Metrics for stabilization of fecal sludge and relation to dewatering metrics

Abstract

Stabilization and dewatering are essential treatment mechanisms for the management of fecal sludge (FS) that accumulates in onsite containment, but reliable predictors of treatment performance are lacking. FS in Lusaka, Zambia is typically 80–98% water, which when delivered to treatment first requires dewatering, followed by stabilization of varying levels of organic matter. In addition, varying levels of stabilization are themselves observed to influence dewatering performance. Therefore, this study evaluated rapid and low-cost metrics of stabilization and their relation to dewaterability. Fourteen metrics of stabilization were evaluated based on 11 criteria in a decision matrix. Four metrics were selected to then evaluate method performance and suitability with FS samples (n = 27). The relation between stabilization and dewatering performance of collected samples were analyzed, and also following anaerobic stabilization in the laboratory. The study found that metrics based on physical–chemical characteristics such as volatile/total solids (VS/TS) and biological oxygen demand/chemical oxygen demand (BOD/COD) were not reliable for measuring FS stabilization and its relation to dewaterability. Metrics that rely on microbial activity such as SOUR (specific oxygen uptake rate) are more promising based on the consistent results obtained throughout this study. HIGHLIGHTS Agreed-upon metrics of stabilization are needed for fecal sludge.; Metrics for wastewater and compost were evaluated for their applicability to fecal sludge.; Biological metrics (e.g. SOUR) are more representative than physical–chemical characteristics (e.g. VS/TS).; Anaerobic digestion, stabilization metrics, and dewatering performance were not consistent.;

Keywords

• anaerobic digestion
• dewatering performance
• fecal sludge
• stability index
• stabilization indicator