Comparison of faecal sludge management toolbox and conventional approaches for selection of treatment technologies

Abstract

Over 80% of the population in SSA, depend on OSS. The OSS generate Faecal Sludge (FS) that should be safely managed. Poorly managed FS cause public health and environmental risks. Lack of appropriate planning tools has been identified as a critical gap in planning of FSM. To compound the problem further, the FSM toolbox that has been developed based on the Asian context do not provide pre-defined solutions and need to be contextualized to suit specific country’s needs. This study compared the FSM Toolbox and conventional methods for selection of treatment technologies in Uganda. The selected plants design reports were reviewed and their environmental site conditions and socio-economic factors were assessed. FS samples were collected and analysed for physico-chemical and biological characteristics. The raw faecal sludge (FS) characteristics were used to calculate the efficiencies, following series of treatment stages, based on theoretical values from literature for comparison of the FSM toolbox and “as-built” technologies performances. The study confirmed that treatment site selection also depend on topography, land, wetlands existence and access, in addition to the predefined FSM toolbox input parameters. In comparison, the FSM toolbox technologies such as mechanical dewatering, disinfection and lime addition for tertiary treatment were not implemented in Uganda. However, the "as-built" and FSM toolbox technologies were comparable for removal of TSS with efficiencies of 99.8% and 99.4% respectively. The removal efficiencies of 100% for faecal coliforms was achieved in three plants, except Lubigi plant with efficiencies of 99.7% and 66.3% for FSM toolbox and "as-built" options respectively. The FSM toolbox efficiencies of 99.5%, 95.1%, 98.9% and 88.7% were higher compared to "asbuilt" of 98.8%, 92.9%, 94.5% and 67.5% for removal of BOD, NH4-N, Ortho-PO4 and P respectively. The "as-built" technologies had higher efficiencies of 99.8% and 98.2% compared to FSM toolbox of 99.4% and 98.4% for removal of TSS and COD. However, both options met the standards for removal of Zn and Fe. The FSM toolbox removal efficiencies of 97.2% and 65.7% were higher than the "as-built" efficiencies of 93.2% and 65.0% for removal of TN and FOG. The "as-built" technologies efficiency of 48.5% for Fe, Zn and Pb was higher than the 35.3% for those of FSM toolbox technologies. In comparison with standards, "as-built" and FSM toolbox technologies met standards for the removal of Zn and BOD for all plants. Both options didn’t meet the standards for removal of TN and Pb for the plants, but they met the standards for the removal of TSS, COD, Fe, faecal coliforms and phosphorus in three plants. However, the “as-built" technologies met the standards of Fe, P, Pb, and NH4-N at only one plant. While the FSM toolbox technologies met the standards for the removal of Ortho-PO4 at all the plants, but the "as-built" met the standards at only two plants. The FSM toolbox investment and O&M costs were exorbitantly expensive than the "as-built" across all the plants. Designers can use the FSM toolbox for quick decisions but detailed designs should be context specific, based on feasibility studies, due to variable FS characteristics.