Effect of different temperatures on denitrifying bacteria in UMSR reactor under Fe0 and electromagnetic field

Urban sewage typically has a low C/N ratio. To meet discharge standards, additional organic carbon and temperature control are often added to wastewater treatment plants (WWTPs) to aid denitrification. In this study, a lab-scale up-flow micro-aerobic sludge reactor (UMSR) with 1.5 mg/L dissolved oxygen (DO) was used to treat 50 mg/L ammonia nitrogen (NH ₄ ⁺ -N) without external organic carbon. The reactor was kept at a controlled at two different temperatures of 15°C and 34°C for the survey, with a hydraulic retention time (HRT) of 2.5 hours. Fe⁰ ≤ 0.3 µm was added to the reactor at 3 g/L, alongside a 48-mT magnetic field. The results assessed the reactor's removal efficiency and denitrifying bacteria enrichment. At 15°C, NH ₄ ⁺ -N and NO ₃ ⁻ -N removal efficiencies were 54.4% and 58.1%, respectively; at 34°C, they were 49.7% and 42.2%. Illumina sequencing revealed enriched denitrifying bacteria at 34°C by coupling MF with Fe ⁰ , including Gemmobacter at 2.6%, ammonia-oxidizing bacteria (AOB) Nitrosomonas at 1.6%, moderately thermophilic and CO ₂ fixation Ignavibacterium at 0.5%, and heterotrophic denitrification Dokdonella at 0.2%. Also noted was a sharp decrease at 34°C by coupling MF with Fe ⁰ of Gemmatimonas at 1.3%, and moderately thermophilic Tepidisphaera at 1%. BLAST-detected identity bacteria strains, and PICRUSt-predicted bacterial community functions were detected. The KGGE dataset presenting decreased enzymes at 34°C, such as (narl), (narH), (narG), (nasC), (anfG), and (nasB), while (nifK) showed an increase at 34°C.