Emissions of Inorganic and Organic Arsenic Compounds via the Leachate Pathway from Pretreated Municipal Waste Materials: A Landfill Reactor Study

The emission of arsenic (As) with leachate from mechanically biologically pretreated municipal solid waste (MBP-MSW) was quantified over one year using landfill simulation reactors. Arsenic mobilization and transformation processes were studied by simulating different environmental conditions (anoxic conditions with underlying soil or oxic/anoxic conditions). Amounts of mono-, di-, and trimethylated As in MBP-MSW prior to simulation were <48 μg As kg⁻¹ and were magnified to 300−390 μg As kg⁻¹ under anoxic conditions, whereas methylated As was undetectable in the oxic setup. The highest leachate concentrations (up to 84 μg L⁻¹) occurred during the first four weeks of manipulation. The annual As_total release with leachates averaged 19.6, 7.6, and 4.5 μg kg⁻¹ under an anoxic environment with underlying soil, oxic conditions, and anoxic conditions, respectively, with 15−50% occurring as organic As. The annually released As represented 0.2−0.8% of the As_total pool, suggesting that As mobilization from waste is a slow process. The anoxia diminished As release rates, whereas anoxic conditions with underlying soil material elevated the As mobilization, probably due to reductive dissolution of soil-derived Fe and Mn (hydr)oxides. The mass balance of methylated As in MBP-MSW and leachates before and after the treatments highlights As methylation under anoxic conditions and demethylation under oxic landfill conditions.