spacing and pumps.

Indirect measurements of field-scale hydraulic conductivity of waste from two landfill sites

Management and prediction of the movement and distribution of fluids in large landfills is important for various reasons. Bioreactor landfill technology shows promise, but in arid or semi-arid regions, the natural content of landfilled waste may be low, thus requiring addition of significant volumes of water. In more humid locations, landfills can become saturated, flooding gas collection systems and causing sideslope leachate seeps or other undesirable occurrences. This paper compares results from two different approaches to monitoring water in waste. At the Brock West Landfill in eastern Canada, positive pore pressures were measured at various depths in saturated waste. The downward seepage flux through the waste is known, thus the vertical saturated hydraulic conductivity of the waste at this landfill was determined to be 3 × 10 −7 cm/s. By comparison, the Spadina Landfill in western Canada is predominantly unsaturated. The infiltration of moisture into the waste was measured using moisture sensors installed in boreholes which determined arrival time for moisture fronts resulting from major precipitation events as well as longer-term change in moisture content resulting from unsaturated drainage during winter when frozen ground prevented infiltration. The unsaturated hydraulic conductivity calculated from these data ranged from approximately 10 −6 cm/s for the slow winter drainage in the absence of significant recharge to 10 −2 cm/s or higher for shallow waste subject to high infiltration through apparent preferential pathways. These two very different approaches to field-scale measurements of vertical hydraulic conductivity provide insight into the nature of fluid movement in saturated and unsaturated waste masses. It is suggested that the principles of unsaturated seepage apply reasonably well for landfilled waste and that the hydraulic behavior of waste is profoundly influenced by the nature and size of voids and by the degree of saturation prevailing in the landfill.

Evaluation of Methane Oxidation Efficiency of Two Biocovers: Field and Laboratory Results

Biocovers constitute a promising technology to reduce fugitive and residual emissions from landfills throughout their operational life and after gas collection systems are turned off. The aim of this study was to assess the efficiency of two substrate materials in oxidizing CH4 into CO2 under field conditions and in the laboratory (column tests). The two substrates evaluated were: 1) a mixture of sand and compost, and 2) the same sand-compost mixture with gravel added. The oxidation rates obtained in the field attained a maximum of 576 g CH4 m-2·day-1 for one of the substrates and 352 g CH4 m-2·day-1 for the other, with oxidation efficiencies nearly of 100%. These maximum values were much higher than those obtained in the laboratory: 115 and 118 g CH4 m-2·day-1, respectively, for an oxidation efficiency of 96% in both cases. The exact causes for the discrepancy between field and laboratory results were not identified, but it was hypothesized that vegetation on the surface of the passive methane oxidati...

Aluminum Waste Reaction Indicators in a Municipal Solid Waste Landfill

Subtitle D landfills may contain aluminum from residential and commercial solid waste, industrial waste, and aluminum pro- duction wastes. Some aluminum-bearing waste materials, particularly aluminum production wastes, may react with liquid in a landfill and cause uncontrolled temperature increases, significant changes in gas composition and pressure, nuisance odors, and changes in leachate composition and quantity. Such reactions may also cause degradation of leachate quality (e.g., increased ammonia, sodium, potassium, chloride, and TDS concentrations), combustion of the surrounding waste, damage to engineered components (gas collection systems, leachate collection systems, and liner system materials), and slope instability. Temperatures exceeding 150°C (300°F), generation and accumulation of undesirable explosive and toxic gases (e.g., hydrogen, acetylene, ammonia, carbon monoxide, and benzene), and gas pressures exceeding 210 kPa (30.5 psi) have been observed. Water from leachate recirculation, precipitation, the waste, or groundwater infiltration can initiate the exothermic reaction if aluminum production wastes are present. This paper uses a case history to illustrate some indicators of an aluminum reaction and problems that can develop from such a reaction in a Subtitle D landfill. DOI: 10.1061/(ASCE)GT.1943-5606.0000581. © 2012 American Society of Civil Engineers. CE Database subject headings: Solid wastes; Leaching; Aluminum (chemical); Waste disposal; Landfills. Author keywords: Solid waste; Leachate; Stability; Leachate recirculation; Aluminum; Exothermic chemical reaction; Waste disposal; MSW; Subsurface fire.

