Nitrogen Removal Efficiency And Enzyme Activities In Baffled Subsurface-flow Constructed Wetlands With Aquatic Plants Added As Exogenous Carbon Source

Aiming at the problems in the treatment of constructed wetland such as nitrate-rich wastewater with low carbon content and deficiency of carbon source,the author improves the denitrification efficiency of constructed wetlands by adding aquatic plant material as carbon source.In this study,the baffled subsurface-flow constructed wetland systems were used to simulated the quality of wastewater by using pistia stratiotes,water hyacinth,reed and mixed straw as supplementary carbon sources,and to analyse the positive and negative effects of carbon source addition into consideration.In order to provide practical basis in the constructed wetlands for the application of plant carbon sources,the text studied the denitrification efficiency and nitrogen conveconversion,simultaneously detecting the changes of Cellulose,P-glucoside enzyme,Dehydrogenase,Urease,Protease and Catalase in the different positions of the each experimental device before adding carbon source and the early and late period after adding carbon source.So as to provide theoretical and practical basis for the application of plant carbon source enhanced denitrification artificial wetland.The main results are as follows.Through the static release experiment,it was found that the organic matter release of three kinds of plant resource of pistia stratiotes,water hyacinth and reed stalks reached the highest at the initial of the experiment,the release amounts of COD reached 31.08 mg/g,25.11 mg/g and 21.41 mg/g,respectively.And then decreased immediately and maintained at a low level,However,with the process of releasing,some pollutions such as N,P and so on were released too.The highest release accumulation of TN and TP is Pistia stratiotes which were 9.07mg/g and 0.69mg/g,while the release accumulation of reed were minimum which were 5.11 mg/g and 0.31 mg/g respectively.The dissolved oxygen concentration and the oxidation-reduction potential of each unit along the baffled subsurface-flow constructed wetlands were always lower than that of the control system,indicating that the dosing of the carbon source contributes to the formation of the reducing environment.Through the baffled subsurface-flow constructed wetlands and detection of the average removal efficiency of NO3--N in each device,and the order was:Pistia stratiotes system(52.03 9%±14.61)>Mixing system(47.23%± 11.86)>reed system(45.19%± 11.29)>water hyacinth system(43.01%±22.88),and experimental systems were significantly higher than the blank system(p<0.05).And initial release rate of NO3--N and TN were faster,but with the experiment proceeding,carbon source consumption,the removal rate followed by a drop.The result showed that there were nitrogen release of plant biomass and an accumulation of NO2-and NH4+ make the TN removal efficiency of each experimental system is lower than that of NO3--N,besides,the addition of plant biomass significantly enhanced the denitrification efficiency in the constructed wetlands.Concentrations of NO2-and NH4+ were significantly positively correlated with the removal rate of NO3’-N(p<0.05).Considering the removal of NO3--N regarded as the positive effect and taking Nitrogen transformation and organic matter flow out with the effluent as negative effects of carbon source addition,the mixed straw is the best choice for this experiment.The author found that the activity of different enzymes in each position was at a low level in the system,which was not fed with carbon source,and the activity of different kinds of enzymes in other systems was affected by the carbon source dosing,and the activity reached the maximum at the initial time after adding the carbon source.And the activity of different enzymes in the carbon source dosing area located in the wetland surface was higher than that in the middle,lower part of the carbon source dosing area,as well as the surface position where there has no carbon source applied.