Manganese in natural waters II. Evidence for microbiological oxidation of Mn (II)

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Abstract
The oxidation of Mn(II) to Mn(IV) in natural waters has been investigated. Various hypotheses have been put forward for the mechanism of oxidation of Mn(II) of which only biological oxidation was found to occur in the aquatic system studied. The effect of adsorption, usually associated with the oxidation of Mn(II) was not observed in our study. The oxidation kinetics can be divided into three periods. The first period is the induction time corresponding to the growth of microorganisms that act as oxidising agents for Mn2 aq +. During this stage Mn2 aq + remains constant. This period is followed by a decrease in Mn2 aq + concentration following zero order rate law. Finally in the third period the decrease in Mn2 aq + follows a first order rate law. The microorganisms acting as oxidising agents for Mn(II) have been identified to be filamentous Gallionella type bacteria and Leptothrix discophora.