Efficacy of Strychnos potatorum seed powder for turbidity reduction in rural water sources in Zambia: A laboratory-scale jar-test evaluation

Abstract

Household water treatment in rural Zambia remains challenging due to limited infrastructure and high turbidity levels in surface water sources. Seed powder of Strychnos potatorum L., a locally available botanical material, offers potential as a low-cost natural coagulant. This study evaluated its coagulation performance under controlled laboratory (jar-test) conditions using field-sourced raw water. Jar tests were conducted at varying doses (1–6 g/L) to assess turbidity reduction over a 60-minute settling period. Key physicochemical parameters (pH, conductivity, and major ions) were analysed before and after treatment and compared against Zambia Bureau of Standards (ZABS) and WHO guideline values. No microbiological analyses were performed in this study; therefore, bacteriological performance was not assessed. The 4 g/L dose achieved optimal performance, reducing turbidity from 25.9 NTU to 7.37 NTU (approximately 72% reduction) within 30–40 min, with rapid floc formation and settling observed. Higher doses (5–6 g/L) did not improve performance further. Post-treatment results also showed reduced conductivity (780–404 µS/cm) and decreases in Ca²⁺, Cl⁻, and Na⁺ concentrations, while pH remained within acceptable limits. Although substantial turbidity reduction was achieved, final values remained slightly above the ZABS drinking-water guideline of 5 NTU, indicating that S. potatorum functions primarily as a clarification (coagulation) step rather than a complete water treatment solution. Therefore, additional post-treatment disinfection would be required for safe consumption. Overall, S. potatorum represents a promising low-cost, locally available natural coagulant for improving water clarity and basic physicochemical quality in resource-limited settings, particularly during periods of elevated turbidity.