Rheology of sludge in pour-flush toilets: understanding the requirements for pit emptying technology design

Pour-flush (PF) toilets are seen as bridging the gap between basic on-site sanitation and the water-borne sewerage systems that people aspire to. Limited studies have been conducted on the rheological properties of PF sludge, which are a key component in designing and selecting appropriate pit emptying equipment. Samples from active and standing PF leach pits were tested for moisture content and viscosity. The two variables were linked using the fresh faeces viscosity model (Woolley et al., 2014). A second model was used to demonstrate how the volume and moisture of material in standing PF leach pits changed over time. This showed that PF leach pits could be emptied using a pump within two months of active use. Alternatively, PF leach pits can be left for up to five years after which the volume will have reduced to 45 % of the original volume and can be dug out manually.