Composition and Characteristics of Faecal Sludge from Various Onsite Pit Technologies and User Categories in Dar es Salaam, Tanzania

Abstract

This study investigates the composition and characteristics of faecal sludge (FS) from different pit technologies (cesspits, pit latrines, septic tanks) and user categories (commercial, industrial, institutional, and residential) in Dar es Salaam, Tanzania, with a view for informed treatment and resource recovery strategies. FS samples exhibited varying concentrations of pH, electrical conductivity (EC), total solids (TS), and volatile solids (VS), COD and nutrients. pH values ranged from 2.83 to 8.41, with no statistically significant differences based on pit technology type or user category. However, the extremely low pH observed in samples from industrial pits suggests possible disposal of industrial chemicals in these sanitation systems. EC levels were notably higher in pit latrines and residential areas, likely due to waste disposal practices in homes, with concentrations 3-5 times above regulatory limits, raising concerns about their impact on treatment effectiveness and re-use potential. TS and VS concentrations also varied, with cesspits showing the highest TS levels and pit latrines exhibiting higher VS, indicating fresher sludge and potential for biogas production, as reflected by a VS/TS ratio ranging from 53.32% to 70.42%. Nutrient analysis revealed elevated levels of phosphate, nitrate and ammonia, particularly in pit latrines and residential pits, highlighting both resource recovery opportunities and challenges for treatment processes. While FS generally fell into the dilute category (TS < 3%), the high concentrations of other parameters underscore the need for a larger treatment footprint per unit volume of FS. The VS/TS ratio suggests that FS is not fully stabilized, indicating potential for further degradation and resource recovery. Additionally, the characteristics of FS suggest potential opportunities for deriving fertilizer and solid fuel. However, ensuring the hygiene of the sludge is crucial for its safe use, particularly in agricultural applications, and further studies are needed to confirm its sanitation.