UPTAKE OF PHOSPHATE AND NITRATE USING LABORATORY CULTURES OF LEMNA MINOR L

The use of the Lemna minor L. species of duckweed is an emergent technology that may be effective for the removal of nitrogen and phosphorus from enriched waters. The goal of this project is to find a cost-effective method of removing nitrogen and phosphorus from fresh water resources that have received loadings of these nutrients in stormwater runoff. This research examined the uptake of nitrogen and phosphorus by cultures of duckweed, L. minor L., cultivated in the laboratory under controlled environmental conditions. L. minor L. was grown in Plexiglas reactors (1600-mL) using modified Hillman growth medium. The effect of Lemna on phosphorus and nitrogen uptake and plant growth was measured over a two-week period. Two approaches were used: a batch and continuous flow method. For the latter method, a mass balance calculation was performed using measurements of the mass of phosphorus and nitrogen added in the influent, the mass taken up in the growing Lemna biomass, and the mass exiting in the effluent. A mass balance for high nitrogen, low phosphorus media (650 ppm N and 150 ppm P) indicated that 7% of the nitrogen and 10% of the phosphorus was removed by the plant uptake over the 14-day period of operation.