Quantifying capture efficiency of gas collection wells with gas tracers.

A new in situ method for directly measuring the gas collection efficiency in the region around a gas extraction well was developed. Thirteen tests were conducted by injecting a small volume of gas tracer sequentially at different locations in the landfill cell, and the gas tracer mass collected from each test was used to assess the collection efficiency at each injection point. For 11 tests the gas collection was excellent, always exceeding 70% with seven tests showing a collection efficiency exceeding 90%.

Performance evaluation of an anaerobic/aerobic landfill-based digester using yard waste for energy and compost production.

The objective of this study was to evaluate a new alternative for yard waste management by constructing, operating and monitoring a landfill-based two-stage batch digester (anaerobic/aerobic) with the recovery of energy and compost. The system was initially operated under anaerobic conditions for 366 days, after which the yard waste was aerated for an additional 191 days. Off gas generated from the aerobic stage was treated by biofilters.

Mitigating methane emissions and air intrusion in heterogeneous landfills with a high permeability layer.

Spatially variable refuse gas permeability and landfill gas (LFG) generation rate, cracking of the soil cover, and reduced refuse gas permeability because of liquid addition can all affect CH(4) collection efficiency when intermediate landfill covers are installed. A new gas collection system that includes a near-surface high permeability layer beneath the landfill cover was evaluated for enhancing capture of LFG and mitigating CH(4) emissions. Simulations of gas transport in two-dimensional domains demonstrated that the permeable layer reduces CH(4) emissions up to a factor of 2 for particular spatially variable gas permeability fields.

Quantifying factors limiting aerobic degradation during aerobic bioreactor landfilling.

A bioreactor landfill cell at Yolo County, California was operated aerobically for six months to quantify the extent of aerobic degradation and mechanisms limiting aerobic activity during air injection and liquid addition. The portion of the solid waste degraded anaerobically was estimated and tracked through time. From an analysis of in situ aerobic respiration and gas tracer data, it was found that a large fraction of the gas-filled pore space was in immobile zones where it was difficult to maintain aerobic conditions, even at relatively moderate landfill cell-average moisture contents of 33-36%.

An empirical method to estimate the viscosity of mineral oil by means of ultrasonic attenuation.

This paper presents an empirical method for measuring the viscosity of mineral oil. In a built-in pipeline application, conventional ultrasonic methods using shear reflectance or rheological and acoustical phenomena may fail because of attenuated shear wave propagation and an unpredictable spreading loss caused by protective housings and comparable main flows. The empirical method utilizing longitudinal waves eliminates the unknown spreading loss from attenuation measurements on the object fluid by removing the normalized spreading loss per focal length with the measurement of a reference fluid of a known acoustic absorption coefficient.