Hydrogel bioreactor drives Feammox and synergistically removes composite pollutants: Performance optimization, microbial communities and functional genetic differences.

Mixed pollutant wastewater has been a difficult problem due to the high toxicity of water bodies and the difficulty of treatment. Rice husk biochar modified with nano-iron tetroxide (RBC-nFeO) by polyvinyl alcohol cross-linking internal doping was used to introduce iron-reducing bacteria Klebsiella sp. FC61 to construct a bioreactor. The results of the long-term operation of the bioreactor showed that the removal efficiency of ammonia nitrogen (NH-N) and chemical oxygen demand best reached 90.18 and 98.49%, respectively. In addition, in the co-presence of Ni, Cd, and ciprofloxacin, the bioreactor was still able to remove pollutants efficiently by RBC-nFeO and bio-iron precipitation inside the biocarrier. During the long-term operation, Klebsiella was always the dominant species in the bioreactor. And the sequencing data for functional prediction showed that the biocarrier contained a variety of enzymes and proteins involved in Feammox-related activities to ensure the stable and efficient operation of the bioreactor.