Impact of substrate gradient on start-up of partial nitritation-anammox process

Relevance. Partial nitritation-anammox represents a cost-effective biological nitrogen removal that has a lot of potential as an alternative process to conventional nitrification/denitrification. However, the sensitivity of the process to operating and environmental conditions limits its widespread application. Aim. To study the impact of substrate gradient on the start-up of partial nitritation-anammox in continuously stirred tank reactor and plug-flow up-flow reactor. Methodology. Modified activated sludge model number 1 (ASM 1) in MATLAB environment was implemented. Time-based aeration control was incorporated in the model (10 minutes on/20 minutes off). Concentration of dissolved oxygen between 0.2 and 0.8 mg-O2/L during the aeration phase was simulated. Results and conclusion. It was found that partial nitritation-anammox could be successfully started-up in both reactors in less than 200 days under the given operating conditions. In addition, changes within the bacterial communities could occur in the course of operation of reactors. The abundance of anammox bacteria, heterotrophic bacteria, and ammonia oxidising bacteria could decrease with reactor height, while the growth of nitrite oxidising bacteria could vary with reactor height in plug-flow up-flow reactor due to the dynamics of nitrite (NO2–) generation and depletion in different levels within the reactor. Overall, partial nitritation-anammox implementation in continuously stirred tank reactor and plug-flow up-flow reactor is feasible.