Synergistic Enrichment And Influence Factors Of Denitrifying Anaerobic Methane Oxidizing Archaea And Bacteria

Denitrifying anaerobic methane oxidation?DAMO?couples the processes of anaerobic methane oxidation and denitrification,making sense in nitrogen removal of wastewater.The microorganisms involved in DAMO process include nitrate-dependent anaerobic methane oxidizing?Na-DAMO?archaea and nitrite-dependent anaerobic methane oxidizing?Ni-DAMO?bacteria.The enrichment of DAMO microorganisms usually adopts the sequential batch reactor?SBR?or the hollow-fiber membrane biofilm reactor?Hf MBR?.However,the too long enrichment time limits the application of DAMO process.In this work,the effects of circulating flow rate,membrane packing density,inoculum concentration,series Hf MBR and Fe²⁺ concentration on the synergistic enrichment of Na-DAMO archaea and Ni-DAMO bacteria were explored to accelerate the enrichment of DAMO microorganism.The main results were as follows: 1.The effects of circulating flow rate,membrane packing density and inoculum concentration on the start-up enrichment of DAMO microorganisms were explored,and the proper start-up conditions were proposed.Parallel Hf MBR was used to culture DAMO microorganisms.Low circulation flow rate,medium or high membrane packing density,and medium inoculum concentration are more favorable for the enrichment of DAMO microorganisms during the startup stage.Circulation flow rate and membrane packing density had no significant effect on nitrogen removal efficiency,but low inoculum concentration significantly reduced nitrate removal efficiency.High circulation flow rate,low membrane packing density and low inoculum concentration made the ratio of methane to nitrate consumption rate more deviated from theoretical value.High circulation flow rate aggravated the diffusion of oxygen,resulting in the rapid growth of aerobic methanotrophs.Na-DAMO archaea were abundant under the conditions of low circulation flow rate,high membrane packing density and medium inoculum concentration,and Ni-DAMO bacteria were abundant under the conditions of low circulation flow rate,medium packing density and medium inoculum concentration,implying a positive effect on the growth of DAMO microorganisms.2.The efficacy of series Hf MBR to enriching DAMO microorganisms was explored,and DAMO microorganisms were successfully enriched.Series Hf MBR performs well on the enrichment of DAMO microorganisms.Parameters including the nitrogen removal efficiency,the abundance and relative abundance of DAMO microorganisms,the microstructure of the biofilm characterized the efficacy of series Hf MBR on DAMO microbial enrichment.Nitrate removal rate gradually increased by 4.1 times from day 23 to day 90.From the beginning to the end of operation,the average abundance of Na-DAMO archaea and Ni-DAMO bacteria increased by 92.9 and 136.6 times,and the average relative abundance increased by 65.4 and 340.7 times,respectively.At the end of operation,biofilm with a thickness of 40-240 ?m was formed,and the direct "cell to cell" contacts between Na-DAMO archaea and Ni-DAMO bacteria were observed,which was beneficial to the transfer of nitrite from Na-DAMO archaea to Ni-DAMO bacteria.3.The effect of Fe²⁺ concentration on DAMO microbial enrichment was explored,and the better condition was identified.The effects of two Fe²⁺ concentrations of 20 ?mol L^-1 and 40 ?mol L^-1 on the enrichment of DAMO microorganisms were compared,and the Fe²⁺ concentration of 40 ?mol L^-1 did better in DAMO microbial enrichment and the formation of microbial aggregates.On the 100 th day of operation and uner the Fe²⁺ concentration of 40 ?mol L^-1,the substrate consumption rates were higher,and the net consumption rate of methane and nitrate were respectively 56.3% and 58.6% higher than those under the Fe²⁺ concentration of 20 ?mol L^-1;DAMO microorganisms were more abundant,and the abundance of DAMO microorganisms was 11.7% higher than that under the Fe²⁺ concentration of 20 ?mol L^-1;The size of microbial aggregates was larger,and the size of aggregates ranged from 10 ?m to 20 ?m,with the size no more than 5 ?m under the Fe²⁺ concentration of 20 ?mol L^-1.The capacity of biomass retention was higher,and the VSS concentration was 2.0 times of that under the Fe²⁺ concentration of 20 ?mol L^-1.