respectively, and TP (efficiency of 94.5%). Although the concentration
of nutrients varied greatly, primarily because of the raw manure
variations and rain fluctuations that occurred during the
experimental period, the efficiency remained high. The median values
and standard deviation obtained during the experimental period
can be observed in Table 3 and Fig. 2.
Most of the TKN load applied to the serial duckweed ponds was
removed after one year. Moreover, approximately 260 kg of nitrogen
was recovered from the water (Table 4). However, it is necessary
to express the applied load in terms of the application rate to
compare the results with other authors. In this way, the TKN surface
application rate was approximately 46 kg/haday, and the removal
rate was 43.7 kg/haday or 4.4 g/m2day (Table 5). Cheng et al.
(2002a) reported the highest removal rates in their investigation
of the nitrogen removal from swine waste by Lemna minor; they
found removal rates of 3.4 g TKN/m2day (in vitro experiment) and