Dynamic Simulation of Landfill Waste Stabilization

A system dynamics model is developed and tested to determine the significant processes and appropriate level of detail required to capture dynamic behavior important in managing biodegradation in landfills. Uniform, spherical, solid waste particles are assumed to hydrolyze from the outer surface to produce simple sugars; fermentation, acetogenesis, and methanogenesis produce methane and carbon dioxide as end products. Representative reactions, sufficient to carry all hydrolyzed small chain carbon molecules to stabilization, are used for stoichiometric relationships. Microbial populations consume their respective substrates according to classical Monod kinetics. Results of simulation experiments suggest that hydrogen inhibition of fermentation and acetogenesis is critical to the empirically observed time course of landfill gas generation. In addition, an uninhibited anaerobic pathway producing CO2 without the production of H2 is required to produce the large CO2 peak often seen early in the stabilization process. Further simulation experiments suggest appropriate model refinement that allows efficient exploration of management strategies to enhance landfill stabilization. For example, forced ventilation during any phase of degradation can be shown to decrease efficiency or inhibit overall degradation.