Competition between two microbial populations in a sequencing fed-batch reactor and its implications for waste treatment applications

Pure and simple competition between two microbial populations in a sequencing fed-batch reactor (SFBR) was studied both at the theoretical and experimental level. Competition occurred for a single chemical pollutant which could serve as the sole carbon and energy source for both competitors. A mathematical model describing the process under inhibitory kinetics (as is usually the case with hazardous and toxic substances) was derived and theoretically analyzed. The model predicts that the dynamics of a SFBR, and the kinetics of biodegradation, result in a complex set of operating regimes in which neither species, only one species, or both species survive in a steady cycle. The model also predicts the existence of multiple outcomes, achievable from different start-up conditions, in some domains of the operating parameter space. The experimental system involved phenol as the model pollutant, and two species capable of utilizing phenol as their sole carbon and energy source. These species were Pseudomonas putida (ATCC 17514) and Pseudomonas resinovorans (ATCC 14235). A methodology was developed to accurately determine the kinetics of phenol biodegradation by each individual species in pure culture batch experiments. It was found that both species biodegrade phenol following Andrews\u27 kinetics. The experimentally determined kinetic parameters were then used with the model equations to predict the behavior of a SFBR employing both species together. The model predictions were experimentally tested by inoculating a SFBR with both species and operating under conditions falling in different regimes of the operating parameter space. In all cases there was excellent agreement between the predicted and measured concentrations of phenol, total biomass, and the biomass of each individual species. All different types of behavior of the system predicted by the analysis of the model were experimentally confirmed including the existence of multiple outcomes under the same operating, but different start-up conditions. This study shows how serious discrepancies can arise in scale-up of biological treatment systems if population dynamics are not taken into account. This study also confirms experimentally the theory of microbial competition in periodically forced bioreactors