Mechanics of compressibility and strength of solid waste in bioreactor landfills

Bioreactor landfills are operated to enhance refuse decomposition, gas production, and waste stabilization. A major aspect of bioreactor landfill operation is the recirculation of collected leachate back through the refuse mass. The overall objective of the research was to develop an understanding of change in refuse compressibility and strength during accelerated waste decomposition in landfills operated as bioreactors. An experimental program was performed to provide data on parameters describing MSW compressibility and strength properties as a function of the state of decomposition, gas generation, and physical characteristics of waste particles. Refuse samples were generated in laboratory-scale reactors that were operated under conditions designed to simulate decomposition in both traditional and bioreactor landfills. The reactors were destructively sampled to obtain refuse at various states of decomposition, based on the reactor's methane production rate curve. In addition, the state of decomposition was quantified by measurement of the concentrations of cellulose (C), hemicellulose (H), and lignin (L). Reactors were sampled to obtain refuse in the anaerobic acid phase, the accelerated methane production phase, and early and late in the decelerated methane production phase.; Test results indicated shredding of MSW affects mainly initial compression. The shear strength is affected by shredding as the light-weight reinforcing materials are shredded into smaller pieces during specimen preparation. The coefficient of primary compression (Cc) for all samples showed an increasing trend with decreasing (C+H)/L. The creep index (C_α) is independent of the state of waste decomposition and the biological index yielded the highest values (C_β = 0.19) when samples were actively decomposing and had substantial methane potential remaining.; Testing results indicated measured shearing angle for bioreactor samples decreased from 32° to 24° as (C+H)/L ratio decreased from 1.29 to 0.25. The predicted shear behavior by the developed model for shear stress displacement was matched with experimental results.; Settlement prediction using a developed model considered all the aspects of settlement. Seven case studies show that the model predicts landfill settlement well including the biological decomposition component.