Study On Efficacy And Mechanism Of Nitrogenous Wastewater Treatment In CW-MEC

Compared with the traditional wastewater treatment process,the bioelectrochemical system(BES)has the characteristics of low cost,high efficiency and not easy to cause secondary pollution.However,further cost reduction and system amplification have been the limiting factors for the industrialization of the bioelectrochemical system.Coupling the constructed wetland(CW)with microbial electrolytic cell(MEC)can reduce the construction and operation cost of the system to a certain extent,and improve the pollutant removal capacity and electrochemical performance of the system.At present,there are very few researches on the coupling system of constructed wetland and microbial electrolytic cell(CW-MEC).Therefore,a vertical CW-MECcoupling system has been constructed in this experiment,and the performance of CW-MEC system has been studied under the conditions of different applied voltage(0.4V,1.0V and 2.0V),with or without cathode aeration,different influent modes(batch and continuous flow)and different HRT(12h,24h and 3 6h)Finally,the operation mechanism of CW-MEC has been studied from microbial diversity analysis.The main results are as follows:(1)The optimal performance of CW-MEC can be obtained when the applied voltage is 2V,there is aeration at the cathode,the inflow mode is batch,and the HRT is 24h.After the cathode is aerated,the removal efficiency of COD and NH4+-N in CW-MEC cathode have increased by 11.7%and 23.47%respectively.Under sequencing batch,the removal efficiency of COD,NH4+-N and TN in CW-MEC cathode have increased by 20.33%,15.54%and 0.38%respectively,and in CW-MEC anode have increased by 41.32%,9.97%and 9.46%respectively.With 24h of HRT and sequential batch,the removal efficiency of COD and NH4+-N in CW-MEC cathode were 97.20 ±4.61%and 74.03 ± 4.90%respectively,and in CW-MEC anode were 88.43 ± 10.36%and 55.85 ±3.50%respectively.The applied voltage is directly proportional to the maximum output power density of CW-MEC.The maximum power density of CW-MEC system is 66.31mW/m2 when 2V of applied voltage and aeration at the cathode.(2)Continuous aeration at the cathode was helpful to the voltage stability of CW-MEC.The voltage of the both BES can be increased under sequencing batch.In different operation modes,CW-MEC had better electrochemical performance and smaller internal resistance than CW-MFC,and the electrochemical performance of CW-MFC had poor recovery.The vertical flow constructed wetland can provide a good anaerobic environment for BES and ensure the oxidation-reduction reaction in BES to be carried out stably.The performance of CW MEC anode was mainly affected by the influent mode,but not by the external aeration and HRT(3)Based on the analysis of microbial diversity,CW-MEC community structure was significantly different with CW and CW-MFC,and the microbial abundance and evenness of CW-MEC were higher than CW and CW-MFC.In phylum level,the dominant bacteria in CW-MEC are Proteobacteria,Bacteroidetes,Firmicutes,Actinobacteria,Actinobacteria and Chloroflexi.In genus level,there were a large number of glucose degrading bacteria in CW-MEC and control group.In addition,there were also a lot of nitrifying bacteria and denitrifying bacteria in CW-MEC cathode,such as anaerobic nitrifying bacteria:Norank-f-anaerolineaceae(1.0%),aerobic denitrifying bacteria:Terrimonas(0.39%),Zogloea(2.97%),Acinetobacter(2.86%)(5.81%),Unclassified-f-comamonadaceae(5.81%),facultative anaerobic denitrifier:Dechloromonas(0.69%).Meanwhile,there were a lot of electrochemical active bacteria,such as Unclassified-f-enterobacteriaceae(1.99%),Desulfovibrio(1.23%).There are a lot of norank-f-bacteroides-vadinha17(4.09%)in the anode of CW-MEC,which is a facultative anaerobic bacteria and an electrochemical active bacteria with strong denitrification ability.The above results show that CW-MEC has a strong nitrification and denitrification ability,and there has simultaneous nitrification and denitrification process in CW-MEC cathode.