How Arsenic Fate is Coupled to Sulfur Biomineral Formation in Landfills
Lowering the Maximum Contaminant Level for arsenic in drinking water in the U.S., has caused a significant increase in the volume of ABSR generated by drinking water utilities. Because of their high adsorption capacity and low cost, iron sorbents are used treatment technology and, when the sorbent’s capacity is spent, these ABSRs are disposed in municipal solid waste (MSW) landfills. However, a mature landfill is a biotic, reducing environment, which causes arsenic mobilization from the ABSR. It is well documented that iron and sulfur redox cycles largely control arsenic cycling and play key roles in arsenic disposition in the landfill microcosm. The primary routes of iron and sulfate reduction in landfills are microbially mediated and biomineralization is a common by-product. Biomineralization may lead to formation of minerals such as siderite (FeCO3), vivianite (Fe3(PO4)2), iron sulfide (FeS), goethite (FeOOH), and realgar (AsS). In this work, microbial reduction and biomineralization of iron, sulfur, and arsenic species are evaluated as processes that both cause arsenic release from landfilled ABSR and may possibly provide a means to re-sequester it in a recalcitrant solid state. The work uses flow-through laboratory-scale columns in which controlled conditions similar to those found in a mature landfill prevail. The feed contains lactate as the carbon source and primary electron donor, and ferric iron, arsenate, and a range of sulfate concentrations as primary electron acceptors. Preliminary results show that the concentration of sulfate fed to the system affects the biomineral formation, and that the relative amounts and sequence of precipitation of biominerals affect the free arsenic concentration that can seemingly be engineered by the concentration of sulfate fed to the system. It was observed that increase in sulfate concentration favors sulfur mineral formations.