N2O generation via nitritation at different volumetric oxygen transfer levels in partial nitritation-anammox process

Abstract

Volumetric oxygen transfer coefficient (KLa) is an important parameter affecting oxygen transfer and nitrogen conversion during biological wastewater management. However, how the generation of nitrous oxide (N2O) responds to the variation of KLa levels is unclear. In this study, N2O generation via the main pathway, which was confirmed to be nitritation, at different KLa levels was investigated in a partial nitritation-anammox (PN-A) reactor run as a sequencing batch reactor. The results showed that N2O generation in the PN-A process, which was described using the maximum N2O generation rate (MGR), the duration of N2O generation (DG), and the N2O generation factor, was affected by KLa levels and the limiting factors of the nitritation process, i.e., oxygen transfer and nitritation activity. DG always decreased with the increase of KLa, indicating that the process of N2O generation lasted for a shorter time at higher KLa. With the increase of KLa, MGRs remarkably increased when oxygen transfer was the limiting factor, while slightly reduced when nitritation activity became the limiting factor. As a result, with the increase of KLa levels, the N2O generation factor remarkably increased at lower KLa levels when oxygen transfer was the limiting factor, but significantly reduced at higher KLa levels when nitritation activity became the limiting factor. These results revealed how N2O generation via nitritation responded to different KLa levels and the limiting factors of the nitritation process. Based on these results, practical suggestions to mitigate the N2O generation in PN-A process operated in a batch mode were recommended.