Kinetics of nitrous oxide (NO) formation and reduction by Paracoccus pantotrophus.

Nitrous oxide (NO) is a powerful greenhouse gas emitted from wastewater treatment, as well as natural systems, as a result of biological nitrification and denitrification. While denitrifying bacteria can be a significant source of NO, they can also reduce NO to N. More information on the kinetics of NO formation and reduction by denitrifying bacteria is needed to predict and quantify their impact on NO emissions. In this study, kinetic parameters were determined for Paracoccus pantotrophus, a common denitrifying bacterium. Parameters included the maximum specific reduction rates, [Formula: see text], growth rates, [Formula: see text], and yields, Y, for reduction of NO (nitrate) to nitrite (NO), NO to NO, and NO to N, with acetate as the electron donor. The [Formula: see text] values were 2.9 gN gCOD d for NO to NO, 1.4 gN gCOD d for NO to NO, and 5.3 gN gCOD d for NO to N. The [Formula: see text] values were 2.7, 0.93, and 1.5 d, respectively. When NO and NO were added concurrently, the apparent (extant) kinetics, [Formula: see text], assuming reduction to N, were 6.3 gCOD gCOD d, compared to 5.4 gCOD gCOD d for NO as the sole added acceptor. The [Formula: see text] was 1.6 d, compared to 2.5 d for NO alone. These results suggest that NO and NO were reduced concurrently. Based on this research, denitrifying bacteria like P. pantotrophus may serve as a significant sink for NO. With careful design and operation, treatment plants can use denitrifying bacteria to minimize NO emissions.