[In-situ remediation of polluted water body by planting hydrophytes].

In an experimental enclosure system, floating plant Eichhornia crassipes was planted in summer and submersed plant Elodea nutalli was planted in winter to reestablish water ecosystem, and to investigate the effects of the hydrophytes on the removal of nitrogen and phosphorus from polluted water body and the improvement of water transparency. The results showed that compared with the control and native pond water, the water body planted with hydrophytes had a low level of nutrients. E. crassipes had a fast growth, with its covered area increased from 100 m2 to 470 m2 in the first 15 days, and to 65% of the water area after 44 days. The total nitrogen, ammonium nitrogen, nitrite nitrogen, CODMn and chlorophyll a decreased to a lower level, and the water transparency increased significantly, reaching to a depth of 1.7-1.8 m (i.e., to the bottom of the pond). After October, the total phosphorus kept on about 0.1 mg L(-1). Due to the increased water transparency, E. nutalli became the dominant species and covered 1/3 of the water area, playing an important role in purifying water quality, keeping water physicochemical properties in good status, and improving water transparency. It was concluded that planting hydrophytes in polluted water body could efficiently reduce its nutrients level and control the overgrowth of algae, being an important way in improving the water quality of eutrophicated water body.

In-situ nitrogen removal from the eutrophic water by microbial-plant integrated system.

OBJECTIVE: This study was to assess the influence of interaction of combination of immobilized nitrogen cycling bacteria (INCB) with aquatic macrophytes on nitrogen removal from the eutrophic waterbody, and to get insight into different mechanisms involved in nitrogen removal. METHODS: The aquatic macrophytes used include Eichhornia crassipes (summer-autumn floating macrophyte), Elodea nuttallii (winter-growing submerged macrophyte), and nitrogen cycling bacteria including ammonifying, nitrosating, nitrifying and denitrifying bacteria isolated from Taihu Lake. The immobilization carriers materials were made from hydrophilic monomers 2-hydroxyethyl acrylate (HEA) and hydrophobic 2-hydroxyethyl methylacrylate (HEMA). Two experiments were conducted to evaluate the roles of macrophytes combined with INCB on nitrogen removal from eutrophic water during different seasons. RESULTS: Eichhornia crassipes and Elodea nuttallii had different potentials in purification of eutrophic water. Floating macrophyte+bacteria (INCB) performed best in improving water quality (during the first experiment) and decreased total nitrogen (TN) by 70.2%, nitrite and ammonium by 92.2% and 50.9%, respectively, during the experimental period, when water transparency increased from 0.5 m to 1.8 m. When INCB was inoculated into the floating macrophyte system, the populations of nitrosating, nitrifying, and denitrifying bacteria increased by 1 to 2 orders of magnitude compared to the un-inoculated treatments, but ammonifying bacteria showed no obvious difference between different treatments. Lower values of chlorophyll a, COD(Mn), and pH were found in the microbial-plant integrated system, as compared to the control. Highest reduction in N was noted during the treatment with submerged macrophyte+INCB, being 26.1% for TN, 85.2% for nitrite, and 85.2% for ammonium at the end of 2nd experiment. And in the treatment, the populations of ammonifying, nitrosating, nitrifying, and denitrifying bacteria increased by 1 to 3 orders of magnitude, as compared to the un-inoculated treatments. Similar to the first experiment, higher water transparency and lower values of chlorophyll a, COD(Mn) and pH were observed in the plant+ INCB integrated system, as compared to other treatments. These results indicated that plant-microbe interaction showed beneficial effects on N removal from the eutrophic waterbody.