Nitrogen Removal And Microbial Community Of Two-stage Tidal Flow Constructed Wetlands Under Low Temperature

For improving the self-purification ability of water ecology,the upgrading of the first grade a tail water in the treatment plant has become a developing trend.Constructed wetland has many advantages by using the action between filter material,plant and microorganism to remove pollutants.However,its treatment effect is greatly affected by climate as the purification effect of water quality in low temperature is obviously worse.Aiming at this problem,this study constructed a small two-stage tidal flow constructed wetlands coupling device?TFCWs?.These systems were connected in series,where planted Myriophyllum verticillatum L,filled gravel,limestone and zeolite,and added the fixed carbon sources,to achieve the enhancement of wetland operation effect under low temperature conditions.At the meantime,the community structure of nitrogen removal microorganisms was analyzed.the results are as follows.a.The two-stage TFCWs system can effectively save treatment time,and the removal efficiency is significantly improved.With the exception of TN,the other indicators of wastewater are in accordance with Class IV of the Environmental Quality Standards for Surface Water while TN with local standards.b.When the submerged:emptied time is 16 h:8 h and system run once,the C?N?P removal effect of the two-stage TFCWs system is more stable and the operation mode is simpler.The high-throughput sequencing results showed that the speciesrichness of Alpha Diversity index in experimental?was higher than that of experimental?,as the speciesdiversity of each functional gene was more complicated.c.DO?p H and T in the two-stage TFCWs system significantly affected the stucture of AOA,while the COD,NH₄⁺-N,NO₃^--N,NO₂^--N and TN concentrations significantly affected AOB?nar G?nir S and nrf A communities.The fixed carbon source added at the bottom in he device A can released COD slowly,significantly affecting nar G?nir S and nrf A community composition of each filter layer,where the relative abundance of genus Pseudomonas increased,and as a result the removal of the NO₃^--N is significantly improved.d.The competition for DO and NH₄⁺-N in low temperature makes the competition of AOA and AOB in this two-stage TFCWs system,in which AOB is more sensitive to the concentration of pollutants in influent conditions than AOA.In addition,Nitrosospira and Nitrosomonas are the main removal indicator genera for NH₄⁺-N,hence the removal rate of NH₄⁺-N after stabilization exceeded 95%.e.Except for the inhibitory relationship between Pseudomonas and other three genera,all the other genera cooperate in symbiosis.Pseudomonas and Rhodobacter are the indicator genera for NO₃^--N concentration in effluent,since Zoogloea for NO₂^--N concentration.At low temperature season,the Alpha Diversity index of nar G and nrf A were larger,of which the responsibility are to remove NO₃^--N.However,the dominant genere Thauera,Arthrobacter?belong to nar G?and Solitalea?Lacunisphaera?belong to nrf A?did not significantly remove the NO₃^--N concentration,leading its as the main component of TN in the effluent.