Vertical Microbial Stratification in a Three-Layer Biotrickling Filter Strengthens Simultaneous Anammox and Denitrification for Synergistic Decontamination of Trimethylamine and Nitric Oxide in Combustion Flue-Gas-Heated Sludge-Drying Off-Gas

Co-treatments of trimethylamine (TMA) and nitric oxide (NO) in sludge drying off-gas receive little attention. Hitherto, TMA biofiltration shows limited nitrogen elimination; microbial collaboration in biofilters is conventionally attributed to horizontal biofilm stratification. This work elucidates vertical microbial stratification-driven simultaneous anammox-denitrification (SAD) in a three-layer biotrickling filter for decontamination of TMA and NO (loads: 44 gTMA m–3 h–1, 219 gNO m–3 h–1; 2–8% O2). Optimal removal efficiency of TMA and NO at 2% O2 attained 99% and 96%, respectively, equivalent to 71% and 29%, 25% and 38%, and 3% and 29% at the bottom, middle, and top layers. 91% of C and 99% of N were mineralized to CO2 and N2. From bottom to top, TMA declined but NO enhanced in performance, causing a C/N drop; dominant genera shifted from TMA-degrading denitrifiers to anammox bacteria; O2 mass transfer weakened; TMA removal pathway shifted from aerobic degradation to denitrifying degradation, while that of NO shifted from denitrification to anammox. These effects became more prominent at lower O2 levels. Along bed height, denitrification and anammox sequentially played leading roles in SAD: TMA was degraded to CO2 and NH3 with O2 then NO; NO was reduced to N2 with TMA then NH3. Vertical stratification gradually upgraded the removal progress toward thorough decontamination. This study provides new insights that vertical stratification can act as a driving force of functional synergy in biofiltration systems.