Verification of exponential distribution of arrival and service times at municipal solid waste facilities

Vehicle queuing at municipal solid waste (MSW) facilities causes economic and environmental damage. In the United States, typical MSW receiving facilities (transfer, recycling, energy recovery, and landfill) have three queues: one at the entrance weighing station, one at the waste tipping location, and one at the exit weighing station. A common method of determining queue behavior relies on equations that assume exponentially distributed arrival and service times, but there has not been a comprehensive study to determine whether this assumption is valid for a variety of MSW facilities and conditions. In this study, data were gathered from two transfer stations, two energy recovery plants, and one transfer/landfill facility. Among the five facilities there was a variety of queuing styles. The data were plotted as an inverse exponential relationship and linearized. The linearized plots were regressed and R ² values were calculated. It was determined that the negative exponential relationship can be used to describe arrival times at all three queues and service times at weighing queues. The queuing equations are therefore theoretically supported for use at entering and exiting weighing queues and moderately theoretically supported for use at tipping queues.     

Approach for the use of MSW settlement predictions in the assessment of landfill capacity based on reliability analysis

In the analysis and design of municipal solid waste (MSW) landfills, there are many uncertainties associated with the properties of MSW during and after MSW placement. Several studies are performed involving different laboratory and field tests to understand the complex behavior and properties of MSW, and based on these studies, different models are proposed for the analysis of time dependent settlement response of MSW. For the analysis of MSW settlement, it is very important to account for the variability of model parameters that reflect different processes such as primary compression under loading, mechanical creep and biodegradation. In this paper, regression equations based on response surface method (RSM) are used to represent the complex behavior of MSW using a newly developed constitutive model. An approach to assess landfill capacities and develop landfill closure plans based on prediction of landfill settlements is proposed. The variability associated with model parameters relating to primary compression, mechanical creep and biodegradation are used to examine their influence on MSW settlement using reliability analysis framework and influence of various parameters on the settlement of MSW are estimated through sensitivity analysis.     

Municipal solid waste management in Africa: strategies and livelihoods in Yaoundé, Cameroon

This paper provides an overview of the state of municipal solid waste (MSW) management in the capital of Cameroon, Yaoundé, and suggests some possible solutions for its improvement. The institutional, financial, and physical aspects of MSW management, as well as the livelihoods of the population, were analyzed. Our study revealed that distances and lack of infrastructure have a major impact on waste collection. Garbage bins are systematically mentioned as the primary infrastructure needed by the population in all quarters, whether it be a high or low standard community. The construction of transfer stations and the installation of garbage bins are suggested as a solution to reduce distances between households and garbage bins, thus improving waste collection vehicle accessibility. Transfer stations and garbage bins would enable the official waste collection company to expand its range of services and significantly improve waste collection rates. Several transfer stations have already been set up by non-governmental organizations (NGOs) and community-based organizations (CBOs), but they require technical, institutional and funding support. Research is needed on the quality and safety of community-made compost, as well as on soil fertility in urban and peri-urban areas. Most of the stakeholders, municipalities, the official waste collection company and households acknowledge the need for better monitoring and regulation of MSW management. The urban community of Yaoundé also needs to maintain its support of MSW management and promote the sustainability of NGOs and CBOs operating in underserved areas not yet covered by adequate infrastructures. A major opportunity for implementation of such waste policy is the heavily indebted poor countries (HIPC) program dedicated to urban planning and good governance.     

Optimization of municipal solid waste management in Port Said - Egypt

Optimization of solid waste management systems using operational research methodologies has not yet been applied in any Egyptian governorate. In this paper, a proposed model for a municipal solid waste management system in Port Said, Egypt is presented. It includes the use of the concept of collection stations, which have not yet been used in Egypt. Mixed integer programming is used to model the proposed system and its solution is performed using MPL software V4.2. The results show that the best model would include 27 collection stations of 15-ton daily capacity and 2 collection stations of 10 ton daily capacity. Any transfer of waste between the collection station and the landfill should not occur. Moreover, the flow of the district waste should not be confined to the district collection stations. The cost of the objective function for this solution is 10,122 LE/day (equivalent to 1716 US dollars). After further calculations, the profit generated by the proposed model is 49,655.8 LE/day (equivalent to 8418.23 US dollars).     

