Molecular Insights into the Transformation of Dissolved Organic Matter in a Full-Scale Wastewater Treatment Plant

The compounds generated during wastewater treatment processes might increase the complexity and chemical risk assessment of wastewater-derived dissolved organic matter (DOM) released into receiving water. This study applied Fourier transform ion cyclotron resonance mass spectrometry to investigate the dynamic changes in wastewater composition at the molecular level in a full-scale municipal wastewater treatment plant (WWTP). Approximately 63.1% of the detected molecules in the effluent were derived from the influent. N/S-containing molecules were more effectively removed than CHO molecules in the studied WWTP. The dealkylation and oxygen addition reactions of N-containing molecules, along with the predominant N-addition reactions of removed molecules observed in anaerobic and oxic tanks, contributed to the higher N/C_wa in the effluent than in the influent. However, the S-containing molecules could be effectively removed via S-loss reactions in the anoxic/anaerobic/oxic (inverted A/A/O) processes. Dealkylation and oxygen addition reactions were found to be the predominant reaction types in all tanks of the inverted A/A/O processes. More oxidized molecules with higher aromaticity and unsaturation degree were observed in the effluent than in the influent. Our findings provide a comprehensive view of the transformation of wastewater DOM in a full-scale WWTP and offer valuable insights into effluent water quality.