Improvement of electrical resistivity tomography for leachate injection monitoring

Leachate recirculation is a key process in the scope of operating municipal waste landfills as bioreactors, which aims to increase the moisture content to optimize the biodegradation in landfills. Given that liquid flows exhibit a complex behaviour in very heterogeneous porous media, in situ monitoring methods are required. Surface time-lapse electrical resistivity tomography (ERT) is usually proposed. Using numerical modelling with typical 2D and 3D injection plume patterns and 2D and 3D inversion codes, we show that wrong changes of resistivity can be calculated at depth if standard parameters are used for time-lapse ERT inversion. Major artefacts typically exhibit significant increases of resistivity (more than +30%) which can be misinterpreted as gas migration within the waste. In order to eliminate these artefacts, we tested an advanced time-lapse ERT procedure that includes (i) two advanced inversion tools and (ii) two alternative array geometries. The first advanced tool uses invariant regions in the model. The second advanced tool uses an inversion with a “minimum length” constraint. The alternative arrays focus on (i) a pole–dipole array (2D case), and (ii) a star array (3D case). The results show that these two advanced inversion tools and the two alternative arrays remove almost completely the artefacts within +/?5% both for 2D and 3D situations. As a field application, time-lapse ERT is applied using the star array during a 3D leachate injection in a non-hazardous municipal waste landfill. To evaluate the robustness of the two advanced tools, a synthetic model including both true decrease and increase of resistivity is built. The advanced time-lapse ERT procedure eliminates unwanted artefacts, while keeping a satisfactory image of true resistivity variations. This study demonstrates that significant and robust improvements can be obtained for time-lapse ERT monitoring of leachate recirculation in waste landfills.     

Contribution of 3-D time-lapse ERT to the study of leachate recirculation in a landfill

Leachate recirculation is a key process in the operation of municipal waste landfills as bioreactors. It aims at increasing the moisture content to optimise the biodegradation. Because waste is a very heterogeneous and anisotropic porous media, the geometry of the leachate plume recirculation is difficult to delineate from the surface at the scale of the bioreactor site. In this study, 3-D time-lapse electrical resistivity tomography (ERT) was used to obtain useful information for understanding leachate recirculation hydrodynamics. The ERT inversion methodology and the electrode arrays were optimised using numerical modelling simulating a 3-D leachate injection scenario. Time-lapse ERT was subsequently applied at the field scale during an experimental injection. We compared ERT images with injected volumes to evaluate the sensitivity of time-lapse ERT to delineate the plume migration. The results show that time-lapse ERT can accomplish the following: (i) accurately locate the injection plume, delineating its depth and lateral extension; (ii) be used to estimate some hydraulic properties of waste.     

Impact of landfill liner time–temperature history on the service life of HDPE geomembranes

The observed temperatures in different landfills are used to establish a number of idealized time–temperature histories for geomembrane liners in municipal solid waste (MSW) landfills. These are then used for estimating the service life of different HDPE geomembranes. The predicted antioxidant depletion times (Stage I) are between 7 and 750 years with the large variation depending on the specific HDPE geomembrane product, exposure conditions, and most importantly, the magnitude and duration of the peak liner temperature. The higher end of the range corresponds to data from geomembranes aged in simulated landfill liner tests and a maximum liner temperature of 37 °C. The lower end of the range corresponds to a testing condition where geomembranes were immersed in a synthetic leachate and a maximum liner temperature of 60 °C. The total service life of the geomembranes was estimated to be between 20 and 3300 years depending on the time–temperature history examined. The range illustrates the important role that time–temperature history could play in terms of geomembrane service life. The need for long-term monitoring of landfill liner temperature and for geomembrane ageing studies that will provide improved data for assessing the likely long-term performance of geomembranes in MSW landfills are highlighted.     