Increasing business value through proper design and operation of landfill gas collection and control systems

Increasing business value through proper design and operation of landfill gas collection and control systems

LCA and economic evaluation of landfill leachate and gas technologies

Landfills receiving a mix of waste, including organics, have developed dramatically over the last 3–4 decades; from open dumps to engineered facilities with extensive controls on leachate and gas. The conventional municipal landfill will in most climates produce a highly contaminated leachate and a significant amount of landfill gas. Leachate controls may include bottom liners and leachate collection systems as well as leachate treatment prior to discharge to surface water. Gas controls may include oxidizing top covers, gas collection systems with flares or gas utilization systems for production of electricity and heat. The importance of leachate and gas control measures in reducing the overall environmental impact from a conventional landfill was assessed by life-cycle-assessment (LCA). The direct cost for the measures were also estimated providing a basis for assessing which measures are the most cost-effective in reducing the impact from a conventional landfill. This was done by modeling landfills ranging from a simple open dump to highly engineered conventional landfills with energy recovery in form of heat or electricity. The modeling was done in the waste LCA model EASEWASTE. The results showed drastic improvements for most impact categories. Global warming went from an impact of 0.1 person equivalent (PE) for the dump to −0.05 PE for the best design. Similar improvements were found for photochemical ozone formation (0.02 PE to 0.002 PE) and stratospheric ozone formation (0.04 PE to 0.001 PE). For the toxic and spoiled groundwater impact categories the trend is not as clear. The reason for this was that the load to the environment shifted as more technologies were used. For the dump landfill the main impacts were impacts for spoiled groundwater due to lack of leachate collection, 2.3 PE down to 0.4 PE when leachate is collected. However, at the same time, leachate collection causes a slight increase in eco-toxicity and human toxicity via water (0.007E to 0.013PE and 0.002 to 0.003 PE respectively). The reason for this is that even if the leachate is treated, slight amounts of contaminants are released through emissions of treated wastewater to surface waters. The largest environmental improvement with regard to the direct cost of the landfill was the capping and leachate treatment system. The capping, though very cheap to establish, gave a huge benefit in lowered impacts, the leachate collection system though expensive gave large benefits as well. The other gas measures were found to give further improvements, for a minor increase in cost.

Influences of mixed expiratory sampling parameters on exhaled volatile organic compound concentrations

Breath gas analysis is a promising technology for medical applications. By identifying disease-specific biomarkers in the breath of patients, a non-invasive and easy method for early diagnosis or therapy monitoring can be developed. In order to achieve this goal, one essential prerequisite is the reproducibility of the method applied, i.e. the quantification of exhaled volatile organic compounds (VOCs). The variability of breath gas VOC measurements can be affected by many factors. In this respect, sampling-specific parameters like flow rate and volume of exhalation, exhalation with or without breath holding, exhalation in single or multiple breathing and volume of air inhaled before breath gas exhalation can play a vital role. These factors affecting the measurements must be controlled by optimizing the sampling procedure. For such an optimization, it is important to know how exactly the different parameters affect the exhaled VOC concentrations. Therefore, a study has been undertaken in order to identify some effects of different breath sampling-specific parameters on the exhaled VOC profile using the mixed expired breath sampling technique. It was found that parameters such as filling the sampling bag with high or low flow rate of exhalation, with multiple or single exhalations, in different volumes of exhalation, with breath holding and under different surrounding air conditions significantly affect the concentrations of the exhaled VOCs. Therefore, the specific results of this work should be taken into account before planning new breath gas studies or developing new breath gas collection systems in order to minimize the number of artefacts affecting the concentration of exhaled VOCs.

One-Dimensional Gas Flow Models for Municipal Solid Waste Landfills: Cylindrical and Spherical Symmetries

The purpose of this technical note is to present two analytic solutions for modeling one-dimensional gas flow in municipal solid waste landfills with horizontal gas collection systems. In previous work, vertical flow was considered. In the present communication, situations in which cylindrical or spherical symmetry apply are considered. These models, although not perfect descriptions of typical landfill geometries, should be useful during the “roughing-out” stage of gas collection systems and may be used to estimate maximum pressures with a minimal effort. Because all the requisite background is developed in the cited reference; the reader is directed to consult it for that purpose.

