Research On Mechanism Of Methane Anaerobic Oxidation (AOM) Driven By Manganese Minerals In Constructed Wetland

Constructed wetlands are important sewage treatment structures.Because of its simple structure and easy maintenance,it is suitable for areas with low sewage treatment requirements.Constructed wetlands are important sources of CH₄ and CO₂emissions.The increase in greenhouse gases is the main cause of global warming.CH₄and CO2 are also the major greenhouse gases in the atmosphere.Therefore,it is very important to study the reduction of CH4 and CO2 in constructed wetlands.The experiment uses manganese mineral as a filler to establish artificial wetlands to study the mechanism and effect of anaerobic oxidation of methane in wetlands.First,we monitored the operation conditions of constructed wetlands from time to time,including organic removal effect,pH change value and effluent Mn²⁺concentration.Monitoring the internal characteristics of constructed wetlands,including organic matter content,pH value and Mn²⁺concentration at different depths.Then,based on the stable operation of the constructed wetland,Sample from the matrix and extract the DNA.Analysis of microbial diversity and community structure in wetlands by high-throughput sequencing.Finally,an anaerobic bottle device was set up for the activity test,the anaerobic oxidation effect of methane was verified,the carbon transfer route in the man-made wetland with manganese ore filler was analyzed,the anaerobic oxidation efficiency of methane was calculated,and the utilization status of different types of electron acceptors was verified.The main conclusions are as follows:（1）In constructed wetlands,sewage flows from bottom to top,glucose is decomposed into small-molecule organics at the bottom,and the pH of the sewage decreases.In the middle of the wetland system,methane is generated in the system to consume hydrogen ions,and the pH of the wastewater rises.Anaerobic oxidation of methane occurs in constructed wetlands.The consumption of hydrogen ions increases the pH of the wastewater.Mn²⁺and HCO₃^-ions combine to form MnCO₃ precipitates that remain in the wetland.The removal efficiency of dissolved organic carbon in water from manganese ore filling constructed wetland is better than that of gravel packing artificial wetland.The effluent DOC of manganese ore group and gravel group were12.37±8.44 mg/L and 12.53±6.10 mg/L,respectively.The average removal rates of DOC were 92.68±2.79%and 91.01±2.32%,respectively.Long-term monitoring results show that the CH₄ and CO₂ fluxes of the manganese ore fill constructed wetland are smaller than those of the gravel constructed wetland.After the operation was stabilized,the CH₄ emissions of the manganese ore group and the gravel group were 2.43g/（m2·Day）and 4.40 g/（m2·Day）,respectively,while the CO₂ emission fluxes were0.22 g/（m2·Day）and 2.42 g/（m2·Day）respectively.（2）The DNA sequencing results showed that the microbial diversity index of the manganese-contained constructed wetland system was higher than that of the ordinary gravel constructed wetland system.Bacteria,the manganese ore filler artificial wetland group and the gravel packing constructed wetland group have similar community structure at the level of bacteria.The dominant phylums are Proteobacteria,Bacteroidetes and Chloroflexi.The genus levels of the two species are similar but their abundance is different.The dominant genuses are Flavobacterium,methylotenera,methylophilaceae and Pseudomonas and Hydrogenophaga,Azoarus and geobacter.In the aspect of archaea,the composition of the microbial communities in the manganese ore-filled constructed wetland and the gravel-packed constructed wetlands were similar,but their abundance varied greatly.Euryarchaeota and Miscellaneous_Crenarchaeotic are the dominant archaea of the manganese ore group,accounting for 68.21%and 30.67%respectively.Miscellaneous_Crenarchaeotic and Thaumarchaeota are dominant archaea in the gravel group,accounting for 83.15%and 3.61%respectively.The microbial community structure and abundance in the two genera levels are quite different.The dominant species in the manganese ore group are Methanosarcina and Methanobacterium.The dominant bacteria in the gravel group were Methanosarcina,Methanobacterium,and Methanomassiliicoccus.（3）The anaerobic bottle test validated the anaerobic oxidation of methane-driven methane,in which the anaerobic oxidation rate of methane was 0.226μmol/hour.In the methanogenesis inhibition test,the removal rate of DOC by microorganisms was84.12±10.46μmol/Day,and the generation rates of CH₄ in the constructed wetland and non-manganese-controlled groups were 34.38±7.47μmol/Day and 50.74±8.65μmol/Day,respectively,and CO₂ production.The rates were 37.42±14.25μmol/Day and111.53±24.79μmol/Day,respectively.The results of anaerobic oxidation of methane driven by different types of electron acceptors show that manganese minerals,δ-MnO₂and Ferrite can all be reduced by the bacterial liquid and coupled with the anaerobic oxidation of methane.SO₄^2-cannot be used as an electron acceptor.