Efficiency, Microbial Communities, and Nitrogen Metabolism in Denitrification Biological Filter: Insights into Varied Pore Ceramsite Media

This study presented an investigation into the role of ceramsite pore structures in optimizing DNBFs for nitrate-contaminated water treatment. Through systematic comparison of three ceramsite media (CE1, CE2, CE3) with distinct pore structures, we elucidated the microbial mechanisms underlying nitrate removal efficiency by analyzing denitrification performance, biomass accumulation, EPS, microbial community structure, and nitrogen metabolic function. Results demonstrated that the CE2 medium, characterized by an effective porosity (pore size > 0.5 μm) of 55.8% and an optimal porosity (pore size 0.5-25 μm) percentage of 83.1%, achieved superior nitrate removal efficiency (87.8%) with an R_vd of 0.82 kg TN/(m³·d) at HRT = 1.5 h, outperforming CE1 (0.74 kg TN/(m³·d)) and CE3 (0.68 kg TN/(m³·d)). Enhanced performance was mechanistically linked to CE2's higher biomass accumulation (8.5 vs. 7.8 mg/m² in CE1 and 6.9 mg/m² in CE3) and greater EPS production (48.5 vs. 44.7 in CE1 and 35.4 mg/g in CE3), which facilitated biofilm resilience under hydraulic stress. Microbial analysis revealed CE2's unique enrichment of a higher relative abundance of <i>Proteobacteria</i> (90.1% vs. 67.2% in CE1 and 47.4% in CE3) and denitrifying taxa (unclassified_f_Comamonadaceae: 42.7%, unclassified_f_Enterobacteriaceae: 35.3%). PICRUST2 showed 1.2- and 1.4-fold higher abundance of denitrification genes (<i>narGHI</i>, <i>nosZ</i>) compared to CE1 and CE3, respectively. These findings establish that optimizing ceramsite pore structure, particularly increasing the optimal porosity ratio (pore size 0.5-25 μm) can enhance denitrification efficiency, offering a scalable strategy for cost-effective groundwater remediation. This work provides actionable criteria for designing high-performance DNBFs, with immediate relevance to industrial and municipal wastewater treatment systems facing stringent nitrate discharge limits.