Environmental management by the learning curve

This is a futuristic appreciation of waste management challenges and their solution by means of good management models. A literature review, administrative initiatives, research results, and experiences from practice are combined in this study to render an evolutionary picture of the change in paradigm relative to municipal solid waste possible to occur between 2000 and 2025. The principal stages of progress in the 25 years studied were: the correct characterization of municipal solid waste as a function of geographical location and recycling potential, the divided collection model and its corresponding learning curve, correct opportunity cost accounting tools, and the generally admitted and accepted changeover of municipal solid waste treatment from a technical to a management problem. It is reported that as a result of this progress, the municipal landfill is a species in extinction. Regional landfills with long life spans are the rule in 2025.     

Systems analysis as support for decision making towards sustainable municipal waste management--a case study.

During the last decade, systems analysis has become a more frequently used tool in municipal waste management. This paper investigates how one such analysis, carried out in a Swedish county, was perceived by local municipal officers and politicians as support in the decision-making process. A questionnaire was sent to municipal officers and politicians in local government committees and municipal councils. The respondents considered the most important aspects in evaluating scenarios to be: possibilities for municipal co-operation to minimize cost and negative environmental influence; sound working conditions for refuse disposal personnel; low emissions of greenhouse gases; keeping household economy in mind; and using technologies that are known and reliable. Aspects of relatively low importance were the number of locally generated job opportunities, and minimizing work efforts for the households. The study also showed differences between male and female respondents and between politicians and municipal officers, on how scenarios were valued and on which aspects of the systems analysis were of greatest importance for this valuation. Respondents, on average, were satisfied with the systems analysis, and its usefulness as a decision-support tool. However, more work should be carried out to explain and present the results of the systems analysis to further improve its usefulness.     

Comparing the performance of landfill liner systems

 Some minimum design requirements for landfill liner systems were compared, and the performance of several Japanese liner systems was investigated by two-dimensional (2D) contaminant transport analysis. We demonstrate that (1) the performance of each system specified by the Japanese Ministry of Health and Welfare (at present the Ministry of Health, Labor, and Welfare) varies, (2) the adsorption characteristics of the mineral barrier has a significant effect on the contaminant transport process, and (3) a geomembrane layer in the barrier system is very efficient in reducing the peak concentration of contaminants in the groundwater beneath a landfill even if the geomembrane has a number of defects. Under the conditions considered, the analysis results show that a liner system without a geomembrane layer should be avoided. Received: July 4, 2001 / Accepted: March 26, 2002     

A review of aqueous-phase VOC transport in modern landfill liners

Leachates from municipal solid waste (MSW) and hazardous waste landfills contain a wide range of volatile organic compounds (VOCs) in addition to inorganic compounds. VOCs have been shown to migrate and contaminate the surrounding environment and impair the use of groundwater. Therefore, the effectiveness of modern landfill liner systems to minimize migration of VOCs is of concern. Most modern landfills employ a composite liner consisting of a geomembrane overlying a compacted clay liner or a geosynthetic clay liner. The geomembrane is often believed to be the primary barrier to contaminant transport. However, for VOCs, the clay component usually controls the rate of transport since VOCs are shown to diffuse through geomembrane at appreciable rates. Additionally, analyses have shown that transport of volatile organic compounds (VOCs) generally is more critical than transport of inorganic compounds (e.g., toxic heavy metals), even though VOCs are often found at lower concentrations in leachates. Therefore, the effectiveness of modern landfill liner systems to minimize migration of VOCs and transport of VOCs through clay liners and modeling of transport through composite liners merit scrutiny. This paper presents a review of recent research by the author and others on these topics. A systematic and comprehensive approach to determine mass transport parameters for transport of VOCs in liquid phase through compacted clay liners, geosynthetic clay liners (GCLs), and geomembranes has enabled to develop realistic models to predict mass flux of VOCs through modern composite liners and provide a quantitative basis to evaluate potential for transport of dissolved VOCs and the equivalency of different composite liners.     

