Kinetic modelling of selenite reduction by Enterococcus spp in batch reactors

Abstract

Selenite (SeO3 2-) is a toxic selenium oxyanion which readily bio-accumulates in the food chain. Enterococcus species were found to reduce SeO3 2- to elemental selenium (Se0) more rapidly (in 1 h) as compared to other known selenite reducing bacteria. The kinetics of the reduction by the Enterococcus species was investigated in aerobic batch reactors. The data fitted to the kinetic models was obtained from the reduction of various SeO3 2- concentrations under established optimum conditions (3.5 h, 35±2 °C, pH ≥ 8). The results of these biological experiments were modelled and the biokinetic parameters were estimated with a first order kinetic model for selenite reduction and elemental selenium accumulation. The AQUASIM software for the simulation of aquatic systems was used for generating the models. The estimated parameters for selenite reduction and elemental selenium formation by the biotic system were the reaction rate constant of k= 0.562 h-1 and yield coefficient, YSe0/Se4+ = 0.761. The yield coefficient for the amount of glucose removed per mM of SeO3 2- , YGlc/Se4+, was not constant and depended of the concentration of selenite being reduced. The model presented in this work was able to fit the experimental data but more work still has to be done in order to develop a more concise model.