Numerical modeling of gas and heat generation and transport: I. model formulation

A mathematical model for the generation and transport of gas and heat in a sanitary landfill was developed based on earlier work on the Mountain View Controlled Landfill Project (MVCLP) in California, U.S.A. The present model incorporates biokinetic model equations describing the dynamics of the microbial landfill ecosystem into multi-layer, time-dependent transport and generation of gas and heat models. It is based on the fundamental principles governing the physical, chemical and microbiological processes in a porous media context such as a sanitary landfill. The model includes biochemical and temperature feedback loops to simulate the effects of their corresponding parameters on microbiological processes. The resulting integrated biokinetic, gas and heat generation and transport model was used to simulate field data from the MVCLP and to assess the sensitivity of model results to biological parameters. The model can be used to predict the rate and total production of methane in a landfill. The present work is presented in a series of three papers: (I) model formulation; (II) model application; and (III) sensitivity analysis*

Estimating and enhancing methane yield from municipal solid waste

Methane gas is an energy source that can be produced from the decomposition of organic materials in municipal solid waste landfills. The feasibility of exploiting this source of energy is continually increasing due to continuing trends in population increase and urbanization resulting in significant increases in solid waste production and potential methane generation. Indeed, during the last decade, there has been considerable growth in the number of landfill gas recovery and utilization systems. This paper describes estimation methods used in assessing methane yield and generation rates from municipal solid waste landfills. Parameters affecting methane generation rates and models used to predict these rates are described. The effect of controlling the refuse bacterial content as a management practice to enhance methane yield was evaluated using a gas generation-microbial growth model that is based on the sequential degradation of organic materials in anaerobic systems

Modeling leachate generation and transport in solid waste landfills

Numerous mathematical models have been developed to simulate processes governing leachate occurrence and behaviour in landfills. The emphasis of these models have generally been on estimating leachate quantity and quality in order to control its associated environmental impacts, particularly on ground and surface water pollution, enhance methanogenesis and landfill stabilization, and provide guidance in the design of leachate control, recirculation and collection systems. These models have been successful to a limited extent, more in estimating leachate quantity than its composition, because of inherent uncertainties associated with estimating model parameters that can adequately describe the complex biological, chemical, and physical processes in landfills. They become increasingly useful as more field data are obtained and used for calibration and validation purposes. This paper presents a review of mathematical models designed to simulate leachate generation and transport in municipal solid waste landfills. The paper also describes future needs and potential improvements to current modelling techniques

Numerical modeling of gas and heat generation and transport: II. model application

A mathematical model for the generation and transport of gas and heat in a sanitary landfill was developed based on earlier work on the Mountain View Controlled Landfill Project (MVCLP) in California, U.S.A. The present model incorporates biokinetic model equations describing the dynamics of the microbial landfill ecosystem into multi-layer, time-dependent transport and generation of gas and heat models. It is based on the fundamental principles governing the physical, chemical and microbiological processes in a porous media context such as a sanitary landfill. The model includes biochemical and temperature feedback loops to simulate the effects of their corresponding parameters on microbiological processes. The resulting integrated biokinetic, gas and heat generation and transport model was used to simulate field data from the MVCLP and to assess the sensitivity of model results to biological parameters. The model can be used to predict the rate and total production of methane in a landfill. The present work is presented in a series of three papers: (I) model formulation; (II) model application; and (III) sensitivity analysis*

Temperature effects in modeling solid waste biodegradation

Microbial growth models are often used to evaluate anaerobic biodegradation processes and estimate gas generation rates from solid waste decomposition in sanitary landfills. Temperature effects on anaerobic processes have been commonly evaluated in anaerobic digestion studies by deriving mathematical expressions relating media temperature to biokinetic parameters of microbial growth models. Such expressions have not been derived or are rarely used in estimating gas generation rates from solid waste landfills. The first part of this paper presents a review of gas generation-microbial growth modeling techniques applied in simulating biodegradation and gas generation processes in solid waste landfills. The review includes a description of solid waste hydrolysis with temperature effects on hydrolysis rates and biokinetic parameters. The second part of the paper describes the incorporation of kinetic expressions into a gas generation-microbial growth model. Model simulation results were in good agreement with data from a landfill field test. The model indicated that hydrolysis rates of waste constituents were the rate limiting step in the methanogenic process. Temperature had a greater effect on the modeled system at the beginning of the simulation. At later stages, steady state conditions prevail and temperature effects were minimal. The model can be used to estimate methane generation rates from solid waste landfills and more importantly, identify control parameters in a landfill environment

A numerical model for methane production in managed sanitary landfills

A mathematical model for the production and transport of biogenic gases in a landfill is developed based on earlier work on the Mountain View Landfill Project in California. The present model incorporates biokinetic model equations for the microbial landfill ecosystems dynamics in a multi-layer, time-dependent gas flow and production model. It is based on first principles of the physics, chemistry, and microbiological processes controlling the production and transport of biogenic gases in a porous media context such as a landfill. The model includes chemical/biokinetic feedback loops for chemical parameter influence on microbiological rate processes. The resulting integrated biokinetic/gas transport model is based on the first principles governing the biokinetics of municipal landfill environment, and the physics of gas-migration. The model was calibrated and verified using approximately 4 years of methane production data from the Mountain View Controlled Landfill Project. Hydrolysis rate appears to be the most sensitive parameter controlling gas generation production. The model can be used to predict the rate and total production of methane in a landfill. <br/