Bioadsorptive removal of pollutants and emerging metallic pollutants from surface water using sustainable plant-based materials.

Abstract

This study investigates the efficacy of Moringa oleifera and onion seed powders as sustainable, plant-based coagulants for treating polluted surface water collected from Mallathahalli and Somanahalli Lakes in Karnataka, India. Surface water samples were collected during the post-monsoon season (October-November 2024), and a total of 36 grab samples (18 from each lake) were obtained following IS 3025 guidelines to ensure representative sampling and data reliability. Key physicochemical parameters such as turbidity, color, pH, conductivity, and chemical oxygen demand (COD) and metallic pollutants were analyzed before and after treatment. Based on pH, dosage, and contact time, optimal operational conditions for coagulation flocculation were determined using Central Composite Design (CCD) and Response Surface Methodology (RSM). The optimized dosage-time combination (5-6% dosage and 25-45 min contact time) yielded removal efficiencies within the target range of 50-70% for multiple parameters. Results indicated that both M. oleifera and onion seed powder significantly reduced turbidity and color, with onion powder showing superior removal efficiencies for heavy metals. Specifically, onion seed achieved up to 95% Cu and 84% Zn removal, outperforming M. oleifera in most cases. Mechanistic analysis revealed that metal removal was facilitated by adsorption, chelation, and ion exchange interactions involving cationic proteins, flavonoids, and organosulfur compounds present in the coagulants. Variations in removal performance between the two lakes were attributed to differences in initial water chemistry, pH, ionic background, and natural organic matter (NOM). The findings support the application of M. oleifera and onion seed powder as eco-friendly alternatives to chemical coagulants for rural and urban water purification, especially in regions facing water quality challenges and heavy metal contamination. This research offers a scalable and sustainable approach to improving water quality using low-cost, biodegradable materials.