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Oxygen is a key operational parameter in biological nutrient removal wastewater treatment plants. Dissolved oxygen (DO) concentrations greater than 2 mg DO/L are commonly used in the aerobic stage of treatment to achieve complete nitrification. However, aerated-anoxic processes exhibit efficient nitrification under microaerophilic conditions. From a microbial ecology perspective, it is possible that the efficient nitrification at low DO conditions in aerated-anoxic reactors is due to the presence of nitrifying bacteria highly adapted to the low-DO environment. To test this hypothesis, we tracked the dynamics of the ammonia-oxidizing bacteria (AOB) population in labscale chemostat reactors operated at low and high DO concentrations. The reactors were initially seeded with activated sludge from a full-scale WWTP in which the AOB community was mostly composed of AOB belonging to the N. oligotropha lineage. Results from amoA-based terminal restriction fragment length polymorphism and comparative amoA sequence analyses showed that a high-DO environment selected for a group of AOB belonging to the N. europaea lineage and characterized by having a 219- bp/270-bp terminal fragment pair. The low-DO environment also selected for AOB of the N. europaea lineage, but the dominant organisms were characterized by having a 491- bp/491-bp terminal fragment pair, indicating that they conformed a distinct group of AOB. The low-DO environment also enriched for organisms having a 219-bp/270-bp pair, but comparative sequence analyses showed that they belonged to a cluster phylogenetically distinct from the high-DO enriched AOB.

Document Type: Research Article


Publication date: 2002-01-01

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