Characterization and prediction of fecal sludge parameters and settling behavior in informal settlements in Nairobi, Kenya

Abstract

The safe management of fecal sludge (FS) relies on different treatments, processes, and disposal options in different contexts. Waste transfer stations can improve FS management particularly in resource-constrained areas, including low-income urban informal settlements, by providing a safe discharge and treatment location. Low-footprint options for FS treatment are sensitive to the characteristics of incoming FS, which are typically highly variable, difficult to predict, and differ significantly from the characteristics of traditional wastewater. The success of low-footprint technologies relies on the monitoring of incoming FS characteristics, such as total solids (TS), total suspended solids (TSS), chemical oxygen demand (COD), ammonia, electrical conductivity (EC), and pH. Monitoring the characteristics of incoming FS typically relies on the use of a laboratory, which can be expensive and time-consuming, particularly in resource-constrained areas. Useful correlations between easy to measure parameters and difficult to measure parameters may provide useful information related to the monitoring of FS, while reducing the need for laboratory analysis. In this paper, we describe a sampling campaign at a waste transfer station in Nairobi, Kenya managed by Sanergy Inc., to characterize and observe settling behavior of FS collected from manually emptied pit latrines. The investigation found that easy to measure parameters (e.g., TS, turbidity) could be used to approximate difficult to measure parameters (COD, TSS). Additionally, rapid measurements (turbidity) could be used to approximate time-intensive parameters (TS, COD, TSS) to aid in the design, operation and monitoring of FS treatment facilities in resource and space-constrained areas.