Fig. 5. Nitrogen and phosphorus removal rates of fat duckweed, biofilm (uptake by attached algae and bacteria), and coupled nitrification–denitrification (n/d) of attached bacteria in duckweed-covered domestic wastewater dependent on the initial nutrient concentrations. Removal rates of duckweed refer to the surface of the system whereas those of the biofilm and nitrification–denitrification refer to the growth surface available on duckweed and walls of the system. For the curve fit of the N removal by duckweed, one data point (Experiment 1 without duckweed growth) was excluded. Data from Körner and Vermaat (1998).