Analysis of Biosolids Equilibrium Moisture and Drying

Provided that moisture is well managed, biosolids, or digested wastewater sludge, can be converted from an expense to a resource of renewable energy Toward this goal, the equilibrium moisture content (EMC) for biosolids was determined experimentally in the ranges of 10-84% relative humidity and 30-60 degrees C. Several well-known models were used to fit the h EMC data, including a new one that considers mixing and swelling effects on water activity. The rate of drying was measured as a function of temperature and gas velocity in a 3-inch fluidized bed. The drying rate increased with temperature and was independent of gas velocity. In all cases, the drying, rate continously decreased; no period of constant rate was observed. This indicates that the dominant resistance to drying was internal diffusion. (C) 2009 American Institute of Chemical Engineers Environ Prog, 28: 291-298, 2009