Enhanced Sewage Sludge Drying with a Modified Solar Greenhouse

Alice Sorrenti, Santo Fabio Corsino, Francesco Traina, Gaspare Viviani and Michele Torregrossa
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Alice Sorrenti: Department of Engineering, University of Palermo, Viale delle Scienze, 90128 Palermo, Italy
Santo Fabio Corsino: Department of Engineering, University of Palermo, Viale delle Scienze, 90128 Palermo, Italy
Francesco Traina: Department of Engineering, University of Palermo, Viale delle Scienze, 90128 Palermo, Italy
Gaspare Viviani: Department of Engineering, University of Palermo, Viale delle Scienze, 90128 Palermo, Italy
Michele Torregrossa: Department of Engineering, University of Palermo, Viale delle Scienze, 90128 Palermo, Italy

Clean Technol., 2022, vol. 4, issue 2, 1-13

Abstract: This work reports the results obtained with an innovative configuration of a closed-static solar greenhouse for sludge drying. The novelty of the solar greenhouse configuration consisted in using a forced ventilation system to provide hot air for sludge drying and the utilization of solar irradiation for energy supply. Wet sewage sludge (97% humidity) was successfully dried up to a residual humidity close to 5% after 25 days during wintertime. The increase of the airflow rate supplied under the sludge bed improved the sludge drying rate. Moreover, the fraction of volatile suspended solids decreased from 70% to 41% after 13 days, indicating that air supply promoted the simultaneous stabilization of the sludge as a side-effect to the drying process. Overall, the specific energy consumption per ton of evaporated water was estimated to approximately 450 kWh/t, resulting in about 55% of energy demand lower than a conventional thermal drying system, while using only free solar energy. The achieved high weight reduction of up to 99% implies a noticeable reduction of the excess sludge handling costs, indicating that solar greenhouse drying is a highly interesting opportunity for sludge drying in medium-small sized WWTPs.

Keywords: excess sludge reduction; convective drying; greenhouse; renewable energy; solar sludge drying; sustainable sludge management (search for similar items in EconPapers)
JEL-codes: Q2 Q3 Q4 Q5 (search for similar items in EconPapers)
Date: 2022
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