Drying of faecal sludge using infrared radiation (South Africa)

A study in Durban, South Africa, investigated using infrared (IR) radiation to dry and pasteurize faecal sludge for safe reuse as a soil conditioner or biofuel. Two IR lamps, shortwave (SW) and medium wavelength (MW) were tested at varying intensities and distances from the sludge. The optimal conditions were found to be 75% intensity with MW lamps at distances of 7.5 cm and 10 cm. The key findings of the study showed that IR radiation reduced sludge volume by 86%, resulting in dried sludge with nutrient values suitable for use as a soil conditioner (14 g/kg TN and 20 g/kg TP) and as a potential biofuel (18 MJ/kg).

Additionally, the drying process effectively pasteurized the sludge, eliminating detectable E. coli concentrations and helminth eggs. Using medium wave IR radiation at the identified optimal conditions led to lower specific energy consumption (12,080 kWh/t), faster drying rates (3.89 kg/h.m²), increased drying efficiency (27.4%), and a moisture content reduction of 2.6%. These findings have the potential to promote a circular economy by providing a sustainable and efficient method for treating faecal sludge, making it a valuable resource for agriculture and energy production.