| 摘 要： |
Air-immobile regions in composting piles obstruct O-2 mass transport and exacerbate the formation and emission of harmful off-gases. However, effective methods for measuring the parameters of these air-immobile regions are lacking. With quartz sand piles, this study first adjusted the circumstances of a gas tracer test (gas tracer, its injection volume, and chamber type) using the two-region model (TRM). The effects of beta (proportional coefficient of gas in the air-mobile region) and omega (mass exchange coefficient) on the breakthrough curves (BTCs) of the gases were then explored. Finally, an inverse calculation method was used to measure the feature parameters of air-immobile regions in two composting piles (temperature-increasing and thermophilic phases) and estimate the O-2 concentrations in different composting piles (50, 100, 200 cm whole height; layers of 50, 100, 200 cm height in a 200-cm high pile). The results showed that the optimal conditions were achieved when 100 mL helium (He) as the gas tracer and a cylinder with a height/diameter ratio of 3 as the chamber were used. With the simulating composting piles, increasing beta or omega slowed breakthrough and decreased peak concentration in BTCs of a gas tracer. Tracer-inverse calculation protocol can be used to efficiently estimate the volume ratios of air-immobile regions (phi) and first-order mass transfer coefficient (alpha), with the values of 39%/46% and 0.001/0.006 min(-1) in the composting piles during temperature-increasing /thermophilic phase. The TRM also predicted the O-2 con-centration in the off-gas or air-mobile/immobile regions of the temperature-increasing-phase composting piles. |
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