Spatial heterogeneity of electron donating capacity: A regulatory indicator for Arsenic bio-oxidation under...

Arsenic (As) contamination in aquifer poses a serious threat to drinking water safety. Microbially driven As(III) oxidation is a key natural attenuation and remediation pathway, yet most studies have focused on static conditions, overlooking the role of hydrodynamics. This study used column experiments to investigate how hydrodynamic conditions shape the spatial heterogeneity of electron donating capacity (EDC) in aquifer media and thereby regulate As(III) biooxidation. Three treatments were compared: LS (biostimulation), AJ (Bioaugmentation), and LS+AJ (combined enhancement). Results showed that EDC exhibited three-stage variation during the experiment, with the late-stage increase significantly positively correlated with As(III) breakthrough time. The LS+AJ group achieved optimal EDC recovery and the latest As(III) breakthrough (40 days), attributed to Fe(II)-As(III) co-oxidation cycles and enhanced electron transfer via conductive minerals. Statistical analysis indicated that As(III) positively drove EDC changes, whereas total iron's negative effect reflected the loss of Fe(II)-derived electron donation upon oxidation to Fe(III). Functional bacteria such as Acinetobacter coexisted synergistically with iron-reducing and ammonia-oxidizing microbial communities, maintaining system performance in arsenic oxidation. This study elucidates how hydrodynamics regulate microbial arsenic oxidation by altering the heterogeneity of medium EDC, and demonstrates that EDC can serve as a measurable indicator to guide the timing and location of remediation agent application in dynamic aquifer systems, thereby improving remediation efficiency and resource allocation.