Enhancement of nitrogen removal from low C/N wastewater under the optimization of electron donors utilization based...

Efficient treatment of low carbon-nitrogen ratio (C/N) wastewater is crucial for environmental protection, yet traditional biological treatment always struggle with simultaneous nitrogen and phosphorus removal due to limited carbon sources. This study aims to address this challenge by optimizing the sequencing batch biofilm phosphorus recovery reactor (SBBPR) system, integrating it with a biofilm electrode reactor (BER), and incorporating phosphorus recovery unit to release the electron donors competition during the simultaneous nitrification, denitrification and phosphorus removal (SNDPR) process. The innovative combination of SBBPR and BER provides additional electron donors (e.g., H₂) through electrolysis, reducing reliance on organic carbon, while activated alumina enhances phosphorus adsorption and enables resource recovery. At C/N of 3.0 and 2.5, the system achieved total nitrogen (TN) removal rates of 70.77 ± 5.61% and 65.53 ± 6.27%, respectively, and total phosphorus (TP) removal rates of 92.01 ± 10.39% and 93.21 ± 7.39%, respectively. Microbiological analysis revealed enrichment of polyphosphate-accumulating organisms (PAOs), denitrifying phosphorus-accumulating organisms (DPAOs), and denitrifying glycogen-accumulating organisms (DGAOs), whose synergistic interactions drove the SNDPR process. Furthermore, the addition of activated alumina is beneficial to the removal of phosphorus and enables its recovery rate to reach 46.26 ± 0.56%. The incorporation of activated alumina provides the primary pathway for phosphorus adsorption and recovery. Phosphorus recovery via adsorption alleviated carbon source competition, thereby indirectly enhancing nitrogen removal efficiency. Mechanism analysis revealed a synergistic interaction of chemical and biological process to optimize carbon flow and drive the SND process. This study demonstrates a feasible and sustainable approach for nutrient removal and phosphorus recovery in low-carbon wastewater, offering valuable insights for advancing wastewater treatment technologies.