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 0.06h, and temperatures ranging from 30 to 40°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°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 C)/h, respectively. The maximum specific growth rate was found to be 0.077h. 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°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 ×10−3 mM. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 65: 44–53, 1999.