Mathematical Modelling of Molybdate reduction by a dye-decolorizing bacterium and the study of activation energy for reduction

A molybdenum-reducing bacterium with the novel ability to decolourise various dyes is reported. The absorption spectrum of the molybdenum reduced product suggested that it is a reduced phosphomolybdate. Optimum conditions for molybdenum reduction were ammonium sulphate 4g/L, pH of 8 and at 37°C. Arabitol was the best electron donor. The highest Mo-blue was observed at the phosphate concentration of 2.5 mM and sodium molybdate at 10 mM. <em>Pseudomonas</em> sp. MM02 was able to decolourise the dye tartrazine maximally at 75.9%, followed by Reactive Red 120 at 75.4 % and Reactive Brown 10 at 63.63%. Substrate inhibition kinetics was investigated and based on the best model; Haldane, the maximum specific reduction rate, the concentration of substrate at the half-maximal reduction rate, and inhibition constant represented by <em>qmax</em>, <em>ks</em> and <em>Ki</em> were 6.71 μmole Mo-blue h-1, 9.97 mM and 65.59 mM, respectively. The heavy metals mercury and silver at 1 mg/L completely inhibited molybdenum reduction. The effect of aluminium, a common soil metal in Malaysia on the molybdenum reduction rate was mathematically modelled. The best model was Wang giving the model constants maximum reduction rate of 0.283 Mo-blue h-1, while the saturation constant (<em>Kc</em>) and inhibitory constant (m) were 5.957 mM and 5.224 mM, respectively. The plot of ln μmax against 1/T to study the effect of temperature on Mo-blue production was carried out. Regression analysis from 31-40°C resulted in activation energy of 45.074 kJ mol-1, while in the temperature range from 40-45°C, the activation energy was 49.48 kJ mol-1.