The effect of temperature on the continuous ferrous-iron oxidation kinetics of a predominantly Leptospirillum ferrooxidans culture

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(CO2,) -r(O2) 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 Fe2+ and 0.7970 mmol Fe2+/ mmol l/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 Fe2+/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 x 10(-3) mM. (C) 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 65: 44-53, 1999.