Ammonium oxidizing bacterial populations in South African activated sludge wastewater treatment plants.

This is the first study that describes ammonium oxidizing bacterial populations and correlations of these populations with a range of criteria in activated sludge wastewater treatment plants in South Africa. In this study, not only the influent but also the activated sludge chemistry was comprehensively characterized. Multivariate statistical analyses were used to determine the relative significances of the geographical location (factor: site), wastewater treatment plant process (factor: configuration), seasonality (factor: season), and environmental parameters on the ammonium oxidizing bacterial genera in six municipal activated sludge wastewater treatments plants from two sites (the cities of Cape Town and Ekurhuleni). The geographical location (site) was significant for selection of the ammonium oxidizing genera (Global ANOSIM R value = 0.538, p = 0.001). It was established that the inter-site differences were not climatic in origin, nor related to the composition of the influent, but were rather driven by the activated sludge chemistry. It was found using BEST analysis that the activated sludge ammonia, activated sludge total phosphate, and activated sludge total chemical oxygen demand were the most significant (p < 0.001) drivers for ammonium oxidizing bacterial selection (ANOSIM Global R value 0.419) and were significantly higher in the activated sludge from the City of Cape Town wastewater treatment plants. Nitrosospira was the most abundant ammonium oxidizing bacterial genus, with notably higher relative and estimated actual abundances in the City of Cape Town wastewater treatment plants than the City of Ekurhuleni wastewater treatment plants. The strong selection of Nitrosospira in the City of Cape Town wastewater treatment plants with higher nutrient concentrations strongly suggests that high concentrations of activated sludge ammonia, activated sludge total phosphate, and activated sludge total chemical oxygen demand are key selective drivers for this genus. PRACTITIONER POINTS: First comprehensive study describing ammonium oxidizing bacterial populations in Southern African domestic activated sludge wastewater treatment plants. The geographical location (site) was significant for selection of different ammonium oxidizing genera (Global ANOSIM R value = 0.538, p = 0.001). Inter-site differences driven by the activated sludge chemistry, not climate or influent wastewater composition. Selection of Nitrosospira driven by high concentrations of activated sludge ammonia, total phosphate and total chemical oxygen demand.