Abstract

Coupling of biogeochemical processes occurs between different waste components and waste layers during decomposition of wastes materials deposited in landfills by mechanisms similar to those occurring in marine sediments (i.e., sediment batteries). In landfills, moisture serves as a medium for transfer of electrons and protons under anaerobic conditions for decomposition reactions to proceed spontaneously, although some reactions occur very slowly. However, the role of moisture in landfills in view of pore sizes and pore size distributions, time dependent changes in pore volumes, heterogeneity of waste layers, and associated impacts on moisture retention and transport characteristics in landfills are not well understood. The moisture transport models developed for granular materials (e.g., soils) are not appropriate to describe the conditions at landfills due compressible and dynamic conditions in landfills. During waste decomposition processes, absorbed water and water of hydration can be transformed to free water and/or become mobilized as liquid or vapor, creating a medium for transfer of electrons and protons between waste components and waste layers. The characteristics of different municipal waste components were compiled and analyzed for pore size, surface energy, and moisture retention and penetration for electron-proton transfer for continuance of decomposition reactions in landfills over time. Categorization of pore sizes appropriate for waste components and a representative water retention curve for conditions in landfills were developed to clarify the terminology and highlight the differences between the landfill conditions and granular materials (e.g., soils) for use of appropriate terminologies. Water saturation profile and water mobility were analyzed by considering water as a transfer medium for carrying electrons and protons for sustaining long-term decomposition reactions.

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