Improvement of the solar drying process of sludge using thermal storage.

Improvement of the drying process of sludge issuing from the coagulation/flocculation of landfill leachate was investigated using thermal storage systems, which consisted of a rock bed with air preheated by a solar air heater passing through the system. Sludge runs were dried inside the solar dryer with and without thermal storage, as well as outside the dryer. The values for the solar energy accumulated per mass of sludge required to obtain a stable sludge mass were 107.5 kJ/kg (with thermal storage), 240 kJ/kg (without thermal storage) and 580.5 kJ/kg, outside the dryer. The values for the energetic efficiency of the drying process were 38.13% and 16.45% for the processes with and without thermal storage, respectively. The net heat input to the storage system during the charging stage was 420 W and 120 W for the discharging stage, resulting in a global energy efficiency in the storage system of 0.28. The thermal efficiency of the solar drying with and without thermal storage system was 37.8% and 22.2%, respectively.