Gas phase dispersion in compost as a function of differentwater contents and air flow rates

• Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as afunction of gas flow velocity and compost volumetric water content using oxygen and nitrogenas tracer gases. The compost was chosen because it has a very wide water content range andbecause it represents a wide range of porousmedia, including soils and biofilter media. Columnbreakthrough curves for oxygen and nitrogen were measured at relatively low pore gasvelocities, corresponding to those observed in for instance soil vapor extraction systems orbiofilters for air cleaning at biogas plants or composting facilities. Total gas mechanicaldispersion–molecular diffusion coefficients were fitted from the breakthrough curves using aone-dimensional numerical solution to the advection–dispersion equation and used todetermine gas dispersivities at different volumetric gas contents. The results showed that gasmechanical dispersion dominated over molecular diffusion with mechanical dispersion for allwater contents and pore gas velocities investigated. Importance of mechanical dispersionincreased with increasing pore gas velocity and compost water content. The results furthershowed that gas dispersivity was relatively constant at high values of compost gas-filledporosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity.Results finally showed that measurement uncertainty in gas dispersivity is generally highest atlow values of pore gas velocity.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Oceanografi, hydrologi och vattenresurser (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Oceanography, Hydrology and Water Resources (hsv//eng)

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