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

Microcosms were prepared to test if added mineral Fe 3+ and SO 4 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 (CaSO 4 •2H 2O); 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 CaSO 4 2− and Fe(OH) 3 were used as electron acceptors: CaSO 4 2− by first order kinetics ( k≅0.12 week −1) and Fe 3+ by zero order kinetics ( k≅0.16 mM week −1). The addition of either CaSO 4 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 CH 4 and CO 2. It is suggested that reduced Fe and S minerals could be used to assess organic contaminant degradation occurring due to Fe 3+ and SO 4 2− microbial reduction processes for natural attenuation studies.