Effect of Dissolved Oxygen on Oxic/Anoxic Diauxic Lag of <i>P. denitrificans</i>

Abstract

Nitrogen is removed in suspended growth wastewater treatment systems by passing mixed liquor from an aerobic zone in which nitrification takes place to an anoxic zone in which denitrification takes place. Following the switch from oxygen to nitrate as terminal electron acceptor, a diauxic lag may occur. The present study tested the hypothesis that lower dissolved oxygen concentrations in the aerobic phase lead to shorter diauxic lags. Bacterial cultures exposed to low dissolved oxygen concentrations (<0.70 mg/L) during the aerobic growth phase had significantly shorter diauxic lags than cultures grown at air saturation. Furthermore, these cultures generally grew faster during the anoxic phase. These results indicate that the effect of dissolved oxygen concentration in aerobic reactors on diauxic lags and anoxic growth rates in anoxic reactors should be considered in the design and operation of nitrogen-removing, suspended growth biological treatment processes.