Nexus between influent organic carbon fractions and carbon capture patterns in high-rate contact stabilization...

While the high-rate contact stabilization (HiCS) process could effectively remove dissolved organic matter (DOM), the fate of DOM at the molecular level has been largely unexplored. This study investigated how distinct influent organic carbon fractions (IOCF) in screening and aerated grit chamber effluents shaped the carbon capture and the bacterial community structure in HiCS process. The transformation of DOM in HiCS process was detected by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and fluorescence spectroscopy to provide molecular insights into the removal and generation of DOM species. The results showed that compared with the on-site A²O process, the HiCS process achieved optimal chemical oxygen demand (COD) removal (85 ± 6%) and carbon capture (35 ± 11%) when the IOCF was characterized by a high particulate COD (pCOD) proportion. This composition favored anabolism and robust biological carbon storage, as well as the production of extracellular polymeric substances that facilitated carbon capture via bioflocculation. Under low-sCOD conditions, Chryseobacterium dominated the initial DOM hydrolysis, while the resulting metabolites were subsequently assimilated by secondary consumers (e.g., Hydrogenophaga) and stored as glycogen or polyhydroxyalkanoates, alongside anabolic macromolecular synthesis. Conversely, high sCOD availability promoted catabolic DOM mineralization over carbon capture, coinciding with Enhydrobacter proliferation and sulfur-mediated metabolism. These findings revealed how distinct IOCF regulated microbial community structure and carbon capture efficiency, particularly regarding DOM succession, thereby providing engineering guidance for optimizing the positioning of the HiCS process to facilitate carbon-neutral upgrading of the existing WWTPs.