From Laboratory to Field: Unveiling Microbial Community Dynamics to Optimize a Bioaugmentation System with Engineered Redox Zones for Nitrogen Removal in Polluted Waters

The remediation of nitrogen-polluted receiving waters remains a significant challenge, particularly due to the frequent disconnect between understanding the mechanistic action of microbial inoculants and designing effective, field-applicable treatment processes. This study aimed to bridge this gap by evaluating a commercial composite microbial inoculant and translating the insights into a practical in situ system. Laboratory-scale experiments identified an “aerobic-anoxic” operational mode as optimal, achieving an initial NH4+-N removal efficiency of 95.6% (reducing from 55.6 mg/L to <1.0 mg/L) within the first 7 days. Simultaneously, a distinct three-stage nitrogen transformation process was established, driving the terminal total nitrogen (TN) concentration down to a remarkable 2.6 mg/L, which corresponds to a superior cumulative TN removal efficiency of 95.90%. Concurrently, robust organic matter degradation and phosphorus clearance were achieved, yielding final laboratory removal efficiencies of 67.4% for COD and 6.4% for TP. High-throughput sequencing revealed that this performance was driven by significant microbial succession and environmental filtering, with functional genera such as Sediminibacterium (contributing to early-stage organic degradation and nitrogen transformation) and Kocuria (acting as metabolic drivers under transitioning redox conditions) becoming predominant during specific degradation phases. Based on these mechanistic findings, a pilot-scale, partitioned treatment system (aerobic bio-contact oxidation zone followed by a hybrid anoxic zone) was designed and implemented in a black-odorous river channel. The system demonstrated robust performance over 60 days, sustaining average removal rates of 93.2% for NH4+-N and 91.3% for TN. This work provides a validated framework that directly links the elucidation of microbial community dynamics under engineered conditions to the successful development of a manageable bioaugmentation strategy for treating nitrogen-contaminated receiving waters.