Study On The Mechanism Of Iron Matrix Coupled With Iron Plaque To Promote Nitrogen And Phosphorus Removal In Constructed Wetlands

Due to the advantages of low cost and environmental protection in sewage treatment,constructed wetlands has developed into an advanced treatment method for effluent from traditional centralized sewage treatment systems in the past few decades,but its existing problems in the actual treatment process cannot be ignored.On the one hand,the lack of oxygen supply in wetlands limits the treatment effect of a variety of pollutants;on the other hand,microbial degradation and assimilation is easily weakened by changes in water supply conditions.Therefore,it is of great theoretical and practical significance to further improve the treatment efficiency of wetland system and optimize the treatment efficiency of nitrogen,phosphorus and other pollutants.In view of the overall efficiency of nitrogen and phosphorus removal in constructed wetlands is not high.and most of the optimization methods require additional energy supply,which leads to increased operating costs.Moreover,there are few researches on adding iron matrix to promote the efficiency of nitrogen and phosphorus removal in wetlands.In this paper,a plant hydroponic system with iron film was established firstly.By comparing with the hydroponic system without iron film,the influence of root iron film on the removal of conventional pollutants was clarified Furthermore,the up-flow vertical subsurface flow constructed wetland system with iron matrix containing different amounts of iron ore was constructed,and the effects of iron matrix coupled with iron film on nitrogen and phosphorus removal and its mechanism were studied.The addition of this experiment laid a theoretical foundation for the practical application of constructed wetland with iron matrix.The main conclusions of this study are as follows:(1)The presence of iron plaque enhanced the removal effect of nitrogen and phosphorus by hydroponic system.Compared with the control group,the experimental Fe group containing iron plaque significantly enhanced the removal of NH4+-N,TN and TP,and the maximum removal rates reached 53.34%,58.73%and 44.55%,respectively.In the control group,the maximum removal rates of NH4+-N and TN were only 19.43%and 26.78%,and TP was barely removed,even showing phosphorus release(2)The iron plaque improved the DO environment around the root system and promoted the activity of aerobic microorganisms.The DO in all growth chambers was above 2mg/L,and the DO in the Fe group was significantly higher than that in the control group(P<0.05),which could explain the good removal of NH4+-N in the Fe group.The formation of iron plaque on root surface increased the concentration of DO around the root by changing root characteristics,thus further promoting the removal of Nh4+-N.(3)The removal efficiency of total nitrogen and total phosphorus was 56.25±3.55%,while that of the control group was 47.56%.The removal efficiency of total nitrogen and total phosphorus in the wetland with iron ore was 56.25±3.55%.In terms of total phosphorus removal,compared with 61.80%in the control group,the average TP removal rate of 5%matrix iron ore was as high as 77.73%,while the removal rate of the experimental group containing 15%matrix iron ore was only 59.5 1%.Therefore,the addition ratio of 5%matrix iron ore is more favorable to the removal of nitrogen and phosphorus than that of 15%matrix iron ore.Compared with the control system,the proportion of total nitrogen removal by microbial interaction was 44.82±5.62%,and the proportion of total phosphorus removal by substrate adsorption was 37.50±0.50%,showing stronger microbial and substrate adsorption.In the experimental wetland system,the oxides of Fe(Ⅲ)are mainly Fe2O3 and Fe(OH)3,and the oxides of Fe(Ⅱ)are mainly FeO.(4)The addition of iron ore enhanced the microbial activities in the constructed wetland,especially those related to nitrogen,phosphorus and Fe.In the wetland system,Thiobacillus and Dechloromonas were dominant genera,which produced redox process of iron,and the α microbial diversity index showed an increasing trend,indicating that the microbial community structure of the wetland showed higher microbial diversity and richness.