Law And Mechanism Of Microbial Production Affecting Carbon Flux And Nitrogen Flux In Wetland

Wetland is an important carbon sink and nitrogen sink system on earth.Its emissions of methane(CH4)and nitrous oxide(N2O)are important sources of global greenhouse gases(GHGs).Embedding microbial fuel cells into wetlands and exploring the impact of bioelectrochemical processes on GHGs emissions have great significance to control GHGs emissions from wetlands.Therefore,the purpose of this paper is to plant the Acorus calamus on the anode of the system to build a new "rhizosphere" anode wetland microbial fuel cell(CWMFC).The results showed that there is a certain relationship between GHGs emissions and generation of power in the system.By changing the structure and operating parameters of the system,the effects of rhizosphere electrode activities on power generation and carbon flux/nitrogen flux of the system are studied.Moreover,the competition or coexistence mechanism of electro-bacteria with methanogens,ammonia-oxidizing bacteria,and denitrifying bacteria in the process of microbial power generation is further explored by high-through sequencing.This paper explains the relationship between microbial electricity production,carbon conversion,and nitrogen conversion in wetland,as well as analyzes the main ways and mechanisms of reducing GHGs such as CH4 and N2O in wetland.Subsequently,it discusses the return path of C element and N element in the system through the relationship between electricity production,gas production and microbiological analysis.The specific research contents are as follows:(1)Through the establishment experiment,it is known that when the anode material is carbon fiber felt,the cathode material is CAF,the electrode spacing is 10 cm,the cathode area is 0.0096 m2,and maximum power density of the system is 2.99 W/m3.In this case,the maximum removal rates of COD and TN are 95.99%and 62.98%,respectively.Under this condition,the GHGs has also been well controlled,and the average emission flux of CH4 is 0.77± 0.05 mg/(m2·h),the average emission volume fraction of N2O is 0.02 ± 0.0006%.According to the data analysis,and the conditions of the above system construction,the amount GHGs emission will be minimized.(2)Heavy metal ions can effectively reduce GHGs emissions.CH4 and N2O emissions from plant systems are about 0.43 ± 0.05 mg/(m2·h)and 0.006 ± 0.003%(non-planted plants:0.14 ± 0.02 mg/(m2·h)and 0.004 ± 0.0003%),respectively.When the power density decreases to 1.92 ± 0.07 W/m3(non-planted plants:1.52 ± 0.06 W/m3),the GHGs emission is effectively controlled,but the output voltage of the system is reduced.The effect of substrate concentration on CH4 and N2O is quite opposite.When the substrate concentration is 200 mg/L,the CH4 emission is about 2.18 ± 0.06 W/m3,and the N2O emission is larger.When the substrate concentration is increased to 500 mg/L,the volume fraction of N2O is 0.002 ± 0.0005%,the CH4 emission flux increases to the largest.Through Pearson correlation analysis,it was found that with the increase of coulomb efficiency,N2O emission showed a positive correlation,while CH4 showed a negative correlation.(3)Through high-throughput sequencing and the analysis of the above experimental results,it can be seen that most substrates are consumed by microorganisms to produce electrons,and the richness of electrogenic bacteria community is complex and diverse,which contains microbials,including Acinetobacter,Bacteroidetes and Geobacter.The species of methanogens and nitrifying bacteria are less,including Methanothrix,Methanobacterium,Methanolinea,Nitrospira and Denitratisoma.The flow distribution of C and N elements in the system was analyzed.Microorganisms used substrates to meet their own needs,accounting for 40.28%and 78.98%of TC and TN,respectively.During the experiment,the action of plant roots and matrix will also adsorb some substrates,result in the decrease of TC and TN concentrations to 20.1%and 19.6%,respectively.In the fate of the system,the emission fluxes of CO2 and CH4 are larger than N2O,which are 24.12%and 10.94%,respectively.While N2O accounts for only 0.5%.The remaining small amount of carbon and nitrogen sources finally flow out of the system.The new "rhizosphere" anode CW-MFC in this paper has the functions of "removing organic pollutants from water,reducing GHGs emission and green production capacity",which points out a new direction and idea to controlling GHGs emission in wetland.