Removal Of Nitrogen And Phosphorus Pollutant In Aquaculture Wastewater Utilizing Suaeda Salsa Constructed Wetlands And Its Underlying Molecular Mechanism

Vertical subsurface flow constructed wetlands(VSFWs)have been widely used in wastewater treatment,but few studies have utilized them in aquaculture wastewater treatment.It is proper to treat biodegradable aquaculture wastewater containing a large amount of nitrogen and phosphorus nutrients,organic matter,and salts utilizing constructed wetlands(CWs).Introducing CWs into aquaculture wastewater treatment can not only increase the removal efficiency of nitrogen pollutants in CWs,but also promote the anammox process.In this study,we established the CW small-scale plots with Suaeda salsa(S.salsa)and carried out the research on the removal of nitrogen and phosphorus pollutants in the aquaculture wastewater.We explored the removal performance of nitrogen and phosphorus nutrients in aquaculture wastewater using S.salsa CWs to provide scientific basis for practical application.In addition,we researched its underlying biological mechanism to provide theoretical gist for further optimization of CWs.Finally,on the basis of the previous research,we studied the influence of different salinity on quantity and abundance of anammox bacteria.The main conclusions are as follows:(1)Although the removal efficiency of total nitrogen(TN)decreased with the gradual increase of the salinity,the removal efficiency of TN and total phosphorus(TP)in the CWs remained above 65%.The removal efficiency of ammonia nitrogen decreased with the increase of salinity,and the nitrite had obvious accumulation under higher salinity,and the nitrate removal performance was stable.(2)The concentration of ammonia nitrogen and nitrate at the upper layer(0-20cm)fallen dramatically due to the increasing salinity,leading to the highest removal efficiency.Through the 0-40cm substrate,the nitrate removal efficiency of 2%and 3%salinity was higher than others.There was no nitrite accumulation without salinity addition and the accumulation of nitrite became more and more obvious with the increasing salinity,which was potentially beneficial to anammox process.(3)Bacterial community distribution was significant affected by salinity and substrate depths.The value of OTU gradually decreased with the increasing salinity,which indicating that the biodiversity of system has been reduced due to the salinity pressure.The bacteria abundance and diversity peaked at the upper layer(0-20cm)under the salinity of 0%,which maxmized at the middle layer(20-40cm)under the salinity of 2%.Among the 22 phyla in ecosystem,Proteobacteria were the most abundant phylum.A large number of microorganism had not been discovered and sequenced due to its rich diversity.(4)All anammox bacteria stemmed from Planctomycetes.With inceasing salinity,partial fresh water anammox bacteria gradually transferred to the ocean anammox bacteria.Anammox bacteria could adapt to 3%salinity.Despite of its rich abundance,anammox bacteria was still not dominant species in systems.During this experiment,we have recognized the potential of utilizing salinity to promote the anammox process.