Solar Thermal Dewatering in Faecal Sludge Management

This research project focused on understanding the way in which faecal sludge dries on a material level. Faecal sludge pose’s huge health and environmental problems within the developing world, but by implementing faecal sludge management systems these issues can be reduced. This research is of great importance as understanding the way in which faecal sludge dries can improve the efficiency and effectiveness of new and developed drying techniques. In turn this will mitigate many of the health and environmental issues facing the developing world. The aim of this project was to investigate how faecal sludge dries under differing conditions to help predict how efficiently newly developed drying technologies will work. Faecal sludge from ventilated pit latrines (VIP), urine diversion toilets (UDDT) and anaerobic baffled reactors (ABR) along with fresh faeces (HF) were analysed using both UV-Vis-NIR and STA-FTIR analysis to identify their drying properties. UV-Vis-NIR spectroscopy was used to analyse the reflectance and transmission properties of faecal sludge, identifying how it interacts with the radiation produced from the whole solar spectrum. This allowed the depth of penetration to be identified along with the absorbance potential of each type of faecal sludge. When analysing the whole solar spectrum VIP, UDDT, ABR and HF had a total absorbance 87%, 86%, 85% and 65% respectively, indicating that solar thermal drying was an excellent drying process. To understand the drying trends and energy demand needed to remove moisture from faecal sludge, STA-FTIR was carried out. This demonstrated the variability found within the moisture retention properties of faecal sludge, along with the importance of fully understanding the drying system used to ensure that no energy is wasted within the process. pH and nutrient content were found to play an important role within a faecal sludge ability to dry, meaning that UDDT sludge reached the lowest final moisture content of ~23% due to the removal of nutrients within the urine diversion process, while VIP sludge dried to the lowest moisture content (~8%) due to it having a neutral pH