Nanobubble-driven carbon–electron reprogramming enhances nitrogen removal in algal–bacterial granular sludge treating low-C/N wastewater

Description

Low-carbon-to-nitrogen (C/N) wastewater constrains biological nitrogen removal by limiting the reducing equivalents available for nitrite and nitrate reduction. Using sequencing batch reactors, we show that air nanobubbles (NBs) strengthened algal–bacterial granular sludge by improving carbon–electron allocation. At an influent C/N ratio of 2, the NBs-amended reactor exhibited a maximum relative increase of 87.7% in total nitrogen removal and maintained lower nitrite and nitrate residuals than the control. NBs promoted granule maturation, protein-rich extracellular polymeric substance (EPS) accumulation, and a biologically buffered reactive oxygen species regime. Carbon-partitioning and pathway-perturbation assays indicated faster acetate assimilation and greater allocation of acetate-derived carbon to denitrification; perturbation of the glyoxylate-shunt or oxidative-isocitrate route reduced final TN removal, with a maximum relative decrease of 20.8%. EPS electron-donating, electron-accepting, and total electron-transfer capacities increased by 57.1%, 114.3%, and 71.4%, respectively, together with faster ABTS-accessible electron transfer and lower charge-transfer resistance. Functional-gene profiles were consistent with strengthened coupling among carbon conservation, EPS redox buffering, and downstream NOX reduction. These findings identify NBs as a potential process-intensification strategy for improving the use of limited organic carbon in low-C/N wastewater treatment.

Steps to reproduce

http://10.17632/6b78d877rm.1

Institutions

• Anhui Agricultural University

  Anhui, Hefei

Categories

Licence