A critique of risk modeling and risk assessment of municipal landfills based on U.S. Environmental Protection Agency techniques

Environmental risks are a growing public concern in America. The threat of contaminated drinking water from municipal solid waste (MSW) landfills is receiving increased attention from citizens and from the United States Environmental Protection Agency (USEPA). Examination of USEPA data collected from MSW landfills reveals approximate risks posed by these landfills. USEPA research suggests that 60% of MSW landfills present less than a 1 in 10 billion risk of cancer incidence. Another 6% pose risks less than 1 in a billion, while 17% present risks less than 1 in a million. This study addresses the USEPA risk assessment techniques and models for estimating MSW landfill risks. USEPA data for toxic constituents of landfill leachate are also analysed in order to better understand the difficulties encountered in estimating landfill risks. The study also presents a brief discussion of public perceptions of risk as they relate to communicating the USEPA landfill model results to those who might be affected.     

Optimization for MSW logistics of new Xicheng and new Dongcheng districts in Beijing based on maximum capacity of transfer stations

The new Xicheng and new Dongcheng districts of Beijing in 2010 were chosen as the research object. Based on the analysis of the current municipal solid waste (MSW) logistics system, the transfer station’s processing capacity and the terminal treatment facilities' conditions of the two new districts and other districts, a MSW logistics system was built using geographic information system (GIS) and analytic network process methods considering transregional treatment. The new logistics (MSW from new Xicheng was collected for Majialou. MSW from old Dongcheng and Xuanwu was collected for Datun and Xiaowuji, respectively) proved to be an improvement with a 10 % less collection fee, 111 % output–input ratio after transfer station (include) and 0.8:4.6:4.6 I:C:L (incineration:compost:landfill). After Nangong, Gaoantun II and Asuwei incineration are established, the output–input ratio of the new logistics will reach 114 %, and I:C:L will reach 3.6:4.2:2.2 which is environmentally friendly and nearer to the 4:3:3 Beijing government target. For a full load of every transfer station, the complement schemes were also presented and contrasted based on GIS analysis. The results have great theoretical and practical significance in transregional treatment and improving resource management level of MSW.     

Assessment of waste settlement models based on the long-term settlement data measured at a multi-stage MSW landfill in Korea

Journal of Material Cycles and Waste Management - An assessment of municipal solid waste (MSW) settlement models was carried out based on analyses of field-scale data measured at landfill #1 of the...     

Constitutive model for municipal solid waste incorporating mechanical creep and biodegradation-induced compression

A constitutive model is proposed to describe the stress–strain behavior of municipal solid waste (MSW) under loading using the critical state soil mechanics framework. The modified cam clay model is extended to incorporate the effects of mechanical creep and time dependent biodegradation to calculate total compression under loading. Model parameters are evaluated based on one-dimensional compression and triaxial consolidated undrained test series conducted on three types of MSW: (a) fresh MSW obtained from working phase of a landfill, (b) landfilled waste retrieved from a landfill after 1.5 years of degradation, and (c) synthetic MSW with controlled composition. The model captures the stress–strain and pore water pressure response of these three types of MSW adequately. The model is useful for assessing the deformation and stability of landfills and any post-closure development structures located on landfills.     

An attempt to perform water balance in a Brazilian municipal solid waste landfill

This paper presents an attempt to model the water balance in the metropolitan center landfill (MCL) in Salvador, Brazil. Aspects such as the municipal solid waste (MSW) initial water content, mass loss due to decomposition, MSW liquid expelling due to compression and those related to weather conditions, such as the amount of rainfall and evaporation are considered. Superficial flow and infiltration were modeled considering the waste and the hydraulic characteristics (permeability and soil-water retention curves) of the cover layer and simplified uni-dimensional empirical models. In order to validate the modeling procedure, data from one cell at the landfill were used. Monthly waste entry, volume of collected leachate and leachate level inside the cell were monitored. Water balance equations and the compressibility of the MSW were used to calculate the amount of leachate stored in the cell and the corresponding leachate level. Measured and calculated values of the leachate level inside the cell were similar and the model was able to capture the main trends of the water balance behavior during the cell operational period.     

Prediction of syngas quality for two-stage gasification of selected waste feedstocks

This paper compares the syngas produced from methane with the syngas obtained from the gasification, in a two-stage reactor, of various waste feedstocks. The syngas composition and the gasification conditions were simulated using a simple thermodynamic model. The waste feedstocks considered are: landfill gas, waste oil, municipal solid waste (MSW) typical of a low-income country, the same MSW blended with landfill gas, refuse derived fuel (RDF) made from the same MSW, the same RDF blended with waste oil and a MSW typical of a high-income country. Energy content, the sum of H2 and CO gas percentages, and the ratio of H2 to CO are considered as measures of syngas quality. The simulation shows that landfill gas gives the best results in terms of both H2+CO and H2/CO, and that the MSW of low-income countries can be expected to provide inferior syngas on all three quality measures. Co-gasification of the MSW from low-income countries with landfill gas, and the mixture of waste oil with RDF from low-income MSW are considered as options to improve gas quality.     

