Investigation of olive mill sludge treatment using a parabolic trough solar collector

The olive mill sludge treatment system developed in this study is an indirect solar dryer driven by a solar parabolic trough collector (PTC). A heat exchanger is implemented to heat air with hot oil coming from the solar collector. The developed hot air dryer can treat up to 50 kg of olive mill sludge distributed over six trays at once. The designed system and its components are described, along with their experimental and simulated performance evaluations. With a mean direct normal irradiation (DNI) higher than 800 W/m2 and a 3 m/s airflow speed, a maximum drying air temperature of 128 degrees C was measured. The drying air temperature could be maintained above 100 degrees C for 10 h. This high temperature is advantageous for the drying problems associated with the presence of oil in the sludge to be dried. The high temperature can also reduce the drying time required to achieve the target moisture content needed for sludge valorization as biomass by 30%. The designed dryer configuration with an adjustable air blower leads to homogeneous sludge treatment. As a result, the position of the sludge inside the drying chamber has no significant effect on the drying rate. The overall analysis shows that maximum thermal efficiency of 58% can be achieved with the 23,909 kWh of thermal energy generated by the system throughout the simulated year of operation. This solar thermal energy supply leads to the mitigation of 15899.69 kg (eq) of CO2 emissions.