New insights into NO emission and electron competition under different chemical oxygen demand to nitrogen ratios in a biofilm system.

Nitrous oxide (NO) is a greenhouse gas that could accumulate during the heterotrophic denitrification process. In this study, the effects of different chemical oxygen demand to nitrogen ratio (COD/N) on NO production and electron competition was investigated. The electron competition was intensified with the decrease of electron supply, and Nos had the best electron competition ability. The model simulation results indicated that the degradation of NOx-Ns was a combination of diffusion and biological degradation. As reaction proceeding, NO could accumulate inside biofilm. A thinner biofilm and a longer hydraulic retention time (HRT) might be an effective way to control NO emission. The application of mathematical model is an opportunity to gain deep understanding of substrate degradation and electron competition inside biofilm.