Geomicrobial and Geochemical Redox Processes in a Landfill-Polluted Aquifer

The distribution of different dominant microbial-mediated redox processes in a landfill leachate-polluted aquifer (Grindsted, Denmark) was investigated. The most probable number method was utilized for detecting bacteria able to use each of the electron acceptors, and unamended incubations were utilized to detect the activity of the redox processes using the investigated electron acceptors. The redox processes investigated were methane production and reduction of sulfate, Fe(III), Mn(IV), and nitrate. The presence of methanogenic bacteria and methanogenic activity were observed close to the landfill. Sulfate-reducing bacteria and sulfate reduction were observed in the area where methanogenesis took place, but were also observed further downgradient in the leachate plume. Fe(III)-reducing bacteria were found in almost all samples from the entire anaerobic leachate plume, but no ongoing Fe(III)-reduction was observed. Sediment analysis with respect to iron species supports these findings, because no clear zone of Fe(III) depletion has been found in the leachate plume. Nitrate-reducers were found in a large section of the plume, but denitrification was observed only in the outskirts of the plume where nitrate was present.