The adaptability of Ottelia to the four kinds of sewage and its purification efficiency were studied during the first phase of the experiment, which lasted for two months (12 May, 2013–11 July, 2013). The container used in the experiment was 167# polyethylene vat (bottom diameter of 500 mm, average diameter of 600 mm, and height of 1000 mm), whereas 400 mm-thick washed sand was used as sediment. Three replicates and one blank were set for each group of simulated sewage. Six Ottelia strains of uniform growth (average height of 410 mm, fresh weight of about 37 g) were planted in the three replicates, and no plants were grown in the blank group. The nitrogen and phosphorus contents in the four kinds of sewage were simulated by adding different amounts of potassium dihydrogen phosphate, potassium nitrate, and ammonium sulfate, as specified in Table 1.
Other nutrients were added through tenfold dilution with reference to Hoagland solution (Table 2).