Fig. 2. Exponential chemical oxygen demand (COD) removal curves in differently treated wastewater. Multiple comparisons of fitted curves were made across all possible combinations. The COD removal was significantly faster in treatments containing duckweed compared with the control, whereas treatments with artificial duckweed, air bubbling, or both were not significantly different from either the control or the duckweed treatment. For curve fit parameters see Körner et al. (1998). Data points represent means of four replicates; for clarity, standard errors were omitted. Data from Körner et al. (1998).