Coupled electron transfer and community assembly of the bi-functional PMo12@MIL-88A (Fe) based on surface-confinement microenvironments to accelerate nitrate bioreduction

Electron transfer rates and microbial community were important limiting factors influencing denitrification, so a bi-functional material (electron shuttle: PMo12 + conductive material: MIL-88A (Fe), P@M) was constructed to achieve a high denitrification efficiency. The nitrate and nitrite bioreduction rates were 9.79 mg/(L center dot h) and 4.71 mg/(L center dot h) respectively, which were 1.58 and 2.94 folds higher than those in the control system, and P@M could maintain functional stability in the SBR system. From the perspective of interfacial interactions between P@M and microorganisms, "surface-confinement function microregion" was formed based on van der Waals force interactions and contributed to the enhanced electron transfer efficiency. From the perspective of electron transfer, the electrochemical analyses (cyclic voltammetry, differential pulse voltammetry and Tafel), electron transport system activity, membrane permeability, metagenomic next-generation sequencing and the increased cytochrome c content proved that P@M enhanced intracellular and extracellular electron transfer during denitrification. Based on the results of enzyme activity, extracellular denitrification influenced by extracellular electron transfer was the main rate-limiting step in nitrate bioreduction compared to intracellular denitrification. From a community assembly perspective, P@M could act as a deterministic abiotic factor to dynamically regulate microbial community assembly, which allowed electroactive microorganisms, ROS-scavenging microorganisms, and nitrate-reducing metal-oxidation microorganisms to occupy appropriate ecological niches for accelerating nitrate bioreduction. This study provides a promising strategy for the application of bi-function materials in biotreatment.