A comparison of isothermal with nonisothermal drying kinetics of municipal sewage sludge

Abstract

Thermal drying behavior of the municipal sewage sludge in nitrogen atmosphere was explored using a thermal analysis technique under isothermal and nonisothermal drying conditions. The Midilli model, ${\text{MR}} = \exp ( - kt^{\text{n}} ) + bt$, was the best suitable for predicting both the isothermal and nonisothermal drying behavior of the sewage sludge with the highest R ². The isothermal drying apparent activation energies of the first falling rate period and the second falling rate period were 18.03 and 11.87 kJ mol⁻¹, respectively. The nonisothermal drying apparent activation energies of sewage sludge were from 33.61 to 47.37 kJ mol⁻¹ in the first falling rate period and from 20.47 to 33.43 kJ mol⁻¹ in the second falling rate period, respectively. In two falling rate periods, the dominant mechanism functions for the isothermal drying were identical, $- \ln (1 - \alpha )$. The dominant mechanism functions for the first falling rate period and the second falling rate period in the nonisothermal drying were described by $[ - \ln (1 - \alpha )]^{1/2}$ and $[ - \ln (1 - \alpha )]^{1/3}$, respectively.