Potential of Lemna minor for removal of methylene blue in aqueous solution: Kinetics, adsorption mechanism, and degradation pathway

Abstract

Dye wastewater produced from textile industry effluent contains non-biodegradable complex chemical compounds that harmful to living organism. Thus, treating dye wastewater before releasing it into surface water is extremely important. Lemna minor is one of ideal aquatic plants that can be used as phytoremediator of various pollutants. The objective of this research is to determine the potential and mechanism of Lemna minor to remove methylene blue (MB). This research was conducted in batch reactor. The effect of plant weight (1, 2, 3 g), contact time (0–4 days), and initial concentration (25, 50, 75 mg/L), as well as reaction kinetics and adsorption isotherms of MB removal were also determined. Results showed that equilibrium plant weight, contact time, and concentration were achieved at 2 g of plant weight for 2 days with 82.48 ± 1.09% of removal efficiency in 50 mg/L of MB concentration. For kinetics, all initial plant weights and concentration were well fitted with pseudo-second-order model, while the adsorption isotherm is Freundlich isotherm models with q max of 1.14 mg/g. Based on those, the adsorption process of MB by L. minor was determined as chemisorption. Our results also found that the removal mechanisms of MB by L. minor are phytosorption (hydrogen bonding and electrostatic interaction) and biodegradation (desulfurization and denitrification). Our findings showed that the removal processes of MB by L. minor were influenced by plant weight, initial concentration, and contact time. Therefore, it can be concluded that L. minor can be used as a phytoremediation agent to remove pollutants. • The removal mechanism of MB by L. minor was proposed. • Phytosorption and biodegradation are removal mechanisms of MB. • Pseudo-second order model describe the reaction kinetic of MB removal. • Freundlich was best fitted isotherms for MB removal by L. minor . • The q max value of L. minor to adsorb MB was 1.14 mg/g.