Evolution of faecal sludge chemical and physical characteristics during drying

The effect of drying on faecal sludge chemical and physical properties for its reuse as agricultural product and biofuel was explored in this investigation. The nutrient content, calorific value and thermal properties were determined for faecal sludge samples dried at different moisture contents, in two different drying apparatus, one based on convective drying and the other on infrared drying. The results show that the nutrient content and calorific value were not affected during drying. On the contrary, drying modified the chemical form of nitrogen in the sludge, by binding it more tightly to the solid structure. Moreover, drying led to the increase of the thermal diffusivity, which improves its quality as biofuel by enhancing its ability to conduct heat. Faecal sludge, after being dried, could be used in agriculture as an organic fertilizer of slow nitrogen and phosphorous release, and as a biofuel with similar characteristics than wood.