A decision support system for the operational planning of solid waste collection

This study presents the conception, modeling, and implementation of a decision support system applied to the operational planning of solid waste collection systems, called SCOLDSS. The main functionality of the system is the generation of alternatives to the decision processes concerning: (a) the allocation of separate collection vehicles, as well as the determination of their routes and (b) the determination of the daily amount of solid waste to be sent to each sorting unit, in order to avoid waste of labor force and to reduce the amount of waste sent to the landfills. To develop the computer system, a combination of quantitative techniques was used, such as: simulation of discrete events and algorithms/heuristics for vehicle allocation and routing. The system was developed using the Borland Delphi environment and the commercial software Arena to carry out the simulations. We also present a computational study with real-life data from the solid waste collection in Porto Alegre, Brazil, in which we show that the results provided by the computational system outperform the operation planning currently adopted.     

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     

Hydrologic evaluation of landfill performance (HELP) modeling in bioreactor landfill design and permitting

The practice of operating municipal solid waste landfills as bioreactor landfills has become more common over the past decade. Because simulating moisture balance and flow is more critical in such landfills than in dry landfills, researchers have developed methods to address this problem using the hydrologic evaluation of landfill performance (HELP) model. This paper discusses three methods of applying the HELP model to simulate the percolation of liquids added to landfill waste: the leachate recirculation feature (LRF), the subsurface inflow (SSI) feature, and additional rainfall to mimic liquids addition. The LRF is simple to use but may not be able to bring the landfill to bioreactor conditions. The SSI feature provides a convenient user interface for modeling liquids addition to each layer. The additional rainfall feature provides flexibility to the model, allowing users to estimate the leachate generation rate and the leachate head on bottom liner associated with daily variation in the liquids addition rate. Additionally, this paper discusses several issues that may affect the HELP model, such as the time of model simulation, layers of liquids addition, and the limitations of the HELP model itself. Based on the simulation results, it is suggested that the HELP model should be run over an extended period of time after the cessation of liquids addition in order to capture the peak leachate generation rate and the head on the liner (HOL). From the perspectives of leachate generation and the HOL, there are few differences between single-layer injection and multiple-layer injection. This paper also discusses the limitations of using the HELP model for designing and permitting bioreactor landfills.     

The performance of a natural treatment system for landfill leachate with special emphasis on the fate of organic pollutants.

A natural treatment system for the treatment of leachate was studied at Moskogen landfill in southern Sweden. This facility consists of three consecutive ponds and a soil-plant (SP)-system. A test area, receiving water from the third pond with the same hydraulic load as the SP-system, was used for estimation of the latter system. Quality parameters including biochemical oxygen demand, total organic carbon, ammonium, nitrate, orthophosphate, and total suspended solids along the treatment line were determined as well as soluble metals (Cu, Cd, Zn, Cr, Ni, and Pb). In addition a thorough investigation along the treatment line has also been performed concerning volatile organic compounds and semi-volatile organic compounds. Non-polar organic compounds were investigated using gas chromatography-mass spectrometry. Quantification was based on the assumption of equal response for the compounds found in comparison with the chosen marker substances. For polar, water-soluble compounds the measurements were restricted to phenolic compounds using high-performance liquid chromatography. Several different types of organic compounds were found in the raw leachate including aromatics, benzene-sulfonamides, biphenyls, naphthalene, organic phosphates, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, phenols and phthalates. The treatment system efficiently reduced organic pollutants, heavy metals, and nitrogen/phosphorous compounds. Most metals and organic compounds in the leachate were already significantly reduced to a low level in the treatment ponds and ammonium-N was efficiently transformed to nitrate-N in the SP-system.     

