Nitrogen Removal Processes In Constructed Wetland And Its Influencing Factors

Traditional nitrogen removal processes include nirtrification and denitrification,however it has been changed by the discovery of anaerobic ammonium oxidation.It is significant for the ecological restoration of wetland by nitrification and denitrification process as well as anaerobic ammonia oxidation process.This article focuses on the nitrogen removal process involving microorganisms,and the remove rate of the ammonium,nitrate and total nitrogen in the constructed wetland were measured,and the nitrification activity and denitrification activity as well as the anammox rate of the constructed wetland substrates were also determined in this study.Microcosm incubations under anaerobic conditions were established to identify key factors affecting denitrification and anammox.Our results showed that:（1）It is different for the removal efficiency of nitrogen of water in constructed wetlands in different period.The average removal rate of TN in the water of constructed wetland was90.77%.The removal rate of ammonia was 88.71%.The average removal rate of nitrate in constructed wetlands was only 22.01%.The average removal rate of nitrite in constructed wetland was 48.95%,and increased first then decreased during the period.（2）There is a big difference in nitrification and denitrification activity in different time.Overall,the nitrification activity in September were highest,followed by March.So as to the denitrification activity.The nitrification potential rate（PNR）was significantly positively correlated with ammonia oxidizing bacteria（AOB）amo A gene abundance and ammonia oxidizing archaea（AOA）amo A gene abundance.Denitrification enzyme activity（DEA）was significantly positively correlated with the abundance of AOB amo A gene and positively correlated with nir S gene abundance.The water temperature has the biggest influence on the abundance of AOA amo A gene,followed by the organic matter content.And the organic matter has the biggest influence on the abundance of AOB amo A,followed by the p H and NO₃^--N concentrations.The NO₃^--N had the biggest influence on the abundance of nir S gene,followed by the organic matter,and the NH₄⁺-N content of overlying water.The dominant group in AOB mainly includes 4 genera,and the sum of relative abundance can reach 87.48%.The dominant group in AOA mainly includes 4 genera,and the sum of relative abundance can reach 99.85%.The dominant groups of nir S denitrifying microorganisms mainly include 5 genera,and the sum of relative abundance can reach 97.72%.（3）In isotopic incubation experiment,results showed that the rate of denitrification in constructed wetland was highest in August,followed by September and then October,In August,the denitrification rate was（29.67±15.96）nmol N g^-1h^-1,and in October it was（11.57±5.79）nmol N g^-1h^-1.The anammox rate showed the opposite situation,the highest rate is in October（3.22±0.28）nmol N g^-1h^-1,and the lowest was in August（0.42±0.08）nmol N g^-1h^-1.The contribution rate of anammox to N₂in constructed wetland substrates was 21.78%in October.The contribution rate of anammox in artificial wetlands was 0.94%in September,which was the lowest.（4）Different environmental factors have different effects on anammox and denitrification processes.It showed that the denitrification of substrates increases with the increase of NO₃^--N concentration,and the anammox also shows an increase with the increase of NO₃^--N concentration.Denitrification rate and anammox rate in the substrate increased with the increase of temperature.The optimum temperature for substrate denitrification is 25-35°C.The optimum temperature for anammox is 35°C.The addition of exogenous carbon has a strong promoting effect on denitrification,but it has little effect on the anammox.Different types of carbon sources have different effects on denitrification activity,and glucose is more beneficial to increase denitrification activity than sodium acetate.The powder made by Typha orientalis and phragmites communis,have significant differences in the promotion of denitrification and anammox.Denitrification and anammox rate are higher in the addition of typha orientalis powder than that of the addition of phragmites communis powder.