The nexus between aeration intensity and organic carbon capture in contact-stabilization process: Insights from molecular structure transition of dissolved organic matters

Traditional energy-intensive pollution control pattern poses great challenges to the sustainable development of urban cities, necessitating the implementation of more compact and cost-effective biological treatment technology. High-rate contact stabilization (HiCS) process can effectively capture low-concentration organic carbon matters from municipal wastewater. However, the role of dissolved oxygen (DO) concentration at stabilization phase-a critical determinant of carbon capture efficiency-remains poorly understood, thus hindering its operation optimization and application. This work investigated the impact of DO content at the stabilization phase on the effluent quality and carbon capture efficiency of HiCS process from the perspectives of sludge dissolved organic matter (DOM) composition and microbial metabolism activity changes. The results showed that optimal carbon capture efficiency (52.1 %) and the lowest effluent chemical oxygen demand concentration were achieved at a DO concentration of 1 mg/L. Elevated DO levels would increase the aromaticity of DOM in sludge, rendering it more recalcitrant to microbial degradation. In addition, higher DO concentration induced a metabolic shift towards endogenous respiration among the microbial community, leading to the increased release of DOM and microbial metabolites, which in turn deteriorated the effluent quality. The findings of this work highlight the necessity of controlling appropriate aeration intensity when applying HiCS in practical application, to both effectively minimize organic carbon mineralization and operational energy consumption while without sacrificing pollutant removal performance.