The Dynamic Response Of Nitrogen Transformation To The Dissolved Oxygen Variations And Recovery Processes In CWs

In recent years,with the progress of social economy and the development of agricultural production,water pollution problems have become prominent,and the eutrophication of water bodies has been serious,which has affected human production and life.Too much nitrogen is one of the factors that cause eutrophication of water.Constructed wetland is an ecological technology that effectively removes nitrogen from water.Exploring the best operating parameters of constructed wetland to reduce the operating costs is important to human survival and development.Dissolved oxygen is an important factor affecting nitrogen removal efficiency of constructed wetlands.Now researches are mostly aimed at the stable operation of constructed wetland systems.But there are few studies on the processes of new stable state formation and recovery to the original level after frequent dissolved oxygen variations,which makes the conversion of constructed wetlands difficult.Therefore,our research aimed to investigate the dynamic process of the responses of the aerobic and anaerobic SSs?SS-AE and SS-AN,respectively?in CWs to DO fluctuations,changed the traditional fixed periodic aeration to optimize the supply of dissolved oxygen to explore the disturbance and recovery of dissolved oxygen changes better,improve the nitrogen removal efficiency of the constructed wetland,confirm the microbial mechanism and broaden the application of the constructed wetland.By constructing two kinds of Lab-scale constructed wetlands?CWs?,including the long-term aerated CWs disturbed by short-term aeration-stopping?AE-D?and the long-term no-aerated CWs disturbed by short-term aeration?AN-D?,detection of genes amo A and nir S in AE-D and AN-D under aeration and aeration-stopping?Ae and As?interruptions for 1,7,and 14 days to quantify the processes of the stable states?SS?formation and recovery in dissolved oxygen?DO?,pollutants removal efficiency?RE?of Ammoniacal nitrogen?NH₄⁺-N?and Nitrate nitrogen?NO₃^--N?and the activity of the key nitrogen-cycle function genes amo A and nir S?RNA level abundance?.The results of this study show that the processes of new temporary SS formation and recovery to the original level with the transformation between Ae and As were and the RNA abundance of amo A and nir S.1.The SS formation and recovery in DO could be finished in 0.56-7.75 h after the transformation between Ae and As.For both the AE-D and AN-D reactors,the transformation of DO from the anaerobic SS to the aerobic SS was more rapid than the reverse transformation,and there was a significant correlation between the time required to reach SS-AN_DO from SS-AE_DO after the As interruption and the number of aeration days in the past 30 days for both systems.The DO fluctuated between 5.60mg/L and 10.96 mg/L at the attained SS-AE_DO;while the DO ranged from 0.00 mg/L to 0.77 mg/L at the attained SS-AN_DO.Both AE-D and AN-D have formed an aerobic-anaerobic alternating system.2.The new stable states and the recovery from the aeration/no-aeration after the Ae and As transformation.And it needs longer time for NO₃^--N than that for NH₄⁺-N to recover to the original RE.The recovery time was 8.1-31.0 h after one-day Ae and As interruptions in AE-D and AN-D,respectively;Seven-day Ae and As interruptions took 5.0%to 115.5%longer recovery time than one-day interruption.It suggested that the longer aeration/aeration-stopping interruptions need longer AE-D reactor,AN-D reactor generally need longer recovery time after aeration/aeration-stopping disruptions.Both the AE-D and AN-D reactors generally 61.9-95.9%for AE-D and AN-D reactors,respectively.It shows that the unstable periodic aerobic-anaerobic conversion of the systems is beneficial to the nitrification reaction.While NO₃^--N RE fluctuated greatly.The REs of NO₃^--N were-25.6-46.5%and-9.2-97.3%for AE-D and AN-D reactors,respectively.3.In AE-D and AN-D reactors,q PCR was used to analyze and detect the key nitrogen-cycle function genes amo A and nir S of nitrification and denitrification.Result suggested that both amo A and nir S activities were sensitive to the aeration or aeration-stopping interruption.Aeration could enhance the activity of nitrification gene amo A and inhibit the activity of denitrification gene nir S.In amo A activity,it took 60.8 h for AE-D to form a new temporary SS at As period,during when the RNA amo A copies had a 88.5%decrease;while it took 287.2 h for AN-D to form a new SS at Ae period,during when RNA amo A copies had a 36.4-times increase.In nir S activity,it took 75.2-85.8 h for the formation of the new SSes after the Ae and As transformation.After 7-day Ae and As interruptions,it took 218.7 h and 27.0 h for the recovery of amo A activity in AE-D and AN-D,respectively,while it took 38.2-58.2 h for the recovery.It suggested that long stable aerobic condition was important for keeping high amo A activity of reactor biofilm,while the high nir S activity of biofilm could form at both stable aerobic and anaerobic conditions.Therefore,the temporary SS formation and recovery by Ae and As transformation performed different speeds between that in DO,REs of NH₄⁺-N and NO₃^--N and the activity of genes amo A and nir S,which can be finished in tens of minutes to several hours,several hours to tens of hours,and tens of hours to hundreds of hours,respectively.