LAUSR

Abstract Micro-aerobic reactors (MARs) play an important role in simultaneous nitrification, denitrification, and organics removal but are affected by the C/N ratio. In this study, high C/N ratio food-processing wastewater was treated using two-step MARs. The average removal efficiencies of total nitrogen and chemical oxygen demand during the MAR process were 84.21% and 95.43%, respectively. The efficiency of simultaneous nitrification and denitrification was 88.87% and 17.26% in MAR-1 and MAR-2, respectively; simultaneously, organic matter was efficiently degraded. Protein-like materials were biodegraded preferentially, and the degree of change in fulvic-like substances was the greatest during the MAR processes. This was attributed to the spatial distribution of the dissolved oxygen concentration in a single MAR, which may influence the microbial community composition (e.g., that of Nitrospira) and the regulation of gene functions.