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Enhanced Nitrogen Removal and Distribution Distributions of Microbial Genes Associated with Nitrogen Cycling in A Vertical-flow Biofilter Treating Domestic Wastewater

Honglei Wang, Duntao Shu, Na Deng, Gehong Wei, and Tongshun Wang

Vertical-flow biofilters have been investigated as a sustainable technology for nitrogen (N) and chemical oxygen demand (COD) removal from domestic wastewater. However, the distribution contributions of microbial genes responsible for removing N remain largely unexplored, particularly along the depth gradient in vertical-flow biofilters. Here, a three-stage vertical-flow bio-filter (three stages: P1, P2, and P3) achieved large removal efficiencies for total nitrogen (TN; 87.00% and 33.69 g/m2·d), NH4 +-N (95.90% and 24.17 g/m2·d) and COD (92.00% and 558.15 g/ m2·d). The removal contributions of NH4+-N and TN in P1, P2, and P3 can be ranked as follows: P1 (45.9% and 38.4%, respectively) >P2 (39.6% and 28.2%, respectively) >P3 (10.6% and 20.5% respectively). The results revealed that amoA/bacteria, (nirK + nirS + nosZ)/bacteria, amoA/anammox and anammox/bacteria were the predominant gene groups responsible for NH4+-N and TN removal in P1, P2 and P3 and the contributions of these gene groups along the depth gradient of the bio-filter. Specifically, the NO3--N removal rate in P3 was notably enhanced and collectively governed by the (napA + narG) and nxrA gene groups. Integrated analyses confirmed that the coupling of nitrification and denitrification governed the enhanced removal of NH4+-N and TN in P1. Combining anammox and nitrification contributed to the removal of NH4+-N and TN in P2. Enhanced anammox and denitrification accounted for the robust TN reduction in P3. This study indicated that biofilters have great potential applicability for treating domestic wastewater without a sequential chain of treatments and extra aerations.