Kinetics of nitrous oxide (N(2)O) formation and reduction by Paracoccus pantotrophus

Nitrous oxide (N(2)O) 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 N(2)O, they can also reduce N(2)O to N(2). More information on the kinetics of N(2)O formation and reduction by denitrifying bacteria is needed to predict and quantify their impact on N(2)O 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(3)(−) (nitrate) to nitrite (NO(2)(−)), NO(2)(−) to N(2)O, and N(2)O to N(2), with acetate as the electron donor. The [Formula: see text] values were 2.9 gN gCOD(−1) d(−1) for NO(3)(−) to NO(2)(−), 1.4 gN gCOD(−1) d(−1) for NO(2)(−) to N(2)O, and 5.3 gN gCOD(−1) d(−1) for N(2)O to N(2). The [Formula: see text] values were 2.7, 0.93, and 1.5 d(−1), respectively. When N(2)O and NO(3)(−) were added concurrently, the apparent (extant) kinetics, [Formula: see text] , assuming reduction to N(2), were 6.3 gCOD gCOD(−1) d(−1), compared to 5.4 gCOD gCOD(−1) d(−1) for NO(3)(−) as the sole added acceptor. The [Formula: see text] was 1.6 d(−1), compared to 2.5 d(−1) for NO(3)(−) alone. These results suggest that NO(3)(−) and N(2)O were reduced concurrently. Based on this research, denitrifying bacteria like P. pantotrophus may serve as a significant sink for N(2)O. With careful design and operation, treatment plants can use denitrifying bacteria to minimize N(2)O emissions. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13568-016-0258-0) contains supplementary material, which is available to authorized users.