An environmental-friendly approach for phytoremediation of zinc ion by <i>Lemnaceae</i> species: process behavior and characterization studies

Phytoremediation is a promising approach grounded in green and sustainable development principles for decontaminating water and soil. Among the studied duckweed species (<i>Spirodela polyrhiza</i>, <i>Wolffia arrhizal</i>, and <i>Lemna minor</i>), <i>S. polyrhiza</i> exhibited the highest zinc removal efficiency of 88.50% by day 7, followed by <i>L. minor</i> and <i>W. arrhiza</i> with removal efficiency of 78.69 and 38.59%, respectively. This study investigated the effects of environmental factors, including initial zinc ion concentration (50, 100, 150, 200, and 250 mg/L), solution pH (pH 5, 6, 7, and 8), and macrophytes mass (5, 10, 15, 20, and 25 g) on the phytoremediation of the zinc ion from synthetic wastewater by <i>S. polyrhiza</i>. The process effectively treated 500 mL of synthetic wastewater containing 100 ppm zinc ion and the process could be enhanced to achieve the removal efficiency of 90% by adjusting the solution pH to slightly acidic (pH 5) and increasing the mass of duckweed to its saturation point (20 g). Excessive zinc intake by duckweed led to chlorophyll reduction, negatively impacting the duckweed growth rate. Scanning electron microscopy (SEM) analysis revealed that the duckweed fronds’ surface became uneven after the treatment, with the irregular small particles attached due to cellular damage. The energy dispersive X-ray (EDX) analysis confirmed the successful uptake and accumulation of zinc in the duckweed cells from the synthetic wastewater. In conclusion, duckweed-based phytoremediation demonstrates significant potential for removing zinc ion from wastewater, at low and moderate concentrations. This study presents a novel application of duckweed species, particularly <i>Spirodela polyrhiza</i>, for efficient phytoremediation of zinc ion from synthetic wastewater. The research uniquely investigates the influence of various environmental factors including solution pH, initial heavy metal concentration and initial mass of macrophyte on the phytoremediation. There is limited research regarding the phytoremediation by duckweed species, especially in evaluating the performance of different species under a high-stress environment. Therefore, it is worthwhile to investigate the ability of different species of duckweed during phytoremediation in terms of their bioconcentration. Besides, there is a very limited understanding of the plant response toward the high stress environment and therefore, this study provides valuable insight into the plant’s mechanism for managing excess uptake of zinc ions. This research highlights the ability of different duckweed species to treat the high-zinc concentrated wastewater and provides insight into the effect of excess micronutrients within the duckweed itself. This research not only advances the understanding of heavy metal remediation processes but also contributes to developing optimized strategies for wastewater treatment.