Development of techniques for measuring water and fluid flow properties in solid waste in landfills.

摘要

Seven pilot-scale partitioning gas tracer tests (PGTTs) were conducted to assess its accuracy and reproducibility for measuring water in municipal solid waste landfills. Tests were conducted in the same location over a 12-month period, and measured moisture conditions ranged from possible dry waste to refuse with a moisture content of 24.7%. The final moisture content of 24.7% was in reasonable agreement with gravimetric measurements of excavated refuse, where the moisture content was 26.5 +/- 6.0CI %. Laboratory tests were used to assess the utility of the PGTT for measuring water in small pores, water sorbed to solid surfaces, and the influence of dry waste on PGTTs. These experiments indicated that when refuse surfaces are not completely solvated with water, PGTTs may produce misleading results (negative estimates) of water saturation and moisture content.;Two field-scale PGTTs were performed to evaluate the utility of the PGTT method for measuring water saturation and moisture content in a full-scale bioreactor landfill, where waste biodegradation resulted in elevated temperatures and significant landfill gas production. The average water saturation and moisture content were measured for waste volumes of approximately 20 m 3 and results compared to gravimetric measurement of moisture content made on samples collected from the landfill. In the center of the landfill, the moisture content estimated from the PGTT was (Mc = 0.26 +/- 0.03, which was nearly identical to the gravimetric measurement of waste samples taken from the same region (Mc = 0.28). PGTT estimated moisture contents in a dry area of the landfill were much smaller (Mc= 0.10 +/- 0.01) and consistent with available gravimetric measurements. Biodegradation of tracers and temporal variations in landfill gas production were minimal and did not influence the tests. These field experiments demonstrate the utility of the PGTT method for measuring water saturation and estimating moisture content in bioreactor landfills with active waste degradation and generation of landfill gases. However, use of the PGTT to estimate the in situ moisture content requires estimates of the refuse porosity, dry bulk density, and temperature, which might limit its application.;Laboratory experimental procedures were developed to obtain constitutive relations for fluid flow in refuse. Five different types of experiments were conducted for the same column without any disturbance to model waste samples: a drainage experiment, a multi step outflow experiment, measurement of total porosity, saturated hydraulic conductivity tests, and gas permeability experiments. A similar set of experiments has never been performed before on a single waste sample. From these measurements, constitutive relationships were developed with HYDRUS-1D for refuse samples that assume either a single or dual domains within the media. To simplify method development, the refuse samples consisted entirely of newspaper, which were prepared in two particle sizes and packed to compression cells to replicate typical stress conditions in landfills. The dual permeability model performed significantly better than the single porosity model in fitting the data, suggesting that a dual domain description of these refuse samples was required to describe water flow. Results also indicate that the properties of fracture domain, which characterizes the pores between refuse particles, is affected by the size of waste materials. These experiments confirmed the utility of the laboratory procedures developed for this work, and indicate that laboratory measurements are useful for characterizing the matrix domain of refuse waste samples.