R. C. Joshi

A model to estimate the methane generation rate constant in sanitary landfills using fuzzy synthetic evaluation

This paper presents a model using fuzzy synthetic evaluation to estimate the methane generation rate constant, k, for landfills. Four major parameters, precipitation, temperature, waste composition and landfill depth were used as inputs to the model. Whereas, these parameters are known to impact the methane generation, mathematical relationships between them and the methane generation rate constant required to estimate methane generation in landfills, are not known. In addition, the spatial variations of k within a landfill combined with the necessity of site-specific information to estimate its value, makes k one of the most elusive parameters in the accurate prediction of methane generation within a landfill. In this paper, a fuzzy technique was used to develop a model to predict the methane generation rate constant. The model was calibrated and verified using k values from 42 locations. Data from 10 sites were used to calibrate the model and the rest were used to verify it. The model predictions are reasonably accurate. A sensitivity analysis was also conducted to investigate the effect of uncertainty in the input parameters on the generation rate constant.

Effect of ion concentration on diffusion through clay

The applicability of an equation that suggests the effective diffusion coefficient of ions through a charged porous medium is linearly related to the square root of the concentration of ions is evaluated. Data from experiments on diffusion of NaCl and LiCI solutions through Na and Li bentonites were analyzed using the proposed equation. Plots of effective diffusion coefficient versus square root of concentration are consistent with the formulation that the effective diffusion coefficient declines linearly with the square root of concentration. The analysis also indicates that effective diffusion coefficient of an ion is dependent on the counter ion in solution as well as that at the clay exchangeable site. For solutions up to 0.07 meq/cc, the results further indicate that it is feasible to combine all the porous medium characteristics into a single factor referred to as the apparent tortuosity factor.