Optical and molecular characteristics of urban wastewater dissolved organic matter: insights into their correlations†

Urban domestic wastewater is a significant source of dissolved organic matter (DOM) in aquatic environments, critically impacting urban water quality. This study integrates the optical properties and molecular features of DOM, providing a comprehensive understanding of its behavior in urban sanitary sewage. Utilizing ultraviolet-visible (UV-vis) spectroscopy, three-dimensional synchronous fluorescence spectroscopy, and ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS), we establish a robust bidirectional correlation between optical properties and molecular characteristics. Our findings reveal that urban domestic wastewater is predominantly composed of protein-like substances and microbial humic components, rich in heteroatoms and homologous compounds. The established correlations between optical and molecular features validate the DOM characterization system, demonstrating consistency between photochemical properties and molecular characteristics. Molecules related to photochemical parameters align with high H/C and low O/C ratio regions. The correlation analysis indicates that the highly associated areas are the fluorescent domains of protein-like materials and microbially derived humic-like substances. This innovative approach provides actionable insights for urban water quality management, highlighting the critical role of these methods in effective environmental monitoring.