Purification Effect,Mechanism And Engineering Demonstration Of Myriophyllum Aquaticum Floating Bed For Eutrophic Water

In this study,the water culture experiment and field experiment were carried out with Myriophyllum aquaticum as floating-bed plant.To compare the difference of water purification ability with other common floating-bed plants and study on the influence of different coverage rates on the purification effect of the floating bed of Myriophyllum aquaticum.At the same time,taking Zongjiaqiao River in Yixing as an example,an engineering demonstration was carried out to analyze the rule of root-to-shoot ratio and nitrogen-phosphorus migration in different stages,and put forward the management strategy of Myriophyllum aquaticum as a floating-bed plant.The effects of plant floating bed system on microbial diversity and bacterial community structure in different regions were analyzed by 16sDNA method.Finally,through the long-term monitoring of the water quality of the Zongjiaqiao River,in order to evaluate the effect of engineering measures on the restoration of the Zongjiaqiao River,the purpose of this paper is to provide a reference basis for the popularization and use of the floating bed.?1?The results of water culture test showed that the growth and reproduction ability and water purification ability of Myriophyllum aquaticum was stronger.Under the condition of water culture,the removal rate of TN was increased by 44.73%,and the removal rate was 81.48%in Hollow cabbage and Oenanthe javanica treatment groups.The removal rate of NH₄⁺-N was 80.13%,which was 80.13%higher than that of Hyacinth and Oenanthe javanica,and there was no significant difference among several floating-bed plants on the removal of NO₃^--N,and the removal efficiency of Myriophyllum aquaticum was 80.13%.The removal efficiency of TP by plants was lower than that of TN.Among the six species of aquatic plants,the best removal rates were found to be Hollow cabbage,Eichhornia crassipes,Oenanthe javanica and Myriophyllum aquaticum,respectively,reaching 69.74%,66.85%,64.16%and59.28%,respectively.The effect of treatment with Iris pseudacorus and Alternanthera philoxeroides was relatively poor.?2?The results of field test show that the floating bed can obviously improve the water quality of eutrophic water body.The floating bed can effectively buffer the change of pH in the pool and keep it between 7.5 and 7.0.However,the presence of floating bed prevented the air from diffusing oxygen into the water,and the concentration of DO in the treatment group was significantly lower than that in the control group?p<0.01?.In addition,the presence of floating bed could significantly improve the removal rate of pollutants in the treatment group?p<0.01?.In this experiment,the increase of floating bed coverage of Myriophyllum aquaticum is also beneficial to the removal of pollutants.The average removal rates of TN?NH₄⁺-N and TP were 85.55%,84.03%and 91.52%,respectively,with no significant difference between 20%and 30%coverage rates?p>0.05?.The optimal residence time for removal of different target pollutants is also different,The optimal residence time of TN and Chl-a is 15 days,NH₄⁺-N is 5 days,and the best optimal residence time for TP?COD_Mn and NO₃^--N is 20 days or more.?3?The results of in-situ engineering demonstration of Myriophyllum aquaticum floating bed show that regular harvesting and effective management are of great significance to improve the efficiency of floating bed system.It is suggested that the whole plant should be harvested many times after July.The growth cycle of the Myriophyllum aquaticum was concentrated from April to August,and the proportion of water was less than that of underwater for most of the time,and there was no significant difference in TN,TP content between the above and underwater parts.TN was the highest from June to September,with an average of 32.38 g/kg,TP was highest between July and September,with an average of 6.56 g/kg.Compared with March,the total biomass?dry weight?of the floating bed increased 7.36 times,the N content increased 13.38 times,and the P content increased 9.77 times in the six months.It is estimated that the floating bed relies on plant absorption to remove 581.74 kg N and114.03 kg P elements.As an aquatic plant,Myriophyllum aquaticum has strong adaptability and reproduction ability and can withstand low temperature.It can be widely used as a floating-bed plant.?4?The results of microbial diversity analysis show that the floating bed system can significantly improve the biodiversity of the water body under the floating bed and the open water area.Through the analysis of the community structure at the level of phylum classification,it was found that the main dominant microbe communities were Proteobacteria,Actinobacteria,Cyanobacteria,Bacteroidetes,Chloroflexi,Acidobacteria.The sum of relative abundance ratio accounted for 89.6%⁹8.7%of total relative abundance.In this study,although the proportion of Cyanobacteria in open water and under floating bed is relatively small,the average value is still 19%.There is still the possibility of cyanobacteria breeding in large numbers and further deterioration of water quality.?5?Through long-term monitoring,it can be found that the water quality purification effect of Zongjiaqiao River after treatment is obvious.By September2018,the average concentrations of DO,COD_Mn,NH₄⁺-N,TN and TP in the check section of Zongjiaqiao River had basically eliminated the black odor,and the average values of the concentrations of TN,TN and TP in the river water had met the target requirements.However,during the operation of the demonstration project,due to factors such as rainfall,flood discharge and season,the concentration of pollutants in Zongjiaqiao River fluctuated greatly,which in turn affected the purification of NH₄⁺-N,COD_Mn and other pollutants in the river to a certain extent.It is necessary to strengthen the water surface cleaning and plant maintenance,especially to protect the floating bed of Myriophyllum aquaticum from man-made damage.