Dewaterability of faecal sludge and its implications on faecal sludge management in urban slums

The current practices of faecal sludge management in urban slums pose risks to public health and environmental pollution. Given that faecal sludge contains high water content, dewatering it presents an important step of managing it effectively. This paper therefore explores the applicability of dewatering as the first step in decentralized treatment of faecal sludge (FS) generated from pit latrines, the commonest sanitation technology used in urban slums. A total of 22 and 10 FS samples were collected from lined and unlined pit latrines, respectively. The high moisture content of 92.4 and 83.4 % of FS from lined and unlined pit latrines, respectively, depicted a need for dewatering. Dewaterability extent and rate were measured in terms of per cent cake solids and capillary suction time, respectively. The average dewaterability extent of FS from unlined pit latrines (31.8 %) was significantly higher than that of lined latrines (18.6 %) (p = 0.000) while the dewaterability rate (1122 and 1485 s of FS from lined and unlined pits, respectively) was not significantly different (p = 0.104), although very low compared to sewage sludge. To obtain high dewaterability extent of FS from lined pit latrines, volatile solids should be reduced and sand content increased. To maintain high dewaterability extent of FS from unlined pit latrines, the particle sizes should be ae1 mm. The results from this study suggest that FS from pit latrines in Kampala can be conveniently dewatered without thickening, thereby reducing costs of FS management.