Contact time and dissolved oxygen concentration modulate carbon capture via shifting microbial metabolism preference in high-rate contact stabilization process

The high-rate contact stabilization (HiCS) process enables energy-efficient carbon capture from wastewater, yet the interactions of contact phase parameters require clarification. This study systematically investigated the effects of contact time (Tc: 10 – 40 min) and dissolved oxygen concentration (DOc: below 0.2, 0.5, 1.0 mg L⁻¹) on carbon flow, metabolic pathways, and microbial community dynamics. HiCS rapidly achieved carbon capture within 20 min, extending Tc would trigger particulate COD re-release. DOc was identified as the critical parameter significantly influencing carbon flow and pathways (p < 0.05). Carbon capture was predominantly governed by sorption and storage pathway at DOc 0.5 mg L⁻¹, whereas DOc 1.0 mg L⁻¹ shifted carbon towards oxidation and biomass formation. Functional microbial niche succession corroborated these metabolic transitions. HiCS achieved a 49 % ± 6 % carbon capture efficiency through extracellular polymeric substance (EPS)-mediated bioflocculation at optimized Tc 20 min and DOc 0.5 mg L⁻¹, providing feasible strategies for regulation.