Variability of faecal sludge characteristics and its implication for dewaterability across different on-site sanitation containments in unplanned settlements in Dar es Salaam, Tanzania

Abstract

Abstract This article evaluates the physical-chemical parameters of Faecal Sludge (FS) as possible predictors of dewatering performances. Also, the variability of FS dewatering characteristics was assessed from different containments and in different seasons in relationship with dewatering performance. A total of 120 samples were collected and analyzed during the rainy and dry seasons in April and July 2019, respectively, to capture seasonal variability. FS from pit latrines (PT) took longer to dewater followed by mixer containments, while soak-away sludge (SO) took a relatively short time to dewater. Also, FS from PT was found to have a high amount of settled solids, hence high % of TS in dry cakes. Slow dewatering and turbid supernatant corresponded to high pH, electrical conductivity and total solids, but cake solids after dewatering were correlated with total solids of FS. The FS dewaterability was higher for SO (DI = 0.9) and least for PT (DI = 0.3). Seasonal variability of FS dewaterability within the containments was higher for PT (DI = 0.74) and least for SO (DI = 0.5). Planning of FS treatment plants including sizing and design for effective dewatering performance, variation of physical-chemical dewatering predictors in sources and season could provide a relatively low-cost way to predict dewatering performance.