Design and testing of a solar thermal drying system for drying of source separated faecal solids

The provision of adequate sanitation has been a challenge for developing countries with limited resources such as water, energy and capital for infrastructure. The Water Research Commission (WRC) of South Africa initiated the Sanitation Accelerator in 2017, currently termed the Re-Engineered Toilet with the aim for South African innovators to develop sanitation technologies suited to the South African context. The technology in this study was supported under the program and this paper outlines its development of the technology from basic research to prototype testing. The technology uses source separation of urine and faeces and then treats the streams separately. A prototype was developed for the drying system which uses solar and wind energy to dry the faeces. The prototype was tested with simulated faeces at different ambient conditions of temperature and humidity. Simulated faeces were used to mitigate immediate hygiene risks associated with handling human excreta. Parameters measured were the drying temperature in the drying tunnel and the final moisture content of the samples after 34-hour residence time in the drying bed. At moderate ambient conditions, drying temperatures reached minimum and maximum of 8°C and 64°C respectively at an average humidity of 47%. A final moisture content of 7.2% was achieved. At dry and hot conditions, the prototype reached minimum and maximum temperatures of 9 °C and 69°C respectively at an average humidity of 42%. A final moisture content of 4.4% was reached. At high humidity, the prototype reached minimum and maximum temperatures of 15°C and 46°C respectively. The humidity in this case was 76% and the final moisture content was 19.4%. ● The current flushing toilet is wasteful of water and energy, scarce resources in developing countries. ● Solar energy can be successfully incorporated into innovative sanitation technologies ● Solar drying reduces the cost of energy required to dry faecal solids ● A prototype for solar drying of source-separated faecal solids was designed and tested ● Solar drying performs differently under different ambient conditions