Contribution And Purification To Denitrification And Phosphorus Removal Of Remediating Eutrophicated River In Confluence Area From Farmland Using Aquatic Plant-microbe Integrated System

Agricultural non-point source pollution is becoming the main source of pollution in current surface water bodies.The farmland drainage carrying a large amount of unabsorbed nutrients such as nitrogen and phosphorus is discharged directly into the river in confluence area from farmland,which has resulted in the eutrophication of water bodies.In the paper,the eutrophicated river in confluence area from farmland was remediated by the use of aquatic plant-microbe integrated system.Improvement effect of the project on river water quality and total reduction of pollutants such as nitrogen and phosphorus in water were analysised.Based on engineering application research,further research on the effects of different aquatic plants and bio-fillers in purifying river water bodies in summer and winter was studied.Main ways of nitrogen and phosphorus removal from water and removal contribution of each pathway in different treatment systems was carefully analysised.And the effects of aquatic plants on microbial community composition were studied by high-throughput sequencing technology.Main removal mechanism of nitrogen and phosphorus pollutants in process of remediation of eutrophicated river in confluence area from farmland using aquatic plant-microbe integrated system.The results of this paper can provide theoretical support for the ecological restoration project.The main results are as follows:(1)In response to the eutrophicated river in confluence area from farmland,the ecological restoration project of the river was carried out in one of villages in the city of Zhenjiang,Jiangsu province.River water quality was obviously improved.Before the project,the river belonged to level inferior V,and the water quality of the monitored section was much better than level V.During the ecological restoration project,the total reduction of nitrogen and phosphorus was about 2271.87 kg and 167.0 kg,and the reduction rates of nitrogen and phosphorus in the river reached to 43.87%and 32.62%,respectively.These results indicated that N and P absorption by aquatic plants was one of the important ways in water quality improvement;N and P removal through sedimentation and deposition due to microbial activity might be the main ways on N and P reduction in eutrophicated rivers.(2)In the summer experiment,each treatment has a good purification effect on water pollutants.The concentrations of TN,TP and COD_Cr in water are significantly reduced,which are better than level V.At the end of the experiment,the removal rate of TN from Iris pseudacorus+Myriophyllum elatinoides+bio-filler combination is up to 74.5%;Eichhornia crassipes+bio-filler treatment has the highest removal rate of TP of 73.2%.The combination of aquatic plants and bio-fillers has better purification effects on pollutants than single aquatic plants.The biomass increase and absorption of nitrogen and phosphorus of single aquatic plants in water bodies are ranked from high to low as Eichhornia crassipes>Myriophyllum elatinoides>Iris pseudacorus is the best aquatic plant for purification.The reduction of N and P in aquatic plant-biofiller combination is greater than that of single aquatic plants.In the single aquatic plant treatment,the self-absorption of aquatic plants is the main way to remove N and P from water bodies;Microbes and other effects are important ways.In the aquatic plant-biofiller combination treatment,microbes and other effects are the main ways to remove N from the purification system;the absorption of aquatic plants is an important way.Plant uptake is still the main pathway for P removal in water,and microbes and other functions are important pathways.(3)Under low temperature conditions in winter,the activity of microbes was greatly inhibited,and bio-filler film was less effective.Three cold-tolerant plants can grow normally but grow slowly.Single plant treatment sorted by biomass increase from large to small for Lolium perenne>Oenanthe javanica>Myriophyllum elatinoides.Each treatment can effectively remove pollutants from water bodies,ensuring that the concentrations of TN,TP and COD_Cr were superior to surface V water standards.At the end of the experiment,the removal rate of TN from Oenanthe javanica+bio-filler combination is up to 53.5%;Lolium perenne treatment has the highest removal rate of TP of 55.7%.Lolium perenne is the preferred plant for low temperature conditions in winter.The removal mechanism of N and P by aquatic plant-biofiller combination is the same as that of single aquatic plants.The self-absorption of plants is the main way to remove N and P in water.Physical precipitation is an important way to remove N and P from purification systems.Microbes and other effects have the least contribution to the removal of N and P in purification systems.(4)According to the Chao1 index and the shannon index,aquatic plants can increase the abundance and diversity of microbial species populations.According to PCA analysis,aquatic plants have a greater impact on the microbial community composition.Proteobacteria,Chloroflexi,and Bacteroidetes are the relatively abundant microbial flora in the composition of each microbial community,mainly playing the role of nitrogen and phosphorus removal.Aquatic plants effectively reduce the relative abundance of Cyanobacteria on the filler and reduce the risk of severe eutrophication.In the process of joint restoration of aquatic plants and microbes,aquatic plants can increase the diversity of microbial species composition on bio-fillers,improve the abundance of related nitrogen and phosphorus-removing microbial flora,and help to strengthen the reduction of N and P by microbial units.In summary,the addition of bio-filler will have a significant improvement in water purification effect and reduction of N and P compared to single aquatic plants.Aquatic plants can increase the abundance and diversity of microbial species and enhance the removal of N and P by microbes.The absorption of aquatic plants and the removal of nitrogen and phosphorus by microbes are the main ways to remove N and P from water.Therefore,Aquatic plant-microbe integrated remediation technology can effectively control heavy polluted rivers in confluence area from farmland.Field engineering practice and simulation test results confirm that the combination of Eichhornia crassipes(Mart.)Solms+bio-filler(summer)and Lolium perenne L.+bio-filler(winter)has the best effect on water purification and can be applied in the practice of restoration engineering.