Analysis On Efficiency And The Influencing Factors Of Nitrogen And Phosphorus Removal In Different Salt Marsh Wetland Types

With the rapid economic development in recent years,the accompanying environmental problems have also negatively affected the ecosystem of the Yangtze River estuary.The relationship between various ecological factors indicates that the increase of inorganic nitrogen and phosphate in the Yangtze River Estuary is beneficial to the growth of phytoplankton,and eventually leads to frequent occurrence of red tides.According to the geographical features and water quality of the Yangtze River Estuary,submerged plant surface flow wetland(SPSFW),emergent plant surface flow wetland(EPSFW)and floating bed wetland(FBW)were constructed on site.The nitrogen and phosphorus removal effects of the three systems were compared during more than one year of operation.The effects of seasons and hydraulic retention time(HRT)on nitrogen and phosphorus removal were examined.The microbial community structure of the three systems was analyzed.These could provide theoretical basis and data support in low-salinity and low-polluting water treatment.The results showed that:(1)When the HRT was 3d,the influent total nitrogen(TN)concentration was 2.99 ± 1.11mg/L,and the total phosphorus(TP)concentration was 0.14 ± 0.07 mg/L,the removal rate of TN by SPSFW,EPSFW and FBW was: summer> spring> autumn> winter,which were 58.29±15.71%、50.39±19.05% and 55.08±16.17% in summer.The removal efficiency of TP in SPSFW and EPSFW was almost independent of temperature changes,and the average annual removal rate was 65.26 ± 25.87% and 51.65 ± 28.18%,respectively.The treatment efficiency of TP in FBW decreased in winter.(2)The removal rate of TN by extended HRT was relatively small in the high-temperature stage and the low-temperature stage,and could be effectively improved in the medium-temperature stage.When the HRT was 1.5d,the removal efficiency of TP by three systems decreased with decreasing temperature.(3)The microbial community structure richness of the three systems had downward trend with the extension of HRT.Proteobacteria,Chloroflexi,Bacteteroidetes and Actinobacteria were the dominant flora in the system.The abundance of denitrifying bacteria an dephosphorizing bacteria tends to decreased after the temperature increased.Based on field experiments,submerged plant surface flow wetland(SPSFW*),emergent plant surface flow wetland(EPSFW*)and unplanted plants control wetland(CW)were constructed in the laboratory.The effects of salinity on nitrogen removal were investigated.The results showed that:(1)The treatment efficiency of SPSFW* and EPSFW* was significantly better than that of CW.(2)When the HRT was 3d,the influent TN concentration was 2.32 ± 0.31mg/L,and the salinity was 0 ‰,3 ‰,7 ‰,10 ‰,the TN removal rate in EPSFW* maintained a high level,with an average of 90.13 ± 5.05%.However,with the increase of salinity,the TN removal rate in SPSFW* and CW showed a process of rising first and then falling.In summary,SPSFW,EPSFW and FBW all had good nitrogen and phosphorus treatment effects in summer.But compared with FBW,SPSFW and EPSFW were more resistant to temperature drops and were more suitable for long-term nitrogen and phosphorus removal.In addition,emergent plants(reeds)could tolerate higher salinity than submerged plants(foxtail algae).