Development of a purpose built landfill system for the control of methane emissions from municipal solid waste

In the present paper, a new system of purpose built landfill (PBLF) has been proposed for the control of methane emissions from municipal solid waste (MSW), by considering all favourable conditions for improved methane generation in tropical climates. Based on certain theoretical considerations multivariate functional models (MFMs) are developed to estimate methane mitigation and energy generating potential of the proposed system. Comparison was made between the existing waste management system and proposed PBLF system. It has been found that the proposed methodology not only controlled methane emissions to the atmosphere but also could yield considerable energy in terms of landfill gas (LFG). Economic feasibility of the proposed system has been tested by comparing unit cost of waste disposal in conventional as well as PBLF systems. In a case study of MSW management in Mumbai (INDIA), it was found that the unit cost of waste disposal with PBLF system is seven times lesser than that of the conventional waste management system. The proposed system showed promising energy generation potential with production of methane worth of Rs. 244 millions/y ($5.2 million/y). Thus, the new waste management methodology could give an adaptable solution for the conflict between development, environmental degradation and natural resources depletion.     

A design chart for estimation of horizontal displacement in municipal landfills

This paper describes the development of a design chart for the estimation of maximum horizontal displacement within a municipal landfill using the height and the side slope of the landfill. The design chart is based on the results of a finite element parametric study in which the behaviour of the municipal solid waste (MSW) was modeled using a non-linear elastic hyperbolic model. The model input parameters, i.e. non-linear stiffness, shear strength and unit weight of MSW, were obtained from laboratory testing data and an extensive stochastic numerical modelling exercise. Non-linear variations of unit weight as well as Young’s modulus of MSW with depth were incorporated in the finite element analyses. The validity of the design chart was assessed using field monitoring results from a large landfill located in Ontario, Canada.     

Research on solid waste management system: to improve existing situation in Corlu Town of Turkey

Over the past decades, uncontrolled population growth and rapid urbanization and industrialization have resulted in environmental problems in Corlu Town, Turkey. One of the most important problems is solid waste due to inadequate management practices. Nowadays, increasing public awareness of the environment compels local authorities to define and to adopt new solutions for waste management. This paper presents a general overview of current solid waste management practices in Corlu Town and principles of the recommended municipal solid waste (MSW) management system. In Corlu, 170 tonnes of municipal solid waste are generated each day, or 1.150 kg per capita per day. Approximately one-half of the municipal solid waste generated is organic material and 30% of the MSW consists of recyclable materials. The recommended system deals with maximizing recycling and minimizing landfilling of municipal solid waste, and consists of separation at source, collection, sorting, recycling, composting and sanitary landfilling. This study also analyzed the recommended system with respect to feasibility and economics. To evaluate whether the suggested system is cost effective or not, the operating cost of the recommended system and market prices of recyclable materials were compared, and the results show that the recommended system will reduce required landfill volume up to 27% of compared to the present situation. The profit of the recommended system is estimated to be about 80 million US dollars.     

Logistical management and private sector involvement in reducing the cost of municipal solid waste collection service in the Tubas area of the West Bank

This paper addresses the problems of the municipal solid waste (MSW) collection system in the Tubas district of Palestine. More specifically, it addresses the often-voiced concerns pertaining to low efficiency as well as environmental problems. This was carried out through a systematic methodological approach. The paper illustrates how a private company applied a logistical management strategy, by rescheduling the MSW collection system, reallocating street solid waste containers and minimizing vehicle routing. The way in which the MSW collection timetable was rescheduled decreased the operating expenses and thus reduced MSW collection costs. All data needed to reschedule the collection timetable and optimize vehicle routing were based on actual field measurements. The new MSW collection timetable introduced by a private company was monitored for a period of a month. The new system resulted in an improvement in the MSW collection system by reducing the collection cost to a level that is socially acceptable (US dollars 3.75/family/month), as well as economically and environmentally sound.     

