[Effects of Wastewater Nitrogen Concentrations and NH4+/NO3- on Nitrogen Removal Ability and the Nitrogen Component of Myriophyllum aquaticum (Vell.) Verdc].

Solution culture experiments were conducted to investigate the effect of wastewater nitrogen levels and NH4+/NO3- on nitrogen removal ability and the nitrogen component of Myriophyllum aquaticum. Experiments with three nitrogen levels and NH4+/NO3- were set up as follows:20, 100, and 200 mg·L-1and NH4+/NO3- 1:0, 0.5:0.5, and 0:1. The results showed that the biomass of plants increased fastest during the first week. The plants treated with NH4+/NO3-=1:0 with nitrogen levels of 20 and 100 mg·L-1 and those treated with NH4+/NO3-=0.5:0.5 with a nitrogen concentration of 200 mg·L-1 exhibited higher biomass than the others. The removal rates of water total nitrogen, ammonium nitrogen, and nitrate nitrogen during the first week were the maximum for all treatments and increased with water nitrogen levels. There were no significant differences in the removal rate between ammonium nitrogen and nitrate nitrogen with a nitrogen level of 20 mg/L, while with nitrogen levels of 100 and 200 mg·L-1, the nitrate removal rates were higher than those for ammonium nitrogen. The Myriophyllum aquaticum nitrogen accumulation and its contribution rate to nitrogen removal from water and sediment were all increased with water nitrogen levels and increased fastest during the first week. The contribution rate of nitrogen accumulated by plants with NH4+/NO3-=0:1 was the highest with nitrogen levels of 20 mg·L-1, while plants with NH4+/NO3-=0.5:0.5 were the highest with nitrogen levels of 100 and 200 mg·L-1. The protein, amino, and nitrate nitrogen contents in Myriophyllum aquaticum plants were all increased by increasing water nitrogen levels with a ranking of protein content > amino nitrogen content > nitrate nitrogen content. The protein concentrations in plants with NH4+/NO3-=1:0 and NH4+/NO3-=0.5:0.5 were higher regardless of water nitrogen levels, while the amino nitrogen concentration in plants with NH4+/NO3-=1:0 and the nitrate nitrogen content in plants with NH4+/NO3-=0:1 were higher than the others. It was concluded that the nitrogen removal ability of Myriophyllum aquaticum was improved by raising water nitrogen levels under the tested condition, which indicates that Myriophyllum aquaticum could purify high nitrogen wastewater. Myriophyllum aquaticum is an ammonium-nitrophile, but had the strongest capacity for growing and removing wastewater nitrogen exhibited with higher than 100 mg·L-1 nitrogen levels only with equal NH4+ to NO3-. The nitrogen component concentrations of protein, amino, and nitrate in Myriophyllum aquaticum plant were all affected by the ratio of NH4+/NO3-.

[Effect of Wastewater Nitrogen Concentrations on Nitrogen Removal Ability of Myriophyllum aquaticum].

Myriophyllum aquaticum, which is an important plant for constructed wetlands, has powerful purification ability for wastewater, however, the relationship between nitrogen removal ability of Myriophyllum aquaticum and wastewater nitrogen concentrations is still unclear. In this study, pot culture experiment was conducted to investigate the effect of wastewater nitrogen levels on nitrogen removal ability of Myriophyllum aquaticum. 7 nitrogen levels were set up as following:2, 5, 10, 20, 100, 200, 400 mg·L-1. The results showed that when the wastewater nitrogen concentration was not higher than 20 mg·L-1, Myriophyllum aquaticum with 20 mg·L-1 of nitrogen concentration grew best in the first 3 weeks; the removal rates of total and ammonia nitrogen were nearly 100% after one week, while the nitrate nitrogen concentrations were very low and varied little; the nitrogen contents of Myriophyllum aquaticum had no significant change, the upper part nitrogen content was higher than the underneath, Myriophyllum aquaticum could also remove nitrogen from the sediment. When wastewater nitrogen concentrations were 100-400 mg·L-1, Myriophyllum aquaticum with 200 mg·L-1 of nitrogen concentration grew best from 4th to 5th week; the removal rates of total nitrogen were 76.5%, 71.5% and 48.1% in the three treatments, and the removal rates of ammonia nitrogen were 99.6%, 99.3% and 60.2% respectively, while the removal rates of nitrate nitrogen were all about 50% and there was no significant difference among treatments; the nitrogen contents of Myriophyllum aquaticum increased with nitrogen levels, but the difference between upper part and underneath was not remarkable, showing uniform distribution; nitrogen accumulations by Myriophyllum aquaticum and sediment accounted for 27.9%-48.4% and 12.2%-24.4% of total nitrogen loss in wastewater. Therefore, the nitrogen removal ability of Myriophyllum aquaticum should be inhibited by higher wastewater nitrogen level, the ammonia nitrogen removal rate was significantly higher than nitrate, the mechanism of Myriophyllum aquaticum nitrogen accumulation and distribution should also be affected by wastewater nitrogen level, and further research is needed.