Study On Purification Performance And Microbial Community Characteristics Of Constructed Wetland For Mariculture Tail Water Treatment

The mariculture tail water contains a large number of N and P nutrients.A series of eco-environmental problems will be caused because of direct discharged tail water.The constructed wetland sewage treatment system originates from the simulation of natural wetlands and can be used for advanced treatment of pollutants in mariculture tail water.It has the main characteristics of good purification effect,stable effluent quality,strong nitrogen and phosphorus removal capacity,convenient operation and maintenance management,low capital construction and operation cost,strong adaptability to load changes,and is suitable for the treatment of intermittent discharge sewage and so on.This kind of system has outstanding technical advantages and broad application prospects in the treatment of mariculture tail water.Relying on two types of composite vertical flow constructed wetland systems for the treatment of mariculture tail water,this thesis focuses on the removal effects of nitrogen and phosphorus nutrients in the two different systems,discussed the adsorption capacity of the substrate to nitrogen and phosphorus in the wetlands.We explored the community composition and diversity of microorganisms by high-throughput sequencing technology,and revealed the relationship with nitrogen removal which provided a theoretical basis for the construction of an efficient filter medium-plant-microbe composite ecosystem.The main results are as following:?1?The removal rates of NO₃^--N,NO₂^--N,NH₄⁺-N,TN and TP by constructed wetland simulation system were 92.77%,99.19%,99.65%,85.94%and 48.94%,respectively.The main place of nitrogen removal was down-flow pool,and the main place of phosphorus removal was up-flow pool.The removal rates of NO₃^--N,NO₂^--N,NH₄⁺-N,TN and TP by medium pilot constructed wetland were 92.08%,599.74%,94.48%,76.70%and 75.90%,respectively.The main place for nitrogen and phosphorus removal were primary wetland.The nutrient removal effect of the constructed wetland simulation system was more stable,and it was speculated that the internal of the medium pilot constructed wetlands was in a state of anoxia,the both concentrations of inorganic nitrogen in the effluent of the two kinds of constructed wetlands conformed to the first-class standard of"Mariculture Water Discharge Requirements".?2?Pseudo-first-order kinetic equation,pseudo-second-order kinetic equation and Elovich equation could well describe the adsorption characteristics of three kinds of fillers for NH₄⁺-N and TP.The theoretical equilibrium NH₄⁺-N adsorption capacity of fine sand,cinder and macadam were 100.928 mg·kg^-1,130.358 mg·kg^-1and 96.924mg·kg^-1,respectively.The theoretical equilibrium phosphorus adsorptions capacity of fine sand,cinder and macadam were 39.298 mg·kg^-1,96.916 mg·kg^-1and 38.741mg·kg^-1,respectively.The chemical factor was the main factor to control the adsorption rate,and the cinder had the best adsorption effect on NH₄⁺-N and phosphorus in the culture tail water.?3?The community composition and diversity of microorganisms may have an impact on nitrogen removal in wetlands.The?diversity of medium plot constructed wetland was significantly higher than that of constructed wetland simulation system.In the same system,the?diversity of plant roots was significantly higher than that of the filter medium layer.The microbial composition of plant roots was significantly different from that of the filter medium layer.The dominant bacteria in the constructed wetland simulation system were Proteobacteria,Bacteroides,and Campylobacter,and the dominant bacteria in the medium pilot constructed wetland were Proteobacteria,Bacteroides,Actinomycetes,and Campylobacter.Among them,Proteobacteria was the most important phyla in the constructed wetlands,accounting for more than 50%in both systems.Proteobacteria was found in this study in a total of 3 classes,arranged in terms of abundance from high to low as?-proteobacteria,?-proteobacteria and?-proteobacteria.The abundance of Actinomycetes in the lower layer of the medium pilot constructed wetland was high,it was speculated that there was a problem of nutrient deficiency in the low-layer of medium pilot constructed wetland.Total 15 generas of bacteria related to denitrification were identified in this sequence,including Nitrosomonas and Nitrosospira with ammonia oxidation function;and genus of Nitrospira with nitrification function;Acinetobacter,Pseudomonas,Bacillus,Dechloromonas,Rhodanobacter,Thauera,Flavobacterium,Rhodococcus,Acidovorax,Hydrogenophaga,Hyphomicrobium and Thiobacillus with denitrification function.Denitrifying bacteria were dominant in the two kinds of wetlands,and the abundance of nitrifying bacteria in the medium pilot constructed wetland was higher than that of the constructed wetland simulation system.Based on the denitrification effect and the sequencing results,it was inferred that there was a short-cut nitrification-denitrification pathway.