In situ nutrient removal from aquaculture wastewater by the aquatic vegetable Ipomoea aquatica on floating beds
浮床水蕹菜对养殖水体中营养物的去除效果研究

To investigate the nutrient removal in the aquaponic system, pilot scale test was carried out in six earthen ponds with 2000 m2 from June to November in 2007. The aquatic vegetable Ipomoea aquatica with 200 m2 was planted on floating beds in three ponds. Another three ponds without the vegetable were considered as control. The same fish weight was stocked in the planted and control ponds, but with different fish species. At the end of experiment, the fish production in planted ponds (1467 kg) was significantly higher than in control ponds (1203 kg) (P < 0.05). Percentage removal of total nitrogen (TN) and total phosphorus (TP) by harvested fish in control ponds was 25.17% and 15.27%, respectively. Percentage removal of TN and TP by harvested fish in planted ponds was 30.02% and 21.68%, respectively. The fresh weight of harvested vegetable was 4000±350 kg; and the percentage removal of TN and TP was 8.41% and 4.85%, respectively. In the middle and late period of the experiment, the contents of chemical oxygen demand (COD) and chlorophyll a (Chl a) in planted ponds were significantly lower than in control ponds, and the transparency was significantly higher than in control ponds. The concentration of dissolved oxygen (DO) in planted ponds was higher than 5 mg/L during the experiment, whereas the concentration of DO in control ponds decreased sharply in the last month. The results suggested that the water quality could be improved effectively and the higher fish density could be stocked in the aquaponic system.