Analysis of nitrous oxide production and system performance for a full-scale anammox plant combining activated sludge and granular activated carbon biofilm: a model-based study

In this work, experimental and long-term one-dimensional mathematical modelling approaches were combined to investigate the mechanisms and the main drivers influencing on emission of nitrous oxide in a full scale anammox plant whereby anaerobic ammonium oxidation (anammox), ammonia oxidizing bacteria, nitrite oxidizing bacteria and heterotrophic denitrifying bacteria enriches in activated sludge treatment process, then grow on granular activated carbon surfaces as biofilms. The model was calibrated and validated using the actual real-time data of nitrogen components concentration in the effluent. The abundancy of various genera of anammox as dominant microbial group was estimated in the model by quantitative fluorescent in situ-hybridization (FISH) and image processing. A parameter identifiability protocol was applied to express the growth kinetic characteristics of microbial groups in the plant. Since nitrous oxide (N2O) is a greenhouse gas with important impacts on our environment, various pathways of the formation of nitrous oxide were considered and simulated. Finally, the system performance in terms of nitrogen and carbon biological removal efficiency and nitrous oxide production of the plant was optimized and analyzed under different simulation scenarios such as different total nitrogen loading rate, organic substrate rate as well as hydraulic retention times.