Kinetic modeling of a mixed culture of Pseudomonas Denitrificans and Bacillus subtilis under aerobic and anoxic operating conditions

The kinetics of biological denitrification have been studied and several models, with varying degree of complexity, to be used for design purposes have been presented in the recent years. However, most of these kinetic studies were performed with mixed (and not well defined) microbial systems, such as activated sludge. In the present work, kinetic experiments were carried out in order to study the dynamic characteristics of a defined mixed culture of the denitrifiers Pseudomonas denitrificans and Bacillus subtilis under anoxic and aerobic conditions in a defined synthetic medium involving a mixture of organic substrates, in the presence of nitrates and/or nitrites. Denitrification was assumed to occur by the consecutive reduction of nitrates to nitrites and then to nitrogen gas without accumulation of intermediate gaseous products. The behavior of these defined mixed cultures was predicted using a kinetic model based on the kinetic models that have already been developed for each bacterium separately and the predictions were compared with the results from mixed culture experiments. The overall mathematical model that was developed and validated in the present work is capable of describing the behavior of the mixed culture in the above conditions, i.e. the nitrates and nitrites reduction kinetics, the cell growth, and the organic carbon utilization rates.