Potential Application of Tamarind Seed Extract as Coagulant Aid in Alum-Based Removal of Polyamide Microplastics

Abstract The widespread presence of microplastics (MPs) in aquatic ecosystems raises concerns for ecological sustainability and human health. This study explores a cost-effective and operationally simple coagulation-flocculation-sedimentation (CFS) process using tamarind seed (TS) as a natural coagulant or coagulant aid to remove polyamide (PA) MPs. Three coagulant systems, alum, TS and a combined system of alum with TS (alum-TS) were tested. The alum-TS system achieved the highest removal efficiency in a distilled water matrix at pH 7, using 15 mg/L alum and 50mmg/L TS. Optimal CFS parameters include rapid mixing at 200 rpm for 2 min, followed by slow mixing at 50 rpm for 30 min, and a settling phase of 30 min. Fitting the optimized experimental data to Brownian coagulation kinetics indicated that the removal of PA MPs by alum-TS follows second-order kinetics. Increasing MPs concentration, water hardness and anionic surfactants reduced removal efficiency, whereas salinity, cationic surfactants and humic acid improved it up to certain optimal levels. Tests on various water matrices, river, lake, tap water, and municipal wastewater, achieved removal efficiencies between 95.1 ± 0.85% and 98.76 ± 0.46%. The removal mechanism involved a combination of charge neutralization, adsorption bridging, and sweep flocculation. The findings demonstrate that tamarind seed extract can effectively serve as a natural coagulant aid to conventional coagulants, enhancing microplastic removal in aquatic environments. Graphical Abstract