Denitrification Performance And Optimization Of Nitrate-Dependent Anaerobic Methane Oxidation In Membrane Bioreactor (N-Damo-MBR)

Nitrate-dependent anaerobic methane oxidation?N-damo?is a process in which microorganisms use methane as an electron acceptor to reduce nitrate under anaerobic conditions.The process is coupled with nitrate reduction and methane oxidation,and has dual functions of denitrification and methane removal.It has scientific and practical value for understanding the earth carbon and nitrogen cycle,and developing wastewater treatment technology.However,the functional microorganisms driving this process have a long generation time,and the environmental regulatory factors for their growth are not clear.It is difficult to increase the biomass,and the removal rate of pollutants is low.Based on the theoretical analysis of Membrane bioreactor?MBR?holding microorganisms,activated carbon enhanced methane supply capacity to provide carriers for microorganisms,the membrane reactor was coupled with N-damo process to form N-damo-MBR process.The denitrification performance experiment,the hydraulic retention time?HRT?influence experiment and the activated carbon intensification experiment of the process were carried out.The nitrogen conversion efficiency,rate and load rate were statistically analyzed.The kinetics of matrix reaction was investigated,and the microbial community structure and its changes were identified and analyzed.The potential of N-damo-MBR process was explored and its internal mechanism was analyzed.The main conclusions of the study are as follows:?1?MBR can effectively increase N-damo microorganisms and improve the nitrogen removal performance based on N-damo.The cultivation of N-damo microorganisms by MBR experienced three processes of adaptation period,rapid growth period and slow growth period.The rate of nitrogen removal increased from9.78±2.68 mgN·L^-1·d^-1 to 44.91±5.71 mgN·L^-1·d^-1,which increased by 3.6 times.The chemometric relationship verification results show that the actual N/C consumption ratio in the N-damo-MBR process is 1.600±0.094,which is close to the theoretical value of 1.6.The membrane fouling period of the reactor was 17d.?2?HRT significantly affects the nitrogen removal efficiency and microbial community structure of the N-damo-MBR process.The total nitrogen removal rate of the reactor reached a maximum of 100%at a HRT of 3d.The total nitrogen removal load and nitrate removal rate reached the maximum at 1.5d HRT,which increased from17.23 mgN·L^-1·d^-1 to 44.20 mgN·L^-1·d^-1 and 11.74±0.84 mgN·L^-1·d^-1 to 48.11±1.34mgN·L^-1·d^-1,respectively.HRT should be selected according to different treatment purposes.Shortening HRT will aggravate the membrane fouling phenomenon of n-damo-mbr process and shorten the membrane fouling cycle.Candidatus Methanoperedens and Candidatus Methylomirabilis are predominant microorganisms in the N-damo-MBR system.The abundance of 16SrRNA and functional gene MCRA of anme-2d was increased and reached the maximum at 1.5d of HRT.Both NC1016SrRNA and functional gene pmoA abundance were increased compared with the initial state,and both reached the maximum value under 3d HRT.?3?The addition of Granular activated carbon?GAC?can effectively improve the performance of the N-damo-MBR reactor.The rate of nitrogen removal rate increased from 10.29 mgN·L^-1·d^-1 to a maximum of 36.81 mgN·L^-1·d^-1,increasing by 2.08 times.The denitrification efficiency of the reactor was also increased from 40%to 100%and remained stable.The porous structure of the surface of the GAC is beneficial to the adhesion of microorganisms,and its methane adsorption performance increases the opportunity and supply of microorganisms to utilize methane,and can effectively delay the rate of membrane fouling.The microbial community structure in the reactor was significantly optimized.The proportion of Euryarchaeota gates belonging to N-damo archaea increased from 64.3%to 86.2%,and the NC10 gate abundance of N-damo bacteria increased from 27.1%to 56.9%.The relative abundance of microbial species predominant in GAC has decreased significantly.The qPCR results showed that the16SrRNA of N-damo archaea and bacteria and the abundance of N-damo bacterial functional gene pmoA increased,indicating that GAC could effectively increase the abundance of n-damo bacteria and thereby improve the metabolic activity of microorganisms.