Effect Of The Migration And Transformation Of Iron On The Endogenous Reduction Of H₂S In Landfill

The phenomenon of "stench nuisance" around landfill, which is caused by the continuous hydrogen sulfide (H2S) emission, has become one of the important environmental hazards. To solve this problem, special session of landfill was simulated by static batch testing, the simulated landfill was dynamic running, and semi-aerobic transformation were adopted in this paper to study the endogenous reduction behavior of H2S caused by the migration and transformation of iron in landfill. The results showed that the iron which was "hidden" in the landfilled refuse could affect the H2S emission behavior, both at the early rapid degradation stage and the later reclamation stage of landfill during the static simulation process. About95%of sulfur, originally released as gas phase in the form of H2S without iron, could be fixed effectively as ferrous sulfide with iron during the rapid degradation stage. Thus, it could be avoided to release H2S into the air directly. Although the emission of H2S was unexpectedly promoted in a short time after reclamation, due to the rapid conversion of sulfide to elemental sulfur (over80%) promoted by iron, the risks of H2S declined by reducing the duration of high H2S concentration emission. The max H2S concentration released from the anaerobic simulated landfill in the initial period of rapid stabilization by dynamic continuous running was19.4mg m-3and24.1mg m-3in CL and RL, respectively. It was much higher than that specified in the Chinese odor pollutant emission standard. The inhibitory mechanism of H2S was different because of the migration and transformation behavior of iron inside the landfill. The iron in traditional anaerobic landfill could precipitate73.3%of H2S to ferrous sulfide. But for the anaerobic landfill with leachate recirculation, the ferrous content in the landfilled refuse was greatly improved by the migration and transformation cycle of iron in landfill. Also, the biological and chemical oxidation ability of H2S enhanced. Compared with CL, it could reduce23.1%of sulfide in RL. It further revealed from the dynamic follow-up study after semi-aerobic transformation, the oxide reduction behavior of iron in landfill layer greatly improved and the migration behavior of iron weakened, longer time for valence transition and the contact with the landfilled refuse result in the changes of the reduction mechanism of H2S, which transformed from the ferrous sulfide precipitation to oxidation mainly, as a result, it can continuously reduce the potential of H2S emission. However, the H2S concentration released from the cover layer of simulated landfill was still7-8times more than that specified in the standard. Especially, the H2S emission didn’t drop, but actually increased with leachate recirculation due to the changes in the redox state of the iron under semi-aerobic process. This contamination risk couldn’t be ignored. The conclusions obtained in this study may provide theoretical basis for enhancing the endogenous reduction of H2S by using the iron "hidden" in the landfilled refuse.