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Nitrogen and phosphorus removal from swine lagoon liquid by growing Lemna minor 8627, a promising duckweed identified in previous studies, was investigated under in vitro and field conditions. The rates of nitrogen and phosphorus uptake by the duckweed growing in the in vitro system were as high as 3.36 g m2 day1 and 0.20 g m2 day1, respectively. The highest nitrogen and phosphorus removal rates in the field duckweed system were 2.11 g m2 day1 and 0.59 g m2 day1, respectively. The highest observed duckweed growth rate was close to 29 g m2 day1 in both conditions.

Wastewater concentrations and seasonal climate conditions had direct impacts on the duckweed growth and nutrient removal in outdoor tanks. The rate of duckweed production in diluted swine lagoon liquid increased as the dilution rate increased. Duckweed assimilation was the dominant mechanism for nitrogen and phosphorus removal from the swine lagoon liquid when the nutrient concentration in the wastewater was low, but became less important as nutrient concentration increased. Reasonably high light intensity and a longer period of warm temperature could result in a higher growth rate for the duckweed. Preacclimation of the duckweed with swine lagoon liquid could accelerate the startup of a duckweed system to remove nutrients from the wastewater by preventing the lag phase of duckweed growth.