Effect Of Nitrogen And Phosphorus Removal By Aquatic Plant Combined With Aerobic Denitrifying Bacteria

Eutrophication has become one of the most concerned environmental issues around the world,which seriously threatens the safety of aquatic environment on which human beings depend.The research focuses on the aquaculture tail water,one kind of eutrophication water.Currently,attributed to the advantages of safety,high efficiency and sustainability,biological purifying methods have attracted wide attention around the world,among which aquatic plant and aerobic denitrifying microorganism have great application prospect.Aquatic plant methods have the advantages of low purification cost,simple operation and no secondary pollution.Nevertheless,the purification efficiency of aquatic plant is to be further improved.Aerobic denitrifying microorganism overcomes the shortcoming that nitrification and denitrification must be carried out separately in traditional biological nitrogen removal,making simultaneous nitrification and denitrification possible,which improves nitrogen removal efficiency and saves the cost.However,the vast majority of aerobic denitrifying bacteria are heterotrophic,whose growth and denitrification are greatly dependent on organic sources in the environment,and the low carbon environment in aquaculture effluent has become the key limiting factor for bacterial nitrogen and phosphorus removal.Therefore,the present research selected two life-form aquatic plant,including Eichhornia crassipes and Vallisneria natans and four aerobic denitrifying bacteria of Microbacterium oxydans,Pseudomonas stutzeri,Bacillus velezensis and Rhizobium rosettiformans to investigate the effect of plant-microorganism combined removal of nitrogen and phosphorus.With the utilization and analysis of the interaction between plant and microorganism,the goal of further improving efficiency of nitrogen and phosphorus removal was achieved.The main research content and result are as follows:1 By controlling the temperature,light and other conditions,the effect of two aquatic plant combined with four aerobic denitrifier on nitrogen and phosphorus removal in summer（30℃）and autumn（16℃）were researched.It was found that the cooperating plant and denitrifier significantly promoted efficiency of nitrogen and phosphorus removal.The best combination of Vallisneria natans and denitrifier was plant-Microbacterium oxydans（P-Mic）and plant-Bacillus（P-Bac）.P-Mic removed8.19 and 6.84 mg/L of NO₃^--N at 30℃and 16℃,respectively,and eliminated82.71%and 72.65%of TN at 30℃and 16℃,respectively.P-Bac eliminated 1.21mg/L of PO₄^3--P at 16℃and removed 96.46%and 99.45%of TP at 30℃and 16℃,respectively.The best combination of Eichhornia crassipes and denitrifier at 30℃were plant-Rhizobium（P-Rhi）,which removed 12.67 mg/L of NO₃^--N,1.84 mg/L of PO₄^3--P,75.08%of TN and 61.75%of TP.The best combination of Eichhornia crassipes and denitrifier at 16℃were plant-Microbacterium oxydans（P-Mic）and plant-Bacillus（P-Bac）,among which the former eliminated 7.47 mg/L of NO₃^--N and 46.93%of TN,and the latter removed 1.53 mg/L of PO₄^3--P and 50.14%of TP.2 In the research,Microbacterium oxydans promoted the growth of Vallisneria natans significantly at 16℃,and Vallisneria natans growth was inhibited in certain treatments,probably caused by low temperature and the competition for nutrients between plant and denitrifier.Furthermore,the aerobic denitrifying bacteria were capable of promoting Eichhornia crassipes growth,significantly increasing plant biomass at 30℃and apparently alleviating the plant decay at 16℃.The denitrifier increased the plant TN and TP content to varying degrees.Significant correlation between plant TN content and TN removal rate at 30℃and 16℃and the significant correlation between plant TP content and TP removal rate at 30℃indicated that plant absorption was closely related to nitrogen and phosphorus removal from wastewater.The effect of aerobic denitrifier on plant root activity,leaf chlorophyll content,leaf soluble sugar content and leaf soluble protein content reflected the mulifunctionality of aerobic denitrifier in regulating the physiological characteristics of Eichhornia crassipes.3 The effect of Eichhornia crassipes on aerobic denitrifying bacteria could be obtained by the nitrogen and phosphorus removal experiment with the root exudate extracted from Eichhornia crassipes root as the carbon source of aerobic denitrifier.The results were as follows:the extract from root had the capability of promoting growth of aerobic denitrifying bacteria and significantly improving the efficiency of nitrogen and phosphorus removal.Four aerobic denitrifier was capable of secreting IAA,and the root water extract stimulated Microbacterium oxydans to secrete more IAA,but whether denitrifier secreted other substance to affect the Eichhornia crassipes growth and development needs further investigation.The key denitrification enzyme specific activity of aerobic denitrifying bacteria did not increase,meaning that the enhanced ability of bacterial nitrogen and phosphorus removal might not be attributed to the enhancement of denitrification capacity of unit bacteria,but to the improvement of microbial growth.4 Plant absorption played a major role in the nitrogen and phosphorus removal by aquatic plant combined with Rhizobium rosettiformans,among which the absorption by Myriophyllum spicatum accounted for 73.94%and 86.13%of nitrogen and phosphorus removal from water,respectively.As Rhizobium rosettiformans was combined with Eichhornia crassipes and Vallisneria natans,on the one hand,the nitrogen removed by microbe,including microbial absorption and aerobic denitrification of Rhizobium rosettiformans into nitrogenous gas,accounted for 41.07%and 49.16%of nitrogen removal from water,respectively;on the other hand,the phosphorus absorbed by microorganism accounted for 47.16%and 38.90%of the phosphorus removal,respectively.Aerobic denitrifying Rhizobium rosettiformans also played an important part in the combined process of nitrogen and phosphorus removal.