Integrating multi-criteria decision analysis for a GIS-based hazardous waste landfill sitting in Kurdistan Province, western Iran

The evaluation of a hazardous waste disposal site is a complicated process because it requires data from diverse social and environmental fields. These data often involve processing of a significant amount of spatial information which can be used by GIS as an important tool for land use suitability analysis. This paper presents a multi-criteria decision analysis alongside with a geospatial analysis for the selection of hazardous waste landfill sites in Kurdistan Province, western Iran. The study employs a two-stage analysis to provide a spatial decision support system for hazardous waste management in a typically under developed region. The purpose of GIS was to perform an initial screening process to eliminate unsuitable land followed by utilization of a multi-criteria decision analysis (MCDA) to identify the most suitable sites using the information provided by the regional experts with reference to new chosen criteria. Using 21 exclusionary criteria, as input layers, masked maps were prepared. Creating various intermediate or analysis map layers a final overlay map was obtained representing areas for hazardous waste landfill sites. In order to evaluate different landfill sites produced by the overlaying a landfill suitability index system was developed representing cumulative effects of relative importance (weights) and suitability values of 14 non-exclusionary criteria including several criteria resulting from field observation. Using this suitability index 15 different sites were visited and based on the numerical evaluation provided by MCDA most suitable sites were determined.     

Effects of volatile organic compounds on clay landfill liner performance

Clay borrow materials intended for use in a clay liner system were found to be contaminated by low concentrations of volatile organic chemicals (VOCs). The suspected source of contaminants was a nearby Superfund site where similar compounds were found in soil and groundwater. Based on these observations, questions were raised regarding the potential effects of VOCs on the performance of the clay materials as a landfill liner.Laboratory experiments were conducted to evaluate the effects of three levels of soil precontamination and two types of permeants. Atterberg tests showed that the precontaminations (acetone and m-xylene) and the simulated leachate (methylene chloride, trichloroethylene, and toluene), at the concentrations used, did not impact clay-pore fluid interaction. Sedimentation tests showed that the impact of methylene chloride, trichloroethylene, and toluene on sediment volume and rate of settlement was not detectable up to the maximum concentration level of 100 ppm for each chemical.From the permeation tests, acetone in the precontaminated samples was generally flushed out within three pore volumes but m-xylene was not detected (above the detection limit of 0.01 mg 1⁻¹) in the permeant effluent. The stabilized permeabilities of the specimens ranged from 0.2 × 10⁻⁷ to 3.0 × 10⁻⁷ cms⁻¹. It was found that precontamination of the clay at the levels studied did not affect organic chemical leachate transport/adsorption discernibly when compared with clean clay, and no measurable retardation or adsorption of VOCs in clay liners occurred in either clean clay or precontaminated clay.     

Suitability analysis for siting MSW landfills and its multicriteria spatial decision support system: Method,implementation and case study

Multicriteria spatial decision support systems (MC-SDSS) have emerged as an integration of geographical information systems (GIS) and multiple criteria decision analysis (MCDA) methods for incorporating conflicting objectives and decision makers’ (DMs’) preferences into spatial decision models. This article presents a raster-based MC-SDSS that combines the analytic hierarchy process (AHP) and compromise programming methods, such as TOPSIS (technique for order preference by similarity to the ideal solution) and Ideal Point Methods. To the best of our knowledge it is the first time that a synergy of AHP and compromise programming methods is implemented in raster-driven GIS-based landfill suitability analysis. This procedure is supported by a spatial decision support system (SDSS) that was developed within a widely used commercial GIS software package. A real case study in the Thrace region in northeast Greece serves as a guide on how to conduct a suitability analysis for a MSW landfill site with the proposed MC-SDSS. Moreover, the procedure for identifying MSW disposal sites is accomplished by performing four computational models for synthesizing the DMs per criterion preferential system. Based on the case study results, a comparison analysis is performed according to suitability index estimations. According to them Euclidean distance metric and TOPSIS present strong similarities. When compared with Euclidean distance metric, TOPSIS seems to generate results closer to that derived by Manhattan distance metric. The comparison of Chebychev distance metric with all the other approaches revealed the greatest deviations.     

