Comparison Between Two Solar Drying Techniques of Sewage Sludge: Draining Solar Drying and Drying Bed
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ORIGINAL PAPER
Comparison Between Two Solar Drying Techniques of Sewage Sludge: Draining Solar Drying and Drying Bed Azza Masmoudi1,3 · Ahlem Ben Sik Ali1 · Hatem Dhaouadi2 · Hatem Mhiri1 Received: 30 April 2020 / Accepted: 26 October 2020 © Springer Nature B.V. 2020
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. Graphic Abstract
Keywords Sewage sludge · Draining greenhouse · Drying bed · Drying kinetics · Effective diffusivity · Natural and forced convection
* Azza Masmoudi [email protected] Extended author information available on the last page of the article
Abbreviations DB Drying bed DG Draining greenhouse DS Dry solid content (%) Deff Diffusion coefficient (m2/s)
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FC Forced convection Fr Flow rate (m3/s) k Slope L Half thickness of the product sample (m) mi Initial mass (kg) n Number of terms taken into account N Number of experimental points NC Natural convection R2 Coefficient of determination V Drying rate (kg water/kg DS.h) Vi Initial volume (m3) W0 Initial weight of the sample (kg) Wd Weight of the dry solid which is obtained by putting the sample in an oven at 105 °C for 24 hours (kg) WWTP Wastewater treatment plant x Sample thickness (m) X Average moisture content (kg water/kg DS) Xeq Equilibrium moisture content Xi Initial moisture content Xr Reduced moisture content Xr exp,i ith experimental reduced moisture content Xr pre,i ith reduced moisture content predicted by each model z Number of constants ρ Density (kg/m3) α Absorptivity ε Emissivity τ Transmission coefficient χ2 Chi-square parameter
Statement of Novelty Since drying is an important step in sewage sludge treatment, we present, in this paper, a comparative study to the performances of the drying bed and the draining greenhouse under natural and forced convection in summer and winter. This is significant because we investigate the characteristics of two solar drying techniques. In fact, the draining solar drying is considered as an innovative solution in the area of sanitation. By coupling the solar drying with the filtration o
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