Resistance to forced airflow through layers of composting organic material

•The pressure gradient may be represented by the Shedd, Hukill & Ives and Hunter models.•The Shedd method was statistically considered that which best represented the studied phenomenon.•The static pressure drop of airflow increased as a power of thickness of the material layer.•The composting process contributed to a reduced pressure gradient of airflow.•Sugarcane bagasse caused the greater pressure drop of airflow passing through the coffee husks.

The objective of this study was to adjust equations to estimate the static pressure gradient of airflow through layers of organic residues submitted to two stages of biochemical degradation, and to evaluate the static pressure drop of airflow thought the material layer. Measurements of static pressure drop in the layers of sugarcane bagasse and coffee husks mixed with poultry litter on day 0 and after 30 days of composting were performed using a prototype with specific airflow rates ranging from 0.02 to 0.13 m3 s−1 m−2. Static pressure gradient and specific airflow rate data were properly fit to the Shedd, Hukill & Ives and Ergun models, which may be used to predict the static pressure gradient of air to be blown through the organic residue layers. However, the Shedd model was that which best represented the phenomenon studied. The static pressure drop of airflow increased as a power of the material layer thickness and showed tendency for decreasing with the biochemical degradation time of the organic material.