Application of the US decision support tool for materials and waste management

The US Environmental Protection Agency (US EPA) launched the Resource Conservation Challenge (RCC) in 2002 to help reduce waste and move towards more sustainable resource consumption. The objective of the RCC is to help communities, industries, and the public think in terms of materials management rather than waste disposal. Reducing cost, finding more efficient and effective strategies to manage municipal waste, and thinking in terms of materials management requires a holistic approach that considers life-cycle environmental tradeoffs. The US EPA's National Risk Management Research Laboratory has led the development of a municipal solid waste decision support tool (MSW-DST). The computer software can be used to calculate life-cycle environmental tradeoffs and full costs of different waste management or materials recovery programs. The environmental methodology is based on the use of life-cycle assessment and the cost methodology is based on the use of full-cost accounting. Life-cycle inventory (LCI) environmental impacts and costs are calculated from the point of collection, handling, transport, treatment, and disposal. For any materials that are recovered for recycling, offsets are calculated to reflect potential emissions savings from use of virgin materials. The use of the MSW-DST provides a standardized format and consistent basis to compare alternatives. This paper provides an illustration of how the MSW-DST can be used by evaluating ten management strategies for a hypothetical medium-sized community to compare the life-cycle environmental and cost tradeoffs. The LCI results from the MSW-DST are then used as inputs into another US EPA tool, the Tool for the reduction and assessment of chemical and other environmental impacts, to convert the LCI results into impact indicators. The goal of this paper is to demonstrate how the MSW-DST can be used to identify and balance multiple criteria (costs and environmental impacts) when evaluating options for materials and waste management. This type of approach is needed in identifying strategies that lead to reduced waste and more sustainable resource consumption. This helps to meet the goals established in the US EPA's Resource Conservation Challenge.     

A new economic instrument for financing accelerated landfill aftercare

The key aspects of landfill operation that remain unresolved are the extended timescale and uncertain funding of the post-closure period. This paper reviews the topic and proposes an economic instrument to resolve the unsustainable nature of the current situation. Unsustainability arises from the sluggish degradation of organic material and also the slow flushing of potential pollutants that is exacerbated by low-permeability capping. A landfill tax or aftercare provision rebate is proposed as an economic instrument to encourage operators to actively advance the stabilization of landfilled waste. The rebate could be accommodated within existing regulatory and tax regimes and would be paid for: (i) every tonne of nitrogen (or other agreed leachate marker) whose removal is advanced via the accelerated production and extraction of leachate; (ii) every tonne of non-commercially viable carbon removed via landfill gas collection and treatment. The rebates would be set at a level that would make it financially attractive to operators and would encourage measures such as leachate recirculation, in situ aeration, and enhanced flushing. Illustrative calculations suggest that a maximum rebate of up to ～€50/tonne MSW would provide an adequate incentive.     

Municipal solid waste landfill siting using intelligent system

Historically, landfills have been the dominant alternative for the ultimate disposal of municipal solid waste. This paper addresses the problem of siting a new landfill using an intelligent system based on fuzzy inference. 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 topography and geology, natural resources, socio-cultural aspects, and economy and safety. The system will rank sites on a scale of 0-100%, with 100% being the most appropriate one. A weighting system is used for all of the considered factors. The results from testing the system using different sites show the effectiveness of the system in the selection process.     

Predicted performance of clay-barrier landfill covers in arid and semi-arid environments

Conventional landfill cover systems for municipal solid waste include low-permeability compacted clay barriers to minimize infiltration into the landfilled waste. Such layers are vulnerable in climates where arid to semi-arid conditions prevail, whereby the clay cover tends to desiccate and crack, resulting in drastically higher infiltration, i.e., lower cover efficiency. To date, this phenomenon, which has been reported in field observations, has not been adequately assessed. In this paper, the performance of a cover system solely relying on a clay barrier was simulated using a numerical finite element formulation to capture changes in the clay layer and the corresponding modified hydraulic characteristics. The cover system was guided by USEPA Subtitle-D minimum requirements and consisted of a clay layer underlying a protective vegetated soil. The intrinsic characteristics of the clay barrier and vegetative soil cover, including their saturated hydraulic conductivities and their soil-water characteristic curves, were varied as warranted to simulate intact or "cracked" conditions as determined through the numerical analyses within the proposed methodology. The results indicate that the levels of percolation through the compromised or cracked cover were up to two times greater than those obtained for intact covers, starting with an intact clay hydraulic conductivity of 10(-5)cm/s.     

