Abundance of amoA genes of ammonia-oxidizing archaea and bacteria in activated sludge of full-scale wastewater treatment plants

In this study, the abundance and sequences of amoA genes of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were determined in seven wastewater treatment plants (WWTPs) whose ammonium concentrations in influent and effluent wastewaters varied considerably (5.6–422.3 mgN l−1 and 0.2–29.2 mgN l−1, respectively). Quantitative real-time PCR showed that the comparative abundance of AOA and AOB amoA genes differed among the WWTPs. In all three industrial WWTPs, where the influent and effluent contained the higher levels of ammonium (36.1–422.3 mgN l−1 and 5.3–29.2 mgN l−1, respectively), more than four orders of magnitude higher numbers of AOB amoA genes than AOA amoA genes arose (with less than the limit of detection of AOA amoA genes). In contrast, significant numbers of AOA amoA genes occurred in all municipal WWTPs (with ammonium levels in the influent and effluent of 5.6–11.0 mgN l−1 and 0.2–3.0 mgN l−1, respectively). Statistical analysis suggested that compared to other plants’ parameters, the ammonium levels in the plants’ effluent showed correlation with the highest p value to the abundance of AOA amoA genes.