Reduciton Of Methane In Wetland System And Anaerobic Oxidation Of Methane Driven By Manganese Ore

The methane?CH₄?emission from wetlands is known as one of the mainpaths of the greenhouse gases sources and sinks,causing global warming and widespread concerns by social and scientific communities.However,the existing researches focused on the process and mechanism of methane emission from wetlands,while less understanding the feasibility of methane reduction and the process in wetland system.This research focuses on the cooperation of manganese?Mn?-drive dissimilatory metal reduction and anaerobic oxidation of CH₄?AOM?,which could significantly reduce CH₄ emission from the wetlands.Experiments were conducted to investigate the CH₄emission in a vertical constructed wetland using Mn ores as substrates?Mn-CW?;to investigate the mechanisms of Mn-drive AOM;to enrich the AOM microorganisms which can use Mn?IV?as the electron acceptor.By comparing CH₄ emission in wetlands using different substrates,studying carbon transformation and mass balance in wetlands,and performing the molecular microbiological analysis,the pathway of CH₄reduction in the Mn-CW has been explored,providing a new method for CH₄ reduction.In this study,the following research progress and academic achievement has been obtained:?1?Experiments on CH₄ reduction in the Mn-CW has been conducted to investigate the effects of Mn on the CH₄ emission.The results show that both CWs can achieve high rates of organic pollutants,the average organic removal rates are above 90%.The Mn-CW is better in pollutant removal than the wetlands using gravel as substrates?Gr-CW?.The Mn-CW can also efficiently reduce CH₄ emission which was 45.3%less than that in Gr-CW?2?The transformation and sink of carbon in the Mn-CW,and the organic carbon removal pathway in the wetland have been studied.Based on the results,inorganic carbon precipitation had the highest carbon percentage?47.4%of the TC input?,followed by CH₄ emissions?15.7%?in the Mn-CW.In the Gr-CW,which represent the traditional anaerobic wetland,the carbon removal mainly through the anaerobic digestion.Hence,the DIC of the outflow and CH₄ emissions flux were the two major carbon sources,accounting for about 70%of the TC input.During the experiment,the degradation of organic matter is accompanied by the formation of Mn²⁺,and the Mn²⁺concentration is negatively correlated to the solubility inorganic carbon concentration along the CW.In addition,the concentration of Mn²⁺in the outflow was very low?1.45±0.68 mg/L?,indicating that no notable Mn loss occurred in the Mn-CW.?3?The Mn-drive AOM in the wetland and the key microorganisms in this process has been investigated,including the AOM microorganisms.The results show that dominant microorganisms in the Mn-CW are dissimilatory Mn?IV?-reducing bacteria and hydrogenotrophic methanogens?archaea?.The dominant microorganisms in the Gr-CW are both hydrogenotrophic methanogens and acetotrophic methanogens and the abundance of dissimilatory Mn?IV?-reducing bacteria was lower than that in Mn-CW.The lack of acetotrophic methanogens in the Mn-CW in this study implies that the presence of Mn ore may inhibit the growth of acetotrophic methanogens,resulting in the lower CH₄ emission.The AOM archaea is also observed in the Mn-CW,and the dominant AOM archaea belongs to ANME-2d cluster.It could be concluded that anaerobic oxidation driven by manganese ore existing in the Mn-CW.?4?The transformation of carbon and methane by functional microorganisms in Mn-CW was studied.The isotope experiment and mass balance both prove that Mn?IV?-drive AOM exist in the Mn-CW,and most of the newly generated ¹³CO₂ was in the form of liquid and solid phases.Compared with Gr-CW,the mean AOM rate in the Mn-CW was estimated as 1.64 g C/m²/day which accounted for approximately 66%of the CH₄ emissions reduction.The addition of manganese ore can improve the removal efficiency of organic carbon in the Mn-CW.The removal rate of organic carbon in the process of dissimilar metal reduction is 20.82mmol/day/g dry sludge,accounting for52.3%of the total organic carbon removal,while the removal rate of organic carbon of methanogenesis is 15.31mmol/day/g dry sludge,accounting for 38.5%of the total organic carbon removal.?5?This research enriched the AOM archaea which can use Mn?IV?as electron acceptor and the relationship between the growth of AOM archaea and the anaerobic oxidation rate of CH₄ was also discussed.Both natural Mn?IV?and synthetic Mn?IV?can be used in this Mn?IV?-drive AOM.The amount of AOM archaea using?-MnO₂ as electron acceptor was higher than that using natural Mn?IV?.Both the ratio of Mn?IV?reduction and Mn²⁺generation to methane oxidation were close to 4:1,which accord to the stoichiometry equation of CH₄ oxidation driven by Mn?IV?.Correlation analysis showed that the AOM process was accompanied by the growth of ANME-2d cluster,and there was a significant positive correlation between the change of AOM rate and the abundence of ANME-2d cluster during the cultivation period,with the correlation coefficient R² up to 0.95.This primary result shows that AOM may be a process involving cooperation of multiply microorganisms.The results demonstrate the Mn?IV?-drive AOM was mainly domain by the ANME-2d cluster.