Water content dynamics in biofiltration: The role of humidity and microbial heat generation

Mass and energy balances were performed on a compost biofilter to identify the mechanisms for water content change in the compost bed material. Three mechanisms were identified: humidity fluctuations at the inlet and outlet, heat generation from microbial oxidation, and gradients in the water potential. Microbial oxidation and humidity fluctuations were the dominant mechanisms for water content changes. Time domain reflectometry was used to estimate on-line volumetric water content in the bed material. Biofiltration experiments demonstrated a moving front of temperature increase and water evaporation associated with the microbial oxidation of toluene. The localized microbial heat generation evaporated sufficient water from consecutive sections of the bed, eventually impairing degradation throughout the entire column.