Design optimization and standardization of an environmental availability test under both acidic and alkaline conditions

The objective of this study was to design a procedure for an environmental availability test under both acidic and alkaline conditions for solid wastes and recycled materials and products. The procedure was designed on the basis of the Dutch availability test NEN 7371. Bottom ash from a municipal solid waste incinerator and copper slag were used as test materials. The influences of the type and intensity of liquid stirring apparatus and the open area ratio of the top of the leaching vessel were investigated experimentally, and partial least-squares modeling was applied as multivariate data analysis for the simultaneous evaluation of the three leaching conditions. Interlaboratory validation was then carried out with the participation of seven laboratories in accordance with JIS Z 8402-2/ISO 5725-2. Both repeatability and reproducibility were found to be acceptable, but precise calibration of the pH electrode is required. The proposed procedure will provide sufficient accuracy as a standard test method.     

Predicting the compressibility behaviour of tire shred samples for landfill applications

Tire shreds have been used as an alternative to crushed stones (gravel) as drainage media in landfill leachate collection systems. The highly compressible nature of tire shreds (25-47% axial strain on vertical stress applications of 20-700 kPa) may reduce the thickness of the tire shred drainage layer to less than 300 mm (minimum design requirement) during the life of the municipal solid waste landfill. There hence exists a need to predict axial strains of tire shred samples in response to vertical stress applications so that the initial thickness of the tire shred drainage layer can be corrected for compression. The present study performs one-dimensional compressibility tests on four tire shred samples and compares the results with stress/strain curves from other studies. The stress/strain curves are developed into charts for choosing the correct initial thickness of tire shred layers that maintain the minimum thickness of 300 mm throughout the life of the landfill. The charts are developed for a range of vertical stresses based on the design height of municipal waste cell and bulk unit weight of municipal waste. Experimental results also showed that despite experiencing large axial strains, the average permeability of the tire shred sample consistently remained two to three orders of magnitude higher than the design performance criterion of 0.01cm/s for landfill drainage layers. Laboratory experiments, however, need to verify whether long-term chemical and bio-chemical reactions between landfill leachate and the tire shred layer will deteriorate their mechanical functions (hydraulic conductivity, compressibility, strength) beyond permissible limits for geotechnical applications.     

GIS-based approach for optimized siting of municipal solid waste landfill

The exponential rise in the urban population of the developing countries in the past few decades and the resulting accelerated urbanization phenomenon has brought to the fore the necessity to develop environmentally sustainable and efficient waste management systems. Sanitary landfill constitutes one of the primary methods of municipal solid waste disposal. Optimized siting decisions have gained considerable importance in order to ensure minimum damage to the various environmental sub-components as well as reduce the stigma associated with the residents living in its vicinity, thereby enhancing the overall sustainability associated with the life cycle of a landfill. This paper addresses the siting of a new landfill using a multi-criteria decision analysis (MCDA) and overlay analysis using a geographic information system (GIS). The proposed system can accommodate new information on the landfill site selection by updating its knowledge base. Several factors are considered in the siting process including geology, water supply resources, land use, sensitive sites, air quality and groundwater quality. Weightings were assigned to each criterion depending upon their relative importance and ratings in accordance with the relative magnitude of impact. The results from testing the system using different sites show the effectiveness of the system in the selection process.     

A review of municipal solid waste composition in the United Kingdom

The move from landfill-based to resource-based waste management systems requires a greater knowledge of the composition of municipal solid waste. This paper draws together the findings of municipal solid waste (MSW) compositional surveys undertaken in the United Kingdom. The results from recent surveys show a good agreement over the composition of household-collected waste, but less agreement over civic amenity site waste composition. There is insufficient data to allow comparisons of the commercial waste element of municipal waste or of the other components, and further work is necessary to produce more reliable estimates of the composition of these streams. The use of questionnaire surveys and analysis of the results suggests that the size and age profile of a household influence the generation of household-collected waste. Some research suggests that the waste container provided by the local authority and the socio-economic classification of a household also influence household-collected waste generation, but other studies failed to find this link. Further research is required to investigate this by surveying all of the waste disposal routes available to specific households.     