Estimation of Landfill Gas Generation Rate and Gas Permeability Field of Refuse Using Inverse Modeling

Landfill methane must be captured to reduce emissions of greenhouse gases; moreover it can be used as an alternative energy source. However, despite the widespread use of landfill gas (LFG) collection systems for over three decades, little information about their capture efficiency is available, because LFG generation rates usually remain unknown. Therefore, to assess the efficiency of greenhouse gas capture and to estimate the amount of fugitive emissions, LFG generation rates should be properly determined. In addition, to improve the capture efficiency of methane while minimizing air intrusion from the atmosphere, it is important to quantify gas flow patterns within landfills. In this study, a methodology to quantify methane generation rates and to estimate the gas permeability field was examined using inverse modeling. To account for the heterogeneous, but spatially correlated structure of refuse, the pilot point method involving geostatistical techniques and optimization algorithms was used. Synthetic observation data were generated from forward simulations for a pumping test and a baro-pneumatic test, and these data were used to test the inversion procedure. The inverse model was able to reproduce the spatial permeability distribution using the transient pressure changes in response to the withdrawal of LFG during the pumping test. The LFG generation rate was also successfully estimated using the data from the baro-pneumatic test with errors less than 2%. While this methodology was developed and successfully tested using synthetic data, it will be investigated in the future using field data from the bioreactor test cells at the Yolo County Central Landfill, CA.

Evaluation of the geotechnical properties of MSW in two Brazilian landfills

The characteristics of municipal solid waste (MSW) play a key role in many aspects of waste disposal facilities and landfills. Because most of a landfill is made up of MSW, the overall stability of the landfill slopes are governed by the strength parameters and physical properties of the MSW. These parameters are also important in interactions involving the waste body and the landfill structures: cover liner, leachate and gas collection systems. On the other hand, the composition of the waste, which affects the geotechnical behavior of the MSW, is dependent on a variety of factors such as climate, disposal technology, the culture and habits of the local community. It is therefore essential that the design and stability evaluations of landfills in each region be performed based on the local conditions and the geotechnical characteristic of the MSW. The Bandeirantes Landfill, BL, in São Paulo and the Metropolitan Center Landfill, MCL, in Salvador, are among the biggest landfills in Brazil. These two disposal facilities have been used for the development of research involving waste mechanics in recent years. Considerable work has been made in the laboratory and in the field to evaluate parameters such as water and organic contents, composition, permeability, and shear strength. This paper shows and analyzes the results of tests performed on these two landfills. The authors believe that these results could be a good reference for certain aspects and geotechnical properties of MSW materials in countries with similar conditions.

LCA comparison of windrow composting of yard wastes with use as alternative daily cover (ADC)

This study compared the environmental impacts of composting yard wastes in windrows with using them in place of soil as alternative daily cover (ADC) in landfills. The Life Cycle Assessment was made using the SimaPro LCA software and showed that the ADC scenario is more beneficial for the environment than windrow composting. ADC use is also a less costly means of disposal of yard wastes. This finding applies only in cases where there are sanitary landfills in the area that are equipped with gas collection systems and can use yard wastes as alternative daily cover. Otherwise, the environmentally preferable method for disposal of source-separated yard wastes is composting rather than landfilling.

Reappraisal of the role of turpentine vapor in noncondensible gas explosions

Turpentine has been identified as the cause of numerous fires and explosions within the pulp and paper industry. Explosions in the noncondensible gas (NCG) collection systems caused by total reduced sulfur (TRS) compounds have usually been minor and caused minimal damage, but explosions caused by turpentine could be catastrophic. When flammable conditions have been created by insufficient dilution, air leakage into the system, or accumulation and breakthrough of TRS gases or turpentine vapor at a chip bin, it is conceivable that turpentine vapor created near-optimum flammable mixtures more often than TRS gases did. In these cases, the burning velocity would have been close to the maximum. On the other hand, when flammable conditions were created due to insufficient dilution of a stream of high volume, low concentration gases (HVLCs) or due to air leakage into a stream of low volume, high concentration gases (LVHCs), then the flammable mixture formed would be expected to have been off-stoichiometric: lean in the former case and rich in the latter case. In both cases, the burning velocity could have been much lower than in the near-stoichiometric mixture. The violence of explosions caused by turpentine is attributed to its capability to form near-stoichiometric mixtures more easily than the other components of NCGs.

