Drying Performance of a Combined Solar Greenhouse Dryer of Sewage Sludge

Fatiha Berroug, Yassir Bellaziz, Zakaria Tagnamas, Younes Bahammou, Hamza Faraji (), El Houssayne Bougayr and Naaila Ouazzani
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Fatiha Berroug: Laboratory of Fluid Mechanic and Energy, Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakech 40000, Morocco
Yassir Bellaziz: Laboratory of Fluid Mechanic and Energy, Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakech 40000, Morocco
Zakaria Tagnamas: Team of Solar Energy and Aromatic and Medicinal Plants, ENS, Cadi Ayyad University, Marrakech 40000, Morocco
Younes Bahammou: Laboratory of Fluid Mechanic and Energy, Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakech 40000, Morocco
Hamza Faraji: National School of Applied Sciences, Cadi Ayyad University, Marrakech 40000, Morocco
El Houssayne Bougayr: Laboratory of Engineering & Applied Technologies, Higher School of Technology, Sultan Moulay Slimane University, Beni Mellal 23000, Morocco
Naaila Ouazzani: National Center of Studies and Research on Water and Energy, Cadi Ayyad University, Marrakech 40000, Morocco

Sustainability, 2024, vol. 16, issue 22, 1-20

Abstract: The solar drying of sewage sludge in greenhouses is one of the most used solutions in wastewater treatment plants (WWTPs). However, it presents challenges, particularly in terms of efficiency and drying time. In this context, the present study explores the drying performances of an innovative Combined Solar Greenhouse Dryer (CSGD) for sewage sludge. The system integrates rock bed storage (RBS), a solar air collector (SAC), and a solar greenhouse dryer (SGD). A numerical model, developed using TRNSYS software, predicts the drying kinetics of sewage sludge through hourly dynamic simulations based on the climatic conditions of Marrakesh, Morocco. Experimental validation confirmed the accuracy of the model. The results reveal that integrating the SAC with the SGD during the day and the RBS with the SGD at night significantly enhances the drying efficiency of the sewage sludge. During daylight hours, the SAC generates hot air, reaching maximum temperatures of 64 °C in January and 109 °C in July. Concurrently, the outlet air temperature of the RBS rises notably during the day, corresponding to the charging phase of the storage unit. Moreover, during the night, the RBS air temperature exceeds ambient temperatures by approximately 7–16 °C in January and 11–37 °C in July. This integration leads to a substantial reduction in drying time. The reduction in sewage sludge water content from 4 kg/kg of dry solid (20% dry solid content) to 0.24 kg/kg of dry solid (80% dry solid content) is related to a decrease in the drying time from 121 h to 79 h in cold periods and from 47 h to 27 h in warm periods. The drying process is significantly enhanced within the greenhouse, both during daylight and nocturnal periods. The CSGD system proves to be energy-efficient, offering an effective, high-performance solution for sewage sludge management, while also lowering operational costs for WWTPs. This innovative solar drying system combines a thermal storage bed and a solar collector to enhance drying efficiency, even in the absence of sunlight.

Keywords: drying efficiency; greenhouse dryer; rock bed system; sewage sludge; solar collector; TRNSYS simulation moisture content (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2024
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