Laboratory Efficacy of a Woven Geotextile, Nonwoven Geotextile, and Nylon Mesh in Dewatering and Filtering Simulant Fecal Sludge and Field Effectiveness of a Nonwoven Geotextile Geobag in Bangladesh

Abstract

In humanitarian contexts, fecal sludge treatment is critical to prevent the spread of infectious diseases. Geotextiles are permeable fabrics used in geobag treatment plants to dewater liquid wastes, but data on their efficacy for dewatering and filtering fecal sludge are limited. The aim of the study was to address knowledge gaps on geobag efficacy with fecal sludge, to contribute to guidance in humanitarian settings. We evaluated the laboratory efficacy of three fabrics used in humanitarian contexts (a woven geotextile, a nonwoven geotextile, and a 100-μm nylon mesh mimicking locally available material) to dewater and filter simulant fecal sludge, over five layers of sludge addition, with and without lime conditioning. The woven geotextile had the greatest effluent volume (851 mL); most-dewatered sludge (sludge dewatered to the greatest extent) [16% total solids (TS)] and greatest reductions of total suspended solids (TSS) (80%), E. coli [−1.2 log10 reduction value (LRV)], and chemical oxygen demand (COD) (22%). The nonwoven geotextile had the highest dewatering flow (61.2 L/h·m2) and lowest reductions of TSS (75%), E. coli (−1.8 LRV), and COD (9%). The nylon mesh had the lowest effluent volume (784 mL), the least-dewatered sludge (dewatered to the least extent) (10% TS), and slowest dewatering flow (15.1 L/h·m2). The woven geotextile was the most efficacious fabric for both dewatering and filtering, but the two other fabrics obtained meaningful dewatering and filtering performance. Lime addition led to incomplete dewatering for all fabrics. Our results led to recommendations for fecal sludge treatment in humanitarian contexts, including prioritizing woven geotextiles, with locally available nylon mesh as a short-term acceptable option, and not using lime. Filtering performance was higher for the Bangladesh geobag than in the laboratory, which is attributed to differences in field and laboratory configurations. Further research on the effectiveness of fabrics and simulant sludge in actual humanitarian contexts is indicated. Implementation of fecal sludge geobag treatment plants is a promising solution for humanitarian contexts, but data on their efficacy for fecal sludge are limited. We evaluated fabrics used in humanitarian contexts (a woven geotextile, a nonwoven geotextile, and a 100-μm nylon mesh mimicking locally available material) to dewater and filter simulant fecal sludge. We evaluated the use of lime as a conditioner to help dewatering, because lime is widely available and used for pathogen inactivation and liquid–solid separation in humanitarian contexts. Woven geotextile was the most efficacious fabric for both dewatering and filtering. This is consistent with manufacturer advice and previous research. The nylon mesh obtained meaningful dewatering and filtering performances. We recommend prioritizing woven geotextiles for fecal sludge treatment in humanitarian contexts, with locally available nylon mesh as a short-term acceptable option. Lime addition led to incomplete dewatering for all fabrics, and thus is not recommended. Other studies found clear dewatering and filtering improvements using conditioners such as chitosan or polymers, which were not evaluated herein.