N2OPNA · Understanding Nitrous Oxide Production from The Mainstream Partial Nitritation and Anammox Process

Understanding Nitrous Oxide Production from The Mainstream Partial Nitritation and Anammox Process

Mainstream partial nitritation/anammox (PNA) is a cost-effective technology for biological nitrogen removal from wastewater. However, to achieve high nitrogen removal rates and efficiencies in mainstream PNA process is of high complexity considering dynamic characteristic of municipal wastewater (regarding composition, quantity, pH, temperature, etc.) and the competition among different microbes for substrates and space. The key point for PNA process is to suppress nitrite oxidizing bacteria (NOB), which can be achieved by using inhibitors. Two internal inhibitors, free nitrous acid (FNA) and free ammonia (FA) have great advantages over others, attributing to their readily availability and sustainability in WWTPs. The FNA and FA from sidestream can be applied for NOB suppression in the sludge returning line. However, relevant research on how AerAOB, NOB and AnAOB respond to FNA and FA stress in one-stage PN/A process remains scarce. Another challenge of the PNA process is the emission of nitrous oxide (N2O). The destruction of stratospheric ozone layer has become a significant environmental issue in 21st century, which is contributed largely by N2O. N2O is also a potent greenhouse gas with a global warming potential (GWP) of approximately 265 times stronger than carbon dioxide. N2O production from PNA process remains far from fully understood, and a fundamental understanding of the mechanisms is highly desired to further optimize the process. In this project, the hybrid reactor technology and the NOB-inhibiting return-sludge treatment with realistic FNA/FA levels in full-scale sidestream were combined to achieve mainstream PN/A process. The immediate stress impact of FNA/FA levels and contact time on the activities of AerAOB, NOB and AnAOB were investigated in batch reactor, while long-term recovery was assessed in an integrated film activated sludge (IFAS) reactor, with sludge as flocs and biofilm on carriers during a period of 10 months. The shift of microbial community in flocs and carriers and N2O emissions were closely followed under different stress conditions. Economic potential of the combined technology was assessed. The final goal was to optimize the stress treatment conditions to maximize N removal efficiency and minimize N2O emissions in the IFAS reactors.

Data: CORDIS, © European Union