Phytoremediation potential of the duckweeds Lemna minuta and Lemna minor to remove nutrients from treated waters

Phytoremediation potential of duckweeds (Lemna minuta, Lemna minor) to remove nutrients from simulated wastewater wasanalyzed. In two separate experiments, the two species were grown for 28 days in waters enriched with nitrate and phosphate tosimulate nutrient concentrations of domestic wastewater.Water physical and chemical measurements (temperature, pH, conductivity,oxygen) and plant physiological and biochemical analysis (biomass, relative growth rate-RGR, nutrient and chlorophyllcontents, peroxidative damage, bioconcentration factor-BCF) were made to test and compare the phytoremediation capacity ofthe two Lemna species. L. minuta biomass increased almost tenfold during the time-course of the treatment resulting in adoubling of the mat thickness and a RGR of 0.083 ± 0.001 g/g day. Maximum frond content of phosphate was reached by day21 (increase over 165%) and nitrate by day 7 (10%). According to the BCF results (BCF > 1000), L. minuta was ahyperaccumulator for both nutrients. On the other hand, L. minor biomass and mat thickness decreased continuously duringincubation (RGR = - 0.039 ± 0.004 g/g day). In L. minor fronds, phosphate content increased until day 14, after which there wasa decrease until the end of the incubation. Frond nitrate content significantly decreased by day 7, but then remained relativelyconstant until the end of the experiment. L. minor proved to be hyperaccumulator for phosphates, but not for nitrates. Resultsindicated L. minuta has a greater potential than L. minor to remove both nutrients by bioaccumulation, especially phosphates,demonstrated also by better physiological and biochemical responses. However, during the incubation, the chlorophyll content ofL. minuta mat did continuously decrease and peroxidative damage had increased until day 14, indicating that the system wasunder some kind of stress. Strategies to avoid this stress were discussed.