Nitrogen removal and microbial community variation in a shallow constructed wetland with Fe–C porous filter material as substrate

This study aims to examine the nitrogen removal characteristics and microbial community variation at low hydraulic retention time (HRT) in a shallow constructed wetland (SCW) using iron–carbon (Fe–C) porous filter material (PFM) as substrate. Effects of influent nitrogen forms and chemical oxygen demand (COD)/N ratio on nitrogen removal performance at HRT of 1 day were investigated. Results showed that total nitrogen (TN) removal declined with the decrease of influent NH₄⁺-N-to-NO₃⁻-N ratio. When the influent NH₄⁺-N/NO₃⁻-N ratio was 0.1, TN removal decreased by 15.4% compared with that at ratio of 2.0. The increase of influent COD/N ratio enhanced NO₃⁻-N reduction, and TN removal reached 74.5% at influent COD/N ratio 7.0. The microbial community was analyzed for the biofilm samples on Fe–C PFM at front (WF), middle (WM), and back (WB) of SCW. Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes were dominant bacteria phyla. The relative abundance of genera involved in the nitrification and denitrification decreased with the influent flow. The iron autotrophic denitrifying and macromolecular organics degrading bacteria were abundant in the middle and back of SCW. Microbial nitrification and denitrification, plant uptake, and plant synergism contributed to 86.3%, 7.41%, and 19.9% of N removal, respectively. These results demonstrated that the SCW with Fe–C PFM as substrate was efficient in nitrogen removal at low HRT.