Kinetics of nutrient removal and biomass production by duckweed Wolffia arrhiza in continuous-flow mesocosms

The nutrient removal and biomass production with duckweed Wolffia arrhiza was assessed using laboratory-scale continuous-flow mesocosms fed with model wastewater. Average removal rates of nitrogen and phosphorus by vegetative fronds were 0.03-0.18 mg-N/m2/d and 0.023-0.079 mg-P/m2/d, respectively. The maximum production rates of the vegetative fronds and the turions were respectively 86-160 g-wet/m2/d and 55-64 g-wet/m2/d, depending on the nutrient concentration. The kinetic data of the biomass and nutrient concentrations were analyzed using a mathematical model, which showed that the maximum specific growth rate of W. arrhiza was 0.35-0.38 d−1, whereas the turion formation was induced when the specific growth rate decreased below 0.085-0.12 d−1 in low-nitrogen conditions. The model developed in this study is applicable for predicting the wastewater treatment performance and biomass production of preferential biomass, the protein-rich vegetative fronds, the starch-rich turions, or total biomass of W. arrhiza.