Harnessing Lemna minor for Sustainable Wastewater Remediation: Advances, Challenges, and Future Prospects

Water pollution is a current issue of concern around the world and there is a dire need to develop sustainable, cost effective and eco-safe wastewater treatment solutions. Lemna minor (duckweed) is becoming famous among aquatic macrophytes as an effective phytoremediator because of its fast growth, adaptability and wide spectrum of pollutants that it removes. Decades of studies have confirmed that L. minor can have a significant positive water quality impact by increasing wastewater oxygenation, decreasing organic loads, and alleviating pathogens, and, at the same time, improving physicochemical characteristics including transparency and odor. Savings of up to 75% in biochemical oxygen demand (BOD5), 70% in chemical oxygen demand (COD), 72 % in ammonium, 82 % in phosphate, 67 % in total nitrogen, and 96 % in total phosphorus have been reported in a variety of wastewater streams, such as municipal wastewater, industrial wastewater, and agricultural wastewater. Moreover, L. minor has a good metal uptake efficiency and the removal percentage of iron is 91.7% with the accumulation of large proportions of copper, chromium, cadmium, lead and zinc. In addition to remediation potential, L. minor provides an added value of production of protein-rich biomass (up to 75.24% crude protein), applicable to animal feed, bioenergy, and other bioproducts, which corresponds to the principles of the circular economy. Addition of duckweed into current treatment systems, including secondary clarifier tanks, or cultivated microbial and algal consortia also increases pollutant removal and decreases reliance on tertiary treatments. However, the variability of the performance under the influence of the wastewater composition (e.g. landfill leachate, nutrient imbalances) and the possibility of the re-release of nutrients during the decay of biomass pose significant issues. Quick biomass harvesting, optimization of the cultivation environment, and genetic or biotechnological advances are all potential tools to maximize efficiency. This review paper reveals both opportunities and challenges of phytoremediation by Lemna minor.