Comparison Between Two Solar Drying Techniques of Sewage Sludge: Draining Solar Drying and Drying Bed

Abstract

A comparative study to the performances of the drying bed and the draining greenhouse was made in summer and winter. During each season, the first experience was conducted in the drying bed. The two other experiences were carried out in the draining greenhouse under natural and forced convection. The results show that in terms of drying time, the draining greenhouse under forced convection can be the best technique of sludge drying. For the drying curves, in the three cases of drying in summer and the case of drying bed in winter, only the decreasing speed phase (phase 2) is present. However, in both cases of drying in the draining greenhouse in winter, the curves did not follow any regular shape. Twelve models were tested to fit the drying kinetics of the sludge. For all experiences, Midilli-Kucuk model was chosen as the best model. The values of the effective diffusivity varied between 5.76 × 10−10 and 8.51 × 10−10 in summer and between 1.77 × 10−10 and 3.36 × 10−10 in winter.