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Electron Transfer Capacities and Reaction Kinetics of Peat Dissolved Organic Matter

2006; American Chemical Society; Volume: 41; Issue: 1 Linguagem: Inglês

10.1021/es061323j

1520-5851

Markus Bauer, Tobias Heitmann, Donald L. Macalady, Christian Blodau,

Microbial Fuel Cells and Bioremediation

Information about electron-transfer reactions of dissolved organic matter (DOM) is lacking. We determined electron acceptor and donor capacities (EAC and EDC) of a peat humic acid and an untreated peat DOM by electrochemical reduction and reduction with metallic Zn and H2S (EAC), and by oxidation with complexed ferric iron (EDC) at pH 6.5. DOC concentrations (10−100 mg L-1) and pH values (4.5−8) were varied in selected experiments. EAC reached up to 6.2 mequiv·(g C)-1 and EDC reached up to 1.52 mequiv·(g C)-1. EDC decreased with pH and conversion of chelated to colloidal iron, and the electron-transfer capacity (ETC) was controlled by the redox potential Eh of the reactant (ETC = 1.016·Eh − 0.138; R 2 = 0.87; p = 0.05). The kinetics could be adequately described by pseudo first-order rate laws, one or two DOM pools, and time constants ranging from 2.1 × 10-3 d-1 to 1.9 × 10-2 d-1 for the fast pool. Reactions were completed after 24−160 h depending on the redox couple applied. The results indicate that DOM may act as a redox buffer over electrochemical potentials ranging from −0.9 to +1.0 V.