Nitrite Looping: Plausible Phenomenon or Mathematical Nuance?

摘要

Two biochemical pathways were used to model a counter-diffusion biofilm that performedsimultaneous nitrification-denitrification (SND): one characterized by parallel denitrification andthe other by sequential denitrification. Nitrite looping, a phenomenon in which denitrificationproduced-NO_2~- is oxidized to NO_3~- rather than following the traditional denitrification pathwayto N_2, was shown to occur in sequential denitrification models. In the mathematical simulationsconducted, nitrite looping triggered suboptimal conditions including (i) inefficient CODutilization, (ii) inefficient O_2 utilization, and (iii) NO_2~- accumulation. Simulations suggested thatthick biofilms (700μm vs 300μm) would minimize the magnitude of nitrite looping. From thistheoretical study, it was proposed that nitrite looping within SND biofilms is a plausibleoccurrence. The theory of nitrite looping simply requires that denitrification-produced NO_2~-interacts with NOOs prior to being reduced to N_2, which could occur due to close spatialproximity of bacteria or mechanisms that transport denitrification-produced NO_2~- from anoxic toaerobic regions.