Faecal sludge accumulation and characterization in informal settlements of Kampala: insights for facilities design

The design and management of onsite sanitation containments for faecal sludge (FS) in informal settlements presents significant public health and environmental challenges, exacerbated by limited data on sludge accumulation and quality. This study aimed to determine properties and accumulation rate of FS in pit latrines and septic tanks to improve sanitation design and management strategies. Fieldwork was conducted in 22 onsite containments (11 pit latrines and 11 septic tanks) in Kawempe Division, Kampala. The in-situ FS volume was measured using a Volaser device, while laboratory analyses determined key physico-chemical parameters, including total solids (TS), volatile solids (VS), and chemical oxygen demand (COD). The findings revealed median FS accumulation rates of 214 L/cap year for pit latrines and 348 L/cap year for septic tanks, with significant variability across different containment types. Correlation analysis showed a strong relationship between TS and VS (R2 = 0.93), while TS and COD exhibited a moderate correlation (R2 = 0.47). These insights suggest that TS can be a cost-effective proxy for VS estimation, reducing laboratory analysis costs in resource-limited settings. This study provides data for optimizing faecal sludge management (FSM), supporting the design of more efficient sanitation systems in high-density urban settlements. The findings contribute to improved sludge containment planning, desludging frequency estimation, and the selection of appropriate treatment technologies in similar contexts.