Study On The Reduction Of Methane And Carbon Removal Pathways In The Constructed Wetland Of Manganese Ore

With the strengthening of the global greenhouse effect,the control of greenhouse gas emissions has become one of the most important tasks faced by all mankind in twenty-first century.Methane in the atmosphere is the second largest greenhouse gas after CO₂,but its impact on global climate change is up to 30%.Due to the lack of oxygen in the bottom of the wetland,it is under anaerobic or anoxic conditions,and organic compounds produce a large amount of methane gas under the action of methanogens.Wetland,as the biggest methane natural emission source,is making wetland methane emission become a major global environmental problem and climate issue.The mitigation of methane in wetlands has attracted great attention from the scientific community.This experiment based on the special oxygen supply environment in constructed wetland,using natural manganese ore as the substrate of wetland,studied abatement effect of high manganese minerals on methane emission from wetland system,and explored methane abatement mechanism from wetlands driven by manganese minerals,supplying new methodological and theoretical guidance for methane emission reduction in wetland system.This experiment mainly studied effect of pollutants removal and methane abatement in constructed wetlands,respectively using manganese ore and gravel as filler matrix,under the condition of two kinds of carbon sources,sodium acetate and glucose,and comparatively analyzed microbial diversity and population structure in constructed wetland system.And the carbon removal pathways of the wetland system was analyzed,defining the distribution and direction of carbon in wetland.The main conclusions of the experiment are as follows:（1）Manganese ore filler and gravel packing constructed wetland systems all had better removal effect on COD under two kinds of carbon sources,the removal rate all maintaining at 70%⁹0% after stable operation;The removal efficiency of NH₄⁺-N was not ideal,the average removal rate was 20%⁴0%.Removal effects in manganese ore and gravel packing wetlands on COD and NH₄⁺-N had little difference under different carbon sources.In the case of one of the carbon sources（sodium acetate or glucose）,the removal effects of artificial wetland system with manganese ore as matrix filler on carbon and nitrogen in sewage were obviously superior to wetland system with gravel as substrate.（2）When sodium acetate was used as carbon source,methane emission of manganese ore and gravel packing artificial wetland systems in single period（5 days）were respectively 24.92±15.72 mg and 146.61±39.58 mg,and compared with gravel group,methane emission from manganese ore was reduced by more than 80%.When glucose was used as carbon source,methane emission measured from wetland systems was 2³ times than that using acetic acid as carbon source.However,the amount of methane produced by manganese ore group was still far less than that of gravel group,and during the experiment,the average discharge was only 26.58% of gravel group.Generally speaking,the manganese ore filling artificial wetland system all had the obvious abatement effect on the methane emissions under the two kinds of carbon sources,reducing 70%⁹0% compared to the gravel packing wetland.（3）Under two kinds of carbon sources,manganese ore and gravel packing filler artificial wetland systems contained similar microbial species（phylum level）,and the dominant bacteria were all Proteobacteria、Bacteroidetes、Chloroflexi,but bacterial species（genus level）had large difference.Under two kinds of carbon sources,Methanogens and other bacteria related to the removal of pollutants were all present,and there into a high abundance of devolutive metal reducing bacteria was detected in the manganese wetland but not detected in the gravel group,so it was speculated that substrate competition effect between metal reducing bacteria and methanogenic bacteria in manganese ore wetland inhibited methanogenesis process of Methanogens,thus reducing methane emissions.（4）In the case of the same influent carbon source,carbon output modes of manganese ore packing and gravel packing artificial wetland systems had a big difference,and there into most carbon removal in gravel group relied on CH₄ and CO₂ discharge from anaerobic fermentation,which was a traditional anaerobic wetland,but gaseous CH₄ and CO₂ emissions were all relatively small in manganese group,most of the carbon existing in the Solid-liquid two-phase in the form of dissolved inorganic carbon and carbonate precipitation,so the mix of manganese minerals had an inhibitory effect on the CH₄ emission and meanwhile had a certain abatement effect on the emission of CO₂.