Examination of nitrogen accumulation rate in a Lemna minor aquatic system

Duckweed species from the subfamily Lemnaceae are small, free-floating aquatic macrophytes capable of thriving in diverse environments. Studies have demonstrated that duckweed can be used to recover nutrients from its growth medium or wastewater. The plant biomass produced can be utilized as a source of protein or starch for animal feed or the production of value-added products such as biofuels. To investigate the kinetics of nitrogen accumulation within a Lemna minor aquatic system, a series of batch reactors were employed to simulate the continuous growth of the plants. The study aimed to elucidate the dynamics of nitrogen conversion in a controlled long term batch system. Lemna minor plants were cultivated for 75 days in 30 petri dishes, each containing 45 mL of synthetic hydroponic nutrient solution. Regular analyses were conducted on the reactors to measure nitrogen components, phosphates, and Total Organic Carbon (TOC). Nitrogen equilibrium was closely monitored throughout the cultivation period to assess alterations in nitrogenous components within the samples. By the end of the cultivation period, frond count and dry biomass had increased from 30 plants to 243 and from 2.5 mg to 40.2 respectively, exhibiting exponential growth after an initial lag phase lasting 31 days. During the exponential phase, protein content ranged from 28.5% to 38.8%. Nitrate concentration, the primary nitrogen source in the medium, decreased by 79.1%, while phosphorus levels were reduced by 97.4% by the end of the experiment. The results also revealed significant variations in total nitrogen content over time, ranging from a decrease of 45.6% to an increase of 8.0% compared to the initial levels, suggesting the possible contribution of denitrification and biological nitrogen fixation.