Start-up performance of a full-scale bioreactor landfill cell under cold-climate conditions

A 0.49-ha bioreactor landfill cell containing approximately 32,400 metric tons of municipal solid waste was constructed and operated at the Northern Oaks Recycling and Disposal Facility in Harrison, Michigan, USA. Design of this full-scale research cell included a network of 48 temperature and moisture sensors, leachate collection basins, and gas sampling ports, which provided for continuous temperature and moisture data and periodic measurements of both the quantity and composition of the leachate and gas produced. The data indicated that methane generation started approximately 3 months after filling in lifts that were placed during summer, but not until 8 months for those filled during the winter. Temperature data indicated that near-0 degrees C temperatures persisted within the lifts filled during winter for more than 6 months, and that gas production was minimal during this period. These results suggest that in addition to maintaining optimal moisture levels within the waste mass, temperature control must be a key design consideration in cold climates.     

LCA-IWM: a decision support tool for sustainability assessment of waste management systems

The paper outlines the most significant result of the project 'The use of life cycle assessment tools for the development of integrated waste management strategies for cities and regions with rapid growing economies', which was the development of two decision-support tools: a municipal waste prognostic tool and a waste management system assessment tool. The article focuses on the assessment tool, which supports the adequate decision making in the planning of urban waste management systems by allowing the creation and comparison of different scenarios, considering three basic subsystems: (i) temporary storage; (ii) collection and transport and (iii) treatment, disposal and recycling. The design and analysis options, as well as the assumptions made for each subsystem, are shortly introduced, providing an overview of the applied methodologies and technologies. The sustainability assessment methodology used in the project to support the selection of the most adequate scenario is presented with a brief explanation of the procedures, criteria and indicators applied on the evaluation of each of the three sustainability pillars.     

Mechanically-biologically treated municipal solid waste as a support medium for microbial methane oxidation to mitigate landfill greenhouse emissions

The residual fraction of mechanically-biologically treated municipal solid waste (MBT residual) was studied in the laboratory to evaluate its suitability and environmental compatibility as a support medium in methane (CH(4)) oxidative biocovers for the mitigation of greenhouse gas emissions from landfills. Two MBT residuals with 5 and 12 months total (aerobic) biological stabilisation times were used in the study. MBT residual appeared to be a favourable medium for CH(4) oxidation as indicated by its area-based CH(4) oxidation rates (12.2-82.3 g CH(4) m(-2) d(-1) at 2-25 degrees C; determined in CH(4)-sparged columns). The CH(4) oxidation potential (determined in batch assays) of the MBT residuals increased during the 124 d column experiment, from <1.6 to a maximum of 104 microg CH(4) g(dw)(-1) h(-1) (dw=dry weight) at 5 degrees C and 578 microg CH(4) g(dw)(-1) h(-1) at 23 degrees C. Nitrous oxide (N(2)O) production in MBT residual (<15 microg N(2)O kg(dw)(-1) d(-1) in the CH(4) oxidative columns) was at the lower end of the range of N(2)O emissions reported for landfills and non-landfill soils, and insignificant as a greenhouse gas source. Also, anaerobic gas production (25.6 l kg(dw)(-1) during 217 d) in batch assays was low, indicating biological stability of the MBT residual. The electrical conductivities (140-250 mS m(-1)), as well as the concentrations of zinc (3.0 mg l(-1)), copper (0.5 mg l(-1)), arsenic (0.3 mg l(-1)), nickel (0.1 mg l(-1)) and lead (0.1 mg l(-1)) in MBT residual eluates from a leaching test (EN-12457-4) with a liquid/solid (L/S) ratio of 10:1, suggest a potential for leachate pollutant emissions which should be considered in plans to utilise MBT residual. In conclusion, the laboratory experiments suggest that MBT residual can be utilised as a support medium for CH(4) oxidation, even at low temperatures, to mitigate greenhouse gas emissions from landfills.     

