Effect of pH on ferrous-iron oxidation kinetics of Leptospirillum ferrooxidans in continuous culture

The ferrous-iron oxidation kinetics of Leptospirillum ferrooxidans were studied at dilution rates ranging from 0.01 to 0.10 h(-1) and pH values ranging from pH 1.10 to 1.70. The growth rate, and the oxygen and ferrous-iron utilisation 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(Fe)(2+), -r(O2) and r(CO2), and the correlation found to be good. The bacterial culture maintained at pH 1.30 achieved the greatest measured maximum growth rate. An increase in the pH from pH 1.10 to pH 1.70 did not affect the maximum yield and maintenance coefficients, or the maximum specific ferrous-iron and oxygen utilisation rates. However, the kinetic constants in bacterial ferrous-iron oxidation, viz. K-Fe2 and K-O2, increased linearly with increasing pH, across the range from pH 1.10 to 1.70. The kinetics could be described in terms of the ferric/ferrous-iron ratio using a Michaelis-Menten based model modified to account for the effect of pH on K-Fe2 and K-O2. Furthermore, the threshold concentration of ferrous-iron increased with a decrease in the pH of the solution. (C) 1999 Elsevier Science S.A. All rights reserved.