Nitrogen Removal Characteristics Of Strain XP1 And Its Enhanced Denitrification In Constructed Wetlands

At present, pollution of nitrogen has been wide concerned. The nitrogen release to water is lead to eutrophication and water degradation, which impacts the growth and reproduction of aquatic creatures. Nitrogen is easily accumulated in soil profile that will lead to the soil quality deterioration, which is harmful to plants growth. With the generated increasingly serious nitrogenous pollution, removal of nitrogen in the water has became to be a hot issue of water pollution control. Constructed wetland is used widely in wastewater treatment because of its easy to establish and administration, cheaper, lower energy consumption and better nature reserve.In our study, denitrifying bacterium strain XP1 was screened by dilute soil suspension-spread plate techniques from soil that sampled from the rhizosphere of Typha latifolia. The capable of denitrification, ecological factor and growth curve were investigated.The results showed that the most suitable carbon source for denitrification was citrate sodium. The appropriate pH value range for XP1 was 7.0～9.0, in which 8.0 was the optimum. The optimal molar ratio of carbon/nitrogen and initial concentration of nitrogen were 7 and 30mg/L. After 8 hours cultivation, XP1 reached logarithmic phase in which XP1 could remove nitrogen effectively and the removal rate of TN was more than 90% at last in the best conditions. According to the morphology observation, the strain belonged to Grame-negative bacillic and was about (0.25～0.3)×(0.6～0.8)μm. Based on the 16S rDNA sequence and phylegenetic tree, it could be concluded that the strain was identified as Paenibacillus sp..The bacterial strain XP1 was inoculated into rhizosphere of the three plants in the lab. For studying the enhanced denitrification and the change of XPl in the rhizosphere soils of three plants (Arundo donax, Phragmites australis and Typha), research was analyzed by denaturing gradient gel electrophoresis (DGGE).The results showed that without the enhanced denitrification of simulated wetlands, the order of nitrogen removal capacity in the three wetlands was Arundo donax> Phragmites australis> Typha in the same conditions. The quantitative order of the dominant microorganisms around the three plants was Arundo donax> Phragmites australis> Typha, although there was no obvious difference in the diversity of microorganisms. The ratio of indigenous strain XP1 in the rhizosphere soils of the three plants was 1.5:1.3:1, and compared to the control group, the enhanced denitrification of the three plants were increased frome 14% 56% 56% to more than 98%, which meant the XP1 had a significant enhancement in denitrification. When TN concentration of the wetland was less than that of the class III criteria in the Environmental Quality Standards for Surface Water China (p(TN)≤lmg/L), the diversity and quantities of the microorganisms in the three plants root soils decreased, though there was no marked change in the microbial community structure. For strain XPI, the quantities in three plants roots soils decreased by up to 40%,50% and 67%, respectively.