Microbial degradation of simulated landfill leachate: Solid iron/sulfur interactions

Microcosms were prepared to test if added mineral Fe³⁺ and SO₄^2- could treat landfill leachate and to examine intrinsic microbial/mineral interactions related to natural attenuation. Two oxidized native sediments were used from central Oklahoma. Three types of anoxic microcosms were prepared which included the addition of: (1) mineral ferrihydrite (Fe(OH)₃); (2) mineral gypsum (CaSO₄^•2H₂O); and (3) no mineral amendments. Each received a synthetic leachate consisting of 2000 mg/l non-purgable organic carbon (NPOC). Measurements of substrate consumption, dissolved ions, mineral utilization/precipitation, and biological gases were made over 12 weeks. The added CaSO₄^2- and Fe(OH)₃ were used as electron acceptors: CaSO₄^2- by first order kinetics (k≅0.12 week^-1) and Fe³⁺ by zero order kinetics (k≅0.16 mM week^-1). The addition of either CaSO₄^2- or Fe(OH)₃ did not increase organic carbon degradation rates over methanogenesis, which was predominate in the non-amended microcosm set. Adding solid electron acceptors promoted carbonate and sulfide mineral formation and controlled greenhouse gases including CH₄ and CO₂. It is suggested that reduced Fe and S minerals could be used to assess organic contaminant degradation occurring due to Fe³⁺ and SO₄^2- microbial reduction processes for natural attenuation studies.