Sustainable use of longan seed waste as a natural coagulant aid for low-cost and eco-friendly water treatment

Conventional water treatment relies on chemical coagulants like alum, which, despite being effective, generate harmful alumina residues and significant non-biodegradable sludge. Furthermore, alum is costly and associated with neurological risks and freshwater acidification. Seeking safer, eco-friendly, and cost-effective alternatives, this study systematically evaluated the coagulation efficiency of Longan Seed Powder (LSP), derived from the abundant agricultural waste of the Dimocarpus longan fruit. LSP, primarily composed of 82.31% starch, was characterized, and its potential was assessed in systematic Jar test experiments conducted in 1 L batches using kaolin-based synthetic and raw river water. To ensure statistical robustness, all conditions were performed in triplicate (n = 3), using both untreated (negative) and alum-only (positive) controls for comparison. When tested alone, LSP achieved limited turbidity removal (