Performance And Denitrifier Microbial Analysis For Vertical Flow Constructed Wetland Treating Eutrophic Brackish Water

In recent years,the eutrophic brackish water of coastal rivers and lakes becomes a growing problem.The removal performance of nitrogen?N?and phosphorus?P?of vertical flow constructed wetland when treating eutrophic brackish water and abundances of denitrifying bacteria were investigated,which was of great significance to reveal denitrification mechanism of the constructed wetland.The nitrification of the constructed wetland was inhibited,and the denitrification efficiency decreased.The results showed the removal rate of total nitrogen?TN?decreased by 9%and 24%for planted system and non-planted system,respectively,when the salt concentration was 0.5%.When salt concentration was 1%,Lythrum salicaria L wilted and the removal rate of TN reduced to 28%.The removal rate of ammonia nitrogen?NH₄⁺-N?decreased by 9%and 33%of planted system and non-planted system,respectively,when the salt concentration was 0.5%.When salt concentration was 1%,the removal rate reduced to 58%.With the increase of salt concentration,the removal efficiency of nitrate nitrogen?NO₃^--N?of wetland system remained more than 95%.The phosphorus removal efficiency remained more than90%,which was little affected by salinity.The differences between planted system and non-planted system was little,which suggested plant uptake only accounted for a small proportion in the phosphorus removal,and the main pathway of phosphorus removal was the adsorption effect of media.Under different salt concentration levels,the abundance of amoA gene in plant rhizosphere was more than one in the non-rhizosphere,and more than the control group.And the amoA gene abundance of ammonia oxidizing bacteria decreased with the increase of salinity concentration,and its percentage was also reduced almost 50%.It showed that salt concentration affected the nitrification indirectly through inhibiting the ammonia oxidizing bacteria'growth.Under different salt concentration levels,the abundance of nos Z,napA,nirK and nirS genes in plant rhizosphere was higher than the non-rhizosphere.And the abundance and percentage of four genes decreased with the increase of salinity concentration,which explained that the denitrifying bacteria can adapt to the environmental conditions.By analyzing TN,NH₄⁺-N and NO₃^--N removal efficiency showed that nitrification mainly appeared in 46-65cm,the soil media area.By analyzing amoA,nosZ,napA,nirK and nirS gene abundance showed soil media contained richer denitrifier microbial communities.Soil media contained rich microbial community,thus ensuring the denitrification performance.Phosphorus decreased mainly in46-65cm,in the soil media area,followed by ceramsite media area.Adsorption test results showed that a greater adsorption capacity of the soil than one of ceramsite,and there were competitive adsorption under salinity stress.The OTU clustering analysis of the constructed wetland system showed that at a0.5%level salinity concentration,plant played a role in keeping microbial community diversity.Under 0.05%and 0.5%salinity concentration plant can enrich the microbial community,and with the salinity concentration increasing,the unique OTU number decreased gradually of the samples.