Optimisation of MSW collection routes for minimum fuel consumption using 3D GIS modelling

Collection of municipal solid waste (MSW) may account for more than 70% of the total waste management budget, most of which is for fuel costs. It is therefore crucial to optimise the routing network used for waste collection and transportation. This paper proposes the use of geographical information systems (GIS) 3D route modelling software for waste collection and transportation, which adds one more degree of freedom to the system and allows driving routes to be optimised for minimum fuel consumption. The model takes into account the effects of road inclination and vehicle weight. It is applied to two different cases: routing waste collection vehicles in the city of Praia, the capital of Cape Verde, and routing the transport of waste from different municipalities of Santiago Island to an incineration plant. For the Praia city region, the 3D model that minimised fuel consumption yielded cost savings of 8% as compared with an approach that simply calculated the shortest 3D route. Remarkably, this was true despite the fact that the GIS-recommended fuel reduction route was actually 1.8% longer than the shortest possible travel distance. For the Santiago Island case, the difference was even more significant: a 12% fuel reduction for a similar total travel distance. These figures indicate the importance of considering both the relief of the terrain and fuel consumption in selecting a suitable cost function to optimise vehicle routing.     

Comparison of selected aerobic and anaerobic procedures for MSW treatment

This paper considers selected efficiency rates and process data of aerobic and anaerobic procedures for the treatment of municipal solid waste and residual waste. Data are exclusively related to mechanical-biological treatment (MBT) procedures for generating waste appropriate for landfilling. The following aspects are regarded: general framework conditions for the application of MBT, efficiency of decomposition and of stabilisation, air and water emissions and energy balances. The presented data can be used for more efficient planning. In comparison to aerobic processes, anaerobic digestion can be ecologically advantageous, particularly with regard to exhaust emissions and energy balances. On the other hand, the wastewater emissions and the wastewater treatment required must be regarded as disadvantageous. Due to the relatively short period of operational history of most anaerobic processes for mechanical-biological waste treatment and thus limited experiences, operational reliability of anaerobic processes is slightly lower. Extensive biological stability of the treated waste for low-emission disposal cannot be reached by anaerobic digestion alone, but only in combination with additional aerobic post-treatment. In connection with the utilisation of renewable energies and the rising relevancy of climate protection, it can be affirmed that anaerobic digestion for the treatment of municipal solid waste has a high potential for further development.     

石化企业VOCs无组织排放源强的反演模拟

针对石化行业面源无组织排放VOCs难以准确定量的问题,建立了基于开路式傅里叶变换红外光谱技术(OP-FTIR)的面源污染源源强反演模型,并进行了现场模拟试验。试验结果表明,风向、风速、大气稳定度、监测距离、数据处理周期等都是影响反演模型准确性的重要灵敏度参数。以反演源强Q_P与实际排放量Q的比值(Q_P/Q)为量化指标,对各影响因素进行优化处理,确定了构建反演模型适用的边界条件。当各灵敏度参数稳定于适用边界条件之内时,Q_P/Q为0.85~0.90。     

Protective effect of overlying geosynthetic on geomembrane liner observed from landfill field tests and inclined board laboratory experiments.

