Abstract
Measurements of landfill gas emissions from a single site frequently show large variations in chemical composition and magnitude, often on the same time scale as the monitoring interval. These changes are generally ascribed to faulty instrumentation or mysterious alterations in the internal biological processes. This paper demonstrates a simple deterministic physical mechanism able to explain many of these changes, and discusses the implications this has for monitoring strategies. The main conclusions are that the total rate of gas venting depends linearly on the rate of change of the atmospheric pressure, with the stoichiometric variations depending additionally on the physical characteristics and moisture distribution within the site.
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Abbreviations
- k :
-
decay factor for gas evolution/solution rate, s−1
- q i :
-
mass rate at which molecules of gas i are evolved, kg m−3 s−1
- t :
-
time, s
- u :
-
Darcy water velocity, m s−1
- v :
-
net Darcy gas velocity, m s−1
- z :
-
depth co-ordinate, positive downwards, m
- C j :
-
dissolved concentration of solute i, kg m−3
- D b ij :
-
binary diffusion coefficient of gases i and j in free space, m2 s−1
- D ij :
-
modified binary diffusion/dispersion coefficient of gases i and j, m2 s−1
- E i :
-
combined diffusion and dispersion coefficient of gas i, m2 s−1
- E wi :
-
combined diffusion and dispersion coefficient of solute i, m2 s−1
- H :
-
Henry's constant, kg m−3 Pa−1
- K:
-
permeability of site to gas flow, m2 s−1 Pa−1
- K v :
-
vertical permeability of site to gas flow, m2 s−1 Pa−1
- P :
-
total pressure of gas, Pa
- P i :
-
partial pressure of ith gas, Pa
- Q :
-
total rate of gas evolution, kg m−3 s−1
- S i :
-
rate at which molecules of gas i are created by biochemical activity, kg m−3 s−1
- T 1/2 :
-
half life for gas evolution/solution, s
- V :
-
an arbitrary volume within the landfill
- ∂V :
-
surface surrounding volume V
- λ i :
-
conversion factors from gas densities to pressures, Pa m3 kg−1
- ϑ :
-
void fraction occupied by gas
- θ :
-
void fraction occupied by water
- ρ i :
-
density of ith gas, kg m−3
- τ i, τw :
-
tortuosities for diffusion in gas and water phases
- Ω:
-
rate of gas evolution/solution, kg m−3 s−1
References
Bogner, J., Vogt, M., Moore, C., and Gartman, D.: 1987, Gas pressure and concentration gradients at the top of a landfill, Proceedings GRCDA 10th International Landfill Gas Symposium.
Rettenberger, G.: 1990, Gas migration: measurement and monitoring, Proceedings Landfill Gas: Energy and Environment '90, ISBN 0-7058-1628-1.
Young, A.: 1990, Volumetric Change in Landfill Gas Flux in Response to Variations in Atmospheric Pressure, Waste Management & Research 8, pp. 379–385.
Chapman S. and Cowling, T. G.: 1970, The Mathematical Theory of Non-Uniform Gases, 3rd edition, Cambridge University Press, pp. 343–357.
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Young, A. The effects of fluctuations in atmospheric pressure on landfill gas migration and composition. Water Air Soil Pollut 64, 601–616 (1992). https://doi.org/10.1007/BF00483369
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DOI: https://doi.org/10.1007/BF00483369