Infra-red drying of faecal sludge (The Netherlands)

This experimental study used two MIR halogen lamps of a 400 W in an enclosed steel housing. The main focus was to assess the impact of the MIR enclosed drying system on the: drying rate, moisture content, pathogenic content, nutrient values and the specific energy consumption (SEC). The experimental parameters—mass (50,100 and 150g), distance to the lamp (10,15 and 20 cm), and lamp intensity (50%-100%) – were varied to identify the optimal drying conditions. The sludge was dried until an average moisture content of ~0.1949 9g/g was achieved which is equivalent to an average of 75% moisture reduction. After drying, the sludge was analysed for total solids (TS), volatile solids (VS), microbiological content, total phosphorus (TP), and total nitrogen (TN) to determine its potential for reuse as biofuel and soil fertilizer. The calorific value was also assessed to evaluate its potential as a biofuel. Key findings include a 75% volume reduction, TP levels of 2.4 g/kg (a 78% reduction), TN levels of 31 g/kg, and an average calorific value of ~16 MJ/kg, consistent with previous studies. Pathogen removal efficiency was notable, with a log inactivation of ~6 for total coliforms and E. coli. The optimum conditions for drying were identified at 100 g mass, 10 cm distance, and 100% lamp intensity. Under these conditions, the dried sludge was deemed suitable for reuse as both biofuel and fertilizer. The optimal SEC was 11,598 kWh/tonne, which was lower than the previous system from Ayat (2023) and achieved a volume reduction 0f 79%, while a microwave pilot study of Akurut (2022) achieved an average of 75% reduction.