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

Nitrous oxide (N sub(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 sub(2)O, they can also reduce N sub(2)O to N sub(2). More information on the kinetics of N sub(2)O formation and reduction by denitrifying bacteria is needed to predict and quantify their impact on N sub(2)O emissions. In this study, kinetic parameters were determined for Paracoccus pantotrophus, a common denitrifying bacterium. Parameters included the maximum specific reduction rates, q, growth rates, mu , and yields, Y, for reduction of NO sub(3) super(-) (nitrate) to nitrite (NO sub(2) super(-)), NO sub(2) super(-) to N sub(2)O, and N sub(2)O to N sub(2), with acetate as the electron donor. The q values were 2.9 gN gCOD super(-1) d super(-1) for NO sub(3) super(-) to NO sub(2) super(-), 1.4 gN gCOD super(-1) d super(-1) for NO sub(2) super(-) to N sub(2)O, and 5.3 gN gCOD super(-1) d super(-1) for N sub(2)O to N sub(2). The mu values were 2.7, 0.93, and 1.5 d super(-1), respectively. When N sub(2)O and NO sub(3) super(-) were added concurrently, the apparent (extant) kinetics, q sub(app), assuming reduction to N sub(2), were 6.3 gCOD gCOD super(-1) d super(-1), compared to 5.4 gCOD gCOD super(-1) d super(-1) for NO sub(3) super(-) as the sole added acceptor. The mu sub(app) was 1.6 d super(-1), compared to 2.5 d super(-1) for NO sub(3) super(-) alone. These results suggest that NO sub(3) super(-) and N sub(2)O were reduced concurrently. Based on this research, denitrifying bacteria like P. pantotrophus may serve as a significant sink for N sub(2)O. With careful design and operation, treatment plants can use denitrifying bacteria to minimize N sub(2)O emissions.