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

Maifanite-amended pyrite biofilter for efficient autotrophic denitrification of low-C/N mariculture tailwater: mechanistic insights into microbial nitrogen–sulfur–iron coupling

Study on the Aerobic Denitrification Nitrogen Removal Characteristics and Microbial Degradation Mechanism of the Air-Lift Multistage Integrated Reactor

This study evaluates an air-lift multistage integrated reactor designed for township wastewater treatment. Under controlled aeration, the reactor established distinct dissolved oxygen zones (1.06, 1.46, and 1.89 mg/L from bottom to top) and maintained high mixed liquor suspended solids (MLSS), which together promoted both aerobic and anaerobic denitrification. During extended operation, the system achieved average removal efficiencies of 93.3% for chemical oxygen demand (COD), 96.2% for NH4+-N, 74.9% for total nitrogen (TN), and 92.9% for total phosphorus (TP). Concurrently, the evolution of extracellular polymeric substances (EPS) and enhanced sludge activity─as shown by increases in dehydrogenase activity (DHA) and specific oxygen uptake rate (SOUR)─contributed to the formation of microenvironments favorable for nutrient removal. High-throughput sequencing revealed a dynamic shift in microbial community composition, marked by enrichment of functional genera such as Pseudomonas, Flavobacterium, and Acinetobacter, and by a significant increase in the abundance of the napA gene linked to aerobic denitrification. The above results indicate that the air-lift multistage integrated reactor process has significant application potential in rural sewage treatment.

Concentration threshold for polyethylene microplastics impacting nitrogen transfor-mation in heterotrophic nitrification-aerobic denitrification systems.

Heterotrophic nitrification-aerobic denitrification (HN-AD) enables simultaneous nitrification and denitrification under aerobic conditions. However, the pathways and mechanisms by which microplastics (MPs) affect HN-AD mediated nitrogen transformation remain unclear, limiting the development of remediation strategies for co-polluted aquatic systems. To address this gap, microcosm tests integrated with optical characterization and high-throughput 16S rRNA sequencing were conducted to evaluate polyethylene microplastic (PE-MPs) influences. Results revealed a concentration-dependent dual effect where PE-MPs suppressed nitrite oxidation and denitrification, featuring a distinct inhibition threshold and inducing NO2--N accumulation up to 8.0 times the control level. Mechanistically, PE-MPs acted as physical carriers that promoted microbial colonization and biofilm development, thereby facilitating microbial community dispersion and boosting the transformation. Concurrently, leaching of chemicals from PE-MPs reduced microbial abundance and diversity, depressing nitrite oxidation. Notably, the relative abundance of HN-AD functional taxa increased with rising PE-MPs concentrations. Emergent dominant phyla, Myxococcota and Patescibacteria, were significantly enriched, indicating adaptive. These opposing forces define the critical concentration threshold where the promotion of ammonia oxidation shifts to inhibition and the overall denitrification collapses. Ultimately, the concentration-driven battle between physical and chemical disrupts the HN-AD microbial community, severely hindering nitrogen transformation. This study provides mechanistic insights into the complex interplay between MPs and nitrogen transformation, offering novel perspectives for optimizing bioremediation strategies in MPs and nitrogen co-polluted aquatic systems.

Impact of the Fenton pretreatment on enhanced biological phosphorus removal: emphasizing variations in microbial community and metabolism

Synergistic operational optimizations and microbial responses stabilize filamentous-dominated continuous-flow partial denitrification-anammox at low-temperature.

The operational stability of continuous-flow partial denitrification-anammox (PD/A) systems is frequently constrained by insufficient nitrite supply and temperature sensitivity of anammox bacteria, particularly under low-temperature stress. In such conditions, filamentous bacteria often proliferate excessively, and their overgrowth has long been associated with reactor instability and performance deterioration. Here, we demonstrate stable nitrogen removal in a filamentous-dominated continuous-flow PD/A reactor at an average temperature of 16.7 °C through operational optimizations and microbial responses. The reactor achieved 89.8 % total nitrogen removal, with ammonium and nitrate removal efficiencies of 97.2 % and 91.5 %, respectively, with anammox contributing up to 98.3 % of nitrogen removal. Metagenomic analyses revealed that the filamentous genus Sphaerotilus dominated the microbial community (29.3-41.5 %) but sustained the genomic potential for nitrite availability to support anammox. Genome-centric reconstruction confirmed that a Sphaerotilus-affiliated MAG5 possessed adaptive features under low temperature. Additional heterotrophs, including Leptothrix, Rubrivivax, and Thauera, harbored genomic potential for auxiliary nitrate-to-nitrite conversion. Crucially, the synergy between this genomic potential for nitrite provision and engineered biomass retention (specifically mesh filtration and regular sludge return) facilitated the enrichment of Ca. Brocadia, increasing its relative abundance from 2.4 % to 5.4 %. Concurrently, Ca. Brocadia reinforced low-temperature adaptability by expanding the genetic potential of energy-generating carbon metabolic pathways and increasing its contribution to the cold shock protein gene cspA from 6.6 % to 21.0 %. Collectively, this study reveals that integrating strategic biomass retention with microbial responses provides a viable pathway to sustain stable nitrogen removal in filamentous-dominated continuous-flow PD/A systems.

Enhanced nitrogen removal at psychrophilic conditions through bioaugmentation with immobilized bacterial cells capable of heterotrophic nitrification‐aerobic denitrification

Low temperature severely restricts the nitrogen removal efficiency of biological wastewater treatment processes. To address this challenge, this study applied an immobilization technique using the cold‐adapted strain Pseudomonas sp. f6 to enhance nitrogen removal under low‐temperature conditions. Among three carrier materials evaluated (bio‐cord, MBBR, and ceramic filler), bio‐cord exhibited the best immobilization performance, achieving 1.6‐ and 1.3‐fold higher COD Cr removal efficiency than MBBR and ceramic filler, respectively. Notably, the highest nitrogen removal efficiency was observed at 10 °C, with the addition of nitrate‐N, where the COD Cr and NH 4 + ‐N removal efficiencies were 1.10 and 1.15 times those at 15 °C, respectively. This counterintuitive result demonstrates that Pseudomonas sp. f6 maintains high metabolic activity despite decreasing temperatures. Microbial community analysis further revealed a key ecological mechanism: as the temperature declined, the relative abundance of Pseudomonas sp. f6 gradually increased, and it shifted from the second to the first dominant genus, indicating superior cold tolerance of Pseudomonas over Thauera . This study provides an effective low‐temperature‐resistant immobilized bio‐cord system for enhanced nitrogen removal and identifies a temperature‐driven succession pattern of functional bacteria. These findings offer both theoretical insights and practical engineering support for biological nitrogen removal in cold‐region wastewater treatment. © 2026 Society of Chemical Industry (SCI).