Tracer method to measure landfill gas emissions from leachate collection systems

This paper describes a method developed for quantification of gas emissions from the leachate collection system at landfills and present emission data measured at two Danish landfills with no landfill gas collection systems in place: Fakse landfill and AV Miljø. Landfill top covers are often designed to prevent infiltration of water and thus are made from low permeable materials. At such sites a large part of the gas will often emit through other pathways such as the leachate collection system. These point releases of gaseous constituents from these locations cannot be measured using traditional flux chambers, which are often used to measure gas emissions from landfills. Comparing tracer measurements of methane (CH 4) emissions from leachate systems at Fakse landfill and AV Miljø to measurements of total CH 4 emissions, it was found that approximately 47% (351 kg CH 4 d −1) and 27% (211 kg CH 4 d −1), respectively, of the CH 4 emitting from the sites occurred from the leachate collection systems. Emission rates observed from individual leachate collection wells at the two landfills ranged from 0.1 to 76 kg CH 4 d −1. A strong influence on emission rates caused by rise and fall in atmospheric pressure was observed when continuously measuring emission from a leachate well over a week. Emission of CH 4 was one to two orders of magnitude higher during periods of decreasing pressure compared to periods of increasing pressure.

Development of a Practical Method for the Estimation of Maximum Lateral Displacement in Large Landfills

An extensive database of mechanical properties of municipal solid waste (MSW) is available as a result of significant advances made in the past few years in terms of understanding its mechanical behavior. It is, however, difficult to interpret and use this database in practice because of inherent heterogeneity of MSW and the variations in the sampling and testing procedures. The database also appears to be dominated by shear strength properties and contains limited information on elastic properties. As such, it is rather difficult to estimate the deformation within landfills and to quantify its effect on the performance and the integrity of leachate and gas collection systems installed within landfills. This paper presents results from an extensive on-going research program at the University of Saskatchewan to study the mechanical behavior of MSW. This research program includes laboratory and field testing of intact and recompacted MSW samples and numerical simulations incorporating stochastic modeling. A practical tool in the form of a design chart is presented, which can be used for the estimation of maximum horizontal displacement in a landfill using the height and the side slope of the landfill and the unit weight and the elastic properties of MSW. The validity of the design chart is confirmed using the results from an instrumented municipal landfill located in eastern Canada.

Design and application of Hadamard-injectors coupled with gas and supercritical fluid sample collection systems in Hadamard transform-gas chromatography/mass spectrometry

A novel Hadamard transform-gas chromatography/mass spectrometry (HT-GC/MS) system equipped with on-line sample collection systems is described. A Hadamard-injector was successfully designed and then coupled with an on-line adsorption/desorption system for detecting volatile organic compounds (VOCs) and a supercritical fluid extraction (SFE) system, respectively, by HT-GC/MS. Six VOCs and three pesticides were used as model compounds. In the former case, an activated-charcoal trap was used to trap VOCs from the indoor air. After 10 L of indoor air had passed through the trap, the condensed components were heated and simultaneously injected into the GC column through the Hadamard-injector, based on Hadamard codes. In a second experiment, a sample of rice was spiked with three types of pesticides and the sample then extracted using a commercially available supercritical fluid extractor. After extraction, the extracted components were transferred to a holding tank and simultaneously injected into the GC column also using the Hadamard-injector. The findings show that, in both cases, the combination of on-line sample collection methods and the use of the Hadamard transform resulted in improved sensitivity and detection. Compared to the single injection used in most GC/MS systems, the signal-to-noise (S/N) ratios were substantially improved after inverse Hadamard transformation of the encoded chromatogram.

Influence of High-Permeability Layers for Enhancing Landfill Gas Capture and Reducing Fugitive Methane Emissions from Landfills

Gas collection systems of various designs have been used to control landfill gas emissions, which can be problematic, particularly before installation of final landfill covers. In this work, an innovative gas collection system that includes a permeable layer near the top surface of landfills was evaluated for enhancing capture of landfill gas and reducing fugitive methane emissions. A computational model that accounts for advective and diffusive fluxes of multiple gas components was used to evaluate the efficiency of this new design for intermediate landfill covers. The utility of the high-permeability gas-conductive layer was illustrated for several conditions of interest including varying refuse permeability, varying degrees of permeability anisotropy, and temporal atmospheric pressure changes. Simulations showed that the permeable layer decreased methane emissions by 43% when the horizontal to vertical permeability ratio for refuse was kh ∕ kv =3 and the domain average kh =3× 10−12 m2 , while reduction...