Potential use of black soldier fly larvae to reduce faecal sludge quantity from lined and unlined pit latrines in urban slums : a case study of Bwaise in Kampala, Uganda
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Faecal sludge management (FSM) in urban slums is faced with a number of challenges due to the nature of settlement and high population density and this prompts the residents and pit emptiers to illegally dump FS into the living environment, leading to environmental and health risks. This study was therefore, carried out to assess potential use of black soldier fly larvae (BSFL) in faecal sludge samples collected from pit latrines in urban slums in Kampala. The faecal sludge (FS) samples were collected from both lined and unlined pit latrines in Bwaise I parish in Kampala, at various depths 0.1m, 0.5m, 1.0m and 1.5m below the surface of the sludge top level. These were mixed to obtain one composite sample for each type of pit latrine. The samples were then analyzed to determine their characteristics that are suitable for breeding BSFL, and determine optimum feeding rate, larvae density and moisture content and hence, efficiency of BSFL in reducing FS quantity from both lined and unlined pit latrines. The study showed that faecal sludge from both lined and unlined pit latrines within the urban slum is suitable for breeding BSFL. The optimum feeding rate, larvae density and moisture content for BSFL in reducing FS is 50 mg/larvae/day, 200 larvae and 60% respectively. The efficiency of BSFL in reducing faecal sludge from lined and unlined pit latrines was found to be 69% and 63% respectively with no significant differences in reduction between the two type of pit latrines. The present of BSFL resulted to significant increase in pH (8.54 p = 0.036 and 8.43 p = 0.042 for lined and unlined pit latrines respectively), ammonium nitrogen (247 p < 0.01 and 349 p = <0.01 for lined and unlined pit latrines respectively), total nitrogen (1799 p = < 0.01 and 1712 p < 0.01 for lined and unlined pit latrines respectively) and most metal concentration in the treatment residues. All the parameters of the residues analyzed were within the allowable limit for use as compost except moisture content and helminth eggs concentrations, and this implies that the residues require additional treatment before application in agriculture. BSFL has a high potential in reducing FS quantity from both lined and unlined pit latrines and therefore, it has high potential to contribute to faecal sludge management in the urban slum communities.