Enhanced Denitrification and Microbial Mechanism in Secondary Effluent Treatment Using Combined Iron–Carbon Microelectrolysis and Deep Bed Filters

This study developed an innovative system coupling iron–carbon microelectrolysis with a deep bed denitrification filter (DBDF) for the advanced treatment of secondary effluent. The key innovation lay in revealing the synergistic pollutant removal mechanisms through microbial community succession and metabolism pathway enhancement. Results showed that the effluent concentrations of total nitrogen, nitrate, and total phosphorus were stabilized below 2.5, 0.55, and 0.25 mg/L, and 41.05% of chemical oxygen demand was removed. Microorganisms in the microelectrolysis column (MEC) and DBDF all varied with the change of reactors height. The dominant genera in the MEC were Dechloromonas, Dechlorosoma, and uncultured_bacterium_f_Rhodocyclaceae, and the abundance of NO₃^– dependent Fe oxidizing Dechloromonas reached 20.15% at sampling point I. Acinetobacter, Hydrogenophaga, uncultured_bacterium_f_Rhodocyclaceae, Flavobacterium, and Thauera were the dominant genera in the DBDF. The pathways of N metabolic, carbohydrate metabolism, and energy metabolism all maintained high abundance in the combined process.