An inexact multi-objective dynamic model and its application in China for the management of municipal solid waste

With the development of science and technology, solid waste management has become a serious environmental problem for most communities all over the world. This paper presents a multi-objective optimization model for the management of municipal solid waste (MSW) via an uncertainty approach. In this model, the system cost of solid waste management and the environmental impact are considered as the main objectives, and some necessary constraints based on the characteristics of China are included; additionally, Pollution loss theory is applied to evaluate the environmental impact.This model is applied to the City of Fo Shan, China. Compared with the primary project of Fo Shan, which is provided by the government, the results of the optimization procedure show that the overall system cost could be reduced by $1–2.4/ton, i.e., $3.7 million/yr. The model presented in this paper was proven to be an effective response to the multi-objective solid waste management problem, and provides a new technique to optimize MSW management and operation. Why is the optimization result better? By analyzing the modelling with respect to function, constraints, and results, we conclude that the profit would be augmented due to the amount of the waste that would be treated by recycling technology, which would increase rapidly during the planning time; thus, the total system cost could be reduced accordingly.     

The role played by environmental factors in the integration of a transfer station in a municipal solid waste management system

Transfer stations are an integral part of present-day municipal solid waste management systems. The main criteria used to decide on the location of a transfer station has traditionally been the minimization of transport costs, since it is cheaper to transport great amounts of waste over long distances in large loads than in small ones. In this study, we are going to consider the environmental factor in order to compare the feasibility of using a transfer station integrated within a waste management system. Applying the Life Cycle Assessment technique will enable us to obtain an objective parameter that quantifies the environmental impact of transportation and of operating a transfer station. Taking the current rates of solid wastes generation in the Plana region of Castellón (Spain) as our starting point, in this study we compare the environmental costs involved in the process of taking municipal wastes directly to the nearest waste treatment facility, with those involved in a waste management system integrating a transfer station. Comparing these two cases, an average reduction of 16.8% in the environmental impact can be obtained when a transfer station is incorporated in the waste management system.     

Parametric study of MSW landfill settlement model

A newly developed and validated constitutive model that accounts for primary compression and time-dependent mechanical creep and biodegradation is used for parametric study to investigate the effects of model parameters on the predicted settlement of municipal solid waste (MSW) with time. The model enables the prediction of stress strain response and yield surfaces for three components of settlement: primary compression, mechanical creep, and biodegradation. The MSW parameters investigated include compression index, coefficient of earth pressure at-rest, overconsolidation ratio, and biodegradation parameters of MSW. A comparison of the predicted settlements for typical MSW landfill conditions showed significant differences in time-settlement response depending on the selected model input parameters. The effect of lift thickness of MSW on predicted settlement is also investigated. Overall, the study shows that the variation in the model parameters can lead to significantly different results; therefore, the model parameter values should be carefully selected to predict landfill settlements accurately. It is shown that the proposed model captures the time settlement response which is in general agreement with the results obtained from the other two reported models having similar features.     

Perpetual landfilling through aeration of the waste mass; lessons from test cells in Georgia (USA).

Municipal solid waste (MSW) landfills worldwide are experiencing the consequences of conventional landfilling techniques, whereby anaerobic conditions are created within the landfilled waste. Under anaerobic conditions within a landfill site slow stabilization of the waste mass occurs, producing methane, (an explosive 'green house' gas) and leachate (which can pollute groundwater) over long periods of time. As a potential solution, it was demonstrated that the aerobic degradation of MSW within a landfill can significantly increase the rate of waste decomposition and settlement, decrease the methane production and leachate leaving the system, and potentially increase the operational life of the site. Readily integrated into the existing landfill infrastructure, this approach can safely and cost-effectively convert a MSW landfill from anaerobic to aerobic degradation processes, thereby effectively composting much of the organic portions (one of the potentially polluting elements in a conventional landfill site) of the waste. This paper summarizes the successful results of two separate aerobic landfill projects located in Georgia (USA) and discusses the potential economic and environmental impacts to worldwide solid waste management practices.     

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.     

Mechanical behavior of typical hazardous waste and its influence on landfill stability during operation

The stability of hazardous waste (HW) landfill is a major security risk to the landfill environmental safety. The mechanical behavior of waste controls many aspects of landfill design and operation, including stability and settlement issues and the integrity of geosynthetic and liner components. This study presents the results of a laboratory experiment to learn the mechanical properties of HW collected from the Hangzhou HW landfill. Measured mechanical behavior was compared with results for municipal solid waste (MSW) to assess their discrepancies. The particle size of HW was analyzed by the sieving and hydrometer methods. Because HW comes primarily from industrial plants in the form of sludge or slag, their particle sizes are generally smaller than those of MSW. This study indicates that the shear strength parameters of HW are more sensitive to the methods of testing and calculation than those of MSW. Numerical simulations demonstrate that the safety factor of a landfill is affected by the mechanical properties of HW, especially cohesion and friction angle. Because of the lower particle size and wider compression ratio, compared to MSW, an HW landfill should be taken more care in its operational procedures so as to increase its stability.