Manganese Oxidation Induced by Water Table Fluctuations in a Sand Column
On–off cycles of production wells, especially in bank filtration settings, cause oscillations in the local water table, which can deliver significant amounts of dissolved oxygen (DO) to the shallow groundwater. The potential for DO introduced in this manner to oxidize manganese(II) (Mn(II)), mediated by the obligate aerobe Pseudomonas putida GB-1, was tested in a column of quartz sand fed with anoxic influent solution and subject to 1.3 m water table changes every 30–50 h. After a period of filter ripening, 100 μM Mn was rapidly removed during periods of low water table and high dissolved oxygen concentrations. The accumulation of Mn in the column was confirmed by XRF analysis of the sand at the conclusion of the study, and both measured net oxidation rates and XAS analysis suggest microbial oxidation as the dominant process. The addition of Zn, which inhibited GB-1 Mn oxidation but not its growth, interrupted the Mn removal process, but Mn oxidation recovered within one water table fluctuation. Thus transient DO conditions could support microbially mediated Mn oxidation, and this process could be more relevant in shallow groundwater than previously thought.
Additional Information© 2011 American Chemical Society. Received: August 9, 2011; Revised: November 11, 2011; Accepted: November 29, 2011; Published: November 29, 2011. We acknowledge financial support from Eawag, an NSF Graduate Research Fellowship, and NSF EAR-3 0525387. Colleen Hansel and Deric Learman (Harvard University, Boston, MA) generously provided P. putida GB-1 and assisted in its cultivation. We acknowledge the Angströmquelle Karlsruhe (ANKA, Karlsruhe, Germany) for the provision of beamtime at the XAS and SUL-X beamlines and thank Stefan Mangold, Jörg Göttlicher and Ralph Steininger for their assistance during data collection. Sam Webb (Stanford Synchrotron Radiation Laboratory, Menlo Park, NJ) is acknowledged for kindly providing reference XAS spectra for different Mn oxides. Supporting Information Schematic of experimental setup, results of oxidation assays, relative effluent Br concentrations, XAS results for sand in column, linear combination fitting of XAS spectra, XRF depth profile for P, pseudofirst order rate coefficients for Mn oxide reduction by P. putida GB-1, mass balance after the reduction assays, effluent pH values, and details of abiotic Mn oxidation rate calculations. This material is available free of charge via the Internet at http://pubs.acs.org.
Supplemental Material - es2027828_si_001.pdf