AOB

An analysis of nitrite-oxidizing bacteria in the activated sludge process of a full-scale partially nitrifying wastewater treatment plant revealed Nitrospira and Nitrobacter averaged 1013 cells?L-1 and 1012 cells?L-1, respectively. Correlation coefficients linking shifts in NOB community to operational or environmental variables illustrated Nitrospira were negatively correlated to nitrite (r = -0.45, P<0.01), while Nitrobacter showed no significant relationship to nitrite (P=0.1017). Nitrospira was negative correlation to DO (r = -0.46, P<0.01) and positively correlated to temperature (r = 0.59, P<0.0001). However, Nitrobacter was positively correlated to DO (r = 0.38, P<0.01) and HRT (R = 0.33, P<0.05), as well as negatively correlated to temperature (r = -0.49, P<0.001) suggesting niche adaptations within the NOB community. The positive association between Nitrobacter and DO supports a selective advantage over Nitrospira in completely nitrifying plants. Given the operational schematic at this WWTP, Nitrospira contributed more to nitrification than Nitrobacter in this WWTP