The Microbial Effects On Nitrogen Cycling And Ecological Dynamics Model In Horizontal Subsurface Flow Constructed Wetlands

The performance and mechanisms of horizontal subsurface flow contructed wetlands reed/gravel bed system of Guanting Reservoir were studied for the preventive treatment of the pollution of potable water sources. The study includes:(1) The Nitrogen removal rate and main factor analysis of horizontal subsurface flow constructed wetlands;(2) The forms distribution and transformation rule;(3) The analysis of the frictional distribution and population of Nitrogen transformation microbes in the system;(4) The microbial diversity research in the system;(5) The featured denitrifiers were screened,the physiological and biochemical characteristics were analyzed and identified;(6) Modeling of nitrogen cycles in horizontal subsurface flow contructed wetlands.The major research findings are as follows:(1) On the condition that the average hydraulic stayed for 3.85 hours, through Nitrogen removal analysis of horizontal subsurface flow constructed wetlands. The system exhibits certain decontamination ability. The influent COD,NH₄⁺-N,NO₃^--N,Org-N and TN are 7.8¹2.7mg·L^-1,0.05¹5.0mg·L^-1,1.3⁵.2mg·L^-1,0.66⁵.18mg·L^-1,2.2²0.0mg·L^-1. The annual average removal rate of the gravel bed below the reed wetlands system are 25.8%,10.0%,42%,31.2% and 18.9%.Seasonal variation has a significant effect on the removal rate of the polluted elements. System removal rate has a little decrease in the elements of COD,NH₄⁺-N,NO₃^--N,Org-N and TN in cold season. Removal rate of every elements are about 11.2%,6.5%,31.0%,20.5% and 15%.(2) Seasonal variation has a significant effect on the factors of temperature and pollutionload rate. If the influent temperature changes from 0.9℃to 24.8℃, a positive corelation is found between the removal rate of various forms of Nitrogen elements'volume and the temperature. The constants K_v of NH₄⁺-N,NO₃^--N,Org-N and TN are 0.01⁰.2d^-1,0.03⁰.3d^-1,0.07⁰.3d^-1and 0.02⁰.15d^-1. Meanwhile, the volume removal rate constants K_v20 are 0.0769,0.1673,0.1508 and 0.0732 d^-1 when the temperature is 20℃.It interprets that the wetlands have stronger capability to reduce NO₃^--N and Org-N than NH₄⁺-N. The removal rate of NH₄⁺-N and Org-N are logarithms related to load rate. When the load rate of NH₄⁺-N is 15gN·m^-2·d^-1 , its removal rate of 1.02 gN·m^-2·d^-1 is the maximum. At the same time, when the load rate of Org-N is 3.2 gN·m^-2·d^-1 , its removal rate of 0.36 gN·m^-2·d^-1 is the maximum. (3) Five major factors were established by analyzing principal factors in five outlet water has a negative correlation with water temperature. The 2nd and 3rd have a positive correlation with wetland fill NO₃^--N and NH₄⁺-N load. The 4th and 5th factors have closest relations and negative correlation with influent DO and ORP. The sort order of the major factors in the sixteen indicators are: temperature> NO₃^--N load > NH₄⁺-N load > DO > ORP. The sequence is slightly different from the five outlet indicators.As an independent eco-system, the effect factors in artificial marshland are more complex and unceratin ; however, temperature is still the major element among all elements.(4) Having compared the nitrification/denitrification strength and respiration intensity of rhizosphere and non- rhizosphere, the researcher finds rhizosphere worked significantly better than non- rhizosphere. The study on denitrification groups such as ammonifying bacteria, nitrite bacteria, nitrifying bacteria and denitrifying bacteria shows the order of magnitude of ammoniation bacteria is 10⁸ 10¹⁰cfu and its distribution regularity change is not found. And it did not necessarily linked wetlands spatial position (length); When the order of magnitude of nitrification bacteria is 10³¹0⁷MPN, Bacterial nitrification is reducing at the wetland fill end, especially in warm days. The distribution did not significantly change when the magnitude of nitrifying bacteria is 10⁵ 10⁷MPN.In warm season, the number of nitrifying bacteria is at the front end and the middle is higher than the tail end. The tail end is slightly higher than the front end of wetlands when the number of denitrifying bacteria level is in 10⁴¹0⁷MPN.(5) The use of PCR-DGGE technique reflects the real level of the microbial population structure and distribution in subsurface flow constructed wetland system. Microbial diversity in horizontal subsurface flow constructed wetland decreases along the waterflow direction first. Through the correlation analysis between frictional COD in the wetland system and the Shannon index, we found frictional COD change and Shannon index correlated well in the reed-gravel system , and different spatial distribution of microbial diversity have different effectiveness of disposing organic matter in different seasons.(6) Nine selected denitrifying bacteria showed some ability of denitrification, and the denitrification reation occurs mainly in the logarithmic phase of cell growth, and the reaction rate speeds up gradually with the biomass increases. The comparison of denitrification capacity shows that bacterial strain DF2 and DF3 have the highest deni trification efficiency; they can remove 90% TN in 72h, and the final removal rate remains at about 95%. We focus on the removal characteristics of strain DF2 by using 16SrDNA to identify strain DF2; compared with reference strains,we determined the phylogenetic position of the strain, and the results show that the strain belongs to the Dexter's genus, no similar reports were available until now.(7) Nitrification and denitrification in horizontal subsurface flow constructed wetland are the main methods to transform nitrogen, the rates respectively reach 0.791gN·m^-2·d^-1 and 0.823gN·m^-2·d^-1; Secondly, plants'absorption of nitrogen is 0.747gN·m^-2·d^-1; precipitation and regeneration rates have reached 0.514gN·m^-2·d^-1 and 0.446gN·m^-2·d^-1; other contributory means are plant-corruption 0.282gN·m^-2·d^-1 and mineralization 0.0126 gN·m^-2·d^-1. The main influencing factors in conversion and removal of nitrogen in the system in decreasing order are denitrification, plant intake and sedimentation. Denitrification takes up 60.7% of the total nitrogen removal, plant uptake accounts for 34.3%, and 5.0% in precipitation, the modelachieved certain accuracy and rationality in predicting the results.