Geosynthetic liner systems are generally installed in landfill sites to prevent toxic leachate from escaping into the adjoining environment by utilizing their impervious characteristics. Therefore, it is important to protect the geomembrane from being damaged or destroyed during all phases of landfilling, namely landfill construction, waste tipping and landfill closure. This paper presents firstly the observed performance of a geomembrane liner from a landfill site where the geomembrane liner was installed on the slopes of a Korean landfill; and secondly the results of an inclined board laboratory test. Two types of experiments were conducted to identify the protecting effect of the overlaying geosynthetic on the geomembrane liners. At a testing landfill site, the slope consisted of three different sub-inclines and two 2-m-wide intermediate levels. The sub-inclines were each 8 m in vertical height and their angle of inclination was 1: 1.5 (vertical: horizontal). The reported observations were made for a time period of approximately 1 year, until the landfill was filled with wastes to the top of the uppermost slope. In addition, inclined board laboratory tests were carried out. During the inclined board test, a base table is inclined slowly and steadily until the block located on the base table starts to slide, when the tension and displacements of two geosynthetics, namely the geomembrane liner and protecting geotextile, are measured. In conclusion, test results showed that the down-drag force generated by waste accumulation and sliding of upper material was to a large extent dissipated through the elongation of the protecting geosynthetic overlying the geomembrane and thus was not transferred to the geomembrane. Unless the protecting geosynthetic undergoes structural failure, this stress relaxation phenomenon continues to occur so that the magnitude of tensile force to be applied on the geomembrane remains marginal.     

Quantification of landfill emissions to air: a case study of the Ano Liosia landfill site in the greater Athens area.

Fugitive pollutant emissions from municipal solid waste landfills have the potential to cause annoyance and health impacts in the surrounding residential areas. The overall objective of this research was to perform an assessment of fugitive pollutant emissions and a dispersion analysis downwind of a specific landfill site. The study was performed at the closed Ano Liosia landfill site which is located in the greater Athens area. The human exposure from priority to health-risk pollutants emitted from landfill, such as vinyl chloride and benzene, was estimated by the landfill gas emission LandGEM 2.01 software combined with the atmospheric long-term dispersion model ISC3-LT. The emission and meteorological conditions under which the models were applied referred to the worst-case scenario. This scenario was used for the evaluation of the maximum human exposure assessed beyond the Ano Liosia landfill towards the residential areas. The above scenario provides the minimum downwind distance of the health-risk zone which is calculated to be equal to 1.5 km from the landfill. Within this distance the assessed air pollutant concentration for several air pollutants was significantly above the World Health Organization reference lifetime exposure health criteria. Finally, the applied methodology was used in the Ano Liosia landfill, where atmospheric concentrations of pollutants measured in the field were compared with model predictions.     

Greenhouse gases accounting and reporting for waste management – A South African perspective

This paper investigates how greenhouse gases are accounted and reported in the waste sector in South Africa. Developing countries (including South Africa) do not have binding emission reduction targets, but many of them publish different greenhouse gas emissions data which have been accounted and reported in different ways. Results show that for South Africa, inventories at national and municipal level are the most important tools in the process of accounting and reporting greenhouse gases from waste. For the development of these inventories international initiatives were important catalysts at national and municipal levels, and assisted in developing local expertise, resulting in increased output quality. However, discrepancies in the methodology used to account greenhouse gases from waste between inventories still remain a concern. This is a challenging issue for developing countries, especially African ones, since higher accuracy methods are more data intensive. Analysis of the South African inventories shows that results from the recent inventories can not be compared with older ones due to the use of different accounting methodologies. More recently the use of Clean Development Mechanism (CDM) procedures in Africa, geared towards direct measurements of greenhouse gases from landfill sites, has increased and resulted in an improvement of the quality of greenhouse gas inventories at municipal level.     

Assessment of mobility and bioavailability of contaminants in MSW incineration ash with aquatic and terrestrial bioassays

