Biological Nitrous Oxide Abatement by Paracoccus denitrificans in Bubble Column and Airlift Reactors

Abstract

Nitrous oxide (N₂O), with a global warming potential 300 times higher than that of CO₂, represents 6.2 % of the total greenhouse gas emission inventory worldwide. Furthermore, N₂O is considered the most critical O₃- depleting substance emitted in this XXI century. In spite of the environmental relevance of this pollutant, very little research on biotechnologies for the treatment of N₂O emissions has been conducted. In this study, the potential of a bubble column (BCR) and an internal loop airlift (ALR) bioreactors of 2.3 L was evaluated for the abatement of N₂O from industrial emissions from nitric acid plants along 62 days of operation. The systems were inoculated with a methylotrophic Paracoccus denitrificans strain (DSM 413) and continuously supplied with methanol as a carbon and electron donor source for the anoxic reduction of N₂O. The simulated waste gas consisted of a N₂ gas stream containing 1 ± 0.1 % of O₂ and 3377 ± 312 ppm_v of N₂O at the inlet of theBCR and 1 ± 0.1 % of O₂ with N₂O concentration of 3617 ± 342 ppm_v at the inlet of the ALR. This N₂-laden stream was supplied at a constant flow rate of 110 ml min^-1 in each reactor. The performance of the BCR was characterized by a steady state N₂O removal efficiency (RE) of 87 ± 3 % with CO₂ productions of 308 ± 36 gm^-3 d^-1 and total suspended solid (TSS) concentrations of 867 ± 109 mg L^-1. On the other hand, the ALR showed a N₂O RE of 88 ± 2 % with productions of CO₂ of 346 ± 28 g m^-3 d^-1 and TSS concentrations of 874 ±88 mg L^-1. This work constitutes, to the best of our knowledge, the first systematic study of a biotechnology for the continuous abatement of N₂O from nitric acid plants.