Rheological Characterisation of Faecal Sludge in Lavender Hill Treatment Plant, Ghana Rheological Characterisation of Faecal Sludge

Abstract

Rheological properties of faecal sludge have emerged as effective indicators for fluid characterisation, driven by growing needs in wastewater and faecal sludge treatment plants worldwide. This study analysed the rheological properties of faecal sludge received at the Lavender Hill Treatment Plant in Ghana. Samples were collected from the outlets of key treatment units at the Lavender Hill faecal treatment plant, a 3,500 m³/day facility. The sludge samples were taken from primary sludge, dewatered sludge, dewatered leachates, anaerobically digested sludge, and activated sludge. The analysis revealed that although faecal sludge characteristics varied widely across regions, the choice of treatment technology and shear-induced orientations were critically relevant to its rheological behaviour. The rheological properties of faecal sludge were influenced by the type, test protocols, and inherent properties. Despite these factors, faecal sludge remained a non-Newtonian fluid. However, variations in solids concentration, sludge type, and the treatment method or process unit employed resulted in pseudoplastic, dilatant, thixotropic, or rheopectic behaviour. This study has demonstrated that in-depth knowledge of faecal sludge rheology is essential for the design, management, optimisation, and operation of faecal sludge treatment plants.