Research On Methane Reduction Technology In Semi-aerobic Landfill Based On Dissimilatory Iron Reduction

Bearing the property of energy-free self ventilation, reduction of CH₄innerproduction and promotion of the stabilization of waste through the formation ofaerobic region, semi-aerobic landfill has become an optimized option for small tomedium-sized utilization of landfilling. However, the high organic content of wasteand deteriorated operation of landfill in China inhibited the application ofsemi-aerobic method， hence, technical improvement is needed. As a matter of fact,the dissimilatory iron reduction process induced by anaerobic microorganism endowsthe “oxygen-free mineralization” of organics in the anaerobic region, and theabundant existence of Fe in landfilled waste can greatly promote this process, thusgives the possibility of CH₄reduction in the semi-aerobic landfill.Based on aforementioned background, this study firstly concentrated on theanalysis of content and distribution characteristic of Fe in anaerobic and semi-aerobiclandfill; following with the landfill column test and the simulation of dynamictransformation and dissimilatory reduction process of Fe; at last, batch experimentswere conducted for the investigation of CH₄reduction mechanism by dissimilatoryiron reduction process, and the “Fe electron pump” theory was developed.As results shown, the average concentration of Fe in landfill is between18.5and31.1g/kg. About1.4%of the Fe are reduced through dissimilatory iron reductionprocess, the Fe（II）/Fe（III） ratio is negatively related to the DOC of landfill waste（p<0.05）, so coupled Fe dissimilatory reduction is one of the most important pathwayof organic degradation. As shown in the column tests, the Fe dissimilatory reductionshowed higher rate at initial landfill days when organic were being drasticallydegraded, the process became mitigated as the degradation of organics slowed down.The released Fe in semi-aerobic and anaerobic leachate were214.9and3053.8mg,respectively, which were0.057‰and0.81‰of total Fe amount in waste. The uniqueaerobic and facultative environment in semi-aerobic landfill gives lower verticalmobility and thus stabilizes the existence of Fe in landfill.The inhibiting effect of dissimilatory iron reduction on the production of CH₄can be attributed to that the dissimilatory reduction of Fe restrains the activity of methanogenic bacteria, as well as depletes the intermediate product necessary for themethanogenesis process such as H2, so as to cut off the matrix supply formethanogenic bacteria and finally inhibits the inner production of CH₄. Fe（III）species show different inhibiting effect on the production of CH₄, for example,organic Fe such as ferric citrate can effectively promote the degradation of matrix,and totally inhibit the production of CH₄, the optimized addition amount is16000mg/kg. The “Fe electron pump” theory was developed based on the uniqueoxygen environment in the semi-aerobic landfill. Through electron balancecalculation, the reduction of CH₄production induced by “Fe electron pump” effectenhanced dissimilatory iron reduction in semi-aerobic landfill can be as high as3.7⁹.7%.This study investigated the theory of oxygen-free mineralization of landfill wastebased on dissimilatory iron reduction process, brought new and important light in theinhibition of inner CH₄production in non-ventilation region for semi-aerobic landfill.