Study Of Ecological Floating Island Technology For Nitrogen And Phosphorus Removal From Poultry And Livestock Breeding Wastewater

In recent years,China’s livestock and poultry breeding industry has made great progress,which has not only met people’s demand for food,but also brought serious threats to the surrounding ecological environment.Waste water from livestock and poultry breeding has become an important source of nitrogen and phosphorus pollution in China.At present,although various physical and chemical methods are studied more in theory,there are some problems in practical application,such as large investment,complex operation and secondary pollution.Ecological floating bed technology is a new method of water ecological treatment.It has many advantages,such as less investment,no secondary pollution and beautification of the environment.（1）In order to screen the dominant species of ecological floating island suitable for different concentrations of nitrogen and phosphorus in tailrace of livestock and poultry wastewater,5 kinds of effluents,such as Oenanthe javanica,Eichhornia crassipes,lris sibirica,Thalia dealbata and lris pseudacorus,and 3 kinds of submerged plants,such as Myriophyllum verticillatum,Elodea nuttallii and Ceratophyllum demersum,were selected.The growth characteristics of these 8 plants under different concentrations of nitrogen and phosphorus and their removal efficiency of ammonia nitrogen,total phosphorus and COD in water were investigated through simulation experiments.Curve regression and Principal Component Analysis were carried out to obtain the comprehensive evaluation of plant purification function.The results showed that the removal ability of Eichhornia crassipes and Thalia dealbata was significantly higher than that of other aquatic plants at a low concentration of nitrogen and phosphorus(NH₄⁺-N:80～120 mg·L^-1,TP:8～16 mg·L^-1).Oenanthe javanica and lris pseudacorus had obvious advantages in removing the high concentration of nitrogen and phosphorus(NH₄⁺-N:180～220 mg·L^-1,TP:30～35 mg·L^-1),and they also had good adaptability.Myriophyllum verticillatum had better purification effect in submerged plants,and biomass increased significantly（P<0.05）;Although Eichhornia crassipes has good purification capacity,it is easy to cause secondary environmental problems,so we should choose carefully and adjust measures according to local conditions.（2）An artificial floating island is an ecological restoration technology that aims to create sustainable ecosystems and improve biodiversity.The floating island system exploits the combination of aquatic plants,microorganisms,and extracellular enzymes to purify wastewater.We investigated the purification efficiency of eight aquatic plant species（Ceratophyllum demersum,Elodea nuttallii,Eichhornia crassipes,lris pseudacorus,lris sibirica,Myriophyllum verticillatum,Thalia dealbata and Oenanthe javanica）cultured in wastewater.The relationships of plant purification capacity with extracellular enzyme activity and microbial community were analyzed to explore the crucial factors that affect the plant purification capacity and the mechanism of pollutants removal in different plant systems.Three plant species,namely Oenanthe javanica,Thalia dealbata,and lris pseudacorus,were the most effective for purification of ammonium-nitrogen（NH₄⁺-N）,total phosphate（TP）,and chemical oxygen demand（COD）with maximum efficiencies of 76.09%,85.87%,and 89.10%,respectively.Urease,alkaline phosphatase（AP）,andβ-glucosidase activities were significantly and positively correlated with root system development（P<0.05）.Activities of urease and AP were positively correlated with NH₄⁺-N and TP removal,respectively.The magnitude of urease and AP activity was generally consistent with the plant’s capacity to remove NH₄⁺-N and TP.β-Glucosidase activity and COD removal were not significantly correlated.The dominant microbial phylum in each species treatment was Proteobacteria.Alphaproteobacteria and Bacteroidia showed greater involvement in degradation of pollutants in the experimental system.（3）The transcriptome sequencing of aquatic plant roots in the environment with high and low concentrations of nitrogen and phosphorus was carried out by taking water crescens as an example.The differences in gene expression of aquatic plants in the presence of different concentrations of nitrogen and phosphorus at the gene level were explored through library sequencing and assembly,Unigene functional annotation,and analysis of differentially expressed genes.The results showed that the metabolic pathways involved in metabolism were the most,and the small metabolic pathways involved in global and summary metabolic pathways accounted for the largest proportion.Compare two of three groups of samples（LNP versus CK,HNP vs CK,LNP vs HNP）,differences in gene expression analysis（|log₂FC|1 or higher,FDR 0.01 or less）,cut the number of the genes were greater than raising gene.The KEGG enrichment results of LNP vs CK,HNP vs CK and LNP vs HNP were investigated,and 401,389 and 404 genes were annotated for the three genes,respectively.The differentially expressed genes between the two groups of samples and the control samples under different concentrations of nitrogen and phosphorus were mainly reflected in ribonucleic acid.By comparing the two groups of samples,the differentially expressed genes were mainly in the synthesis of ribonucleic acid,photosynthesis and related proteins.This sequencing has shown that functional genes such as ribonucleic acid,photosynthesis and photosynthetic system antenna proteins play a key role in the purification of nitrogen and phosphorus in the Oenanthe javanica root system in this environment with different nitrogen and phosphorus concentrations.