Incineration of municipal solid waste (MSW) is a waste treatment method which can be sustainable in terms of waste volume reduction as well as a source of renewable energy. In the process fly and bottom ash is generated as a waste material. The ash residue may vary greatly in composition depending on the type of waste incinerated and it can contain elevated levels of harmful contaminants such as heavy metals. In this study, the ecotoxicity of a weathered, untreated incineration bottom ash was characterized as defined by the H14 criterion of the EU Waste Framework Directive by means of an elemental analysis, leaching tests followed by a chemical analysis and a combination of aquatic and solid-phase bioassays. The experiments were conducted to assess the mobility and bioavailability of ash contaminants. A combination of aquatic and terrestrial bioassays was used to determine potentially adverse acute effects of exposure to the solid ash and aqueous ash leachates. The results from the study showed that the bottom ash from a municipal waste incineration plant in mid-Sweden contained levels of metals such as Cu, Pb and Zn, which exceeded the Swedish EPA limit values for inert wastes. The chemical analysis of the ash leachates showed high concentrations of particularly Cr. The leachate concentration of Cr exceeded the limit value for L/S 10 leaching for inert wastes. Filtration of leachates prior to analysis may have underestimated the leachability of complex-forming metals such as Cu and Pb. The germination test of solid ash and ash leachates using T. repens showed a higher inhibition of seedling emergence of seeds exposed to the solid ash than the seeds exposed to ash leachates. This indicated a relatively low mobility of toxicants from the solid ash into the leachates, although some metals exceeded the L/S 10 leaching limit values for inert wastes. The Microtox® toxicity test showed only a very low toxic response to the ash leachate exposure, while the D. magna immobility test showed a moderately high toxic effect of the ash leachates. Overall, the results from this study showed an ecotoxic effect of the solid MSW bottom ash and the corresponding ash leachates. The material may therefore pose an environmental risk if used in construction applications. However, as the testing of the solid ash was rather limited and the ash leachate showed an unusually high leaching of Cr, further assessments are required in order to conclusively characterize the bottom ash studied herein as hazardous according to the H14 criterion.     

Numerical simulation of municipal solid waste combustion in a novel two-stage reciprocating incinerator

A mathematical model was presented in this paper for the combustion of municipal solid waste in a novel two-stage reciprocating grate furnace. Numerical simulations were performed to predict the temperature, the flow and the species distributions in the furnace, with practical operational conditions taken into account. The calculated results agree well with the test data, and the burning behavior of municipal solid waste in the novel two-stage reciprocating incinerator can be demonstrated well. The thickness of waste bed, the initial moisture content, the excessive air coefficient and the secondary air are the major factors that influence the combustion process. If the initial moisture content of waste is high, both the heat value of waste and the temperature inside incinerator are low, and less oxygen is necessary for combustion. The air supply rate and the primary air distribution along the grate should be adjusted according to the initial moisture content of the waste. A reasonable bed thickness and an adequate excessive air coefficient can keep a higher temperature, promote the burnout of combustibles, and consequently reduce the emission of dioxin pollutants. When the total air supply is constant, reducing primary air and introducing secondary air properly can enhance turbulence and mixing, prolong the residence time of flue gas, and promote the complete combustion of combustibles. This study provides an important reference for optimizing the design and operation of municipal solid wastes furnace.     

Greenhouse gases emission from municipal waste management: The role of separate collection

The municipal solid waste management significantly contributes to the emission in the atmosphere of greenhouse gases (e.g. CO₂, CH₄, N₂O) and therefore the management process from collection to treatment and disposal has to be optimized in order to reduce these emissions. In this paper, starting from the average composition of undifferentiated municipal solid waste in Italy, the effect of separate collection on greenhouse gases emissions from municipal waste management has been assessed. Different combinations of separate collection scenarios and disposal options (i.e. landfilling and incineration) have been considered. The effect of energy recovery from waste both in landfills and incinerators has also been addressed. The results outline how a separate collection approach can have a significant effect on the emission of greenhouse gases and how wise municipal solid waste management, implying the adoption of Best Available Technologies (i.e. biogas recovery and exploitation system in landfills and energy recovery system in Waste to Energy plants), can not only significantly reduce greenhouse gases emissions but, in certain cases, can also make the overall process a carbon sink. Moreover it has been shown that separate collection of plastic is a major issue when dealing with global warming relevant emissions from municipal solid waste management.