[Characteristics of Anaerobic Methane Removal Coupled to Fe(Ⅲ) Reduction in Aged Refuse]

Landfills are the third largest iron reservoir and one of the largest sources of methane release. Iron, as a kind of transition metal, plays a particularly important role in environmental biogeochemistry and is closely linked to the biogeochemical cycle of C, S and N. The aged refuse could be utilized as bio-cover material to improve the removal of contaminants. Therefore, this work investigated the effect of iron reduction on anaerobic removal of methane, and the interactions of ferric iron with nitrate and sulfate in the aged refuse. The columns were operated as landfill bio-covers and recirculated leachate with addition of FeCl₃ solution. In the experiment, three columns were used, two of them were used as controls (named as B1 and B3), B1 was fed with leachate and CH₄, whereas B3 was only recirculated with leachate adding FeCl₃. The treatment B2 was fed with the above two substrates. During the operation of columns, the contents of CH₄, CO₂ and N₂ in the gas, and the concentrations of NO₃^-, NO₂^-, NH₄⁺, SO₄^2-, Fe(Ⅲ) and Fe(Ⅱ) in the leachate and refuse were respectively determined. The results showed that adding ferric iron obviously enhanced the removal of methane in anaerobic aged refuse, the decrease of methane content with time obeyed zero-order kinetic, and the rate of methane removal(denoted as CH₄/aged refuse)reached 1.28 mmol·(kg·d)^-1. In the anaerobic condition, methane could improve the reduction of Fe(Ⅲ) to dissolved, active and bioavailable Fe(Ⅱ). The active Fe(Ⅱ) probably coupled to the transformation of NO₃^- and SO₄^2-, and thus accelerated the removal of NO₃^- and SO₄^2-.