Adsorption of residual methyl green by extracellular polymeric substance of Lysinibacillus sp. SS1: A sustainable approach to wastewater treatment

Water pollution due to overuse of dyes or improper remediation in industrial settings is posing a threat to aquatic life, environment and health. Due to world-wide scarcity of clean water, treatment and re-utilization of wastewater is the top-most priority, aiding in achievement of sustainable development goals. Even after suitable wastewater treatment, residual pollutants persist, leading to their over-accumulation on recurrent release at the same site. Hence, in this context, the present study reports the adsorption of methyl green dye at trace concentrations (< 10 mg/L) by EPS secreted by Lysinibacillus SS1 (EPS-SS1). One-variable-at-a-time strategy was employed to obtain maximum adsorption % and capacity of 99.14 and 1057.11 mg/g at 8 mg/L methyl green, 7.5 mg/L EPS, at pH 8, 35 ºC, with no agitation in 40 min contact time. The data for adsorption process fit Freundlich isotherm and PSO kinetics at highest R² of 0.9982 and 0.9859 for non-linear and linear forms respectively. This implied that the adsorbent surface is heterogenous, with varied surface energies, resulting in multi-layer adsorption. Therefore, it was confirmed that energy-efficient adsorption by EPS-SS1 is an effective, eco-friendly method of residual pollutants in contaminated wastewater with easy scale-up.