Electrospinning‐Graphene Promoted Low‐Temperature Nitrogen Removal of Immobilized ANAMMOX Granules

To address the limited nitrogen removal performance of anaerobic ammonium oxidation (ANAMMOX) processes at low temperatures, this study successfully enhanced the low-temperature nitrogen removal performance of immobilized ANAMMOX granules by electrospinning (ES) and reduced graphene oxide (RGO). The lab-scale experimental results indicated that the total inorganic nitrogen (TIN) removal efficiency of novel immobilized ANAMMOX granules (M3) coated with 70-μm-thick chitosan/polyacrylonitrile electrospun membranes (CS/PAN-ES) and modified with 1.0 mg/(gVSS) RGO was significantly higher than M1 (common immobilized granules) and M2 (immobilized granules modified with 1.0 mg/(gVSS) RGO) at 4°C-13°C, especially at 4°C (60.9%-71.0%). These improvements were attributed to the stimulation of ANAMMOX activity at low temperatures by RGO and the enhanced structural stability of immobilized granules by CS/PAN-ES membranes. Furthermore, based on 16S rRNA sequencing analysis, CS/PAN-ES membranes and RGO synergistically promoted the growth of Candidatus Kuenenia (6.2% → 21.6%) and increased the abundance of functional genes nirK, hzs, and hzo at 4°C-13°C. This represents an important mechanism by which CS/PAN-ES membranes and RGO synergistically improved the extremely low-temperature activity of immobilized ANAMMOX granules. This study provides an effective strategy for the application of ANAMMOX processes in low-temperature environments.