Releasing behavior of zinc in recirculated bioreactor landfill.

The purpose of this research was to determine the releasing behavior of zinc in municipal solid waste (MSW) in landfill site with respect to refuse and leachate as an inseparable system. Two simulated bioreactor landfills, one with leachate recirculation and the other without, were operated in room temperature for 320 days. Results showed that the content of zinc in MSW could amount to 591.29+/-31.33-632.14+/-18.98 microg g(-1) dry weight(-1) (DW(-1)). It exceeded the set standard for "Environmental quality standard for soil" (< or =500 microg g(-1) DW(-1)) and had high potential environmental risk. The releasing behavior of zinc in refuse mainly experienced speciation of solid-Zn, Zn(2+), ZnHCO(3)(+), ZnCO(3), Zn(OH)(+), Zn(OH)(2), Zn(NH(3))(4)(2+), ZnS, etc. Zinc in refuse showed behaviors of staggered migration and retention, which corresponded with the degradation process of refuse in bioreactor landfill. The Zn(2+) concentration in leachate, which varied correspondingly with releasing behavior of zinc in refuse, were 0.75 mg L(-1) to 3.13 mg L(-1) and had no great difference in landfill with different operation modes (CL and RL). However, the amount of Zn(2+) leached out from refuse, which accounted for 28.70 mg and 130.67 mg after 320 day's operation, respectively. More attention should be paid to the inseparable system including refuse and leachate together.