title: The effect of temperature on the continuous ferrous-iron oxidation kinetics of a predominantly Leptospirillum ferrooxidans culture.
abstract: The ferrous-iron oxidation kinetics of a bacterial culture consisting predominantly of Leptospirillum ferrooxidans were studied in continuous-flow bioreactors. The bacterial culture was fed with a salts solution containing 12 g/L ferrous-iron, at dilution rates ranging from 0.01 to 0.06 l/h, and temperatures ranging from 30 to 40 degrees C, at a pH of 1.75. The growth rate, and the oxygen and ferrous-iron utilization rates of the bacteria, were monitored by means of off-gas analysis and redox-potential measurement. The degree-of-reduction balance was used to compare the theoretical and experimental values of r(CO(2)), -r(O(2)) and -r(Fe(+2)), and the correlation found to be good. The maximum bacterial yield on ferrous-iron and the maintenance coefficient on ferrous-iron, were determined using the Pirt equation. An increase in the temperature from 30 to 40 degrees C did not appear to have an effect on either the maximum yield or maintenance coefficient on ferrous-iron. The average maximum bacterial yield and maintenance coefficient on ferrous-iron were found to be 0.0059 mmol C/mmol Fe(2+) and 0.7970 mmol Fe(2+)/mmol C)/h, respectively. The maximum specific growth rate was found to be 0.077 l/h. The maximum specific ferrous-iron utilization rate increased from 8.65 to 13.58 mmol Fe(2+)/mmol C/h across the range from 30 to 40 degrees C, and could be described using the Arrhenius equation. The kinetic constant in bacterial ferrous-iron oxidation increased linearly with increasing temperature. The ferrous-iron kinetics could be accurately described in terms of the ferric/ferrous-iron ratio by means of a Michaelis-Menten-based model modified to account for the effect of temperature. A threshold ferrous-iron level, below which no further ferrous-iron utilization occurred, was found at a ferric/ferrous-iron ratio of about 2500. At an overall iron concentration of 12 g/L, this value corresponds to a threshold ferrous-iron concentration of 78.5 x10(-3) mM.
authors.affiliation: Gold Fields Minerals Bioprocessing Laboratory, Department of Chemical Engineering, University of Cape Town, Rondebosch, 7701, South Africa.
authors.forename: A W
authors.initials: AW
authors.lastname: Breed
authors.forename: C J
authors.initials: CJ
authors.lastname: Dempers
authors.forename: G E
authors.initials: GE
authors.lastname: Searby
authors.forename: M N
authors.initials: MN
authors.lastname: Gardner
authors.forename: D E
authors.initials: DE
authors.lastname: Rawlings
authors.forename: G S
authors.initials: GS
authors.lastname: Hansford
mesh_terms: D001419:Bacteria / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D001483:Base Sequence; D019149:Bioreactors; D001709:Biotechnology; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D016133:Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D007501:Iron