A system dynamic modeling approach for evaluating municipal solid waste generation,landfill capacity and related cost management issues

As planning for sustainable municipal solid waste management has to address several inter-connected issues such as landfill capacity, environmental impacts and financial expenditure, it becomes increasingly necessary to understand the dynamic nature of their interactions. A system dynamics approach designed here attempts to address some of these issues by fitting a model framework for Newark urban region in the US, and running a forecast simulation. The dynamic system developed in this study incorporates the complexity of the waste generation and management process to some extent which is achieved through a combination of simpler sub-processes that are linked together to form a whole. The impact of decision options on the generation of waste in the city, on the remaining landfill capacity of the state, and on the economic cost or benefit actualized by different waste processing options are explored through this approach, providing valuable insights into the urban waste-management process.     

A feasibility study of thermal hydrolysis by-products as barrier layer materials in the final cover system for a landfill

Most sludge has historically been disposed of in landfills and by ocean dumping but, because of its heavy metal content, this will be totally banned in Korea starting in 2012, based on the London Dumping Convention. Therefore, treatment and disposal methods that are environmentally friendlily are urgently required. The recycling of sewage sludge is a good treatment method for solving sludge problems in an environmentally friendly way. In this study, physical and environmental tests were conducted to evaluate the feasibility of using the by-products of thermal hydrolysis of sewage sludge as barrier layer materials in the final cover systems for landfills. In addition, testing methods for freezing-thawing (KS F 2332) and wetting-drying (KS F 2330) cycles were conducted to assess the effects of cold and hot soil climates starting from pavement. These tests yielded positive results for alternative materials for the barrier layer in a final cover system for a landfill.     

A laboratory study on migration of K+ in a two-layer landfill liner system.

Contaminant transport through the clay liner and the underIying secondary leachate drain layer (SLDL) in landfills was studied through a laboratory test, and analysis method on the transport of K+ in a two-layer soil system. The soils used for this study were Ariake clay and the underlying layer, Shirasu soil from the Kyushu region of Japan, representing the clay liner material and SLDL material, respectively. The effective diffusion coefficients (De) of the selected target chemical species, potassium (K+) for the Ariake clay and Shirasu soil were back-calculated using a computer program, and it was found that values of De derived from this study were consistent with those previously published. The hypothesis that the mechanical dispersion process can be negligible has been proved to be reasonable based on both the observation that the predicted values fit the experimental data and the analyses of two dimensionless parameters. Parametric analysis showed the transport of K+ through the soils is controlled by advection-diffusion rather than diffusion only, whereas at low Darcy velocity (i.e. < or = 10(-9) m s(-1)), transport of K+ would be controlled by diffusion. The test results and parametric analysis may be applied in design of landfill liners and SLDLs, particularly in coastal areas.     

A multi-component two-phase flow algorithm for use in landfill processes modelling

This paper describes the finite difference algorithm that has been developed for the flow sub-model of the University of Southampton landfill degradation and transport model LDAT. The liquid and gas phase flow components are first decoupled from the solid phase of the full multi-phase, multi-component landfill process constitutive equations and are then rearranged into a format that can be applied as a calculation procedure within the framework of a three dimensional array of finite difference rectangular elements.The algorithm contains a source term which accommodates the non-flow landfill processes of degradation, gas solubility, and leachate chemical equilibrium, sub-models that have been described in White and Beaven (2013).The paper includes an illustration of the application of the flow sub-model in the context of the leachate recirculation tests carried out at the Beddington landfill project. This illustration demonstrates the ability of the sub-model to track movement in the gas phase as well as the liquid phase, and to simulate multi-directional flow patterns that are different in each of the phases.